Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

PUBLICATION NO. FHWA-HRT-24-010 FEBRUARY 2024 

Implementation of Phased 

Array Ultrasonic Testing (PAUT) 

For Bridge Welds
FOREWORD

This study aims to elevate the quality control standards in steel bridge fabrication by expanding 

the available testing options beyond conventional ultrasonic and radiographic inspection. The 

research evaluates the feasibility and effectiveness of phased array ultrasonic testing, an 

innovative technology, for its potential integration into bridge weld nondestructive inspection 

processes as an efficient alternative to radiographic testing.(1)

This report is tailored for professionals involved in or overseeing steel bridge fabrication shop 

inspection, encompassing bridge owners, their quality control representatives, and third-party 

inspection firms. The findings and recommendations of this study empower these stakeholders to 

make informed decisions and embrace advanced inspection methodologies to enhance the overall 

quality control of steel bridge fabrication projects.

Jean A. Nehme, Ph.D., P.E. 

Director, Office of Infrastructure

Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) in the interest of information exchange. The U.S. Government assumes no liability for 

the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document. 

Non-Binding Contents

Except for the statutes and regulations cited, the contents of this document do not have the force 

and effect of law and are not meant to bind the public in any way. This document is intended 

only to provide clarity to the public regarding existing requirements under the law or agency 

policies. While this document contains nonbinding technical information, you must comply with 

the applicable statutes and regulations.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts its programs and processes to 

ensure continuous quality improvement. 
TECHNICAL DOCUMENTATION PAGE

1. Report No.

FHWA-HRT-24-010

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Implementation of Phased Array Ultrasonic Testing (PAUT) For Bridge

Welds

5. Report Date

February 2024

6. Performing Organization Code

7. Author(s)

Nikesh Jose (ORCID: 0009-0002-0043-379X) and Hoda Azari (ORCID: 

0000-0002-7340-0035)

8. Performing Organization Report No.

9. Performing Organization Name and Address:

Highway Technology Partners, LLC

9220 Rumsey Road, Suite 100

Columbia, MD 21045

10. Work Unit No.

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report; October 2016–March 

2023

14. Sponsoring Agency Code

HRDI-20

15. Supplementary Notes

The contracting officer’s representative was Dr. Hoda Azari (HRDI-20; ORCID: 0000-0002-7340-0035).

16. Abstract

The objective of this study is to improve the quality control of steel bridge fabrication by expanding the available 

nondestructive testing options beyond conventional ultrasonic testing (UT) and radiographic inspection methods. 

The primary focus of this research is to assess the acceptability of phased array ultrasonic testing (PAUT) as an 

alternative to radiography when the governing American Welding Society (AWS) specification mandates the latter 

for fabrication inspection.(1,2) To achieve this goal, the research team created a series of representative heavy 

section steel welds containing fabricated discontinuities. Subsequently, the team inspected these welds using 

PAUT, conventional UT, and radiography.

(3–5) The study successfully demonstrated the feasibility of employing 

PAUT on typical bridge complete joint penetration butt welds. Notably, the researchers observed a strong 

correlation among the results obtained from PAUT, conventional UT, and radiography within the limited sample 

set used for this study. Based on the research findings, this study offers two key recommendations. First, it 

suggests fabricating and inspecting a more comprehensive matrix of representative flaw types, joint configurations, 

and plate thicknesses. Second, the study proposes evaluating ultrasonic beam modeling techniques to reduce the 

number of additional specimens required for testing.

17. Key Words

Nondestructive evaluation, phased array ultrasonic testing, PAUT,

conventional ultrasonic testing, weld inspection, steel bridge

18. Distribution Statement

No restrictions. This document is 

available to the public through the 

National Technical Information Service, 

Springfield, VA 22161.

https://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

87

22. Price

N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
ii
iii

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION ................................................................................................ 1

CHAPTER 2. TECHNICAL APPROACH ................................................................................ 3

Equipment ............................................................................................................................... 3

PAUT .................................................................................................................................. 3

Pulse-Echo (PE) Technique ................................................................................................ 4

Standardization ................................................................................................................... 6

Calibration Blocks .............................................................................................................. 6

CHAPTER 3. SPECIMEN FABRICATION ............................................................................. 7

Submerged Arc Welding (SAW) ........................................................................................... 7

ESW-NG .................................................................................................................................. 7

Fabrication of Test Specimens ............................................................................................... 7

CHAPTER 4. DATA ACQUISITION ........................................................................................ 9

Scan Plan Development .......................................................................................................... 9

Acquisition and Analysis Procedure ................................................................................... 19

Subtask 1 ........................................................................................................................... 19

Subtask 2 ........................................................................................................................... 20

Subtask 3 ........................................................................................................................... 20

Subtask 4 ........................................................................................................................... 21

Subtask 5 ........................................................................................................................... 21

Subtask 6 ........................................................................................................................... 21

Subtask 7 ........................................................................................................................... 22

Data Analysis ......................................................................................................................... 22

CHAPTER 5. COMPARISON OF CONVENTIONAL UT, RT, AND PAUT ..................... 25

CHAPTER 6. FINAL COMPARATIVE PAUT, CONVENTIONAL UT, AND RT 

RESULTS .................................................................................................................................... 31

CHAPTER 7. SUMMARY ......................................................................................................... 43

CHAPTER 8. CONCLUSIONS ................................................................................................. 45

CHAPTER 9. RECOMMENDATIONS ................................................................................... 47

APPENDIX A. PROCEDURE ................................................................................................... 49

Ultrasonic Phased Array Examination Equipment and Accessories ............................... 49

Standardization ..................................................................................................................... 50

Horizontal Sweep .............................................................................................................. 50

TCG................................................................................................................................... 50

Encoder Standardization ................................................................................................... 50

Acceptance criteria ............................................................................................................... 50

Examination........................................................................................................................... 52

Evaluation .............................................................................................................................. 52

APPENDIX B. TEST RESULTS ............................................................................................... 53

Specimen TP1 ........................................................................................................................ 53
iv

Specimen TP2 ........................................................................................................................ 55

Specimen TP3 ........................................................................................................................ 58

Specimen TP4 ........................................................................................................................ 61

Specimen TP5 ........................................................................................................................ 64

Specimen ESW-2CP.............................................................................................................. 66

Specimen ESW-12CP............................................................................................................ 69

Specimen SAW-12CP ........................................................................................................... 71

Specimen HF1........................................................................................................................ 74

Specimen HF2........................................................................................................................ 76

REFERENCES ............................................................................................................................ 79
v 

LIST OF FIGURES

Figure 1. Image. Linear scanning. .................................................................................................. 3

Figure 2. Image. Sectorial scanning. ............................................................................................... 4

Figure 3. Schematic. Phased array PE technique. ........................................................................... 5

Figure 4. Photo. International Institute of Welding (IIW) block.(2). ............................................... 5

Figure 5. Photo. TCG standardization block.(2) .............................................................................. 6

Figure 6. Schematics. TP1 scan plans for test specimens. ............................................................ 10

Figure 7. Schematics. TP2 scan plans for test specimens. ............................................................ 11

Figure 8. Schematics. TP3 scan plans for test specimens. ............................................................ 12

Figure 9. Schematics. TP4 scan plans for test specimens. ............................................................ 13

Figure 10. Schematics. TP5 scan plans for test specimens. .......................................................... 14

Figure 11. Schematics. ESW-2CP scan plans for test specimens. ................................................ 15

Figure 12. Schematics. ESW-12CP scan plans for test specimens. .............................................. 16

Figure 13. Schematics. SAW-12CP scan plans for test specimens. ............................................. 17

Figure 14. Schematics. HF1 scan plans for test specimens. ......................................................... 18

Figure 15. Schematics. HF2 scan plans for test specimens. ......................................................... 19

Figure 16. Photo. Example of labeling of specimens. .................................................................. 20

Figure 17. Photo. Example of the etched specimen. ..................................................................... 21

Figure 18. Schematic. Example of CAD drawing based on the etched weld metal. .................... 21

Figure 19. Image. A-, B-, C-, and S-scan images. ........................................................................ 22

Figure 20. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP1 (butt-weld specimen). .............................................................. 25

Figure 21. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP2 (butt-weld specimen). .............................................................. 26

Figure 22. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP3 (butt-weld specimen). .............................................................. 26

Figure 23. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP4 (butt-weld specimen). .............................................................. 27

Figure 24. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP5 (butt-weld specimen). .............................................................. 27

Figure 25. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen HF1 (butt-weld specimen). ............................................................. 28

Figure 26. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen ESW-2CP (butt-weld specimen). .................................................... 28

Figure 27. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen ESW-12CP (butt-weld specimen). .................................................. 29

Figure 28. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen SAW-12CP (butt-weld specimen). ................................................. 29

Figure 29. Graph. Discontinuity depth comparison—UT and PAUT. ......................................... 32

Figure 30. Graph. Scatter plot for discontinuity depth—UT versus PAUT. ................................ 32

Figure 31. Graph. Discontinuity length comparison—RT and PAUT ......................................... 33

Figure 32. Graph. Scatter plot for discontinuity length—PAUT versus RT. ............................... 34

Figure 33. Graph. Discontinuity length comparison—UT and PAUT. ........................................ 35

Figure 34. Graph. Scatter plot for discontinuity length—UT versus PAUT. ............................... 36

Figure 35. Graph. PAUT, UT, and RT detection and rejection results. ........................................ 43
vi 

Figure 36. Photo. Robotic arm. ..................................................................................................... 49

Figure 37. Image. Sensitivity level.(2) ........................................................................................... 51

Figure 38. Photo. TP1 unprocessed etched. .................................................................................. 53

Figure 39. Photo. TP1 etched image with weld edge traced. ........................................................ 54

Figure 40. Schematic. TP1 dimensions. ........................................................................................ 54

Figure 41. Schematic. TP1 CAD image with traced HAZ dimensions. ....................................... 54

Figure 42. Images. Composite scan view for test specimen TP1. ................................................ 55

Figure 43. Photo. TP2 unprocessed etched image. ....................................................................... 56

Figure 44. Photo. TP2 etched image with weld edge traced. ........................................................ 56

