Applying Ultrasonic Testing 

in Lieu of Radiography for 

Volumetric Examination of 

Carbon Steel Piping

Office of Nuclear Regulatory Research

NUREG/CR-7204

PNNL-24232
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infringe privately owned rights.
Applying Ultrasonic Testing 

in Lieu of Radiography for 

Volumetric Examination of 

Carbon Steel Piping

Manuscript Completed: May 2015

Date Published: September 2015

Prepared by: 

T. L. Moran, M. Prowant, C. A. Nove*, A. F. Pardini, 

S. L. Crawford, A. D. Cinson, and M. T. Anderson

Pacific Northwest National Laboratory

P.O. Box 999

Richland, WA 99352

*U.S. Nuclear Regulatory Commission

C. A. Nove, NRC Project Manager

NRC Job Code V6097

Office of Nuclear Regulatory Research

NUREG/CR-7204

PNNL-24232

 

iii

ABSTRACT

Confirmatory research is being conducted for the U.S. Nuclear Regulatory Commission at the 

Pacific Northwest National Laboratory to assess the effectiveness and reliability of advanced 

nondestructive examination methods as they are applied to pressure boundary components and 

other materials installed in light-water reactors. The work reported here provides an initial 

technical evaluation of the capabilities of phased-array ultrasonic testing to supplant traditional 

radiographic testing for detection and characterization of welding fabrication flaws in carbon 

steel welds. The work was performed on a limited set of piping girth welds and welded plates 

containing varied types and sizes of volumetric and planar fabrication flaws. Phased-array

ultrasonic data were acquired using transmit-receive shear waves at 4.0 and 5.0 MHz, and 

compared to consensus evaluations and computed radiography in correlating detection and flaw 

characterization capabilities. The results show that, for carbon steel, phased-array ultrasonic 

testing is capable of detecting all but very small volumetric flaws, and is much more capable of

detecting planar flaws than standard radiographic techniques. The study also shows that 

characterization of flaws using ultrasonic testing (i.e., determining whether a flaw is volumetric 

or planar in nature) can be highly subjective based on operator experience; thus, radiographic 

imaging may have an advantage over ultrasonic imaging in this regard. Finally, several 

technical knowledge gaps were discovered as a result of this work, including the lack of 

appropriate performance demonstration standards and robust acceptance criteria for fabrication

weld inspection (i.e., fitness for service versus workmanship standards).

v

FOREWORD

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code 

(Code) requires the nuclear power plant owner to use the requirements of the construction code 

for repair and replacement activities. Typically, the ASME Code requires the use of 

radiographic testing (RT) for examination of welds for fabrication baseline. Radiography is 

considered to be sensitive to typical welding fabrication-related flaws such as slag and porosity 

and provides a radiographic image as the permanent evidence of the examination. 

Unfortunately, radiography has several disadvantages, including: (1) high costs associated with 

the extensive number of personnel required to secure the area where the radiography is being 

performed, (2) disruption of work in nearby areas, and (3) the radiological dose related to both 

planned and potentially accidental exposures associated with transporting, positioning, and 

exposing a source for the radiographic examinations.

The nuclear industry would prefer to use ultrasonic testing (UT) in lieu of radiography for these 

fabrication examinations as UT does not have the disadvantages associated with RT. In 

addition, UT results may be obtained in near real-time, while there are time delays associated 

with obtaining RT results.

Several ASME Code Cases have been published that allow the use of ultrasonic testing in lieu 

of radiography for weld inspection. To date, none of these Code Cases have been approved by 

the U.S. Nuclear Regulatory Commission (NRC) as the NRC has several concerns about using 

UT in lieu of RT. 

In 2009, the NRC funded Pacific Northwest National Laboratory (PNNL) to perform a literature 

review (Moran et al. 2010) to help understand issues related to the interchangeability of UT and 

RT. The study included an assessment of the state-of-the-art in ultrasonic equipment and 

techniques, and how this technology compared to standard practice radiographic techniques. 

The study identified several significant technical gaps such as lack of performance standards

and acceptance criteria for fabrication/construction weld inspection (i.e., fitness for service 

versus workmanship standards).

The NRC funded confirmatory research at PNNL to address many of the gaps identified in the 

2009 study. Their work assessing the capability and effectiveness of using ultrasonic 

examinations in lieu of radiography for detecting welding fabrication flaws in carbon steel piping 

welds is described in this NUREG/CR. A key result is that phased array ultrasonic testing has 

the ability to successfully detect flaws in carbon steel welds to performance levels comparable 

to, or even greater than, that achievable with radiography when examinations are performed 

from both sides of the weld and the weld crown is removed; however, when access limitations 

exist, detection capability may be degraded. Another key result of this study was the 

determination that flaw characterization is very analyst subjective, thus the advisability of 

applying flaw type specific acceptance criteria (such as applying current workmanship 

standards) is questionable. The results provided in this NUREG/CR support a more robust 

technical basis for Staff reviews of both the proposed ASME Code Cases as well as licenseesubmitted relief requests. 

vii

CONTENTS

ABSTRACT .................................................................................................................................iii

FOREWORD.................................................................................................................................v

FIGURES.....................................................................................................................................ix

TABLES.....................................................................................................................................xiii

EXECUTIVE SUMMARY............................................................................................................xv

ACKNOWLEDGMENTS............................................................................................................xxi

ACRONYMS AND ABBREVIATIONS ....................................................................................xxiii

1 INTRODUCTION................................................................................................................1-1

2 BACKGROUND .................................................................................................................2-1

2.1 Motivation for Study ....................................................................................................2-1

2.2 Summary of Previous Work – Worldwide ...................................................................2-4

2.3 Overview of Applicable Weld Inspection Codes .........................................................2-5

2.4 Fundamental Differences Between UT and RT ..........................................................2-6

2.5 Conventional UT versus Phased-Array UT.................................................................2-8

3 LABORATORY SPECIMENS AND FLAWS .....................................................................3-1

3.1 Carbon Steel Pipe Specimens and Flaws...................................................................3-1

3.2 Navy Plate Specimens and Flaws ..............................................................................3-4

4 EQUIPMENT AND METHODS USED FOR PA-UT...........................................................4-1

4.1 Focal Laws..................................................................................................................4-1

4.2 Phased-Array Probes and Modeling...........................................................................4-2

4.2.1 4.0-MHz TRS Probe – Use of Existing Ultrasonic Phased Array......................4-2

4.2.2 5.0-MHz TRS Probe – Development of Optimized Phased Array.....................4-6

5 EQUIPMENT AND METHODS USED FOR RT.................................................................5-1

5.1 X-ray Vault ..................................................................................................................5-1

5.2 X-ray Machine.............................................................................................................5-2

5.3 X-ray Imaging Media...................................................................................................5-3

5.4 X-ray Imaging Hardware and Software.......................................................................5-4

5.5 X-ray Inspection Protocols ..........................................................................................5-5

5.6 Interpretation of Flaw True State Results ...................................................................5-7

5.7 PNNL RT Performed on the Navy Plates....................................................................5-8

6 LABORATORY ULTRASONIC RESEARCH VARIABLES...............................................6-1

6.1 PA-UT System ............................................................................................................6-1

6.2 Scanning Protocols.....................................................................................................6-3

6.2.1 Calibration for Carbon Steel Pipe......................................................................6-3
viii

6.2.2 Calibration for Navy Plates and Re-scan of Carbon Steel Pipe B1A ................6-3

6.2.3 Examination and Volume of Inspection.............................................................6-4

6.3 Indication Characterization .......................................................................................6-10

7 ANALYSIS OF INITIAL DATA...........................................................................................7-1

7.1 Piping Weld Assessment ............................................................................................7-1

7.1.1 Flaw Detection ..................................................................................................7-1

7.1.2 Flaw Sizing......................................................................................................7-23

7.2 Navy Plate Assessment............................................................................................7-26

7.2.1 Navy Flaw Detection and Characterization Protocol.......................................7-27

7.2.2 PNNL UT Flaw Characterization Study...........................................................7-27

7.2.3 Comparison of Navy RT with PA-UT for Flaw Detection and 

Characterization..............................................................................................7-32

8 CONCLUSIONS AND RECOMMENDATIONS..................................................................8-1

9 REFERENCES...................................................................................................................9-1

APPENDIX A – ANALYSIS SUMMARY – FROM INDUSTRY QUESTIONNAIRE ................. A-1

APPENDIX B – RT AND UT DETECTION RESULTS FOR ALL IMPLANTED AND 

BONUS FABRICATION FLAWS IN THE CARBON STEEL PIPING............ B-1
ix

FIGURES

3-1 Carbon Steel Pipe-to-Pipe (B1A, B2A, B3A, and B4A) Specimens Used for 

This Study; Various Fabrication Flaws Exist in Weld Regions ........................................3-2

3-2 Single Bevel Weld Configurations in the Carbon Steel Pipe Specimens: 

(a) Weld Crown Ground Flush, (b) Weld Crown Present.................................................3-3

3-3 Carbon Steel Navy Test Plate Numbers 10 (Upper Left), 18 (Upper Right), and 

23 (Lower); Various Fabrication Flaws Exist in Weld Regions ........................................3-5

3-4 Double-V Butt Weld Configurations Used in the Navy Carbon Steel Plates....................3-5

4-1 The ZETEC Advanced Phased-Array Calculator is Useful for Generating Focal 

Laws (left) and Simulating the Sound Field for the Focal Law (right) to 

Determine Idealized Beam Characteristics......................................................................4-2

4-2 4.0-MHz TRS Phased-Array Probe .................................................................................4-3

4-3 Phased-Array Directivity of the 4-MHz Array Steered to 15 Degrees from the 

Natural Refracted Angle of 60 Degrees. Off-axis grating lobe is present and 

indicated by the black arrow at approximately −34 degrees............................................4-4

