NGN/SP/NDT/2
Specification for
Non-Destructive Testing of Welded Joints on
Construction and Fabrication Projects
September 2019
NGN/SP/NDT/2
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Contents
Page
Foreword
4
Disclaimer
4
Brief History
4
Mandatory and non-mandatory requirements
5
Approval
6
Key changes
6
1. Scope
7
2. References
7
3. Definitions
7
4. Destructive Testing
7
5. Non-Destructive Testing Method
8
6. Personnel Qualification
8
7. Non-Destructive Testing of Procedure Welds
8
8. Non-Destructive Testing of Production Welds
9
9. Radiographic Examination
11
10. Manual Ultrasonic Examination of Welded Joints
12
11. Automatic Ultrasonic Examination for Pipeline
16
12. Phased Array Ultrasonic Examination for Pipework
16
13. Magnetic Particle Flaw Detection
17
14. Dye Penetrant Flaw Detection
18
15. Non-Destructive Testing of Repaired Production Welds
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16. Records
18
Appendix A – References
19
Appendix B – Management of Site Radiography
21
Appendix C – Site Radiation Safety Monitoring Checklist & Report Sheet
29
Appendix D – Requirements for Automatic Ultrasonic Inspection (AUT) for Pipeline
Fabrication/Construction & Phased Array Ultrasonic (PAUT) for Pipework
Construction
33
Appendix E – Non-Destructive Testing
50
Endnote
56
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Foreword
This document was approved by the appropriate Technical Authority Level (TAL) and Standards
Steering Group (SSG) for use throughout Northern Gas Networks Limited (NGN).
NGN documents are revised, when necessary, by the issue of new editions. Users should ensure that
they are in possession of the latest edition by referring to the NGN Register of Documents available
on NGN intranet.
Compliance with this document does not confer immunity from prosecution for breach of statutory
or other legal obligations.
Contractors and other users external to NGN should direct their requests for further copies of NGN
documents to the department or group responsible for the initial issue of their contract
documentation.
Disclaimer
This safety and engineering document is provided for use by NGN and such of its contractors as are
obliged by the terms and conditions of their contracts to comply with this document. Where this
document is used by any other party it is the responsibility of that party to ensure that this
document is correctly applied.
Brief History
First published as NGN/SP/NDT/2
June 2004
EPSG/T03/867
Amended into NGN format
July 2007
Updated to include the use of phase
array ultrasonic (PAUT) on inspection
of pipework and pipeline. Updating of
the reference list and Competence of
the inspectors.
July 2017
Version 2.0
Review to address regular deviations
around the design of calibration
blocks. Blocks can now be designed to
BS EN ISO 13588 as opposed to ASME
BPVC Section V which are not readily
available.
August 2019
NGN/SP/NDT/2
Version 3.0
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Non-material change to re-instate
missing bullet points in Appendix D.
June 2020
Version 3.1
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Mandatory and non-mandatory requirements
In this document:
Must:
Indicates a mandatory requirement
Should:
Indicates best practice and is the preferred option. If an alternative method
is used then a suitable and sufficient risk assessment must be completed to show that the
alternative method delivers the same, or better, level of protection.
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Approval
Technical Authority Level:
Andrew Middleton
05th September 2019
19th September 2019
Standards Steering Group:
Key Changes
Section
Amendments
D 4.3.1 & D 4.11.2
PAUT qualification requirements amended to the satisfaction of NGN,
rather than ASME standards.
D 4.3.5, D 4.3.9, D 4.5.4 & D
4.5.5.
BS EN ISO 13588 specified for calibration blocks in place of ASME
standards.
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Specification for
Non-Destructive Testing of Welded Joints on
Construction and Fabrication Projects
1.
Scope
This Specification defines the minimum or additional NGN requirements necessary for non-destructive
examination of welded joints. Where National or International standards referenced in this document
require specific items to be agreed between the contracting parties, the requirements of this
specification must apply. This specification is not intended for the revalidation of welded joints in
pressure containing components. In such cases reference to NGN/PR/NDT/1 should be made.
This Specification details the requirements for non-destructive examination of welded joints in carbon,
carbon manganese and stainless steel materials specified for use on the NGN Gas Network only.
Where non-destructive testing alone cannot confirm that a welded joint fully meets the acceptance
criteria of a qualified welding procedure, additional destructive testing may be needed to prove that the
requirements of the appropriate welding standard or specification have been met.
2.
References
Unless otherwise specified, the latest edition, including addenda and revisions, of the documents listed in
Appendix A must apply.
3.
Definitions
For the purpose of this specification the terms and definitions used in BS EN 1330 must apply.
Employer: NGN acting directly or through an authorised representative.
Class I Welding: For the purpose of this specification, Class I welding must be categorised as those welds
which are designed to operate at pressures greater than 7 bar.
Class II Welding: For the purpose of this specification, Class II welding must be categorised as those welds
that are designed to operate at pressures not greater than 7 bar.
4.
Destructive Testing
The Employer reserves the right to require the complete removal of production welds to prove that the
mechanical properties of the weld conform to specification criteria. Destructive testing must consist of
the removal of complete welds for mechanical testing in accordance with the appropriate welding
standard or specification.
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5.
Non Destructive Testing Method
5.1
General
The method of non-destructive testing (NDT) used must be capable of producing indications of
imperfections which can be accurately interpreted and evaluated in order to assess whether the defect
acceptance criteria specified in the relevant welding standard have or have not been met. The results of
the non-destructive testing must be recorded and must include the location, size and nature of all flaws
detected.
5.1.1 Operators of all types of non-destructive testing equipment should be required to demonstrate
to the approval of the Employer the capability of the equipment and examination procedure to detect
flaw indications. The operator may be asked to demonstrate their ability to make correct interpretation
of defect indications given by the equipment.
5.1.2 Welds must be examined in the as welded, or post weld heat-treated condition (PWHT), as
applicable. If the weld has been subject to PWHT the non-destructive testing must follow this treatment.
Local dressing of the weld reinforcement may be required to confirm transverse indications.
5.1.3 Where local dressing is used to aid the interpretation of non-destructive testing or to confirm
defect indications, care must be taken to maintain the material minimum design thickness.
6.
Personnel Qualification
Personnel performing non-destructive examination in accordance with this specification must have
qualifications from a scheme meeting the requirements of BS EN ISO 9712 (e.g. PCN, CSWIP or ACCP).
Acceptance of certification by the inspection company in accordance with a written practice meeting the
recommendations in SNT-TC-1A or ANSI/ASNT CP-189 shall be subject to review and agreement by
Employer.
The Employer may consider personnel approved to an alternative qualification scheme as a variation to
the specification.
7.
Non Destructive Testing of Procedure Test Welds
7.1
General
Non-destructive testing on weld procedure qualification test welds must conform to the welding
procedure qualification standard and this specification.
All non-destructive testing must be carried out on the test pieces prior to cutting of the test specimens
for mechanical test. Any post-weld heat treatment that is specified shall be completed prior to nondestructive testing.
The quality of the test welds must be determined by non-destructive testing after weld specimens have
been allowed to cool to ambient temperatures in production conditions for a minimum of 24 hours.
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Non-destructive testing procedure specifications must be submitted to the Employer and be approved
prior to weld testing.
All test butt welds must be examined visually and by X-radiography. Automatic Ultrasonic Testing (AUT)
may be substituted for X-radiography when agreed between the contracting parties. If AUT is used, then
it must be carried out in accordance with Appendix D of this specification.
Non-destructive testing procedure specifications must be submitted to the Employer for approval prior to
production welding commencing.
The weld root region must be examined by magnetic particle inspection (MPI) or dye penetrant
inspection (DPI), as appropriate, where access permits.
All fillet test welds must be examined visually and by MPI or DPI as appropriate. MPI must be the
preferred method to be used for the examination of carbon steel welds. The DPI method must be used
for the examination of austenitic stainless steel welds. Complementary non-destructive testing methods,
such as Ultrasonic Testing, may be required to identify flaw characteristics.
7.1.1 The results from visual examination and non-destructive testing must be assessed according to
the appropriate acceptance criteria of the welding standard specified.
8.
Non Destructive Testing of Production Welds
8.1
General
8.1.1 Non-destructive testing must be performed in accordance with the Inspection and Test Plan and
Quality Control Procedure developed for the project. As a minimum, the extent of non-destructive
testing (percentage or number of production welds to be examined) must meet the requirements of the
construction code and this specification.
8.1.2 All completed welds must be examined visually in accordance with BS EN ISO 17637. To verify
compliance with the approved welding procedure, where practicable, individual weld passes, in particular
the root bead, must be examined during welding. When a completed weld cap is still above the
minimum inter-pass temperature stated in the approved welding procedure, repairable welding defects
revealed by visual examination may be removed and re-welded.
8.1.3 In addition to the requirements of the construction code, 100% volumetric examination by Xradiography or a fully automated ultrasonic system must be applied for the butt welds in the following
circumstances:
•
•
•
Pipelines designed to transport category D and E fluids. The fluid categorisation is defined in
table 1 of BS PD 8010-1.
Pipelines designed to transport category B and C fluids at hoop stresses above 77% of SMYS.
Pipework and sections of pipelines designed to transport category B and C fluids in stations and
terminal.
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•
•
•
•
•
Pipelines designed to category B and C fluids within populated areas, such as residential areas,
shopping centres and designated commercial and industrial area.
Pipelines with river, lake and stream crossings, including overhead crossings or crossings on
bridge.
Pipelines on railway or public rights-of-way, including tunnels, bridges and overhead crossing.
Pipelines in offshore and coastal water.
Pipelines or pipework where “golden welds” are permitted in-lieu of pressure (strength) testing.
8.1.4 In addition to the requirements of the construction code, 100% surface crack detection by either
MPI or DPI as appropriate must be applied for the branch connection weld designed to transport
category B, C, D and E fluids.
8.1.5 When required by the Employer, the primary method of weld examination must be
supplemented by a complementary method of non-destructive testing. Supplementary inspection may
include the following scenarios:
•
•
•
•
Supplementary examination is required for a specific number of welded joints to enable early
identification of potential welding problems.
Surface crack detection method to support volumetric inspection and vice versa.
Additional volumetric weld examination method to support the primary volumetric weld
examination method (Ultrasonic Testing to support Radiography Testing or vice versa) or
additional surface crack detection method (Dye Penetrant Test to support Magnetic Particle
Inspection).
Complementary methods may include Positive Material Identification, Hardness Test, Field
Metallography Replica and Lamination Examination.
Employer must specify the supplementary non-destructive testing method to be used, the number of
welds to be examined and the extend of the examination.
8.1.6 Non-destructive testing procedure specifications must be submitted to the Employer for
approval prior to production welding commencing.
