CLASS GUIDELINE
DNV-CG-0051
Edition January 2022
Non-destructive testing
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DNV AS
FOREWORD
DNV class guidelines contain methods, technical requirements, principles and acceptance criteria
related to classed objects as referred to from the rules.
©
DNV AS January 2022
Any comments may be sent by e-mail to rules@dnv.com
This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this
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employees (“DNV”) for proved loss or damage arising from or in connection with any act or omission of DNV, whether in contract or in tort
(including negligence), shall be limited to direct losses and under any circumstance be limited to 300,000 USD.
This document supersedes the December 2015 edition of DNVGL-CG-0051.
The numbering and/or title of items containing changes is highlighted in red.
Changes January 2022
Topic
Major update
Rebranding to DNV
Reference
Description
Sec.1 to Sec.8
The document is updated and aligned with applicable rules,
standards and general practice, including but not limited to
alignment with IACS UR W33 Non-destructive testing of ship
hull steel welds - Rev.1 Corr1 Aug 2021 and IACS UR W34
Advanced non-destructive testing of materials and welds - New
Dec 2019.
Sec.7 and App.A
The former guideline for NDT of TMCP materials and root area
of single side welds have been included as requirements in
Sec.7. The new appendix gives a guideline for qualification of
PAUT and TOFD procedures.
All
This document has been revised due to the rebranding of DNV
GL to DNV. The following have been updated: the company
name, material and certificate designations, and references to
other documents in the DNV portfolio. Some of the documents
referred to may not yet have been rebranded. If so, please see
the relevant DNV GL document.
Editorial corrections
In addition to the above stated changes, editorial corrections may have been made.
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Changes - current
CHANGES – CURRENT
Changes – current.................................................................................................. 3
Section 1 General.................................................................................................... 7
1 General................................................................................................ 7
2 References........................................................................................... 8
3 Definitions and abbreviations............................................................ 11
Section 2 Personnel qualifications, methods selection, procedures and reports.... 14
1 Personnel certification and qualification............................................14
2 Selection of testing method...............................................................15
3 Extent of testing................................................................................ 15
4 Information required prior to testing................................................ 16
5 Time of testing.................................................................................. 16
6 Requirements to NDT procedures...................................................... 16
7 Final report........................................................................................ 17
Section 3 Eddy current testing..............................................................................19
1 Scope................................................................................................. 19
2 Definitions..........................................................................................19
3 Personnel qualifications.....................................................................19
4 Information required (prior to testing)............................................. 19
5 Surface conditions............................................................................. 20
6 Equipment..........................................................................................20
7 Testing............................................................................................... 21
8 Acceptance criteria............................................................................ 24
9 Evaluation of indications................................................................... 24
10 Reporting......................................................................................... 24
Section 4 Magnetic particle testing....................................................................... 29
1 Magnetic particle testing of welds..................................................... 29
2 Magnetic particle testing of components........................................... 38
Section 5 Penetrant testing.................................................................................. 46
1 Scope................................................................................................. 46
2 Personnel qualifications.....................................................................46
3 Equipment/testing material...............................................................46
4 Compatibility of testing materials with the parts to be tested............47
5 Preparation, pre-cleaning and testing............................................... 48
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Contents
CONTENTS
7 Acceptance criteria............................................................................ 52
8 Post cleaning and protection............................................................. 53
9 Retesting............................................................................................53
10 Reporting......................................................................................... 53
Section 6 Radiographic testing............................................................................. 56
1 Scope................................................................................................. 56
2 Personnel qualifications.....................................................................57
3 General.............................................................................................. 57
4 Techniques for making radiographs...................................................62
5 Acceptance criteria............................................................................ 75
6 Reporting........................................................................................... 75
Section 7 Ultrasonic testing.................................................................................. 76
1 Scope................................................................................................. 76
2 Definitions and symbols.................................................................... 76
3 Personnel qualifications.....................................................................77
4 Requirements for equipment............................................................. 77
5 Testing volume.................................................................................. 80
6 Preparation of scanning surfaces...................................................... 81
7 Parent material testing......................................................................82
8 Range and sensitivity setting............................................................ 82
9 Testing techniques - weld connections.............................................. 87
10 Welds in austenitic stainless and duplex (ferritic-austenitic)
stainless steel.....................................................................................107
11 Acceptance criteria, weld connections........................................... 111
12 Reporting, weld connections..........................................................112
13 Ultrasonic testing of rolled steel plates......................................... 113
14 Ultrasonic testing of castings........................................................ 115
15 Ultrasonic testing of forgings........................................................ 118
16 PAUT - automated phased array for testing of welds.................... 122
17 TOFD of welds............................................................................... 131
Section 8 Visual testing...................................................................................... 147
1 Scope............................................................................................... 147
2 Information required prior to testing.............................................. 147
3 Requirements for personnel and equipment.................................... 147
4 Testing conditions............................................................................147
5 Testing volume................................................................................ 148
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Contents
6 Inspection.......................................................................................... 51
7 Evaluation of indications..................................................................148
8 Visual testing of repaired welds...................................................... 149
9 Acceptance criteria.......................................................................... 149
10 Reporting....................................................................................... 149
Appendix A Guidelines for qualification of PAUT and TOFD procedures............... 150
1 Guideline for qualification of PAUT procedure................................. 150
2 Guideline for qualification of TOFD procedure................................. 154
Changes – historic.............................................................................................. 159
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Contents
6 Preparation of surfaces................................................................... 148
Section 1
SECTION 1 GENERAL
1 General
1.1 Introduction
This document is developed in order to represent the Society's general requirements, recommendations
and best practices for non-destructive testing (NDT) of metallic materials. This document is referred to in a
number of DNV rules and standards, and has been adopted and used extensively throughout the years. It is
developed and maintained by DNV. In addition to several updates related to the standard NDT methods, this
latest revision has included further details related to new and more advanced NDT methods.
1.2 Objective
The objective of this document is to facilitate that NDT is carried out in a uniform and consistent way.
1.3 Scope
This class guideline applies to non-destructive testing using the following methods:
—
—
—
—
—
—
eddy current testing
magnetic particle testing
penetrant testing
radiographic testing, including digital and computed radiography
ultrasonic testing, including phased array and time-of-flight diffraction
visual testing.
The requirements for methods, equipment, procedures, reporting, and the qualification and certification of
personnel for visual examination and non-destructive testing of castings, forgings, rolled materials and fusion
welds are specified.
Acceptance criteria are specified and may be applied where the referring rules or standard do not give
detailed acceptance criteria.
1.4 Application
In general, this class guideline shall be adhered to whenever specified in the applicable Society's rules and
standards, and may be used for guidance whenever non-destructive testing is otherwise required by the
Society. The use of other standards or specifications may, however, be granted if an equivalent or stricter
testing procedure is applied.
The requirements are applicable for testing of C-Mn steels, low alloy steels, duplex steels and other stainless
steels as specified. Requirements for NDT and visual examination of other materials shall be evaluated on
case by case basis.
The specified acceptance criteria apply where the referring rules or standard do not give detailed acceptance
criteria.
Guidance note:
The standard may be referred and used e.g. by regulatory bodies, purchasers and builders without involvement of DNV, i.e. where
DNV's certification, verification or classification is not required. For such cases, and where the class programme is indicating that
something shall be agreed with, submitted to, approved, etc. by the Society (DNV), it shall then be agreed, submitted, approved
etc. by a verifier mandated by the referrer to verify compliance.
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International, national and local safety and environmental protection regulation shall always be observed.
2 References
2.1 General
This class guideline incorporates references to other publications. The relevant references are cited
at the appropriate places in the text and constitute provisions of this class guideline. Latest edition of
the publications shall be used unless otherwise specified or agreed with the Society. Other recognised
publications may be used provided it can be shown that they meet or exceed the requirements for the
publications referenced below.
2.2 DNV references
Table 1 lists DNV references used in this document.
Table 1 DNV references
Document code
Title
DNV-RU-SHIP Pt.2
Ch.4 Sec.7
Non destructive testing of welds
DNV-OS-C401
Fabrication and testing of offshore structures
DNV-OS-D101
Marine and machinery systems and equipment
DNV-CG-0550
Maritime services – terms and systematics
2.3 Other references
Table 2 lists other references used in this document.
Table 2 Other references
Document code
Title
ASTM A388
Standard Practice for Ultrasonic Examination of Steel Forgings
ASTM A609
Standard Practice for Castings, Carbon, Low-Alloy, and Martensitic Stainless Steel, Ultrasonic
Examination Thereof
ASTM E747
Standard Practice for Design, Manufacture and Material Grouping Classification of Wire Image
Quality Indicators (IQI) Used for Radiology
ASTM E2491
Standard Guide for Evaluating Performance Characteristics of Phased-Array Ultrasonic Testing
Instruments and Systems
ASTM E2597
Standard Practice for Manufacturing Characterization of Digital Detector Arrays
EN 1330-1
Non-destructive testing – Terminology - Part 1: List of general terms
EN 1330-2
Non-destructive testing – Terminology - Part 2: Terms common to the non-destructive testing
methods
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Section 1
1.5 Safety
Title
Section 1
Document code
EN 1330-3
Non-destructive testing – Terminology - Part 3: Terms used in industrial radiographic testing
EN 1330-10
Non-destructive testing – Terminology - Part 10: Terms used in visual testing
EN 10160
Ultrasonic testing of steel and flat product of thickness equal or greater than 6 mm (reflection
method)
EN 10228
Non-destructive testing of steel forgings – Part 1: Magnetic particle inspection; - Part 2: Penetrant
testing; - Part 3: Ultrasonic testing of ferritic or martensitic steel forgings; - Part 4: Ultrasonic
testing of austenitic and austenitic-ferritic stainless steel forgings
EN 12543
Non-destructive testing. Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing. Pinhole camera radiographic method
EN 12679
Non-destructive testing. Radiographic testing. Determination of the size of industrial radiographic
gamma sources
IACS Rec.68
Guidelines for non-destructive examination of hull and machinery steel forgings
IACS Rec.69
Guidelines for non-destructive examination of marine steel castings
ISO 2400
Non-destructive testing - Ultrasonic testing - Specification for calibration block No. 1
ISO 3059
Non-destructive testing – Penetrant testing and magnetic particle testing – Viewing conditions
ISO 3452
Non-destructive testing - Penetrant testing – Part 1: General principles; – Part 2: Testing of
penetrant materials; – Part 3: Reference test blocks; – Part 4: Equipment
ISO 4986
Steel and iron castings - Magnetic particle testing
ISO 4987
Steel and iron castings - Liquid penetrant testing
ISO 4993
Steel castings; Radiographic inspection
ISO 5576
Non-destructive testing - Industrial X-ray and gamma-ray radiology - Vocabulary
ISO 5577
Non-destructive testing - Ultrasonic testing - Vocabulary
ISO 5579
Non-destructive testing - Radiographic testing of metallic materials using film and X- or gamma rays
- Basic rules
ISO 5580
Non-destructive testing; Industrial radiographic illuminators; Minimum requirements
ISO 5817
Arc-welded joints in steels – Guidance on quality levels for imperfections. Welding – Fusionwelded joints in steel, nickel, titanium and their alloys (beam welding excluded) – Quality levels for
imperfections
ISO 6520-1
Welding and allied processes – Classification of geometric imperfections in metallic materials – Part
1: Fusion welding
ISO 7963
Non-destructive testing - Ultrasonic testing - Specification for calibration block No. 2
ISO 9712
Non-destructive testing – Qualification and certification of NDT personnel
ISO 9934
Non-destructive testing – Magnetic particle testing
ISO 10042
Welding – Arc-welded joints in aluminium and its alloys – Quality levels for imperfections
ISO 10675
Non-destructive testing of welds - Acceptance levels for radiographic testing
ISO 10863
Non-destructive testing of welds - Ultrasonic testing - Use of time-of-flight diffraction technique
(TOFD)
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Title
Section 1
Document code
ISO 11666
Non-destructive testing of welds – Ultrasonic testing – Acceptance levels
ISO 11699
Non-destructive testing – Industrial radiographic film
ISO 12706
Non-destructive testing – Penetrant Testing – Vocabulary
ISO 12707
Non-destructive testing - Magnetic particle testing - Vocabulary
ISO 12718
Non-destructive testing - Eddy current testing - Vocabulary
ISO 13588
Non-destructive testing of welds - Ultrasonic testing - Use of automated phased array technology
ISO 14096-1
Non-destructive testing - Qualification of radiographic film digitalisation systems - Part 1:
Definitions, quantitative measurements of image quality parameters, standard reference film and
qualitative control
ISO 15548
Non-destructive testing – Equipment for eddy current examination.
ISO 15549
Non-destructive testing – Eddy Current Testing – General Principles
ISO 15626
Non-destructive testing of welds - Time- of-flight diffraction technique (TOFD) - Acceptance levels
ISO 16811
Non-destructive testing - Ultrasonic testing - Sensitivity and range setting
ISO 16828
Non-destructive testing. Ultrasonic testing. Time-of-flight diffraction technique as a method for
detection and sizing of discontinuities
ISO/TS 16829
Non-destructive testing - Automated ultrasonic testing - Selection and application of systems
ISO 17635
Non-destructive examination of welds – General rules for metallic materials
ISO 17636-1
Non-destructive examination of welds
Radiographic testing – Part 1: X- and gamma-ray techniques with film
ISO 17636-2
Non-destructive testing of welds
Radiographic testing - Part 2: X- and gamma-ray techniques with digital detectors
ISO 17637
Non-destructive examination of fusion welds – Visual examination
ISO 17638
Non-destructive testing of welds – Magnetic particle testing
ISO 17640
Non-destructive examination of welds – Ultrasonic testing – Techniques, testing levels, and
assessment
ISO 17643
Non-destructive examination of welds – Eddy Current Examination of welds by complex plane
analysis.
ISO 18563
Non-destructive testing - Characterization and verification of ultrasonic phased array equipment
ISO 19232
Non-destructive testing – Image quality of radiographs
ISO 19285
Non-destructive testing of welds - Phased array ultrasonic testing (PAUT) - Acceptance levels
ISO 19675
Non-destructive testing - Ultrasonic testing - Specification for a calibration block for phased array
testing (PAUT)
ISO 22232
Non-destructive testing - Characterization and verification of ultrasonic test equipment
ISO 22825
Non-destructive testing of welds - Ultrasonic testing - Testing of welds in austenitic steels and
nickel-based alloys
ISO 23243
Non-destructive testing - Ultrasonic testing with arrays - Vocabulary
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Title
ISO 23277
Non-destructive examination of welds – Penetrant testing– Acceptance levels.
ISO 23278
Non-destructive examination of welds – Magnetic particle testing - Acceptance levels
ISO 23279
Non-destructive testing of welds – Ultrasonic testing – Characterization of indications in welds
SNT-TC-1A
Personnel Qualification and Certification in Nondestructive Testing
Section 1
Document code
3 Definitions and abbreviations
3.1 Definitions of verbal forms and terms
The general verbal forms defined in Table 3 are used in this document. The general terms defined in Table 4
are used, and the specific terms relevant for magnetic particle testing (MT) and penetrant testing (PT) are
given in Table 5.
Table 3 Definition of verbal forms
Term
Definition
shall
verbal form used to indicate requirements strictly to be followed in order to conform to the document
should
verbal form used to indicate that among several possibilities one is recommended as particularly
suitable, without mentioning or excluding others
may
verbal form used to indicate a course of action permissible within the limits of the document
Table 4 Definition of terms
Term
Definition
acceptance level
prescribed limits below which a component is accepted
defect
one or more flaws whose aggregate size, shape, orientation, location or properties do not meet
specified requirements and is therefore rejectable
discontinuity
lack of continuity or cohesion, an intentional or unintentional interruption in the physical structure or
configuration of a material or component
external
discontinuity
surface discontinuity
false indication
test indication that could be interpreted as originating from a discontinuity but which actually
originates where no discontinuity exists
flaw
in NDT, a synonym for a discontinuity
imperfections
any deviation from the ideal weld, i.e. discontinuity in the weld or a deviation from the intended
geometry
indication
representation of a discontinuity that requires interpretation to determine its significance
non-planar
discontinuity
discontinuity having three measurable dimensions, e.g. slag, porosity
non relevant
indication
indications from something on the test piece which is expected, i.e. internal splines, drilled holes,
weld geometries
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Definition
planar
discontinuity
discontinuity having two measurable dimensions, e.g. crack, lack of fusion
quality level
description of the quality of a weld on the basis of type, size and amount of selected imperfections
shallow
discontinuity
discontinuity open to the surface of a solid object which possesses little depth in proportion to the
width of this opening
subsurface
imperfection
imperfection that is not open to a surface or not directly accessible
testing
testing or examination of a material or component in accordance with this class guideline, or a
standard, or a specification or a procedure in order to detect, locate, measure and evaluate flaws
Table 5 Definition of terms relevant to MT or PT indications
Term
Definition
aligned indication
three or more indications in a line, separated by 2 mm or less edge-to-edge
leakage field
the magnetic field formed outside of a magnet when there is a crack in the magnet
linear indication
indication in which the length is at least three times the width
non-linear indication
indication of circular or elliptical shape with a length less than three times the width
non-open indication
indication that is not visually detectable after removal of the magnetic particles or that
cannot be detected by the use of dye penetrant testing
open indication
indication visible after removal of the magnetic particles or that can be detected by the use
of penetrant testing
relevant indication
indication that is caused by a condition or type of discontinuity that requires evaluation
Only indications which have any dimension greater than 1.5 mm shall be considered
relevant.
3.2 Abbreviations
The abbreviation described in Table 6 are used in this document.
Table 6 Abbreviations
Abbreviation
Definition
ACFM
alternating current field measurement
AUT
automated ultrasonic testing
CR
computed radiography
DR
digital radiography
ET
eddy current testing
HAZ
heat affected zone
IACS
international assosiacion of class societies
MT
magnetic particle testing
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Section 1
Term
Definition
NDT
non-destructive testing
PAUT
phased-array ultrasonic testing
PT
penetrant testing
RT
radiographic testing
TMCP
thermo mechanically controlled processed
TOFD
time-of-flight diffraction
UT
ultrasonic testing
VT
visual testing
WPS
welding procedure specification
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Section 1
Abbreviation
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1 Personnel certification and qualification
1.1 General
All testing shall be carried out by qualified and where required, certified personnel. The NDT operators and
the supervisors shall be certified according to a third party certification scheme based on ISO 9712 or ASNT
Central Certification Program (ACCP). SNT-TC-1A may be accepted if the NDT company's written practice
is reviewed and accepted by the Society. The supplier's written practice shall as a minimum, except for
the impartiality requirements of a certification body and/or authorised body, comply with ISO 9712. The
certificate shall clearly state the qualifications as to which testing method, level and within which industrial
sector the operator is certified.
1.2 NDT operators
1.2.1 General
NDT operators performing testing shall, unless otherwise specified by the referring rule or standard, be
certified at minimum Level 2 in the testing method and industrial sector concerned.
Operators performing testing and visual examination shall have passed a visual acuity test such as required
by ISO 9712 or a Jaeger J-w test. The documented test of visual acuity shall be carried out at least once
within 12 months.
1.2.2 Testing of duplex, stainless and nickel alloy steel welds
Operators performing testing of welds with duplex, stainless and nickel alloy steel welds shall have
documented experience or dedicated training for this type of ultrasonic testing.
For special methods such as TOFD, DR, CR, PAUT, AUT, UT of austenitic stainless steel/duplex/nickel alloy
materials mock-up test under DNV supervision may be required.
Guidance note:
Mock-up tests is intended both for qualification of the procedure and verification of the operator's ability to detect and disposition
relevant indications.
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1.2.3 Ultrasonic testing of tubular node welds
Personnel performing ultrasonic testing of tubular node welds (i.e. tubular TKY connections) shall undergo a
practical test in the typical connections to be tested. The practical test shall have a scope as described in ISO
9712 for industrial sector, welds (w). See also Sec.7 [3].
1.3 NDT supervisor
Supervisors shall, unless otherwise agreed with the Society, be certified level 3 in the testing method
and industrial sector concerned, and should have sufficient practical background in applicable materials,
fabrication, and fabrication technology. Company appointed level 3 not holding the required competence is
not accepted.
The supervisor shall be available for scheduling and monitoring of the performed NDT. The supervisor is
also responsible for development, verification and approval of the NDT procedures in compliance with the
applicable rules.
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Section 2
SECTION 2 PERSONNEL QUALIFICATIONS, METHODS SELECTION,
PROCEDURES AND REPORTS
Method of NDT shall be chosen based on ability to detect relevant discontinuities and shall be considered
for the material, joint geometry and welding process used. Combination of two or more methods should
always be considered to ensure higher probability of detection. Typical NDT-methods applicable for different
materials and joints are shown in Table 1.
Table 1 Selection of testing method
Clad
NDT
method
Materials
Weld
weld
plate
Plate
T-joint,
Partial
T-joint
Butt
Fillet
Castings
Forgings
VT
All
X
X
X
X
X
X
X
X
X
MT
Ferromagnetic C
and C-Mn/ Alloy/
1)
Duplex
-
-
X
X
X
X
X
X
X
PT
Nonferromagnetic,
Aluminium/ CuAlloys/
SS/ Duplex
X
-
X
X
X
X
X
X
X
X
X
X
-
X
X
-
X
X
-
-
-
-
-
X
-
2)
2)
X
-
X
X
X
X
X
2)
2)
UT
4)
Aluminium/
C and C-Mn/
Alloy/
SS/Duplex
RT
3)
ET
2)
Aluminium/
C and C-Mn/
Alloy/
SS/Duplex
All
1)
Method is applicable with limitations for Duplex, shall be approved case-by-case by the Society.
2)
May be used subject to case-by-case approval by the Society.
3)
Recommended for t ≤ 40 mm.
4)
Only applicable for welds with t ≥ 10 mm, unless otherwise qualified.
3 Extent of testing
The extent of testing shall comply with the requirements given in the relevant parts of the rules, standards or
specifications.
If a non-conforming discontinuity is detected, the scope of testing shall be extended as required by applicable
rules or standard. Corrective actions shall be taken to ensure that all similar defects will be detected.
The Society reserves the right to alter the test positions and/or to extend the scope of NDT against the NDT
Plan in case of doubts about proper workmanship.
Prior to NDT all welds shall be 100% visually inspected by qualified personnel. The qualifications shall be
documented by the builder/manufacturer.
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Section 2
2 Selection of testing method
Section 2
4 Information required prior to testing
Prior to testing, the following information shall be known to the operator:
—
—
—
—
—
—
—
—
—
—
—
manufacturing method (weld, casting, forging, rolled product, etc.)
heat treatment
grade of parent material
welding parameters and conditions used to make the weld
location and extent of welds to be tested
weld surface
geometry
coating type and thickness
casting details
forging details
rolling directions.
Operators may ask for further information that will be helpful in determining the nature of discontinuities.
5 Time of testing
If not otherwise specified in the applicable rules, the following applies:
— When heat treatment is performed, the final NDT shall be carried out when all heat treatments have been
completed and material has cooled to ambient temperature.
2
2
— For steel grades with minimum yield strength in the range 420 N/mm to 690 N/mm (e.g. NV 420 to NV
690 grades), final inspection and NDT shall not be carried out before 48 hours after completion, except
where PWHT is required. At the discretion of the Society, a longer interval and/or additional random
inspection at a later period may be required, for example in case of high thickness welds.
— For hull structural welds on steel with specified minimum yield greater than 690 MPa, NDT shall not be
carried out before 72 hours after completion of welding. At the discretion of the Society, the 72 hours
interval may be reduced to 48 hours for radiographic testing (RT) or ultrasonic testing (UT) inspection,
provided there is no indication of delayed cracking, and a complete visual and random magnetic particle
(MT) or penetrant testing (PT) inspection to the satisfaction of the Society is conducted 72 hours after
welds have been completed and cooled to ambient temperature.
When heat treatment is performed, the final NDT shall be carried out when all heat treatments have been
completed. The requirement for the delay period may be relaxed after PWHT (at temperature ≥ 550°C),
subject to agreement with the Society.
6 Requirements to NDT procedures
6.1 General
Where specified in the applicable rules and standards, written NDT procedures shall be prepared and
agreed or approved by the Society, and where required, the procedures shall be qualified by testing and
demonstration. NDT procedures may use this class guideline as a reference document without repeating
the text herein, as relevant. The relevant content given in this class guideline indicates the expectations to
the content of an NDT procedure. Where the techniques described in this class guideline are not applicable,
detailed written procedures shall be prepared and accepted by the Society before the testing is carried out.
Non-destructive testing shall be performed in accordance with written and where required, approved
procedures that, as a minimum, contain following information:
— reference to applicable rules and standards
— material grades
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thickness range
methods and specific testing techniques
extent of testing
details on testing equipment
details for equipment calibration
consumables (including brand name)
details on reference block
sensitivity settings
testing parameters and variables
acceptance level and criteria
assessment of discontinuities
reporting and documentation
reporting forms
extensions requirements.
Section 2
—
—
—
—
—
—
—
—
—
—
—
—
—
—
All non-destructive testing procedures shall be approved and signed by the responsible level 3 supervisor.
Note:
Procedures and techniques may be established by other competent personnel, e.g. level 2, but shall be verified and approved by
personnel certified to level 3 in the applicable NDT method.
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6.2 Procedure qualification
NDT procedure qualification is required for advanced NDT methods, UT of duplex and other stainless-steel
grades and for UT of thicknesses below 10 mm.
Qualification shall demonstrate that applied procedure achieves 100% coverage of tested volume and
is adequate in reliability, repeatability and accuracy for detection and sizing of relevant indications. The
qualification of the procedure is normally project specific and shall only be valid when all essential testing
variables remain nominally the same as covered by the documented qualification.
Qualification shall be performed by means of practical demonstration on project specific validation blocks.
Unless otherwise agreed with the Society, validation blocks shall be of representative geometry, material/
properties and contain agreed natural and/or artificial discontinuities with size and types that are typical
for the manufacturing process. Number, size, and location of discontinuities should be adequate to ensure
reliability of testing.
CR and DR procedures shall be qualified by making radiographic exposures of a welded joint or base material
with the same or typical configuration and dimensions, and of material equivalent to that which shall be
used in production radiography. Requirements for process technique in Sec.6 shall be met, and detection and
characterization of all relevant indications shall be achieved.
7 Final report
All NDT shall be properly documented in such a way that the performed testing can be easily retraced at a
later stage. The reports shall identify the unacceptable defects present in the tested area, and a conclusive
statement as to whether the weld satisfies the acceptance criteria or not.
When defects shall be reported, the defect information shall include defect type, size, lateral, and longitudinal
position (as applicable for the test method) in relation to datums.
The report shall include a reference to the applicable standard, NDT procedure, and acceptance criteria. In
addition, as a minimum, the following information shall be given:
— object and drawing references
— place and date of examination
— material type and dimensions
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—
—
—
—
—
—
post weld heat treatment, if required
location of examined areas, type of joint
welding process used
name of the company and operator carrying out the testing including certification level of the operator
surface conditions
temperature of the object, if relevant
number of repairs if specific area repaired twice or more
contract requirements e.g. order no., specifications, special agreements etc.
sketch, photograph, photocopy, video, written description showing location and information regarding
detected defects
extent of testing
test equipment used
description of the parameters used for each method
description and location of all recordable indications
examination results with reference to acceptance level
signatures (ordinary signatures or electronic signatures) of personnel responsible for the testing.
Other information related to the specific method may be listed under each method.
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Section 2
—
—
—
—
—
—
—
—
—
1 Scope
This section defines eddy current testing techniques (ET) for detection of surface breaking and near surface
planar defects in:
— welds
— heat affected zone
— parent material.
ET may be applied on coated and uncoated objects and the testing may be carried out on all accessible
surfaces on welds of almost any configuration.
For other applications than weld testing, it is recommended that eddy current testing is done according to
ISO 15549.
Usually, it may be applied in the as-welded condition. However, a very rough surface may prevent an efficient
testing.
The electromagnetic testing method includes the techniques eddy current testing and alternating current field
measurement (ACFM). If ACFM is applied, written procedures shall be established according to recognised
standards and are subjected for approval by the Society before the testing starts.
2 Definitions
In addition to definitions given in Sec.1 [3] and ISO 12718 the following applies:
Table 1 Definition of terms relevant to ET
Term
Definition
balance
compensation of the signal, corresponding to the operating point, to achieve a
predetermined value, for example zero point
impedance plane diagram
graphical representation of the focus points, indicating the variation in the impedance of a
test coil as a function of the test parameters
noise
any unwanted signal which could corrupt the measurement
phase reference
direction in the complex plane display chosen as the origin for the phase measurement
probe
eddy current transducer
Physical device containing excitation elements and receiving elements.
lift off
indication visible after removal of the magnetic particles or that can be detected by the use
of contrast dye penetrant
3 Personnel qualifications
See Sec.2 [1].
4 Information required (prior to testing)
See general information in Sec.2 [4].
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Section 3
SECTION 3 EDDY CURRENT TESTING
Depending on the sensitivity requirements, the eddy current method is able to detect surface cracks through
non-metallic coating up to 2 mm thickness. Coating thickness in excess may be considered if the relevant
sensitivity is maintained.
Excessive weld spatters, scale, rust and damaged paint may influence sensitivity by separating the probe (lift
off) from the test object and shall be removed before the inspection.
It shall also be noted some types of coating, such as zinc primers, could seriously influence the results as
they could deposit electrical conductive metallic material in all cracks open to the surface.
Normally, zinc rich shop primer used for corrosion protection (typical thickness max. 30 µm) will not influence
the testing.
6 Equipment
6.1 Instrument
6.1.1 General
The instrument used for the testing described in this class guideline shall at least have the features described
in [6.1.2] to [6.1.6].
6.1.2 Frequency
The instrument shall be able to operate at the frequency range from 1 kHz to 1 MHz.
6.1.3 Gain/noise
After compensation (lift off), a 1 mm deep artificial defect shall be indicated as a full screen deflection
through a coating thickness corresponding to the maximum expected on the object to be tested.
Further, a 0.5 mm deep artificial defect shall be indicated through the same coating thickness by a minimum
noise/signal ratio of 1 to 3.
Both requirements shall apply to the chosen probe and shall be verified on a relevant calibration block.
6.1.4 Evaluation mode
The evaluation mode uses both phase analysis and amplitude analysis of vector traced to the complex plane
display. Evaluation may be by comparison of this display with reference data previously stored.
6.1.5 Signal display
As a minimum, the signal display shall be a complex plane display with the facility to freeze data on the
screen until reset by the operator. The trace shall be clearly visible under all lighting conditions during the
testing.
6.1.6 Phase control
The phase control shall be able to give complete rotation in steps of no more than 10° each.
6.2 Probes
6.2.1 Probes for measuring thickness of coating
The probe shall be capable of providing a full screen deflection lift-off signal on the instrument when moved
from an uncoated spot on a calibration block to a spot covered with the maximum coating thickness expected
on the object to be tested. The probe shall operate in the frequency range from 1 kHz to 1 MHz. The probes
shall be clearly marked with their operating frequency range.
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Section 3
5 Surface conditions
The diameter of the probe shall be selected relative to the geometry of the component under test. Such
probes shall be able to operate when covered by a thin layer on non-metallic wear-resistant material over the
active face. If the probe is used with a cover, then the cover shall always be in place during the calibration.