4-4 Simulations of the Beams Created by the 4.0-MHz TRS Arrangement for 45, 

60, and 70 Degrees in 25.4-mm (1.0-in.) Thick Carbon Steel Pipe .................................4-5

4-5 Simulations of the Beams Created by the 4.0-MHz TRS Arrangement 

60 Degrees in 50.8-mm (2.0-in.) Thick Carbon Steel Plate.............................................4-5

4-6 5-MHz TRS Phased-Array Probe on Wedge Assembly ..................................................4-6

4-7 5.0-MHz Probe Directivity Model Steered 15 Degrees (top) and 20 Degrees 

(bottom). The onset of a grating lobe is shown in the bottom image indicated 

by the black arrow............................................................................................................4-8

4-8 5.0-MHz Probe, 60-Degree Beam Simulation on 25.4-mm (1.0-in.) Thick Pipe 

Component. Target focus at 3/4T (T = wall thickness). ..................................................4-9

4-9 5.0-MHz Probe, 60-Degree Beam Simulation on 50.8-mm (2.0-in.) Thick Plate 

Component. Target focus at 3/4T (T = wall thickness). ..................................................4-9

5-1 PNNL Radiography Facility and X-ray Vault....................................................................5-2

5-2 X-ray Machine..................................................................................................................5-3

5-3 X-ray Controller................................................................................................................5-3

5-4 RT Imaging Media and Placement ..................................................................................5-4

5-5 Reader and Screen Shot of SENTINEL Vision HR Software Application........................5-5

5-6 Penetrameter Image Quality Indicator.............................................................................5-5

5-7 Placement of Penetrameter on Pipe................................................................................5-6

5-8 Typical Radiographs Displaying the Use of a Penetrameter ...........................................5-7

5-9 (a) Example of the Specimen Set-up and Labeling for Plate 18 for CR 

Examination with the Radiographic Parameters. (b) Digital Image of a Section 

of Plate 18........................................................................................................................5-8
x

6-1 DYNARAY and Motor Control Drive Unit.........................................................................6-2

6-2 Automated Scanner and PA-UT Probes on Piping Specimen (top) and Navy 

Plate Specimen (bottom) .................................................................................................6-2

6-3 Flame Cut Edges of Plate 23...........................................................................................6-3

6-4 (a) ASME Code, Section XI, Inservice Inspection Volume – Inner 1/3 

Thickness and (b) Inspection Volume required for Repair/Replacement –

Entire Thickness ..............................................................................................................6-4

6-5 Axial Multi-line (a) and Raster (b) Scanning Looking for Circumferentially 

Oriented Flaws (parallel to weld centerline).....................................................................6-6

6-6 Techniques for Scanning that Use 1⁄2-V (first leg of sound), Full-V (second leg 

of sound), and 1-1/2–V (third leg of sound) .....................................................................6-7

6-7 True Depth, Focusing at a Fixed Depth, and Half Path, Focusing at a Fixed 

Part Path, Focal Styles are Demonstrated ......................................................................6-8

6-8 “0” Stamp Shown for Navy Plate 23 (etched lines drawn over with marker for 

scanning).........................................................................................................................6-9

6-9 PNNL’s Scanning Station 1 and Station 2 for Plate 10....................................................6-9

7-1 Example of Near-Side and Far-Side Designation in UT Data Analysis ...........................7-2

7-2 Description of a Typical PA-UT Analysis Screen Identifying Relevant Features 

and Locations of Weld Responses ..................................................................................7-3

7-3 Weld Schematic for Lack of Fusion .................................................................................7-4

7-4 Radiographic Image of Lack of Fusion ............................................................................7-4

7-5 Ultrasonic Image of Lack of Fusion .................................................................................7-5

7-6 Weld Schematic of Lack of Penetration (incomplete penetration)...................................7-6

7-7 Photograph and Radiographic Image of Incomplete Penetration....................................7-6

7-8 Ultrasonic Image of LOP..................................................................................................7-7

7-9 Weld Schematic of Crack ................................................................................................7-8

7-10 Radiographic Image of a Crack. Note: This image has been magnified 2X to 

enhance the visibility of the flaw for the reader................................................................7-8

7-11 Ultrasonic Image of a Crack ............................................................................................7-9

7-12 Weld Schematic of Slag...................................................................................................7-9

7-13 Radiographic Image of Slag Inclusions. Note: This image has been magnified 

6X to enhance the flaw visibility for the reader. .............................................................7-10

7-14 Ultrasonic Image of Slag................................................................................................7-11

7-15 Weld Schematic of Porosity...........................................................................................7-11

7-16 Radiographic Image of Cluster Porosity. Note: This image has been 

magnified approximately 2X to enhance the visibility of the flaw for the reader. ...........7-12

7-17 Ultrasonic Image of Porosity..........................................................................................7-13

7-18 Example of Bonus Flaws ...............................................................................................7-14
xi

7-19 Example of a Radiograph Being Converted into a Flaw Map Which is Used to 

Aid in Interpretation of Detection Capability of UT (blue) and RT (red) .........................7-14

7-20 RT and UT Detection Results for All Implanted (intentional) Fabrication Flaws ............7-15

7-21 RT and UT Detection Results for All Bonus (unintentional) Fabrication Flaws..............7-16

7-22 Example of LOF that was Not Detected by RT..............................................................7-17

7-23 Schematic of LOF and Concave Weld Root as Shown in 7-22 PA-UT and 7-24 

RT Images .....................................................................................................................7-17

7-24 RT Image of Concave Weld Root..................................................................................7-18

7-25 Bonus Flaws Missed by UT (38) or RT (32) ..................................................................7-19

7-26 Adjacent Flaws Easily Discernible with RT....................................................................7-20

7-27 Example of Side Wall LOF (D-scan view on left and C-scan view on right) ..................7-21

7-28 Schematic of a Phased-Array Multiple Angle Inspection...............................................7-22

7-29 Schematic of Phased-Array Inspection from Near and Far Side of the Weld................7-22

7-30 Example Radiograph Showing Sizing Methods Using RT Software..............................7-24

7-31 Length Measurement of Incomplete Penetration Flaw ..................................................7-24

7-32 Results of Independent Flaw Type Analysis..................................................................7-31

7-33 Flaw Map of Plate 18 Station 1, Axes Units are in mm..................................................7-33

7-34 Flaw Map of Plate 18 Station 2, Axes Units are in mm..................................................7-34

7-35 Flaw Map of Plate 10 Station 1, Axes Units are in mm..................................................7-35

7-36 Flaw Map of Plate 10 Station 2, Axes Units are in mm..................................................7-36

7-37 Flaw Map of Plate 23, Axes Units are in mm.................................................................7-37

xiii

TABLES

3-1 Range of Flaw Types and Sizes Contained in the Four Carbon Steel Pipe-toPipe Welded Specimens..................................................................................................3-4

3-2 Flaw Types and Range of Sizes Contained in the Navy Test Plates...............................3-6

4-1 Ultrasonic Array Physical Specifications..........................................................................4-7

6-1 Characteristics of Flaw and Geometric Indications........................................................6-10

7-1 RMSE Length Sizing Summary: (-) indicates typically under sizing and (+) 

indicates typically over sizing.........................................................................................7-26

7-2 Flaw Type Decision Matrix.............................................................................................7-29

7-3 Flaw Detection/Characterization Analysis between Navy Consensus Calls, 

PNNL UT, and PNNL RT Calls......................................................................................7-40

xv

EXECUTIVE SUMMARY

Because of varied operational considerations, commercial nuclear power plants (NPPs) replace 

components and their appurtenant systems, either partially or in-total, throughout their operating 

lifetimes. These replacements must be performed according to original fabrication codes, using 

the nondestructive examination (NDE) methods listed therein to determine if fabrication 

processes, such as welding, meet the acceptance standards required. Most U.S. fabrication 

codes and standards require radiographic testing (RT), one of the oldest NDE methods, to be 

performed in assessing the quality of these replacement components. However, the use of RT,

with its practical issues of potential radiation exposures, inherent delays in producing 

acceptance results, and ultimately higher costs to implement, make other volumetric NDE 

methods more attractive for current repair and replacement activities. The U.S. Nuclear 

Regulatory Commission (NRC) continues to receive requests from NPP licensees to allow the 

application of ultrasonic testing (UT) in lieu of RT for these replacements.

Both RT and UT are two internationally-recognized NDE methods that are commonly used to 

volumetrically interrogate structural materials and their welds. Historically, RT is the most 

widespread method applied to evaluate the fabrication of components used in U.S. nuclear 

power plants, while UT is prevalent for examinations of these components during their service 

lifetimes. Because of the physical manner in which each of these methods interacts with the 

materials being examined, varied capabilities and limitations exist with respect to flaw detection 

and characterization. Thus, while each method is capable of detecting a spectrum of flaws

resulting from fabrication welding processes, the differences in physical/material interactions 

can make each method sensitive to different flaw types—radiography tends to be best suited to 

detect volumetric flaws such as slag and porosity, while ultrasound is more capable of detecting

planar flaws such as cracks and lack-of-fusion. As a result of these differences, as well as in 

consideration of the inherent strengths of each of the methods, the two methods are not 

traditionally believed to be interchangeable; rather, they are complementary.

In recognition of the industry’s needs, the NRC requested that Pacific Northwest National 

Laboratory (PNNL) perform a limited scope evaluation to assess the capability and 

effectiveness of advanced phased-array UT (PA-UT) techniques for detecting and 

characterizing fabrication flaws in carbon steel piping welds. The PA-UT results have been 

compared to RT data acquired from current piping weld mock-ups and from a similar Navy study 

performed in the 1980s on carbon steel plate materials. Specific issues were identified that 

would need to be resolved in order for the NRC to generically accept UT in lieu of RT for welds 

fabricated during repair/replacement. Some of these issues include:

• Acceptance criteria must be defined for ultrasonic examinations performed during 

repair/replacement activities. If ASME Section III acceptance criteria are applied, the ability 

to characterize flaws as planar or volumetric is required. In contrast, applying ASME 

Section XI acceptance criteria alone may result in accepting welds with poor quality of 

workmanship.
xvi

• Detection reliability of UT for fabrication flaws has not been well documented. Ultrasonic 

examination at NPPs is primarily used for inservice examinations, and the method is wellsuited for detecting and sizing service-induced planar flaws (surface-connected). 