8.1.7 All non-destructive testing must be completed prior to pressure (strength) testing or
coating/insulation activities, where it is applicable.
8.1.8 All final non-destructive testing must be completed after the completion of Post Weld Heat
Treatment, where is its applicable.
8.1.9 The time delay before the final non-destructive testing must be in accordance with the
Inspection and Test Plan. If the time delay is not specified in the Inspection and Test Plan, a time delay of
at least 24 hours is required for carbon manganese steel with yield strength not greater than 450MPa
and weld heat input not greater that 3kJ/mm. For a higher strength steel or higher heat input, the time
delay must be agreed with Employer prior to production weld commence.
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9.
Radiographic Examination
9.1
General
9.1.1 The main requirement of the ionising radiation regulations is that NDT contractors should adopt
working practices capable of keeping radiation exposures of employees as low as reasonably practicable.
If work involves routine radiography of readily moveable articles, an assessment must be made to
establish whether site radiography is appropriate or if the articles should be taken to a cell for
examination. Appendix E provides a flowchart and guidance to facilitate the assessment.
9.1.2 It is not NGN policy to use sealed sources, i.e. Gamma isotopes, for weld examination. However,
conditions may exist that prevent the practical use of X-ray or ultrasonic methods, and in such
circumstances the Employer should consider the use of alternative NDT methods. Any alternative
procedures or methods of weld examination proposed must be approved by the Employer and be
qualified, prior to weld testing commencing.
9.1.3 Radiography must be carried out in accordance with BS EN ISO 17636-1 and to the requirements
of this specification. The minimum standard of radiography produced must be in accordance with Class B
(improved techniques). Class A must not be permitted without the written agreement of the Employer
and only where Class B cannot be achieved for sound technical reasons.
9.1.4 The use of fluoro-metallic screens or pre-packed films may be used provided that radiographic
quality level, contrast and density requirements as per section 9.1.2 and 9.6 are achieved. Damaged
screens must not be used. The Employer has the final decision whether screens or the use of pre-packed
films are acceptable for further use.
9.1.5 Only fine grain high contrast direct type film or ultra-fine grain high contrast direct type film
meeting the requirements of BS EN ISO 11699-1 Class C4 must be used. The film type must be stated on
the radiographic procedure sheet and must be approved for use by the Employer.
9.1.6
All radiographs must be interpreted when dry.
9.1.7 Permanent marking of the pipe as in BS EN ISO 17636-1, Clause 6.5 must be by waterproof
marker only. No hard stamping must be permitted.
9.1.8
Suitable padding must be used on external X-ray sets to prevent damage to the pipe coating.
9.2
Radiographic Personnel
Radiography must be carried out in accordance with national and company safety standards. All
personnel engaged in radiography must be familiar with the current legislation with respect to carrying
out work with ionising radiation.
Each radiographic crew must consist of at least two people. Each member of the crew must hold, as a
minimum, Radiographic Testing (Weld) level 2 qualification from a scheme meeting the requirements of
BS EN ISO 9712. Prior to submitting radiographs to the Employer, the films must be viewed by personnel
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holding a valid Radiographic Interpreter (Weld) level 2 qualification from a scheme meeting the
requirements of BS EN ISO 9712. They must confirm that the quality of the radiographs meets the
requirements of this specification before submission to the Employer.
9.3
Radiation Protection
The exposure of the human body to X-rays or Gamma-rays can be injurious, therefore it is essential that
when radiographic equipment is used, adequate precautions are taken to protect all persons in the
vicinity of the operation.
Radiography must not be undertaken unless the radiographers fully comply with the requirements of The
Ionising Radiation Regulations (IRR99) and the recommendations given in the Approved Code of Practice
and Guidance (Working with ionising radiation). Attention is drawn to the need for audible and visual
warning arrangements. Regular monitoring of radiation levels by the radiographers is required.
9.4
Radiation Safety Monitoring
NGN has an obligation to its employees, contractors and members of the public to monitor the standard
of radiological safety maintained by radiographic contractors on NGN sites. The items listed in Appendix B
must be regularly monitored by NGN or their representative and the results recorded.
9.5
Radiographic Procedures
9.5.1 Radiographic examination of fusion welded circumferential butt welds in steel pipes
must be carried out as described in BS EN ISO 17636-1, using techniques 7.1.4, 7.1.3, 7.1.8 or
7.1.6 (i.e. the preferred order), as appropriate.
9.5.2 Where fittings are welded to other fittings or to short lengths of pipe, technique number 7.1.3 of
BS EN ISO 17636-1 may be used. When using technique 7.1.3 then the number of exposures required
must be calculated using BS EN ISO 17636-a figure A.1.
9.5.3 Where BS EN ISO 17636-1 technique No 7.1.6 is used for pipe to pipe weld exposures, a
minimum of three exposures 120° or 60° apart in that order (i.e. the preferred order), must be made.
Pipe to fitting and fitting-to fitting butt welds will require a greater number of exposures to achieve
satisfactory coverage. Superimposed images are not permitted.
9.5.4 When using technique 7.1.8 then the number of exposures required must be calculated using BS
EN ISO 17636-1 figure A.2. Where technique 7.1.8 is used to examine pipeline butt welds, the 6 o’clock
weld location must be positioned in the centre of the diagnostic film length.
9.5.5 When a complete circumferential weld is radiographed in a single exposure with the source
inside the pipe (technique 6.1.4), at least one of the image quality indicators (IQI) must be placed outside
the pipe at the 6 o’clock location. When a circumferential weld is radiographed using multiple exposures,
an IQI must be located at each end of the diagnostic film length with the thinnest wire outermost.
9.5.7 For examining branches of the forged set-in type, panoramic type techniques, where the
complete weld is examined in one exposure, are not permitted. The weld must be examined in separate
exposures with the X-ray focal point positioned at normal incidence to the area being examined to within
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5 as shown in Figure 1. Either the single-wall, single-image or the double-wall, single-image technique
should be used. When the single-wall, single-image technique is used (technique 6.1.3), the film must be
placed against the inner pipe or fitting surface with the X-ray focal spot on the outside. The focal-spot-tofilm distance must be not less than 690 mm. When access and/or other fittings prevent correct alignment
of the beam, the double- wall, single-image technique (technique 6.1.8) must be used. Branches not
greater than 150 mm nominal bore require a minimum of four exposures equidistant round the weld
circumference. Branches of 200 mm nominal bore require a minimum of six exposures equidistant round
the circumference. Exposures of larger branches, or branches with proportions significantly different
from those shown in Figure 1, must be subject to agreement with the Employer.
Figure 1 – X-Ray Focal Spot Positioning
A= Film Centres (4 Film Exposures)
B= Focal Spot
9.6
Radiography Density
9.6.1 For pipe and fittings of the same nominal wall thickness, the radiographic density measured
immediately adjacent to the weld reinforcement must be within the range 2.5 to 3.5.
9.6.2 For pipe to pipe joints between pipes of different nominal wall thicknesses, where the thicker
pipe has been transitioned to match the bore of the thinner pipe, the radiographic density measured
immediately adjacent to the weld reinforcement must be within the range to 2.5 to 3.8.
9.6.3 Where the difference in wall thickness between the components being joined is substantial, i.e.
certain types of fitting to pipe and fitting to fitting, the radiographic density measured in sound weld
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metal (typical of the average weld and reinforcement through thickness) must be within the range 2.3 to
3.3.
If a film density within this range cannot be achieved in one exposure, either a sandwich technique using
fine grain, high contrast film and ultra-fine grain, high contrast film (technique 6.1.9), or two separate
exposures of the weld must be made.
9.7
Approved Radiographic Procedures
All radiographic procedures, details of the radiographic techniques and test radiographs* for each
procedure must be submitted to the Employer for approval prior to production radiography commencing.
The procedure details must include the following:
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
Technique
Type of equipment and kV rating.
Type of film.
Intensifying screens.
Shielding.
Geometric relationship defined by sketch.
Limit of film coverage.
Tube voltage and exposure.
Material thickness range.
Type of image quality indicator and positions.
Processing.
Note: An example radiographic procedure specification is given in Appendix E.
* To qualify a radiographic procedure three individual radiographs must be made of each weld configuration covered by
that procedure (preferably using the procedure test weld), this is used to establish consistency of the radiographic
procedure. The x- ray equipment must be re-positioned for each exposure.
9.8
Approved Radiographic Procedures
9.8.1 All unexposed film must be stored in a clean, dry place where the surrounding conditions must
not detrimentally affect the emulsion. At the discretion of the Employer, the radiographic contractor
must demonstrate to the Employer’s satisfaction that the film can be processed, using the site facilities,
to have a fog level not greater than 0.3.
9.8.2 The film must be processed such as to allow storage without deterioration for a minimum of
three years. Adequate washing of the processed film is required to reduce residual fixer content. Where
the quantity of work allows, a Thiosulphate test is required on 1 film in 45 and the results recorded in a
register held at site. The procedure for this test must be submitted to the Employer for approval prior any
work commencing.
9.8.3 If radiographic images are to be stored digitally on compact disc, the proposed method of
storage, retrieval and the definition and sensitivity of the recorded image must be approved by the
Employer prior to storage commencing.
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Any software required to view the results must be included on the data disc. Any software licenses must
be agreed prior to production welds being examined. The software version/number must be clearly
visible on all display presentations. The software must be capable of displaying the retrieved radiographic
image in the original format viewed by the interpreter at the time of sentencing.
10.
Manual Ultrasonic Examination of Welded Joints
10.1 General
When required by the Employer, manual ultrasonic examination must be applied to welds as described in
BS EN ISO 17640 and this specification.
10.1.1 Before ultrasonic examination is carried out, scanning surfaces must be thoroughly cleaned
and weld spatter removed to permit examination, as required in BS EN ISO 17640, Clause 8. In order
to prevent pipe wall thinning the pipe surface must not be prepared by dressing.
10.1.2 Ultrasonic examination of welded joints must be undertaken as required by the Employer. This
must include:
a) Welds between pipes with wall thickness 8mm and greater.
b) Welds not subject to hydrostatic pressure test (golden welds).
c) In support of radiographic interpretation or to confirm other indications.
10.2 Ultrasonic Equipment
The flaw detector and probes will be in accordance with BS EN ISO 17640, i.e. A-scan presentation
capable of working at a test frequency of 1 MHz TO 6 MHz.
10.3 Ultrasonic Equipment Performance
The combined performance of the ultrasonic equipment must be checked in accordance with BS EN
12668 and must be comply with the permitted tolerances for each function.