The probe shall operate at a selected frequency in the range from 100 kHz to 1 MHz. Probes to be used in
specially difficult accessible areas along and in welds are typical an absolute, shielded pencil probe operating
at 200 kHz or 500 kHz.
6.3 Accessories
6.3.1 Calibration block
A calibration block, of the same type of the material as the component to be tested shall be used. It shall
have EDM (electric discharge machined) notches of 0.5, 1.0 and 2.0 mm depth, unless otherwise agreed with
the Society. Tolerance of notch depth shall be ± 0.1 mm. Recommended width of notch shall be ≤ 0.2 mm.
6.3.2 Non-metallic sheets
Non-metallic flexible strips of a known thickness to simulate the coating or actual coatings on the calibration
block shall be used.
It is recommended that non-metallic flexible strips be multiples of 0.5 mm thickness.
6.3.3 Probe extension cables
Extension cables may only be used between the probe and the instrument if the function, sensitivity and the
resolution of the whole system can be maintained.
6.4 Systematic equipment maintenance
The equipment shall be checked and adjusted on a periodic basis for correct functioning in accordance with
standard ISO 15548 - all parts. This shall only include such measurements or adjustments, which can be
made from the outside of the equipment. Electronic adjustments shall be carried out in case of device faults
or partial deterioration or as a minimum on an annual basis. It shall follow a written procedure. The results of
maintenance checks shall be recorded. Records shall be filed by owner.
7 Testing
7.1 General information for coating thickness
7.1.1 General
The coating thickness on the un-machined surface is never constant. However, it will influence the sensitivity
of crack detection. The lift off signal obtain from the object to be tested shall be similar to the signal obtain
from the calibration block, i.e. it shall be within 5° either side of the reference signal. In the event that
the signal is out of this range, a calibration block more representative of the material to be tested shall be
produced/ manufactured.
7.1.2 Calibration
— Select frequency to desired value between 1 kHz and 1 MHz, depending on probe design, for instance a
broad band pencil probe set at 100 kHz.
— Place the probe in air and balance the equipment.
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Section 3
6.2.2 Probes for weld testing
For testing of welds, probes specially designed for this purpose shall be used. The probe assembly shall be
differential, orthogonal, tangential or equivalent which is characterised by having a minimal dependency on
variations in conductivity, permeability and lift off in welded and heat-affected zones.
7.1.3 Measuring of coating thickness
— Balance the equipment with the probe in air.
— Place the probe on selected spots adjacent to the weld or area to be tested. Note the signal amplitudes.
— The thickness of the coating may be estimated by interpolation between the signal amplitudes from the
known thicknesses, see Figure 9.
— The estimated coating thickness shall be recorded.
7.2 Testing of welds in ferritic materials
7.2.1 Frequency
The frequency shall be chosen according to the material (conductivity, permeability), the defect (type,
location, size) and the probe design. It is suggested to use a frequency around 100 kHz.
7.2.2 Calibration
Calibration is performed by passing the probe over the notches in the calibration block, see Figure 7. The
notched surface shall first be covered by non-metallic flexible strips having a thickness equal to or greater
than the measured coating thickness.
The equipment sensitivity is adjusted to give increasing signals from increasing notch depths. The 1 mm
deep notch shall give signal amplitude of approximately 80% of full screen height. The sensitivity levels shall
then be adjusted to compensate for object geometry.
Calibration check shall be performed periodically and at least at the beginning and the end of the shift and
after every change in working conditions.
When the calibration is complete it is recommended the balance is adjusted to the centre of the display.
Calibration procedure:
— select frequency to 100 kHz
— use the X- and Y- controls to adjust the spot position to the centre of the screen (X-axis) and minimum
one and a half screen divisions above the bottom line (Y-axis), ensuring that no noise signal is fully
displayed on the screen
— place the probe on the uncovered calibration block ensuring it is not close to any of the notches. Balance
the equipment
— to obtain a correct defect display, run the probe over the representative notch. Care should be taken that
the longitudinal axis of the probe is kept parallel to the notches and the scanning direction is at right
angles to the notch. Indications from the notch will appear on the screen. The phase angle control is in
the vertical upwards direction
— the sensitivity level shall be adjusted to compensate for the coating thickness measured under [7.1.3]
using the following procedure:
— place the non-metallic sheets of the actual thickness corresponding to the measured coating thickness
on the calibration block, or the nearest higher thickness of the non-metallic sheets
— place the probe on the covered calibration block, ensuring it is not close to any of the notches and
balance the equipment
— run the probe over the 1.0 mm deep notch. Adjust the gain (dB) control until the signal amplitude from
the notch is in 80% of full screen height.
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Section 3
— Use the X- and Y-controls to adjust the position of the spot until it is on the right hand side of the screen.
Move the probe on and off the calibration block. Adjust the phase angle control until the movement of the
spot is horizontal.
— Place the probe on the uncovered calibration block ensuring it is not close to any of the notches. Repeat
this on the same spot of the block now covered with 0.5, 1.0 and 1.5 mm non-metallic sheets.
— Note the different signal amplitudes, see Figure 8.
The testing may be split into two parts: the heat affected zones (25 mm each side of the weld), see Figure 1,
Figure 2, Figure 3 and the weld surface, see Figure 4.
It shall be noted that the reliability of the testing is highly dependent on the probe relative to the surface
(weld) under test. Care shall also be taken to ensure that the probe is at the optimum angle to meet the
varying surface conditions in the heat affected zone.
For probes of differential coil type, the sensitivity is affected by the orientation of the imperfection relative to
the coil. Therefore, care shall be taken that this also is controlled during the testing.
Guidance note:
Especially defects with an orientation of 45° to the main direction of the probe movement could be difficult to detect.
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7.2.4 Detectability of imperfections
The ability to detect imperfections depends on many factors.
Some recommendations are made below to take account of the limiting factors which affect indications
detectability.
— Material of calibration block:
Testing of metalized welds/components require equivalent calibration blocks and established calibration
procedures.
— Conductive coatings:
Conductive coatings reduce the sensitivity of the test. The maximum coating thickness shall also be
reduced and depending on the conductivity.
— Non-conductive coatings:
Non-conductive coatings reduce the sensitivity of the test depending on the distance between the probe
and the test object.
— Geometry of the object:
The shape of the object and the access of the probe to the area under test reduce the sensitivity of the
test. Complex weld geometries such as cruciform and gusset plates shall be tested relative to the complex
geometry and possible orientation of the indications.
— Orientation of coils to the indication:
Directional induced current; the induced current is directional, therefore care shall be taken to ensure that
the orientation of current is perpendicular and/or parallel to the expected indication position.
— Inclination:
Care shall be taken to ensure the optimum angle of the coils relative to the area under test is maintained.
7.3 Procedure for examination of welds in other materials
As previous stated, the eddy current method is also applicable to welds in other materials such as aluminium,
duplex, stainless steels and titanium.
The procedure for testing of such welds shall generally include the same items as in [7.2] but the choice of
frequency, probes, calibration and scanning patterns shall be optimised to the actual materials, and may
deviate considerably from what is recommended for ferritic materials.
Therefore, the testing shall be based on practical experience with suitable equipment and probes, and shall
be shown in a specific procedure.
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Section 3
7.2.3 Scanning
The weld surface and 25 mm of each side of the weld (including the heat-affected zones) shall be scanned
with the chosen probe(s). As far as the geometry of the test objects permits, the probe shall be moved in
directions perpendicular to the main direction of the expected indications. If this is unknown, or if indications
in different directions are expected, at least two probe runs shall be carried out, one perpendicular to the
other.
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
If acceptance criteria are not defined, evaluation criteria in [9] should be used. This is provided a sensitivity
adjustment for welds in ferritic steel of 80% of FSH from the 1.0 mm deep notch in the reference block.
9 Evaluation of indications
An indication is defined as an area displaying an abnormal signal compared to that expected from that area
of the object under test.
In the event of a non-acceptable indication being noted, see Figure 5, a further investigation of the area is
requested, e.g. by using magnetic particle testing.
A longitudinal scan shall be performed and the length of the indication noted.
Where possible a single pass scan along the length of the indication shall be performed to obtain the signal
amplitude. The maximum amplitude shall be noted, see Figure 6. This is provided a sensitivity adjustment for
welds in ferritic steel of 80% of FSH from the 1.0 mm deep notch in the reference block.
If there is a need for further clarification or when the removal of an indication shall be verified, it is requested
that the testing is supplemented with other non-destructive testing methods like magnetic particle testing
(MT) or penetrant testing (PT).
Where a non-acceptable indication is noted, but no depth information is possible alternative NDT method
such as ultrasonic and/or Alternating Current Potential Drop techniques shall be used to determine the depth
and orientation of the indication.
10 Reporting
In addition to the items listed under Sec.2 [7] the following shall be included in the eddy current report:
—
—
—
—
—
probes, type and frequency
phase, e.g. 180° and/or 360°
identification of reference blocks used
calibration report
reporting level, if different from acceptance level.
Figure 1 First scan of heat affected zones - Probe movement almost perpendicular to weld axis
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Section 3
8 Acceptance criteria
Section 3
Figure 2 Probe angle (at scans shown in Figure 1 shall be adjusted to meet varying surface
conditions)
Figure 3 Recommended additional scans of heat affected zones - Probe movement parallel to the
weld axis
Guidance note:
Both scanning patterns in Figure 1 and Figure 3 are mainly for longitudinal defects. Therefore, the probe orientation shall always
be in position giving maximum sensitivity for the defect direction.
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Section 3
Figure 4 Scan of weld surface - Transverse/longitudinal scanning technique to be used relative to
weld surface condition
Figure 5 Defect evaluation using transversal scanning techniques
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Section 3
Figure 6 Defect evaluation using single pass longitudinal technique in heat affected zones
Figure 7 Calibration on notches
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Section 3
Figure 8 Coating thickness measurement (Calibration procedure. Vertical shift adjustment
between readings)
Figure 9 Coating Thickness Measurement. (Vertical shift adjustment between readings)
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Section 4
SECTION 4 MAGNETIC PARTICLE TESTING
1 Magnetic particle testing of welds
1.1 Scope
This part of the class guideline specifies magnetic particle testing techniques for the detection of surface
imperfections in ferromagnetic welds including the heat affecting zones using the continuous wet or dry
method. It can also detect imperfections just below the surface, but its sensitivity reduced rapidly with depth.
If such imperfections shall be detected with high reliability, additional inspection methods shall be used.
Techniques recommended are suitable for most welding processes and joint configurations.
1.2 Definitions and symbols
See Sec.1 [3].
1.3 Information required (prior to testing)
See Sec.2 [4].
1.4 Personnel qualifications
See Sec.2 [1].
1.5 Magnetizing
1.5.1 Equipment
Unless otherwise agreed with the Society the following types of alternate current-magnetising equipment
shall be used:
— AC electromagnetic yoke
— current flow equipment with prods
— adjacent or threading conductors or coil techniques.
The magnetising equipment used shall comply with the requirements of ISO 9934-3 or equivalent standards.
Where prods are used, precautions shall be taken to minimise overheating, burning or arcing at the contact
tips. Removal of arc burns shall be carried out where necessary. The affected area shall be tested by a
suitable method to ensure the integrity of the surface. The prod tips should be steel or aluminium to avoid
copper deposit on the part being tested.
a)
Use of alternating current magnetization
The use of alternating current gives the best sensitivity for detecting surface imperfections. Preferably,
alternating current, AC electromagnetic yoke shall be used. Each AC electromagnetic yoke shall have
a lifting force of at least 44 N lifting a weight of 4.5 kg (10 lb.) at the maximum pole space that will be
used.
b)
The pole of the magnet shall have close contact with the component.
Use of direct current magnetization
Unless otherwise agreed with the Society, use of DC magnets shall be avoided, due to limitation
of the different equipment and the difficulty to obtain sufficient magnetic field/strength for several
configurations for surface imperfections.
If accepted used, each DC electromagnetic yoke shall have a lifting force of at least 175 N, i.e. lifting a
weight of 18 kg (40 lb.) at the maximum pole space that will be used.
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Use of permanent magnets
Use of permanent magnets are not allowed at all, due to limitation of the different equipment and the
difficulty to obtain sufficient magnetic field/strength for several configurations for surface imperfections.
1.5.2 Verification of magnetization
The adequacy of the surface flux density shall be established by one or more of the following methods:
— by using a component containing fine natural or artificial discontinuities in the least favourable locations
— by measuring the tangential field strength as close as possible to the surface using a Hall effect probe the
appropriate tangential field strength can be difficult to measure close to abrupt changes in the shape of
a component, or where flux leaves the surface of a component, relevant for other techniques than yoke
technique
— by calculation of the approximate tangential field strength. The basis for the calculations are the electrical
current values specified in Table 1, Table 2 and Table 3
— by verification of lifting force on material similar to test object
— other methods based on established principles.
Guidance note:
Flux indicators, placed in contact with the surfaces under examination, can provide a guide to magnitude and direction of the
tangential field, but should be used with care to verify that the field strength is acceptable.
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1.6 Overall performance test
Before testing begins, a test to check the overall performance of the testing shall be done. The test shall be
designed to ensure a proper functioning of the entire chain of parameters including equipment, the magnetic
field strength and direction, surface characteristics, detecting media and illumination.
The most reliable test shall use representative test pieces containing real imperfections of known type,
location, size and size-distribution i.e. 'Castrol' strips type II. Where these are not available, fabricated test
pieces with artificial imperfections, of flux shunting indicators of the cross or shim type may be used. The test
pieces shall be demagnetized and free from indications resulting from previous tests.
1.7 Surface condition and preparation
Satisfactory results are usually obtained when the surfaces are in the as-welded condition. However, surface
preparation by grinding or machining may be necessary where surface irregularities could mask indications.
Prior to testing the surface shall be free from scale, oil, grease, weld spatter, machining marks, dirt, heavy
and loose paint and any other foreign matter that may affect the sensitivity. It may be necessary to improve
the surface condition e.g. by abrasive paper or local grinding to permit accurate interpretation of indications.
When testing of welds is required, the surface and all adjacent areas within 25 mm shall be prepared as
described above.
There shall be a good visual contrast between the indications and the surface under test. For non-fluorescent
technique, it may be necessary to apply a uniform thin, adherent layer of contrast paint. The total thickness
of any paint layers shall normally not exceed 50 µm.
1.8 Application techniques
1.8.1 Field directions and examination area
The detectability of an imperfection depends on the angle of its major axis with respect to the direction to the
magnetic field.
To ensure detection of imperfections in all orientations, the welds shall be magnetized in two directions
approximately perpendicular to each other with a maximum deviation of 30°. This may be achieved using
one or more magnetization methods.
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Section 4
c)
Figure 1 Sketches indicating the non-tested area close to the pole pieces
1.8.2 Typical magnetic particle testing techniques
Application of magnetic particle testing techniques to common weld joint configurations is shown in Table
1, Table 2, and Table 3. Values are given for guidance purposes only. Where possible the same directions of
magnetization and field overlaps should be used for other weld geometry’s to be tested. The dimension a, the
flux current path in the material, shall be greater or equal to the width of the weld and the heat affected zone
+50 mm and in all cases the weld and the heat affected zone shall be included in the effective area.
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Section 4
When testing incorporates the use of yokes or prods, there will be an area of the component, in the area of
each pole piece or tip that will be impossible to test due to excessive magnetic field strength, usually shown
by furring of particles, see Figure 1. Adequate overlap of the tested areas shall be ensured.
Material type:
Ferromagnetic material
Section 4
Table 1 Typical magnetizing techniques for yokes
Dimensions in mm
75 ≤ d ≤ 250
b ≤ 0.5d
1
β ≈ 90°
d1 ≥ 75
b1 ≤ 0.5d1
2
b2 ≤ d2 – 50 (minimum overlap 50)
d2 ≥ 75
d1 ≥ 75
d2 ≥ 75
3
b1 ≤ 0.5 d1
b2 ≤ d2 – 50 (minimum overlap 50)
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Section 4
Material type:
Ferromagnetic material
Dimensions in mm
d1 ≥ 75
d2 ≥ 75
4
b2 ≤ d2 – 50 (minimum overlap 50)
b1 ≤ 0.5 d1
Table 2 Typical magnetizing techniques for prods, using a magnetization current 5 A/mm (r.m.s.)
prod spacing
Material type:
Ferromagnetic material
Dimensions in mm
a ≥ 75
b1 ≤ a - 50 (minimum overlap 50)
b2 ≤ 0.8 a
1
b3 ≤ 0.5 a
β ≈ 90°
a ≥ 75
b1 ≤ 0.8 a
2
b2 ≤ a – 50 (minimum overlap 50)
b3 ≤ 0.5 a
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Section 4
Material type:
Ferromagnetic material
Dimensions in mm
a ≥ 75
b1 ≤ 0.8 a
3
b2 ≤ a – 50 (minimum overlap 50)
b3 ≤ 0.5 a
a ≥ 75
b1 ≤ a – 50 (minimum overlap 50)
4
b2 ≤ 0.8 a
b3 ≤ 0.5 a
Table 3 Typical magnetizing techniques for flexible cables or coils
Material type:
Ferromagnetic material
Dimensions in mm
20 ≤ a ≤ 50
N×I≥8D
1
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Section 4
Material type:
Ferromagnetic material
Dimensions in mm
2
20 ≤ a ≤ 50
N×I≥8D
3
20 ≤ a ≤ 50
N×I≥8D
Legend: N = number of turns; I = current (r.m.s.); a = distance between weld and coil or cable.
1.9 Detecting media
1.9.1 General
Detecting media may be either in dry powder or liquid form and the magnetic particles shall be either
fluorescent or non-fluorescent. The detecting media shall be traceable to a batch certificate or data sheet
documenting compliance with ISO 9934-2 or equivalent.
1.9.2 Dry particles
The colour of the dry particles (dry powder) shall provide adequate contrast with the surface being examined
and they may be of fluorescent or non-fluorescent type. Dry particles shall only be used if the surface
temperature of the test object is in the range 57°C to 300 °C.
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1.9.4 Verification of detection media performance
Checking of wet particles concentration shall be carried out as per ISO 9934-2. Concentration between 0.1%
and 0.4% is considered acceptable for fluorescent wet particles. Concentration between 1.0% and 2.5% is
considered acceptable for colour contrast wet particles.
Verification of the detection media shall be carried out periodically to confirm continuing satisfactory
performance. The verification shall be carried out on components having known or artificial surface
imperfections, or on premagnetized reference pieces, preferably either Castrol strips type II or MTU block.
1.10 Viewing conditions
1.10.1 General
The viewing conditions shall be in accordance with ISO 3059.
1.10.2 Fluorescent technique
With fluorescent particles the testing is performed using an ultraviolet light, called black light. The testing
shall be performed as follows:
— the testing shall be performed in darkened area where the visible light is limited to a maximum of 20 lx
— photo chromatic spectacles shall not be used
— sufficient time shall be allowed for the operator's eyes to become dark adapted in the inspection booth,
usually at least 1 min
— UV radiation shall not be directed in the operator’s eyes. All surfaces which can be viewed by the
operators shall not fluoresce
— the test surface shall be viewed under a UV-A radiation source. The UV-A irradiance at the surface
2
2
inspected shall not be less than 10 W/m (1000 µW/cm ).
1.10.3 Colour contrast technique
The test surface for colour contrast method shall be inspected under daylight or under artificial white
luminance of not less than 500 lx on the surface of the tested object. The viewing conditions shall be such
that glare and reflections are avoided.
1.11 Application of detecting media
After the object has been prepared for testing, magnetic particle detecting medium shall be applied by
spraying, flooding or dusting immediately prior to and during the magnetization. Following this, time shall be
allowed for indications to form before removal of the magnetic field.
When magnetic suspension is used, the magnetic field shall be maintained within the object until the majority
of the suspension carrier liquid has drained away from the testing surface. This will prevent any indications
being washed away.
Dependent on the material being tested, its surface condition and magnetic permeability, indications will
normally remain on the surface even after removal of the magnetic field, due to residual magnetism within
the part. However, the presence of residual magnetism shall not be presumed, post evaluation techniques
after removal of the prime magnetic source may be permitted only when a component has been proven by
an overall performance test to retain magnetic indications.
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Section 4
1.9.3 Wet particles
The colour of the wet particles shall provide adequate contrast with the surface being examined and they
are available in both fluorescent and non-fluorescent concentrates. The particles are suspended in a suitable
liquid medium such as water or petroleum distillates. When using wet particles, the temperature range of the
wet particle suspension and the surface of the test object should be within 0°C ≤ T ≤ 57°C.
Certain indications may arise not from imperfections, but from spurious effects, such as scratches, change
of section, the boundary between regions of different magnetic properties, weld toes or magnetic writing.
These are defined as false indications. The operator shall carry out any necessary testing and observations
to identify and if possible, eliminate such false indications. Light surface dressing may be of value where
permitted.
1.13 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
If no acceptance criteria are defined, acceptance criteria as specified below may be applied.
The quality for welds shall normally comply with ISO 5817 quality level C, Intermediate. For highly stressed
areas more stringent requirements, such as quality level B, may be applied, see Table 4.
Table 4 Quality levels and acceptance levels for magnetic particle testing (MT)
Quality levels in
accordance with ISO 5817
Testing techniques and
levels in accordance with
ISO 17638 or DNV-CG-0051
Acceptance levels in
accordance with ISO 23278
B
C
2×
Level not specified
2×
D
Type of indication
Linear indication
ℓ = length of indication [mm]
Non-linear indication
d = major axis dimension [mm]
1)
3×
Acceptance level
1)
1
2
3
ℓ ≤ 1.5
ℓ≤3
ℓ≤6
d≤2
d≤3
d≤4
Acceptance level 2 and 3 may be specified with a suffix '×' which denotes that all linear indications shall
be assessed to level 1. However the probability of detection of indications smaller than those denoted by
the original acceptance level can be low.
1.14 Demagnetization
After testing with alternating current, residual magnetization will normally be low for low carbon steels, and
there will generally be no need for demagnetization of the object.
If required, the demagnetization shall be carried out within a method and to a level agreed with the Society.
The demagnetization shall be described in the procedure for magnetic particle testing.
1.15 Reporting
In addition to the items listed in Sec.2 [7] the following shall be included in the magnetic particle testing
report:
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Section 4
1.12 False indications
type of magnetization equipment
testing technique
type of current
detection media
viewing conditions
demagnetization, if required
lifting force
other means of magnetic field strength verification.
Section 4
—
—
—
—
—
—
—
—
2 Magnetic particle testing of components
2.1 Scope
This part of the class guideline specifies magnetic particle testing techniques for the detection of surface
imperfections in ferromagnetic castings and forgings using the continuous wet or dry method. It may
also detect imperfections just below the surface, but its sensitivity reduced rapidly with depth. If such
imperfections shall be detected with high reliability, additional inspection methods shall be used.
2.2 Definitions and symbols
See Sec.1 [3].
2.3 Information required (prior to testing)
See Sec.2 [4].
2.4 Personnel qualifications
See Sec.2 [1].
2.5 Magnetizing
The minimum magnetic flux density (B) regarded as adequate for testing is 1 T. The applied magnetic field
(H) required to achieve this in low alloy and low carbon steels is determined by the relative permeability of
the material. This varies according to the material, the temperatures and also with the applied magnetic field
and for these reasons it is not possible to provide a definitive requirement for the applied magnetic field.
However typically a tangential field of approximately 2 kA/m will be required.
It shall be magnetized with an AC current enabling true r.m.s. measurements of the current value.
For steels, with low relative permeability, higher tangential field strength may be necessary. Typically, a
tangential field of approximately 4 kA/m to 8 kA/m will be required. If magnetization is too high, spurious
background indications may appear, which could mask relevant indications.
If cracks or other linear discontinuities are likely to be aligned in a particular direction, the magnetic flux shall
be aligned perpendicular to this direction where possible.
The flux may be regarded as effective in detecting discontinuities aligned up to 60° from the optimum
direction. Full coverage may then be achieved by magnetizing the surface in two perpendicular directions.
Magnetic particle testing should be regarded as a surface NDT method, however discontinuities close to
the surface may also be detected. For time varying waveforms the depth of magnetisation (skin depth) will
depend on the frequency of the current waveform. Magnetic leakage fields produced by imperfections below
the surface will fall rapidly with distance. Therefore magnetic particle testing is not recommended for the
detection of imperfections other than on the surface it may be noted that the use of smooth DC or rectified
waveforms may improve detection of imperfections just below the surface.
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The adequacy of the surface flux density shall be established by one or more of the following methods:
— by testing a representative component containing fine natural or artificial discontinuities in the least
favourable locations, i.e. a 'Castrol strip' type II or type A
— by measuring the tangential field strength as close as possible to the surface Information on this is given
in ISO 9934-3
— by calculating the tangential field strength for current flow methods. Simple calculations are possible in
many cases, and they form the basis for current values specified in ISO 9934-1
— by the use of other methods based on established principles.
2.7 Preparation of surfaces
Areas to be tested shall be free from dirt, scale, loose rust, weld spatter, grease, oil and any other foreign
matter that may affect the test sensitivity.
The surface quality requirements are dependent upon the size and orientation of the discontinuity to be
detected. The surface shall be prepared so that relevant indications can be clearly distinguished from false
indications.
Non-ferromagnetic coatings up to approximately 50 μm thick, such as unbroken adherent paint layers, do
not normally impair detection sensitivity. Thicker coatings reduce sensitivity. Under these conditions, the
sensitivity shall be verified.
There shall be a sufficient visual contrast between the indications and the test surface. For the nonfluorescent technique, it may be necessary to apply a uniform, thin, temporarily adherent layer of approved
contrast aid paint.
The component needs to be thoroughly demagnetised prior to MT – testing to avoid false indications are
produced.
The roughness of the machined test areas shall not exceed an average roughness of Ra = 12.5 µm for premachined surface, and Ra = 6.3 µm for final machined surface.
2.8 Magnetizing techniques
2.8.1 General
This section describes a range of magnetization techniques. Multi-directional magnetization may be used to
find discontinuities in any direction. In the case of simple-shaped objects, formulae are given in ISO 9934-1
for achieving approximate tangential field strengths. Magnetizing equipment shall meet the requirements of
and be used in accordance with ISO 9934-3.
It is not allowed to employ prods on final machined surfaces.
Contact points visible on the surface shall be ground and to be retested by yoke magnetization if they will not
be removed by the following machining.
Where magnetisation is achieved in partial areas, AC magnetisation shall normally be used. The DC
magnetisation method shall only be used upon special agreement with the Society and in cases where
indications on opposite surfaces or below the surface are sought.
It shall be ensured that in the contact areas overheating of the material to be examined is avoided. In the
case of AC magnetisation the tangential field strength on the surface shall be at least 4 kA/m and shall not
exceed 8 kA/m. It shall be checked by measurements that these values are adhered to or test conditions
shall be determined under which these values may be obtained.
Where the probable nature and orientation of flaws in a forging may be forecast with confidence as, for
example, in certain long forged parts, and where specified in the enquiry or order, magnetization may be
performed in a single direction.
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Section 4
2.6 Verification of magnetization
The following guide values apply with respect to the application of the magnetic particles and magnetisation:
a)
b)
magnetisation and application: at least 3 seconds
subsequent magnetisation: at least 5 seconds.
2.8.2 Current flow techniques
2.8.2.1 Axial current flow
Current flow offers high sensitivity for detection of discontinuities parallel to the direction of the current.
Current passes through the component, which shall be in good electrical contact with the pads. A typical
arrangement is shown in Figure 2. The current is assumed to be distributed evenly over the surface and shall
be derived from the peripheral dimensions. An example of approximate formula for the current required to
achieve a specified tangential field strength is given in ISO 9934-1. Care shall be taken to avoid damage
to the component at the point of electrical contacts. Possible hazards include excessive heat, burning and
arcing.
Legend:
1 Specimen
2 Flaw
3 Flux
4 Current
5 Contact pad
6 Contact head
Figure 2 Axial current flow
2.8.2.2 Prods, current flow
Current is passed between hand-held or clamped contact prods as shown in Figure 3, providing an inspection
of a small area of a larger surface. The prods are then moved in a prescribed pattern to cover the required
total area. Examples of testing patterns are shown in [1.8.1] and Table 5. Approximate formulae for the
current required to achieve a specified tangential field strength are given in ISO 9934-1.
This technique offers the highest sensitivity for discontinuities elongated parallel to the direction of the
current. Particular care shall be taken to avoid surface damage due to burning or contamination of the
component by the prods. Arcing or excessive heating shall be regarded as a defect requiring a verdict on
acceptability. If further testing is required on such affected areas, it shall be carried out using a different
technique.
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Section 4
Unless residual magnetization techniques are used, the detecting medium shall be applied immediately prior
to and during magnetization. The application shall cease before magnetization is terminated. Sufficient time
shall be allowed for the indications to build up before moving or examining the component or structure under
test.
Key:
1 = flux
2 = specimen
3 = current
4 = flaw
5 = transformer primary coil.
Figure 3 Induced current flow
2.8.3 Magnetic flow techniques
2.8.3.1 Threading conductor (central conductor)
Current is passed through an insulated bar or flexible cable, placed within the bore of a component or
through an aperture, as shown in Figure 4.
This method offers the highest sensitivity for discontinuities parallel to the direction of current flow. The
example of approximate formula given in ISO 9934-1 for a central conductor is also applicable in this case.
For a non-central conductor, the tangential field strength shall be verified by measurement.
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Section 4
2.8.2.3 Induced current flow
Current is induced in a ring shaped component by making it, in effect, the secondary of a transformer, as
shown in Figure 3. An example of an approximate formula for the induced current required to achieve a
specified tangential field strength is given in ISO 9934-1.
Section 4
Key:
1 = insulated threading bar
2 = flaw
3 = flux
4 = current
5 = sSpecimen.
Figure 4 Threading conductor
2.8.3.2 Portable Yoke
The poles of an AC electromagnet (yoke) are placed in contact with the component surface as shown in
[1.8.1] and Table 1. The testing area shall not be greater than that defined by a circle inscribed between the
pole pieces and shall exclude the zone immediately adjacent to the poles. An example of a suitable testing
area is shown in [1.8.1].
Guidance note:
The magnetization requirements defined in this section of the class guideline is only achievable by the use of AC.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
2.8.3.3 Rigid coil
The component is placed within a current-carrying coil so that it is magnetized in the direction parallel
to the axis of the coil, as shown in Figure 5. Highest sensitivity is achieved for discontinuities elongated
perpendicular to the coil axis.
When using rigid coils of a helical form, the pitch of the helix shall be less than 25% of the coil diameter.
For short components, where the length to diameter ratio is less than 5, it is recommended to use magnetic
extenders. The current required to achieve the necessary magnetization is thus reduced.
An example of an approximate formula is given in ISO 9934-1 for the current required to achieve a specified
tangential field strength.
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Section 4
Key:
1 = current
2 = specimen
3 = flux
4 = flaws.
Figure 5 Rigid coil
2.8.3.4 Flexible coil
A coil is formed by winding a current-carrying cable tightly around the component. The area to be tested
shall lie between the turns of the coil, as shown in Table 3 in [1.8.2].
ISO 9934-1 and Table 3 in [1.8.2] give approximate formulae for the current required to achieve a specified
tangential field strength.
2.9 Detecting media
See [1.9].
2.10 Viewing conditions
See also [1.10].