Figure 45. Schematic. TP2 dimensions. ........................................................................................ 57

Figure 46. Schematic. TP2 CAD image with traced HAZ with dimensions. ............................... 57

Figure 47. Image. Composite scan view for test specimen. .......................................................... 57

Figure 48. Photo. TP3 unprocessed etched image. ....................................................................... 58

Figure 49. Photo. TP3 etched image with weld edge traced. ........................................................ 59

Figure 50. Schematic. TP3 dimensions. ........................................................................................ 59

Figure 51. Schematic. TP3 CAD image with traced HAZ with dimensions. ............................... 60

Figure 52. Images. Composite scan view for test specimen TP3. ................................................ 60

Figure 53. Photo. TP4 unprocessed etched image.(8) .................................................................... 61

Figure 54. Photo. TP4 etched image with weld edge traced.(8) ..................................................... 62

Figure 55. Schematic. TP4 dimensions. ........................................................................................ 62

Figure 56. Schematic. TP4 CAD image with traced HAZ with dimensions. ............................... 63

Figure 57. Images. Composite scan view for test specimen TP4. ................................................ 63

Figure 58. Photo. TP5 unprocessed etched image. ....................................................................... 64

Figure 59. Photo. TP5 etched image with weld edge traced. ........................................................ 65

Figure 60. Schematic. TP5 dimensions. ........................................................................................ 65

Figure 61. Schematic. TP5 CAD image with traced HAZ with dimensions. ............................... 66

Figure 62. Images. Composite scan view for test specimen TP5. ................................................ 66

Figure 63. Photo. ESW-2CP unprocessed etched image. ............................................................. 67

Figure 64. Photo. ESW-2-CP etched image with weld edge traced. ............................................ 67

Figure 65. Schematic. ESW-2CP dimensions............................................................................... 68

Figure 66. Schematic. ESW-2CP CAD image with traced HAZ with dimensions. ..................... 68

Figure 67. Images. Composite scan view for test specimen ESW-2CP. ...................................... 68

Figure 68. Photo. ESW-12CP unprocessed etched image. ........................................................... 69

Figure 69. Photo. ESW-12CP etched image with weld edge traced. ............................................ 70

Figure 70. Schematic. ESW-12CP dimensions............................................................................. 70

Figure 71. Schematic. ESW-12CP CAD image with traced HAZ with dimensions. ................... 70

Figure 72. Images. Composite scan view for test specimen ESW-12CP at IP1. .......................... 71

Figure 73. Photo. SAW-12CP unprocessed etched image. ........................................................... 72

Figure 74. Photo. SAW-12CP etched image with weld edge traced. ........................................... 72

Figure 75. Schematic. SAW-12CP dimensions. ........................................................................... 73

Figure 76. Schematic. SAW-12CP CAD image with traced HAZ with dimensions. ................... 73

Figure 77. Images. Composite scan view for test specimen SAW-12CP at IP1. ......................... 73

Figure 78. Photo. HF1 unprocessed etched image. ....................................................................... 74

Figure 79. Photo. HF1 Etched image with weld edge traced. ....................................................... 75

Figure 80. Schematic. HF1 dimensions. ....................................................................................... 75

Figure 81. Schematic. HF1 CAD image with traced HAZ with dimensions. ............................... 75
vii 

Figure 82. Images. Composite scan view for test specimen HF1 at IP1. ..................................... 76

Figure 83. Photo. HF2 unprocessed etched image. ....................................................................... 77

Figure 84. Photo. HF2 etched image with weld edge traced. ....................................................... 77

Figure 85. Schematic. HF2 dimensions. ....................................................................................... 78

Figure 86. Schematic. HF2 CAD image with traced HAZ with dimensions. ............................... 78

Figure 87. Images. Composite scan view for test specimen HF2 at IP1. ..................................... 78
viii

LIST OF TABLES

Table 1. Test specimens. ................................................................................................................. 8

Table 2. List of index offsets used in scan plan for the test specimens. ......................................... 9

Table 3. Variance in the test results. ............................................................................................. 36

Table 4. PAUT, conventional manual UT, and RT results. .......................................................... 37

Table 5. Probe and wedge. ............................................................................................................ 49

Table 6. Discontinuity classification. ............................................................................................ 51

Table 7. PAUT acceptance criteria. .............................................................................................. 51
ix

LIST OF ABBREVIATIONS AND ACRONYMS

AASHTO American Association of State Highway and Transportation Officials 

ARL automatic reject level

AWS American Welding Society

CAD computer-aided design 

CJP complete joint penetration

CP complete penetration

DRL disregard level 

ESW electroslag welding 

ESW-NG electroslag welding, narrow gap 

FSH full screen height

HAZ heat-affected zone 

HF Hirschfeld

IIW International Institute of Welding

IP index position 

NDE nondestructive evaluation 

PAUT phased array ultrasonic testing

PE pulse echo

RT radiographic testing 

SAW submerged arc welding

SDH side-drilled hole

SSL standard sensitivity level

TCG time-corrected gain

TOFD time of flight diffraction

TP test plate

UT ultrasonic testing

1 

CHAPTER 1. INTRODUCTION

This study assesses the acceptability of phased array ultrasonic testing (PAUT) as an alternative 

to radiography.(1) The quality of the welds in the bridges is inspected and assessed in compliance 

with the American Association of State Highway and Transportation Officials 

(AASHTO)/American Welding Society (AWS) D1.5M/D1.5 in Bridge Welding Code.

(2) To 

inspect the full volume of the complete joint penetration (CJP) welds, nondestructive evaluation 

(NDE) methods, such as ultrasonic testing (UT) and radiographic testing (RT) are utilized.(3–6)

Based on the joint type, welding process, and member design stress, the choice of the NDE 

method to inspect the welds changes. Currently, the code requires RT for CJP welds subjected to 

tensile or reversal stresses, as well as for the electroslag welding narrow gap process (ESW-NG) 

and electroslag welding (ESW). When CJP groove welds in butt joints subject only to 

compression or shear require testing, either RT or UT shall be used.

(2) In recent years, the UT 

field has experienced remarkable innovation.(6) Notably, several manufacturers have introduced 

PAUT systems with real-time, fast data acquisition.

(1) These PAUT systems feature a matrix of 

multiple transducers, with some capable of housing up to 128 elements within a single probe. 

In the 2015 edition of AWS D1.5, the PAUT technique was acknowledged as a recognized 

inspection technology for use instead of conventional UT on CJP butt welds.(2) Weld inspection 

using the UT method comprise raster scanning using a single crystal transducer that produces 

sound beams at one of the angles—70°, 60°, and 45°—as stipulated by the code. In phased array 

inspection, the probe consists of multiple small transducers (elements) that can steer the 

ultrasonic beam electronically in the test medium at multiple angles, improving the inspection 

coverage of the weld’s cross section, eliminating the need for manual raster of a single element 

transducer across the plate surface. Furthermore, using multiple beams facilitates the generation 

of extradimensional data, enabling visualization of discontinuity size, shape, and location with 

greater precision. Additionally, when coupled with encoded line scans, PAUT data can be 

digitally stored as permanent records, much like a radiograph, a feat not achievable with 

conventional UT. 

While AWS D1.5 in Bridge Welding Code indicates some support for using PAUT, further 

investigation and validation are necessary to potentially replace the RT method for these other 

applications. This report presents the developmental efforts conducted at the NDE Laboratory, a 

part of the Federal Highway Administration’s (FHWA) Turner-Fairbank Highway Research 

Center (TFHRC), to assess the state of PAUT technology and its potential application as an 

approved alternative to RT in the AASHTO/AWS D1.5M/D1.5 in Bridge Welding Code.

(2)

The work reported herein involved comprehensively reviewing the current state of practice in 

inspecting welds using PAUT; developing a preliminary technical approach to inspect CJP butt 

welds, with and without transitions; fabricating suitable test specimens; developing detailed scan 

plans for sample test specimens with CJP butt welds; and comparing test results from PAUT, 

UT, and RT. Following the guidelines provided in AWS D1.5 2020 Annex J on advanced 

ultrasonic examination, the researchers inspected and analyzed 10 test specimens.(2) The indepth 

analysis of PAUT data obtained was utilized to determine location and sizing information related 

to the discontinuities. The report also compares PAUT results to those data obtained using 

conventional UT and RT with statistical correlations. 

3 

CHAPTER 2. TECHNICAL APPROACH

EQUIPMENT

PAUT

An ultrasonic phased array probe consists of multiple elements, usually ranging between 16 and 

128, with each element functioning as an individual ultrasonic transducer. These elements can be 

arranged in various patterns, with the simplest being a linear array. The ultrasonic wavefronts 

can be excited by pulsing the elements individually or as a group, and their combination 

generates the beam profile. By varying the timing of the excitation for each element, the beam 

profile can be modified, and focal laws are used to control the amplitude and time delay for each 

element.

Three primary electronic scanning techniques are used for controlling the beam profile using a 

linear array pattern of the elements:

(1)

1. Linear scanning: A subset or group of the array elements are pulsed to form the desired 

beam profile, and then the applicable focal law giving this beam profile is electronically 

multiplexed along the length of the array (figure 1). This electronic scanning technique is 

akin to mechanically scanning a conventional (single-crystal) probe along a distance 

equal to the length of the larger phased array probe. In the current market, most 

commercially available arrays have up to 128 elements, which are typically pulsed in 

groups of 8 to 16. 

Source: FHWA. 

Figure 1. Image. Linear scanning. 

2. Dynamic depth focusing: The focal laws are varied to electronically move the focal point 

along the nominal beam axis. 
4 

3. Swept angular (sectorial or azimuthal) scanning: By selecting specific focal laws, the 

beam is electronically steered to a fixed angle of incidence or swept through a wide 

angular range (figure 2). 

Source: FHWA. 

Figure 2. Image. Sectorial scanning. 

Pulse-Echo (PE) Technique 

This process uses a transducer to both transmit and receive the ultrasonic pulse, as presented in

figure 3. The received ultrasonic pulses are separated by the time the sound takes to reach the 

different surfaces from which the sound is reflected. The size (amplitude) of a reflection is 

related to the size of the reflecting surface. 