10.4 Ultrasonic Flaw Detector Calibration
Calibration of the flaw detector, cable and probe combination must be carried out prior to each
ultrasonic examination using the standard test block as described in BS EN ISO 2400 or BS EN ISO 7963.
10.4.1 Calibration of the probe beam angles must be carried out at least daily using the test block. The
flaw detector time base and amplification must be calibrated before examining each weld.
10.5 Ultrasonic Weld Examination
A probe of 60 to 70 refraction angle, 4 MHz to 5 MHz frequency with a crystal area of approximately
80mm2 must be used. When examining for lack of side fusion or lack of inter-run fusion, the weld must
be scanned in a zig-zag manner, the probe being moved between the weld reinforcement and one skip
distance. The beam must be directed at the weld length normally. The weld must be scanned from both
sides,
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10.5.1 The reference level must be set using Technique 1 described in BS EN ISO 17640 section 10.2. All
indications greater than 20% DAC must be investigated and reported. Indications greater than 50% DAC
or 6dB must be reported and evaluated. The position, length (depth within the weld if required) and
amount by which the DAC is exceeded must be recorded. It is recommended that reference blocks be
representative of the material under test, i.e. same grade, curvature, surface finish and wall thickness.
Notes:
1) Where an indication is investigated, it is sufficient to confirm that a flaw reflector is present and
does not exceed 50% DAC.
2) Where a flaw reflector exceeds 50% DAC the dynamic characteristics of the flaw must be fully
evaluated.
Pipe Thickness
Examination Level
Notes
8mm<t<15mm
A
T-scan required
15mm<t<40mm
B
T-scan required
10.6 Qualification of Personnel
Operators must be qualified, as a minimum, to Ultrasonic Testing (Weld) level 2 qualification from a
scheme meeting the requirements of BS EN ISO 9712.
10.7 Ultrasonic Examination Procedure
Written ultrasonic examination procedures must be submitted to the Employer for approval prior to
testing commencing. Each procedure must satisfy the requirements of BS EN ISO 17640 clause 5.3 and
specify the relevant information required in Clause 5.2.
10.8 Examination of Pipe Material
All pipe which is to be cut back must be examined visually prior to and after cutting. The pipe material
around planned cut-outs for nozzles, branches and cut pipe ends for pipe wall thicknesses greater than
6.1 mm, must be ultrasonically examined for 100 mm each side of the proposed cut line to ensure
freedom from unacceptable laminations. This must be done as described in BS EN 10160 using method
5.1a to calibrate the test equipment. In such cases the probe must be moved in a zig-zag manner in a
zone 100 mm wide.
11.
Automatic Ultrasonic Examination for Pipeline
Automatic Ultrasonic Testing (AUT) of pipeline must be carried out in accordance with the requirements
of Appendix D.
12.
Phased Array Ultrasonic Examination for Pipework
Phased array ultrasonic testing (PAUT) may be performed in lieu of radiography for pipework
construction. The PAUT must be carried out in accordance with the requirements of Appendix D.
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13.
Magnetic Particle Flaw Detection
13.1 General
When required by the Employer, Magnetic Particle Inspection (MPI) as described in BS EN ISO 17638
must be used. Inspection personnel must be qualified to Magnetic Particle Testing (Weld) level 2
qualification from a scheme meeting the requirements of BS EN ISO 9712.
The preferred method of magnetising components must be by AC electromagnetic yoke or the coil
technique, the prods method must not be used. Permanent magnets must not be used unless specifically
agreed and approved by the Employer. Permanent magnets should only be considered for use where
access precludes the use of an AC electromagnetic yoke. Only wet detection media methods must be
used.
13.2 Equipment Performance
The overall performance of the Magnetic Particle Examination technique must be confirmed prior to use.
Either representative test pieces containing real or artificial flaws, or portable shim type flux indicators
must be used. AC electromagnetic yokes must demonstrate a lifting power of 4.5 kg and a pull off force
equivalent to 2.25 kg at a maximum pole spacing of 200 mm.
Portable flux indicators must not be used with permanent magnets. A guide to the adequacy of
permanent magnets with a pole spacing greater than 75 mm, is that the magnet should demonstrate a
lifting power of 18 kg and a pull off force equivalent to 9 kg. The maximum pole spacing permitted is 50
mm and the pull off force must be demonstrated on a sample of the actual component thickness and
material under test.
The methods to be used to confirm overall performance of the technique and frequency of test must be
stated on the approved Magnetic Particle Examination procedure.
13.3 Magnetic Particle Inspection Procedure
A specific examination procedure must be submitted for the Employer’s approval prior to
commencement of any MPI.
13.3.1 When examining welds, the technique used must ensure full coverage of both weld and heat
affected zones. Magnetising techniques as described in BS EN ISO 17638 section 5.6.2 must be used.
13.3.2 Welds must be examined in the as-welded condition, apart from set-in fittings (i.e. sweepolet
type). The internal (where possible) and external weld reinforcement of sweepolet type fittings must be
dressed to avoid false or misleading indications. When required by the Employer, local dressing of other
weld types must be made, to permit accurate interpretation of indications.
13.3.3 Demagnetisation of the weld or material surfaces following MPI is not generally required.
However, consideration should be given to component demagnetisation should excessive magnetism
affect subsequent Operations (the NGN/SP/P/2 specification gives guidance on demagnetisation
techniques for pipeline applications).
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13.3.4 The results of all MPI examinations must be recorded and be assessed in accordance with the
relevant welding standard or specification.
14.
Dye Penetrant Flaw Detection
14.1 General
When required by the Employer, Dye Penetrate Inspection (DPI) as described in BS EN ISO 3452-1 must
be used. Inspection personnel must be qualified to Dye Penetrate Inspection level 2 qualification from a
scheme meeting the requirements of BS EN ISO 9712.
14.2 Dye Penetrant Inspection Procedure
A specific examination procedure must be submitted for the Employer’s approval prior to
commencement of any DPI
14.2.1
Mechanical pre-cleaning must not be carried out.
14.2.2
The results of all DPI must be recorded and assessed to the relevant specification.
15.
Non-Destructive Testing of Repaired Production Welds
15.1 General
Defective welds that have been repaired must be re-examined visually and by non-destructive testing.
15.1.1 Repair areas must be examined using radiography or a manual ultrasonic technique in
accordance with this specification. If the inspection is carried out using manual ultrasonic methods then a
separate procedure must be approved by NGN prior to the work commencing.
15.1.2 If the repair is conducted by fully removing the defective weld and re-welding by an automated
or fully mechanized welding system, the new weld may be examined using AUT to these procedures.
16.
Records
The results of all non-destructive testing examinations must be recorded on an appropriate record form.
The examination report must include, as a minimum, the information required by the appropriate
national standard and this specification. Examples of record forms are included in Appendix E.
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Appendix A
References
IGEM/TD series
Recommendations on Transmission and Distribution Practice
S.I. No. 3232
The Ionising Radiations Regulations including the IRR 1999
S.I. No. 1713
The Confined Spaces Regulations
BS EN ISO 9001
Quality Management Systems
BS EN ISO 138588
Non-Destructive Testing of Welds. Ultrasonic Testing. Use of
Automated Phased Array Technology
BS ENO ISO/IEC/170202
Conformity assessment – Requirements for the Operation of Various
Types of Performing Bodies Performing Inspection.
BS EN ISO 9712
Non-Destructive Testing – Qualifications and Certification of NDT
Personnel
BS EN ISO 17636-1
Radiographic Examination of Welded Joints
BE EN ISO 19232-1
Non-Destructive Testing. Image Quality of Radiographs. Determination
of the Image Quality using Image Quality Indicators.
BS EN ISO 19232-2
Determination of the Image Quality Value using Step/Hole-Type Image
Quality Indicators
BS EN ISO 17638
Magnetic Particle Testing
BS EN ISO 3452-1
Penetrant Testing – General Principles
BS EN ISO 3452-2
Penetrant Testing – Testing of Penetrant Materials
BS EN ISO 3452-3
Penetrant Testing – Reference Test Blocks
BS EN ISO 11699-1
Industrial Radiographic Film Classification of Film Systems for Industrial
Radiography
BS EN ISO 17637
Visual Testing of Fusion-Welded Joints
BS EN ISO 17640
Ultrasonic Testing. Techniques, Testing Levels and Assessment
BS EN ISO 16828
Non – Destructive Testing. Ultrasonic Testing. Time-of-Flight Diffraction
technique as a Method for Detection and Sizing of Discontinuities.
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BS 7910
Guide on Methods for Assessing the Acceptability of Flaws in Metallic
Structures
BS EN 12668 Part 2
Characterisation and Verification of Ultrasonic Equipment. Probes.
BS EN 10160
Ultrasonic Testing of Steel Flat Product of Thickness Equal or Greater
than 6mm (Reflection Method)
BS EN ISO 2400
Specification for Calibration Block No.1 for Ultrasonic Examination of
Welds
BS EN ISO 7963
Specification for Calibration Block No. 2 for Ultrasonic Examination of
Welds
BS EN 1330
Non-Destructive Testing – Terminology – Part 1 List of General Terms
BS PD 8010-1
Pipeline Systems – Part 1: Steel Pipelines on Land – Code of Practice
NGN/PR/NDT/1
Procedure for Carrying Out Non-Destructive Testing of Plant and
Equipment
NGN/SP/P/2
Specification for Welding of Landing Pipelines and Installations
Designed to Operate at Pressures Greater than 7 Bar. (Supplementary
to BS 4515-1)
NGN/PM/SHE/18
Confined Spaces
IRR99
Ionising Radiations Regulations 1999.
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Appendix B
Management of Site Radiography
B1. Scope
This procedure identifies the controls necessary for the management of site radiography. Adherence to
these requirements must be audited as per the requirements of construction checklist Appendix C.
This procedure must also be used to determine the most appropriate method of conducting radiography.
The procedure provides a decision tree, which must be used to determine whether items requiring
radiography testing should be transported off-site to a purpose-built enclosure for radiography.
Implementation of these requirements does not imply that sufficient data has been included to
demonstrate compliance with Ionising Radiation Regulations, it is the responsibility of the Radiographic
Subcontractor and the main works contractor to ensure these regulations are complied with in full.
B2. Introduction
The main requirement of the Ionising Radiations Regulations is that NDT contractors should adopt
working practices capable of keeping radiation exposures of employees as low as reasonably practicable.
The HSE guidance on complying with Ionising Radiations Regulations clearly states that if work involves
routine radiography of readily moveable articles it is nearly always reasonably practicable to carry it out
in an adequately shielded enclosure or cabinet. Where practicable, using a suitable shielded enclosure
must always be the first choice for radiography work. This enclosure can either be constructed on site or
articles can be transported to a purpose-built enclosure off site.