Where viewing is obstructed, the component or equipment shall be moved to permit adequate viewing of all
areas. Care shall be taken to ensure that indications are not disturbed after magnetization has stopped and
before the component has been inspected and indications recorded.
2.11 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
If no acceptance criteria are defined, acceptance criteria as specified in Table 5 may be applied.
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Quality class acc. to EN 10228-1
Parameter for evaluation
3
1)
×
2)
2
6.3 µm < Ra < 12.5 µm
×
×
Ra ≤ 6.3 µm
×
×
Recording level: length of indications [mm]
≥5
≥2
≥2
≥1
max. allowed length Lg of aligned or isolated indications Ln [mm]
20
8
4
2
max. allowed cumulative length of indications Lk [mm]
75
36
24
5
max. allowed number of indications on the reference area
15
10
7
5
1)
Class of quality not applicable for testing of surfaces with machining allowance exceeding 3 mm.
2)
Class of quality not applicable for testing of surfaces with machining allowance exceeding 1 mm.
3)
Class of quality not applicable for surfaces of fillets and oil hole bores of crankshafts.
4
2) , 3)
1
×
3)
Ra = arithmetical mean deviation of the profile
Four quality classes shall be applied to a forging or to parts of a forging. Quality class 4 is the most stringent,
determining the smallest recording level and the smallest acceptance standard. For forgings for general
application supplied in the as-forged surface condition only, quality classes 1 and 2 are applicable. For closed
die forgings, quality class 3 shall be the minimum requirement.
The applicable quality class(es) shall be agreed between the purchaser and supplier prior to the inspection.
Table 5 details recording levels and acceptance criteria that shall be applied for four quality classes.
NOTE: Where agreed with the Society, recording levels and acceptance criteria different from those detailed
in Table 5 may be used.
For hull and machinery steel forgings, IACS Rec. No. 68 is regarded as an example of an acceptable standard
for acceptance criteria.
For marine steel castings IACS Rec. No. 69 is regarded as an example of an acceptable standard for
acceptance criteria. For other castings, ISO 4986 is an example of a typical acceptable standard for
acceptance criteria.
2.12 Demagnetization
When required at the time of enquiry and order, post-test demagnetization shall be carried out by an
appropriate technique, in order to achieve the minimum residual field strength value. If viewing for
indications is carried out after demagnetization, indications shall be preserved by a suitable method.
The residual magnetic field strength shall not exceed 400 A/m unless a lower value is required. Where the
specified value is exceeded, the part shall be demagnetised and the value of the residual magnetic field
strength be recorded.
There are occasional circumstances when demagnetization is necessary before testing is carried out. This is
when the initial level of residual magnetism is such that adherent swarf, opposing fluxor spurious indications
could limit the effectiveness of the test.
Magnetic field remaining after magnetization may be determined by detecting the residual field strength
using a residual field meter, a Hall effect instrument or by an agreed physical method (e.g. compass test or
paper clip test). Generally this will require moving the sensitive element all over the part and observing the
maximum level. Care shall be taken when using Hall effect instruments because these usually are designed
to measure tangential field strength.
Demagnetization can be achieved by using an alternating field (i.e. AC) with an initial field strength equal to,
or greater than, that used for magnetization and then gradually lower the field towards zero.
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Section 4
Table 5 Acceptance criteria for magnetic particle testing of forgings according to EN 10228-1
Section 4
2.13 Reporting
See [1.15].
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1 Scope
This section describes penetrant testing used to detect imperfections which are open to the surface of
the tested material. It is mainly applied to metallic materials, but may also be performed on non-metallic
materials, e.g. non-porous surfaces like ceramics or plastics.
2 Personnel qualifications
See Sec.2 [1].
3 Equipment/testing material
UV-A lamps shall be checked at least once a month.
The equipment for carrying out penetrant testing depends on the number, size and shape of the part to be
tested. A product family is understood as a combination of the penetrant testing products/materials.
Cleaner, penetrant, excess penetrant remover and developer shall be from one manufacturer and shall be
compatible with each other as a complete brand system.
Colour contrast product family, penetrant products certified to sensitivity level 2 in accordance with ISO
3452-2 are accepted. Penetrant products certified and qualified to other standards may be considered for
acceptance subject to special evaluation by the Society. Sensitivity level 2 for colour contrast product family
shall be defined using type 1 reference block (ref. ISO 3452-3). The type 1 reference block consists of a set
of four nickel-chrome plated panels with 10 μm, 20 μm, 30 μm and 50 μm thickness of plating, respectively.
The sensitivity of colour contrast penetrant systems is determined using the 30 μm and 50 μm panels. The
type 1 panels are rectangular in shape with typical dimensions of 35 mm × 100 mm × 2 mm, see Figure
1. Each panel consists of a uniform layer of nickel-chromium plated on to a brass base, the thickness of
nickel-chromium being 10 μm, 20 μm, 30 μm and 50 μm respectively. Transverse cracks are made in each
panel by stretching the panels in the longitudinal direction. The width to depth ratio of each crack should be
approximately 1:20.
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Section 5
SECTION 5 PENETRANT TESTING
Section 5
Dimensions in mm.
Key:
1)
2)
Transverse cracks.
Nickel chromium plating thickness 10 μm, 20 μm, 30 μm and 50 μm respectively.
Figure 1 Type 1 references block
4 Compatibility of testing materials with the parts to be tested
The penetrant testing products shall be compatible with the material to be tested, the use for which the part
is designed and compliant with ISO 3452-2.
When examining nickel base alloys, all penetrant materials shall be analysed individually for sulphur content,
unless it can be documented that the sulphur content is not exceeding 200 ppm by mass.
When examining austenitic or duplex stainless steel and titanium, all penetrant materials shall be analysed
individually for halogens content, unless it can be documented that the total halogens content is not
exceeding 200 ppm by mass. These impurities may cause embrittlement or corrosion, particularly at elevated
temperatures.
The penetrant products (penetrant, remover and developer) shall be traceable to a batch certificate or data
sheet documenting compliance with one or more of the following combinations from ISO 3452-1.
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Penetrant
Type
I
II
Denomination
Fluorescent penetrant
Colour contrast penetrant
Excess penetrant remover
Method
Developer
Form
Denomination
A
Water
a
Dry
B
Lipophilic emulsifier
b
Water soluble
C
Solvent
Class 2: Non-halogenated
c
Water suspendable
D
Hydrophilic emulsifier
d
Solvent based
(non-aqueous for Type I)
Water and solvent removable
e
Solvent based
(non-aqueous for Type II)
E
1)
Denomination
1)
Section 5
Table 1 Testing products
Method E relates to application. Penetrant material qualified for method A are also considered qualified for method E.
Under no circumstances is a fluorescent liquid penetrant examination to follow a colour contrast dye
examination on the same component.
5 Preparation, pre-cleaning and testing
5.1 General
The penetrant process shall be as stated below and as illustrated in Figure 2.
5.2 Preparation and pre-cleaning of the surface
5.2.1 General
Contaminants, e.g. scale, rust, oil, grease or paint shall be removed, if necessary using mechanical or
chemical methods or a combination of these methods. Pre-cleaning shall ensure that the test surface is free
from residues and that it allows the penetrant to enter any defects/discontinuities. The cleaned area shall be
large enough to prevent interference from areas adjacent to the actual test surface.
Scale, slag, rust, etc., shall be removed using suitable methods such as brushing, rubbing, abrasion, blasting,
high pressure water blasting, etc. These methods remove contaminants from the surface and generally are
incapable of removing contaminants from within surface discontinuities. In all cases and in particular in
the case of shot blasting, care shall be taken to ensure that the discontinuities are not masked by plastic
deformation or clogging from abrasive materials. If it is necessary, to ensure that discontinuities are open to
the surface, subsequent etching treatment shall be carried out, followed by adequate rinsing and drying.
5.2.2 Drying
As the final stage of pre-cleaning, the object to be tested shall be thoroughly dried, so that neither water
or solvent remains in the defects/discontinuities. Where wire brushing or grinding is applied to remove
imperfections that would interfere with the examination, the material thickness shall not be reduced below
the minimum thickness permitted by the design specification and the dressed areas shall be faired with the
surrounding surface.
After surface preparation and cleaning has been performed, a visual examination of the surface is usually
undertaken.
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Section 5
5.3 Application of penetrant
5.3.1 Methods of application
The penetrant may be applied to the object to be tested by spraying, brushing, flooding or immersion.
Care shall be taken to ensure that the test surface remains completely wetted throughout the entire
penetration time.
5.3.2 Temperature
In order to minimize moisture entering defects/discontinuities, the temperature of the test surface shall
generally be within the range from 10°C to 50°C. In special cases temperatures as low as 5°C may be
accepted, provided the penetrant system is qualified for this temperature using a comparison block.
For temperatures below 10°C or above 50°C only penetrant product families and procedures approved in
accordance with recognised standard for this purpose shall be used.
5.3.3 Penetration time
The appropriate penetration time depends on the properties of the penetrant, the application temperature,
the material of the object to be tested and the defects/discontinuities to be detected. The penetration
time shall be in accordance with the time used by the manufacturer when certifying the product family in
accordance with ISO 3452-2 for sensitivity level 2 and at least 15 minutes.
5.4 Excess penetrant removal
5.4.1 General
The application of the remover medium shall be done such that no penetrant is removed from the defects/
discontinuities. It is not allowed to spray the cleaner directly upon the surface to be tested.
5.4.2 Water
The excess penetrant shall be removed using a suitable rinsing technique. Examples: spray rinsing or wiping
with a damp cloth. Care shall be taken to minimize any detrimental effect caused by the rinsing method and
to avoid excessive washing. The temperature of the water shall not exceed 45°C. The water pressure shall
not exceed 50 psi (3.4 bar).
5.4.3 Solvent
Generally, the excess penetrant shall be removed first by using a clean lint-free cloth. Subsequent cleaning
with a clean lint-free cloth lightly moistened with solvent shall then be carried out. Any other removal
technique shall be approved by the Society. Care shall be taken to minimize any detrimental effect caused by
the rinsing method.
5.4.4 Emulsifier
Hydrophilic (water-dilutable):
To allow the post-emulsifiable penetrant to be removed from the test surface, it shall be made water
washable by application of an emulsifier. Before the application of the emulsifier, a water wash should be
performed in order to remove the bulk of the excess penetrant from the test surface and to facilitate a
uniform action of the hydrophilic emulsifier which be applied subsequently.
The emulsifier shall be applied by immersion or by foam equipment. The concentration and the contact time
of the emulsifier shall be evaluated by the user through pre-test according to the manufacturers’ instruction.
The predetermined emulsifier contact time shall not be exceeded and the contact time shall be stated in
the procedure. After emulsification, a final wash shall be carried out. Care shall be taken to minimize any
detrimental effect caused by the rinsing method and to avoid excessive washing.
Lipophilic (oil-based):
To allow the post emulsifiable penetrant to be removed from test surface, it shall be rendered waterwashable by application of an emulsifier. This shall only be done by immersion. The emulsifier contact time
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This time shall be sufficient to allow only the excess penetrant to be removed from the test surface during
the subsequent water wash. The emulsifying time shall not be exceeded. Immediately after emulsification, a
water wash shall be carried out. Care shall be taken to minimize any detrimental effect caused by the rinsing
method and to avoid excessive washing.
5.4.5 Water and solvent
First the excess water washable penetrant shall be removed with water. Subsequent cleaning with a clean
lint-free cloth, lightly moistened, with solvent shall be then carried out. Care shall be taken to minimize any
detrimental effect caused by the rinsing method and to avoid excessive washing.
5.4.6 Excess penetrant removal check
During excess penetrant removal the test surface shall be visually checked for penetrant residues. For
fluorescent penetrants, this shall be carried out under a UV-A source.
5.5 Drying
In order to facilitate rapid drying of excess water, any droplets and puddles of water shall be removed from
the object.
Except when using water-based developer the test surface shall be dried as quickly as possible after excess
penetrant removal, using one of the following methods:
— wiping with clean, dry, lint-free cloth
— forced air circulation
— evaporation at elevated temperature.
If compressed air is used, particular care shall be taken to ensure that it is water and oil-free and applied
pressure on surface of the object is kept as low as possible.
The method of drying the object to be tested shall be carried out in a way ensuring that the penetrant
entrapped in the defects/discontinuities does not dry.
The surface temperature shall not exceed 45°C during drying unless otherwise approved by the Society.
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Section 5
shall be evaluated by the user through pre-test according to the manufacturers’ instruction and the contact
time shall be stated in the procedure.
The developer shall be maintained in a uniform condition during use and shall be evenly applied to the test
surface. The application of the developer shall be carried out as soon as possible after the removal of excess
penetrant.
Table 2 Overview of developers
Type of Developer
Dry powder
Description
May only be used with fluorescent penetrants.
Shall be uniformly applied to the test surface.
Techniques for application: dust storm, electrostatic spraying, flock gun, fluidized bed or storm
cabinet.
The test surface shall be thinly covered; local agglomerations are not permitted.
Water-suspendable
and
Water soluble
A thin uniform application shall be carried out.
Techniques for application: by immersion in agitated suspension or by spraying with suitable
equipment in accordance with the approved procedure.
Immersion time and temperature of the developer shall be evaluated by the user through pre-test
according to the manufacturers’ instruction.
The immersion time shall be as short as possible to ensure optimum results.
The object shall de dried by evaporation and/or by the use of a forced air circulation oven.
Solvent-based
The developer shall be applied by spraying uniformly.
Techniques for application: the spray shall be such that the developer arrives slightly wet on the
surface, giving a thin, uniform layer. The thickness of the developer layer shall be so thin that one
vaguely will see the surface through.
Usually this requires a spraying distance of minimum 300 mm.
5.6.1 Developing time
The developing time shall as a minimum be the same as the penetration time, however, longer times may be
agreed with the Society. The developing time shall be stated in the test procedure to ensure repeatable test
results with respect to defect sizing. The development time begins:
— immediately after application when dry developer is applied
— immediately after drying when wet developer is applied.
To verify the penetrant procedure, it is recommended to use a reference object with known defects such
as test panel type 2 described in ISO 3452-3 or equivalent. The test panel type 2 and penetrant products
shall before testing achieve the same temperature as relevant for the actual testing to be performed. The
minimum defect size to be detected shall respond to the maximum acceptable defect size.
6 Inspection
6.1 General
Generally, it is advisable to carry out the first examination just after the application of the developer or soon
as the developer is dry. This facilitates a better interpretation of indications.
The final inspection shall be carried out when the development time has elapsed.
Equipment for visual examination, such as magnification instruments or contrast spectacles, may be used.
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Section 5
5.6 Application of developer
Section 5
6.2 Viewing conditions and inspection parameters
6.2.1 Fluorescent technique
Viewing technique and inspection parameters for fluorescent technique are given in Table 3.
Table 3 Viewing technique and inspection parameters for fluorescent technique
Inspection-parameter
Control device
Limits/Values
UV-A radiation
UV A – intensity testing device
400 mm distance between test object and UV lamp.
UV intensity ≥ 10 W/m²
Ambient light
Lux meter
Max. 20 lux
Test medium
Reference Block Type 1 (ISO 3452-3)
Reference Block Type 2 (ISO 3452-3)
Control of inspection material
Photo chromatic spectacles shall not be used.
Sufficient time shall be allowed for the operators eyes to become dark-adapted in the inspection area, at
least 1 min.
UV radiation shall not be directed in the operator’s eyes.
6.2.2 Colour contrast technique
Viewing technique and inspection parameters for colour contrast technique are given in Table 4.
Table 4 Viewing technique and inspection parameters for colour contrast technique
Inspection-parameter
Control device
Limits/Values
Ambient light
Lux meter
Min. 500 lux
Test medium
Reference block type 1 (ISO 3452-3)
Reference block type 2 (ISO 3452-3)
Control of inspection material
The viewing conditions shall be such that glare and reflections are avoided.
7 Acceptance criteria
7.1 General
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory. If no acceptance criteria are defined, acceptance
criteria as specified below may be applied.
The indication produced by penetrant testing do not usually display the same size and shape characteristics
as the imperfections causing that indication, it is the size of the indication, (bleed out) which shall be
assessed against the values referred to or given below.
7.2 Welds
See also [7.1].
The quality shall normally comply with Level 2X. For highly stressed areas more stringent requirements, such
as level 1, may be applied, see Table 5.
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Type of indication
Acceptance level
a)
1
2
3
Linear indication
ℓ = length of indication
ℓ ≤ 2 mm
ℓ ≤ 4 mm
ℓ ≤ 8 mm
Non-linear indication
d = major axis dimension
d ≤ 4 mm
d ≤ 6 mm
d ≤ 8 mm
a)
Section 5
Table 5 Acceptance levels for indications
Acceptance levels 2 and 3 may be specified with suffix 'x' which denotes that all
linear indications detected shall be evaluated to level 1.
However, the probability of detection of indications smaller than those denoted by
the original acceptance level could be low. Linear defect such like crack, lack of
fusion and lack of penetration is NOT acceptable regardless of length.
7.3 Forgings
For hull and machinery forgings, IACS Rec. No.68 is regarded as an example of an acceptable standard. For
other forgings, EN 10228-2 is regarded as an example of an acceptable standard.
7.4 Castings
For marine steel castings IACS Rec. No. 69 is regarded as an example of an acceptable standard. For other
castings, ISO 4987 is regarded as an example of an acceptable standard.
8 Post cleaning and protection
8.1 Post cleaning
After final inspection, post cleaning of the object is necessary only in those cases where the penetrant testing
products could interfere with subsequent processing or service requirements.
8.2 Protection
If required a suitable corrosion protection shall be applied.
9 Retesting
If retesting is necessary, e.g. because no unambiguous evaluation of indication is possible, the entire test
procedure, starting with the pre cleaning, shall be repeated.
The use of a different type of penetrant or a penetrant of the same type from a different supplier is not
allowed unless a thorough cleaning has been carried out to remove penetrant residues remaining in the
defects/discontinuities.
10 Reporting
In addition to the items listed under Sec.2 [7] the following shall be included in the penetrant testing report:
— penetrant system used, e.g. coloured or fluorescent
— penetrant product
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application methods
penetration and development time
viewing conditions
test temperature.
Section 5
—
—
—
—
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Section 5
Figure 2 Main stages of penetrant testing, sequence of operations
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Section 6
SECTION 6 RADIOGRAPHIC TESTING
1 Scope
1.1 General
This section describes fundamental techniques for radiography with the objective of enabling satisfactory and
repeatable results. The techniques are based on generally recognized practice and fundamental theory of
the subject. This section of the class guideline applies to the radiographic testing of fusion welded joints in
metallic materials and radiographic flaw detection of non-welded metallic materials.
1.2 Definitions and symbols
In addition to that given in Sec.1 [3], the symbols defined in Table 1 apply.
Table 1 Definition of symbols
Term and symbol
Definition
Unit
diameter, De
the nominal external diameter of a pipe/tube
mm
effective film length,
EFL
the area of the film that shall be interpreted
mm
IQI
image quality indicator
minimum source–to–
object distance, fmin
the minimum allowable distance between the focal spot and the source side of
the object
nominal thickness, t
the nominal thickness of the parent material only. Manufacturing tolerances
shall not be taken into account
object–to–film
distance, b
the distance between the radiation side of the test object and the film surface
measured along the central axis of the radiation beam
mm
penetrated thickness, the thickness of the material in the direction of the radiation beam calculated
w
on the basis of the nominal thickness
mm
source size, d
mm
-
the size of the radiation source
mm
Guidance note:
Source size is according to EN 12679 for gamma ray sources or EN 12543 for Xray tubes.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
source–to–object
distance, f
the distance between the source of the radiation and the source side of the test
object measured along the central axis of the radiation beam
mm
source–to–film
distance, SFD
the distance between the source of radiation and the film measured in the
direction of the beam
mm
Ug
geometrical unsharpness
mm
In addition, relevant definitions for digital radiography given in ISO 17636-2 also apply.
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See Sec.2 [1].
In addition, requirements for radiation protection qualification should be in accordance with national
legislation or international standards.
However, operators only producing radiographs and not performing film interpretation may be qualified and
rd
certified in RT at level 1 in accordance with an accredited 3 party certification scheme based on ISO 9712.
3 General
3.1 Protection against ionizing radiation
When using ionizing radiation, local, national or international safety precautions and legislation shall be
strictly applied.
3.2 Surface preparation
The inside and outside surfaces (e.g. cap and root of welds) to be tested by x-ray/gamma-ray shall be
sufficiently free from irregularities that may mask or interfere with the interpretation.
Where surface imperfections or coatings cause difficulty in detecting defects, the surface shall be ground
smooth or the coatings shall be removed. Otherwise, surface preparation is not necessary. Unless otherwise
specified, radiography shall be carried out after the final stage of manufacture, e.g. after grinding or heat
treatment.
3.3 Identification of radiographs
Each radiograph shall be properly marked to clearly indicate the hull number or other equivalent traceable
identification and to identify the exact location of the area of interest. The images of these symbols shall
appear in the radiograph outside the region of interest where possible and shall ensure unambiguous
identification of the section. Permanent markings shall be made on the object to be tested, in order to
accurately locate the position of each radiograph. Where the nature of the material and/or service conditions
do not permit permanent marking, the location may be recorded by means of accurate sketches.
If the weld does not clearly appear on the radiograph, markers, usually in the form of lead arrows or other
symbols, shall be placed on each side of the weld.
The images of these letters should appear in the radiograph to ensure unequivocal identification of the
section.
3.4 Overlap of radiographs
When exposing radiographs of an area with two or more separate films/detectors, they shall show overlap
sufficiently to ensure that the complete region of interest is radiographed. This shall be verified by high
density marker placed on the surface of the object which will appear on each film/digital image.
3.5 Types and position of Image quality indicator (IQI)
3.5.1 General
The quality of the image shall be verified by use of IQIs in accordance with ISO 19232-1 and (for digital
images) ISO 19232-5. ASTM E747 IQIs may be used if the material group of this standard fits better to the
testing task. Tables for the conversion of wire numbers from the standards ASTM E747 and ISO 19232-1 are
given in both standards. By agreement between contracting parties and with the Society, other image quality
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Section 6
2 Personnel qualifications
IQI shall be selected from either the same alloy material group or grade or from an alloy material group with
less radiation absorption than the material being tested.
3.5.2 Single wire IQI
The IQI used shall be placed on the source side of the test object, at the centre of the area of interest, along
the centre beam, w, and in close contact with the surface of the object. The IQI shall be located in a section
of a uniform thickness characterized by a uniform optical density on the film. If not otherwise approved by
the Society, wire penetrameter should be used.
The wires shall be perpendicular to the weld and its location shall ensure that at least 10 mm of the wire
length shows in a section of uniform optical density, which is normally in the parent metal adjacent to the
weld. For exposures in accordance with Figure 5 and Figure 6, the IQI may be placed with the wires across
the pipe axis and they should not be projected into the image of the weld. The visible wire length may be
shorter than 10 mm for De < 50 mm. The visible wire length shall be ≥ 20% of De.
For exposures in accordance with Figure 5 and Figure 6, the IQI type used may be placed either on the
source side or on the film side. If an IQI cannot be physically placed on the side of the weld facing the source
of radiation, the IQI may be placed in contact with the back surface of the weld. This shall be indicated by
the placement of a lead letter 'F' near the IQI and this shall be recorded in the test report.
For pipe diameter, De ≥ 200 mm and with the source centrally located, at least three IQIs should be placed
equally spaced at the circumference. The film(s) showing IQI image(s) are then considered representative of
the whole circumference.
3.5.3 Duplex wire IQI
Following the procedure outlined in Annex C of ISO 17636-2, a reference image is required for the
detector
verification of the basic spatial resolution of the digital detector system ( SRb
). In this case, the duplex
wire IQI (ISO 19232-5) shall be positioned directly on the digital detector. The basic spatial resolution or
duplex wire value shall be determined to verify that the system hardware meets the requirements specified
as a function of the penetrated material thickness in Table 5. For double wall double image inspection, the
detector
SRb
shall correspond to the values of Table 5 chosen on the basis of twice the nominal single wall
thickness as the penetrated material thickness.
When used on production radiographs, the duplex wire IQI shall be placed on the source side of the object,
and positioned as described for single wire IQIs.
For calculation of SNRN from measured SNR the value SRb
detector
shall be used if the magnification ≤ 1.2.
image
If the basic spatial resolution is measured in the digital image ( SRb
), it shall not exceed the maximum
values specified as a function of the penetrated material thickness in Table 5.
For double wall double image technique (Figure 5 or Figure 6), with the duplex wire IQI on the source side of
the pipe, the pipe diameter, De is taken as the value b for determination of fmin and for determination of the
image
required basic spatial resolution ( SRb
) from Table 5.
The duplex wire IQI shall be positioned tilted by a few degrees (2° to 5°) to the digital rows or columns of
the digital image.
3.6 Evaluation of image quality
3.6.1 Film quality
Exposed films shall be viewed in accordance with ISO 5580.
The image of the IQI on the radiograph shall be tested and the number of the smallest wire which can be
discerned shall be determined. The image of the wire is acceptable if a continuous length of at least 10 mm is
clearly visible in a section of uniform optical density.
The image quality obtained shall be recorded on the radiographic testing report. The type of IQI used shall
also be clearly stated.
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Section 6
indicators with the same radiographic attenuation as the test object and same dimensions as defined in ISO
19232-1 may be used.
From the examination of the radiographic image of the wire IQI, the number of the smallest wire which can
be discerned shall be determined. The image of a wire is accepted if a continuous length of at least 10 mm
is clearly visible in a section of uniform characterized by a uniform grey value (mean) in the digital image ,
typically in the HAZ near the weld. See also [3.5.2], for the exception of DWDI evaluation of small pipes.
The duplex wire IQI shall be evaluated with the profile function of the image processing system in the linear
or linearized GV image as stated in ISO 19232-5.
The image quality shall be determined in the unprocessed (raw) image, the wire IQI shall be evaluated
and the achieved values shall fulfil the requirements of Table 2, Table 3 or Table 4. Where the images are
evaluated after application of digital processing e.g. using filters, the image quality shall additionally be
determined and satisfy the given requirements in the final processed condition.
3.7 Minimum image quality values
Table 2, Table 3 and Table 4 show the minimum quality values for ferrous materials. They may be applied for
nonferrous materials unless otherwise agreed with the Society.
Table 2 Single-wall technique, wire IQI on source side
1)
1)
Nominal thickness, t [mm]
Nominal wire diameter [mm]
IQI value
t ≤ 1.5
0.050
W19
1.5 < t ≤ 2.5
0.063
W18
2.5 < t ≤ 4
0.080
W17
4<t≤6
0.100
W16
6<t≤8
0.125
W15
8 < t ≤ 12
0.16
W14
12 < t ≤ 20
0.20
W13
20 < t ≤ 30
0.25
W12
30 < t ≤ 35
0.32
W11
35 < t ≤ 45
0.40
W10
45 < t ≤ 65
0.50
W9
65 < t ≤ 120
0.63
W8
120 < t ≤ 200
0.80
W7
200 < t ≤ 350
1.0
W6
t > 350
1.25
W5
If it is not possible to place the IQI on the source side, the IQI shall be placed on the film side and
the image quality determined from comparison exposure with one IQI placed on the source side
and one on the film side under the same conditions.
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Section 6
3.6.2 Digital image quality
The digital images shall be evaluated on a monitor. The monitor and the viewing conditions shall fulfill the
requirements of [4.14].
Penetrated thickness, w [mm]
Nominal wire diameter [mm]
IQI value
w ≤ 1.5
0.050
W19
1.5 < w ≤ 2.5
0.063
W18
2.5 < w ≤ 4
0.080
W17
4<w≤6
0.100
W16
6<w≤8
0.125
W15
8 < w ≤ 15
0.16
W14
15 < w ≤ 25
0.20
W13
25 < w ≤ 38
0.25
W12
38 < w ≤ 45
0.32
W11
45 < w ≤ 55
0.40
W10
55 < w ≤ 70
0.50
W9
70 < w ≤ 100
0.63
W8
100 < w ≤ 170
0.80
W7
170 < w ≤ 250
1.0
W6
w > 250
1.25
W5
Section 6
Table 3 Double-wall technique, double image, IQI on source side
Table 4 Double-wall technique, single or double image, IQI on film side
Penetrated thickness, w [mm]
Nominal wire diameter [mm]
IQI value
w ≤ 1.5
0.050
W19
1.5 < w ≤ 2.5
0.063
W18
2.5 < w ≤ 4
0.080
W17
4<w≤6
0.100
W16
6 < w ≤ 12
0.125
W15
12 < w ≤ 18
0.16
W14
18 < w ≤ 30
0.20
W13
30 < w ≤ 45
0.25
W12
45 < w ≤ 55
0.32
W11
55 < w ≤ 70
0.40
W10
70 < w ≤ 100
0.50
W9
100 < w ≤ 180
0.63
W8
180 < w ≤ 300
0.80
W7
w > 300
1.0
W6
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Section 6
3.8 Maximum unsharpness and basic spatial resolution
Table 5 Maximum unsharpness for all techniques
Minimum IQI value and
maximum unsharpness
[mm] (per ISO 19232-5)
Maximum basic spatial resolution
image
SRb
[mm]
w ≤ 1.5
D 13+
0.08
0.04
1.5 < w ≤ 4
D 13
0.063
0.05
4<w≤8
D12
0.080
0.063
8 < w ≤ 12
D 11
0.125
0.08
12 < w ≤ 40
D 10
0.16
0.10
40 < w ≤ 120
D9
0.20
0.13
120 < w ≤ 200
D8
0.25
0.16
w > 200
D7
0.32
0.20
Penetrated thickness, w [mm]
1)
1)
For double wall technique, single image, the nominal thickness t shall be used instead of the
penetrated thickness w.
detector
Both the inherent unsharpness (ui = 2SRb
) of a digital detector system and the geometric unsharpness
(ug) contribute to the total unsharpness (uT) in the image if not corrected by means of geometric
magnification:
(1)
Therefore, it is important that the distance fmin shall be increased to compensate for any additional
unsharpness of the detector system.
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4.1 Test arrangements
The radiographic techniques in accordance with Figure 1 through Figure 9 are recommended.
The elliptical technique in accordance with Figure 5 should not be used for external diameters De > 100 mm,
wall thickness t > 8 mm and weld widths > De /4. Two 90° displaced images are sufficient if t/ De <0.12. The
distance between the two weld images shall be about one weld width.
When it is difficult to carry out an elliptic test at De ≤ 100 mm, the perpendicular technique in accordance
with Figure 6 should be used. In this case three exposures 120° or 60° apart are required.
For test arrangements in accordance with Figure 7 and Figure 8, the inclination of the beam shall be kept as
small as possible and be such as to prevent superimposition of the two images.
Other radiographic techniques may be used, when the geometry of the piece or differences in material
thickness do not permit use of one of the techniques listed in Figure 1 to Figure 9. Radiographic techniques
for castings, applicable test arrangements and requirements shown in ISO 4993, Annex A, shall be used.
Multi-film techniques shall not be used to reduce exposure times on uniform sections. The use of multi-film
techniques shall be pre-qualified.
Guidance note:
The minimum number of radiographs necessary to obtain an acceptable radiographic coverage of the total circumference of a butt
weld in pipe shall be in accordance with ISO 17636-1 or 2, Figure A.1 and Figure A.2.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
Legend:
S = radiation source
F = film/detector
b = the distance between the radiation side of the test object and the film surface measured along the
central axis of the radiation beam
f
= the distance between the source of the radiation and the source side of the test object measured along
the central axis of the radiation beam
t = the nominal thickness of the parent material.