Fabrication examinations are aimed at finding surface and sub-surface flaws that result from 

the welding process including both planar and volumetric flaws.

• NPP materials, joint designs, welding methods, and expected flaw types are not typically 

represented by the few round-robin exercises performed during the 1980s and early 1990s.

Additionally, these older studies used somewhat outdated NDE methods such as 

conventional manual UT and film-based RT, as opposed to today’s methods such as 

encoded PA-UT and digital RT.

• Performance demonstration is the current approach used to qualify UT examinations in the 

nuclear industry. Requirements for performance demonstration for equipment, procedures, 

and personnel used for UT examinations in lieu of RT as applied to repair/replace activities 

are yet to be determined. Some issues remaining to be addressed are the numbers and 

types of flaws/mock-ups needed to demonstrate robust UT applications and what level of 

statistically-based acceptance criteria are needed to provide appropriate screening for 

competent UT systems, given that fabrication variables are different than those for inservice 

inspection.

• Documentation requirements/recordkeeping remains to be assessed. RT provides a record 

of the inspection in the form of the radiographic image. It is unclear as to the minimum 

record requirements that should be maintained for UT; for example, format of data, content, 

etc.

An open literature review was conducted to determine if significant issues that needed to be 

resolved to replace RT with UT had previously been investigated. The review identified four key 

factors, including detection capabilities, false call rates, costs, and procedural aspects. 

Detection capabilities are generally described with probability of detection (POD) curves, often 

determined through round-robin exercises. Eight significant round robins, or similar studies, 

carried out in the past 30 years were reviewed. 

The results of the round robins indicate that UT is superior to RT for detection of planar flaws; 

however, RT has been shown to be comparable or superior for detection of volumetric flaws. 

These results are strongly dependent on the particular UT techniques applied. Overall costs 

and procedural complexity appear to be comparable for both UT and RT. Sizing capability 

(closely linked to false call rates) has not been studied as extensively as detection, but the two 

techniques appear to be similar for flaw length sizing, while UT has an advantage for flaw 

(through-wall) depth sizing.
xvii

Conclusions from previous international work relevant to the current study include the following:

• POD comparisons are strongly dependent on the flaw type and orientation, and on 

evaluation criteria.

• RT is more sensitive to crack planes parallel to the RT beam, while UT is more sensitive to 

planes perpendicular to the UT beam direction.

• Both RT and UT show drops in sensitivity for misoriented cracks and for flaws smaller than 

1 mm.

• Encoded UT is vastly superior to non-encoded UT in terms of visualization and analysis of 

images, recordkeeping, and overall POD.

Some additional considerations:

• New welding methods may reduce the incidence of fabrication flaws.

• High-sensitivity encoded UT examinations (such as PA-UT) are slightly more expensive than 

non-encoded conventional UT, but should reduce risk and down-time later in the operating 

lifetime of the plant, as recorded data images of examination weld volumes provide valuable 

baseline information used to characterize reflections detected during subsequent 

examinations.

• UT performance demonstration methods have been developed primarily for examinations 

aimed at detecting service degradation. These methods will likely need to be modified for 

volumetric fabrication examinations as fabrication flaw types are significantly different than 

those resulting from service degradation.

Empirical laboratory work to assess PA-UT capabilities and limitations in detecting and 

characterizing fabrication flaws was performed on several carbon steel welds. Four carbon 

steel pipe-to-pipe full penetration butt-welded specimens, three representing ASME Code,

Section III, Class 2 piping welds and one representing ASME Code, B31.1 (Pressure Piping) 

welds, were obtained from various nuclear inspection vendors. These piping weld mock-ups 

had been fabricated by the inspection vendors in order to assess their own PA-UT procedures 

and provide limited demonstrations of capability for their clients. In addition, three HY-80 steel 

welded test plates, two fabricated with purposely induced discontinuities and one removed from 

a decommissioned submarine hull (all on loan to PNNL from the Naval Surface Warfare Center, 

Carderock Division) were examined. PNNL performed PA-UT and computed radiography to 

provide data for making the comparative assessments detailed in this report.

The results of the laboratory investigations show that PA-UT is capable of detecting all planar 

flaws in the piping specimens that were observed using digital radiography, except for two small 

lack of fusion flaws that were approximately 1.8 mm ( 0.07 in.) and 3.8 (0.14 in.) in length. PAUT also detected five implanted and 32 bonus (non-intentional) planar flaws that went 

undetected using RT. Further, PA-UT was shown to be capable of detecting all but one of the 

intended volumetric flaws observed in radiographic images. As implemented, PA-UT did not 

detect 35 bonus (non-intentional) volumetric flaws imaged by RT; most (31 of 35) of these were
xviii

nominally less than 4 mm (0.15 in.) in size. This value is smaller than the theoretical focal spot 

size of the PA-UT probe at these metal paths. It is believed the non-detections may be the 

result of the amplitude threshold that was set to eliminate the need to analyze many very small 

reflectors.

In terms of flaw characterization, PNNL applied a decision protocol similar to what is being 

performed by industry analysts when determining whether the flaws are volumetric or planar in 

nature. The initial use of this protocol, or decision matrix, resulted in poor corroboration 

between three PNNL analysts when using limited weld volume data because of the presence of 

weld crowns. The OD weld crowns prevented full scans over the volumes of interest producing

shortened, or restricted, amplitude and signal echo-dynamic responses for certain beam angles

needed to inform the analysis process.

However, when full volume scans of specimens could be made where weld crowns had 

previously been removed (ground flush), results of analyst-defined volumetric or planar flaw 

characterizations appeared to markedly improve. This indicates that field weld crown removal 

may be necessary in order to assist in flaw characterization.

It was noted that certain ultrasonic responses do not display all of the “ideal” characteristics for 

each of the flaw attributes being assessed by a standard decision matrix; this requires analysts 

to choose which flaw attributes are more valued, or weighted, over others when characterizing 

flaws as being either volumetric or planar. The use of a weld cross-sectional profile over-laying 

the PA-UT images was helpful in locating a flaw within the weld volume, but there is analyst 

subjectivity in placement of this overlay, which could also affect flaw typing. Thus, the results 

illustrate the subjective, analyst-dependent nature of using PA-UT (even with a decision matrix) 

to differentiate varied fabrication flaw types. It is recommended that all performance-based 

methods and mock-ups developed to demonstrate personnel capability include sufficient 

variability of flaw types for assessing these characterization skills.

In the nuclear industry, radiography has historically been the primary NDE method for 

fabrication flaw acceptance, while UT has widely been the volumetric method of choice for 

detecting service-induced degradation. Fabrication examinations include the entire volume of 

the weld and adjacent base material, and are aimed at detecting welding flaws that may occur 

anywhere within this defined volume of interest. Conversely, inservice examinations are 

generally aimed at material volumes subject to service degradation, such as at the inner onethird of piping welds, including the heat-affected zone and limited adjacent base materials. 

Additionally, ultrasonic techniques for piping weld examinations have evolved to provide 

focused sound fields near the inside diameter for detection of surface-connected cracks, 

because this is where the preponderance of service degradation has occurred. As a result of 

these differences, as well as in consideration of the inherent strengths of each of the methods, 

UT and RT are not believed to be interchangeable, but complementary.

Issues remain to be addressed in order for the NRC to consider UT as a viable alternative to RT 

for repair and replacement activities in nuclear power plants. For instance, it is clear that PA-UT 

has the ability to successfully detect flaws in carbon steel welds at performance levels 

comparable to, or even greater than, that achievable with RT when examinations are performed 
xix

from both sides of the weld and the weld crown is removed. However, PA-UT may result in 

degraded detection capability when only single-side weld access is available; even more so if 

weld crowns remain in place. Overall, PA-UT sizing of fabrication flaws in carbon steel piping 

welds fell within tolerances that may be considered acceptable for certain performance criteria, 

such as that found in ASME Section XI, Appendix VIII. However, the applicability of this 

acceptance standard, having been derived from performance demonstrations on planar cracklike flaws, to welding fabrication flaws, is questionable. Further, in terms of characterization 

required for the application of ASME Code, Section III-type flaw acceptance criteria, the results 

of this study indicate that the ability to adequately characterize flaws as either planar or 

volumetric is very analyst subjective. Thus, whether it is appropriate to apply current welding 

fabrication acceptance criteria, which is highly dependent on UT characterization, also remains 

questionable.

An area outside the scope of the work reported here is the industry-proposed application of 

established standards governing UT performance demonstrations for service-induced flaws 

(cracks) to UT performance demonstrations for full-volume weld examinations aimed at 

detecting welding fabrication flaws. It is unclear whether direct application of these existing 

standards will result in acceptable and reliable performance results. As such, a full assessment 

of appropriate performance demonstration requirements for fabrication UT remains to be 

performed.

Finally, because the PA-UT method is predominately being used in lieu of RT for piping 

replacements in limited systems at selected operating NPPs (e.g., for ASME B31.1 

examinations), only PA-UT was assessed in this study. Whether conventional UT methods 

could be successfully applied for these applications remains unknown at the present time. 

Further, this work was limited to fine-grained, carbon steel piping butt welds. No conclusions 

should be drawn regarding the applicability of UT in lieu of RT for other nuclear power plant 

weld materials or configurations.

xxi

ACKNOWLEDGMENTS

The work reported here was sponsored by the U.S. Nuclear Regulatory Commission (NRC) and 

conducted under NRC Job Code Number V6097. Carol Nove was the NRC project manager for

this work and provided valuable guidance, technical direction and input to this report. 