The flowchart in figure E1.0 of this Appendix provides a process which demonstrates that the selected
method for conducting radiography keeps radiation exposures of employees as low as reasonably
practicable.
Where site radiography is the only practicable option the objective of this document is to provide best
practice guidelines to enable radiographic subcontractors to undertake site radiography in a safe,
consistent and auditable manner across all projects.
B3. Roles and Responsibilities
The main responsibility for the implementation of this procedure lies with the specialist Radiographic
Sub- contractor and the main works Contractor.
Adequate information on radiation safety must be included within the contractor’s site induction talk and
relevant toolbox talks must be provided to personnel likely to be in the vicinity of radiographic works.
All personnel are responsible for ensuring that site radiography is undertaken in a safe manner, any
deviation to the planned safe system of work must be reported immediately to the project supervisor for
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rectification. A formal audit should be undertaken to ensure these requirements are implemented as per
the checklist in Appendix B.
B4. Radiography Options
Where radiography is required during the construction or modification of a Pipeline, AGI, Compressor
Station or Terminal the following options are available to the NDT contractor:
a) Radiography is carried out in-situ with suitable local shielding and boundary monitoring.
b) Radiography is carried out on sire in a controlled area with suitable local shielding and boundary
monitoring
c) Radiography is carried out on sire in a temporary enclosure.
d) Articles are transported off site where radiography is carried out in a purpose-built enclosure.
B5. Radiography Decision Tree
The flowchart in Figure B.1 should be used to determine which is the most appropriate method of
carrying radiography. The size and transportability of pipework fabrications will vary throughout a
project, therefore, to take account of this the flowchart will need to be run more than once.
The factors which must influence the selection of the most appropriate radiography method for each
stage of a project are:
a) The ability to pre-fabricate and radiograph pipework off site.
b) The transportability of pipework fabricated on site, which can be broken down further as:
I.
Fabrications which are only transportable off site; and
II.
Fabrications which are only transportable around the site.
c) The proximity of a purpose-built radiography enclosure to the construction site.
d) The availability of a controlled safe area for radiography on the construction site.
B6. Requirements
B6.1 Submission of Documentation for Client Review
B6.1.1 Project Specific Local Site Rules
As per IRR99 this must include the production of prior risk assessments and the methodology for dealing
with the risks, that must as a minimum identify the following;
•
•
6.1.2
Generic Risks – generally found on all projects:
▪ Road crossings
▪ Public footpaths
Unique Risks – specific features that are unique to the project:
▪ Street works
▪ Working in the vicinity of high-density housing or schools etc.
▪ Specific risks associated with working in AGI’s or compressor stations
Technique Sheers
Technique sheers are required for each technique to be used.
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B6.1.3 Method Statement NGN/Procedures
The Method Statement should identify the practical aspects of undertaking site radiography including:
•
•
•
•
•
•
•
Equipment used;
Equipment ratings;
Type of film;
Storage of film;
Film processing;
Handling of chemicals; and
Manual handling of radiography equipment
B6.1.4 HSE Notification
A copy of the greater than 7 day notification sent to HSE prior to site radiography being undertaken,
advising them of location and timescales involved.
B6.2 General Issues
B6.2.1 Storage of Processed Films
Processed film for record keeping purposes must be stored in a separate location from the dark room.
B6.2.2 Storage of Sealed Sources
When not in use, sealed sources must be stored in a suitable approved transport container, secured
within a secondary non-flammable container identified with appropriate radiation signs.
B6.2.3 Radiation Signs
Appropriate radiation signs must be clearly displayed on the outside of the storage area containing the
sealed source.
B6.2.4 Contact Details
The Radiation Protection Supervisor’s name and contact number must be posted on the cabin where the
sealed source is stored and on the project notice board(s).
B6.2.5 Transportation of Sealed Sources
When sealed sources are in transport on the spread, relevant radiation signs must be posted on both
sides and to the rear of the vehicle. When the source is in the vehicle and is left unattended for any
reason, the vehicle must be left in a secure state to prevent unauthorised access.
B6.2.6 Fire Extinguishers
Appropriate fire extinguishers must be available within the darkroom, sealed source storage area and site
vehicles.
B6.2.7 Disposal of Processing Chemicals
Unless agreed in writing with the EA/SEPA, no disposal of processing chemicals or wash water must be
dispersed to ground.
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B6.2.8 Lifting Equipment
All lifting equipment (slings, belts, chains etc) must be suitably controlled, identified and have current
test certification.
B6.2.9 Inspection and Test Equipment
All inspection and test equipment used to provide primary measurement must be uniquely identified,
subject to formal control and calibrated to a known national standard.
B6.2.10 QMS
The Radiographic Subcontractor must implement and maintain a quality management system in
accordance with ISO 9001 and must be accredited to ISO/IEC 17020.
B6.2.11 Daily Checks
All equipment must be maintained in a serviceable condition and daily equipment checks must be carried
out on cables, crawlers and X-ray equipment.
B6.4 Control of Site Activities
B6.4.1 PPE
All personnel must wear basic construction PPE whilst on the spread (hard hat, hi-vis vest, protective
footwear, overalls), and additional PPE may be required as identified within applicable risk assessments.
B6.4.2 TLDs/Film Badges
Named Thermoluminescent Dosimeter (TLDs) / film badges must be worn at all times by classified
workers and must be clearly visible at all times whilst on the spread, under no circumstance are they to
be left in overall pockets, in crew cabs etc. Consideration should also be given to the use of electronic
dose meters / alarms. Unnamed (i.e. spare numbered) TLD must only be accepted during the first month
of a new worker’s contract period.
B6.4.3 Precautions
Barriers must prevent access from both ends of the spread to the controlled area. The following
precautions must also be included, radiation signs, warning lights, RPS contact details at each end. The
spoil heap and right of way fencing must provide natural boundaries on the other sides, however where
there is a likelihood of public access, e.g. footpaths, playing fields etc, all relevant point of access must
have barriers and relevant signage. It is the responsibility of the radiographic subcontractor to ensure the
requirements of IRR99 are complied with.
B6.4.4 Monitoring of the Controlled Area
No amount of precautions should replace the importance of vigilance and proactive monitoring of the
controlled area, to ensure that corrective action can be taken in the event of persons not involved in the
work approaching the controlled area. The radiographic subcontractor must ensure that monitoring and
patrolling of the controlled area is undertaken on a routine basis and this requirement should be included
for in the Local Rules.
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B6.4.5 Recording Boundary Dose Rates
Boundary dose rates must be recorded in a formal manner identifying the section number and weld
numbers of the location worked for reference. Formal measurement must be undertaken for the first
production exposure on each day, details of person undertaking the test and equipment used must be
recorded. Formal monitoring must be carried out for each subsequent controlled area and verification
that it meets IRR99 requirements must be made. Any change to the size and type of the controlled area
will require formal measurement to be undertaken e.g. work in the AGI etc.
B6.4.6 Record Keeping
The responsible person must undertake daily mobile sealed source accounting and formal records must
be kept to verify this. As a minimum the record must identify source number, location, date and time of
inspection, details of person undertaking inspection.
B6.4.7 Movement Logs
Sealed source movement logs must be kept to identify location of sealed source, this must be completed
when the source is issued for use, as a minimum the record should contain, source number, date and
time issued, recipient of source, date and time returned.
B6.4.8 Spare Accessories
Spare bulbs and batteries must be available with the crew(s) for all safety critical equipment.
B6.4.9 Suitable Shielding
Where risk assessment requires, suitable shielding must be available with the crew(s).
B6.4.10 Spare Calibrated Radiation Detector
A spare calibrated radiation detector must be available with the crew(s) (it is not acceptable to rely on
personnel monitors as the spare).
B6.4.11 Mobile Phones
All radiographic crew(s) must have access to a mobile phone or two-way radio for contact purposes.
B6.4.12 PAT Testing
All relevant portable electrical equipment must be PAT tested.
B6.4.13 Audits
As a minimum the RPS must undertake a formal documented audit on all crews within 5 days of
commencement of site radiography to ensure safety controls are in operation and remain effective.
B6.5 Audit Records/Documentation
The following records/documentation must be available for reference during on site audits. If any of the
following are not present on site, work must not be allowed to commence / continue:
•
•
•
Certificate of registration for radioactive source’s (Environment Agency)
HSE notification of site radiography document
Local rules and risk assessment (with crews)
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•
•
•
•
•
•
•
•
•
•
•
•
•
Technique sheets (with crews)
Procedures/method statement (with crews)
Controlled copy of IRR99
Controlled copy of NGN/SP/P/2
Passbooks for outside workers (if applicable)
Calibration records for inspection and test equipment
Sealed source wipe test results (2 yearly)
Lifting equipment register and certification
Daily source accounting records
Source movement log
Records of boundary dose rates
Records of RPS crew audits
Relevant personnel training records (RPS training, Driver training, QMS inductions, ISO 9712
approvals, Safety passport etc)
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Radiography Decision Tree
Start
7
1
Yes
Pre-fabricate pipework
offsite
Is the pipework to be pre-fabricated
offsite?
No
9
2
Can the pipework be moved around
site?
Yes
Is the pipework in situ or not
transportable from site?
No
Yes
3
10
No
No
Is the risk/cost of transporting
items offsite greater than
constructing a temporary enclosure
onsite?
Will the pipework fit within a
temporary enclosure?
Yes
Yes
4
No
11
Carry out
radiography in-situ
with suitable local
shielding
Is the project of sufficient
value/duration that it is
reasonably practicable to
construct a temporary
enclosure onsite?
Yes
No
5
Carry out radiography in a
safe area with local
shielding
6
8
Carry out radiography in a
temporary enclosure
onsite
Transport items for
radiography to a purpose
built enclosure offsite
Produce appropriate method statements
and risk assessments
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B7. Flowchart Explanation Notes
1) Where this is feasible pipework should be pre-fabricated off site and radiographed in a purpose
built enclosure.
2) Some pipework can only be constructed in situ and therefore will not be transportable from site.
Other pipework fabricated on site will either be too large or heavy to be reasonably practicable
to transport off site.
3) Where pipework fabricated on site is transportable the cost of transporting to a purpose-built
enclosure for radiography should be compared against the cost of constructing a temporary
enclosure on site. Pipework fabricated on site should always be transported off site to a
purpose-built enclosure when this is demonstrated as the least cost option unless it can be
demonstrated that transportation off site actually presents a greater risk to personnel from for
example the lifting Operations required.
4) As assessment should be carried out to determine whether it is reasonably practical to construct
a temporary enclosure on site. Consideration will need to be given to the duration/value of the
project and the amount of radiography which must actually be taking place on site. To avoid the
construction of a temporary enclosure it will need to be demonstrated that the cost is grossly
disproportionate to the reduction in risk which will be gained.