Defect sizing approaches often used in standards and specifications are based on the amplitude of 

the returned signal and correlating it with an equivalent machined reflector, such as a notch or a 

side-drilled hole (SDH) (figure 4). 
5 

Source: FHWA. 

Figure 3. Schematic. Phased array PE technique.

However, the correlation between defect size and amplitude is dependent on several variables, 

such as the material, equipment, and the defect itself. The equipment has potential amplitude 

variations due to the type of pulser, frequency band, cabling, and other inherent electrical 

parameters, but the disparities in the signal amplitude are minimized by the standardization. 

The purpose of standardization is to reduce variations in inspection outcomes by setting and 

maintaining a set of parameters that are calibrated to meet the required standards. Ultrasonics are 

highly sensitive to defect orientation, with roughness; curvature; type (slag, porosity, crack, or 

lack of fusion); and location also playing roles. 

Source: FHWA. 

Figure 4. Photo. International Institute of Welding (IIW) block.

(2).

Two important factors influencing the PE technique are that large discontinuities are generally 

undersized and small discontinuities tend to be oversized. The oversizing of small discontinuities

occurs mainly because small discontinuities act as omnidirectional emitters. Small 

discontinuities emit anywhere inside the beam and thus are influenced by the beam spread. The 

small discontinuity is essentially plotting the width of the sound beam. However, undersizing 

large discontinuities is more critical. In cases where the defect is irregularly shaped and 

inspection is conducted with a fixed-angle transducer beam, lower amplitude signals can result

and nonconservative sizing measurement errors may occur.(1)
6 

Standardization

The research team used a phased array probe with a center frequency of 5 MHz for testing. The 

phased array probes were a one-dimensional linear array type consisting of 64 elements. The 

team used a nominal shear wave refracted 55° from the wedge as the center sound beam angle, 

and they steered the beam electronically from 45° to 70°.(2) The following steps ensure good 

standardization:

(2)

• Phased array element operability check. 

• Sensitivity standardization. 

• Time-corrected gain (TCG). 

• Encoder standardization. 

Calibration Blocks

In the ideal testing scenario, calibration blocks are made of the same material type and are heat 

treated in the same fashion as the test specimen. Different types of reflectors—such as SDHs, 

flat-bottomed holes, and notches—are used to calibrate phased array examinations for angle 

beam inspections. An SDH, which is known to be a well-defined and reproducible reflector, is 

widely used.(1)

The researchers used an IIW block for sensitivity standardization and range settings. The TCG 

phased array standardization block used was 1.25 inches wide, approximately 6.5 inches in 

height, and 26 inches in length. The block had 12 SDHs that were 0.06 inch in diameter. All 

SDHs were perpendicular to the sound beam and parallel to the scanning surface (figure 5).(2)

Source: FHWA. 

Figure 5. Photo. TCG standardization block.(2)
7 

CHAPTER 3. SPECIMEN FABRICATION

SUBMERGED ARC WELDING (SAW)

SAW is an arc welding process that fuses materials together by heating them with an electric arc 

or arcs between a bare electrode(s) and the specimen.(7) The arc is submerged under a blanket of 

granular flux. The filler metal is obtained from melting a solid electrode wire, sometimes with 

additional alloying elements in the flux. The SAW process joins all the weldable steels. The 

process provides high deposition rates, making it excellent for medium and thick sections of 

plates and pipes. Additionally, the process produces deep penetration. The process is typically 

limited to the flat and horizontal fillet positions because of the granular flux used to shield the 

weld puddle. However, with special flux dams, the process can be used in the horizontal groove 

weld position. Since the arc is hidden, only safety glasses are generally required by the welding 

operator. The process generally produces a smooth weld bead with no spatter. A layer of slag is 

left on the weld bead that is normally easy to remove. The deep penetration of the SAW process 

can lead to centerline cracking due to improper width-to-depth ratios in the bead cross sections.

ESW-NG

ESW-NG is a special automatic process normally used by larger fabricators to weld butt joints in 

plates.

(7) Using a single-pass vertical process, ESW-NG offers good productivity and quality in 

heavy structural fabrications. The resistance of current through the slag pool covering the 

complete surface of the weld metal provides the heat for melting. A pool of molten slag is 

formed between the edges of the parts to be welded and the traveling shoes. The metal electrode 

is inserted into the molten slag. The current passes through the electrode, and the molten slag 

heats the slag pool. The electrode wire melts, and the molten metal settles at the bottom of the 

slag pool and solidifies to form the weld metal. Consumable guide tubes are used in narrow 

groove ESW-NG welds for bridge fabrications. Typically, discontinuities like slag, inclusions, 

porosity, undercuts, notches, etc., are not encountered in the ESW-NG process.

FABRICATION OF TEST SPECIMENS

Based on their interactions with other Federal agencies and experts in steel bridge fabrication, 

the researchers initially fabricated eight test specimens.

(1)

 To ensure the welding would represent 

production bridge welding practices, the team manufactured specimens by using two steel bridge 

fabricators. They used the ESW-NG and SAW processes to fabricate the specimens. The 

objective of using two welding processes was to determine the microstructures’ influence on the 

inspection technology. A brief overview of the two welding processes is provided in the 

following sections. The researchers instructed the fabricators to implant discontinuities in the 

specimens they typically encounter during fabrication. The typical discontinuities often found in 

welds are cracks, lack of fusion, lack of penetration, porosity, inclusions, and undercut. One 

approach used in this effort to implant a lack of fusion discontinuity was that a thick rectangular 

shim was used to simulate the lack of fusion discontinuity for an ESW-NG thickness transition 

CJP weld. The team attached a plate to the transition bevel with a fillet weld, and it was thick 

enough such that the molten ESW-NG weld pool would not penetrate through the thickness. 
8 

Later in the project, the researchers fabricated two additional transition butt-weld specimens 

using the ESW-NG process. They developed the fabrication plan in collaboration with the steel 

weld fabricator. The intent in fabricating these additional test specimens was to implant weld 

fusion line cracking using the ESW-NG process. The 10 butt-weld specimens fabricated are 

listed in table 1. The team request both fabricators to perform conventional UT and RT on each 

of the test specimens. 

Table 1. Test specimens. 

Sample 

Number Sample Name

Weld 

Type

Length

(Inches)

Width

(Inches)

Height

(Inches) Transition

1 TP1 SAW 25.0 26.5 1–2 Yes

2 TP2 ESW-NG 28.0 24.5 1.5 No

3 TP3 ESW-NG 22.0 23.5 3.3 No

4 TP4 SAW 36.5 18.0 3.0 No

5 TP5 ESW-NG 30.0 24.5 1.5–2.7 Yes

6 ESW-2CP ESW-NG 48.0 48.0 2.0 No

7 ESW-12-CP ESW-NG 48.0 48.0 1.0–2.0 Yes

8 SAW-12CP SAW 48.0 48.0 1.0–2.0 Yes

9 HF1 ESW-NG 36.0 49.0 2.0–2.5 Yes

10 HF2 ESW-NG 36.0 49.0 2.0–2.5 Yes

CP = complete penetration; HF = Hirschfeld(8); TP = test plate. 
9 

CHAPTER 4. DATA ACQUISITION

SCAN PLAN DEVELOPMENT

The study team based the PAUT data acquisition throughout this research effort on the PE

approach. They developed the scan plans for the butt-weld specimens listed in table 1. The 

strategy in developing these scan plans was to consider the detailed specific attributes of each 

specimen based on the thickness of the specimen, the weld centerline, the weld width, and the 

weld heat-affected zone (HAZ) size. The researchers developed the scan plans using a 

commercial ray tracing software.

(9) The software enables input of the specimen specifics and the 

technical specifications of the phased array probe and the wedge used for inspections. The 

software provides a detailed sound beam center ray path analysis based on the position of the 

probe and the sequence in which the elements are pulsed. The teams used various combinations 

of the beam index points to determine the optimum location for the probe placement. The scan 

plans define the various refracted angles to be used during the examination. The complete 

coverage of the weld and the HAZ was an important aspect in developing the scan plans. The 

researchers developed the scan plans to optimize coverage to fully examine the weld and the 

HAZ. The index offset positions (distance of the wedge front face to the weld center) are 

configured to include the coverage as close to perpendicular to the weld fusion face as 

practicable. Table 2 provides the index offsets used to inspect the plates. Figure 6 to figure 15

present the scan plan for the plates. In the scan plans, index position (IP)1 represents the 

90°-skew direction, and IP2 represents the 270°-skew direction.

Table 2. List of index offsets used in scan plan for the test specimens.

Plate ID

Index Offset (Inches)

90° Skews (IP1) 270° Skews (IP2)

TP1 0.8,0, −0.6, −1.65, −4.5, −6.2 0.5, 0, 2, 3.4, −0.8

TP2 0.4, 1, −0.1, −0.9, −3 0.1,0.9, 3, −0.4, −1

TP3 0.35, −0.15, −1.2, −3.3, −7.25 0.15, 1.2, 3.3, 7.25, −0.35

TP4 0.75, −0.5, −3, −5.7, −6.6 0.5, 3, 5.7, 6.6, −0.75

TP5 −9.5, 0, 1, −0.5, −1.75, −3.5 0.5, 0, 1.5, 3, 6.2

ESW-2CP 0.75, −1, −0.5, −3.5, −5, −7.5 0.5, 3.5, 5, 7.5, −1

ESW-12CP 0, 1, −0.6, −1.5, −3.25, −8 2,3, −0.1, −0.6, −1.4, 0.85

SAW-12CP 0.25,1, −1, −3, −5.5, −7.2 0.5, 0, 1.5, 2.5, 3.2, −1

HF1 0.9,0.25, −0.75, −2.5, −8 0.5, 2 ,4.5, 5.2, 6.2, 7.3, −0.5

HF2 0.7, −0.3, −1.7, −4.2, −6.6, −8.5 0.5, 2, 3.5, 4.7, 6.2, −1

ID = identification.
10 

Source: FHWA. 

A. Scan plan for test specimen test plate (TP)1-IP1. 

Source: FHWA.

B. Scan plan for test specimen TP1-IP2. 

Figure 6. Schematics. TP1 scan plans for test specimens.
11 

Source: FHWA.