The authors would like to express their gratitude to Jeff Devers and Todd Blechinger from LMT 

Inc., a business unit of Curtiss-Wright Flow Control Company, for professional expertise in 

assessing fabrication flaws and supplying materials used in laboratory tests. The authors also 

thank Gordon Forster at Ameren UE Callaway Plant for the use of three piping qualification 

specimens; and Dick Collins, Bruce Bandos, and Robert DeNale from the United States Navy, 

Naval Surface Warfare Center, Carderock Division, for the loan of three carbon steel Navy plate 

specimens, as well as access to a David Taylor Research Center Report, Ultrasonics as an 

Alternative to Radiography for Submarine Hull Weld Inspection, DTRC-SME-90/30, which is 

available only by request to the Commander, Naval Seas Systems Command (SEA 05M2).

PNNL thanks Mr. John Keve and Mr. Nick Furth, the AREVA Federal Services ASNT Level III 

and Level II inspectors, for conducting radiographic analyses on some of the pipe specimens.

At PNNL, the authors would like to thank Dr. Pradeep Ramuhalli for his technical contribution

early in this project. The authors wish to thank Michael Larche for figure development in 

SolidWorks and Photoshop. Finally, the authors would like to express their gratitude to 

Kay Hass for preparing the manuscript, technical editing, and attention to detail in the 

production of this report.

xxiii

ACRONYMS AND ABBREVIATIONS

ASME Code ASME Boiler and Pressure Vessel Code

ASME American Society of Mechanical Engineers

CR computed radiography

dB decibel

FS far-side

FSH full screen height

ID inner/inside diameter

ISI inservice inspection

LOF lack of fusion

LOP lack of penetration

NDE nondestructive examination

NPP nuclear power plant

NRC U.S. Nuclear Regulatory Commission

NS near-side

OD outer/outside diameter

PA phased array

PA-UT phased-array ultrasonic testing

PNNL Pacific Northwest National Laboratory

POD probability of detection

POR porosity

PSI pre-service inspection

RMSE root-mean-square error

RT radiographic testing

RRA repair and replacement activities

SLG slag

SNR signal-to-noise ratio

T wall thickness

TRS transmit-receive dual shear-wave

UT ultrasonic testing

1-1

1 INTRODUCTION

The U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Reactor Regulation (NRR) 

requested the Office of Nuclear Regulatory Research to evaluate the interchangeability of 

radiographic testing (RT) and ultrasonic testing (UT) for welds fabricated during repair and 

replacement activities. NRR intends to use the research results to support regulatory decisions 

associated with examinations required by the American Society of Mechanical Engineers 

(ASME) Boiler and Pressure Vessel Code (Code), Section XI, “Rules for Inservice Inspection of 

Nuclear Power Plant Components.” Specifically, NRR intends to use the findings of this 

research to evaluate licensees’ requests for relief from ASME Code requirements, and 

proposed changes to the ASME Code, as well as Code Cases.

While RT and UT are both volumetric nondestructive examination (NDE) methods, the physics of 

these processes are substantially different. Radiography relies on transmission and 

absorption/attenuation of small wavelength electromagnetic energy (x-rays and gamma rays). 

Ultrasonic testing, on the other hand, 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. Though 

each method is capable of detecting the spectrum of flaws that may result from welding 

processes, the differences in the physics make each method sensitive to a particular flaw type—

radiography is suited to detect volumetric flaws such as slag and porosity, while ultrasound is

more suited to detect planar flaws such as cracks and lack-of-fusion. 

Historically, in the nuclear industry, RT examinations have been performed for fabrication 

acceptance examinations, and UT examinations have been conducted to detect service-induced 

degradation, which is typically manifested as surface-connected cracking or corrosion. Per 

ASME Code, fabrication examinations target the entire volume of the weldment and adjacent 

base material, and are aimed at detecting fabrication-related flaws that may occur anywhere 

within the defined volume of interest. Conversely, inservice examinations typically only 

interrogate material volumes subject to service degradation, such as the inner one-third of 

piping welds, including the heat-affected zone and limited adjacent base material. Ultrasonic 

techniques for piping weld examinations have generally evolved to focus on finding inner 

diameter (ID) surface-connected cracks because this is where the preponderance of service 

degradation has occurred. As a result of these differences, as well as in consideration of the 

inherent strengths of each of the methods, the two methods are not traditionally believed to be 

interchangeable; rather, they are complementary. Further, the NRC questions whether the 

application of current ASME Code, Section XI, Appendix VIII, requirements for performance 

demonstration of ultrasonic methods being used for inservice inspection (ISI) are appropriate to 

be used for performance demonstration for UT of weld fabrication examinations.

This report presents a study conducted at Pacific Northwest National Laboratory (PNNL) to 

assess the capability and effectiveness of using ultrasonic examinations in lieu of radiography 

for detecting welding fabrication flaws in carbon steel piping. Section 2 of this report describes 

the project background and technical decisions that led to this study on carbon steel piping 

welds. Section 3 describes the carbon steel pipe and plate specimens, including details on 

sizes and flaw types, and range of sizes, for the varied flaws evaluated. The design, modeling,
1-2

and implementation of the phased-array probes used in this study can be found in Section 4. 

Section 5 provides a description of the x-ray equipment and procedures used on the carbon 

steel pipes and Navy plate specimens. Section 6 details the use of the phased-array system 

and specific methods employed for the evaluation of the carbon steel specimens in this study. 

Section 7 includes an assessment and comparison of the capabilities of UT and RT on 

fabrication flaws in carbon steel piping and plate welds. Section 8 provides a summary of the 

study, with conclusions and recommendations. Section 9 is a list of references.
2-1

2 BACKGROUND

2.1 Motivation for Study

In 2009–2010, the NRC Office of Research funded PNNL to conduct a literature survey and 

perform an analysis to assess the technical gaps related to replacing radiographic examination 

with ultrasonic examination for newly fabricated welds. The results of the gap analysis were 

documented in PNNL-19086, Replacement of Radiography with Ultrasonics for the 

Nondestructive Inspection of Welds – Evaluation of Technical Gaps – An Interim Report (Moran 

et al. 2010). This assessment revealed that in order to use UT in lieu of RT, as proposed in 

several ASME Code Cases under development, there are many outstanding issues that must 

be resolved including: 

• Assessing the flaw types, locations, sizes, and numbers expected with currently used 

welding fabrication methods;

• Establishing an appropriate “fitness for purpose” acceptance criteria for fabrication/

construction weld inspections, and assessing the ability of the UT method to discriminate 

between different types of relevant fabrication flaws;

• Determining the appropriate technique(s) to be specified (such as spatial encoding) within 

the UT method to be applied; 

• Defining minimum performance demonstration requirements for construction/fabrication 

inspection in light of the fact that the inspection volumes and expected flaw types are very 

different than those related to ISI; and

• Addressing gaps in the ASME Code and providing a technical basis for making 

recommendations for improvements.

Following the gap analysis, the NRC funded a program entitled “Effectiveness and Reliability of 

UT and RT for NDE” at PNNL to begin to address the outstanding issues identified above. As 

work progressed on this program, the specific issues that would need to be resolved in order for 

the NRC to generically accept UT in lieu of RT for welds fabricated during repair and 

replacement activities began to come into focus. To provide clarification and communicate 

these issues, the NRC staff created a list of concerns and presented it to industry to illustrate 

that, although UT is used successfully for Code-required examinations via ISI, the use of UT in 

a repair/replacement scenario was not a matter of simply changing a few aspects of current 

inservice inspection UT procedures. The following are the NRC’s considerations for assessing 

UT for use in lieu of RT (not necessarily in order of relevance or priority):

• The NRC acknowledges that UT has great potential to be used in lieu of RT for repair and 

replacement activities. The benefits of reduced inspection time and occupational exposure 

are significant. However, history has shown that the combined use of RT for weld 

fabrication examinations followed by the use of UT for pre-service inspections (PSI) and ISI

ensures that workmanship is maintained (with RT) while potentially critical, planar fabrication 

flaws are not put into service (with UT). Until studies are completed that demonstrate the 

ability of UT to replace RT for RRA, the NRC is not inclined to generically allow the 

substitution of UT in lieu of RT for weld fabrication examinations.
2-2

• Acceptance criteria: Acceptance criteria must be defined for ultrasonic examinations 

performed during repair/replacement activities. If Section III acceptance criteria are applied, 

the ability to characterize flaws as planar or volumetric is required. In contrast, applying 

Section XI acceptance criteria alone may result in accepting welds with poor workmanship.

• Performance demonstration requirements: What are the requirements for performance 

demonstration for UT equipment, procedures, and personnel used for examinations for 

repair/replace activities? Some issues to be addressed are: what are the required 

flaws/mock-ups and what are the acceptance criteria for length and depth sizing of 

fabrication flaws?

• Materials applicability: Round-robin studies comparing RT and UT performance with a view 

to replacing RT with UT are relatively scarce. Most studies took place in the 1980s and 

early 1990s using manual ultrasonics and film radiography. NPP materials, joint designs, 

welding methods, and expected flaw types are not typically represented by these studies. 

Thus, assessments must be conducted of UT in lieu of RT for NPP materials, using today’s 

UT and RT methods, with a focus on understanding UT applicability in the presence of high 

levels of acoustic noise such as that found in austenitic materials.

• Component applicability: Once a fundamental understanding of UT in lieu of RT is obtained 

via a study with limited scope (piping only), an assessment of the extent of applicability to 

components with complex geometries or other limitations is needed. 

• Examination volume for fabrication: The repair/replacement examination volume is the full 

volume of the weld plus adjacent base material including the heat-affected zone. The ISI 

examination volume is the lower 1/3T plus 1⁄4-in. on either side of weld toe for similar and 

dissimilar metal welds in piping (from ASME Section XI, Figure IWB-2500-8) (ASME 2008). 