5) Where the assessment in 4. Above concludes that radiography is to be carried out on site in a
controlled area the appropriate HSE guidance should be followed to ensure that the radiation
exposures of employees is kept as low as reasonably practicable.
6) Where the assessment in 4. Above concludes that a temporary enclosure must be constructed
on site to carry out radiography, the temporary enclosure should be constructed to the
appropriate HSE guidance giving consideration to the installation of appropriate interlocks which
prevent or terminate an exposure if the door of the enclosure door is opened.
7) Purpose built enclosures should be constructed to the appropriate HSE guidance giving
consideration to the installation of appropriate interlocks which prevent or terminate an
exposure if the door of the enclosure is opened.
8) Although it may not be practicable to transport some items off site because of the size of the
fabrication, these items should still be radiographed in a controlled area on sire if they can be
moved around site.
9) Where pipework will fit within a temporary enclosure it should be transported to such an
enclosure for radiography if it is available on site, otherwise it should be moved to a controlled
area for radiography.
10) Where items fabricated on site cannot be moved because they are constructed in situ the only
reasonably practicable option should be to conduct the radiography in situ providing the
appropriate local shielding. Consideration will have to be given to conducting the radiography
out of hours to ensure that the radiation exposures of employees is kept as low as reasonably
practicable.
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Appendix C
Site Radiation Safety Monitoring Checklist and Report Sheet
Site Radiation Monitoring Checklist and Report Sheet
Project:
Date:
Location:
Radiographic contractor:
a
General notes:
Radiography is a hazardous activity. NGN has a responsibility to members of the public, its own
employees and other contractors to ensure that site radiography is carried out in a safe manner.
No one should enter ‘controlled or supervised radiography zones’ without the permission of
the Radiographer and only when it is safe to do so. ‘Classified personnel ‘are
permitted to enter these zones during an exposure.
b
Only suitably trained personnel must monitor and report on radiation levels and site radiation
safety issues. Prior to starting radiography on site, a review of the appropriate preparations
required must be made using this checklist. Where work is ongoing, regular monitoring of site
radiography is required. Should any of the checks reveal that the work cannot be carried out in
a safe manner and in accordance with the Regulations (or any related documentation or
procedures), work must not commence or cease immediately until rectified.
The use of this checklist by NGN does not relieve the Radiation sub-contractor of their duties and
responsibilities under the Ionising Radiation Regulations.
This record sheet should be circulated to the Project Manager, the Site Occupier and the Site
Safety Officer as appropriate.
c
d
These records should be retained for the duration of the contract unless there are other
requirements to keep them longer.
Abbreviations used:
e
HSE
RPS
Health & Safety Executive
Radiation Protection Supervisor
Item
1
2
3
RCD
TLD
Residual Current Device
Thermo-luminescence Dose meter
Question
Finding
Authorisation for site radiography
✓/X
Comments
Has prior authorisation been granted by
the HSE for industrial radiography using
specified practices?
Is there a copy of the authorization
document available? (A generic
authorisation from the HSE Internet
website may suffice).
Have the HSE been notified that site
radiography is to take place? (28 days
notice may be required).
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4
Have the HSE acknowledged receipt of
notification? (The HSE may not always
provide documentary evidence of
receipt
of notification).
Radiographer
5
6
7
8
9
Are the radiographers qualified to the
ISO 9712 approval scheme or to an
approved equivalent?
Has the RPS been identified in the local
rules?
Is (are) the RPS(s) in attendance?
Is all equipment in good visual
condition?
Are all cables and connectors in good
condition?
Finding
✓ Item checked - Satisfactory
 Item checked - Unsatisfactory
NDT2 Sheet 1 of 3
Site Radiation Monitoring Checklist and Report Sheet (continued)
Item
Question
10
Is the power generator earthed?
11
Is an RCD fitted and operable?
12
Is local shielding required?
13
Are local shielding materials available?
Finding
✓/X
Comments
Barriers, Warning Notices and Signals
15
Have barriers been erected at the
correct distance?
Are the correct warning notices being
displayed?
16
Are spare warning boards available?
17
Is the boundary patrolled?
14
18
19
20
21
22
Are records of boundary dose rate
monitoring available?
Is the x-ray control panel key
adequately controlled?
Are audible/visual warning signals
available and working satisfactorily?
Are spare light bulbs etc. available?
Have all site staff been briefed on the
dangers associated withradiographic
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Operations (Safety induction).
Dosemeters
23
24
25
26
27
Are film badges or TLD being worn by
the radiographers?
Are the TLD’s named, or if numbered
are they traceable to the wearer?
Are badge holders in good condition?
Are surplus badges available on site? (If
specified on contingency plan)
Are TLD readers in use? (If specified on
contingency plan)
Risk assessment, Local rules, Contingency plans
30
Has a prior risk assessment been
made?
Is a copy of the risk assessment
available?
Are local rules and contingency plans
available on site?
31
Are the local rules site specific?
32
Are the radiation employees familiar
with the above documentation?
(see28-31)
28
29
Radiation Monitor
33
34
35
36
Is there a monitor available and
suitable for each source in use?
IS there a spare monitor available?
Are the monitors in current calibration
with valid certificates?
Are the monitors in good condition
without obvious damage?
Finding
✓ Item checked - Satisfactory
 Item checked - Unsatisfactory
NDT2 Sheet 2 of 3
Site Radiation Monitoring Checklist and Report Sheet (continued)
Item
Question
Finding
✓
/X
Comments
Sealed sources
Note: It is not general NGN policy to use sealed sources. However, where they are used on site, in
addition to the above list, the Radiographic sub-contractor must confirm the following items.
37
Are the monitor battery levels
satisfactory?
38
Are spare batteries available?
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39
40
41
42
43
44
45
What type(s) of radioactive isotope (s)
will be used?
Are the source container’s design,
construction and maintenance
appropriate?
Have test to detect leakage been
regularly carried out and recorded?
Is a record sheet (updated daily), which
shows the type, strength and location
of each radiographic isotope in site
available?
Are all sealed sources stored and
transported on site in accordance with
the Ionising Radiations Regulations?
Are contingency plans included in the
local rules in the event of loss or
damage to a radiographic isotope?
Are all emergency tools and equipment
listed in the contingency plan available
for use?
Finding
✓ Item checked - Satisfactory
 Item checked - Unsatisfactory
Notes:
Print Name
Signature
NGN Auditor or representative:
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Appendix D
Requirements for Automatic Ultrasonic Inspection (AUT) for Pipeline
Fabrication/Construction and Phased Array Ultrasonic (PAUT) for
Pipework Construction
D1. Scope
D1.1
The specification details the minimum NGN requirements for an Automatic Ultrasonic Testing
(AUT) system, AUT procedure approval and AUT system operator/interpreter competency for inspection
during pipeline construction.
D1.2 Any AUT system and examination procedure proposed for use must, as a minimum, meet the
requirements of this specification and be approved by NGN prior to any production weld examination
being carried out.
D1.3
This specification also includes the minimum NGN requirement for inspection of pipework welds
during fabrication/construction using Phased Array Ultrasonics (PAUT).
D1.4
Section D4 of this specification may also be used for PAUT on existing pipework. To perform
PAUT on existing welds, the scanning surfaces of the existing pipework must be even and free from
foreign matter likely to interfere with probe coupling (e.g. rust, loose scale, weld spatter, notches and
grooves). Unevenness of the test surface must not result in a gap between probe and test surface
greater than 0.5 mm.
D2. References
BS EN 12668-1 Non-destructive testing – Characterisation and verification of ultrasonic examination
equipment – Part 1: Instruments
BS EN 12668-2 Non-destructive testing – Characterisation and verification of ultrasonic examination
equipment – Part 2: Probes
BS EN 12668-3 Non-destructive testing – Characterisation and verification of ultrasonic examination
equipment – Part 3: Combined equipment
BS EN ISO 16828Non-destructive testing. Ultrasonic testing. Time-of-flight diffraction technique as a
method for detection and sizing of discontinuities
DNV-OS-F101 Automated Ultrasonic Girth Weld Testing Appendix E
DNV-RP-F118
Pipe Girth Weld AUT System Qualification and Project Specific Procedure Validation BS
7910 Guide to methods for assessing the acceptability of flaws in metallic structures
EN ISO 13588
Non-destructive testing of welds - Ultrasonic testing - Use of Automated Phased Array
Technology
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DNV-OS-F101
Appendix E
Automated Ultrasonic Girth Weld Testing
DNV-RP-F118
Pipe Girth Weld AUT System Qualification and Project Specific Procedure Validation
BS 7910
Guide to methods for assessing the acceptability of flaws in metallic structures
NGN/SP/P/2
Welding of Land Pipelines and Installations Designed to Operate at Pressures Greater
than 7 Bar (Incorporating BS 4515)
D3. Automatic Ultrasonic Inspection (AUT) for Pipelines
D3.1 Qualification
D3.1.1 Before an AUT system is used for the inspection of production welds on a pipeline then it must
be qualified in accordance with DNV-RP-F118 for the application it is intended to be used for. The
qualification must be based on the required performance as identified by the requirements for
Probability of Detection (PoD) and sizing ability; or, alternatively, a requirement for defect rejection. The
qualification programme and results must be approved by NGN.
D3.1.2 The qualification is AUT system specific and will only be valid when all essential variables remain
nominally the same as covered by the documented qualification. This specification does not require a
new qualification to be performed provided that the documented performance, i.e. PoD and sizing
ability; meets or exceeds the requirements for the specific application.
D3.1.3 The following items must be agreed by NGN prior to performing the procedure qualification:
•
•
•
•
The qualification block design
The system sizing accuracy for defect heights
The method used to determine the length of defects
The proposed examination procedure.
D3.1.4 Where there are any changes to the essential variable for a system, the equipment may require
re-qualification to DNV-RP-F118. Essential variables must include, but are not limited to the following:
•
•
•
•
•
Welding method and groove geometry, including repair welds (if relevant)
Root and cap probe set-up. This involves the use of hybrid systems where a combination of
Phased Array technology and Pulse Echo single or dual or tandem configurations are used.
Wall thickness, requiring any change in focal law set up, adding or removing legs.
Pipe diameter requiring transducer curvature which may impact on length accuracy. Systems
qualified on samples larger than 12” may not be readily qualified on smaller pipe diameters.
Beam profile and effect of transducer curvature must be determined.
Base material and welding consumables. The distinction is made for materials with substantial
differences in ultrasonic response, for instance between CMn 13% Cr, 13&Cr, duplex or
austenitic steels.
