D ALY S O U I S SI | D S M T E AM
PAUT in Lieu Of RT
Cut the Noise
Agenda
Introduction
PAUT vs RT
Codes
Typical PAUT solution when replacing RT
Case study
Context
 In Oil and Gas and Power Gen industries, PAUT and RT are often placed in direct comparison and opposition.
 Inspection project managers (i.e. A/O) base their selection of the method to be used on one main factor:
Cost.
 The cost is dependent on the time of preparation, time of inspection (setup, scan/shot and interpretation),
number of repairs, etc.
 When compared, most common statements we may hear are: PAUT detect more than RT, PAUT has higher
rejection rate, PAUT data is longer to interpretate...
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Challenges
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PAUT vs RT - Overview
 Radiography and ultrasound are two complimentary nondestructive testing (NDT) techniques. Both can
volumetrically inspect welds and components for defects like cracks, lack of fusion, porosity etc.
 In recent years, the use of ultrasound in lieu of radiography, has gained momentum in practice and with
major code bodies like ASME (American Society of Mechanical Engineers) and API (American Petroleum
Institute).
 The major difference between RT & UT is that Radiographic method is better for detection of discontinuities
having major dimension perpendicular to the surface (parallel to the direction of radiation) and Ultrasonic
method is better for detection of discontinuities orientated parallel to the surface (perpendicular to the
beam direction). However, UT gives more flexibility of inspection by allowing inspection in more direction by
using angle probes if necessary.
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PAUT vs RT - Overview
 It isn’t easy to convert acceptance standards from reference radiographs exactly into ultrasonic acceptance
standards.
 Different categories of discontinuities (A – Gas, B – Sand and Inclusions, C – Shrinkages with subcategories
CA, CB, CC & CD) have different acoustic / reflection characteristics.
 The best practice to achieve a comparable indications analysis is to conduct an Engineering Critical
Assessment (ECA: an analysis, based on fracture mechanics principles, of whether or not a given flaw is safe
from brittle fracture, fatigue, creep or plastic collapse under specified loading conditions.
 Using acceptance criteria based on RT criteria is not a good practice, because the physics of the two
processes are very different
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PAUT vs RT - Overview
 Radiography relies on transmission and absorption/attenuation of small wavelength electromagnetic energy
(x-rays and gamma rays). Pores/inclusions or material discontinuities or gradients will result in different
attenuation values, resulting in differences in the optical density in radiographs.
 Ultrasonics relies on the interaction of acoustic wave energy with flaws in the inspected material. Differences
in density or acoustic impedance result in reflection or scattering of the wave, which is recorded as evidence
of a discontinuity in the material. The result is a time-based record of the scattered acoustic wave that
contains information about the location and distance to a discontinuity.
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PAUT vs RT – Advantages of UT
 No radiation, hazard, or additional licensing or personnel
 No screened off areas, work can go on around ultrasonic testing
 No chemical or waste material compared to film-based radiography
 Real-time analysis for instant evaluation and feedback to welder
 Detected flaws are accurately indicated on components using a live post scan
 Setup and inspection reports in electronic format compared to film-based radiography
 In many cases two radiographers will sentence the same radiograph differently. Very common is difference of
one level in assessment or different characterization of identical discontinuity.*
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PAUT vs RT – Advantages of DR
Digital radiography is based on digital detector systems in which the x-ray image is displayed directly on a computer
screen without the need for developing chemicals or intermediate scanning. (https://youtu.be/6wGhjzJ-69s)
Advantages as marketed by DR companies :
 lower inspection costs by eliminating consumables (X-ray film and film processing chemicals), film processing
equipment, film storage facilities
 inspection results obtained online make it possible to correct welding settings immediately to avoid more defects
 perfect conditions for image examination (zoom, optimal contrast, image enhancement procedures) and
inspection protocol preparation
 easy use of database
 Unlike Computed Radiography (CR), with DDA one can see an image immediately without processing through a
computer.
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PAUT vs RT – Sensitivity x P.O.D x Rejection rate
PAUT
 Amplitude based method: sensitivity is set using a specific reflector which size and type (FBH, SDH, etc.) is selected
based on the project scope and requirements. A given project’s procedure status the scanning sensitivity (gain) and
analysis sensitivity that should be used during the inspection.
 Higher probability of detection (POD) than RT, especially for cracks and lack of fusion
Ultrasound tends to detect planar flaws better than radiography in most studies
 Accurate sizing of defects height and less rejects/repair using Engineers Critical Assessment
Ultrasound allows defect height measurement
volumetric consideration of flaw severity vs. just type and length
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PAUT vs RT – Sensitivity x P.O.D x Rejection rate
Radiography
 Sensitivity: Detection in RT film is dependent on the change in film density or contrast between the
background and the indication. The contrast in the radiograph is a function of several variables such as film
density, graininess, source strength and distance, and specimen thickness. Thus, for crack detectability each
of these quantities plays a critical role.