Figure 1 Test arrangement - for plane walls and single-walls penetration
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Section 6
4 Techniques for making radiographs
a) with film or curved detectors
b) with planar detectors
Legend:
1/S = radiation source
2/D = film or detector
= the distance between the radiation side of the test object and the film surface measured along the
b
central axis of the radiation beam
f
= the distance between the source of the radiation and the source side of the test object measured
along the central axis of the radiation beam
t
= the nominal thickness of the parent material.
Figure 2 Test arrangement for single wall penetration of curved objects
Figure 3 Test arrangement for single wall penetration of curved objects
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Section 6
The ratio of the penetrated thickness at the outer edge of an evaluated area of uniform thickness to that at
the beam centre shall not be more than 1.1.
Section 6
a) with film or curved detectors
b) with planar detectors
Figure 4 Test arrangement for single wall penetration of curved objects. Radiation source located
off-centre inside the object and film outside
Figure 5 Test arrangement for elliptical technique of curved objects for evaluation of both walls
(source and film outside the test object)
This technique may be used for pipe diameter ≤ 100 mm, wall thickness ≤ 8 mm and weld width less than
De/4. It is sufficient with two 90° displaced images if t/D < 0.12. The distance between the two weld images
shall be about one weld width.
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Section 6
Figure 6 Test arrangement for double-wall/double image technique of curved objects for
evaluation of both walls (source and film outside the test object)
When it is difficult to carry out an elliptical examination at De ≤ 100 mm, this perpendicular technique may
be used, see Figure 5. In this case, three exposures 120° or 60° apart are required.
a) with film or curved detectors
b) with planar detectors
Figure 7 Test arrangement for double-wall technique single image of curved objects for
evaluation of the wall next to the film with the IQI placed close to the film
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Section 6
a) with film or curved detectors
b) with planar detectors
Figure 8 Test arrangement for double-wall technique single image (contact) technique for pipe
diameter > 100 mm
1
2
3
4
= copper/nickel and alloys
= steel
= titanium and alloys
= aluminium and alloys.
Figure 9 Multi-film technique for different material thicknesses
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4.2.1 X-ray devices up to 1000 kV
To maintain good flaw sensitivity, the X-ray tube voltage should be as low as possible. The maximum values
of tube voltage versus thickness are given in Figure 10.
For some applications where there is a thickness change across the area of object being tested, a modified
technique with a slightly higher voltage may be used, but it should be noted that an excessively high tube
voltage will lead to a loss of detection sensitivity. For copper and nickel and its alloys, the increment shall
not be more than 60 kV. For steel the increment shall not be more than 50 kV, for titanium and its alloys, not
more than 40 kV and for aluminium and its alloys, not more than 30 kV.
Figure 10 Maximum X-ray voltage for X-ray devices up to 1000 kV as a function of penetrated
thickness and material
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Section 6
4.2 Choice of tube voltage and radiation source
On thin steel specimens, gamma rays from Se 75, Ir 192 and Co 60 will not produce radiographs having as
good defect detection sensitivity as X-rays used with appropriate techniques and parameters.
For certain applications wider wall thickness range may be permitted, if sufficient image quality is achieved.
X-ray equipment with energy 1 MeV and above may be used if special approved by the Society.
In cases where radiographs are produced using gamma rays, the travel time to position the source shall not
exceed 10% of the total exposure time.
Table 6 Penetrated thickness range for gamma ray sources for steel, copper and nickel base alloy.
Radiation source
Penetrated thickness, w [mm]
Se75
14 ≤ w ≤ 40
Ir 192
20 ≤ w ≤ 90
1)
Co 60
1)
60 ≤ w ≤ 150
Co 60 shall not be used for radiographic testing of welds.
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Section 6
4.2.2 Other radiation sources
The permitted penetrated thickness ranges for gamma ray sources are given in Table 6.
Film system classes and metal screens for radiographic testing of steels, aluminium, copper and nickel-based
alloys shall be in accordance with ISO 17636-1 and ISO 11699-1.
When using metal screens, good contact between film and screens is required.
The requirements for film system classes and metal screens for steels, copper and nickel-based alloys are
specified in Table 7.
Table 7 Film system classes and metal screens for steels, copper and nickel-based alloys
Penetrated
thickness, w [mm]
Film system
1)
class
X-ray ≤ 100 kV
-
C3
None or up to 0.03 mm front and back
screens of lead.
100 kV < X-ray ≤ 150 kV
-
C3
Up to 0.15 mm front and back screens of
lead.
150 kV < X-ray ≤ 250 kV
-
C4
0.02 mm to 0.15 mm front and back
screens of lead.
≤ 50
C4
0.02 mm to 0.2 mm front and back
screens of lead.
> 50
C5
0.1 mm to 0.2 mm front and back screens
2)
of lead .
≤ 75
C4
> 75
C5
≤ 100
C3
> 100
C5
Se75
≥ 14
C4
0.02 mm to 0.2 mm front and back
screens of lead.
Ir192
≥ 20
C4
0.1 mm to 0.2 mm front and back screens
2)
of lead .
≤ 100
C4
> 100
C5
Radiation source
250 kV < X-ray ≤ 500 kV
500 kV < X-ray ≤ 1000 kV
1 MeV < X-ray ≤ 4 MeV
Co60
Type and thickness of metal screens
0.25 mm to 0.7 mm front and back
screens of steel or copper.
0.25 mm to 0.7 mm front and back
screens of steel or copper.
0.25 mm to 0.7 mm front and back
screens of steel or copper.
1)
Better film system classes may also be used, see ISO 11699-1.
2)
Ready packed films with a front screen up to 0.03 mm may be used if an additional lead screen of 0.1 mm is placed
between the object and the film.
Table 8 Film system classes and metal screens for aluminium and titanium alloys
Radiation source
Film system
1)
class
Type and thickness of metal screens
X-ray ≤ 150 kV
C3
None or up to 0.03 mm front and 0.15 mm back screens of lead.
150 kV < X-ray ≤ 250 kV
C3
0.02 mm to 0.15 mm front and back screens of lead.
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Section 6
4.3 Film systems and screens
250 kV < X-ray ≤ 500 kV
1)
Film system
1)
class
C3
Section 6
Radiation source
Type and thickness of metal screens
0.1 mm to 0.2 mm front and back screens of lead.
Better film system classes may also be used, see ISO 11699-1.
4.4 Alignment of beam
The radiation beam shall be directed to the centre of the area being tested and should be perpendicular to
the object surface at that point, except when it is demonstrated that certain imperfections are best revealed
by a different alignment of the beam. In this case, an appropriate alignment of the beam may be permitted.
4.5 Digital detector systems and metal screens
4.5.1 Minimum normalized signal-to-noise ratio
For digital radiographic examination, minimum SNRN values as given in Table 9 and Table 10 or minimum
grey values (CR only) shall be achieved.
The SNRN value shall be measured beside the weld near the wire or step hole IQIs in the thicker part of the
parent material in a zone of homogeneous wall thickness and grey values. The grey values in CR (only) shall
be measured in the region of interest in the weldment near the wire or step hole IQI. The roughness of the
material influences image noise and SNRN, hence the minimum SNRN values shall be increased by a factor of
1,4 in comparison to Table 9 and Table 10 if the SNRN measurement is performed adjacent to the weld in the
heat-affected zone, except if the weld cap and root are flush with the parent material.
The minimum SNRN values are given in Table 9 and Table 10 for different radiation sources and material
thicknesses.
4.5.2 Metal screens for IPs and shielding
When using metal front screens, good contact between the sensitive detector layer and screens is required.
This may be achieved either by using vacuum-packed IPs or by applying pressure.
Table 9 and Table 10 show the necessary screen materials and thicknesses for different radiation sources.
Other screen thicknesses may be also be used in agreement with the Society, provided the required image
quality is achieved. The usage of metal screens is applicable in front of IPs, and they may also reduce the
influence of scattered radiation when used with DDAs.
Table 9 Minimum SNRN values (CR and DDA) and metal front screens (for CR only) for digital
radiography of steels, copper and nickel-based alloys
Penetrated
thickness, w [mm]
Minimum
1)
SNRN
X-ray ≤ 50 kV
-
150
none
50 kV < X-ray ≤ 150 kV
-
120
0 to 0.1 (Pb)
2)
150 kV < X-ray ≤ 250 kV
-
100
0 to 0.1 (Pb)
2)
≤ 50
100
0 to 0.3 (Pb)
2)
> 50
70
0 to 0.3 (Pb)
2)
≤ 50
100
70
0 to 0.3 (Pb)
2)
> 50
≤ 100
100
Radiation source
250 kV < X-ray ≤ 350 kV
350 kV < X-ray ≤ 1000 kV
1 MeV < X-ray ≤ 5 MeV
3, 4)
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Type and thickness [mm]
of metal front screens
0.3 to 0.8 (Fe or Cu) + 0.6 to 2 (Pb)
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Se75 and Ir192
Co60
3, 4)
Penetrated
thickness, w [mm]
Minimum
1)
SNRN
Type and thickness [mm]
of metal front screens
> 100
70
≤ 50
100
0 to 0.3 (Pb)
2)
> 50
70
0 to 0.4 (Pb)
2)
≤ 100
100
> 100
70
Section 6
Radiation source
0.3 to 0.8 (Fe or Cu) + 0.6 to 2 (Pb)
1)
If the SNR N is measured in the HAZ/parent material these values shall be multiplied by 1.4, except if the weld cap
and root are flush with the parent material.
2)
Pb screens may be replaced completely or partially by Fe or Cu screens. The equivalent thickness for Fe or Cu is
three times the Pb thickness.
3)
In the case of multiple screens (Fe+Pb), the steel screen shall be located between the IP and the lead screen.
4)
Instead of Fe or Fe+Pb also copper, tantalum or tungsten screens may be used if the required image quality is
proven.
Table 10 Minimum SNRN values (CR and DDA) and metal front screens (for CR only) for digital
radiography of aluminium and titanium alloys
Radiation source
Minimum SNRN
1)
Type and thickness [mm] of metal front screens
X-ray ≤ 150 kV
120
≤ 0.03 (Pb)
150 kV < X-ray ≤ 250 kV
100
≤ 0.2 (Pb)
250 kV < X-ray ≤ 500 kV
100
≤ 0.2 (Pb)
1)
If the SNR N is measured in the HAZ/parent material these values shall be multiplied by 1.4, except if the weld cap
and root are flush with the parent material.
4.6 Reduction of scattered radiation
4.6.1 Filters and collimators
In order to reduce the effect of back-scattered radiation, direct radiation shall be collimated as much as
possible to the section being tested.
With Ir 192 and Co 60 radiation sources or in the case of edge scatter, a sheet of lead may be used as a low
energy scattered radiation filter between the object and the cassette. The thickness of this sheet shall be
between 0.5 mm and 2 mm in accordance with the penetrated thickness.
4.6.2 Interception of back-scattered radiation
If necessary, the film shall be shielded from back-scattered radiation by an adequate thickness of lead, or of
tin, placed behind the film-screen combination.
The presence of back-scattered radiation shall be checked for each new test arrangement by a lead letter
'B' (with a minimum height of 10 mm and a minimum thickness of 1.5 mm) placed immediately behind each
cassette/film. This shall be outside the image of the weld and HAZ in the area of interest (AoI). If the image
of this symbol records as a lighter image on the radiograph, it shall be rejected. If the symbol is darker or
invisible, the radiograph is acceptable and demonstrates good protection against scattered radiation.
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The minimum source to object distance fmin depends on the source size of focal spot size d, on the film to
object distance, b and the maximum allowable geometrical unsharpness. The source size value d, used in
calculations, shall conform to EN 12543 or EN 12679.
The maximum geometrical unsharpness (Ug) is: 0.2 mm.
The minimum source to object distance is calculated from the equation below:
(2)
If the distance b < 1.2 t, the dimension b in the equation above shall be replaced by the nominal thickness,
t.
For critical technical applications in crack-sensitive materials, more sensitive radiographic techniques than
described in this section shall be considered.
When using the elliptical technique described in Figure 5 or the perpendicular technique described in Figure
6, b shall be replaced by the external diameter, De, of the pipe in above equation.
When it is possible to place the radiation source inside the object to be radiographed (techniques shown in
Figure 2) to achieve a more suitable direction of testing, so that a double wall technique (see Figure 7 to
Figure 8) is avoided, the method indicated in Figure 2 should be preferred.
The reduction in minimum source to object distance should not be greater than 20%. When the source is
located centrally inside the object and the film (see Figure 2) and provided that the IQI requirements are
met, this percentage may be increased. However, the reduction in minimum source to object distance shall
be no greater than 50%.
4.8 Unsharpness and source to object distance for digital radiography
detector
Both the inherent unsharpness (ui = 2SRb
) of a digital detector system and the geometric unsharpness
(ug) contribute to the total unsharpness (uT) in the image if not corrected by means of geometric
magnification:
(3)
Therefore, it is important that the distance fmin shall be increased to compensate for any additional
unsharpness of the detector system.
For exposure arrangements set on the basis of Figure 2 b), Figure 4 b), Figure 7 b), and Figure 8 b), the
distance f shall, where practicable, be chosen so that the minimum is not below that given by formulae
below:
(4)
If digital detectors are used, which have a greater inherent unsharpness than X-ray film, conditions a) and
b) are recommended, if similar low total image unsharpness values, as resulted in film radiography, shall be
achieved.
a)
Provided the object is in contact with the detector (this is not valid for any geometric magnification
technique), then select digital detectors so that the detector basic spatial resolution (SR b ) is less than
the values given by formulae (5) depending on the object to detector distance b:
(5)
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Section 6
4.7 Geometrical unsharpness and source to object distance for film
radiography
Where an unsharpness comparable to that obtained with film radiography (ISO 17636-1) shall be
achieved, then f min should be increased compared with the values given by formulae (2) or (4), using
the following formulae (6) provided formulae for SRb (5) is fulfilled):
(6)
4.9 Maximum area for a single exposure
The number of radiographs for complete testing of flat welds and of curved welds with the radiation source
arranged off-centre should be specified.
The ratio of the penetrated thickness at the outer edge of an evaluated area of uniform thickness to that at
the beam centre shall not be more than 1.1.
The densities for film radiography, resulting from any variation of penetrated thickness should not be lower
than those indicated in [4.10] and not higher than those allowed by the available illuminator, provided
suitable masking is possible. The SNRN values resulting from any variation of penetrated thickness should not
be lower than those indicated in Table 9 or Table 10.
The size of the area to be tested includes the welds and the heat affected zones. In general, about 10 mm of
parent metal should also be tested on each side of the weld.
4.10 Density of film radiographs
Exposure conditions should be such that the minimum optical density of the radiograph in the area of
interest, see Figure 11, is minimum 2.3 and not more than 4.0.
The density shall be verified by measuring using an annually calibrated densitometer or by checking the
densitometer using a calibrated film strip as reference. A measuring tolerance of ±0.1 is permitted.
Higher optical densities than given above, may be used where the viewing light is sufficiently bright and in
accordance with ISO 5580. This shall be documented by the manufacturer of the viewing equipment. For
2
densities above 2.5, the minimum luminance through film shall be 10 cd/m .
In order to avoid unduly high fog densities arising from film ageing, development or temperature, the fog
density shall be checked periodically on a non-exposed sample taken from the films being used, handled and
processed under the same conditions as the actual exposed radiograph. The fog density shall not exceed 0.3.
Fog density is defined as the total density (emulsion and base) of a processed, unexposed film.
When using a multi-film technique with interpretation of single films, the optical density of each film shall be
in accordance with density limitations stated above.
If double film viewing is required, the optical density of one single film shall not be lower than 1.3.
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Section 6
b)
Section 6
Figure 11 Area of interest (numbers in [mm])
4.11 Processing
Films should be processed in accordance with the conditions recommended by the film and chemical
manufacturer to obtain the selected film system class per ISO 11699-1. Particular attention shall be paid
to the temperature, developing time and washing time. The film processing shall be controlled regularly in
accordance with ISO 11699-2.
Processing of digital radiographs shall be in accordance with ISO 17636-2, section 7.9.
4.12 Film viewing conditions
The radiographs shall be examined in a darkened area using viewing screens with adjustable luminance in
accordance with ISO 5580. The viewing screens should be masked to the area of interest.
4.13 Quality of radiographs
All radiographs shall be free from mechanical, chemical, or other blemishes to the extent that they do not
mask the image of any discontinuity in the area of interest of the object being tested.
4.14 Monitor viewing conditions and storage of digital radiographs
The digital radiographs shall be examined in a darkened room. The monitor setup shall be verified with a
suitable test image.
The display for image evaluation shall fulfil minimum requirements a) to d):
a)
b)
c)
d)
2
minimal brightness of 250 cd/m
display of at least 256 shades of grey
minimum displayable light intensity ratio of 1:250
display of at least 1 mill. pixels of a pixel size < 0.3 mm.
The original images shall be stored at the full resolution as delivered by the detector system. Only image
processing connected with the detector calibration (see ASTM E2597 for more details) to provide artefact-free
detector images shall be applied before storage of these raw data.
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5 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, the criteria given therein are mandatory.
If no acceptance criteria are defined, acceptance criteria for welds as specified below may be applied. The
standard ISO 17636 below, comprises both part 1 and part 2 of the standard. Referenced ISO 17636, Class B
below is considered to be equivalent to this section of the class guideline.
The quality of welds shall comply with ISO 5817 quality level C. For highly stressed areas more stringent
requirements, such as quality level B, may be applied.
Table 11 Radiographic testing using films and digital detectors
Quality levels in accordance with
ISO 5817 or ISO 10042
Testing techniques and levels
in accordance with ISO 17636
1)
or this class guideline
Acceptance levels in accordance with
ISO 10675-1 or ISO 10675-2
B
B
1
C
D
B
2)
At least A
2
3
1)
Stated testing techniques and levels refers to ISO 17636. The corresponding testing techniques in this class guideline
are compliant with Class B in ISO 17636
2)
The minimum number of exposures for circumferential weld testing may correspond to the requirements given in ISO
17636, class A.
For hull and machinery forgings and castings acceptance criteria shall be agreed with the Society.
6 Reporting
In addition to the items listed under Sec.2 [7] the following shall be included in the radiographic testing
report:
—
—
—
—
—
—
—
—
—
—
—
—
—
—
test arrangement
type and position of image quality indicator(s)
source to film distance and exposure value
geometric unsharpness
required IQI sensitivity
achieved IQI sensitivity
required and achieved density
film type and class used, screens (material type and thickness) and filter (material type and thickness)
source type and activity if gamma ray used
focus/source dimension, source activity
used tube voltage and filament current; if X-ray
system of marking used
film position plan
film processing: manual or automatic, and development conditions.
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Section 6
The data storage shall be redundant and supported by suitable back-up strategies to ensure long-time
storage using lossless data compression only.
1 Scope
This section specifies techniques for ultrasonic testing (UT) of fusion welded joints in metallic materials equal
to and above 10 mm thickness. It is primarily intended for use on full penetrations welds in C, C-Mn steels,
alloy steels and aluminium.
However, techniques for ultrasonic testing of welds in austenitic stainless steel and ferritic-austenitic (duplex)
steels are also described.
In addition, methods for manual ultrasonic testing of rolled steel plates, castings and forgings are covered.
The definitions, techniques and requirements specified in this class guideline will always satisfy the need for
a written procedure. Where techniques described in this class guideline are not applicable to the weld joint
or material to be examined, additional written procedures shall be used. The procedures shall be established
according to recognised standards and are subjected for approval by the Society.
Typical applications which require specific procedures, procedure qualifications and accompanying
requirements are:
—
—
—
—
—
—
—
—
ultrasonic testing of welds in austenitic stainless steel
ultrasonic testing of welds in ferritic-austenitic (duplex) stainless steels
detection of corrosion and/or thickness measurement
estimation of defect size (height) using conventional beam spread diagram (20 dB-drop) or Time-ofFlight-Diffraction (TOFD) technique. TOFD shall be done according to ISO 10863 (or ISO 16828) for
thicknesses above 10 mm and limitations in coverage for surface and back wall shall be taken into
consideration and compensated for. Acceptance levels 1 or 2 according to ISO 15626 shall be used
Phased Array Ultrasonic Testing, PAUT. PAUT shall be done according to ISO 13588. In addition the
requirements for testing volume coverage outlined in this class guideline shall be fulfilled (i.e. there shall
be a normal incidence for the sound to the fusion face in the welds)
Automatic Ultrasonic Testing, AUT
for special application during in-service inspection
testing of objects with temperature outside the range 0°C to 40°C.
2 Definitions and symbols
For the purpose of this section, and in addition to Sec.1 [3], the terms and definitions given in ISO 5577 and
ISO 17635 apply. Additionally, see Table 1.
Table 1 Definition of terms
Term
Definition
6 dB-drop technique
method for defect size assessment, where the probe is moved from a position showing
maximum reflection amplitude until the echo has decreased to its half-value (by 6dB)
amplitude
maximum value of the motion or pressure of a sound wave (echo-height)
back wall echo
pulse reflected from a boundary surface which is perpendicular to the sound beam axis
corrected primary gain
primary gain plus transfer correction
dead zone
zone adjacent to the scanning surface within which reflectors of interest are not revealed
DGS-diagram
series of curves which shows relationship between distance along a beam and gain in dB
for an infinity reflector and different sizes of disc shaped reflectors
manual scanning
manual displacement of the probe on the scanning surface
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Section 7
SECTION 7 ULTRASONIC TESTING
Definition
primary gain
the gain noted when constructing the DAC using the reference block
probe index
intersection point of the sound beam axis with the probe surface
Section 7
Term
The abbreviations described in Table 2 are used in this document.
Table 2 Abbreviations
Abbreviation
Description
DAC
distance amplitude curve
dB
decibel
FBH
flat bottom hole
FSH
full screen height
S
skip distance
SDH
side drilled hole
3 Personnel qualifications
In addition to Sec.2 [1] the following applies:
Personnel performing ultrasonic testing of welds in austenitic and duplex stainless steel material shall be
specially trained and qualified for the purpose according to an ISO 9712 based scheme.
All certificates shall state qualifications as to which application/joint-configuration the operator is qualified
and certified.
Personnel performing ultrasonic testing of tubular node welds (i.e. tubular TKY connections), shall undergo a
practical test in the typical connections to be tested. The practical test shall have a scope as described in ISO
9712 for industrial sector, welds (w).
4 Requirements for equipment
4.1 Test equipment
4.1.1 Test equipment requirements
Any equipment used for testing in conjunction with this document shall comply with the requirements of ISO
22232 (all parts).
In addition, if not already covered by standard above, the ultrasonic instrument shall:
—
—
—
—
—
—
be applicable for the pulse-echo technique and for the double-probe technique
cover at least a frequency range from 1 MHz to 6 MHz
if used for testing of material thickness between 8 mm and 10 mm, cover frequency ranges up to 12 MHz
have a calibrated gain regulator with minimum 2 dB per step over a range of minimum 60 dB
be equipped with digital DAC- display presentation
be able to clearly distinguish echoes with amplitudes at 5% of full screen height.
Each ultrasonic instrument shall have a calibration certificate with reference to its serial number. This
calibration of the instrument shall be performed by a company approved by the manufacturer of the
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4.1.2 Periodic check and calibration of equipment
Calibration, verification and periodic check of all ultrasonic equipment shall be undertaken as per ISO 22232
(all parts). Records shall be filed by the owner of the equipment.
4.2 Probe parameters
4.2.1 Test frequency
The frequency shall be within the range 2 MHz to 5 MHz and shall be selected to consider the properties of
the test object and to comply with acceptance levels specified in the applicable rules. For material thickness
between 8 mm and 10 mm, the frequency shall be within the range 4 MHz to 10 MHz.
Higher frequencies may be used to improve range resolution if this is necessary when using standards for
acceptance levels based on characterization of discontinuities.
Lower frequencies should be used for testing at long sound paths and/or when the material shows high
attenuation.
4.2.2 Angles of incidence
Probes used for testing of welds in C, C-Mn steels and alloy steels shall be straight beam transducers
and angle shear-wave transducers of 35° to 70°. When testing is carried out with transverse waves and
techniques that require the ultrasonic beam to be reflected from an opposite surface, care shall be taken
to ensure that the incident angle of the beam, with the opposite reflecting surface, is not less than 35° and
preferably not greater than 70°. Where more than one probe angle is used, at least one of the angle probes
used shall conform to this requirement. One of the probe angles used shall ensure that the weld fusion faces
are tested at, or as near as possible to, normal incidence. When the use of two or more probe angles is
specified, the difference between the nominal beam angles shall be 10° or greater.
A favourable probe angle when the weld connections are being tested for lack of fusion in the transition
between weld and parent material is the angle which gives incident sound perpendicular to the weld bevel.
The optimal angle for a V-groove is given by the groove geometry and is calculated as shown in Figure 1. If
the calculated angle does not comply with any standard probe angle, the nearest larger probe angle should
be selected, provided there are not other reasons for choosing the smaller probe angle. When use of two or
more angle probes is specified, the difference between the nominal beam angles shall be 10° or greater.
Figure 1 Selection of probe angle for detection of side wall fusion, α = 90° - β, where α is probe
angle and β is weld bevel angle
4.2.3 Element size
The element size of the probe shall be chosen according to the ultrasonic path to be used and the frequency.
The smaller the element, the smaller the length and width of the near field and larger the beam spread in the
far field at a given frequency.
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Section 7
instrument. The calibration is valid for maximum one year. The instrument serial number shall be included in
the calibration report.
Table 3 Material thickness and related element size
Material thickness t [mm]
Element size [mm]
10 to 30
8×9
25 to 80
14 × 14
t > 50
20 × 22
4.2.4 Adaption of probes to curved scanning surfaces
The gap between the test surface and the bottom of the probe shoe shall not be greater than 0.5 mm.
For flat probes on cylindrical or spherical surfaces, compliance this requirement may be checked with the
following equation:
(1)
where:
a = dimension of the probe in the direction of the curvature [mm]
D = diameter of the curvature [mm]
g = calculated gap.
If the calculated value for g is larger than 0.5 mm based on above equation, the probe shoe shall be adapted
to the surface and the sensitivity and time base shall be set accordingly.
For spherical or complex shaped surfaces, the equation above shall be applied in both length and width
direction of the probe (possible differences in curvature and/or probe dimensions).
4.2.5 Coupling media
Different coupling media may be used, but their type shall be compatible with the materials to be examined.
Examples are: contact paste, oil, glycerin, grease. Any couplant causing corrosion on material surface is not
allowed.
The characteristics of the coupling medium shall remain constant throughout the verification, calibration
operations, and the examination. It shall be suitable for the temperature range in which it will be used. If
the constancy of the characteristics cannot be guaranteed between calibration and examination, a transfer
correction may be applied.
After the examination is completed, the coupling medium shall be removed if its presence is liable to hinder
subsequent operations, inspection or use of the object.
The coupling medium used for range and sensitivity setting and for the test shall be the same.
4.3 Calibration blocks
The calibration blocks to be used for time base calibration and for angle determination are defined in ISO
2400 and ISO 7963. These calibration blocks shall preferably have the same acoustic properties as the
material to be tested.
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Section 7
Small probes having 6 mm to 12 mm diameter elements are best suited for short beam path ranges. For
beam path ranges > 100 mm (for single crystal normal beam probes), an element size of 12 mm to 24 mm
is preferred. For rectangular elements the element sizes described in Table 3 related to material thickness
shall be chosen.
Reference blocks shall be made with thickness and side-drilled holes, as described in ISO 16811 Annex B.
The reference block shall normally be manufactured from the actual material tested and at least have
acoustic properties which are within a specified range with respect to the material to be tested and shall
have a surface condition comparable to that of the object to be examined. If these characteristics are not the
same, a transfer correction shall be applied.
When ultrasonic testing shall be performed on steel produced by controlled rolling or thermo mechanical
treatment (TMCP steel), reference blocks shall be both produced perpendicular to, and parallel to, the
direction of rolling. The rolling direction shall clearly be identified on the reference block.
The position and number of reflectors should relate to the scanning of the entire examination zone and shall
cover this zone and at least 1.5 × skip distance.
The consequences of temperature differences between examination object, probes, and reference blocks,
shall be considered and compared to the requirements for the accuracy of the examination. If necessary the
reference blocks shall be maintained within the specified temperature range during the examination.
5 Testing volume
The testing volume is defined as the zone which includes weld and parent material for at least 10 mm on
each side of the weld, or the width of the heat affected zone (HAZ), whichever is greater.
In all cases, scanning shall cover the whole testing volume, see e.g. Figure 2. If individual sections of this
volume cannot be covered in at least one scanning direction, or if the angles of incidence with the opposite
surface do not meet the requirements set out in [4.2.2], alternative or supplementary ultrasonic techniques
or other non-destructive techniques shall be done. This may, require removal of the weld reinforcement. Use
of multiple angle probes scanning in addition to normal probe scanning is required.
The welds shall whenever feasible be tested from both sides on the same surface and include scanning for
both transverse and longitudinal indications. For T-joints and plate thickness above 40 mm, scanning from
both surfaces and all accessible sides shall be performed.
Where configuration or adjacent parts of the object are such that scanning from both sides is not possible
this fact shall be included in the report.
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Section 7
4.4 Reference blocks for testing of welds
Section 7
Legend:
= probe approaching full scanning length
1
2
3
4
a
b
= probe approaching full skip
= probe as close to weld reinforcement as possible
= defined test volume of parent material
= width of testing volume
= scanning zone width, excluding width of weld due to presence of weld cap (at least 1.5 × full skip
distance).
Figure 2 Illustration of testing volume to be covered when scanning for longitudinal
discontinuities
6 Preparation of scanning surfaces
Scanning surfaces shall be wide enough to permit the testing volume to be fully covered (i.e. width shall be
1.5 × full skip distance). Alternatively, scanning from both the upper and the lower surface of the joint shall
be done.
All scanning surfaces shall be free from dirt, loose scale, weld spatter, residues of previous couplant etc. and
shall be of sufficiently uniform contour and smoothness that satisfactory acoustic coupling is maintained.
Waviness of the test surface shall not result in a gap between the probe and test surfaces greater than 0.5
mm. In addition, such features of the surface of the object that may give rise to errors of interpretation shall
be removed prior to testing.
Scanning surfaces and surfaces from which the sound beam is reflected shall allow undisturbed coupling and
reflection.
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The parent metal, in the scanning zone area, shall be tested with straight beam (normal) probes prior to or
after welding. The scanning zone is at least 1.5 × full skip distance (S).
Scanning of parent material is performed in order to reveal laminations, imperfections, large variations in
attenuation or thickness variation, which might influence the angle beam testing.
Where imperfections are found, their influence on the upcoming angle-beam testing shall be assessed and,
if necessary, the techniques adjusted correspondingly. When satisfactory coverage by ultrasonic testing is
seriously affected, other test methods or techniques shall be considered.
The gain setting shall be calibrated on a defect free place on the parent material. The second back wall echo
shall be set to 75% of FSH Imperfections with a cross section larger than the sound beam (loss of back wall
echo) shall be reported. The extent of the imperfections is measured with the aid of the 6 dB-drop method
when complete loss of back wall echo occurs.