A. Scan plan for test specimen TP2-IP1. 

Source: FHWA. 

B. Scan plan for test specimen TP2-IP2. 

Figure 7. Schematics. TP2 scan plans for test specimens.
12 

Source: FHWA.

A. Scan plan for test specimen TP3-IP1. 

Source: FHWA. 

B. Scan plan for test specimen TP3-IP2.

Figure 8. Schematics. TP3 scan plans for test specimens.
13 

 

Source: FHWA.

A. Scan plan for test specimen TP4-IP1. 

Source: FHWA. 

B. Scan plan for test specimen TP4-IP2. 

Figure 9. Schematics. TP4 scan plans for test specimens.
14 

Source: FHWA.

A. Scan plan for test specimen TP5-IP1. 

Source: FHWA. 

B. Scan plan for test specimen TP5-IP2. 

Figure 10. Schematics. TP5 scan plans for test specimens. 
15 

Source: FHWA.

A. Scan plan for test specimen ESW-2 complete penetration (CP)-IP1. 

Source: FHWA. 

B. Scan plan for test specimen ESW-2CP-IP2. 

Figure 11. Schematics. ESW-2CP scan plans for test specimens.
16 

Source: FHWA.

A. Scan plan for test specimen ESW-12CP-IP1. 

Source: FHWA. 

B. Scan plan for test specimen ESW-12CP-IP2. 

Figure 12. Schematics. ESW-12CP scan plans for test specimens.
17 

Source: FHWA.

A. Scan plan for test specimen SAW-12CP-IP1. 

Source: FHWA. 

B. Scan plan for test specimen SAW-12CP-IP2. 

Figure 13. Schematics. SAW-12CP scan plans for test specimens.
18 

Source: FHWA.

A. Scan plan for test specimen Hirschfeld (HF)

(8)

 1-IP1. 

Source: FHWA.

B. Scan plan for test specimen HF1-IP2. 

Figure 14. Schematics. HF1 scan plans for test specimens.
19 

Source: FHWA.

A. Scan plan for test specimen HF2-IP1. 

Source: FHWA. 

B. Scan plan for test specimen HF2-IP2. 

Figure 15. Schematics. HF2 scan plans for test specimens.

ACQUISITION AND ANALYSIS PROCEDURE

The data acquisition and analysis involved seven subtasks.

Subtask 1

The study team made detailed measurements of all the specimens involved in the testing, 

including specimen length, width, and height. 
20 

Subtask 2

The researchers labeled all the specimens (figure 16) with die stamps and photographed them to 

indicate the specimen’s name, surface (top or bottom), and skew angles (90° or 270° side of 

weld).

Source: FHWA. 

Figure 16. Photo. Example of labeling of specimens.

Subtask 3

The team machined all the specimens to make the welds’ cross sections visible. Next, they 

mechanically sanded and polished the weld surface and etching with nital etchant. Once the 

etching was completed, the researchers documented the results and took digital photographs of 

each etched surface, as illustrated in figure 17. 
21 

Source: FHWA. 

Figure 17. Photo. Example of the etched specimen.

Subtask 4

The researchers developed computer-aided design (CAD) drawings using the etched surface 

details to show the specimen plan view and the weld profile dimension (figure 18).(10)

Source: FHWA. 

Figure 18. Schematic. Example of CAD drawing based on the etched weld metal.

Subtask 5

For each test specimen, the study team developed scan plans using the information from etched 

surface details and the CAD drawings. 

Subtask 6

The researchers completed the data acquisition using the scan plans developed in subtask 5. 
22 

Subtask 7

The research team analyzed the data from all the test specimens and performed a final analysis in 

accordance with 2020 AWS D1.5 Annex J on advanced ultrasonic examination(2) and in line with 

the approaches described earlier in this research effort.

DATA ANALYSIS

Using the 5 MHz probe, the team carried out the data acquisition with the PAUT system. The 

scan plans developed, as discussed in the previous section, were implemented in carrying out 

scans on each of the test specimens. They used a combination of A-, B-, C-, and S-scans(6) to 

interpret the data and determine the location and size of the discontinuities. The phased array 

equipment used in this research is capable of generating and displaying sectorial-scan (also 

called S-scan), B-scan, and C-scan images. The scan types are described in the following 

paragraph. 

The researchers use “volume-corrected” C-scans as a first step to determine the approximate 

location of the discontinuities. The term “volume-corrected” refers to the corrections made to the 

image by the PAUT analysis software to properly scale the dimensions across the weld on the 

top C-scan view. Based on the locations of discontinuities inferred from the volume-corrected 

C-scans, the team further analyzed the data using a combination of S-scans and B-scans to 

accurately determine the location and size of each discontinuity. A combination of A-, B-, C-, 

and S-scan images was used to determine the length of the discontinuities (figure 19). 

Source: FHWA. 

Figure 19. Image. A-, B-, C-, and S-scan images. 

The discontinuity length was determined using the 6-dB drop method in accordance with AWS 

D1.5.(2)

 Unlike conventional UT, in which the ultrasonic probe has to be physically moved, 

PAUT data can be analyzed as part of data postprocessing.(5) The data analysis software provides 

cursors that can be moved to determine the peak amplitude of the defect signal.(11) When the 
23 

peak defect signal is isolated, the flaw category can be defined in accordance with AWS D1.5, 

and the cursor is moved in both directions opposite the peak signal to determine flaw length. 

25 

CHAPTER 5. COMPARISON OF CONVENTIONAL UT, RT, AND PAUT

The research team inspected each test specimen by using the conventional single element UT 

system and then using the PAUT system. Based on the AWS D1.5 requirements for conventional 

UT, the discontinuities are classified as follows for a weld under tensile stress:

(2)

• Class A (large discontinuity): Any indication in this category shall be rejected regardless 

of length. 

• Class B (medium discontinuity): Any indication in this category having a length greater 

than 0.75 inch shall be rejected.

• Class C (small discontinuity): Any indication in this category having a length greater than 

2 inches in the middle half, or 0.75-inch length in the top or bottom quarter of the weld 

thickness, shall be rejected.

• Class D (minor discontinuity): Any indication in this category shall be accepted 

regardless of length or location in the weld.

The requirements for welds under compressive stress are less stringent. Table 8.4 and table 8.5 in 

AWS D1.5 provide the acceptance-rejection criteria for tension and compression welds, 

respectively.(2) The team compared the results from conventional UT to the PAUT results 

(see table 4). 

Figure 20 to figure 28 present comparisons of volume-corrected C-scan images to digital 

photographs from RT. The examples include both flat CJP butt welds and transition butt-weld 

specimens. 

Source: FHWA. 

Figure 20. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP1 (butt-weld specimen).
26 

Source: FHWA. 

Figure 21. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP2 (butt-weld specimen).

Source: FHWA. 

Figure 22. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP3 (butt-weld specimen).
27 

Source: FHWA. 

Figure 23. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP4 (butt-weld specimen).

Source: FHWA. 

Figure 24. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen TP5 (butt-weld specimen).
28 

Source: FHWA. 

Figure 25. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen HF1 (butt-weld specimen).

Source: FHWA. 

Figure 26. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen ESW-2CP (butt-weld specimen).
29 

Source: FHWA. 

Figure 27. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen ESW-12CP (butt-weld specimen).

Source: FHWA. 

Figure 28. Image. Comparison of volume-corrected C-scan image to RT digital 

photograph, specimen SAW-12CP (butt-weld specimen). 

Figure 20 to figure 28 also present a subjective degree of correlation between discontinuity 

locations, as determined using volume-corrected C-scans and as revealed in the RT images. RT 

images are typically used only to locate discontinuities. The sizing of the images using RT can 

provide measurements of discontinuity length, but the depth at which the discontinuities occur 

cannot be inferred using RT. PAUT data, however, can be used to locate and size discontinuities. 
30 

This capability of PAUT to locate and size discontinuities provides an advantage of utilizing 

PAUT, particularly when repairs are required, and the repair depth needs to be determined. In 

addition, using RT in an industrial or laboratory setup gives rise to a variety of radiation 

regulatory and safety issues. 
31 

CHAPTER 6. FINAL COMPARATIVE PAUT, CONVENTIONAL UT, AND RT 

RESULTS

The results of the PAUT, conventional UT, and radiography are provided in table 4. The

researchers collected and analyzed the PAUT data at the TFHRC NDE Laboratory. The 

radiography was performed by the specimen fabricators when they welded the TPs.

The discontinuity character column in table 4 is the best judged character for each discontinuity. 

Most of this information comes from the radiographs, where the image of the discontinuity 

provides the most useful characterization information. Planar discontinuities like lack of fusion, 

and most cracks are only detectable by RT when the discontinuity plane aligns with the radiation 

beam. The cracks can also be detected when the width of the lack of fusion is so wide that the 

volume of the discontinuity can be imaged by RT. Most of the lack of fusion in these plates was 

wide enough to be imaged by RT. Figure 29 presents the comparison of depth of the 

discontinuities between conventional UT and PAUT. Figure 30 presents a scatter plot for the 

depth of discontinuities in UT and PAUT. Figure 31 presents the comparison of the length of 

discontinuities between radiography and PAUT. Figure 32 presents a scatter plot for the length 

of discontinuities in RT and PAUT, and figure 33 presents the length comparison of PAUT and 

UT. Slight variations in the depth may arise as PAUT data are collected linearly. In a linear scan, 

the probe is not rastered to maximize the signal from discontinuities, and as a result, small depth 

positioning errors would occur in PAUT.(3)

Scatter plots are commonly used in the visualization of nondestructive testing measurements to 

determine the relationship between dimensions of discontinuities measured using different 

methods.. An identity line is drawn in each scatter plot, representing the measurements plotted 

on the x and y axes that are equal between inspection methods. Correlation factors (R) calculated 

for measurements using PAUT, UT, and RT indicate a strong correlation between them. 

Furthermore, a strong correspondence between the slope of the regression and identity lines and 

low y-intercept values of the regression lines, as shown in the scatter plots, indicate close 

similarities in the measurements.