 Probability of detection (POD): Flaw detection depends on orientation and on sample thickness. In general,
the RT POD for volumetric flaws is generally higher than that for planar flaws and depends on the specimen
geometry and application.
 Sizing of defects is only possible on 2D axis (no height measurements)

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PAUT vs RT – Sensitivity x P.O.D x Rejection rate
PAUT is a highly sensitive method: sensitivity level is set by the inspector based on the procedure being used. Ex: A
PAUT configuration using a 2mm FBH reflector as reference is about 14dB less sensitive than the same configuration
using 2mmSDH reflector, both reflectors are at the same depth.
Higher sensitivity leads to higher POD: When inspecting for small flaws, small size reflectors shall be used to increase
sensitivity however POD could be affected as S/N ratio could be high enough to prevent any detection in noisy areas.
Higher sensitivity leads to higher rejection rate/probability: found indications are rejected or accepted based on the
specific governing accepting criteria. Not all detected indications are automatically rejected.
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PAUT vs RT – Flaws detection and characterization
PAUT + TOFD
Conventional RT
Digital RT
Type of flaws
Detection
Sizing
Characterizatio
n
Detection
Sizing
Characterizatio
n
Detection
Sizing
Characterizatio
n
Porosities
Good
Acceptable
Good
Good
Acceptable
Good
Good
Good
Good
Inclusions
Good
Good
Acceptable
Good
Acceptable
Good
Good
Good
Good
LORF
Good
Good
Good
Poor
Poor
Poor
Acceptable
Acceptable
Acceptable
LORP
Good
Good
Good
Good
Poor
Good
Good
Acceptable
Good
LOSWF
Good
Good
Good
Poor
Poor
Poor
Acceptable
Acceptable
Acceptable
Cracks
Good
Good
Good
Acceptable
Poor
Acceptable
Acceptable
Poor
Acceptable
Hi Lo, Geo, etc.
Good
N/A
Good
Good
N/A
Good
Good
N/A
Good
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PAUT vs RT – Codes
 When replacing RT, PAUT is often combined with TOFD (time-of-flight diffraction). TOFD is very sensitive
therefore it is used as complementary technique and usually it is limited to detection only.
Rejection based on TOFD data should be specified in the procedure.
 For code-based inspections historically these processes were conducted through code cases or appendixes,
but after a large amount of industry practice and success they are being codified directly into the main
bodies of the major code books as seen in the 2010 and beyond ASME Sec. V. Art. 4.
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PAUT in lieu of RT – ASME code
 Ultrasonic Examination (UT) is a permitted volumetric examination method in lieu of the required
Radiographic Examination (RT) in ASME Boiler and Pressure Vessel Code, Sections I, VIII Division 1 and VIII
Division 2.
 It is important to note that for all three code books, the permitted ultrasonic examinations are restricted to
Time-of-Flight Diffraction (TOFD) and Phased Array (PAUT) with computer-based data acquisition and
analysis abilities using automatic or semi-automatic equipment that is mechanically mounted and guided on
the examination surface.
 Manual straight beam UT, manual angle beam UT and manual Phased Array (PAUT) are not permitted as
substitute techniques when using UT in place of required RT.
 Next slides detail the requirements for Sections I and VIII Division 1 & 2.
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PAUT in lieu of RT – ASME code
Section I
 Section I permits UT in place of RT by utilizing Code Cases 2235, 2816, or by using PW-52.1. Code Cases
2235 and 2816 utilize fracture mechanics-based acceptance criteria, while PW-52.1 references Section V,
Article 4, Mandatory Appendix VII, which uses workmanship-based acceptance criteria.
 While the acceptance criteria are different, in all three cases, the use of TOFD or PAUT using equipment
mechanically mounted and guided on the examination surface either through automatic or semiautomatic
means is required.
 Code Case 2235-13 paragraph (d) requires UT to be performed using a “device employing automatic
computer-based data acquisition”. Code Case 2816 has the similar requirement in paragraph (d). PW-52.1
states that UT shall be in accordance with Section V, Article 4, Mandatory Appendix VII. Mandatory Appendix
VII paragraph VII-431 states that ultrasonic examination is to be performed, “using a system employing
automated or semi-automated scanning with computer-based data acquisition and analysis abilities”. Semiautomated and automated are defined terms within Section V, Article 1, Mandatory Appendix I and are listed
below for convenience.