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Reference reflectors, e.g. change from Flat Bottom Hole (FBH) or Notches to other type of
geometries. Diameter of FBH and notch depth may be reduced provided that necessary area
focus and resolution is maintained.
Working temperature range.
System, data acquisition and data treatment.
Software version (except changes affecting viewings, display or bug fixing only)
System operator interpreter training and qualification.
D3.1.5 Before the ultrasonic system is used for examination of production welds, the system set up
must be validated. If any of the echo amplitudes from the reflectors of the calibration block deviate more
than 2dB from the initial calibration, the system must not be used until acceptable corrections have been
made. For an acceptable test 3 satisfactory scans and recalibrations are required.
D3.2 AUT Systems
D3.2.1 The ultrasonic system may use pulse echo, tandem, time-of-flight diffraction (TOFD) and/or
through transmission techniques employing either fixed of phased arrays. It must have a fully automatic
recording system to indicate the location of defects and the integrity of the acoustic coupling.
D3.2.2 The ultrasonic probes must normally operate within a frequency range of 2.5 to 6 MHz however;
it is recognised that certain systems may employ higher frequency probes. If the system uses higher
frequencies then NGN must be advised.
D3.2.3 The system must include probe set specifically designed to detect transverse defect indications
on both the internal and external weld near surface zones. The transverse defect scanning unit does not
require a complimentary TOFD scan.
D3.2.4 The weld scanning direction (clockwise or anti-clockwise relative to a fixed datum) must be
agreed with NGN and must be consistent for all production girth weld examination.
D3.2.5 The system must have sufficient examination channels, configured so that the complete weld
through thickness can be examined in a single circumferential scan.
D3.2.6 The volume of weld examined by each channel must be divided into primary examination zones
of a height not exceeding mm.
Each examination channel must provide:
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A linear A-scan presentation
Adjustable gain control with maximum of 2dB steps over a range of at least 60dB
One or more gates, each adjustable for start position and length
Recording threshold between 5% and 100% of full screen height
Signal outputs that record signal amplitude and time/beam travel distance
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D3.2.7
50mm.
The system must provide an overlap at the start and/or end of the scans of at least
D3.2.8 The recording or marking system must clearly indicate the location of imperfections
relative to the 12 o’clock position of the weld, with a +/- 10mm accuracy. The system resolution
must be such that each segment of recorded data from an individual inspection channel does not
represent more than 1mm of circumferential weld distance.
D3.2.9 The ultrasonic examination equipment performance characteristics must meet the
requirements of BS EN 12668, as appropriate. Instrument amplitude linearity must be within 5%
of the ideal amplitude and must be assessed prior to qualification and production AUT
commencing. Calibration certificates must be available upon request.
D3.2.10 General requirements for Time-of-flight-diffraction systems:
The instrument must provide a record of the TOFD D scan image; this must complement the AUT
system in confirming the presence and sizing of weld defects. TOFD must not be used in place of
Pulse Echo.
D3.2.11 General requirements for Phased Array:
Periodic verification must be performed on the function of required active elements to maintain the focal
law. In addition to this, a system must be in place to prevent any unqualified alterations to agreed focal
laws for the phased array AUT system.
D3.2.12 If conventional transducers are used in addition to the phased array ones, for example
for transverse inspection and ToFD, the information for all transducers must be available in the
same set up and recording system.
D3.2.13 The instrument must meet the requirements for ultrasonic instruments detailed in BS
EN 12688-1.
D3.3 Examination Procedure
D3.3.1 Prior to the examination of any production pipeline welds the proposed examination procedure
must be submitted to NGN for review and acceptance. The procedure must contain but not limited to
the following:
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Brief functional description of the system.
Any limitations of the system with regard to material or weld features including sound velocity
variations, geometry, size, surface finish, material composition etc.
Transducer configuration(s), characteristics, types, coverage.
Number of and height of examination zones, where relevant.
Gate settings.
Ultrasonic instrument, number of channels and data acquisition system.
Phased Array steering system, and the transducer characteristics including the frequency, beam
angle, wedge characteristics, number of elements, and pitch.
Phased Array focal laws (if applicable)
Recording and processing of data.
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Couplant monitoring method.
Temperature range for testing and limitations.
Maximum scanning speed and direction.
Reporting of indications and documentation of calibration and sensitivity settings.
Description of calibration block(s) including type, size and location of all calibration reflectors.
Calibration intervals.
Calibration records.
Identification of inspection starting point, scanning direction.
Method for scanner alignment and maintenance of alignment.
Transducer and overall functional checks.
Height and length sizing methodology.
Instructions for reporting including example of recorder chart and forms to be used.
Diagram showing the weld scan zones for the weld prep to be tested.
Table of indication size against signal amplitude which must be used for indication sizing.
D3.4 Operators
D3.4.1 Details of the contractors proposed AUT operators/interpreters must be submitted to NGN for
review and approval prior to the start of any pipeline weld examination.
D3.4.2 All AUT/TOFD operators and interpreters must as a minimum be qualified to Ultrasonic Testing
(Weld) level 2 qualification from a scheme meeting the requirements of BS EN ISO 9712. Operators and
interpreters possessing an equivalent qualification in an alternative scheme may be proposed by the
contractor for consideration by NGN.
D3.4.3 All operators/interpreters must be trained and competent in the use of the particular AUT/TOFD
equipment that they should be expected to operate. Documentary evidence of adequate training and
ongoing practical ability must be provided to NGN for each proposed operator/interpreter. NGN reserve
the right to request the operators to perform blind testing using the procedure qualification test block to
demonstrate their capability in using the technique. Any “missed” flaws or miscalls of either acceptable
or rejectable flaws/regions may be cause for rejection of the operator.
D3.4.4 Operators/interpreters of all types of AUT/TOFD equipment should be required to demonstrate
under field conditions and to the approval of NGN, their application of the approved contract AUT/TOFD
procedures. This must include their capability to calibrate the equipment properly, to interpret correctly
the indications given by the equipment, and to clearly record and report the results of the examination,
including the location, size and nature of all flaws detected.
D3.4.5 Operators must not be changed without the prior approval of NGN.
D3.5 Preparation
D3.5.1 The scanning band must be positioned adjacent to the completed weld at the same distance
used for calibration of the unit. Prior to welding, a reference line must be scribed on the pipe surface at a
distance specified by the AUT contractor from the centre line of the weld. This will provide a datum to
ensure band positioning within a tolerance of ± 1 mm.
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D3.5.2 The scanning area must be free of spatter and other irregularities, which may interfere with the
movement of the transducers, or the transmission of acoustic energy into the material. The longitudinal
seam welds must be ground flush and smooth for a specified distance, normally in the range of 150 mm
from the factory bevel face to ensure that no transducers are lifted from the pipe surface. The pipe
coating must be cut back from the original factory bevel face for a distance of 150 mm. The internal pipe
seam must be ground back 70 mm from the weld bevel to prevent interference with the ultrasonic beam
during scanning.
D3.5.3 The “0” starting point and the scanning direction must be clearly marked on the surface of the
pipe by permanent marker or paint.
D3.5.4 The location of the pipe seam welds must be identified and recorded on the final inspection
report for each weld.
D3.5.5 The weld and adjacent pipe must be allowed to cool to a maximum temperature of 60 °C before
scanning should commence unless otherwise agreed with NGN.
D3.6 Scanning
D3.6.1 Acoustic coupling must be achieved using a non-toxic liquid medium. When choosing the
medium, consideration must be given to the Health, Safety and Environmental impact of any materials
used.
D3.6.2 No residue from the liquid medium must remain on the pipe surface after the liquid has
evaporated.
D3.6.3 Positive confirmation of acoustic coupling during the weld examination scan is required for each
weld examination. The loss of signal amplitude associated with inadequate coupling must be specified by
the contractor and agreed with NGN (see section D.3.16 a). Any loss of acoustic coupling during a weld
examination may require a complete re-examination of the weld (see Section D.3.16).
D3.6.4 The operator must keep a logbook detailing the performance/characteristics data and
identification for instruments and transducers. The logbook must be updated as changes are made, or, as
additional information is gathered. The logbook must be kept at the place of inspection and be made
available for review upon request.
D3.6.5 Each weld must be numbered in the sequence used in the pipe tracking system as specified by
the NGN inspection team.
D3.6.6 Transition welds joining pipes of different wall thickness must only be examined by AUT when
the thicker material is counter-bored back at least 70 mm from the weld face.
D3.7 Circumferential Scanning Velocity
D3.7.1 The maximum allowable circumferential scanning velocity (Vc), must be determined according to:
Vc ≤ Wc * PRF/3
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Where Wc is the narrowest –6 dB beam width at the appropriate operating distance of all transducers
within the array, and PRF is the effective pulse repetition frequency per transducer.
Or
100 mm per second whichever is the lower.
D3.8 Reference Standard
D3.8.1 A reference block(s) must be used to establish sensitivity, qualify the examination system
and monitor the system performance on an ongoing basis. The block(s) must be manufactured from a
section of (unflawed, project specific) line pipe material provided by NGN or their main contractor.
D3.8.2 The AUT contractor must supply the necessary reference blocks. The design of the block(s)
must be specific to the mechanised welding system weld bevel geometry and pipe thickness to be used
on the project. NGN reserve the right to retain any or all reference blocks on completion of any
pipeline inspection.
D3.8.3 The AUT contractor must submit their design for a reference block(s), detailing the number,
orientation and location of FBH and transverse EDM slot reflectors or other reflectors, to NGN for
approval before manufacture.
D3.8.4 Details of the specific weld geometries must be provided in order to determine the particulars
and numbers of calibration blocks required, including the calibration reflectors required and their
relative positions.
D3.8.5 The preferred principal calibration reflectors are normally 2mm  flat bottom holes (FBH)
and 1mm deep surface slots. Other reflector dimensions and types may, however, be used, if it is
demonstrated during the system qualification that the defect detection and sizing capabilities of the
system is acceptable.
D3.8.6 The calibration blocks must be designed with sufficient surface area so that the
complete transducer array will traverse the target areas in a single pass.
D3.8.7 The calibration block must be identified with a hard stamped unique serial number providing
traceability to the examination work and the material source of supply for which the standard was
manufactured. Records of the serial number, wall thickness, bevel design, diameter and ultrasound
velocity must be kept and be available.
D3.8.8 The machine tolerances for calibration reflectors are:
a) Hole diameters
b) Flatness of FBH
c) All pertinent angles
d) Notch depth
e) Notch length
f) Central position or reference reflectors
g) Hole centre depth
± 0.2mm
± 0.1mm
± 0.1°
± 0.1mm
± 0.5mm
± 0.2mm
± 0.2mm
D3.8.9 The lateral position of all calibration reflectors must be such that there will be no
interference from adjacent reflectors, or from the edges of the blocks.