From the scatter plot (figure 30) for the comparison between the depth measurements between 

the phased array and UT, a strong correlation (correlation factor = 0.953) can be assumed 

between the measured values and the slope of the regression line, which is 0.96. Additionally, 

the scatter plot comparing the length of discontinuities between PAUT and RT (figure 32) 

indicates a strong correlation (R = 0.89) with a regression line slope of 0.9. 

A strong correlation of 0.91 is between the length measured by PAUT and UT, and the 

regression line slope is approximately 1, as observed in the scatter plot (figure 34). 
32 

Source: FHWA. 

Figure 29. Graph. Discontinuity depth comparison—UT and PAUT. 

Source: FHWA. 

Figure 30. Graph. Scatter plot for discontinuity depth—UT versus PAUT. 
33 

Source: FHWA. 

Figure 31. Graph. Discontinuity length comparison—RT and PAUT
34 

Source: FHWA. 

Figure 32. Graph. Scatter plot for discontinuity length—PAUT versus RT. 
35 

Source: FHWA. 

Figure 33. Graph. Discontinuity length comparison—UT and PAUT. 
36 

Source: FHWA. 

Figure 34. Graph. Scatter plot for discontinuity length—UT versus PAUT. 

Table 3 presents the variability in the measurement of depth between UT and PAUT and the 

length between PAUT and UT and between PAUT and RT. Considering the 95-percent limit of 

agreement, the team observed six outliers in the comparison results. The discontinuities 

identified as TP4-Flaw 8,9 and HF2-Flaw 1 indepth comparison; SAW12-CP Flaw 2 in RT and 

PAUT length comparison and TP4-Flaw 2; and ESW2-CP-Flaw 3 in UT and PAUT length 

comparison are the outliers observed. The term flaw is generally used to denote undesirable 

discontinuities in welds. 

Table 3. Variance in the test results. 

Variance

Depth

(UT versus PAUT)

Length

(RT versus PAUT)

Length

(UT versus PAUT)

Maximum 0.5 0.8 1.9

Minimum −0.6 −2.42 −1.6

Average 0.0042 −0.038 0.0481

Standard Deviation 0.239 0.658 0.596

Table 4 indicates that four discontinuities rejected in RT were either accepted or missed by 

PAUT. Such discrepancies in discontinuity acceptance between RT and PAUT are not 

uncommon.(4)

 Additionally, three discontinuities (lack of fusion) detected in PAUT were missed

in radiography, and one rejected discontinuity in PAUT was accepted in RT.
37 

Table 4. PAUT, conventional manual UT, and RT results.

Plate and

Discontinuity ID 

Joint Type

Welding Process

Nominal Plate 

Thickness(Inches)

Discontinuity 

Character

Technique

(RT, Manual UT, 

PAUT)

UT Beam Direction

Start “ Y” Along 

Weld (Inches)

Length (Inches) 

Location “ X” 

Across (Inches) 

UT Depth (Inches)

Amplitude/Rating

D1.5 ACC/REJ

(Tensile)

(2)

TP1, FLAW 1 V2 SAW 1–2 LOF RT — 1 1.94 — — — REJ

TP1, FLAW 1 V2 SAW 1–2 LOF UT 270 1.2 1.8 0.1 0.465 −3 (A) REJ

TP1, FLAW 1 V2 SAW 1–2 LOF PAUT 270 1.68 1.32 0.2 0.402 74% (B) REJ

TP1, FLAW 2 V2 SAW 1–2 LOF RT — 12.7 1.5 — — — REJ

TP1, FLAW 2 V2 SAW 1–2 LOF UT 90 12.6 1.5 −0.1 0.212 −5 (A) REJ

TP1, FLAW 2 V2 SAW 1–2 LOF PAUT 90 13.1 1.19 −0.1 0.19 30% (C) REJ

TP1, FLAW 3 V2 SAW 1–2 LOF RT — 24.5 0.5 — — — REJ

TP1, FLAW 3 V2 SAW 1–2 — UT — — — — — — MISS

TP1, FLAW 3 V2 SAW 1–2 — PAUT — — — — — — MISS

TP2, FLAW 1 SQ ESW-NG 1.5 LOF RT — 0.75 2.6 — — — REJ

TP2, FLAW 1 SQ ESW-NG 1.5 LOF UT 90 0.75 2.4 0.5 0.78 −6 (A) REJ

TP2, FLAW 1 SQ ESW-NG 1.5 LOF PAUT 90 0.64 2.42 0.3 0.73 49% (C) REJ

TP2, FLAW 2 SQ ESW-NG 1.5 LOF/TUN

G

RT — 13.1 5.5 — — — REJ

TP2, FLAW 2 SQ ESW-NG 1.5 LOF/TUN

G

UT 90 13.4 5.1 0.2 0.6 −2 (A) REJ

TP2, FLAW 2 SQ ESW-NG 1.5 LOF/TUN

G

PAUT 90 13.3 5.43 0 0.45 40% (C) REJ

TP3, FLAW 1 SQ ESW-NG 3.3 LOF RT — 3.5 1.6 — — — REJ

TP3, FLAW 1 SQ ESW-NG 3.3 LOF UT 270 3.5 1.2 −0.3 0.81 −2 (A) REJ

TP3, FLAW 1 SQ ESW-NG 3.3 LOF PAUT 270 3.5 1.1 −0.5 0.66 44% (C) REJ

TP3, FLAW 2 SQ ESW-NG 3.3 Slag RT — 9.6 6.3 — — — REJ

TP3, FLAW 2 SQ ESW-NG 3.3 Slag UT 90 9.9 5.3 0.1 0.2 −4 (A) REJ

TP3, FLAW 2 SQ ESW-NG 3.3 Slag PAUT 90 10.1 5.3 0 0.36 90% (A) REJ

TP3, FLAW 3 SQ ESW-NG 3.3 Slag RT — 20.7 3.1 — — — REJ

TP3, FLAW 3 SQ ESW-NG 3.3 Slag UT 90 20.7 3 0 0.32 −1 (A) REJ
38 

Plate and

Discontinuity ID 

Joint Type

Welding Process

Nominal Plate 

Thickness(Inches)

Discontinuity 

Character

Technique

(RT, Manual UT, 

PAUT)

UT Beam Direction

Start “ Y” Along 

Weld (Inches)

Length (Inches) 

Location “ X” 

Across (Inches) 

UT Depth (Inches)

Amplitude/Rating

D1.5 ACC/REJ

(Tensile)(2)

TP3, FLAW 3 SQ ESW-NG 3.3Slag PAUT 90 21.2 2.4 0.1 0.55 31% (C) REJ

TP3, FLAW 4 SQ ESW-NG 3.3 LOF RT— 22.4 1.7——— REJ

TP3, FLAW 4 SQ ESW-NG 3.3 LOF UT 270 21.8 1.9−0.4–0.4 2.90 (A) REJ

TP3, FLAW 4 SQ ESW-NG 3.3 LOF PAUT 270 22.4 1.2−0.4–0.4 3.08 53% (B) REJ

TP4, FLAW 1 V2 SAW3 LOF RT— 1.75 1.45——— REJ

TP4, FLAW 1 V2 SAW3 LOF UT 90 1.83−0.2 1.94−7 (A) REJ

TP4, FLAW 1 V2 SAW3 LOF PAUT 90 2.38 1.94−0.2 1.8 34% (C) ACC

TP4, FLAW 2 V2 SAW3 LOF RT— 2.7 1.5——— REJ

TP4, FLAW 2 V2 SAW3 LOF UT— 1.83−0.7 1.94−7 (A) REJ

TP4, FLAW 2 V2 SAW3 LOF PAUT 270 3.7 1.1−0.7 1.98 118% (A) REJ

TP4, FLAW 3 V2 SAW3 LOF RT— 15.3 3.3——— REJ

TP4, FLAW 3 V2 SAW3 LOF UT— 16 3.2—04 (C) REJ

TP4, FLAW 3 V2 SAW3 LOF PAUT 90 16.34 3.59 0.4 0.1 101% (A) REJ

TP4, FLAW 4 V2 SAW3 LOF RT— 17 4.1——— REJ

TP4, FLAW 4 V2 SAW3 LOF UT— 17.5 4.6— 1.60 (A) REJ

TP4, FLAW 4 V2 SAW3 LOF PAUT 90 18.18 4.40 1.8 28% (C) REJ

TP4, FLAW 5 V2 SAW3 LOF RT— 25.5 4.6——— REJ

TP4, FLAW 5 V2 SAW3 LOF UT— 25.2 5.3−0.2–0.2 0.4720 (A) REJ

TP4, FLAW 5 V2 SAW3 LOF PAUT 270 25.91 5.3 0.5 0.62 46% (C) REJ

TP4, FLAW 6 V2 SAW3 LOF RT— 26 0.5——— REJ

TP4, FLAW 6 V2 SAW3— UT—————— MISS

TP4, FLAW 6 V2 SAW3— PAUT—————— MISS

TP4, FLAW 7 V2 SAW3Slag RT— 27.5 1.25——— REJ

TP4, FLAW 7 V2 SAW3— UT—————— MISS

TP4, FLAW 7 V2 SAW3Slag PAUT 270 27.9 1.1 0.2 0.3 52% (B) REJ

TP4, FLAW 8 V2 SAW3— RT—————— MISS
39 

Plate and

Discontinuity ID 

Joint Type

Welding Process

Nominal Plate 

Thickness(Inches)

Discontinuity 

Character

Technique

(RT, Manual UT, 

PAUT)

UT Beam Direction

Start “ Y” Along 

Weld (Inches)

Length (Inches) 

Location “ X” 

Across (Inches) 

UT Depth (Inches)

Amplitude/Rating

D1.5 ACC/REJ

(Tensile)

(2)