Thus, issues such as whether weld crown removal is necessary and what wave modalities 

are required (or allowed) must be addressed to enable full-volume weld examinations. 

Scaling up qualified ISI examination procedures may work, but this must be demonstrated.

• Equipment requirements: Beyond the use of UT methods that encode position and 

amplitude, are there other minimum equipment requirements that must be identified/defined 

such as the use of pulse-echo/phased-array/pitch-catch probes, angle of inspections and 

scan directions, acoustic frequencies employed and the use of first leg only, or first and 

second leg of sound propagation?

• Documentation requirements/record keeping: RT provides a permanent record of the 

inspection in the form of the radiograph. What is required for UT (e.g., format, content, 

etc.)?

• Detection reliability: There is a need to establish that UT can reliably detect and 

characterize fabrication flaws. Ultrasonic examination at NPPs is used for PSI and ISI, and 

the method is well-suited to detecting and sizing service-induced type flaws (surfaceconnected). Fabrication examinations are aimed at finding surface and sub-surface flaws 

that result from the welding process. Additionally, the fabrication acceptance criteria require 

the discrimination of planar vs. volumetric flaws. Does UT provide an adequate ability to 

discriminate between planar and volumetric flaws?
2-3

• Sizing reliability: How do UT and RT compare in their ability to length-size flaws? Does UT 

oversize fabrication flaws? It is noted that UT has an advantage as depth-sizing and 

through-wall locations of flaws are readily determined with UT.

As illustrated by the list above, there are several issues that the NRC staff considers important

to address before generically accepting the use of UT in lieu of RT for repair and replacement 

activities. When the NRC developed the program, the original plan was to look broadly at these 

issues as they applied to a variety of NPP piping materials (carbon steel, stainless steel, and 

dissimilar metal piping welds), welding methods, and sizes (diameters and thicknesses). It 

quickly became apparent that this broad range of applicability combined with the many issues 

that needed to be resolved (the listed items) were beyond the scope of what could be 

accomplished in this initial program. Additionally, feedback from industry suggested that, 

although there is broad desire to use UT in lieu of RT for all NPP welds, the majority of 

upcoming plant RRA would be conducted on carbon steel piping systems. As a result, a 

decision was made to focus the work on carbon steel piping welds. 

Further confirming that this was the correct path for the PNNL project was that in the same 

timeframe, the ASME Code Task Group on Alternate NDE for Repair Replacement Activities 

(TG Alt NDE for RRA) made the decision to stop working on Revision 1 to Code Case N-713, 

“Ultrasonic Examination in Lieu of Radiography,” which applied generically to any material, and 

start work on a new, ferritic-only Code Case, N-831, “Ultrasonic Examination in Lieu of 

Radiography for Welds in Ferritic Pipe.” The TG Alt NDE for RRA members recognized that a 

Code Case focused on carbon steel would be more likely to gain NRC support while addressing 

the majority of repair/replace activities that licensees were implementing at NPPs.

Once the scope of the program was limited to carbon steel welds only, the NRC and PNNL 

wanted to ensure that a broad range of thicknesses of carbon steel welds representing the 

range of thicknesses found in NPPs were evaluated. Unfortunately, thick-section carbon steel

mock-ups with implanted flaws were not readily available. However, several Navy “UT/RT” 

plates were still available. These plates were studied by the Navy in the late 1980s when the 

Navy evaluated UT in lieu of RT for submarine hull weld inspection. The Navy round robin 

compared the results of standard practice manual UT to radiography using three types of 

radiation sources and two types of film on 36 test plates (18 welded for the study and 18 cut 

from a decommissioned submarine). During the study, the Navy identified 212 “consensus” 

flaws in the plates and used the most sensitive technique that detected each of the flaws to 

classify them by type. Sectioning and metallography were performed on several of the plates to 

confirm whether the Navy’s classification protocol was accurate. Though the Navy work was 

conducted over two decades ago, several of the UT/RT test plates still existed, and three were 

made available by the Navy. The goals for including these three test plates in the PNNL study 

were to determine whether UT technology and examination techniques currently used in the 

nuclear industry would support the Navy’s conclusion that UT is a good alternative to RT for 

weld inspection (for thick-section carbon steel welds), and to expand the weld thickness range 

being evaluated under this program.
2-4

2.2 Summary of Previous Work – Worldwide

The topic of replacing radiography with ultrasonic evaluations has received significant attention 

in the past. This section highlights and summarizes information obtained from open literature

reviews pursuant to this issue. Detailed information can be found in Moran et al. (2010).

The review identified four key factors, including detection capabilities, false call rate, costs, and 

procedural aspects. Detection capabilities are generally described with probability of detection 

(POD) curves, often determined through round-robin exercises. As described in Moran 2010, 

several round robin exercises (Forli 1979; Forli and Hansen 1982; Forli and Pettersen 1985; 

DeNale and Lebowitz 1989, 1990; Forli 1990),

1 or similar studies (Ford and Hudgell 1987; Brast 

et al. 1998; Erhard and Ewert 1999; Neundorf et al. 2000; Neundorf et al. 2002; Light 2004; 

Spanner 2005), carried out in the past 30 years indicate that UT is superior to RT for planar 

flaws; however, the evidence appears to show that RT is comparable or superior to UT for 

volumetric flaws. These results are strongly dependent on the particular UT techniques applied. 

Overall costs and procedural aspects appear to be comparable for both UT and RT. Sizing 

capability (closely linked to false call rates) has not been studied as extensively as detection, 

but the two techniques appear to be similar for flaw length sizing, while UT has an advantage for 

flaw (through-wall) depth sizing.

Several ASME Code Cases have been developed that address the use of UT in lieu of RT for 

weld inspection. All require the application of spatially-encoded ultrasonic systems, formal 

demonstration of performance prior to field use, and specific flaw acceptance criteria. Several 

of the ASME Code Cases make use of fracture mechanics to supplant workmanship standards 

with probabilistic risk-based standards. There has been some case-by-case user experience 

with the Code Cases, but no reliability data has been provided.

Relevant conclusions from previous work include the following:

• POD comparisons are strongly dependent on the flaw type and orientation, and on 

evaluation criteria.

• RT is more sensitive to crack planes parallel to the RT beam, while UT is more sensitive to 

planes perpendicular to the UT beam direction.

• UT is affected adversely by coarse-grained microstructures, material anisotropy, surface 

conditions, and other factors associated with acoustic scattering and attenuation.

• Both RT and UT show reductions in sensitivity for misoriented cracks and for flaws smaller 

than 1 mm.

• Encoded UT is vastly superior to non-encoded UT in terms of visualization and analysis of 

images, recordkeeping, and overall POD.

 1 DeNale R and C Lebowitz. 1990. Ultrasonics as an Alternative to Radiography for Submarine 

Hull Weld Inspection. DTRC-SME-90/30, Office of the Assistant Secretary of the Navy, Naval 

Sea System Command, David Taylor Research Center, Bethesda, Maryland. Available only by

request to the Commander, Naval Seas Systems Command (SEA 05M2).
2-5

Some additional considerations:

• New welding methods have reduced the incidence of flaws.

• High-sensitivity encoded UT examinations (such as phased-array UT) may be more 

expensive than non-encoded conventional UT, but should reduce risk and down-time later in 

the operating lifetime of the plant, as recorded data images of examination weld volumes 

provide valuable baseline information used to characterize reflections detected during 

subsequent examinations.

• UT performance demonstration methods have been developed primarily for examinations 

aimed at detecting service-induced degradation. These methods will likely need to be 

modified for volumetric fabrication examinations as fabrication flaw types are significantly 

different than those resulting from service-induced degradation.

2.3 Overview of Applicable Weld Inspection Codes

Title 10 of the Code of Federal Regulations (CFR) Part 50.55a(b) requires that licensees of 

operating U.S. nuclear power plants apply ASME Code Section III, Rules for Construction of 

Nuclear Facility Components, and Section XI, Rules for In-service Inspection of Nuclear Power 

Plant Components. The use of NDE methods for welded components is specified by ASME 

Code, Sections III and XI. In order for a defense-in-depth approach to be successful and to 

facilitate timely corrective actions, NDE must reliably detect and accurately characterize 

degradation that may occur before it reaches a size that could challenge the structural integrity 

of components (Doctor 2007).

ASME Code, Section III (Division 1, Articles NB/NC/ND) defines the volumetric examination 

methods to be applied for fabrication/construction of welds in nuclear components. Specific 

NDE techniques found acceptable for use are described in ASME Code, Section V (Article 2 for 

Radiographic Examination and Article 4 for Ultrasonic Examination). PSI and ISI are defined in 

ASME Code, Section XI. Where volumetric examination methods (UT or RT) are specified, the 

examinations are required to be performed in accordance with Section V, Article 2 for RT or 

Section XI, Appendix I for UT.

As one would expect, acceptance criteria for fabrication/construction, and PSI/ISI, are also 

defined in the relevant ASME Code sections (Section III for fabrication and Section XI for PSI 

and ISI). Acceptance of fabrication flaws is based on welding workmanship standards and not 

on fitness-for-service, with flaw type and length being the primary variables used for 

accept/reject criteria. The through-wall size or though-wall location of the flaw does not factor 

into these acceptance criteria (Doctor 2007). Traditionally, RT has been used versus UT for 

weld fabrication examinations. In contrast, criteria for accepting flaws discovered during PSI 

and ISI are based on fitness-for-service structural considerations founded upon fracture 

mechanics evaluations. UT is the preferred choice for volumetric NDE during PSI/ISI.

Several other industry codes on nondestructive examination of welds are available. In the 

United States, examples include NAVSEA T9074-AS-GIB-010/271 (CHG NOTICE 1) and MILSTD-2035A.
2-6

2.4 Fundamental Differences Between UT and RT

The objective of weld inspection is to detect construction/fabrication flaws, or service-induced

degradation, that may impact the structural integrity of the welded component. Because UT and 

RT are the primary volumetric methods employed to inspect welds, an understanding of the 

underlying physics associated with these types of inspections is important for comparing the 

capabilities and limitations of each method. 