See also [13] for Ultrasonic testing of rolled steel plates.
8 Range and sensitivity setting
8.1 General
Setting of range and sensitivity shall be carried out prior to each testing in accordance with this section and
ISO 16811, taking the influence of temperature into account. The temperature difference during range and
sensitivity setting and during the test shall be within ±15°C.
Checks to confirm settings above, shall be performed at least every 4 hours and upon completion of the
testing. Checks shall also be carried out whenever a system parameter is changed or changes in the
equivalent settings are suspected.
If deviations greater than 2 dB in sensitivity, respectively 1% of range, are found during these checks, the
corrections given in Table 4 shall be carried out.
Table 4 Sensitivity and range corrections
No.
Sensitivity
Correction
1
Deviations ≤ 2 dB
No correction required
2
2 dB < deviation ≤ 4 dB
Setting shall be corrected before the testing is continued
3
Reduction in sensitivity > 4 dB
Setting shall be corrected, and all testing carried out with the
equipment since last check of setting shall be repeated
4
Increase in sensitivity > 4 dB
Setting shall be corrected, and all recorded indications shall be reexamined
No.
Range
Correction
1
Deviations < 1% range
No correction required
2
1% range < deviation ≤2% range
Setting shall be corrected before the testing is continued
3
Deviations > 2% range
Setting shall be corrected, and all testing carried out with the
equipment since last check of setting shall be repeated
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Section 7
7 Parent material testing
One of the following techniques for setting the reference shall be used.
— Technique 1: the reference is a distance-amplitude curve (DAC) for side-drilled holes diameter (DSDH)
given in Table 5. The length of the side-drilled holes and notches shall be greater than the width of the
sound beam at −20 dB amplitude.
Table 5 Diameter, side drilled hole (DSDH) for reference block
Thickness of parent material [mm]
DSDH [mm]
8 ≤ t < 10
Ø 1.5 ± 0.2
10 ≤ t ≤ 100
Ø 3 ± 0.2
t > 100
Ø 6 ± 0.2
— Technique 4: for the tandem technique, the reference is a disk-shaped reflector (flat-bottom hole) of 6
mm diameter (for all thicknesses), perpendicular to the scanning surface. This technique is best suited for
beam angle 45° and thickness t ≥ 40 mm.
8.3 Evaluation and recording levels
The evaluation and recording levels are defined in relevant standards, referenced in the rules. If these levels
are not defined, the values applied during the examination shall be included in the examination report.
All indications equal to or exceeding the evaluation levels shall be evaluated. All indications equal to or
exceeding the recording levels shall be recorded and reported.
8.4 Transfer correction
Any possible difference in attenuation and surface character between the reference block and the object to be
tested shall be checked in the following way: for angle probes, two of the same type as those to be utilized
during the testing shall be used. The probes are placed on the object to be tested as shown in Figure 3. One
of the probes works as transmitter probe, whilst the other acts as receiver. The first echo is maximised and
with the aid of the gain control it is adjusted to reach DAC. The gain setting is noted. Without altering this
gain setting the probes are moved to the reference block. The echo is adjusted to reach DAC and the gain
setting is noted.
Any difference in echo amplitude between the two materials can now be determined with the aid of the gain
control.
If the differences are less than 2 dB, correction is not required.
If the differences are greater than 2 dB but smaller than 12 dB, they shall be compensated for.
If transfer losses exceed 12 dB, the reason shall be considered and further preparation of the scanning
surfaces shall be carried out, if applicable.
When there are no apparent reasons for high correction values, the attenuation, at various locations on the
test object shall be measured. Where it is found to vary significantly, corrective actions shall be considered.
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Section 7
8.2 Reference for sensitivity setting
Section 7
Figure 3 Attenuation and transfer correction
8.5 Corrections for testing of TMCP materials
8.5.1 Introduction
In ultrasonic angle beam examination, no variation arises in refraction angle or echo height with the
propagation direction (longitudinal- or transverse to rolling direction) for isotropic steels, but the influence
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The actual refraction angle varies with the propagation direction; the actual refraction angle can be larger
than the nominal angle in the rolling direction (longitudinal L-direction), while it can be smaller in the
transverse direction (T-direction). The echo height obtained using nominal 45° probe is normally nearly equal
in the L-direction and in the T-direction, where the echo height with the nominal 60° and 70° probe may be
much lower in the L-direction, and the position of its maximum amplitude is unclear.
Transmitted pulse amplitude and actual refraction angle of various types of anisotropic steels may be
determined by the V-path method, shown in Figure 4.
8.5.2 Measurement of difference in angle of refraction and echo height/amplitude
The measurement of the difference in angle of refraction shall be carried out as follows:
Use the same type of probe as shall be used for the flaw examination (60° and 70°) and oppose these
to each other in the direction of L (main rolling direction) or T (perpendicular to the rolling direction) as
shown in Figure 4. Adjust the position of probe so that maximum transmission pulse strength (echo height)
is obtained by the arrangement of V scanning/path. The actual probe angle refraction αL or αT may be
calculated using the formula for skip-distance S between the points of incidence at the position where the
largest transmission pulse strength has been obtained:
(2)
(3)
(4)
The difference between the measured/calculated values of
the nominal probe angle.
αL and αT shall be considered and compared to
Figure 4 Through Transmission Technique
Also the echo height (amplitude) obtained when the probes are positioned respectively in the rolling direction
and perpendicular to the rolling direction shall be considered.
8.5.3 Verification and adjustment (TM/TMCP)
The acoustic anisotropy shall be measured in accordance with [8.5.2]. If the result of the measurement
confirms that the material is anisotropic the following shall be carried out: when the measured angle
refraction deviates more than ± 2°, compared to the nominal probe angle, or the echo height varies more
than ± 2dB the result of this measurement for both angle deviation and the attenuation/damping of the echo
amplitude shall be adjusted and recorded before testing.
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Section 7
of the propagation direction of ultrasonic waves may be significant for anisotropic steels such as TM/TMCP
materials.
Figure 5 Cross section of reference block for TM/TMCP materials
Figure 6 Top view of reference block for TM/TMCP materials
8.5.5 Conclusion for field verification
When ultrasonic testing is performed on TM/TMCP material without having reference block of the actual
material, angle deviation and material attenuation shall be adjusted before start of testing. A material
reference block shall be made for projects that uses large amounts of such material.
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Section 7
8.5.4 Reference block for TM/TMCP materials
When ultrasonic testing is performed on such materials, reference blocks shall be made from the same
material grades (and traceable to heat no.) used in the production. The reference block shall have a
dimension of min. 2 × full skip for 70º angle probe in both longitudinal rolling direction and perpendicular to
the rolling direction, see Figure 5 and Figure 6. A side drilled hole (SDH) of diameter 3.0 mm shall be made
in a depth of ½ or ¾ of the thickness of the block in both directions. Due to deviation in attenuation and
refraction angle for these materials, the result of this measurement shall be adjusted before examination.
During testing of the weld, the noise level, excluding spurious surface indications, shall remain at least 12 dB
below the evaluation level. This requirement may be relaxed but shall be specified prior to testing.
9 Testing techniques - weld connections
9.1 General
Testing of weld connections shall be undertaken for the purpose of revealing possible:
— imperfections in the parent metal (see [7]) and in the transition between weld and parent metal
— imperfections in the weld metal and HAZ.
Applicable testing techniques giving sufficient probability of detection is shown in [9] and [10].
The joint types shown in the following are ideal examples only. Where actual weld conditions or accessibility
do not conform exactly to those shown, the testing technique shall be modified to satisfy the general
requirements of this document and the specific testing level required. For these cases, a written test
procedure shall be prepared.
9.2 Scanning and overlap
9.2.1 Overlap
For a 100% examination, the interval between two successive scan lines should not be greater than the -6 dB
beam width at any depth within the examination volume.
For practical purposes, each pass of the search unit shall overlap a minimum of 10% of the active transducer
(piezoelectric element).
9.2.2 Scanning speed
The choice of scanning speed shall take into consideration the pulse repetition frequency and the ability
of the operator to recognize or of the instrument to record signals. The scanning speed shall under no
circumstances exceed 100 mm/s.
9.2.3 Manual scan path
During angle-beam scanning (as illustrated in Figure 7), a slight swiveling movement with an angle of about
5° and up to an angle of approximately 10° on either side of the nominal beam direction shall be applied to
the probe.
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Section 7
8.6 Signal-to-noise ratio
Section 7
Figure 7 Probe movement for testing of butt welds
9.3 Testing for imperfections perpendicular to the testing surface
Subsurface planar imperfections perpendicular to the testing surface are difficult to detect with single anglebeam techniques. For such imperfections, the double probe (tandem) technique (Technique 4) may be used,
particularly for welds in thicker materials.
Ultrasonic tandem technique shall be used for weld bevel angle less than 15°. Two separate angle probes are
used, and the most favourable sound beam angle, which covers the area in question, is selected. For this
type of testing it is recommended to make a holder for the probes, so that the distance A between the probes
is kept constant, see Figure 8. The probe combination is moved along the weld connection in the distance B
from the centreline.
Figure 8 Double probe technique
9.4 Testing of welds for plate thickness 8 mm to 10 mm
It may not be sufficient to apply a standard test technique for plates with thickness 8 mm to 10 mm and
when access is limited to one side only. Due to the distance of the index point, standard UT probes cannot
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Another challenge is the evaluation of root indications, i.e. differentiation of the signals from defect and from
the geometry of the root. Hence it is required that a special scanning technique is developed and described
for thicknesses below 10 mm. Qualification on project-specific validation blocks shall be performed to ensure
that the applied technique meets detectability, coverage, and evaluation requirements.
It is recommended to use high frequencies probes, 4 MHz-5 MHz, 6 mm to 12 mm diameter elements
(commonly 8 mm x 9 mm) designed to have an exit point (index point) as close as possible to the probe
front. This allows to address the root in half skip and increase the resolution power with higher frequency. It
is generally recommended to perform the scanning on full and 1.5 skips (it is also often necessary to scan
on 2×skip or as much as 3×skip). The probe angle should be in the range of 60° to 70° (70° for the root).
Smooth grinding of the external cap may be required. Scanning the cap with a twin crystal straight beam
probe may required where the weld geometry allows it, which consequently requires the that weld cap is
ground flush.
The personnel responsible for performing an ultrasonic examination of welds in thin plates shall be familiar
with the limitations of the test method and be specifically trained in the practical testing of welds in the
actual thickness range. Qualification tests may be requested to prove the mentioned personnel's proficiency.
A = plate thickness t; 8 mm (for qualification down to 8 mm)
B = distance from root side to side-drilled hole; ¼ t (SDH =1.5 mm diameter, min. 20 mm depth)
C = distance from cap side to side drilled hole; ¼ t (SDH = 1.5 mm diameter, min. 20 mm depth)
D = center thickness side drilled hole; ½ t (SDH = 1.5 mm diameter, min. 20 mm depth)
E = EDM notch at cap side weld toe, depth 1 mm, width max. 0.2 mm, length 20 mm
F = EDM notch at root side weld toe, depth 1 mm, width max. 0.2 mm, length 20 mm
Figure 9 Example of typical validation block for plate thickness 8 mm to 10 mm
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Section 7
approach the weld close enough, resulting in reduced coverage. Another challenge is the evaluation of
root indications, i.e. differentiation of the signals from defect and from the geometry of the root. Hence
it is required that a special scanning technique is developed and described for thicknesses below 10 mm.
Qualification on project-specific validation blocks shall be performed to ensure that the applied technique
meets detectability, coverage, and evaluation requirements.
The location of discontinuities shall be defined by reference to a coordinate or reference system, e.g. as
shown in Figure 10. A point on the testing surface shall be selected as the origin for these measurements.
Where testing is carried out from more than one surface, reference points shall be established on each
surface. In this case, care shall be taken to establish a positional relationship between all reference points
used, so that the absolute location of all discontinuities can be established from any nominated reference
point.
In the case of circumferential welds, this may require the establishment of the inner and outer reference
points prior to assembly for welding.
Figure 10 Coordinate/reference system for defining the location of discontinuities
9.6 Evaluation of indications
9.6.1 General
All relevant indications above the evaluation level shall be assessed as indicated in the following.
9.6.2 Maximum echo amplitude
The echo amplitude shall be maximized by probe movement and recorded in relation to the reference level.
9.6.3 Discontinuity length
The length of a discontinuity, in either the longitudinal or transverse direction shall, where possible, be
determined using the technique specified in the acceptance levels standard, unless otherwise agreed with the
Society.
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Section 7
9.5 Location of discontinuities
Figure 11 Evaluation of length of the defect
9.6.4 Discontinuity height
The height of a discontinuity shall only be determined if required by acceptance criteria in the rules or by
specification.
9.6.5 Characterization of discontinuities
The gain which shall be used in the evaluation of the imperfection is the primary gain.
When scanning, the gain shall be the corrected primary gain plus 6 dB in order to increase the sensitivity to
defects with a difficult orientation. The gain shall then be reduced to the corrected primary dB level when
defect evaluation is carried out. The evaluation level stated in the acceptance criteria shall be used.
Discontinuities shall be characterized in accordance with excerpt from ISO 23279 as shown in Figure 12.
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Section 7
The length of the imperfections shall be evaluated by maximising the echo amplitude in the middle of the
defect. Subsequently, the probe is traversed towards the edge of the imperfection until the echo amplitude
has dropped to the required evaluation level. The centre of the probe is then marked off as the edge of the
imperfection.
Section 7
Where:
Hd = indication echo aplitude
Hd,max=
Hd,min=
=
L
Lspec =
T1 =
T2 =
T3 =
T4 =
maximum echo amplitude
minimum echo amplitude
length
specified length
evaluation level
reference level +6 dB
reference level -6 dB
9 dB shear wave or 15 dB difference
between reflection obtained with a shear
and longitudinal wave respectively.
Stage 1 (T1, i.e. evaluation level): all indications
≤ T1 are not classified.
Stage 2 (T2, i.e. reference level + 6 dB): an
indication being at least twice as reflective as the
reference is classified as planar.
Stage 3 (T3, i.e. reference level - 6 dB): if the
indication echo amplitude is at least half of the
reference echo and, if the imbalance in reflectivity
is greater than or equal to T4, the indication is
classified as planar:
— with T4 = 9 dB for shear waves
— with T4 = 15 dB between reflections obtained
with shear waves and longitudinal waves.
The angles at which the ultrasonic beam
is incident upon the indication shall have a
difference of at least 10°. The comparison shall be
made upon the same area of the indication.
Stages 4 and 5: these criteria shall be fulfilled for
at least two directions of examination.
Stage 5: if the echodynamic pattern does not
match pattern 3, the indication is classified as
non-planar.
The echo patterns are defined in ISO 23279,
Annex C.
Figure 12 Characterization of discontinuities
according to ISO 23279
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Section 7
Discontinuities in the root area of single sided welds shall be distinguished by measuring the horizontal
distances (a) as shown in Figure 13 to Figure 16.
Figure 13 Weld misalignment
Figure 14 Excessive root penetration
Figure 15 Lack of root penetration
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Section 7
Figure 16 Root defect
9.7 Requirements for testing
9.7.1 Probe angle
For testing with several angle probes, the probe angles described in Table 6 are optimal for testing, related to
the thickness.
Table 6 Parent material thickness and related probe angle
Parent material thickness, t [mm]
Probe angle [°]
10 ≤ t < 15
60 and 70
15 < t ≤ 40
45, 60 and 70
t > 40
45, 60 and 70
(70 when ½ V or K groove)
9.7.2 Probe positions
9.7.2.1 General
Probe positions for testing of butt welds are illustrated in Figure 17 to Figure 23 followed by corresponding
tables, Table 7 to Table 13, related to material thickness, test positions, and number of scans.
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Section 7
9.7.2.2 Probe positions and testing of butt welds
where:
1
side 1, related to weld
2
top view
3
side 2 related to weld
4
side view
A, B, C, D, E, F, G, H,
W, X, Y, Z
probe positions (shown on one side only, but shall also be mirrored about the weld
centre line)
b
scanning zone width (SZW) related to skip distance, p, to cover the testing volume
p
full-skip distance.
Figure 17 Probe positions and testing of butt welds
Table 7 Probe positions, beam angles and number of scans for butt welds
Longitudinal discontinuities
Thickness
of parent
material
[mm]
8 ≤ t < 10
Transverse discontinuities
L-scans
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW (min.
number)
2
A or B
1.5p
G (or H)
2
Class guideline — DNV-CG-0051. Edition January 2022
T-scans
Total scans
(min.
number)
Beam
angles
(min.
number)
Probe
positions
5
1 (2)
(C and
D) or (E
1
and F)
Total scans
(min.
number)
2 (4)
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Thickness
of parent
material
[mm]
Transverse discontinuities
L-scans
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW (min.
number)
10 ≤ t < 15
2
A or B
1.5p
G (or H)
15 ≤ t < 40
2
A or B
1.5p
G (or H)
t ≥ 40
2
A and B
1.5p
G (or H)
T-scans
Total scans
(min.
number)
Beam
angles
(min.
number)
Probe
positions
Total scans
(min.
number)
2
5
1 (2)
(C and
D) or (E
1
and F)
2 (4)
2
5
1 (2)
(C and
D) or (E
1
and F)
2 (4)
2
7
2
(C and
D) or (E
1
and F)
4
1)
One angle and two scans if surface is as per [6]. It shall be substituted by scanning from X&Y or W&Z if surface
makes it impossible to perform.
2)
Only to be done if access. Eventually surface preparation as outlined in [6] shall be done.
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Section 7
Longitudinal discontinuities
Section 7
9.7.2.3 Probe positions and testing of full penetration structural T-joint welds
legend:
1
component 1
2
component 2
A, B, C, D, E, F, G, H, W, X, Y, Z
probe positions
a, b, c, d, e, f, g
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 18 Probe positions and testing of full penetration structural T-joint welds
Table 8 Probe positions, beam angles and number of scans for full penetration structural T-joint
welds
Longitudinal discontinuities
Thickness
of parent
material
[mm]
8 ≤ t < 10
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
2
A or B
1,5p
C
c
Total
scans
(min.
number)
4
T-scans
Beam
angles
(min.
number)
2
Probe
positions
(F and G) &
(X and Y) or
(W and Z)
10 ≤ t < 15
2
A or B
1.5p
C
c
7
2
(F and G) &
(X and Y) or
(W and Z)
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SZW
Total
scans
(min.
number)
c
f+g
8
c
f+g
8
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Thickness
of parent
material
[mm]
15 ≤ t < 40
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
2
A or B
1.5p
probe
positions
1)
C
SZW
c
Total
scans
(min.
number)
7
T-scans
Beam
angles
(min.
number)
2
Probe
positions
(F and G) &
(X and Y) or
(W and Z)
40 ≤ t < 100
2
A and B
1.5p
1)
C
c
7
2
(F and G) &
(X and Y) or
(W and Z)
t ≥ 100
3
A and B
1.5p
1)
C
c
8
2
(F and G) &
(X and Y) or
(W and Z)
1)
SZW
Total
scans
(min.
number)
c
f+g
8
c
f+g
8
c
f+g
8
To be substituted by tandem technique from A or B if C is not possible.
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Section 7
Longitudinal discontinuities
Section 7
9.7.2.4 Probe positions and testing of set-through nozzle joint
where:
1
component 1, cylindrical shell/flat plate
2
component 2, nozzle
3
straight-beam probe
A, B, C, W, X, Y, Z
probe positions
a, b, c
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 19 Probe positions and testing of set-through nozzle joint
Table 9 Probe positions, beam angles and number of scans for set-through nozzle joint
Longitudinal discontinuities
Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
Total
scans
(min.
number)
T-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
8 ≤ t < 10
2
A or B
1.5p
C
c
5
2
10 ≤ t < 15
2
A or B
1.5p
C
c
5
2
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Beam
angles
(min.
number)
Probe positions
(X and Y) and
(W and Z)
(X and Y) and
(W and Z)
Total
scans
(min.
number)
2 or 4
2 or 4
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Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
15 ≤ t < 40
2
A or B
1.5p
C
c
t ≥ 40
2
A or B
1.5p
C
c
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Total
scans
(min.
number)
T-scans
Total
scans
(min.
number)
Beam
angles
(min.
number)
Probe positions
5
2
(X and Y) and
(W and Z)
8
9
2
(X and Y) and
(W and Z)
8
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Section 7
Longitudinal discontinuities
Section 7
9.7.2.5 Probe positions and testing of set-on nozzle joint
where:
1
component 1, nozzle
2
component 2, shell
3
straight-beam probe
A, B, C, X, Y
probe positions
a, b, c, x
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 20 Probe positions and testing of set-on nozzle joint
Table 10 Probe positions, beam angles and number of scans for set-on nozzle joint
Longitudinal discontinuities
Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
T-scans
Total
scans
(min.
number)
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
Total
scans(min.
number)
8 ≤ t < 10
3
A or B
1.5p
C
c
4
2
X and Y
4
10 ≤ t < 15
3
A or B
1.5p
C
c
4
2
X and Y
4
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Beam
angles
(min.
number)
Probe positions
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Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
T-scans
Total
scans
(min.
number)
SZW
Total
scans(min.
number)
Beam
angles
(min.
number)
Probe positions
C
c
4
2
X andY
4
1.5p
C
c
7
2
X and Y
4
1.5p
C
c
7
2
X and Y
4
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
15 ≤ t < 40
3
A or B
1.5p
40 ≤ t < 60
3
A and B
60 ≤ t < 100
3
A and B
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Section 7
Longitudinal discontinuities
Section 7
9.7.2.6 Probe positions and testing of structural L-joint
where:
1
component 1
2
component 2
A, B, C, D, E, F, G, H, I, X, Y
probe positions
a, b, c
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 21 Probe positions and testing of structural L-joint
Table 11 Probe positions, beam angles and number of scans for structural L-joint
Longitudinal discontinuities
Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
8 ≤ t < 10
2
(H or A)
and B
1.5p
C
c
10 ≤ t < 15
2
(H or A)
and B
1.5p
C
15 ≤ t < 40
2
(H or A)
and B
1.5p
C
Total
scans
(min.
number)
T-scans
Total
scans
(min.
number)
Beam
angles
(min.
number)
Probe positions
5
2
D and E
4
c
5
2
D and E
4
c
5
2
D and E
4
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Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
probe
positions
SZW
40 ≤ t < 100
3
(H or A)
and B
1.5p
C
c
t ≥ 100
3
(H or A)
and B
1.5p
C
c
Total
scans
(min.
number)
T-scans
Total
scans
(min.
number)
Beam
angles
(min.
number)
Probe positions
7
2
D and E
4
7
2
D and E
4
9.7.2.7 Probe positions and testing of a cruciform joint
where:
1
component 1
2
component 2
3
component 3
A, B, C, D, W, W1, W2, X, X1, X2, Y, Y1, Y2, Z, Z1, Z2,
probe positions
a, b, c, d
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 22 Probe positions and testing of cruciform joint
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Longitudinal discontinuities
Longitudinal discontinuities
Thickness
of parent
material
[mm]
L-scans
Beam
angles
(min.
number)
8 ≤ t < 10
2
10 ≤ t < 15
2
(A or B)
and
(A or B)
and
(C or D)
15 ≤ t < 40
2
(A or B)
and
(C or D)
40 ≤ t < 100
2
T-scans
Probe positions
(C or D)
(A or B)
and
(C or D)
1)
Transverse discontinuities
SZW
and tandem
(A or B) and
(C or D)
1)
and tandem
(A or B) and
(C or D)
1)
and tandem
(A or B) and
(C or D)
1)
and tandem
(A or B) and
(C or D)
1)
1.5p
Total scans
(min.
number)
≥6
Beam
angles
(min.
number)
2
Total scans
(min.
Probe positions
number)
(X1&Y1 &
W1&Z1)
and
16
(X2&Y2 &
W2&Z2)
1.5p
≥6
2
(X1&Y1 &
W1&Z1)
and
16
(X2&Y2 &
W2&Z2)
1.5p
≥6
2
(X1&Y1 &
W1&Z1)
and
16
(X2&Y2 &
W2&Z2)
1.5p
≥6
2
(X1&Y1 &
W1&Z1)
and
16
(X2&Y2 &
W2&Z2)
Tandem technique from A or B and C or D only if possible.
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Table 12 Probe positions, beam angles and number of scans for cruciform joint
Section 7
9.7.2.8 Probe positions and testing of node joint in tubular structure
where:
1
component 1, main pipe
2
component 2, branch pipe
A, B, C, D, F, G, H, X, Y
probe positions
d, f, g, h
scanning zone width (SZW) indicators
t
thickness
p
full-skip distance.
Figure 23 Probe positions and testing of node joint in tubular structure
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Longitudinal discontinuities
Thickness
of parent
material
[mm]
L-scans
Transverse discontinuities
N-scans
Beam
angles
(min.
number)
Probe
positions
SZW
Probe
positions
SZW
8 ≤ t < 10
2
F,G and H
1.5p
D
d
10 ≤ t < 15
2
F,G and H
1.5p
D
15 ≤ t < 40
3
F,G and H
1.5p
40 ≤ t < 100
3
F,G,H and E
1.5p
Total
scans
(min.
number)
T-scans
Total
scans
(min.
number)
Beam
angles
(min.
number)
Probe positions
7
2
X and Y
4
d
7
2
X and Y
4
D
d
10
2
X and Y
4
D
d
11
2
X and Y
4
10 Welds in austenitic stainless and duplex (ferritic-austenitic)
stainless steel
10.1 General
Ultrasonic testing of welds in austenitic stainless steel and duplex (ferritic-austenitic) stainless steel requires
special equipment especially in the area of reference blocks and probes to be used.
Due to the coarse grain structure of the material and the weld metal in particular a probe which generates
compression waves at angles, shall be used in addition to straight beam - and angle shear wave probes.
Physical properties of stainless steels results in a variation of grain size and structure which entails variation
in attenuation and imperfection detectability.
The testing shall be carried out in accordance with specific developed written UT- procedures for the item in
question or procedure qualification if found necessary and shall be approved by the Society.
Scan plans shall be provided to the procedures, showing probe placement, movement, and testing coverage.
The scan plans shall also include the beam angles used, beam directions with respect to weld centreline, the
focusing used, and weld volume tested.
The testing of welds shall be as set out in [3] to [9] and as given in ISO 22825. Exceptions and additions are
given in subsections [10.2] to [10.7].
10.2 Probes
The equipment used for testing shall fulfil the requirements of ISO 22232-1 and ISO 22232-2. The
verification of the combined equipment shall be done in accordance with ISO 22232-3, except for dualelement compression wave angle-beam probes, which may be verified on appropriate reference blocks other
than the blocks mentioned in ISO 22232-3.
Focal curves shall be available for the dual-element probes to be used, determined on a material
representative of the material to be tested.
It shall be verified using reference blocks with actual weld connections, see [10.4] whether angle shear wave
probes are suitable.
In general, a combination using both shear and compression wave angle probes is recommended in addition
to straight beam (normal (0°)) and creep wave probes.
The detectability of 'open to surface' imperfections like incomplete penetration and lack of fusion may
increase using shear wave probes. Sub surface defects closed to the scanning surface shall be detected by
use of creep wave probes.
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Table 13 Probe positions, beam angles and number of scans for node joint in tubular structure
In addition to already stated requirements for coupling media, for austenitic and duplex stainless steel,
impurities such as sulphur, halogens and alkali metals in the couplant shall be restricted.
10.4 Calibration blocks for calibration of amplification
Range setting shall be carried out on appropriate calibration blocks, which are designed to be similar in
dimension to Block No. 2 in accordance with ISO 7963. The dimension of at least one of the radii of the block
used shall be close to the focal distance of the probes, e.g. for calibration of time base for duplex K2 block,
see Figure 24.
Figure 24 Calibration of time base for duplex K2 block
Guidance note:
Angle compression wave probes should only be used for ½ skip (S) scanning.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
10.5 Reference block
Reference blocks for sensitivity setting should contain a weld and be representative in terms of wall
thickness, material, welding procedure, weld shape and structure, and surface condition. It should be noted
that parameters such as heat input, deposition rate, and the number of weld runs have a great impact on the
ultrasonic properties of welds.
Reference reflectors may be side-drilled holes or flat-bottomed holes, dependent on application. Surface
notches to represent surface discontinuities are used at the scanning and opposite surface. These may be
rectangular notches or notches with their reflection side in the local plane of the weld bevel, with a length of
at least 25 mm.
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10.3 Coupling medium
For calibration of amplifier and sensitivity setting on the reference block, see Figure 25.
Figure 25 Reference block for ultrasonic testing of welds in austenitic and austenitic-ferritic steel
Calibration of amplification
Figure 26 Sensitivity setting on reference block
Note:
Reflector holes shall be drilled in both fusion lines whenever two dissimilar materials are welded to each other.
---e-n-d---o-f---n-o-t-e---
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These reference blocks shall have drilled holes (Ø 3 mm or Ø 6 mm depending on thickness) positioned in
depths of 1/4 T, 1/2 T and 3/4 T. The drilled holes (reflectors) shall be located as shown in Figure 25. The
thickness of the reference block shall be sufficient in order to encompass a DAC curve covering the whole
thickness to be tested.
The surface condition of the reference blocks shall be similar to the condition of the parent material to be
tested.
Figure 27 Reference block for creep wave probe
10.6 Range settings
The index point of each probe shall be marked on the probe’s side, after having optimized the echo amplitude
on the radius closest to its focal distance. Since echo optimization can be difficult for high-angle probes and
creeping wave probes, the shear wave component may be used for optimization instead. In that case, the
calibration methodology shall be included in the test procedure.
Optimization of the echoes shall be done on the two radii separately, and by iteration until the signals from
the smaller and the larger radius are on their correct positions.
Alternatively, the time base may be set with the aid of a single-element straight-beam probe on the width
of the calibration block, and subsequent zero-point adjustment with the angle-beam probe placed on the
calibration block, on the radius which is closest to the probe’s focal distance.
For correct geometrical positioning of indications, the influence of different sound velocities between base
material and weld material may be considered, using the reflectors as used in Figure 25. Range setting shall
be carried out prior to each testing. Checks to confirm these settings shall be performed at least every 4 h
and on completion of testing.
Checks shall also be carried out whenever a system parameter is changed or whenever changes in the
equivalent settings are suspected.
10.7 Sensitivity setting and construction of DAC
Sensitivity shall be set as indicated in ISO 22825, [8.1], [8.2] (and [8.4]).
DAC curves shall be constructed from the drilled holes in the parent material of the reference blocks, see
Figure 26.
A maximum response shall then be obtained from the holes in the weld fusion zone and if necessary the gain
setting shall be adjusted such that this response reach DAC, see Figure 26. This shall be the primary gain
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Reference blocks for creep wave probes shall contain 0.5 mm, 1.0 mm and 2.0 mm EDM (electric discharge
machining) notches at the scanning surfaces, see Figure 27.
Another set of DAC curves shall be constructed, as shown in Figure 26, in order to establish sensitivity levels
for instance where the ultrasound is traversing the weld material, when scanning the fusion face.
These sensitivity levels shall be verified against the holes drilled in the base material. Any variations shall
be noted so that echoes reflected from indications within the weld zone may be evaluated for amplitude
response.
It shall be verified on reference blocks with welds produced in accordance with the actual WPS if an 1.5 × S
(full skip scanning) is possible to obtain using shear wave angle probes. Note that angle compression wave
probes should only be used at ½ S scanning.