TP4, FLAW 8 V2 SAW 3 LOF UT — 31.3 0.6 0 2 4(C) ACC

TP4, FLAW 8 V2 SAW 3 LOF PAUT 90 32.6 0.5 0 1.46 34% (C) ACC

TP4, FLAW 9 V2 SAW 3 — RT — — — — — — MISS

TP4, FLAW 9 V2 SAW 3 LOF UT — 34.5 0.6 0 2 4 (C) ACC

TP4, FLAW 9 V2 SAW 3 LOF PAUT 90 35.2 0.5 0 1.46 34% (C) ACC

TP5, FLAW 1 SQ ESW-NG 1.5–2.7 LOF RT — 2 1.75 — — — REJ

TP5, FLAW 1 SQ ESW-NG 1.5–2.7 LOF UT — 2.3 1.8 — 1.38 3 (C) REJ

TP5, FLAW 1 SQ ESW-NG 1.5–2.7 LOF PAUT 90 2.02 2.7 −0.4 1.46 35% (C) REJ

TP5, FLAW 2 SQ ESW-NG 1.5–2.7 LOF RT — 14.5 2.5 — — — REJ

TP5, FLAW 2 SQ ESW-NG 1.5–2.7 LOF UT — 13.5 2.75 — 0.265 −13 (A) REJ

TP5, FLAW 2 SQ ESW-NG 1.5–2.7 LOF PAUT 270 14.7 2.2 — 0.54 28% (C) REJ

TP5, FLAW 3 SQ ESW-NG 1.5–2.7 LOF RT — 22.5 1.88 — — — REJ

TP5, FLAW 3 SQ ESW-NG 1.5–2.7 LOF UT — 23.5 1.7 — 0.593 −3 (A) REJ

TP5, FLAW 3 SQ ESW-NG 1.5–2.7 LOF PAUT 270 23 1.5 — 0.47 36% (C) ACC

ESW-2CP FLAW 1 SQ ESW-NG 2 LOF/Slag RT — 0 2.75 — — — REJ

ESW-2CP FLAW 1 SQ ESW-NG 2 LOF/Slag UT — 0 2.8 0.2 1.99 −3 (A) REJ

ESW-2CP FLAW 1 SQ ESW-NG 2 LOF/Slag PAUT 270 0 3.1 0.3 1.7 196% (A) REJ

ESW-2CP FLAW 2 SQ ESW-NG 2 Porosity RT — 8.25 0.13 — — — ACC

ESW-2CP FLAW 2 SQ ESW-NG 2 Porosity UT — 8.2 0.2 0 1.2 7 (C) ACC

ESW-2CP FLAW 2 SQ ESW-NG 2 Porosity PAUT 90 7.9 0.51 −0.1 1.6 29% (C) ACC

ESW-2CP FLAW 3 SQ ESW-NG 2 Crack RT — 35.5 4 — — — REJ

ESW-2CP FLAW 3 SQ ESW-NG 2 Crack UT — 34.6 2.5 −0.1 0.88 7 (C) REJ

ESW-2CP FLAW 3 SQ ESW-NG 2 Crack PAUT 90 33.56 4.1 −0.2 0.79 30% (C) REJ

ESW-2CP FLAW 4 SQ ESW-NG 2 LOF RT — 46 1 — — — REJ

ESW-2CP FLAW 4 SQ ESW-NG 2 LOF UT — 45.5 1 −0.3–0.3 1.74 −7 (A) REJ

ESW-2CP FLAW 4 SQ ESW-NG 2 LOF PAUT 90 46.3 0.7 −0.3–0.3 1.7 190% (A) REJ
40 

Plate and

Discontinuity ID 

Joint Type

Welding Process

Nominal Plate 

Thickness(Inches)

Discontinuity 

Character

Technique

(RT, Manual UT, 

PAUT)

UT Beam Direction

Start “ Y” Along 

Weld (Inches)

Length (Inches) 

Location “ X” 

Across (Inches) 

UT Depth (Inches)

Amplitude/Rating

D1.5 ACC/REJ

(Tensile)(2)

ESW-12CP FLAW1 SQ ESW-NG1–2Slag RT—0 1.2——— REJ

ESW-12CP FLAW1 SQ ESW-NG1–2Slag UT—0 0.8 0.3 0.977 (A) REJ

ESW-12CP FLAW1 SQ ESW-NG1–2Slag PAUT 2700 0.6 0.4 0.83 101% (A) REJ

ESW-12CP FLAW2 SQ ESW-NG1–2 LOF RT— 461——— REJ

ESW-12CP FLAW2 SQ ESW-NG1–2 LOF UT— 45.5 1.2— 0.630 (A) REJ

ESW-12CP FLAW2 SQ ESW-NG1–2 LOF PAUT 270 45.51 0.4 0.77 51% (B) REJ

SAW-12CP FLAW1 SQ SAW1–2 LOF RT—0 0.38——— ACC

SAW-12CP FLAW1 SQ SAW1–2 LOF UT—0 0.5 0.1 0.2−3 (A) REJ

SAW-12CP FLAW1 SQ SAW1–2 LOF PAUT 900 0.8 0.3 0.12 180% (A) REJ

SAW-12CP, FLAW2 SQ SAW1–2Porosity RT— 23.25 1.38——— REJ

SAW-12CP, FLAW2 SQ SAW1–2Porosity UT— 24.1 3.2 0.2 0.275 (A) REJ

SAW-12CP, FLAW2 SQ SAW1–2Porosity PAUT 270 23.3 3.8 0.4 0.4 48% (C) REJ

SAW-12CP, FLAW3 SQ SAW1–2 LOF RT—————— MISS

SAW-12CP, FLAW3 SQ SAW1–2 LOF UT— 46.51 0.2 0.3−2 (A) REJ

SAW-12CP, FLAW3 SQ SAW1–2 LOF PAUT 90 46.6 0.84 0.3 0.58 42% (C) ACC

SAW-12CP, FLAW4 SQ SAW1–2 LOF RT— 4.5 0.3——— ACC

SAW-12CP, FLAW4 SQ SAW1–2 LOF UT—————— MISS

SAW-12CP, FLAW4 SQ SAW1–2— PAUT—————— MISS

HF1, FLAW 1 SQ ESW-NG2–2.5 LOF RT— 2.5 1.38——— REJ

HF1, FLAW 1 SQ ESW-NG2–2.5 LOF UT— 2.25 2.3−1 1.82 (A) REJ

HF1, FLAW 1 SQ ESW-NG2–2.5 LOF PAUT 90 1.98 2.27−1 2.19 35% (C) REJ

HF1, FLAW 2 SQ ESW-NG2–2.5 LOF RT— 8.5 1.5−1—— REJ

HF1, FLAW 2 SQ ESW-NG2–2.5 LOF UT— 8.2 1.7−1 0.4−22 (A) REJ

HF1, FLAW 2 SQ ESW-NG2–2.5 LOF PAUT—8 2.1−1 0.1 56% (B) REJ

HF1, FLAW 3 SQ ESW-NG2–2.5 LOF RT— 142——— REJ

HF1, FLAW 3 SQ ESW-NG2–2.5 LOF UT— 14.1 1.8−1 1.5−12 (A) REJ
41 

Plate and

Discontinuity ID 

Joint Type

Welding Process

Nominal Plate 

Thickness(Inches)

Discontinuity 

Character

Technique

(RT, Manual UT, 

PAUT)

UT Beam Direction

Start “ Y” Along 

Weld (Inches)

Length (Inches) 

Location “ X” 

Across (Inches) 

UT Depth (Inches)

Amplitude/Rating

D1.5 ACC/REJ

(Tensile)

(2)

HF1, FLAW 3 SQ ESW-NG 2–2.5 LOF PAUT 90 13.9 2.2 −1 1.5 69% (B) REJ

HF2, FLAW 1 SQ ESW-NG 2–2.5 LOF RT — 2.5 1.25 — — — REJ

HF2, FLAW 1 SQ ESW-NG 2–2.5 LOF UT — 3.5 1 −1.2 1.7 0 (A) REJ

HF2, FLAW 1 SQ ESW-NG 2–2.5 LOF PAUT 270 3.3 1.4 −1.1 2.1 52% (B) REJ

HF2, FLAW 2 SQ ESW-NG 2–2.5 LOF RT — 9 3.2 — — — REJ

HF2, FLAW 2 SQ ESW-NG 2–2.5 LOF UT — 9 2.5 — 1.7 −8 (A) REJ

HF2, FLAW 2 SQ ESW-NG 2–2.5 LOF PAUT 90 9.05 2.7 — 2.2 61% (B) REJ

HF2, FLAW 3 SQ ESW-NG 2–2.5 LOF RT — 18 4 — — — REJ

HF2, FLAW 3 SQ ESW-NG 2–2.5 LOF UT — 16.1 2.8 −1 1.8 −7 (A) REJ

HF2, FLAW 3 SQ ESW-NG 2–2.5 LOF PAUT 90 15.5 3.2 −1.2 2.2 174% (A) REJ

—No data.

ACC = accept; LOF = lack of fusion; MISS = missed discontinuity; REJ = reject; SQ = square; TUNG = tungsten; V2 = double vee. 

43 

CHAPTER 7. SUMMARY

The FHWA NDE Laboratory conducted a comprehensive study to assess the feasibility of using 

PAUT as an alternative to RT for inspecting complete joint penetration butt welds in bridge 

structures. The study aimed to understand the fundamental principles of PAUT and develop a 

preliminary technical approach, scan plans for 10 welded TPs, and test procedures based on 

AWS D1.5.

(2) The research team inspected 10 weld specimens using PAUT and compared the 

results with RT and UT test results. The comparative results demonstrated a strong correlation 

between PAUT, UT, and RT, indicating the effectiveness of PAUT in accurately measuring 

discontinuity dimensions. This positive correlation provided compelling evidence of PAUT’s 

capability as a viable alternative to RT for inspecting complete joint penetration butt welds in 

bridges.

However, the study team acknowledges the need for further data collection and evaluation of 

different defect types to confidently recommend the complete replacement of RT with PAUT. 

Additional efforts, such as expanded data collection, defect variation studies, and field 

applications are necessary to fully establish the reliability and applicability of PAUT in lieu of 

RT in bridge-weld inspections. 

Figure 35 summarizes the PAUT, UT, and RT inspection results categorized by the type of 

discontinuities. As depicted in figure 35, the data analysis results from PAUT generally 

demonstrated consistency with those obtained from RT. The lack of agreement in the 

acceptance/rejection of the discontinuities observed is likely attributed to the differences in 

acceptance criteria utilized in RT and PAUT.