RT relies on transmission and absorption/attenuation of short-wavelength, high-energy

electromagnetic waves through the component under examination to essentially provide a 

direct, two-dimensional image of the component on a detector. UT uses high-frequency 

vibrational (acoustic) waves to transmit energy through a material and relies on reflection of 

these waves from internal structures (flaws, geometry, metallurgical interfaces) to provide 

indirect indications of potential defects. These important differences between RT and UT will 

either help or hinder the detection of specific types of anomalies.

One type of weld anomaly occurs when gas is caught within the weld as it solidifies. These 

small gas pockets are typically known as porosity, and may discretely occur throughout the weld 

or can be clustered together in close proximity. Electromagnetic radiation in the RT process 

passes directly through the welded material and is affected by density variations in the weld. 

The porosity is much less dense than the surrounding material; therefore, less attenuated, 

higher levels of radiation will be received by the detector (film, phosphor plate, etc.). This will 

result in the porosity being shown as a darkened shape on the image. The actual shape of the 

porosity has very little effect, if any, on whether it can be detected with RT. This type of 

anomaly is considered volumetric in that there is a three-dimensional quality, or volume,

associated with the gas pocket. Inclusions are another type of volumetric indication where 

instead of being entrapped gas, they may contain foreign materials such as tungsten, or slag

(flux) from the welding process. These types of indications tend to have shapes that include

volumes with large density variations in contrast to the surrounding material; thus, they are 

readily imaged using the RT process. In contrast, ultrasonic examination is dependent on the 

reflection of acoustic waves from abrupt interfacial changes within material structures directly 

related to mismatches in acoustic impedance. While planar interfaces (such as cracks) may 

adequately reflect sufficient UT energy, rounded or volumetric indications tend to scatter the 

acoustic wave, causing a decrease in acoustic energy returning to the detector. This acoustic 

scattering can potentially de-sensitize UT for reliable detection and sizing of volumetric flaws. 

Sound waves that reflect directly back into a receiving transducer, such as from correctly

oriented planar flaws, carry important information that can be used to characterize the flaw type 

and its location. Cracks and lack of fusion (LOF) are considered planar-type flaws as there is 

very little open space between the crack faces or fusion surfaces, essentially producing twodimensional planes. When these planar flaws are oriented properly (perpendicular to the 

acoustic wave propagation) as is normally the case within the fusion zones of welds, much of 

the sound energy is reflected back to the source, making the flaws easily detectable. Because 

of the lack of density difference at a planar flaw, RT is not well suited for detecting cracks unless 

they are oriented parallel with the penetrating radiation, which is rarely the orientation of cracks 

in welds. Therefore, based on the fundamental physics of these two inspection methods, RT 
2-7

and UT have historically been considered to be complementary for detecting fabrication flaws 

typically found in welds; that is, RT is well suited for detecting volumetric flaws while UT is better 

for detecting planar flaws. 

In the fabrication of a weld during construction, or when a repair/replacement activity is 

performed during service, varied types of weld anomalies will occur depending on the welding 

parameters applied. These anomalies are different from service-induced degradation that may

occur in a welded component undergoing operating stresses or environmental exposures. 

Flaws resulting from operating plant stresses and/or environmental conditions that occur 

inservice are typically manifested as cracking or corrosion. As U.S. nuclear power plants 

continue to mature, the most prevalent forms of degradation experienced have been thermal 

and mechanical fatigue cracks, or stress corrosion cracks, although limited instances of material 

loss from pitting and flow-accelerated corrosion have also been experienced. Over the course 

of plant operation, UT has emerged as the preferred volumetric NDE method for inservice 

examinations because of the heightened sensitivity to crack detection, as well as economic and 

other factors. 

As previously noted, ASME Code, Section XI provides requirements for PSI and ISI. 

Additionally, Section XI provides requirements for component repair and replacement activities 

during the operating life of the plant, and invokes the original construction Code; for example, 

ASME Section III, for fabrication acceptance for these activities. Therefore, RRA that involve 

welding typically prescribe radiography as the examination method because of the workmanship 

acceptance criteria described in the construction codes. The physics of crack detection are also 

relevant to fabrication flaw acceptance, as cracks have been shown to be highly detrimental to 

component structural integrity, notwithstanding that cracking is not prevalent when applying

good welding techniques. During RT, a crack is only detectable if it is of sufficient opening width 

and aligned with the direction of the radiation beam. If oriented otherwise, the decrease in 

density can be spread out (projected) over an area wider than the actual crack opening width, 

and the level of contrast imaging (i.e., the signal-to-noise ratio; SNR) is significantly diminished. 

Because of the noise inherent to radiography of structural materials, a small misalignment angle

can cause a significant decrease in projected density to a level below the inherent material 

noise, thus resulting in a loss of image contrast, making the crack undetectable. However, if 

weld cracking during fabrication were to occur, it is typically manifested as a surface effect, and 

can usually be detected by applying the appropriate surface examination method (e.g., liquid 

penetrant, magnetic particle, or eddy current). Most fabrication codes mandate these surface 

examinations in addition to the volumetric methods required.

Because UT has been shown to have good capabilities for crack detection, using this method 

for weld fabrication acceptance should be viable for these types of flaws. However, UT has yet 

to be shown to be equivalent to RT for detection and characterization of other planar and 

volumetric welding anomalies. Recent ASME Code Cases have been developed to extend the 

use of UT for repair and replacement activities and are undergoing review. In this regard, this 

report is intended to provide the NRC with information regarding the application of UT in lieu of 

RT for carbon steel piping welds.
2-8

2.5 Conventional UT versus Phased-Array UT

In performing laboratory activities to assess capabilities and limitations for detecting flaws in 

carbon steel welds, PNNL elected to use phased-array UT (PA-UT) instead of conventional, or 

traditional, UT methods. There were several factors that influenced this decision, including 

enhanced phased-array (PA) image analysis techniques, increased speed of data acquisition, 

and fundamental physical differences that allow advanced PA technology to out-perform 

conventional applications of UT. These differences will be described further below. However, 

at the onset of this work, it was known that PA-UT had been used at several facilities to 

examine welds in non-class carbon steel piping system replacements, so assessing the 

application of PA-UT was a logical choice needed to validate industry applications of UT in lieu 

of RT.

Recent advances in electronics miniaturization, computer processing capabilities, and 

fabrication methods for ultrasonic transducers have enabled PA-UT technology to become a 

viable approach for many field applications. The geometrical design of a PA transducer is 

typically a function of specific implementation variables; that is, geometries such as linear, 

annular, circular, or matrix-array designs are developed to address a particular ultrasonic 

application need (Poguet et al. 2001). However, the basic premise for all PA transducers 

involves a set of small, individual piezoelectric elements that are independently driven. 

Although these elements may be pulsed individually, or in groups, to simulate conventional 

transducer excitation, the real strength of this technique lies in the capability of the system to 

electronically delay each of these elements during both generation and reception of ultrasonic 

sound fields. The wavefronts produced by subsets of elements interfere within the inspected 

component to produce a resultant, phase-integrated ultrasonic wave. This is commonly referred 

to as beam forming. The PA system can, therefore, steer and focus the integrated ultrasonic 

beam within the component. Single-element (conventional) UT typically emits a beam in a fixed 

direction and is limited to only one angle of examination for a given scanning sequence. 

New PA ultrasonic systems are computer-controlled, enabling software to define the groups and 

sequences of elements being electronically delayed. Parameters such as the number of 

individual elements in a virtual element, the delay sequence for firing (voltage excitation) of the 

virtual elements, element amplitudes, and the delays in reception are programmed into the 

system operating software. The setting of these generation and reception parameters for a 

particular response is called a focal law. Because practically all aspects of the sound beam are 

being controlled electronically, many iterations, or sequences of iterations, can be run in nearly 

real time. This allows a single array to examine a volume of material with variable inspection 

angles and focusing depths almost simultaneously. For instance, depending on the array 

design and the component thickness, a one-dimensional linear array, with major axis oriented 

normal to a pipe weld, may interrogate close to an entire planar cross section of the weld by 

sweeping through a series of inspection angles without having to mechanically move the 

transducer toward and away from the weld. Theoretically, an entire pipe weld can then be 

examined with a single circumferential scan motion called a line scan. Most PA systems 

capture, digitize, and store the ultrasonic data, which enhances repeatability and permits off-line 

analysis and imaging. 
3-1

3 LABORATORY SPECIMENS AND FLAWS

This report addresses work at PNNL to assess the interchangeability of UT and RT on carbon 

steel piping and plate welds. Laboratory specimens employed in this study are described below 

in Sections 3.1 and 3.2 for the carbon steel pipe weld specimens and the Navy plate weld 

specimens, respectively. 