The EDM notches on the surface of the reference block, see Figure 27, for creep wave probes shall be used
for sensitivity setting. It is recommended to adjust the echo response from the 1.0 mm notch to 75% of FSH.
11 Acceptance criteria, weld connections
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
Unless otherwise agreed with the Society, all indications in the test volume (defined in [5]) shall follow the
acceptance criteria for the weld connection.
Guidance note:
Indications found in the parent metal and heat affected zone (as included in the test volume defined in [5]), and judged 'beyond
reasonable doubt' to be laminar imperfections originating from the plate rolling process, may typically follow the acceptance
criteria for the plate, see [13.9].
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
If no acceptance criteria are defined, acceptance criteria for welds as specified below may be applied.
The quality of welds shall comply with ISO 5817 Quality Level C. For highly stressed areas more stringent
requirements, such as Quality Level B, may be applied. See further details inTable 14.
Table 14 Ultrasonic testing using pulse-echo technique
Quality levels in
accordance with ISO 5817
Testing techniques and
levels in accordance with ISO
1)
2)
17640
or DNV CG 0051
Acceptance levels in
accordance with ISO 11666
B
at least B
2
C
at least A
3
D
not defined
not required
3)
1)
When characterization of indications is required, ISO 23279 shall apply
2)
Stated testing techniques and levels refers to ISO 17640. All testing techniques in DNV-CG-0051 are compliant with
Testing Level A, B and C ISO 17640
3)
UT is not recommended but can be defined in a specification (with the same requirements as quality level C).
Sensitivity level is based on a SDH as defined in this class guideline.
In addition, the following applies: All indications from which the reflected echo amplitude exceeds the
evaluation levelshall be characterized and all indications characterized as planar (i.e. cracks, lack of fusion
and incomplete penetration) shall be rejected.
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to be used when locating indications on the fusion boundary in those cases where the ultrasonic beam is
passing through the parent metal only.
In addition to the items listed under item Sec.2 [7], the following shall be included in the ultrasonic testing
report:
The test report shall include, as a minimum, the following information:
—
—
—
—
—
—
—
—
—
—
—
—
identification of the test object
the material type, grade and product form
the dimensions of the test object
the location or identification of the weld tested
a sketch showing the geometrical configuration (if necessary)
a reference to the welding procedure and stage of heat treatment (if any)
the state of manufacture
the surface conditions
the temperature of the object, if outside the range 0°C to 40°C
contract requirements, e.g. specifications, guidelines, special agreements
the place and date of testing
identification of testing organizations and identification, certification, and signature of the operator.
The test report shall include the following information related to equipment:
— the manufacturer and type of the ultrasonic instrument, with identification number
— the manufacturer, type, nominal frequency, beam angle and focal distance of probes used with
identification number
— the identification of reference blocks used with a sketch
— the couplant medium.
The test report shall include the following information related to testing technique:
—
—
—
—
—
—
—
—
—
—
—
—
reference to the written test procedure
the extent of testing, including any restrictions
the location of the scanning areas
the reference points and details of the coordinate system
identification of probe positions
the time base range
the method and values used for sensitivity setting
the reference levels
the result of the parent material testing
the standard for acceptance and/or recording levels
the deviations from this document or from contract requirements
any factors which have prevented the testing from being carried out as intended.
The test report shall include a tabular summary (or sketches) providing the following information for recorded
indications:
—
—
—
—
the
the
the
the
coordinates of the indication with details of associated probes and corresponding probe positions
maximum echo amplitude and information, if required, on the type and height of indication
lengths of indications
results of the evaluation in accordance with specified acceptance and/or recording levels.
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12 Reporting, weld connections
13.1 General
This subsection covers manual testing of rolled plates in carbon and alloy steel with thickness ≥ 6.0 mm for
the detection of imperfections which are oriented parallel with the rolled surface.
The intention of the ultrasonic testing shall ensure that the steel plates are free of gross discontinuities such
as planar inclusions or laminations.
13.2 Personnel qualifications
For systems for personnel qualifications see Sec.2 [1] and [3]. However, if the testing is restricted only to
thickness properties of rolled steel plates, level 1 certification in UT is sufficient.
13.3 Ultrasonic instrument
The instrument shall:
—
—
—
—
—
—
be applicable for the pulse-echo technique and for the double-probe technique
cover a minimum frequency range from 1 to 12 MHz
have a calibrated gain regulator with minimum 2 dB pr. step over a range of minimum 60 dB
be equipped with automatic DAC- display presentation
have the opportunity for mounting distance gain size (DGS) -scales on the screen
be able to clearly distinguish echoes with amplitudes of 5% of full screen height.
13.4 Probes
The probes shall be straight beam transducers single- or twin crystal.
Twin crystal probes shall be used when examination is performed on steel plates with nominal thickness less
than 60 mm.
Single or twin crystal probes may be used when testing is performed on steel plates with nominal thickness T
≥ 60 mm.
The single crystal probes shall have a dead zone as small as possible, 15% of the plate thickness or 15 mm
whichever is the smaller. The focusing zone of the twin crystal probes shall be adapted to the thickness of the
plate to be examined.
Selected probes shall have a nominal frequency in the range of 2 MHz to 5 MHz and dimensions Ø 10 mm to
Ø 25 mm.
13.5 Coupling medium and surface conditions
The coupling medium shall ensure an adequate contact between the probe and the surface of the steel plate
to be tested. Water is normally used but other coupling media, e.g. oil or paste, may be used.
The surface condition shall permit at least two successive back-wall echoes to be distinguished when the
probe is placed on any area free from internal imperfections.
13.6 Range and sensitivity setting
13.6.1 Range setting
The calibration of time base shall be carried out using an IIW calibration block, a K2 calibration block or on a
defect free area of the material to be examined.
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13 Ultrasonic testing of rolled steel plates
13.6.2 Sensitivity setting
The calibration of sensitivity is based on echoes reflected from flat bottom holes in reference blocks of carbon
steel. Characteristics curves corresponding to flat bottom holes with various diameters may be supplied
by the manufacturer of the probes. The curves are either presented on a DGS diagram or on DGS - scales
'attachment scales' to be mounted on the screen of the ultrasonic apparatus.
The DGS - scales, which are most commonly used, are developed from the DGS diagrams. Differently sized
reflectors (flat bottom holes 'FBH') may be correlated to the evaluating curves. The FBH reflectors are used
as reference sizes for evaluating echo amplitudes.
By using a DGS - scale it is possible to evaluate echo amplitudes reflected from imperfections quickly and
directly. The evaluation is done by measuring the dB distance from an evaluation curve.
13.7 Evaluation of imperfections
Only imperfections from which the reflected echo amplitude is greater than that of the characteristic curve of
an Ø11 mm FBH shall be considered.
The area of the imperfections shall be determined using the 6 dB-drop technique whenever complete loss of
back wall echo is obtained, see Figure 28.
Figure 28 Half value method
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The time base shall be selected such that there are always at least 2 back-wall echoes (reflections) on the
screen.
Two nearby imperfections shall be considered as one, the area being equal to the sum of the two, if the
distance between them is less than or equal to the length of the smaller of the two.
13.8 Scanning
Scanning comprises in general continuous examination along the lines of a grid made of a 200 mm square
parallel to the edges of the plate, or along parallel or oscillating lines distributed uniformly over the surface,
giving the same degree of control.
Scanning of plate edges comprises a full examination of zone in accordance with Table 15 over the four edges
of the plate.
Table 15 Zone width for steel plate edges
Thickness of plate, T, [mm]
Zone width [mm]
10 ≤ T < 50
50
50 ≤ T < 100
75
100 ≤ T
100
13.9 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
If no acceptance criteria are specified, the quality class S1 – E2 of EN 10160 may be applied.
13.10 Reporting, rolled steel plates
In addition to the items listed under Sec.2 [7], the following shall be included in the ultrasonic testing report:
—
—
—
—
probes, type and frequency
identification of reference blocks used
couplant medium
reporting level, if different from acceptance level.
14 Ultrasonic testing of castings
14.1 General
This subsection covers manual testing of castings, carbon, low-alloy and martensitic stainless steel using the
flat bottom hole calibration technique.
The intention of the testing shall reveal unacceptable internal imperfections.
Testing shall be carried out after final heat treatment when the casting surface has been brought to a
condition suitable for UT.
As an alternative to the flat bottom hole calibration technique the DGS technique may, upon agreement with
the Society, be accepted. The DGS technique is described in [15].
The back wall echo obtained on parallel sections should be used to monitor variations in probe coupling and
material attenuation. Any reduction in the amplitude of the back wall echo without evidence of intervening
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Using single crystal probes the imperfections giving echoes above the characteristic curve for the Ø11 mm
FBH shall be counted and evaluated against the acceptance criteria.
14.2 Personnel qualifications and requirements for equipment
14.2.1 General
See Sec.2 [1] and [3] In addition, the personnel shall be familiar and trained with use of flat bottom hole
calibration technique.
14.2.2 Ultrasonic instrument
The apparatus shall:
—
—
—
—
—
be applicable for the pulse-echo technique and for the double-probe technique
cover a minimum frequency range from 1 to 6 MHz
have a calibrated gain regulator with minimum 2 dB pr. step over a range of minimum 60 dB
be equipped with automatic DAC- display presentation
be able to clearly distinguish echoes with amplitudes of 5% of full screen height.
14.2.3 Probes
The probes shall be straight beam transducers (normal probes) single- or twin crystal.
Twin crystal probes shall be used when testing is performed on castings with nominal thickness T ≤ 25 mm.
Selected probes shall have dimensions Ø 10 mm to Ø 30 mm. The background noise shall not exceed 25% of
the reference curve.
Supplementary:
Angle beam probes shall be used only when agreed upon between the contracting parties or required by the
Society. Typical applications are castings that cannot be effectively tested using a straight beam probe as a
result of casting design or possible discontinuity orientation.
It is recommended to use probes producing angle beam in steel in the range 35° to 75° inclusive, measured
to the perpendicular of the entire surface of the casting being tested.
As a minimum a 45° probe shall be used.
14.3 Surface preparation and coupling medium
All surfaces to be examined shall be free of any substance which may impede the free movement of the
probe or hinder the transmission of ultrasound to the material. Machined surfaces should be preferred for the
final examination.
As coupling medium oil, grease or cellulose gum may be used. The coupling medium used for range and
sensitivity setting shall also be used for testing.
14.4 Range setting
The same equipment shall be used during range setting and testing, i.e. instrument, probes, cables, and
coupling medium.
The temperature of the test object and the calibration-/reference blocks shall be within ±14°C.
Range setting with normal probes shall be performed using K1/K2 calibration blocks or the reference block
for sensitivity setting.
The range for normal probes shall be selected in order to always be at least 2 back-wall echoes (reflections)
on the screen.
The range for the angle probe shall cover minimum a full skip distance if scanning is accessible only from one
surface. If scanning is possible from two surfaces (inside and outside) 0.5 × S is sufficient.
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defects should be corrected. Attenuation in excess of 30 dB/m could be indicative of an unsatisfactory
annealing heat treatment.
14.5.1 General
Basis for the sensitivity setting is a set of test blocks containing flat bottoms holes. The reference blocks shall
have the same acoustic properties or material grade as the material to be examined.
In addiction, the blocks shall be stamped with the reference charge/heat number for traceability to the actual
material certificate, and also be given the same heat treatment as the test object.
The blocks defined in [14.5.2] to [14.5.4] shall be used.
14.5.2 Block no 1
Ultrasonic standard reference blocks as specified in ASTM A609 4.3.3, Figure 1 and Table 1.
The blocks are used for sensitivity setting when using straight beam probes. The dimension of the blocks is
depending of the thickness of the test object. The basic set shall consist of those blocks listed in ASTM A609
Table 1. When section thicknesses over 380 mm shall be tested, an additional block of the maximum test
thickness shall be made to supplement the basic set. The reference reflector shall be a flat bottom hole (FBH)
with diameter 6.4 mm.
14.5.3 Block no. 2
Ultrasonic standard reference block for sensitivity setting when using twin crystal (transmitter/receiver T/R)
probes shall be machined and contain 2.4 mm drilled holes in various depths as shown in ASTM A609 4.3.4,
Figure 2. The block shall be used for sensitivity setting of objects with thickness ≤ 25 mm.
14.5.4 Block no 3
Reference block for angle beam testing is shown in ASTM A609 Figure S1.1. The dimensions of the reference
block shall be according to ASTM A609, Table S1.1.
14.6 Sensitivity setting
14.6.1 Straight beam probes
Sensitivity setting shall include whole of the ultrasonic system, this includes the ultrasonic instrument,
probes, cables and coupling medium.
The blocks that encompass the metal thickness to be inspected shall be used for calibration.
The range of the screen should be selected to be twice the thickness of the object. Establish the DAC using
the set of reference blocks spanning the thickness containing the applicable flat bottom holes.
The casting testing surface will normally be rougher than that of the test blocks, consequently, employ a
transfer mechanism to provide approximate compensation. In order to accomplish this, first select a region
of the casting that has parallel walls and a surface condition representative of the rest of the casting as a
transfer point. Next select the test block whose thickness most closely matches the thickness of the test
object.
Place the search unit on the casting at the transfer point and adjust the instrument gain until the backreflection amplitude through the casting matches that through the test block.
Using this transfer technique the variation in attenuation/surface condition between the reference block and
test object may be found and taken into consideration.
Do not change those instrument controls and the test frequency set during calibration, except the attenuator,
or calibrated gain control, during acceptance examination of a given thickness of the casting. Make a periodic
calibration during the inspection by checking the amplitude of response from the 6.4 mm (2.4 mm for twin
crystal probes) diameter flat-bottom hole in the test block utilized for the transfer.
The attenuator or calibrated gain control may be used to change the signal amplitude during examination
to permit small amplitude signals to be more readily detected. Signal evaluation is made by returning the
attenuator or calibrated gain control to its original setting.
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14.5 Reference blocks
14.6.2 Angle Probes
The angle probe shall be calibrated using a set of calibration blocks with side-drilled holes at 1/4 t, 1/2 t and
3/4 t (where t = thickness of the block).
The hole diameter is depending on the thickness of the casting being tested.
Use the reflection (amplitude) from the side drilled holes to establish the applicable DAC as described
previously in this section.
14.7 Scanning
All surfaces specified for ultrasonic testing shall be completely inspected from both sides, whenever both
sides are accessible. Where scanning is restricted to one side only scanning shall be performed using a twin
crystal probe for the near surface scans (25 mm below surface) and a single probe for the remaining volume.
When practical radial and axial scanning shall be performed.
The operators shall ensure complete coverage of all areas specified for testing by carrying out systematically
overlapping of scans. Minimum scanning speed shall not exceed 100 mm/s and each pass of the search unit
shall overlap a minimum of 10% of the active transducer (piezoelectric element).
14.8 Reporting, casting
In addition to the items listed under Sec.2 [7], the following shall be included in the ultrasonic testing report:
All indications from which the reflected echo response is greater than 100% of DAC shall be reported.
Areas showing 75% or greater loss of back reflection shall be reported if, upon further investigation, the
reduction of reflection is evaluated to be caused by discontinuities.
14.9 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
15 Ultrasonic testing of forgings
15.1 General
This subsection covers manual testing of forgings of carbon or low-alloy steel using the straight- and angle
beam technique. The straight beam technique utilised is the DGS (Distance Gain Size) method.
The intention of the testing shall reveal unacceptable internal discontinuities.
Final testing shall be carried out after heat treatment when the forging surface has been brought to a
condition suitable for UT.
15.2 Personnel qualifications
In addition to Sec.2 [1] and [3] the personnel shall be familiar and trained for use of the DGS method.
15.3 Ultrasonic instrument
The instrument shall:
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During examination of areas of casting having parallel walls recheck areas showing 75% or greater loss of
back reflection to determine whether loss of back reflection is due to poor contact, insufficient couplant,
misoriented discontinuity, etc. If the reason for loss of back reflection is not evident, consider the area
questionable and investigate further.
be applicable for the pulse-echo technique and for the double-probe technique
cover a minimum frequency range from 1 to 6 MHz
have a calibrated gain regulator with minimum 2 dB pr. step over a range of minimum 60 dB
be equipped with automatic DAC- display presentation
have the possibility for automatic DGS-scales on the screen
be able to clearly distinguish echoes with amplitudes of 5% of full screen height.
Section 7
—
—
—
—
—
—
15.4 Probes
Straight beam (normal) probes with frequency 2 MHz - 4 MHz and dimension Ø 10 mm - 30 mm shall be
used. Angle beam probe shall be used as supplementary testing on rings, hollow and cylindrical sections.
It is recommended to use probes producing angle beam in steel in the range 35° to 75° inclusive, measured
to the perpendicular of the entire surface of the forging being tested. As a minimum a 45° probe shall be
used.
15.5 Surface preparation and coupling medium
All surfaces to be tested shall be free of any substance which may impede the free movement of the probe
or hinder the transmission of ultrasound to the material. Machined surfaces should be preferred for the final
examination.
Unless otherwise specified the forgings shall be machined to provide cylindrical surfaces for radial testing
in the cases of round forgings; the ends of the forgings shall be machined perpendicular to the axis of the
forging for the axial testing. Faces of disk and rectangular forgings shall be machined flat and parallel to one
another.
As coupling medium oil, grease or cellulose gum may be used. The coupling medium used for range and
sensitivity setting shall also be used for testing.
15.6 Range setting
The same equipment shall be used duringrange setting and testing, i.e. instrument, probes, cables and
coupling medium.
The range for normal probes shall be selected such that there always are at least 2 back-wall echoes
(reflections) on the screen.
The time base for the angle probe shall cover minimum a full skip distance if scanning is accessible only from
one surface. If scanning is possible from two surfaces (inside and outside 0.5 × S is sufficient.
15.7 Sensitivity setting
15.7.1 Probes
15.7.1.1 Normal probes
DGS scales, matched to the ultrasonic instrument and probes, shall be used for straight-beam testing. The
DGS scale range shall be selected to include the full thickness cross-section of the forging to be tested.
Insert the DGS scale on the ultrasonic instrument screen ensuring the DGS scale baseline coincides with the
sweep line of the instrument's screen. Place the probe on the forging and adjust the first backwall echo to
appear clearly on the CRT screen at the value corresponding to the thickness of the forging.
Adjust the gain until forging back wall echo matches the height of the DGS reference slope within ± 1 dB.
Once adjusted, increase the gain by the dB value shown on the DGS scale for the reference slope.
The instrument is now calibrated and may be used for all solid-cylinder forgings (non-drilled) and plane
backwall forgings. If the ultrasonic instrument is equipment with digital DGS Calibration Interface Program,
this programmay be used.
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Determine the correction value in dB from the Nomogram shown in ASTM A388, Figure X4.1.
Proceed as described above. Using the gain 'Gain-dB' control reduce the flaw detector by the correction value
determined using the Nomogram.
The apparatus is then calibrated for testing cylindrical bored or hollow forgings.
15.7.1.2 Angle probe
Rings and hollow sections with an outside to inside diameter (OD/ID) less than 2.0 to 1.0 should be tested
using angle probes, at least 45° probe as a supplement to the normal probe. Forgings which cannot be tested
axially using normal probes, are also to be tested with the use of angle probes, min. 45° probe.
Set the sensitivity at the instrument for the angle beam testing to obtain an indication amplitude of
approximately 75% of FSH from a rectangular or 60° V-notch on inside diameter in the axial direction and
parallel to the axis of the forgings to be tested.
A separate standard reference block may be used. However, it shall have the same configuration, nominal
composition, heat treatment and thickness as the forgings it represents.
Where a group of identical forgings is made, one of the forgings may be used as the separate sensitivity
setting standard.
Cut the ID depth notch to 3% maximum of the thickness or 6 mm, whichever is smaller, and its length to
approximately 25 mm. At the same instrument setting, obtain a reflection from a similar OD notch. Draw a
line through the peaks of the first reflections obtained from the ID and OD notches. This shall be the distance
amplitude curve (DAC).
When practical utilise the ID notch when scanning from the OD surface and the OD notch when scanning
from the ID surface. Curve wedges or probe-shoes may be used when necessary for a proper contact
between probe and testing surface.
15.8 Scanning
15.8.1 Straight beam probes
All surfaces specified for ultrasonic testing shall be completely inspected from both sides, whenever both
sides are accessible. Where access is restricted to one side only scanning shall be performed using a twin
crystal probe for the near surface scans (25 mm below surface) plus a single probe for the remaining volume.
When practical both radial and axial scanning shall be performed.
On larger diameter rudder stocks and especially axial scanning, the pulse repetition frequency (PRF) shall be
limited to max. 150 Hz to avoid false signals due to interference on larger dimensions.
The scanning rate shall not exceed 100 mm/s.
The operators shall ensure complete coverage of all areas specified for testing by carrying out systematically
overlapping of scans. In general the testing shall be carried out prior to drilling holes, tapers, grooves, or
machining sections to contour.
15.8.2 Angle probes
Rings and hollow sections as specified in item [15.7.1.2] shall be tested using angle probe. The testing shall
be performed by scanning over the entire surface area circumferentially in both the clockwise and counter
clockwise direction from the OD surface.
Forgings which cannot be tested axially by normal probes shall be tested in both axial directions with an
angle beam probe. For axial scanning the notches as specified in item [15.7.1.2] shall be used for calibration.
These notches, placed on the ID and OD surface, shall be perpendicular to the axis of the forging and have
the same dimensions as the axial notch.
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When testing cylindrical hollow forgings the hole of the specimens will cause sound scatter. In these cases a
correction depending of the specimen thickness and the hole diameter is required.
In general, the area containing imperfections, shall be sized (area and length) using the 6 dB drop technique.
The area refers to the surface area on the forgings over which a continuous indication exceeds the
acceptance criteria. This area will be approximately equal to the area of the real defect provided the defect
size is larger than the 6 dB beam profile of the probe.
However, if the real imperfection size is smaller than the 6 dB beam profile, the 6 dB drop technique is
not suited for sizing. The area measured on the surface will, in such cases, be measured too large and not
represent the real indication size.
A guide to classify if the revealed indications are greater or smaller than the 6 dB drop profile is given in EN
10228-3, para. 13.
If the size of the indication is evaluated to be smaller than the 6 dB drop profile at the depth of discontinuity
a graphic plot, that incorporates a consideration of beam spread, should be used for realistic size estimation.
In certain forgings, because of very long metal path distances or curvature of the scanning surfaces, the
surface area over which a given discontinuity is detected may be considerably larger or smaller than the
actual size of the discontinuity; in such cases criteria that incorporate a consideration of beam angles or
beam spread shall be used for realistic size evaluation.
This may include reference blocks identical with the forgings to be tested. In cases of dispute flat bottom
holes or notches, drilled or machined in the reference blocks, may act as reflectors to verify the correct
defect size.
15.10 Reporting, forgings
In addition to the items listed under Sec.2 [7] the following shall be included in the ultrasonic testing report:
When using normal probes:
— All indication from which the reflected echo response exceeds the specified DGS acceptance criteria shall
be reported.
— An indication that is continuous on the same plane and found over an area larger than twice the probe
diameter shall be reported regardless of echo amplitude.
— Areas showing 20% or greater loss of back reflection shall be reported if, upon further investigation, the
reduction of reflection is evaluated to be caused by discontinuities.
When using angle probes:
— Record discontinuities indications equal to or exceeding 50% of the indication from the reference line.
The above reportable indications do not themselves mean that an item will be rejected, unless specified in
the acceptance criteria.
15.11 Acceptance criteria
15.11.1 General
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory.
15.11.2 Alternative acceptance criteria where these are not given by the referring standard
Any reflections caused by discontinuities, exceeding 20% of full screen height (FSH) shall be evaluated and
shall comply with the acceptance criteria for the length as specified by IACS Rec.68.
When 6 dB drop cannot be used for sizing of point-like indications which are smaller than 6 dB beam profile
the probe beam spread to be considered to ensure indication is less than allowable length as specified in
IACS Rec.68.
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15.9 Sizing of imperfections
16.1 Scope
This subsection specifies the application of phased array for semi- or fully automated ultrasonic testing of
fusion-welded joints in metallic materials of minimum thickness 6 mm (PAUT). It applies to full penetration
welded joints of simple geometry in plates, pipes, and vessels, where both the weld and the parent material
are low-alloy and/or fine grained steel.
For the testing of welds in other steel materials this subsection may give guidance. For coarse-grained or
austenitic steels, previous parts of this section and ISO 22825 apply in addition to this subsection.
This subsection provides guidance on the specific capabilities and limitations of phased array for the
detection, location, sizing and characterization of discontinuities in fusion-welded joints. Phased array may be
used as a stand-alone technique or in combination with other NDT methods or techniques, for manufacturing
inspection, pre-service and for in-service inspection.
In the following it is specified a testing level comprising all quality levels for welds.
16.2 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 and ISO 23243 and defined
in Table 16 apply.
Table 16 Definition of terms
Term
Definition
phased array image
one- or two-dimensional display, constructed from the collected information of phased
array operation
indication, phased array
indication
pattern or disturbance in the phased array image which may need further evaluation
phased array setup
probe arrangement defined by probe characteristics (e.g. frequency, probe element
size, beam angle, wave mode), probe position, and the number of probes
probe position, PP
distance between the front of the wedge and the weld centre line
scan increment
distance between successive data collection points in the direction of scanning
(mechanically or electronically)
skewed scan
scan performed with a skewed angle (The skewed angle can be achieved electronically
or by means of probe orientation)
mode, phased array mode
combination of ultrasonic beams created by phased array, e.g. fixed angle, E-scan, Sscan
16.3 Testing level
Quality requirements for welded joints are mainly associated with the material, welding process and service
conditions. To comply with all of these requirements, this section specifies only one testing level comprising
all coverage of welds.
PAUT of welds shall include a linear scan of the fusion face, together with other scans as defined in the
specific test technique.
If the evaluation of the indications is based on amplitude only, it is a requirement that an ‘E’ scan (or linear
scan) shall be utilized to scan the fusion faces of welds, so that the sound beam is perpendicular to the fusion
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16 PAUT - automated phased array for testing of welds
Indications detected when applying testing procedure shall be evaluated either by length and height or by
length and maximum amplitude. Indication assessment shall be in accordance with ISO 19285:2017 or
recognized standards and the specific requirements of the classification society. The sizing techniques include
reference levels, time corrected gain (TCG), distance gain size (DGS) and 6 dB drop. 6 dB drop method shall
only be used for measuring the indications larger than the beam width.
16.4 Information required prior to testing
16.4.1 General
The purpose of the testing shall be defined by the testing procedure. Based on this, the volume to be
inspected shall be determined.
A scan plan shall be provided. The scan plan shall show the beam coverage, the weld thickness and the weld
geometry.
The procedure shall include a documented testing strategy or scan plan showing probe placement, probe
movement, and component coverage that provides a standardized and repeatable methodology for weld
testing. The scan plan shall also include ultrasonic beam angles used, beam directions with respect to the
weld centre line, the focusing used, and the volume to be tested for each weld.
16.4.2 Items to be defined prior to procedure development
Information on the following items is required:
a)
b)
c)
d)
e)
f)
g)
h)
i)
purpose and extent of testing
testing levels
acceptance criteria
specification of reference blocks
manufacturing or operation stage at which the testing shall be carried out
weld details and information on the size of the heat-affected zone
requirements for access and surface conditions and temperature
personnel qualifications
reporting requirements.
16.4.3 Specific information required by the operator before testing
Before any testing of a welded joint can begin, the operator shall have access to all the information as
specified in [16.4.2] together with the following additional information:
a)
b)
c)
d)
written test procedure
type(s) of parent material and product form (i.e. cast, forged, rolled)
joint preparation and dimensions
welding instruction or relevant information on the welding process.
16.5 Requirements for personnel and test equipment
16.5.1 Personnel qualifications
See Sec.2 [1]. The Shipbuilder, manufacturer or its subcontractors is responsible for the qualification and
preferably third party certification of its supervisors and operators to a recognised certification scheme based
on ISO 9712:2012.
The operator carrying out the NDT and interpreting indications, shall as a minimum, be qualified and certified
to level 2 in the NDT method concerned. However, operators only undertaking the gathering of data using
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face ± 6° maximum, recommended ± 2°. This requirement may be omitted if an ‘S’ (or sectorial) scan can
be demonstrated to verify that discontinuities at the fusion face can be detected and sized, using the stated
procedure (note, this demonstration shall utilize reference blocks containing suitable reflectors in location of
fusion zone).
In addition to general knowledge of ultrasonic weld testing, the operators shall be familiar with, and have
practical experience in, the use of ultrasonic phased arrays. Specific training and examination of personnel
shall be performed on representative pieces. These training and examination results shall be documented. If
this is not the case, specific training and examination shall be performed with the finalized ultrasonic testing
procedures and selected ultrasonic test equipment on representative samples containing natural or artificial
reflectors similar to those expected. These training and examination results shall be documented.
16.5.2 Test equipment
16.5.2.1 General
In selecting the system components (hardware and software), ISO/TS 16829 gives useful information.
Ultrasonic equipment used for phased array testing shall be in accordance with the requirements of ISO
18563-1, ISO 18563-2, and ISO 18563-3 when applicable.
16.5.2.2 Ultrasonic instrument
The instrument shall be able to select an appropriate portion of the time base within which A-scans are
digitized.
It is recommended that a sampling rate of the A-scan be used of at least six times the nominal probe
frequency. If smaller sampling frequencies are used, the signal quality shall be demonstrated.
16.5.2.3 Ultrasonic probes
Both longitudinal and shear waves may be used.
Adaptation of probes to curved scanning surfaces shall comply with MUT part of Sec.7. When adapted probes
are used, the influence on the sound beam shall be taken into account.
The number of dead elements on the each active aperture shall be a maximum of 1 out of 16 and dead
elements are not allowed to be adjacent. For active apertures using less than 16 elements, no dead element
is allowed, unless adequate performance is demonstrated.
16.5.2.4 Scanning mechanisms
To achieve consistency of the images (collected data), guiding mechanisms and scan encoder(s) shall be
used.
16.6 Preparation for testing
16.6.1 Volume to be tested
The purpose of the testing shall be defined by the rules. Based on this, the volume to be tested shall be
determined.
For tests at the manufacturing stage, the testing volume shall include the weld and the parent material for at
least 10 mm on each side of the weld, or the width of the heat-affected zone, whichever is greater.
A scan plan shall be provided. The scan plan should show the beam coverage, the weld thickness and the
weld geometry.
It shall be ensured that the sound beam(s) cover(s) the volume to be tested.
16.6.2 Verification of the test setup
The capability of the test setup shall be verified by the use of adequate reference blocks.
16.6.3 Scan increment setting
The scan increment setting along the weld is dependent upon the wall thickness to be tested. For thicknesses
up to 10 mm, the scan increment shall be no more than 1 mm. For thicknesses between 10 mm and 150
mm, the scan increment shall be no more than 2 mm. Above 150 mm, a scan increment of no more than 3
mm is recommended.
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any NDT method and not performing data interpretation or data analysis may be qualified and certified as
appropriate, at level 1.
When TOFD is used, the scan increment shall be in accordance with [17].
16.6.4 Geometry considerations
Care should be taken when testing welds of complex geometry, e.g. welds joining materials of unequal
thickness, materials that are joined at an angle or nozzles. These tests should be planned carefully and
require in-depth knowledge of sound propagation. These tests shall always be carried out after a specific
procedure qualification.