(5)

Source: FHWA. 

Figure 35. Graph. PAUT, UT, and RT detection and rejection results. 

45 

CHAPTER 8. CONCLUSIONS

The comprehensive study highlighted good comparative results between PAUT, conventional 

UT, and RT measurements. While affirming PAUT’s reliability, the research emphasizes the 

necessity for a more extensive evaluation encompassing diverse weld discontinuities and joint 

types for an inclusive assessment. 

1. The results from PAUT, conventional UT, and RT had the following statistical 

correlations:

a. Depth measurements made with UT and PAUT had a correlation factor of 0.95, 

with a maximum, minimum, and average variance of 0.5, −0.6, and .004, 

respectively, and a standard deviation of 0.239. 

b. Length measurements made with RT and PAUT had a correlation factor of 0.89, 

with a maximum, minimum, and average variance of 0.8, −2.42, and −0.038, 

respectively, and a standard deviation of 0.658. 

c. Length measurements made with UT and PAUT had a correlation factor of 0.91, 

with a maximum, minimum, and average variance of 1.9, −1.6, and 0.0481, 

respectively, and a standard deviation of 0.596. 

2. The ultrasonic sound-beam, ray-path analysis carried out to develop the PAUT scan plans 

indicates a need to carry multiple scans along each side of the weld at different probe 

index point offsets from the weld centerline to ensure complete volumetric coverage of 

these relatively thick welds. This scanning approach is applicable to both equal thickness 

butt welds and transition thickness butt welds. 

3. The large-grain microstructure observed in electroslag welds did not influence the 

propagation of ultrasonic waves to a point where the detectability of the implanted flaws 

using 5 MHz shear wave transducer was affected. 

4. The primary objective of this research initiative was to establish PAUT as a viable and 

reliable alternative to radiography. The study results provide substantial support for 

achieving this objective. However, further enhancing the research by developing a more 

comprehensive set of weld discontinuities is essential. This expanded set should 

encompass various discontinuity types, additional welding processes, thicker and thinner 

joints, and tee and corner joints to ensure a fully representative discontinuity evaluation.

47 

CHAPTER 9. RECOMMENDATIONS

The study entailed inspecting 10 specimens that are representative of the weld joints commonly 

used in real-world bridge fabrication. Using the results obtained from this study as a foundation, 

further expansion, incorporating the provided recommendations, can be considered for future 

investigations in bridge weld quality assurance. 

1. Fabricate additional weld specimens to ensure a more complete matrix of representative 

discontinuity types, joint configurations, and plate thicknesses are addressed (including 

transverse discontinuities). The specific new specimen discontinuity types should be 

established after getting additional input from subject matter experts. The expected weld 

discontinuities include longitudinal cracks, transverse hydrogen-related cracks, 

incomplete fusion, incomplete penetration, slag, and piping porosity. 

2. Evaluate the feasibility of using advanced ultrasonic discontinuity modeling software to 

supplement the ultrasonic validation data. Through modeling, the ultrasonic response 

from discontinuities with a different type, size, length, and orientation can be predicted 

and evaluated in accordance with the AWS D1.5 criteria.(2) This modeling should limit 

the number of additional specimens to be fabricated and inspected. The small set of 

actual implanted discontinuities should also be modeled and used to physically validate 

the modeling and provide additional confidence in all the modeling results.

3. Evaluate time of flight diffraction (TOFD)(12) and other advanced UT techniques like 

two-dimensional PAUT arrays,(13)

 total focus method/full matrix capture,

(14)

 pitch-catch 

PAUT,

(13)

 and intermodal total focus method(15) to evaluate potential discontinuity 

detection and discontinuity sizing improvements. The use of TOFD techniques should 

support adding an accurate quantifiable acceptance criterion for this condition. AWS is 

considering adopting new acceptance criteria that utilize the discontinuity through wall 

height because of a general industry trend toward more of a fitness-for-service approach 

to ultrasonic acceptance criteria in lieu of the historic workmanship discontinuity signal 

amplitude-based criteria.

(3)

 TOFD techniques would also support the implementation of 

any type of a fitness-for-service approach.

49 

APPENDIX A. PROCEDURE

ULTRASONIC PHASED ARRAY EXAMINATION EQUIPMENT AND ACCESSORIES

The phased array equipment used in this research is capable of generating and displaying 

sectorial-scan (also called S-scan), B-scan, and C-scan images, which can be stored and recalled 

for subsequent review. 

The same couplant material, including batch number, where applicable, used for standardization

shall be used for examinations. Transducer and wedge shall be, as per table 5, for PAUT. The 

range of angles for the wedge used for inspection is 45°–70°. The scan shall be performed using 

a robotic arm (figure 36) that is programmed to maintain a fixed index offset from the weld 

center line.

An encoder interfaced with the phased array instrument shall be used to track the probe 

movement. The encoder shall be calibrated to coordinate its movement with the PAUT 

equipment. 

Table 5. Probe and wedge. 

Phased Array Transducers and Wedges

Probe Description Frequency (MHz) Number of Elements Element Pitch (inch

Linear array 5 64 0.019

Wedge—55° refracted shear wave wedge 

Source: FHWA. 

Figure 36. Photo. Robotic arm. 
50 

STANDARDIZATION

The equipment standardization was conducted in accordance with AWS D1.5.(2)

Horizontal Sweep

The horizontal sweep shall be adjusted to represent the actual material path distance throughout 

all the configured angles using an IIW block. If the joint configuration or thickness prevents full 

examination of the weld at these settings, the distance standardization shall be made at increased 

screen ranges as depicted in the scan plan.

TCG

The TCG shall be established throughout all configured angles at a minimum of three points 

throughout the material range to be tested in the TCG standardization block (figure 5). The TCG 

shall balance all standardization points within ±5 percent amplitude of each other. 

Encoder Standardization

The encoder shall be calibrated at least weekly and verified through daily in-process checks to be 

within 1 percent of measured length for a minimum of half the total scan length. Encoder 

resolution shall be configured so that data are taken at 1 mm (0.04 inch) increments. 

ACCEPTANCE CRITERIA

The standard sensitivity level (SSL), which determines the test sensitivity of the inspection, shall 

be established at 50 percent ±5 percent of full-screen height of the 1.5 mm (0.06 inch) reflector. 

This decibel level shall be noted as the primary reference level decibel. The automatic reject

level (ARL) shall be defined as 5 dB over SSL above which all discontinuities are rejected 

irrespective of position and size, which equals 89 percent FSH level The discontinuities with 

amplitude less than or equal to disregard level (DRL) shall be defined as 6 dB under SSL, which 

equals 25 percent FSH (figure 37), are always acceptable. The classification of discontinuities 

based on the amplitude level is provided in table 6. The length and amplitude-based acceptance 

criteria is presented in table 7. 
51 

 

Source: FHWA. 

Figure 37. Image. Sensitivity level.(2)

Table 6. Discontinuity classification. 

Discontinuity Classification Description

A >ARL

B >SLL, ≤ARL

C >DRL, ≤SLL

D ≤DRL

Table 7. PAUT acceptance criteria. 

Maximum Discontinuity 

Amplitude Level Obtained

Maximum Discontinuity Lengths by the Type of Loading

Compression Tension

Class A None allowed None allowed

Class B 0.78 inch 0.47 inch

Class C 1.96 inches Middle half of weld: 1.96 inches

Top or bottom quarter of weld: 0.78 inch

Class D Disregard Disregard
52 

EXAMINATION

The encoded line scanning at fixed offsets, as defined by the scan plan, will be performed during 

the data acquisition. The data will be collected at the primary reference level. The robotic arm 

scanner shall be used at a scan speed whereby data dropout shall not exceed 1 percent of the 

recorded data, and no two adjacent data lines shall be missed. The data collected shall be 

complete A-scans with no exclusionary gating and filtering other than the receiver band pass 

filter.

EVALUATION

During data evaluation, the gain shall be increased by 6 dB using the soft gain function in the 

evaluation software.

(11) The length of discontinuities shall be determined by measuring the 

distance between the transducer centerline locations where the indication rating drops 50 percent 

(6 dB) below the rating for the applicable discontinuity classification. The depth of the 

discontinuity is measured as the location of the peak amplitude at the angle producing the 

maximum signal amplitude.
53 

APPENDIX B. TEST RESULTS 

Typical results of the PAUT data acquisition and analysis steps of the test specimens are 

provided in this appendix. 

SPECIMEN TP1

Figure 38 through figure 42 cover specimen TP1. The specimen had the following 

characteristics:

• Weld type: SAW.

• Length: 25.0 inches. 

• Width: 26.5 inches.

• Height: 1–2 inches.

Source: FHWA. 

Figure 38. Photo. TP1 unprocessed etched. 
54 

Source: FHWA. 

Figure 39. Photo. TP1 etched image with weld edge traced.

Source: FHWA. 

" = inches.

Figure 40. Schematic. TP1 dimensions.

Source: FHWA. 

Figure 41. Schematic. TP1 CAD image with traced HAZ dimensions.
55 

Source: FHWA. 

Figure 42. Images. Composite scan view for test specimen TP1. 

Even though the researchers detected the same discontinuity at different IPs, they reported the 

discontinuity sizing from the data corresponding to the IP that had the discontinuity indication 

with the maximum length. In the test specimen TP1, for IP2 and offset 0, the first discontinuity 

was located at 1.68 inches from the start at a depth of 0.40 inch and was 1.32 inches in length.

The second discontinuity indication was observed in IP1 at a 6.0-inch offset, which was located 

at 13.10 inches from the start at a depth of 0.19 inch and was 1.19 inches in length.

SPECIMEN TP2

Figure 43 to figure 47 cover specimen TP2. The specimen had the following characteristics:

• Weld type: ESW-NG.

• Length: 28.0 inches. 

• Width: 24.5 inches.

• Height: 1.5 inches.
56 

Source: FHWA. 

Figure 43. Photo. TP2 unprocessed etched image. 

Source: FHWA. 

Figure 44. Photo. TP2 etched image with weld edge traced.
57 

Source: FHWA. 

Figure 45. Schematic. TP2 dimensions. 

Source: FHWA. 