3.1 Carbon Steel Pipe Specimens and Flaws

Four carbon steel pipe-to-pipe, full penetration butt-welded specimens, three representing

ASME Code, Section III, Class 2 piping welds and one representing ASME Code, B31.1

(Pressure Piping) welds, were obtained from various nuclear inspection vendors. These piping 

weld mock-ups had been fabricated by the inspection vendors in order to assess their PA-UT 

procedures and provide limited demonstrations of capability for their clients. There were two 

355.6-mm (14.0-in.) outside diameter (OD) welded pipe specimens that were approximately 

610 mm (24 in.) in length. One of the specimens was Schedule 80 with a nominal thickness of 

19.05 mm (0.75 in.) and the other was Schedule 120 having a 27.8-mm (1.094-in.) nominal 

thickness. The other two butt-welded specimens were 406.4-mm (16.0-in.) OD carbon steel 

piping, also approximately 610 mm (24 in.) in length. One of these was Schedule 80 pipe with a 

nominal thickness of 21.4 mm (0.844 in.), with the other specimen being Schedule 100 pipe 

having a 26.2-mm (1.031-in.) nominal thickness. All four carbon steel piping weld mock-up 

specimens are shown in Figure 3-1. All of the specimens contain a single bevel weld, one with 

20-degree and 30-degree bevel angles with the weld crown ground flush, and three with a 

37.5-degree bevel angle with the weld crown present [see Figure 3-2(a) and (b) for conceptual 

drawings].
3-2

Figure 3-1 Carbon Steel Pipe-to-Pipe (B1A, B2A, B3A, and B4A) Specimens Used for

This Study; Various Fabrication Flaws Exist in Weld Regions
3-3

Figure 3-2 Single Bevel Weld Configurations in the Carbon Steel Pipe Specimens: 

(a) Weld Crown Ground Flush, (b) Weld Crown Present

The typical carbon steel pipe weld consists of a root pass and a hot (second) pass using a gas 

tungsten arc welding (GTAW – commonly referred to as TIG) method, with the remainder of the 

weld and cover pass (weld crown) filled with a shielded metal arc welding (SMAW – commonly 

referred to as “stick”) method. Specific welding variables such as pass size, heat input, welding 

position, number of passes, etc., used to fabricate the examined pipe specimens are unknown;

however, these specimens contained a cumulative total of 37 implanted (intentional) fabrication 

flaws distributed throughout the entire volume of the welds, including some flaws located in the 

fusion and heat-affected zones. Planar flaws included 11 LOF, 4 incomplete, or lack of 

penetration (LOP), and 12 cracks (three were axially oriented and were not scanned in this 

study because of the presence of a weld crown). Volumetric flaws included 6 slag inclusions 

and 4 areas of porosity. The range of flaw lengths for each type of fabrication flaw is provided in 

Table 3-1.
3-4

Table 3-1 Range of Flaw Types and Sizes Contained in the Four Carbon Steel Pipe-toPipe Welded Specimens

Flaw Type

Length, mm (in.)

Min Max Mean

Planar

LOF 5.7 (0.23) 51.4 (2.02) 11.1 (0.44)

LOP 3.4 (0.14) 13.8 (0.54) 6.5 (0.26)

Crack 10.3 (0.41) 39.2 (1.55) 23.9 (0.94)

Volumetric Slag 6.4 (0.25) 51.1 (2.01) 14.6 (0.57)

Porosity 3.2 (0.13) 7.8 (0.31) 4.8 (0.19)

3.2 Navy Plate Specimens and Flaws

PNNL examined three HY-80 steel welded test plates, two fabricated with purposely induced 

discontinuities and one removed from a decommissioned submarine hull; all were on loan to 

PNNL from the United States Navy, Naval Surface Warfare Center, Carderock Division. The 

two fabricated test plates, Plate Numbers 10 and 18, had overall dimensions of 609.6 mm 

(24.0 in.) by 609.6 mm (24.0 in.) with a nominal thickness of 38.1 mm (1.5 in.). Each had a full 

penetration weld that bisected the plate, with two 279.4-mm (11.0-in.) long testing regions, or 

stations, designated along the weld length. A full weld crown was present on Plate 18, while the 

weld crown was ground flat on Plate 10. As stated above, the other plate, Plate Number 23, 

had been removed from a decommissioned submarine hull weld. This examination specimen

was identical in overall dimensions [609.6 mm (24.0 in.) by 609.6 mm (24.0 in.)] to fabricated 

Plates 10 and 18, but was approximately 55.8 mm (2.2 in.) in thickness and only had one 

304.8-mm (12.0-in.) long designated testing station (see Figure 3-3). Plate 23 contained a 

partial weld crown although it was ground flush in the intended scan area. All three specimens 

contained double-V butt joint weld configurations, with a 45-degree minimum included angle,

weld crown present, and a 4.76-mm (3/16-in.) root gap opening (see Figure 3-4).
3-5

Figure 3-3 Carbon Steel Navy Test Plate Numbers 10 (Upper Left), 18 (Upper Right), and 

23 (Lower); Various Fabrication Flaws Exist in Weld Regions

Figure 3-4 Double-V Butt Weld Configurations Used in the Navy Carbon Steel Plates
3-6

The three carbon steel Navy plate specimens contained 15 fabrication flaws detected by RT 

somewhat randomly located throughout the entire thickness of the weld. Planar flaws included 

6 LOF and 1 crack. Volumetric flaws were 5 slag inclusions and 3 areas of porosity. The range 

of flaw lengths is provided in Table 3-2.

Table 3-2 Flaw Types and Range of Sizes Contained in the Navy Test Plates

Flaw Type

Length, mm (in.)

Min Max Mean

Planar LOF 12.7 (0.5) 33.02 (1.3) 19.95 (0.78)

Crack 15.24 (0.6) 15.24 (0.6) 15.24 (0.6)

Volumetric Slag 10.16 (0.4) 22.86 (0.9) 18.3 (0.72)

Porosity 2.54 (0.1) 15.24 (0.6) 11.0 (0.43)
4-1

4 EQUIPMENT AND METHODS USED FOR PA-UT

A 4.0-MHz phased-array probe on-hand at PNNL was used for initial evaluations conducted on 

the four carbon steel pipe specimens in this study. However, PNNL conducted a modeling and 

design effort to develop a more suitable PA-UT probe. This probe was a 5.0-MHz probe, 

designed and procured for use on for the carbon steel Navy plate specimens and for the rescanning of one carbon steel pipe specimen, B1A. Section 4.1 discusses the focal laws 

necessary for beam formation and focusing. Section 4.2 presents details on the probe modeling 

and design efforts conducted in this study.

4.1 Focal Laws

Prior to performing phased-array examinations, a set of focal laws must be developed for beam 

forming to produce a range of steered and focused angle beams. This is accomplished by 

controlling the firing of individual elements to allow constructive interference of wave-fronts to 

occur within the material under examination. The focal laws are inputs to the data acquisition 

and control software. Software inputs must be made including details about the incident angles 

that are desired to be generated, focusing of the sound field, scanning variables, probe matrix 

design and orientations, etc., to allow the proper element delays to be generated. PNNL uses a 

commercial software tool known as the “ZETEC Advanced Focal Law Calculator” embedded 

within UltraVision version 3.3R4 data acquisition and analysis software, for producing focal 

laws. The focal law calculator performs two functions: (1) focal law generation and 

(2) simulation of a theoretical ultrasonic field produced by the probe when using the generated 

laws. The beam simulation produces a simple image of the probe on the wedge, ray-tracing to 

show the focal depth and steering desired, and energy density mapping to enable the viewer to 

understand how well the sound field may be formed for a particular propagation angle. Grating 

lobes (unwanted energy formed off-axis from the design angle), if present, would also be 

mapped. Figure 4-1 shows an example of the ray tracing for a probe on the left with the sound 

field density mapping on the right. It should be noted that this simulation is generated by 

assuming a homogeneous and isotropic material; that is, no attenuation is included and the 

acoustic velocity in the material is constant for any angle for a particular wave mode. This ideal 

case does not produce an exact representation of sound fields in real components such as 

could be encountered with austenitic weldments. However, this simulation provides a useful 

first-approximation for sound beam modeling and enables the user to estimate sound field 

parameters and transducer performance for optimal array design and focal law development. 
4-2

Figure 4-1 The ZETEC Advanced Phased-Array Calculator is Useful for Generating 

Focal Laws (left) and Simulating the Sound Field for the Focal Law (right) to 

Determine Idealized Beam Characteristics

4.2 Phased-Array Probes and Modeling

4.2.1 4.0-MHz TRS Probe – Use of Existing Ultrasonic Phased Array

Initial ultrasonic PA inspections on the carbon steel pipe specimens used the highest frequency 

PA transmit-receive shear mode probe available at PNNL. This 4.0-MHz shear probe was not 

optimally designed for this application, but was implemented to expeditiously acquire data for an 

initial screening assessment. The information from this initial evaluation would then be used to 

guide the design of a more optimal PA-UT probe in the future. The probe was originally 

designed to examine fine-grained stainless steel piping at the Ignalina Nuclear Power Plant in 

Lithuania to allow for higher resolution inspections (Anderson et al. 2008) and thus was deemed 

generally suitable for examining fine-grain carbon steel piping components. The arrays were 

mounted on a side-by-side Rexolite wedge to operate in a transmit-receive shear (TRS) pitchcatch mode; this configuration is shown in Figure 4-2. The wedge dimensions were 60 × 27 mm 

(2.36 × 1.06 in.) with a 6-degree roof angle, producing a projected cross-over depth at 41 mm 

(1.6 in.). A wedge angle of 39 degrees generated a naturally occurring refracted angle of 

60 degrees in the carbon steel specimens. The transmit-and-receive arrays are each identical 

in design and consist of a 32 × 1 element linear array with an active area of 32 × 16 mm (1.3 ×

0.63 in.) and a bandwidth of 84% at −6 dB. With only one element in each linear array, 

electronic beam skewing in the passive direction was not possible. Contact surfaces of the 

wedges were machined to facilitate acoustic coupling on the pipe surfaces at approximately 

355.6 mm (14.0 in.) and 406.4 mm (16.0 in.) OD dimensions of the two carbon steel pipe 

specimens. 
4-3

Figure 4-2 4.0-MHz TRS Phased-Array Probe

Subsequent modeling of the 4.0-MHz array was conducted using the UltraVision software suite 

in combination with a normalized Huygen’s Principle method for 2D acoustic pressure 

calculations (Wooh and Shi 1999). Representative carbon piping [~25.4 mm (1-in.) thick] and 

carbon plate [~50.8 mm (2-in.) thick] materials were chosen as the bases for the simulations 

using a shear mode velocity of 3230 m/s. The Huygen’s Principle calculation demonstrates the 

PA directivity capability of the probe to azimuthally steer angles in the component. When the 

array is designed with proper individual element sizes and matrix configurations for a particular 

material, a single peak with maximum acoustic pressure will be produced at the desired sweep 

angle. Additional peaks that are present near the primary lobe represent unwanted off-axis 

energy, known as grating lobes. These grating lobes provide an indication of inefficiencies for 

concentrating acoustic energy along the primary axis of the main lobe. If the grating lobes are 

significant, they detract from the ability of the probe to focus energy at the primary angle of 

insonification. They may also create noise in the data. Figure 4-3 graphically represents the 

acoustic pressure calculation when steered 15 degrees from the natural refracted angle of 

60 degrees (as determined by the wedge angle) for the 4.0-MHz array. The figure therefore 

represents the acoustic pressure at a 75-degree refracted angle. The black arrow in the image 

points to the presence of an off-axis theoretical grating lobe generated for this array 

configuration.
4-4

Figure 4-3 Phased-Array Directivity of the 4-MHz Array Steered to 15 Degrees from the 

Natural Refracted Angle of 60 Degrees. Off-axis grating lobe is present and 

indicated by the black arrow at approximately −34 degrees.