For tests of complex geometry, scan plan(s), representative reference block(s), and a performance
demonstration are mandatory.
Note:
In some cases, the number of reference blocks may be reduced by the use of simulation programmes.
---e-n-d---o-f---n-o-t-e---
16.6.5 Preparation of scanning surfaces
Scanning surfaces shall be clean in an area wide enough to permit the test volume to be fully covered.
Scanning surfaces shall be even and free from foreign matter likely to interfere with probe coupling (e.g.
rust, loose scale, weld spatter, notches, grooves). Waviness of the test surface shall not result in a gap
between a probe and the test surface greater than 0.5 mm. These requirements shall be ensured by dressing
the scanning surface, if necessary.
Scanning surfaces may be assumed to be satisfactory if the surface roughness, Ra, is not greater than 6.3
μm for machined surfaces, or not greater than 12.5 μm for shot-blasted surfaces.
When a layer of different material, e.g. coating, paint, cladding, is present on the scanning surface and is not
to be removed, testing after specific procedure qualification is applicable.
16.6.6 Temperature
When not using special high-temperature phased array probes and couplants, the surface temperature of the
object to be tested shall be in the range 0°C to 50°C.
For temperatures outside this range, the suitability of the test equipment shall be verified.
16.6.7 Couplant
In order to generate proper images, a couplant shall be used which provides a constant transmission of
ultrasound between the probes and the test object. The couplant used for the calibration shall be the same as
that used in subsequent testing and post-calibrations.
16.7 Testing of base material
When the test is performed according to this class guideline, a test for the detection of laminations shall be
performed. This may be carried out as part of the test or independently of it.
16.8 Range and sensitivity settings
16.8.1 Settings
16.8.1.1 General
Setting of range and sensitivity shall be carried out prior to each test in accordance with this document. Any
change of the phased array setup, e.g. probe position (PP) and steering parameters, requires a new setting.
Signal-to-noise ratio should be optimized with a minimum of 12 dB for the reference signals, when using Ascans, or with a minimum of 6 dB when using phased-array images.
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The scan increment setting perpendicular to the weld when applicable shall be chosen in order to ensure the
coverage of the test volume.
Section 7
16.8.1.2 Pulse-echo time window
If applicable, the time window used for pulse-echo signals shall include the volume of interest and be
described in the written test procedure.
Ensure that the combination of beams covers the area of interest.
16.8.1.3 Pulse-echo sensitivity settings
1)
General:
After selection of the mode (fixed angle, E-scan, S-scan) the following shall be carried out:
a)
b)
2)
the test sensitivity shall be set for each beam generated (e.g. beam angle, focal point) by the
phased array probe
when a probe with wedge is used, the sensitivity shall be set with the wedge in place.
Focusing:
Different modes of focusing may be applied with phased array probes, e.g. static and dynamic depth
focusing (DDF).
When focusing is used, the sensitivity shall be set for each focused beam.
3)
Gain corrections:
The use of angle-corrected gain (ACG) and time-corrected gain (TCG) enables the display of signals for
all beam angles and all distances with the same amplitude.
4)
Sensitivity settings for different modes of phased array testing:
For weld testing, different modes may be applied, e.g. fixed angles, E-scans, S-scans. After the previous
steps, the reference sensitivity for each beam generated shall be set as for manual UT in this class
guideline, including transfer correction if applicable.
5)
TOFD settings:
If TOFD testing is performed, all settings shall comply with the requirements specified in [17].
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If a reference block was used for initial setting, the same reference block shall be used for checking.
Alternatively, a smaller block with known transfer properties may be used.
If deviations from the initial settings are found during these checks, corrections given in Table 17 shall be
carried out.
Table 17 Sensitivity and range corrections
Sensitivity
Action
Deviation ≤ 4 dB
No action required, data may be corrected by software.
Deviation > 4 dB
The complete chain of measurements shall be checked. If
no defective components are identified, settings shall be
corrected and all tests carried out since the last valid check
shall be repeated.
The required signal-to-noise ratio shall be achieved.
The deviation 4 dB applies for pulse-echo testing. For TOFD, testing a 6 dB deviation is allowed.
Range
Action
Deviation ≤ 0.5 mm or 2% of depth-range, whichever is
greater
No action required.
Deviation > 0.5 mm or 2% of depth-range, whichever is
greater
Settings shall be corrected and all tests carried out since
the last valid check shall be repeated.
16.8.3 Calibration block, reference block and validation block
As defined by ISO 19675, the standard calibration block should be used for velocity, wedge delay, and ACG
calibration.
As defined by ISO 13588, reference block can be used for the sensitivity setting and to determine the general
adequacy of the testing. Please note that, unless otherwise agreed with the Society, DNV does not accept
reference blocks for procedure qualification.
Validation blocks shall be used for qualification purposes as described in App.A.
16.8.4 Reference blocks
16.8.4.1 General
Representative reference blocks shall be used to determine the adequacy of the testing (i.e. coverage,
sensitivity setting). Recommendations and requirements for reference blocks relevant for different materials
are given in this section.
16.8.4.2 Material
The reference block shall be made of similar material to the test object (i.e. with regard to sound velocity,
grain structure, and surface condition).
16.8.4.3 Dimensions and shape
The thickness of the reference blocks is recommended to be between 0.8 times and 1.5 times the thickness
of the test object, with a maximum difference in thickness of 20 mm compared to the test object. The length
and width of the reference block should be chosen such that all the artificial discontinuities can be properly
scanned. For testing of longitudinal welds in cylindrical test objects, curved reference blocks shall be used
having diameters from 0.9 times to 1.5 times the test object diameter. For test objects having a diameter
greater than or equal to 300 mm, a flat reference block may be used.
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16.8.2 Checking of the settings
Settings shall be checked at least every 4 h and after completion of the testing. If the single test takes more
than 4 h, the settings shall be checked after completion of the test.
16.8.4.4 Reference reflectors
For a thickness, t, between 6 mm and 25 mm, at least three reflectors are required. For a thickness t > 25
mm, at least five reflectors are required. Reference reflectors are side-drilled holes.
16.9 Equipment checks
It shall be checked that all relevant channels, probes, and cables of the ultrasonic phased array system
are functional. This check shall be performed daily before and after testing. If any item of the system fails,
corrective action shall be taken and the system shall be retested.
16.10 Procedure qualification
A procedure qualification is required for all testing as per this class guideline. The test procedure shall have
been demonstrated to perform acceptably on representative specimens. A satisfactory procedure qualification
shall take place prior to the first testing.
A satisfactory procedure qualification includes:
a)
b)
c)
detection of all required reflectors
capability of measuring size, position and depth as required by specification
proof of coverage in depth and width.
16.11 Weld testing and scan plan
Before initial testing, the coverage shall be verified with the scan plan and demonstrated on a suitable
reference block.
Acceptable deviations of the probe position relative to the weld centre line shall be documented in the test
procedure, and shall be covered in the scan plan and shown on a reference block.
Some discontinuities detected during the initial scanning can require additional evaluation, e.g. offset-scans,
scans perpendicular to the discontinuity, complementary phased array-setups.
The scanning speed shall be chosen such that satisfactory images are generated. The scanning speed shall
be selected dependent on factors such as number of delay laws, scan resolution, signal averaging, pulserepetition frequency, data acquisition frequency, and volume to be tested. Missing scan lines indicate that the
scanning speed used was too high. A maximum of 5 % of the total number of lines collected in one single
scan may be missed but no adjacent lines shall be missed.
If the length of a weld is scanned in more than one section, an overlap of at least 20 mm between the
adjacent scans is required. When scanning circumferential welds, the same overlap is required for the end
of the last scan with the start of the first scan. If applicable, a control function for the coupling efficiency is
recommended.
16.12 Data storage
The ultrasonic testing (PAUT) shall be performed using a device employing computer-based data acquisition.
All A-scan data covering the test area shall be stored and all data sets with setup parameters shall be
included in the data record. All data shall be stored for a period as agreed with the contracting parties.
16.13 Interpretation and analysis of phased array data
16.13.1 General
Interpretation and analysis of phased array data are typically performed as follows:
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In all cases, with regard to the diameter or curvature, the requirements mentioned in this section are
mandatory. The maximum allowed gap between probe shoe and reference block is 0.5 mm.
assess the quality of the phased array data
identify relevant indications
classify relevant discontinuities as specified
determine location and size of the discontinuities as specified
evaluate the data against acceptance criteria.
16.13.2 Assessing the quality of the phased array data
A phased array (PAUT) test shall be carried out such that satisfactory images are generated which can be
evaluated with confidence. Satisfactory images are defined by appropriate:
a)
b)
c)
d)
e)
f)
coupling
time-base setting
sensitivity setting
signal-to-noise ratio
indication of saturation
data acquisition.
Assessing the quality of phased array images requires skilled and experienced personnel. The personnel
assessing the quality of PAUT images shall decide whether non-satisfactory images require new data
acquisition (re-scanning).
16.13.3 Identification of relevant indications
The phased array technique images both discontinuities in the weld and geometric features of the test object.
In order to distinguish between indications and geometric features, detailed knowledge of the test object is
necessary.
To decide whether an indication is relevant (caused by a discontinuity), patterns or disturbances in the
phased array image shall be evaluated considering shape and signal amplitude relative to general noise level.
16.13.4 Classification of relevant indications
Amplitude, location, and pattern of relevant indications can contain information on the type of the
discontinuity.
Relevant indications shall be classified as specified.
16.13.5 Determination of location
The location of a discontinuity parallel to the weld axis, perpendicular to the weld axis and in the throughwall direction shall be determined from the related indication.
16.13.6 Determination of length and height
The length and height of a discontinuity are determined by the length and height of its indication.
1)
Determination of length:
The length is defined by the difference of the x-coordinates of the indication. The length of an indication
shall be measured as described in ISO 11666.
Alternative techniques for measuring indication length may be used when specified.
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a)
b)
c)
d)
e)
Determination of height:
The height is defined as the maximum difference of the z-coordinates. For indications displaying varying
height along their length, the height shall be determined at the scan position of maximum extent.
a)
Diffracted signals:
If diffracted signals are identified they shall be used to determine height. The height is determined
using:
—
—
—
—
b)
2
1
1
1
diffracted
diffracted
diffracted
diffracted
signals identified from the same discontinuity (upper and lower tip)
signal and a surface signal identified from the same discontinuity
signal and the known wall thickness for root connected indications, or
signal in relation to the surface for surface breaking discontinuity.
Amplitude-based and other signals:
The determination can be based on:
— amplitudes using the reference levels as described in ISO 11666. Other sizing techniques may be
used (TCG, DGS, 6 dB drop)
— the time of flight of reflections (e.g. hollow root, mismatch)
— time of flight of mode converted signals.
16.14 Evaluation against acceptance criteria
After classification of all relevant indications, determination of their location and length, and after
assessment, the discontinuities shall be evaluated against the acceptance criteria of ISO 19285, AL2, if not
specified differently by the relevant part of the rules. For critical welds ISO 19285 AL1 may be used.
16.15 Test report
In addition to relvent parts of [12], the test report shall include at least the following information:
a)
information relating to the object under test:
1)
2)
3)
4)
5)
6)
7)
8)
b)
identification of the test object
dimensions including wall thickness
material type and product form
geometrical configuration
location of the tested welded joint(s)
reference to welding process and heat treatment
surface condition and temperature of the test object
stage of manufacture of the test object
information relating to the test equipment:
1)
2)
3)
4)
manufacturer and type of the phased array instrument including scanning mechanisms with
identification numbers if required
manufacturer, type, frequency of the phased array probes including number and size of elements,
material and angle(s) of wedges with identification numbers if required
details of the reference block(s) with identification numbers if required
type of couplant used
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Section 7
2)
information relating to the test technology:
1)
2)
3)
4)
5)
6)
7)
d)
testing level and reference to a written test procedure
purpose and extent of test
details of datum and coordinate systems
method and values used for range and sensitivity settings
details of signal processing and scan increment setting
scan plan
access limitations and deviations from this document, if any
information relating to the phased array setting:
1)
2)
3)
4)
5)
6)
7)
8)
e)
Section 7
c)
increment (E-scans) or angular increment (S-scans)
element pitch and gap dimensions
focus (calibration should be the same as for scanning)
virtual aperture size, i.e. number of elements and element width
element numbers used for focal laws
maximum deviation of the beam direction from the normal to the weld bevel
documentation on permitted wedge angular range, specified by the manufacturer
documented calibration, time-corrected gain (TCG) and angle-corrected gain (ACG)
information relating to the test results:
1)
2)
3)
4)
5)
6)
7)
reference to the phased array raw data file(s)
phased array images of at least those locations where relevant discontinuities have been detected on
hard copy, all images or data available in soft format
acceptance criteria applied
tabulated data recording the classification, location and size of relevant discontinuities and the
results of evaluation
reference points and details of the coordinate system
date of test
names, signatures and qualification of the test personnel.
17 TOFD of welds
17.1 Scope
This part of the class guideline specifies the application of the time-of-flight diffraction (TOFD) technique to
the semi- or fully automated ultrasonic testing of fusion-welded joints in low-alloyed carbon steel of minimum
thickness 10 mm.
TOFD shall be carried out according to procedure based on ISO 10863 and ISO 15626 with additional
clarifications in this section.
It applies to full penetration welded joints of simple geometry in plates, pipes, and vessels, where both the
weld and the parent material are low-alloyed carbon steel. Where specified and appropriate, TOFD may
also be used on other types of materials that exhibit low ultrasonic attenuation. Where material-dependent
ultrasonic parameters are specified in this section, they are based on low-alloyed carbon steels having
a sound velocity of 5920 (± 50) m/s for longitudinal waves and 3255 (± 30) m/s for shear waves. It is
necessary to take this fact into account when testing materials with a different velocity.
In this guideline TOFD shall not be used as a stand-alone technique. TOFD shall be used in combination
with other non-destructive testing (NDT) methods or techniques. This is due to the fact that there is a
reduced capability for the detection of discontinuities close to or connected with the scanning surface
and with the opposite surface. In most cases, full coverage of these mentioned zones is required. Then
additional measures shall be taken, i.e. TOFD shall be accompanied by other NDT methods or other ultrasonic
techniques.
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The purpose of the testing shall be defined by the testing procedure. Based on this, the volume to be
inspected shall be determined.
A scan plan shall be provided. The scan plan shall show the locations of the probes, beam coverage, the weld
thickness, and the weld geometry.
17.2 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 and ISO 23243 and the
terms in Table 18 apply.
Table 18 Definition of terms
Term
Definition
time-of-flight diffraction image
(TOFD image)
two-dimensional image, constructed by collecting adjacent A-scans while moving the
time-of-flight diffraction setup
time-of-flight diffraction
indication (TOFD indication)
pattern or disturbance in the time-of-flight diffraction image which can need further
evaluation
time-of-flight diffraction setup
(TOFD setup)
probe arrangement defined by probe characteristics (e.g. frequency, probe element
size, beam angle, wave mode) and probe centre separation
beam intersection point
point of intersection of the two main beam axes
lateral wave
longitudinal wave travelling the shortest path from transmitter probe to receiver probe
probe centre separation (PCS)
distance between the index points of the two probes
offset scan
scan parallel to the weld axis, where the beam intersection point is not on the
centerline of the weld
17.3 Testing level
Four testing levels are specified in ISO 10863, each corresponding to a different probability of detection of
imperfections. Due requirement of a written procedure for all TOFD testing as per this guideline, at least
testing level C shall always be used. See further specific requirements to the testing levels C and D in Table
19.
Table 19 TOFD testing levels
Testing level
TOFD setup
Reference block for
setup verification
(see [8.2])
Reference block for
sensitivity settings
(see [10.1.4])
Offset scan
C
As in Table 2
Yes
Yes
a
D
As defined by
specification
Yes
Yes
a
a)
The necessity, number and position of offset scans shall be determined.
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Section 7
Four testing levels are specified in ISO 10863, each corresponding to a different probability of detection of
imperfections. Due requirement of a written procedure for all TOFD testing as per this guideline, at least
testing level C shall always be used.
Section 7
17.4 Information required prior to testing
17.4.1 Items to be defined by specification
Information on the following items is required:
a)
b)
c)
d)
e)
f)
g)
h)
purpose and extent of TOFD testing
testing levels (C or D)
specification of reference blocks, if required
manufacturing or operation stage at which the testing shall be carried out
requirements for: temperature, access and surface conditions
reporting requirements
acceptance criteria
personnel qualifications.
17.4.2 Specific information required by the operator before testing
Before any testing of a welded joint can begin, the operator shall have access to all the information as
specified above, together with the following additional information:
a)
b)
c)
d)
e)
f)
g)
written test instruction or procedure
type(s) of parent material and product form (i.e. cast, forged, rolled)
joint preparation and dimensions
welding procedure or relevant information on the welding process
time of testing relative to any post-weld heat treatment
result of any parent metal testing carried out prior to and/or after welding
discontinuity type and morphology to be detected.
17.4.3 Written test instruction or procedure
A procedure shall be written and include the following information as shown in Table 20. When an essential
variable in table below is to change from the specified value, or range of values, the written procedure
shall require requalification. When a non-essential variable is to change from the specified value, or range
of values, requalification of the written procedure is not required. All changes of essential or nonessential
variables from the value, or range of values, specified by the written procedure shall require revision of, or an
addendum to, the written procedure.
Table 20 Requirements to a TOFD procedure
Requirement
Essential variable
Weld configurations to be examined, including thickness
dimensions and material product form (castings, forgings, pipe,
plate, etc.)
X
The surfaces from which the examination shall be performed
X
Angle(s) of wave propagation in the material
X
Search unit type(s), frequency(ies), and element size(s)/shape(s)
X
Special search units, wedges, shoes, or saddles, when used
X
Ultrasonic instrument(s) and software(s)
X
Calibration [calibration block(s) and technique(s)]
X
Directions and extent of scanning
X
Scanning (manual vs. automatic)
X
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Essential variable
Data sampling spacing (increase only)
X
Method for sizing indications and discriminating geometric from
flaw indications
X
Computer enhanced data acquisition, when used
X
Scan overlap (decrease only)
X
Personnel performance requirements, when required
X
Testing levels, acceptance levels and/or recording levels
X
Non-essential variable
Personnel qualification requirements
X
Surface condition (examination surface, calibration block)
X
Couplant (brand name or type)
X
Post-examination cleaning technique
X
Automatic alarm and/or recording equipment, when applicable
X
Records, including minimum calibration data to be recorded (e.g.,
instrument settings)
X
Environmental and safety issues
X
17.5 Requirements for personnel and test equipment
17.5.1 Personnel qualifications
See Sec.2 [1]. In addition to a qualification by certification to at least level 2 of ultrasonic weld testing, all
personnel shall be competent in the TOFD technique. Documented evidence of their competence is required.
Testing, aquisition of data, final off-line analysis of data, and acceptance of the report shall be performed by
personnel qualified as a minimum to level 2 in accordance with ISO 9712 or equivalent in ultrasonic testing in
the relevant industrial sector.
In cases where the above minimum qualifications are not considered adequate, job-specific training shall be
carried out.
17.5.2 Test equipment
17.5.2.1 Ultrasonic equipment
The ultrasonic instrument used for the TOFD technique shall comply with the requirements of ISO 22232-1,
where applicable.
The TOFD software shall not mask any problems such as loss of coupling, missing scan lines, synchronization
errors or electronic noise.
In addition, the requirements of ISO 16828 shall apply, taking into account the following:
a)
b)
the instrument shall be able to select an appropriate portion of the time base within which A-scans are
digitized
it is recommended that a sampling rate of the A-scan of at least 6 times the nominal probe frequency be
used.
17.5.2.2 Ultrasonic probes
Probes used for the TOFD technique on welds shall comply with ISO 22232-2 and ISO 16828.
Adaptation of probes to curved scanning surfaces shall comply with ISO 17640.
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Section 7
Requirement
17.5.2.3 Scanning mechanisms
The requirements of ISO 16828 shall apply. To achieve consistency of the images (collected data), guiding
mechanisms should be used.
17.6 Preparation for testing
17.6.1 Volume to be tested
Testing shall be performed in accordance with ISO 16828. The purpose of the testing shall be defined by
specification. Based on this, the volume to be tested shall be determined.
The volume to be tested is located between the probes. The probes shall be placed symmetrically about the
weld centreline and additional offset scans may be required.
For manufacturing inspection, the examination volume is defined as the zone which includes weld and parent
material for at least 10 mm on each side. In all cases, the whole examination volume shall be covered.
For in-service inspections, the examination volume may be targeted to specific areas of interest, e.g. the
inner third of the weld body.
17.6.2 Setup of probes
The probes shall be set up to ensure adequate coverage and optimum conditions for the initiation and
detection of diffracted signals in the area of interest. For butt welds of simple geometry and with narrow
weld crowns at the opposite surface, the testing shall be performed in one or more setups (scans) dependent
on the wall thickness, see Table 21. For other configurations, e.g. X-shaped welds, different base metal
thickness at either side of the weld, or tapering, Table 21 may be used as guidance. In this case, the
effectiveness and coverage of the setup shall be verified by using reference blocks. Selection of probes
for full coverage of the complete weld thickness should follow Table 21. Care should be taken to choose
appropriate combinations of parameters.
All the setups chosen for the test object shall be verified by use of reference blocks.
If setup parameters are not in accordance with Table 21, the capability shall be verified by using reference
blocks.
For in-service inspection the intersection point of the beam centrelines should be optimized for the specified
examination volume.
Table 21 Recommended TOFD setups for simple butt welds dependent on wall thickness
Thickness
t [mm]
Number of
TOFD setups
Centre
frequency
f [MHz]
Depth range
∆t [mm]
Beam angle
(longitudinal
waves) α
Element
size [mm]
Beam
intersection
t ≤ 10
1
0 to t
15
70°
2 to 3
2/3 of t
10 < t ≤ 15
1
0 to t
15 to 10
70°
2 to 3
2/3 of t
15 < t ≤ 35
1
0 to t
10 to 5
70° to 60°
2 to 6
2/3 of t
35 < t ≤ 50
1
0 to t
5 to 3
70° to 60°
3 to 6
2/3 of t
50 < t ≤ 100
2
0 to t/2
5 to 3
70° to 60°
3 to 6
2/6 of t
t/2 to t
5 to 3
60° to 45°
6 to 12
5/6 of t
0 to t/3
5 to 3
70° to 60°
3 to 6
2/9 of t
t/3 to 2t/3
5 to 3
60° to 45°
6 to 12
5/9 of t
2t/3 to t
5 to 2
60° to 45°
6 to 20
8/9 of t
100 < t ≤ 200
3
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Section 7
A recommendation for the selection of probes is given in Table 21.
200 < t ≤ 300
Number of
TOFD setups
4
Depth range
∆t [mm]
Centre
frequency
f [MHz]
Beam angle
(longitudinal
waves) α
Element
size [mm]
Beam
intersection
0 to t/4
5 to 3
70° to 60°
3 to 6
2/12 of t
t/4 to t/2
5 to 3
60° to 45°
6 to 12
5/12 of t
t/2 to 3t/4
5 to 2
60° to 45°
6 to 20
8/12 of t
3t/4 to t
3 to 1
50° to 40°
10 to 20
11/12 of t or t
for α ≤ 45°
17.6.3 Scan increment setting
The scan increment setting shall be dependent on the wall thickness to be tested. For thicknesses up to 10
mm, the scan increment shall be no more than 0.5 mm. For thicknesses between 10 mm and 150 mm, the
scan increment shall be no more than 1 mm. Above 150 mm, the scan increment shall be no more than 2
mm.
17.6.4 Preparation of scanning surfaces
Scanning surfaces shall be wide enough to permit the examination volume to be fully covered.
Scanning surfaces shall be even and free from foreign matter likely to interfere with probe coupling (i.a. rust,
loose scale, weld spatter, notches, grooves). Waviness of the test surface shall not result in a gap between
one of the probes and test surface greater than 0.5 mm. These requirements shall be ensured by dressing, if
necessary.
Scanning surfaces may be assumed to be satisfactory if the surface roughness, Ra, is not greater than 6.3
μm for machined surfaces, or not greater than 12.5 μm for shot blasted surfaces.
17.6.5 Temperature
When not using special high-temperature phased array probes and couplants, the surface temperature of the
object to be tested shall be in the range 0°C to 50°C.
For temperatures outside this range, the suitability of the test equipment shall be verified.
17.6.6 Couplant
In order to generate proper images, a couplant shall be used which provides a constant transmission of
ultrasound between the probes and the test object. The couplant used for the calibration shall be the same as
that used in subsequent testing and post-calibrations.
17.6.7 Provision of datum points
In order to ensure repeatability of the testing, a permanent reference system shall be applied.
17.7 Testing of base material
The base material does not generally require prior testing for laminations (typically by using straight-beam
probes), as they are detected during the TOFD weld testing. Nevertheless, the presence of discontinuities in
the base material adjacent to the weld can lead to obscured areas or to difficulties in interpretation of the
data.
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Section 7
Thickness
t [mm]
17.8.1 Settings
17.8.1.1 General
Setting of range and sensitivity in accordance with this guide line and ISO 16828 shall be carried out prior
to each testing. Any change of the TOFD setup, requires a new setting. Noise should be minimized, e.g. by
signal averaging.
17.8.1.2 Time window
The time window shall at least cover the depth range as shown in Table 21:
a)
b)
for full-thickness testing using only one setup, the time window recorded should start at least 1 μs prior
to the time of arrival of the lateral wave, and should extend beyond the first mode-converted back-wall
signal, where possible
if more than one setup is used, the time windows shall overlap by at least 10 % of the depth range.
The start and extent of the time windows shall be verified on the test object.
17.8.1.3 Time-to-depth conversion
For a given PCS, setting of time-to-depth conversion is best carried out using the lateral wave signal and the
back-wall signal with a known material velocity.
This setting shall be verified by a suitable block of known thickness (accuracy 0.05 mm). At least one depth
measurement shall be performed in the depth range of interest, typically by recording a minimum of 20 Ascans.
The measured thickness or depth shall be within 0.2 mm of the actual or known thickness or depth. For
curved components geometrical corrections can be necessary.
17.8.2 Checking of the settings
Checks to confirm the range and sensitivity settings shall be performed at least every 4 hour and on
completion of the testing. Checks shall also be carried out whenever a system parameter is changed or
changes in the equivalent settings are suspected. If a reference block was used for the initial setup, the same
reference block should be used for subsequent checks. Alternatively, a smaller block with known transfer
properties may be used, provided that this is cross-referenced to the initial reference block.
Where a reference block was not used, but instead the test object was used for checking, then subsequent
checks shall be carried out at the same location as the initial check.
If deviations from the initial settings are found during these checks, corrections given in Table 22 shall be
carried out.
Table 22 Sensitivity and range corrections
Sensitivity
Action
Deviation ≤ 6 dB
No action required, data may be corrected by software.
Deviation > 6 dB
Settings shall be corrected and all tests carried out since
the last valid check shall be repeated.
Range
Deviation ≤ 0.5 mm or 2% of depth-range, whichever is
greater
No action required.
Deviation > 0.5 mm or 2% of depth-range, whichever is
greater
Settings shall be corrected and all tests carried out since
the last valid check shall be repeated.
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Section 7
17.8 Range and sensitivity settings
17.8.3.1 General
Depending on the testing level, a reference block shall be used to determine the adequacy of the testing
(e.g. coverage, sensitivity setting). Recommendations for reference blocks are given in ISO 10863.
17.8.3.2 Material
The reference block should be made of similar material to the test object (e.g. with regard to sound velocity,
grain structure, and surface condition).
17.8.3.3 Dimensions and shape
The thickness of the reference block should be representative of the thickness of the test object. Therefore,
the thickness should be limited to a minimum and a maximum value related to the thickness of the test
object.
Thickness of reference blocks is recommended to be between 0.8 times and 1.5 times the thickness of the
test object with a maximum difference in thickness of 20 mm compared to the test object. Care should
be taken that on the centreline between the probes there is no angle smaller than 40° at the bottom of
the reference block. The minimum thickness of the reference block should be chosen such that the beam
intersection point of the chosen setup is always within the reference block.
The length and width of the reference block should be chosen so that all the artificial discontinuities within
the area of interest can be captured within the appropriate scan range.
For testing of longitudinal welds in cylindrical test objects, curved reference blocks shall be used having
diameters from 0.9 times to 1.5 times the diameter of the test object. For objects having a diameter ≥ 300
mm, a flat reference block may be used.
17.8.3.4 Reference reflectors
For thicknesses between 6 mm and 25 mm, at least three reflectors are required. For thicknesses > 25 mm,
at least five reflectors are required. Typical reference reflectors used are side-drilled holes and notches.
Different shapes of notches may be used provided they generate diffracted signals.
17.9 Weld testing
The two probes are scanned parallel to the weld at a fixed distance and orientation in relation to the weld
centreline.
Data collected during a scan can be used for detection and sizing purposes. Further evaluation of TOFD
indications as detected during the initial scanning may require additional scans such as offset scans, scans
perpendicular to the discontinuity or complementary TOFD setups.
Scanning speed shall be chosen such that satisfactory images are generated and with minimum data loss.
The scanning speed is dependent on scan increment, signal averaging, pulse repetition frequency, data
acquisition frequency, and the volume to be tested. Missing scan lines can indicate that too high a scanning
speed has been used. A maximum of 5% of the total number of lines collected in one single scan may be
missed, but no adjacent lines shall be missed.
If a weld is scanned in more than one part, an overlap of at least 20 mm between the adjacent scans is
required. When scanning circumferential welds, the same overlap is required for the end of the last scan with
the start of the first scan.
Reduction of signal amplitude of lateral wave, back-wall signal, grain noise, or mode-converted signals during
a scan by more than 12 dB can indicate loss of coupling. If coupling loss is suspected, the area shall be rescanned. If the results are still not satisfactory, appropriate action shall be taken.
Saturation of the lateral wave or excessive grain noise (> 20% of FSH) during scanning requires corrective
action and re-scanning.
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Section 7
17.8.3 Reference blocks
Section 7
17.10 Interpretation and analysis of TOFD images
17.10.1 General
Interpretation and analysis of TOFD images are generally performed by:
a)
b)
c)
assessing the quality of the TOFD image
identification of relevant TOFD indications and discrimination of non-relevant TOFD indications
classification of relevant TOFD indications in terms of
1)
2)
embedded (linear, point-like)
surface breaking
d)
determination of location (typically position in x-direction and z-direction) and size (length and throughwall extent)
e)
evaluate the data against acceptance criteria.
17.10.2 Assessing the quality of the TOFD image
A TOFD test shall be carried out such that satisfactory images are generated which can be evaluated with
confidence. Satisfactory images are defined by appropriate:
a)
b)
c)
d)
coupling
data acquisition
sensitivity setting
time-base setting.
The operator shall decide whether non-satisfactory images require new data acquisition (re-scanning).
17.10.3 Identification of relevant TOFD indications
Satisfactory TOFD images shall be assessed for the presence of TOFD indications. TOFD indications are
identified by patterns or disturbances within the image.
TOFD is able to image discontinuities in the weld as well as geometric features of the test object. In order
to identify TOFD indications of geometric features, detailed knowledge of the test object is necessary. Those
TOFD indications arising from the intended or actual shape of the test object are considered as non-relevant.