Figure 46. Schematic. TP2 CAD image with traced HAZ with dimensions.

Source: FHWA. 

Figure 47. Image. Composite scan view for test specimen. 

For test specimen TP2, two discontinuity indications at position 0.64 and 13.30 inches from the 

start were reported at IP1. The lengths of these discontinuities were 2.42 and 5.43 inches, 

respectively, and the depth from the top surface was 0.73 and 0.45 inch, respectively. 
58 

SPECIMEN TP3

Figure 48 through figure 52 cover specimen TP3. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 22.0 inches. 

• Width: 23.5 inches.

• Height: 3.3 inches.

Source: FHWA. 

Figure 48. Photo. TP3 unprocessed etched image. 
59 

Source: FHWA. 

Figure 49. Photo. TP3 etched image with weld edge traced.

Source: FHWA. 

Figure 50. Schematic. TP3 dimensions.
60 

Source: FHWA. 

Figure 51. Schematic. TP3 CAD image with traced HAZ with dimensions.

Source: FHWA. 

Figure 52. Images. Composite scan view for test specimen TP3. 

For test specimen TP3, the team detected four indications in PAUT. They observed the first 

discontinuity in IP2 at an offset of 7.25 inches, located at 3.5 inches from the start at a depth of 

0.66 inch and a length of 1.1 inches. The second discontinuity indication was detected at IP1 at 

an offset of 0.35 inch, and the discontinuity was located at 10.1 inches from the start position at a 

depth of 0.36 inch from the top surface and length of this discontinuity was 5.3 inches. The third 

discontinuity indication was observed at IP1 at an offset of −7.25 inches and was located at 

21.2 inches from the start position, at a depth of 0.55 inch from the surface, and the length of this 

indication was measured as 2.4 inches. The fourth discontinuity indication was observed at the 

IP2 at an offset of 7.25 inches, the discontinuity was located at 22.4 inches from the start position 

at a depth of 3.0 inches, and the length of this discontinuity was measured as 1.2 inches.
61 

SPECIMEN TP4

Figure 53 through figure 57 cover specimen TP4. The specimen had the following 

characteristics:

• Weld type: SAW.

• Length: 36.5 inches. 

• Width: 18.0 inches.

• Height: 3.0 inches.

Source: FHWA. 

Figure 53. Photo. TP4 unprocessed etched image.(8)
62 

Source: FHWA. 

Figure 54. Photo. TP4 etched image with weld edge traced.(8)

Source: FHWA. 

Figure 55. Schematic. TP4 dimensions.
63 

Source: FHWA. 

Figure 56. Schematic. TP4 CAD image with traced HAZ with dimensions. 

Source: FHWA. 

Figure 57. Images. Composite scan view for test specimen TP4. 

The study team detected nine discontinuities in test specimen TP4. The discontinuities 

designated with numbers 3 and 4 were detected at IP1 at an index offset position of −5.7 inches 

(table 4). Discontinuity 1 was detected at IP1 and an index offset position of −3.2 inches. 

Discontinuity 2 was detected at an offset of −0.5 inch in IP2 position. Discontinuity 5 was 

observed at IP2, with an index offset position of 5.7 inches, and discontinuity 7 was detected at 

IP2, with an index offset position of 6.6 inches. Discontinuities 8 and 9 were detected at IP1 at 

an index offset of −0.5 inch. Although the discontinuities were observed in different offset scans, 

the amplitude and length vary in each scan position. 
64 

SPECIMEN TP5

Figure 58 through figure 62 cover specimen TP5. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 30.0 inches. 

• Width: 24.5 inches.

• Height: 1.5–2.7 inches. 

Source: FHWA.

Figure 58. Photo. TP5 unprocessed etched image. 
65 

Source: FHWA. 

Figure 59. Photo. TP5 etched image with weld edge traced. 

Source: FHWA. 

Figure 60. Schematic. TP5 dimensions.
66 

Source: FHWA. 

Figure 61. Schematic. TP5 CAD image with traced HAZ with dimensions.

Source: FHWA. 

Figure 62. Images. Composite scan view for test specimen TP5.

In the test specimen TP5, the team observed the first discontinuity indication at 2.02 inches from 

the starting position at a depth of 1.46 inches at the index position of −9.5, IP1.The second 

discontinuity indication was at 14.7 inches from the datum at a depth of 0.54 inch from the 

surface; the length of the indication was 2.2 inches, and it was detected in the IP2, 6.6-inch offset 

position. The third indication was observed at an offset of 3 inches at IP2, located at 23 inches 

from the start position at a depth of 0.47 inch and a length of 1.5 inches. 

SPECIMEN ESW-2CP 

Figure 63 through figure 67 cover specimen ESW-2CP. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 48.0 inches. 

• Width: 48.0 inches.

• Height: 2.0 inches.
67 

Source: FHWA. 

Figure 63. Photo. ESW-2CP unprocessed etched image.

Source: FHWA. 

Figure 64. Photo. ESW-2-CP etched image with weld edge traced.
68 

Source: FHWA. 

Figure 65. Schematic. ESW-2CP dimensions. 

Source: FHWA. 

Figure 66. Schematic. ESW-2CP CAD image with traced HAZ with dimensions. 

Source: FHWA. 

Figure 67. Images. Composite scan view for test specimen ESW-2CP. 

At IP1 and an offset of 5 inches, the researchers noted three discontinuities at 7.9, 33.56, and 

45.2 inches from the start at depths of 1.6, 0.79, and 1.7 inches, respectively. The lengths of the 

discontinuities were 0.51, 4.1, and 0.7 inches. Another discontinuity was located at datum with a 

length of 3.1 inches at a depth of 1.7 inches, and it was detected at an offset position of 5 inches, 

IP2. 
69 

SPECIMEN ESW-12CP

Figure 68 through figure 72 cover specimen ESW-12CP. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 48.0 inches. 

• Width: 48.0 inches.

• Height: 1.0–2.0 inches. 

Source: FHWA. 

Figure 68. Photo. ESW-12CP unprocessed etched image.
70 

Source: FHWA. 

Figure 69. Photo. ESW-12CP etched image with weld edge traced. 

Source: FHWA. 

Figure 70. Schematic. ESW-12CP dimensions.

Source: FHWA. 

Figure 71. Schematic. ESW-12CP CAD image with traced HAZ with dimensions.
71 

Source: FHWA. 

Figure 72. Images. Composite scan view for test specimen ESW-12CP at IP1. 

The research team detected two indications observed in PAUT analysis of the test specimen 

ESW 12-CP at an offset of 3 inches, IP2, and located at 0 and 45.5 inches from the datum, 

respectively. The indications were located at depths of 0.83 and 0.77 inch, respectively.

SPECIMEN SAW-12CP

Figure 73 through figure 77 cover specimen SAW-12CP. The specimen had the following 

characteristics:

• Weld type: SAW.

• Length: 48.0 inches. 

• Width: 48.0 inches.

• Height: 1.0–2.0 inches. 
72 

Source: FHWA. 

Figure 73. Photo. SAW-12CP unprocessed etched image.

Source: FHWA. 

Figure 74. Photo. SAW-12CP etched image with weld edge traced.
73 

Source: FHWA. 

Figure 75. Schematic. SAW-12CP dimensions.

Source: FHWA. 

Figure 76. Schematic. SAW-12CP CAD image with traced HAZ with dimensions. 

Source: FHWA. 

Figure 77. Images. Composite scan view for test specimen SAW-12CP at IP1. 

At the IP1, 0.25 offset, the team noted two discontinuities at 0 and 46.6 inches from the start at a 

depth of 0.12 and 0.58 inch, respectively. The lengths of the discontinuities were 0.8 and 0.84 

inch, respectively. Another discontinuity indication was observed at index offset 0.5, IP2, located 

at 23.3 inches from the datum and at a depth of 0.4 inch, and the length of this indication was 

measured as 3.8 inches.
74 

SPECIMEN HF1

Figure 78 through figure 82 cover specimen HF1. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 36.0 inches. 

• Width: 49.0 inches.

• Height: 2.0–2.5 inches.

Source: FHWA. 

Figure 78. Photo. HF1 unprocessed etched image.
75 

Source: FHWA. 

Figure 79. Photo. HF1 Etched image with weld edge traced.

Source: FHWA. 

Figure 80. Schematic. HF1 dimensions. 

Source: FHWA. 

Figure 81. Schematic. HF1 CAD image with traced HAZ with dimensions.
76 

Source: FHWA. 

Figure 82. Images. Composite scan view for test specimen HF1 at IP1.

The researchers observed the first discontinuity indication at an index offset of −2.5 inches, IP1, 

located at 1.98 inches from the datum position and at a depth of 2.19 inches. The length of this 

indication was measured as 2.27 inches. The second discontinuity was located at 8.06 inches 

from the datum point at a depth of 0.1 inch and a length of 2.1 inches. The team observed this 

indication at an offset position of −8 inches, IP1. The third discontinuity position was at 13.92 

inches from the datum, and the length and depth are 2.2 inches and 1.5 inches, respectively. The 

offset position for this indication was 4.5 inches, IP2. 

SPECIMEN HF2

Figure 83 through figure 87 cover specimen HF2. The specimen had the following 

characteristics:

• Weld type: ESW-NG.

• Length: 36.0 inches. 

• Width: 49.0 inches.

• Height: 2.0–2.5 inches. 
77 

Source: FHWA. 

Figure 83. Photo. HF2 unprocessed etched image. 

Source: FHWA. 

Figure 84. Photo. HF2 etched image with weld edge traced. 
78 

Source: FHWA. 

Figure 85. Schematic. HF2 dimensions.

Source: FHWA. 

Figure 86. Schematic. HF2 CAD image with traced HAZ with dimensions. 

Source: FHWA. 

Figure 87. Images. Composite scan view for test specimen HF2 at IP1.

The research team observed three indications in the test specimen HF2 at the index offset of

−4.2 inches, IP1. They located the first discontinuity at 3.3 inches from the datum at a depth of 

2.1 inches, and the second discontinuity at 9.05 inches from the datum at a depth of 2.2 inches. 

The team detected the third discontinuity at 15.5 inches from the datum at 2.2 inches from the 

surface. 
79 

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