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PAUT in lieu of RT – ASME code
Section I
 Semi-automated ultrasonic examination (SAUT): a technique of ultrasonic examination performed with
equipment and search units that are mechanically mounted and guided, manually assisted (driven), and
which may be manually adjusted by the technician. The equipment used to perform the examination is
capable of recording the ultrasonic response data, including the scanning positions, by means of integral
encoding devices such that imaging of the acquired data can be performed.
 Automated ultrasonic examinations (AUT): a technique of ultrasonic examination performed with the
equipment and search units that are mechanically mounted and guided, remotely operated, and motorcontrolled (driven) without adjustments by the technician. The equipment used to perform the examination
is capable of recording the ultrasonic response data, including the scanning positions, by means of integral
encoding devices such that imaging of the acquired data can be performed.
 As a result, manual UT is not permitted for use as the primary technique for Section I Code examinations
with the exception of PW-44.7.3 examinations of bimetallic tubing when clad strength is included.
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PAUT in lieu of RT – ASME code
Section VIII Division 1&2
 Section VIII Divisions 1 and 2 likewise permit UT in lieu of the required RT. Section VIII Division 1, UW-51(a)(4)
states that this UT must meet the requirements of Section VIII Division 2, paragraph 7.5.5. As a result, a
Certificate Holder performing UT as permitted in UW-51(a)(4), needs to have access to a Section VIII Division
2 code book. UW-51(a)(4) further references Section V, Article 4, Mandatory Appendix VIII, which utilizes
fracture mechanics-based acceptance criteria in conjunction with Mandatory Appendix IX.
 Mandatory Appendix VIII, paragraph VIII-431 requires that ultrasonic examination must be performed, “using
a system employing automated or semi-automated scanning with computer-based data acquisition and
analysis abilities”. Semi-automated and automated were previously defined above are defined terms, while
equipment with computer-based data acquisition and analysis abilities is either TOFD or PAUT.
 There are some specific allowances in Section VIII Division 1 to use manual UT in accordance with Mandatory
Appendix 12, such as for the final closure seam examination. Section VIII Division 2, paragraph 7.5.4 also
permits manual UT examinations on Type 7, and 8 joints in some instances. These allowances for using
manual UT should not be confused with the requirements for using UT in lieu of RT.
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Typical UT Solution when replacing RT
 Acquisition unit with Full Raw A-scan data retention and encoding ability (OmniScan, Focus PX, Focus LT)
 Industrial Scanner (encoder) that repeatedly scan weld or component (Semi or Fully Automatic)
Selection based on number of welds, pipe diameter, and other application variables
 Probes, wedges, couplant delivery and other accessories
 Analysis software OmniPC, Weldsight, etc.
 Calibration and demonstration blocks
 Procedure showing documented inspection strategy, scan plan and essential parameters
 Performance demonstration for equipment, procedure, operator and inspection process
 Proper training and certification for personnel
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Typical UT Solution when replacing RT
Example of suggested scan pattern for thick weld (75mm
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Typical UT Solution when replacing RT
Example of suggested PA scan plan for thick weld (75mm)
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Typical UT Solution when replacing RT
Example of suggested TOFD scan plan for thick weld (75mm)
Refracted Angle°
Freq. (MHz)
Scan Type
PCS (mm)
Refracted Angle°
Freq. (MHz)
Scan Type
PCS(mm)
70
10
Nonparallel
159
55
5
Nonparallel
151
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PAUT in lieu of RT – Sensitivity Calibration
 Sensitivity is set by the inspector using a specific reflector based on the procedure being used. For
amplitude-based inspections, the reference sensitivity (gain) is used to evaluate any found indication.
 The procedure specifies the type and the size of the reference reflector and the method of distance
compensation (TCG, DAC or coefficient). The size of the reference reflector is chosen based on the governing
code or the ECA results if applied.
 A PAUT configuration using a 2mm FBH reflector as reference is about 14dB less sensitive than the same
configuration using 2mmSDH reflector, both reflectors are at the same depth.
 Sensitivity could be checked using a demonstration block.
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PAUT in lieu of RT – Acceptance Criteria
 Once defects have been detected in a component, the inspector should provide information about them to
permit an assessment of whether the component is fit for continued service.
 A found reflector (indication) is considered defect if it is rejected based on the acceptance criteria established
in the used inspection procedure.
 The size (length and height), position (OD, ID, Volume, etc.) and the nature of the defects should be reported
to be used in an assessment of the component’s structural integrity.
 To adequately detect, size and assess defects, the UT technique should be selected adequately, and the
examination should be conducted in accordance with the governing procedure.
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PAUT in lieu of RT – Acceptance Criteria
 Acceptance criteria could be based on a traditional workmanship approach (based on flaws lengths like in
RT) or on an Engineering Critical Assessment (ECA) study (based on fracture mechanics principles). ECA is
also referred as fitness-for-purpose (FFP).