D3.8.10 Dimensional verification of all calibration reflectors and their position must be performed
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and recorded by an independent party. The record of this verification must be presented to NGN
before pipeline production weld are examined.
D3.8.11 A calibration block register must be established. The register must include all calibration
blocks to be used identified with the unique serial number and include the dimensional verification
records, ultrasound velocity, name of the plate/pipe manufacturer and the heat number. The
register must be available for review.
D3.8.12 The surface condition of the reference blocks must be made to be typical of that of the
pipe ends to be AUT scanned, including any roughness due to grit-blasting, surface corrosion,
painting or power brushing.
D3.9 AUT/TOFD System Equipment Calibration
D3.9.1 Static calibration - The system must be set-up and calibrated using the reference standard
block in accordance with the AUT contractors approved procedure.
D3.9.2 For each pulse echo ultrasonic transducer in each examination channel the peak signal
response from the target reflector must be maximised and then adjusted to 80% full screen height
(FSH). This must be the Primary Reference Level (PRE).
D3.9.3 The ultrasonic transducer stand-off distance, the gain level required to attain the PRE,
and the signal to noise ratio (S/N) must be recorded.
D3.9.4 With each transducer positioned for the peak signal response from the calibration
reflector the detection gates are to be set. The gate must start before the theoretical weld
preparation and a suitable allowance must be included to allow for the width of the heat affected
zone, so that complete coverage of the heat affected zone is achieved. The gate ends must be after
the theoretical weld centreline, including a suitable allowance for offset of the weld centreline after
welding.
D3.9.5 Gate settings must be set in accordance with the AUT contractors approved
procedure. The settings for gate start and gate length for each examination channel must be
recorded.
D3.9.6 Ideally for TOFD the time gate start should be at least 1 s prior to the time of arrival
of the lateral wave and should at least extend up to the first back wall echo.
D3.9.7 For phased array, the focal laws must be designed to provide a peak signal from each of
the calibration reflectors as appropriate. This signal must be adjusted to the specified percentage of
full screen height (FSH).
D3.9.8 Dynamic Calibration – With the system optimised the reference/calibration standard must
be scanned at the same travel speed at which the examination will be performed. The positional
accuracy of the recorded target reflectors relative to each other must be within ± 2mm and with
respect to the zero datum be within ± 10mm over the circumference. Gate settings must not deviate
by more than 0.25 mm from the reference positions.
D3.9.9 The output display chart / record produced during the dynamic calibration scan must
confirm that all ultrasonic transducers produce an 80% FSH signal response from each calibration
reflector in its correctly assigned position
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D3.9.10 Subsequent system calibration charts produced during field inspection, must be
comparable with the dynamic output display chart / record and must meet the set-up reference
standards.
D3.9.11 All calibration signals must be within the range 70 to 90% FSH, if during the dynamic
field calibration, the signal falls outside this range then one of the following must apply.
D3.9.12 When a signal is over 90%FSH then the results for all welds scanned since the last
successful calibration must be reviewed and where an indication has been identified in the effected
channel then these must be re-scanned to confirm the original diagnosis.
D3.9.13
If when checking the calibration any signal falls below 70% FSH then all welds inspected
since the last successful calibration scan must be re-tested unless otherwise agreed by NGN.
D3.10 Calibration Frequency
D3.10.1 The system must be calibrated by scanning the reference/calibration block(s) at the start of each
work period and before and after the examination of each weld:
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For the first 20 welds.
At any change of reference/calibration block.
At any change in nominal wall thickness.
At any change of components.
At the completion of each work period.
D3.10.2 Subject to satisfactory performance and at the discretion of NGN, the frequency of calibration
may be reduced to a minimum of 1 calibration scan for each 10 consecutive welds or every 1 hours
whichever comes first.
D3.10.3 Hard copy recordings of all calibration scans, indicating any gain changes required to maintain
sensitivity, must be included as part of the final report. The last weld number examined before
calibration and the time at which the calibration was performed must appear on each calibration chart.
D3.10.4 The peak signal responses from each calibration must be recorded. Any gain changes required to
maintain proper sensitivity must also be recorded.
D3.11 Transverse Cracking
Scanning must be conducted to detect the incidence of cracking which may be transverse to the weld
line, the transverse defect detection channels’ sensitivity should be demonstrated using calibration slots.
These should be in both the inner and outer surface of the calibration sample and of length equal to the
width of the girth weld cap or root plus a further 6 mm. Their through-wall heights should be such as to
guarantee detection of defect heights equivalent to 10% of the wall thickness (e.g. an N10 slot).
This must be done by:
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Using three slots for the internal surface calibration and three slots for the external surface
calibration.
One of the three slots to be at 10% of the wall thickness, one to be at 10% PLUS a height margin
and one to be at 10% MINUS a height margin.
The height margin to be calculated so as to be equivalent to a difference in the ultrasonic beam
path, between the send and receive transducers, of a quarter wavelength, at the transducer
nominal frequency.
The system sensitivity must be set at 9db above that required to give a signal of 80% of full screen height
from the largest signal of the three slots.
D3.12 Repairs
Defective welds that have been repaired must be re-examined visually and by non-destructive testing.
Repair areas must be examined using radiography or a manual ultrasonic technique in accordance with
this specification. If the inspection is carried out using manual ultrasonic methods then a separate
procedure must be approved by NGN prior to the work commencing.
If the repair is conducted by fully removing the defective weld and re-welding the new weld may be
examined using AUT to the agreed procedure.
D3.13 Acceptance/Rejection Criteria
D3.13.1
Before any inspection using this procedure is performed, the criteria for weld defect
acceptance must be agreed with NGN. For normal pipeline projects this should be obtained by using
an Engineering Critical Assessment (ECA), but where this is not available then the requirements of
NGN welding specification NGN/SP/P/2 should be used.
D3.13.2
The defect length should normally be defined as being from the point at which the full
interacting defect first attains a signal of 30% of Full Screen Height (FSH) to that point where it lasts
falls below 30% of FSH.
D3.13.3
Where two or more defects occur in close proximity to each other, they must be
assessed for interaction to the requirements of BS 7910 clause 7.1.2.3, figure 11 and figure 12.
D3.13.4 The ECA requirements are unique to each project / pipe wall thickness and pipe diameter.
An ECA to allow specific defect acceptance criteria must be produced for each pipeline project prior
to the commencement of inspection.
D3.13.5
To allow for combined AUT system and interpreter error, all recorded defect heights must
be increased by an amount to be agreed by the Employer prior to commencement of production weld
examination. This value may vary according to the AUT system used and operator competence. The
AUT contractor must provide evidence and fully demonstrate to the satisfaction of Employer that the
sizing error value to be adopted is accurate.
D3.13.6 All transverse indications that exceed the threshold must be evaluated as cracks.
D3.13.7 When any three out of ten welds consecutively tested fail to meet the ECA acceptance
criteria, then the accept / reject requirements must revert to the workmanship standard of the
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applicable welding standard in use (e.g. NGN/SP/P/2, clause 13). The application of the ECA
acceptance criteria cannot be reintroduced until the reason for the defective welding has been
identified and rectified.
D3.14 Software
D3.14.1
Any software required to view the results must be included on the data disc which
must be provided as part of the final results. Any software licenses must be agreed before any of
the production welds are examined.
D3.14.2
For phased array system, the software must be able to display the scan results,
phased array steering parameters and focal law set up.
D3.14.3
The version number of any software must be clearly visible on all display and
printout presentations.
D3.15 Evaluation and Reporting
D3.15.1 Indications recorded from sources other than weld imperfections must be evaluated. Their
nature must be clearly identified on the examination report.
D3.15.2 The recording threshold for planar detection channels must be at least 6 dB more
sensitive than the reference reflector and must be such that the smallest non-allowable
imperfections are detected.
D3.15.3 The recording threshold for porosity detection channels must be at least 14 dB more
sensitive than the reference reflector.
D3.15.4 It is recommended that the recording threshold for TOFD remains at the calibration threshold.
D3.15.5 Channel output signals must be arranged on the recording media in an agreed order. The
function of each channel must be clearly identified. The hard copy recording must be corrected to
account for any variation introduced due to different circumferential positions of the transducers.
D3.15.6 The welding foreman responsible for weld production must be immediately notified of any
defect recorded during the AUT scan. The exact position of the defect must be marked on the pipe
surface using permanent markers
D3.15.7 The AUT record must be annotated with the size evaluation of each weld imperfection
selected for assessment. Comments must be added, as necessary to allow a later re-evaluation by
another operator.
D3.16 Re-Examination
Welds must be re-examined whenever any of the following occur:
a. Scanning exhibiting a loss of coupling i.e. a drop in echo amplitude of more than
10dB from the level though a clean weld, where the length is more than the
allowable defect length for the effected channel.
b. Any calibration scan that shows that the system is “out of calibration”, must be
subject to the requirements of 11.10.
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D3.17 Inspection Records
D3.17.1 The following Inspection records must be provided:
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A hard copy record of each weld examined
An assessment of the weld quality according to the acceptance criteria
A hard copy record of all calibration scans
Examination data in electronic form
D3.17.2 The electronic data must display the results in the same manner that the operator
viewed at the time of inspection. A print option must be provided as part of the software.
D3.17.3 A Scan and TOFD data must be saved as part of the original weld scan data and included
in the weld record.
D4. Phased Array Ultrasonic Testing (PAUT) for Pipework
D4.1 Limitations
D4.1.1 The welds for new pipework fabrication/construction may be inspected using a Semi
Automated Phased Array Ultrasonic Testing (PAUT) in lieu of Radiography Testing (RT) provided the
following requirements are met:
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The material of construction is carbon steel or low alloy steel
Only pipe to pipe girth weld joints are examined
The wall thickness of the pipe is greater than 6mm
The test temperature is between 0°C and 50°C
Scanning is performed from both sides of the weld.
D4.2 Information to be Provided by NGN
D4.2.1 The following information should be provided by NGN to the PAUT service provider:
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Material specification and product form (cast, forged, rolled, etc.)
Information on the welding procedure, including welding method and joint design.
Time of inspection relative to post weld heat treatment.
Acceptance criteria for weld imperfections (if applicable).
Construction standard used.
Results of any parent material testing prior to and after welding.
Whether transverse defects are to be inspected.
D4.3 Procedure Qualification
D4.3.1 Before any system is used for the inspection of production welds on pipework, the Phased Array
Ultrasonic Testing (PAUT) procedure must be qualified to the satisfaction of NGN / The qualification
programme must be administered by the PAUT supplier.