To decide whether a TOFD indication is relevant (caused by a discontinuity), patterns or disturbances shall
be evaluated considering shape and signal amplitude relative to general noise level. Grey level values or
patterns of neighbouring sections can may be required to be taken into account to determine the extent of a
TOFD indication.
17.10.4 Classification of relevant TOFD indications
17.10.4.1 General
Amplitude, phase, location, and pattern of relevant TOFD indications can contain information on the type of a
discontinuity.
Relevant TOFD indications are classified as indications from either surface-breaking or embedded
discontinuities by analysing the following features:
a)
b)
c)
d)
e)
disturbance of the lateral wave
disturbance of the back-wall reflection
TOFD indications between lateral wave and back-wall reflection
phase of TOFD indications between lateral wave and back-wall reflection
mode-converted signals after the first back-wall reflection.
17.10.4.2 TOFD indications from surface-breaking discontinuities
Surface-breaking discontinuities can be classified into three categories.
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2)
3)
Scanning surface discontinuity: this type shows up as an elongated pattern generated by the signal
emitted from the lower edge of the discontinuity and a weakening or loss of the lateral wave (not always
observed). The TOFD indication from the lower edge can be hidden by the lateral wave, but generally a
pattern can be observed in the mode-converted part of the image. For small discontinuities, only a small
delay of the lateral wave can be observed.
Opposite surface discontinuity: this type shows up as an elongated pattern generated by the signal
emitted from the upper edge of the discontinuity and a weakening, loss, or delay of the back-wall
reflection (not always observed).
Through-wall discontinuity: this type shows up as a loss or weakening of both the lateral wave and the
back-wall reflection accompanied by diffracted signals from both ends of the discontinuity.
17.10.4.3 TOFD indications from embedded discontinuities
TOFD indications of embedded discontinuities usually do not disturb the lateral wave or the back-wall
reflection. Embedded discontinuities can be classified into three categories.
1)
2)
3)
Point-like discontinuity:
this type shows up as a single hyperbola-shaped curve which can lie at any depth.
Elongated discontinuity with no measurable height:
this type appears as an elongated pattern corresponding to an apparent upper edge signal.
Elongated discontinuity with a measurable height:
this type appears as two elongated patterns located at different positions in depth, corresponding to the
lower and upper edges of the discontinuity. The TOFD indication of the lower edge is usually in phase
with the lateral wave. The TOFD indication of the upper edge is usually in phase with the back-wall
reflection.
17.10.4.4 Unclassified TOFD indications
TOFD indications that cannot be classified in accordance with [17.10.4.2] and [17.10.4.3] may require
further testing and analysis.
17.10.5 Determination of location
The location of a discontinuity in the x-direction and z-direction as defined in ISO 16828 is determined from
the data collected in accordance with [17.9]. The location of a point-like discontinuity is sufficiently described
by its x-coordinates and z-coordinates. The location of elongated discontinuities shall be described by the xcoordinates and z-coordinates of their extremities. If the location in the y-direction as defined in ISO 16828
is required, additional scans are necessary. If a more accurate determination of the location is required,
reconstruction algorithms, may be used.
17.10.6 Definition and determination of length and height
17.10.6.1 General
The size of a discontinuity is described by the length and height of its indication.
Length is defined by the difference of the x coordinates of the indication.
The height is defined as the maximum difference of the z coordinates at any given x position.
The length and height measurements are illustrated in Figure 29 to Figure 31.
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Section 7
1)
Section 7
Key:
1 = scanning surface
2 = opposite surface
x1 = start position of discontinuity
x2 = end position of discontinuity
z1 = start depth of discontinuity
z2 = end depth of discontinuity
h = z2 - z1 = height
l = x2 - x1 = length.
Figure 29 Length and height definition of a scanning surface-breaking discontinuity
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Section 7
Key:
1 = scanning surface
2 = opposite surface
x1 = start position of discontinuity
x2 = end position of discontinuity
z1 = start depth of discontinuity
z2 = end depth of discontinuity
h = height (not necessarily z2 - z1)
l = x2 - x1 = length.
Figure 30 Length and height definition of an opposite surface-breaking discontinuity
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Section 7
Key:
1 = scanning surface
2 = opposite surface
x1 = start position of discontinuity
x2 = end position of discontinuity
z1 = start depth of discontinuity
z2 = end depth of discontinuity
h = height (not necessarily z2 - z1)
l = x2 - x1 = length.
Figure 31 Length and height definition of an embedded discontinuity
17.10.6.2 Determination of length
Depending on the type of indication, one of the techniques for length sizing according to 1) or 2) shall be
applied:
1)
2)
Length sizing of embedded indications:
a hyperbolic cursor is fitted to the indication. Assuming the discontinuity is elongated and has a finite
length, this is only possible at each end. The distance moved between acceptable fits at each end of the
indication is taken to represent the length of the discontinuity.
Length sizing of elongated curved surface-breaking indications:
this type of indication does change significantly in the through wall direction.
A hyperbolic cursor is positioned at either end of the indication at a time delay of one third of the
indication penetration. The distance moved between the cursor positions at each end of the indication is
taken to represent the length of the discontinuity.
17.10.6.3 Determination of height
The height measurement shall be done from the A scan and by choosing a consistent position on the signals,
if applicable, taking phase reversal into account. It is recommended to use one of the following methods:
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General:
1)
2)
3)
4)
b)
method 1:
by measuring
method 2:
by measuring
method 3:
by measuring
method 4:
by measuring
Section 7
a)
the transit time between the leading edges of the signals
the transit time between the first peaks
the transit time between the maximum amplitudes
the transit time between the first zero crossings of the signals.
Surface breaking discontinuities:
the height of an indication of a surface breaking discontinuity at the scanning surface is determined by
the maximum difference between the lateral wave and the lower tip diffraction signal.
For a surface breaking discontinuity at the opposite surface, the height is determined by the maximum
difference between the upper tip diffraction signal and the back-wall reflection.
c)
Embedded discontinuities:
the height of an indication of an embedded discontinuity is determined by the maximum difference
between the upper tip diffraction signal and the lower tip diffraction signal at the same x position.
17.11 Acceptance criteria
17.11.1 Acceptance criteria given in the referring rules
After classification of all relevant TOFD indications and after determination of their location and size, they
shall be evaluated against acceptance criteria specified in the rules. If no acceptance criteria in the rules are
given, the acceptance criteria in [17.11.2] shall be used. Based on the evaluation against the acceptance
criteria, the TOFD indications shall be categorized as 'acceptable' or 'not acceptable'.
17.11.2 No acceptance criteria given by the referring rules
17.11.2.1 General
Where no acceptance criteria are specified in the referring rules, or agreed, the acceptance criteria defined in
[17.11.2.3] to [17.11.2.5] apply.
17.11.2.2 Indications from single discontinuities
Table 23 Indications from single discontinuities
Thickness range [mm]
Maximum acceptable
length if h < h2 or h3
Maximum acceptable height if: l ≤ lmax
Surface breaking
1)
indication , h3 [mm]
Embedded
indication, h2 [mm]
Maximum acceptable
2)
height
if: l > lmax
6 < t ≤ 15
0.75 t
1.5
2
1
15 < t ≤ 50
0.75 t
2
3
1
50 < t ≤ 100
40 mm
2.5
4
2
t > 100
50 mm
3
5
2
1)
When indications from surface breaking discontinuities are detected, and the resolution is not sufficient to resolve
the depth, different techniques or methods shall be applied to determine the acceptability. If it is not possible
to apply other techniques or methods all indications from surface breaking discontinuities shall be considered
unacceptable.
2)
Indications with height less than h1 shall not be considered.
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17.11.2.4 Grouping of indications
Point like indications and indications with height smaller than h1 are not considered for grouping.
Grouping of indications is based on the size and the separation of individual indications. The length and the
size of a group shall not be used for further grouping.
For evaluation, a group of indications shall be considered as a single one if:
— the distance between two individual indications along the weld is less than the length of the longer
indication, and
— the distance between two individual indications in the thickness direction of the weld is less than the
height of the higher indication.
In case of an indication with varying height, the maximum local height h as shown in Figure 32 shall be used.
hg for a grouped indication is defined as the sum of the heights of the individual indications plus the distance
between them (see Figure 32).
lg for a grouped indication is defined as the sum of the lengths of the individual indications plus the distance
between them (see Figure 32).
Key:
1, 2, 3 = simple representation of three indications
h = maximum height of indications 1, 2, 3
l = maximum length of indications 1, 2, 3
hg = total height of grouped indications
lg = total length of grouped indications
t = thickness.
Figure 32 Dimensions of grouped indications
17.11.2.5 Point like indications
The maximum acceptable number, N, of single diffraction signals in any 150 mm of weld length may be
calculated with formula below:
(5)
where:
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Section 7
17.11.2.3 Total length of indications
The sum of the lengths of the individual indications larger than h1 measured along the weld over a length of
12 t shall be less than or equal to 3.5 t with a maximum of 150 mm.
Section 7
N = number of indications as specified above, rounded to the higher integer
t = thickness, [mm].
17.12 Test report
In addition to relevant parts of [12], the test report shall include at least the following information:
a)
information relating to the object under test:
1)
2)
3)
4)
5)
6)
7)
8)
b)
information relating to the test equipment:
1)
2)
3)
4)
c)
manufacturer and type of the TOFD equipment scanning mechanisms with identification numbers if
required
manufacturer, type, frequency, transducer size, and beam angle(s) of the probes with identification
numbers if required
details of the reference block(s) with identification numbers if required
type of couplant used
information relating to the test technique:
1)
2)
3)
4)
5)
6)
7)
d)
identification of the test object
dimensions including wall thickness
material type and product form
geometrical configuration
location of the tested welded joint(s)
reference to welding process and heat treatment
surface condition, and temperature if outside the range 0°C to 50°C
stage of manufacture
testing level and reference to a written test procedure, if required
purpose and extent of test
details of datum and coordinate systems
method and values used for range and sensitivity settings
details of signal averaging and scan increment setting
details of offset scans, if required
access limitations and deviations from this document, if any
information relating to the test results:
1)
2)
3)
4)
5)
TOFD images of at least those locations where relevant not-acceptable TOFD indications have been
detected
acceptance criteria applied
tabulated data recording the classification, location and size of relevant TOFD indications and the
results of the evaluation
date of test
names, signatures and qualification of the test personnel.
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1 Scope
This section specifies visual testing of fusion welds in metallic materials and applies unless specified
otherwise in the referring rules or standard. It may also be applied to visual testing of joints prior to welding.
2 Information required prior to testing
See general information under Sec.2 [4].
3 Requirements for personnel and equipment
3.1 Personnel qualifications
See Sec.2 [1].
Alternatively personnel performing visual examination and visual testing of welds may instead have
documented training and qualifications according to NS 477, minimum CSWIP3.1 (level 2), AWS' minimum
CWI or minimum IWI-S or equivalent certification scheme.
3.2 Equipment
The following equipment may be needed:
— for visual testing of welds with limited accessibility: mirrors, endoscopes, boroscopes, fibre optics or TV
cameras
— magnifying lens
— radius gauge
— various set of weld gauges for measuring fillet welds, reinforcement, undercuts, misalignment etc.
— light source
— lux meter.
For all equipment it shall demonstrated sufficient functionality. This means calibration of lux meters at regular
intervals, resolution test for endoscopes, boroscopes, fibre optics or TV cameras, verification of zero mark/
zero readings for all gauges etc. For examples of measuring equipment, see ISO 17637 Annex A.
4 Testing conditions
The luminance at the surface shall be minimum 500 lx.
If required to obtain a good contrast and relief effect between imperfections and background, an additional
light source should be used. All techniques and options that will be able to enhance the detectability of
defects are allowed as far as the surface will not be damaged and/or the product functionality will not be
influenced.
For performance of direct inspection, the access shall be sufficient to place the eye within 600 mm of the
surface to be inspected and at an angle not less than approximately 30°.
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Section 8
SECTION 8 VISUAL TESTING
Section 8
Figure 1 Access for testing
5 Testing volume
If not otherwise agreed all weld connections in question should be 100 % visually inspected.
The testing volume shall as a minimum cover the zone which includes welds and parent metal for at least 20
mm on each side of the weld.
In case of doubt, visual testing should be supplemented by other non-destructive testing methods for surface
inspections.
6 Preparation of surfaces
The weld surface shall be free of weld spatter, slag, scale, oil, grease, heavy and loose paint or other surface
irregularities which might avoid imperfections from being obscured.
It may be necessary to improve the surface conditions e.g. by abrasive paper or local grinding to permit
accurate interpretation of indications.
7 Evaluation of indications
The weld shall be visually tested to check that the following meets the requirements for the agreed
acceptance criteria:
— the profile of the weld face and the height of any excess weld metal
— the surface of the weld is regular and present an even and satisfactory visual appearance
— the distance between the last layer and the parent metal or the position of runs has been carried out as
required as described by the WPS
— the weld merge smoothly into the parent metal.
— the fillet welds have correct throat thickness and geometry
— undercuts, porosity or other surface imperfections to be within the maximum limit
— in case of butt welds it shall be checked that the weld preparation has been completely filled
— in case of single sided butt welds, the penetration, root concavity and any burn-through or shrinkage
grooves are within the specified limits.
Weld zones in stainless steels, nickel and titanium alloys shall be visually inspected and fulfil the criteria for
oxidation levels (annealing colours, corrosion, scratches).
In addition:
— any attachments temporarily welded to the object shall be removed. The area where the attachment was
fixed shall be checked to ensure freedom of unacceptable imperfections
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8 Visual testing of repaired welds
When welds fail to comply wholly or in part with the acceptance criteria and repair is necessary, the following
actions shall be taken:
— if removal of metal exceeds 7% of the wall thickness or 3 mm, whichever is less, repair welding is
required according to an approved procedure
— if the weld is partly removed it shall be checked that the excavation is sufficiently deep and long to
remove all imperfections. It shall also be ensured that there is a gradual taper from the base of the cut
to the surface of the weld metal at the ends and sides of the cut. The width and profile of the cut shall be
prepared such that there is adequate access for re-welding
— it shall be checked that, when a cut has been made through a faulty weld and there has been no serious
loss of material, or when a section of materials containing a faulty weld has been removed and a new
section shall be inserted, the shape and dimensions of the weld preparation meet the requirements
— in case where part of a weld is gouged out the excavated area shall be ground and either magnetic
particle testing or penetrant testing should be carried out prior to re-welding in order to ensure that the
imperfection is removed.
9 Acceptance criteria
Whenever acceptance criteria are defined in the rules, approved drawings, IACS recommendations or other
agreed product standards, these criteria are mandatory. If no acceptance criteria are specified quality class C
– Intermediate of ISO 5817 applies. For highly stressed areas more stringent requirements, such as quality
level B of ISO 5817 may be applied.
10 Reporting
When test reports are required, at least the following information in addition to the items listed under Sec.2
[7] shall be included in the report:
—
—
—
—
—
viewing conditions
imperfections exceeding the acceptance criteria and their location
the extent of testing with reference to drawings as appropriate
test devices used
result of testing with reference to acceptance criteria.
If a permanent visual record of an examined weld is required, photographs or accurate sketches or both
should be made with any imperfections clearly indicated. In case of photo documentation a ruler shall be part
of the picture to serve for size comparison purposes.
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Section 8
— all sharp corners adjacent to the weld shall be rounded. Preparation of edges/structural shapes to be
prepared to an acceptable surface finish.
1 Guideline for qualification of PAUT procedure
1.1 Objective
The objective of this appendix is to provide a systemic approach for the general development and
qualification of the procedure for the use of phased array ultrasonic testing (PAUT) on DNV projects. Mainly
reference standards is this document and ISO 13588.
1.2 General
The general requirements are specified in Sec.7 [16].
As part of the approval of a procedure it shall be carried out a practical demonstration to the Society on
project specific validation blocks, showing that the procedure is adequate in reliability, repeatability and
accuracy for detection and sizing of relevant indications, see further details in Sec.7 [16].
The approval of the procedure is normally project specific and shall only be valid when all essential variables
remain nominally the same as covered by the documented qualification.
Guidance note:
Following parameters are considered essential for the validity of the procedure (see full details in Sec.7 [16]):
—
probes: number of elements, pitch, size of elements
—
focal range, focal law design
—
virtual aperture size
—
wedge characteristics
—
scanning plans/techniques
—
weld geometries, root and cap set up
—
thickness ranges, pipe diameters
—
software.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
1.3 Procedure qualification
The extent of the qualification will normally be established for each project and will reflect the range for
which procedure is intended to be used.
Unless otherwise agreed with the Society, qualification of the procedure shall be performed on validation
blocks with artificial reflectors required for checking sensitivity detectability, coverage, sizing and evaluation.
Validation blocks shall contain:
— representative thickness range to the inspected product
— representative acoustic properties
— representative production welds, including welding methods, weld bevel geometry, dimensions and
tolerances
— representative and agreed natural and/or artificial reflectors with size range of types that are typical for
the manufacturing process
— identification, and defect map with all reflectors, their actual number, type, dimensions and relative
location in the validation block.
Validation blocks shall be traceable to the manufactured material.
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Appendix A
APPENDIX A GUIDELINES FOR QUALIFICATION OF PAUT AND TOFD
PROCEDURES
Qualification shall demonstrate theoretically and practically that 100% coverage of the weld and heat affect
zone (HAZ) is obtained, with adequate beam coverage overlap and signal amplitude for relevant imperfection
sizes.
All relevant reflectors shall be adequately detected, located and sized.
The following will be analysed as part of qualification:
—
—
—
—
—
detectability
accuracy in height sizing (random and systematic deviation)
accuracy in length sizing
accuracy in imperfection depth estimate
characterisation abilities.
All scans shall be given a unique number and the documentation of the test scans shall include hard copy and
electronic output of all raw scans data.
DNV may request additional supporting documents to verify adequacy of the procedure.
Upon successful completion of the qualification scope it is assumed that procedure will remain qualified
within the range of qualification for the project if procedure remains unchanged, i.e. with no changes that are
judged to have an impact on the performance parameters.
The qualification may be validated for application on other projects, if the parameters range of the
qualification are regarded relevant.
1.4 PAUT procedure checklist
Content
1.0 Title page
Requirement
— title
— document no.
— author and approver
— revision and revision status.
2.0 Scope
— scope and purpose of inspection
— applied method and techniques
— material grades and delivery condition, component/weld geometry, thickness
range, joints configuration
— test limitations.
3.0 Reference standards
— reference to applicable rules, standards and codes.
4.0 Terminology and abbreviations
— main terms and abbreviations used in procedure.
5.0 Safety
— company safety practice
— local regulations
— hazard and risks etc.
6.0 Personnel qualification
— training and certification requirements.
7.0 Information prior inspection
— coverage, scanning distance, distance allowable for scanning
— testing volume and weld geometry
— time of testing, minimum 24 hours or 48 hours after welding
— extent of testing
— limitations.
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Appendix A
Number and location of reflectors should be sufficient to ensure reliability of testing. Reflectors shall vary in
length, height and location. Too close spacing and stacking of the imperfections shall be avoided.
8.0 Equipment requirement
Requirement
— details on PAUT instrument as ref. in ISO 18563-1, -2, -3, ASTM E2491
— probes and cables: list of probes used, frequency, number of element, pitch,
element size etc.
— wedges: list of wedges, diameter, wedge angle
— calibration blocks
— reference blocks for sensitivity calibration
— validation blocks used for procedure qualification with described reflectors size,
depth, material grade and delivery condition
— scanner and encoder: type of scanner and encoder used in procedure
— software name and version.
9.0 Couplant
— Type
— Temperature range
— Same couplant shall be used for calibration and testing
10.0 Equipment function
calibration
— dead element check
— velocity calibration
— wedge delay calibration
— sensitivity (ACG) calibration
— TCG set-up
— encoder calibration.
11.0 Equipment system checking
and periodical checking
System checking (every monthly):
— screen high linearity
— amplitude control linearity
— time-based linearity.
Periodical checking:
— every 4hrs checking sensitivity and range deviation.
12.0 Surface compensation,
lamination, transverse scanning
— transfer correction measurement
13.0 Inspection process
— scanning sequence
— lamination and transverse scanning.
— parameters selection.
14.0 Data validation and storage
— scanning speed
— no more than 5% of the total scan area, or adjacent two data missing
— poor couplant
— scanning resolution/increment
— overlap
— data storage, naming system and backup.
15.0 Data assessment and
evaluation
— evaluation levels
— determination of indication length, size, depth, maximum amplitude
— characterized of indications.
16.0 Recording
— recording levels.
17.0 Acceptance criteria
— acceptance criteria in accordance with applicable rule or code requirements.
18.0 Report
— report template as per ISO 13588 or sample PAUT report below.
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Appendix A
Content
Requirement
19.0 Non-compliances
— any non-compliances to the procedure shall be reported to PAUT supervisor and
agreed with the Society.
Appendix A scanning plan
— scanning plan shall cover all joints configurations and thickness range
— scanning plan shall include extent of coverage and demonstrate that complete
volume of the weld and HAZ (10mm from each side) is covered with sectoral
scanning or linear scanning, number of groups
— joints configuration details such as welding bevel, root, weld cap, bevel angle
— focus law
— probe details such as frequency, element number, element size, pitch, gaps, fire
number of elements, angle range, angle incremental change, focal range, start
and end element number for each group
— wedge angle, serial no. curvature and shape
— offset values.
Appendix B
— system calibration tables. Ref. to item 11.0.
Appendix C
— sketches of calibration, reference blocks.
Appendix D
— sketches of validation blocks.
— validation blocks PAUT test results, including detailed defect location maps.
1.5 Report format example
PAUT TESTING REPORT (Phased array ultrasonic testing)
Order No.
Customer
Report No.
Drwg. No Rev No.
Subject
Page___of___
Date:
Manufacture/site
Detail
Sign/ Name
Reference to
Material
Extent of testing
Heat treatment
□ Yes
Code reference:
Joint Type
Structure category
□ No
□ TMCP plate
Procedure no.:
Material/Thickness
Piping class:
Acceptance criteria/level:
Weld groove/weld caps
Welding process:
Surface condition &
Temperature:
Calibration blocks/
thickness/ reflectors
Reference blocks/ thickness/
reflectors
Encode no.
Scanning method:
□ S-scan (sectoral scan)
Wedge type/serial no.
Scanner no.
Frequency [Mhz]
Welder no.
PAUT Parameters and Instrument setup
Instrument type & Serial no.
Testing level:
□ E-scan (Linear scan)
Probe type/Serial no.
Element number/ pitch
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Appendix A
Content
First/
Active
last
elements
element
Angle
range
Scanning
increment
Defect
No.
Defect
Pos.
[mm]
Focus
depth
Offset
[mm]
TCG sensitivity
gain [dB]
Defect
depth
[mm]
Defect
hight
[mm]
Defect
1)
type
Transfer correction
[dB]
S-scan
Group1
E-scan
Group1
E-scan
Group2
Weld No/position
1)
Testing
length
Defect
length
[mm]
Conclusion
Acc/Rej
Remarks:
S = surface breaking, E = embedded
Approved by:
Operators Name/Certificate No:
Verified by:
2 Guideline for qualification of TOFD procedure
2.1 Objective
The objective of this section is to define a systematic approach for the development and qualification of the
procedure for the use of time of flight diffraction testing (TOFD) on DNV projects. Main reference standards
are this document and ISO 10863.
The guideline can be utilised for all materials however care shall be taken for application with anisotropic
materials.
2.2 General
The general requirements are specified in Sec.7 [17].
As part of approval it shall be demonstrated that applied procedure is adequate in reliability, repeatability and
accuracy for detection and sizing of relevant indications.
As part of the approval of a procedure it shall be carried out a practical demonstration to the Society on
project specific validation blocks, showing that the procedure is adequate in reliability, repeatability and
accuracy for detection and sizing of relevant indications, see further details in Sec.7 [17].
The approval of the procedure is normally project specific and shall only be valid when all essential variables
remain nominally the same as covered by the documented qualification.
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Appendix A
Group
No.
Appendix A
Guidance note:
Following parameters are considered essential for the validity of the procedure (see full details in Sec.7 [17]):
—
number of probes: frequency, size of elements, wedge angle
—
PCS setting, beam coverage, beam intersection
—
scanning mechanisms
—
weld geometries, root and cap set up
—
thickness ranges, pipe diameters
—
averaging, sampling rate
—
reference blocks with artificial reflectors
—
dead zone.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
2.3 Procedure qualification
The extent of the qualification will normally be established for each project and will reflect the range for
which procedure is intended to be used.
Unless otherwise agreed with the Society, qualification of the procedure shall be performed on validation
blocks with artificial reflectors required for checking sensitivity detectability, coverage, sizing and evaluation.
Validation blocks shall contain:
— representative thickness range to the inspected product
— representative acoustic properties
— representative production welds, including welding methods, weld bevel geometry, dimensions and
tolerances
— representative and agreed natural and/or artificial reflectors with size range of types that are typical for
the manufacturing process
— identification, and defect map with all reflectors, their actual number, type, dimensions and relative
location in the validation block.
Validation blocks shall be traceable to the manufactured material.
Number and location of reflectors should be sufficient to ensure reliability of testing. Reflectors shall vary in
length, height and location. Too close spacing and stacking of the imperfections shall be avoided.
Qualification shall demonstrate 100% coverage of the weld and heat affect zone (HAZ) with adequate beam
coverage. If ESBEAM tool or Setupbuilder software used for scanning plan, number of validation blocks can
be reduced by agreement with the Society.
All relevant reflectors shall be adequately detected, located and sized.
Reflectors shall be positioned correctly with respect to the weld centerline. Cross sectional plotting of flaw
indications on the indication data sheets may be required in order to determine the location of the reflector.
For detection of reflectors in dead/lind zone, procedure shall define alternative methods or techniques of
testing.
The following will be analysed as part of qualification:
—
—
—
—
—
detectability
accuracy in height sizing (random and systematic deviation)
accuracy in length sizing
accuracy in imperfection depth estimate
characterisation abilities.
All scans shall be given a unique number and the documentation of the test scans shall include hard copy and
electronic output of all raw scans data.
DNV may request additional supporting documents to verify adequacy of the procedure.
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The qualification can be validated for application on other projects, if the parameters range of the
qualification are regarded relevant.
2.4 TOFD procedure checklist
Content
1.0 Title page
Requirement
— title
— document no.
— author and approver
— revision and revision status.
2.0 Scope
— scope and purpose of inspection
— applied method and techniques
— material grades and delivery condition, component/weld geometry, thickness
range, joints configuration
— test limitations.
3.0 Reference standards
— reference to applicable rules, standards and codes.
4.0 Terminology and abbreviations
— main terms and abbreviations used in procedure.
5.0 Safety
— company safety practice
— local regulations
— hazard and risks etc.
6.0 Personnel qualification
— training and certification requirements.
7.0 Information prior inspection
— testing levels
— volume to be inspected, extend of testing
— scanning increment setting
— time of testing, minimum 24 hours or 48 hours after welding
— surface preparation
— temperature range.
8.0 Equipment requirement
— details on TOFD instrument as specified in Sec.7 [17.5.2]
— computer display and software name revision
— recommend probes, frequency, element size, number of setting ups, depth
range, beam intersection etc.
— wedges angle 70, 60, 45; gaps between test surface less than 0.5 mm
— reference blocks for sensitivity calibration
— qualification with described reflectors size, depth, material grade and delivery
condition
— scanning mechanisms type and serial no.
— encoder: type, encoder calibration.
9.0 Couplant
— type
— same couplant shall be used for calibration and testing.
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Appendix A
Upon successful completion of the qualification scope it is assumed that procedure will remain qualified
within the range of qualification for the project if procedure remains unchanged, i.e. with no changes that are
judged to have an impact on the performance parameters.
10.0 Range and sensitivity setting
Requirement
Appendix A
Content
— PCS set-up
— time window
— time to depth conversion
— sensitivity setting.
11.0 Equipment system checking
and periodical checking
System checking (every monthly):
— screen high linearity
— amplitude control linearity
— time-based linearity.
Periodical checking:
— every 4hrs checking sensitivity and range correction.
12.0 Reference blocks
— whether reference blocks need, recommended to be between 0,8 and 1,5 times
the thickness of the test object with a maximum difference in thickness of 20
mm compared to the test object
— validation blocks used for procedure.
13.0 Dead zone limitations,
lamination transverse scanning
— dead zone: supplement with other NDT methods
14.0 Data validation and storage
— scanning speed
— limitations, lamination and transverse scanning.
— no more than 5% of the total scan area, or adjacent two data missing
— amplitude of lateral wave being between 40 to 80% FSH
— adequate couplant
— scanning resolution/increment
— adequate overlap
— data storage, naming system and backup.
15.0 Interpretation and analysis of
data
— characterized of indications: surface breaking defects, embedded defects, point
like or planar like
— flaw length: depth and height.
16.0 Recording
— recording levels.
17.0 Acceptance criteria
— acceptance criteria in accordance with applicable rule or code requirements.
18.0 Report
— report template as per ISO 10863 or sample TOFD report below.
19.0 Non-compliances
— any non-compliances to the procedure shall be reported to TOFD supervisor and
agreed with the Society.
Appendix A scanning plan
— scanning plan shall cover all joints configurations and thickness range, such as
welding bevel, root, weld cap, bevel angle
— number of probes, frequency, element size
— PCS setting, beam intersection
— wedge angle, serial no. curvature and shape
— scanning plan shall include extent of beam coverage and demonstrate that
complete volume of the weld and HAZ (10 mm from each side)
— near surface dead zone and far surface dead zone
— averaging etc.
Appendix B
— system calibration tables. Ref. to Item 11.0
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Requirement
Appendix C
— sketches of reference blocks
Appendix D
— sketches of validation blocks
— validation blocks TOFD test results, including detailed defect location maps.
2.5 Report format example
TOFD TESTING REPORT (Time of flight diffraction)
Order No.
Customer
Report No.
Drwg. No Rev No.
Subject
Page___of___
Date:
Manufacture/site
Detail
Sign/ Name
Reference to
Material
Extent of testing
Heat treatment
Code reference:
Joint Type
Structure category
□ Yes
Procedure no.:
Material/Thickness
Piping class:
Acceptance criteria/level:
Weld groove/weld caps
Welding process:
Surface condition &
Temperature:
□ No
□ TMCP plate
TOFD Parameters and Instrument setup
Instrument type & Serial no.
Reference blocks/ thickness
Scanner no.
Encode no.
Testing level:
Scanning method:
Scanning increment
Couplant
Scanning plan:
Software rev. no.
Limitation of access:
Welder no.
Group
No.
Angle
Frequency
[MHz]
Defect
No.
Defect
Pos.
[mm]
Probe type/No
Weld No/position
1)
Testing
length
Defect
length
[mm]
Crystal
size
[mm]
PCS
[mm]
Sensitivity gain
[dB]
Defect
depth
[mm]
Defect
hight
[mm]
Defect
1)
type
Conclusion
Acc/Rej
Time window
[μS]
Remarks:
S = surface breaking, E = embedded
Approved by:
Verified by:
Operators Name/Certificate No:
Class guideline — DNV-CG-0051. Edition January 2022
Page 158
Non-destructive testing
DNV AS
Appendix A
Content
Changes – historic
CHANGES – HISTORIC
December 2015 edition
This is a new document.
Class guideline — DNV-CG-0051. Edition January 2022
Page 159
Non-destructive testing
DNV AS
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