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PAUT in lieu of RT – Acceptance Criteria
API 1104 - Workmanship Acceptance Criteria
Flaw indication
Maximum allowed length
Crack
0
Linear surface (LS)
25mm aggregated in 300mm or 8% of the weld for welds
less than 300mm
Linear buried (LB)
50mm aggregated in 300mm or 8% of the weld for welds
less than 300mm
Volumetric cluster (VC)
Maximum dimension exceeding 13mm
Volumetric individual (VI)
Maximum dimension of an individual flaw exceeding 6mm
in both length and width
Volumetric root (VR)
Max. Dimension exceeding 6mm or aggregated 13mm in
any 300mm continuous 300mm of weld
Accumulation of relevant indication (AR)
50mm aggregated in 300mm or 8% of the weld for welds
less than 300mm
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PAUT in lieu of RT – Acceptance Criteria
 ECA considers material properties and the flaw size that could cause failure. The maximum acceptable flaw
size with a safety factor is determined to establish the acceptance criteria.
 It can significantly reduce the cost of the construction, or the maintenance of a given component by
minimizing unnecessary repairs.
 ECA allows engineers to assess the suitability of a component containing imperfections for intended service
conditions or fitness for service (FFS).
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PAUT in lieu of RT – Acceptance Criteria
 ECA is performed in accordance with specified codes/standards and uses a computer program to generate
the results.
 Normally an ECA is used to develop ECA Flaw Acceptance Criteria however it can also be used to validate
existing acceptance criteria.
 The ECA will consider the following events:




Reel Installation
Installation Fatigue
Operational Fatigue
Extreme Event Fracture Check at the end of the N Years Design Life.
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Case study: PAUT vs RT vs Macro
Description
 During a qualification process of an offshore pipeline project, the client required the comparison of detection
capabilities and sizing accuracy between PAUT and conventional RT.
 PWZ scanner was used, the setup included PAUT, TOFD and Creeping waves techniques.
 Tests were performed on coupons prepared under the same conditions of onsite production + coupons with
inserted flaws.
 Coupons were cut to perform Macro testing to validate PAUT and RT results
 Examples of resulting data is shown in the next slides.
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Case study: PAUT vs RT vs Macro
Data vizualisation comparison – PAUT
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Case study: PAUT vs RT vs Macro
Data vizualisation comparison – RT
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Case study: PAUT vs RT vs Macro
SWLOF – Macro
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Case study: PAUT vs RT vs Macro
SWLOF – PAUT
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Case study: PAUT vs RT vs Macro
SWLOF – RT
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Case study: PAUT vs RT vs Macro
Slag cluster – Macro
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Case study: PAUT vs RT vs Macro
Slag cluster – PAUT
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Case study: PAUT vs RT vs Macro
Slag cluster – RT
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Case study: PAUT vs RT vs Macro
Reporting PAUT/TOFD
MAX
DEPTH
MAX
LENGTH
FROM HEIGHT
(mm)
OD
(mm)
(mm)
Flaw
ID
START
(mm)
END
(mm)
1
0
10
15
2
2
2
52
76
24
18,2
2
3
125
145
20
8,6
2
Index
offset
LINEAR
VOLUMETRIC
DEFECT
DEFECT TYPE
TYPE
(P, CP)
(LOF,CL,etc)
Used
tech
COMMENTS
START DATUM
SEC/TOF
D
SEC/TOF
D
LOF
LOF noted in the HP from both Sectorial and TOFD
LOF
Sectorial LOF noted. Small HP flaw noted in below not
interactive
Reporting RT
Indication ID
Radiograph
Number
AA1
R1
0
10
AA2
R2
40
AA3
R3
120
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Location (US/DS/Center &
Cap/Root/Mid)
Indication Description/comments
10
DS side near cap
LOF
70
16
DS side near center & cap
LORP
220
16
US side near mid
LOF
Start (mm) End (mm) Length (mm)
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Discussion
 ISP that offer both PAUT and RT, usually tend to offer A/O PAUT first however in several projects, clients are
hard to convince. In Power Gen industry, it is now very common to see a combination of PAUT and DR in the
same project.

Generally, resistance to the replacement of RT by PAUT is based on wrong arguments




Higher sensitivity
Higher P.O.D
Higher rejection rate
Costly solution
 These cliches results from projects where PAUT was used in lieu of RT based on the same acceptance criteria.
 Recently in Canada, PAUT was removed from qualified technique for the inspection of feeder tubes based on
a previous PAUT inspection that resulted in missing several flaws. After investigations, it was found that scan
plans were not set up properly and the UT coverage was poor. Therefore, the blame was to be put on the ISP
rather than on the technique.
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