D4.3.2 The qualification of the PAUT system is only valid when all essential variables remain nominally
the same as covered by the documented qualification. This specification does not require a new
qualification to be performed provided that the documented performance meets or exceeds the
requirements for the specific application being considered.
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Acceptance criteria
Specification of qualification block
Procedure qualification programme
Reporting requirement
D4.3.3 The qualification programme and results must be approved by NGN. NGN has the option
to witness the qualification programme. It is the responsibility of NGN to determine the
acceptability of the procedures based on its review of the qualification test results.
D4.3.4 The qualification must demonstrate acceptable performance on the qualification blocks.
The PAUT contractor must supply the necessary qualification blocks for testing. The reference
blocks used for calibration shall meet the requirements of BS EN ISO 13588 A.2 curved reference
blocks shall be used having diameters from 0.9 to 1.5 times the pipe to be tested OD, for Pipe OF
greater than 300mm a flat reference block may be used. The PAUT contractor must submit their
design for qualification block(s) to NGN for approval before manufacture, detailing the number,
orientation and location of slot reflectors or other reflectors. The slot reflectors should be made
using Electric Discharge Machining (EDM).
D4.3.5
The qualification blocks must be prepared by welding or hot isostatic process (HIP)
and must contain as a minimum three flaws, as follows:
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D4.3.6
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One surface flaw on the side of the block representing the pipe OF surface,
One surface flaw on the side of the block representing the pipe ID surface, and
One subsurface flaw.
Acceptable performance is defined as:
Detection of all flaws in the qualification block
Response from the maximum allowable flaw and other flaws of interest demonstrated to
exceed the reference level for examination as per the procedure
The flaws are sized as being equal to or greater than the actual size (both length and
height)
The flaws are properly categorised (surface or subsurface)
D4.3.7
The PAUT supplier must maintain a record of each procedure qualification test and make
the test records available to NGN upon request. The following parameters must be recorded:
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Search unit details, including the element pitch, size, number and gap dimensions
Focal set up including the plane, depth and sound path (if applicable)
Virtual aperture sizes including the number of elements, element width and effective height
Wedge natural refracted angle
Sweep angular range, and minimum and maximum beam angles
Details of qualification block (thickness, diameter, joint geometry, flaw position and flaw size)
Scanning sensitivity and details of reference block
Probe travel speed
Flaw sizing data
Test date
Details of examiner and details of any test witness
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D4.3.8
Where there are any changes to the essential variables for a system, the procedure may
require re- qualification. Essential variables must include the following:
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All the essential variables listed in BS EN ISO 13588
Changes in welding method and weld join design, including repair welds
Change in wall thickness
Change in pipe diameter (applicable for pipe smaller than DN 300mm)
Base material and welding consumables (The distinction is made for materials with
substantially differences in ultrasonic response, for instance between CMn 13% Cr, duplex or
austenitic steels)
System, data acquisition and data treatment
Software version (except changes affecting viewings, display or bug fixing only)
System operator interpreter training and qualification.
D4.4 Examination Procedures
D4.4.1
Before any testing of production welds can begin, two types of PAUT procedures
must be provided by the PAUT supplier to NGN for review and approval. The two procedures
are a generic procedure and a project specific procedure.
D4.4.2
A generic procedure must be provided and approved by NGN prior to procedure
qualification and include the following:
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The proposed equipment to be used
Proposed procedure qualification programme
Details of the qualification and reference block
Reference standard
Personnel qualifications
Data acquisition and storage
Flaw evaluation and acceptance criteria
Reporting requirement
D4.4.3
The project specific procedure must be provided and approved by NGN prior to
testing of production welds. The project specific procedure must include the following:
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•
Thickness and diameter of the pipe to be inspected
Material of construction and welding method
Weld joint design and dimensions
Details of the scan plans, including the search unit placement, beam angles and beam
steering set up.
D4.5 Calibration and Sensitivity Settings
D4.5.1
The acquisition unit must have a current calibration certification to the
manufacturer’s specification. Calibration periods must not exceed 12 months.
D4.5.2
All relevant channels, probes and cables for the PAUT must be checked for their
functionality. The check must be performed daily before and after testing. If any item fails, all the
tests carried out since the last valid check must be repeated.
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D4.5.3
The setting of range must be carried out prior to each test. The probe velocity must be
calibrated using the V1 block, V2 block or the reference block side drilled holes. The wedge delay
calibration should be performed using the reference block. Range settings must be checked at least
every 4 hours and after the completion of testing. If the deviations are 0.5 mm or 2% of the depthrange, whichever is greater, all the tests carried out since the last valid check must be repeated.
D4.5.4
Sensitivity settings must be carried out prior to each test for every beam generated.
The reference blocks used for calibration shall meet the requirements of BS EN ISO 13588 A.2 curved
reference blocks shall be used having diameters from 0.9 to 1.5 times the pipe to be tested OD, for
Pipe OD greater than 300mm a flat reference block may be used. The PAUT contractor must supply
the necessary reference blocks and must submit their design for a reference block(s) to NGN for
approval before manufacture, detailing the number, orientation and location of Flat Bottom Hole
(FBH) and transverse EDM slot reflectors or other reflectors.
D4.5.5
During the sensitivity setting, the gain control must be set at 80% ± 5% of full
screen height. Sensitivity settings must be checked at least every 4 hours and after the
completion of testing. If the deviations are greater than 4 dB, all the tests carried out since last
valid check must be repeated.
D4.6 Scanner and Encoder
D4.6.1 The probe assembly must run on a mechanical guided scanner capable of maintaining a fixed
and consistent search unit position relative to the weld centreline. If there is an obstruction to fixing the
scanner, the weld must be inspected using Radiographic Testing.
D4.6.2 A position encoder must be incorporated into the scanner mechanism with an accuracy of
better than ± 1 % of the actual distance moved. The encoder must be calibrated on a weekly basis,
with records to be provided to NGN.
D4.7 Operators & Interpreter Qualification
D4.7.1 Details of the contractor’s proposed PAUT operators and interpreters must be submitted to NGN
for review and approval prior to the start of weld examination. NGN has the option to assign a secondary
interpreter who acts on behalf of NGN
D4.7.2 All operators/interpreters must be trained and competent in the use of the particular PAUT
equipment that they should be expected to operate. Documented evidence of adequate training and
ongoing practical ability must be provided to NGN for each proposed operator/interpreter.
D4.7.3 PAUT operators and interpreters must as a minimum be qualified in Ultrasonic Testing Level 2
to a scheme meeting the requirement of ISO 9712. Operators /interpreters possessing an equivalent
qualification under an alternative scheme may be proposed by the PAUT supplier for consideration by
NGN.
D4.7.4 Operators of PAUT equipment must be required to demonstrate under field conditions and
to the approval of NGN, their application of the approved contract PAUT procedures. This must include
their capability to calibrate the equipment properly, to interpret correctly the indications given by the
equipment, to clearly record and report the results of the examination, including the location, size and
nature of all flaws detected.
D4.7.5 Operators of PAUT equipment must have completed PAUT specific training and examination
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on representative pieces. These training and examination results should be documented. If this is not
the case, examination should be performed on representative samples containing natural or artificial
defects similar to those expected.
D4.7.8
Operators must not be changed without the prior approval of NGN.
D4.8 Weld Testing
D4.8.1 The scanning area must be clean, even and free from foreign matter likely to interfere with
probe coupling over an area wide enough to permit the testing volume to be covered.
D4.8.2 The datum must be clearly identified and marked on the equipment. The weld scanning
direction (clockwise or anti-clockwise relative to a fixed datum) must be agreed with NGN and must be
consistent for all production girth weld examination.
D4.8.3
The system must provide an overlap at the start and/or end of the scans of at least 25 mm.
D4.8.4 Each linear scan must be parallel to the weld axis at a constant stand-off distance with the
beam oriented perpendicular to the weld axis.
D4.8.5 The examination area must include the volume of the weld plus the lesser of 25mm
or the thickness of the adjacent parent pipe.
D4.8.6 The maximum allowable circumferential scanning velocity must not exceed 150mm/s and
must be selected such that satisfactory images are generated. The maximum allowable missing lines
are 2 lines per 25 mm of the linear scan and there should be no adjacent line skip.
D4.8.7 If imperfections are found during data acquisition, the exact position of the defect must be
marked on the pipe surface using permanent markers and the welding foreman responsible for weld
production must be immediately notified.
D4.9 Data Acquisition and Storage
D4.9.1 The PAUT must be performed using a device employing computer-based data acquisition. Ascan data must be recorded for the area of interest in an unprocessed form with no thresholding and
must be stored in an electronic storage media. The correspondent equipment set up parameters must
also be stored.
D4.9.2 The data must be clearly identified and referenced to the weld joint numbering system.
D4.9.3 The data must be securely stored and able to be retrieved for a minimum of 5 years
from the project completion date.
D4.10 Evaluation of Phased Array Data
D4.10.1 Upon completion of the data acquisition, the data must be evaluated by a PAUT
interpreter supplied by the PAUT contractor. NGN has the option to provide an NGN
representative to evaluate the phased array data. The data evaluation should ensure the
following:
•
Satisfactory scan images were acquired during the data acquisition, including satisfactory
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•
•
•
coupling, range and sensitivity settings and signal to noise ratio.
Identification and classification of the indications.
Determination of the location and size of the indications.
Evaluation of the indications against the acceptance criteria.
D4.10.2 For any response greater than 20% above the reference level, the location, amplitude and
extent of all reflectors must be investigated.
D4.11 Acceptance Criteria
Before any system is used for the inspection of production welds on the pipeline it shall be qualified to
the satisfaction of NGN. The procedure for qualification may be to scan a weld which may be agreed by
NGN and report any flaws that are outside the acceptance criteria in accordance with the relevant
standard. The results from the qualification scan may be analysed by NGN to confirm acceptance of the
system and operators.
D4.12 Reporting
D4.12.1 As a minimum, the PAUT inspection report must include all the information as listed in section 15
of ISO 13588.
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Appendix E
Non Destructive Testing
The following specimen NDT forms are typical of the format required by NGN for inspection details. The
information given on the sheets is considered to be the minimum needed for the following procedures:
a)
b)
c)
d)
e)
Radiographic Procedure Specifications
Radiographic Inspection Report
Ultrasonic Inspection Report
Magnetic Particle Inspection Report
Weld Report Sheet
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Endnote
Comments
Comments and queries regarding the technical content of this safety and engineering document
should be directed to standards@northerngas.co.uk.
© Northern Gas Networks Limited
This NGN document is copyright and must not be reproduced in whole or in part by any means
without the approval in writing of NGN.
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1100 Century Way
Thorpe Park Business Park
Colton
Leeds
LS15 8TU
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