The 4.0-MHz probe produces a 0.8-mm (0.03-in.) wavelength in carbon steel at its nominal 

center frequency. Example sound field simulations, using the UltraVision software suite, of the 

4.0-MHz beam using one set of focal laws are shown in Figure 4-4. The side view images at 

insonification angles of 45, 60, and 70 degrees show the relative beam intensity when focused 

at the ID region of a 25.4-mm (1.0-in.) thick carbon steel pipe specimen. The light gray 

specimen color represents the pipe thickness (25.4 mm). This simulation indicates that the 

sound field is formed and projected in front of the wedge and through the pipe wall in the region 

of interest. The simulation suggests that this 4.0-MHz probe design may not be optimum for 

insonifying the entire weld region and surrounding material in the carbon steel specimens—

especially at the highest insonification angle (70 degrees). Simulations in the thicker 50.8-mm 

(2-in.) plate material also resulted in non-optimized sound fields for the innermost region, as 

shown in Figure 4-5. 
4-5

Figure 4-4 Simulations of the Beams Created by the 4.0-MHz TRS Arrangement for 45, 

60, and 70 Degrees in 25.4-mm (1.0-in.) Thick Carbon Steel Pipe

Figure 4-5 Simulations of the Beams Created by the 4.0-MHz TRS Arrangement 

60 Degrees in 50.8-mm (2.0-in.) Thick Carbon Steel Plate
4-6

4.2.2 5.0-MHz TRS Probe – Development of Optimized Phased Array

The simulated shortcomings of the 4.0-MHz array, along with initial data analysis on the piping 

specimens, provided valuable guidance toward the design and fabrication of a new ultrasonic 

phased-array probe, specifically built for evaluation of the carbon steel specimens and their 

regions of interest in this UT/RT study. Built upon the concepts of the 4.0-MHz TRS array, a 

5.0-MHz TRS array was designed. A probe frequency of 5.0 MHz was chosen for increased 

resolution (shorter wavelength) and therefore improved sensitivity to smaller defects. 

The 5.0-MHz TRS probe (Figure 4-6) was specifically designed to inspect carbon steel pipe and 

plate components of thickness between 25.4 mm (1 in.) and 55.8 mm (2.2 in.). The array 

design ensured proper beam formation and steering in the azimuthal (active) direction. It 

consists of two 5.0-MHz arrays mounted side-by-side on a Rexolite wedge configuration. A 

layer of cork is used as an acoustic isolation material between the two halves of the wedge to 

eliminate any cross-talk between the two arrays. Both transmit and receive arrays are identical 

in design with each having a 32 × 4 element matrix configuration. Element sizes are 0.38 ×

2.46 mm (0.01 × 0.1 in.) in the active and passive axes, respectively. The total active area of 

each array was 15.26 × 10.14 mm (0.6 × 0.4 in.) with a greater than 60% bandwidth at −6 dB. 

The Rexolite wedge was designed to have a footprint of 59 × 46 mm (2.3 × 1.8 in.) with a wedge 

angle of 36 degrees, generating a natural center angle of 55 degrees in the material, if no 

element delays were to be used. Unlike the 4.0-MHz probe, this array has four rows of 

elements in both transmit and receive arrays enabling the array to electronically steer and focus 

in the passive axis (beam skew). This design eliminated the need for a wedge roof angle and 

enabled the probe to incorporate skew angles of ± 20 degrees. Table 4-1 shows the physical 

differences between the 4.0-MHz TRS and the 5.0-MHz TRS probes.

Figure 4-6 5-MHz TRS Phased-Array Probe on Wedge Assembly
4-7

Table 4-1 Ultrasonic Array Physical Specifications

Probe 4-MHz TRS 5-MHz TRS

Active Aperture 32 mm (1.3 in.) 15.26 mm (0.6 in.)

Passive Aperture 16 mm (0.63 in.) 10.14 mm (0.4 in.)

Active Aperture Elements 32 32

Passive Aperture Elements 1 4

Nominal Shear mode Wavelength(a) 0.8 mm (0.03 in.) 0.65 mm (0.025 in.)

(a) In carbon steel where velocity = 3230 m/s

The smaller individual element sizes in the primary axis of the 5.0-MHz TRS probe show 

superior phased-array directivity according to Huygen’s Principle as compared to the 4.0-MHz

probe. Figure 4-7 shows the 5.0-MHz directivity model steered to 15 degrees and 20 degrees

(from the natural refracted angle of 55 degrees as determined by the wedge angle), top and 

bottom, respectively. Note, when steered to 15 degrees (or an effective refracted angle of 

70 degrees, 15+55) the maximum acoustic pressure peak occurs at 15 degrees without the 

generation of any off-axis grating lobes indicating improved sound field generation and steering

over the 4.0-MHz probe. The bottom image shows the 5.0-MHz probe steered to an angle of 

20 degrees (an effective refracted angle of 75 degrees, 20+55) and the onset of a grating lobe 

is indicated by the black arrow.
4-8

Figure 4-7 5.0-MHz Probe Directivity Model Steered 15 Degrees (top) and 20 Degrees 

(bottom). The onset of a grating lobe is shown in the bottom image indicated 

by the black arrow. 

UltraVision simulations of the 5.0-MHz array similarly performed on the 25.4-mm (1-in.) carbon 

pipe components show the array’s ability to sufficiently penetrate the specimen and beam form 

in the desired focal region. Figure 4-8 depicts a full-volume simulation of a 60-degree beam 

focused at a depth of 19 mm (0.75-in.) as indicated by the red cursor. As shown, the maximum 

sound density of the beam occurs at the target focus and extends through this volume with 

greater than 6 dB insonification at the ID of the pipe (indicated by the darker gray color in the 

images). 
4-9

Figure 4-8 5.0-MHz Probe, 60-Degree Beam Simulation on 25.4-mm (1.0-in.) Thick Pipe 

Component. Target focus at 3/4T (T = wall thickness).

Simulations conducted on the 50.8-mm (2-in.) carbon plate components also show adequate 

beam coverage and focusing capabilities at the 60-degree insonification angle. Figure 4-9

displays the full-volume simulation for the 5.0-MHz array on the thick-plate carbon steel 

component. Here the target focus was again at 19 mm (0.75-in.) as indicated by the red 

horizontal line in the left image. 

Figure 4-9 5.0-MHz Probe, 60-Degree Beam Simulation on 50.8-mm (2.0-in.) Thick Plate 

Component. Target focus at 3/4T (T = wall thickness).
4-10

The comparative simulations and calculations conducted demonstrate the fundamental 

performance improvements made from the design of the 5.0-MHz TRS array. The fine-grained 

microstructure of the carbon steel components minimally affects the propagation of higher 

frequencies used for inspection. As the grain sizes in typical carbon steel components are on 

the order of microns, they are much smaller than the wavelength produced by a 5.0-MHz shear 

probe [0.65 mm (0.025 in.)], thus allowing this frequency to be effectively used for inspection. 

Further, improvements in the selection of the element size and matrix configuration parameters 

in the 5.0-MHz array have significantly improved beam steering in the azimuthal plane. This 

design also enabled the array to electronically skew up to 20 degrees in the passive direction for 

enhanced flaw detection and characterization of off-axis oriented indications.
5-1

5 EQUIPMENT AND METHODS USED FOR RT

The owners of the pipe specimens used in this study provided PNNL with general true-state 

information in the form of drawings, showing the location of the flaw in the pipe specimen and

the approximate length and depth size as well as flaw type. However, because of the nature of 

this assessment, more exact locations and measurements of the flaws were needed, so PNNL 

used both film and computed RT techniques to validate the reported true-state information. The 

PNNL evaluation agreed with most of the information provided by the manufacturer, but some 

flaws were sized more accurately based on high-quality RT images. In addition, other “bonus”

fabrication flaws were observed in the RT images that were not accounted for in the 

manufacturer’s drawings. The bonus flaws were evaluated using the same high-quality RT 

images, thereby providing a consistent sizing standard and reliable methodology for 

characterizing each flaw type. 

For the Navy plates, consensus analytical information was provided to PNNL via test report 

forms that captured both the Navy-performed RT and UT results. In this study, PNNL used the 

Navy consensus data as a reported true state, except where only Navy UT detected a flaw. In 

this case, PNNL ignored the Navy UT-only data for the assessments performed and 

documented in this report. The test reports listed a reference marking on each plate to establish 

a zero point for scanner and index axes. However, of the three Navy test plates examined, a 

clearly marked zero reference point remained on Plate 23 only. Therefore, reference markings 

were created for Plates 10 and 18. As a result, notable differences were initially observed for

reported flaw locations between PNNL UT and Navy RT data. PNNL subsequently performed 

digital RT on Plates 10 and 18 to assist in the data comparison. Position adjustments were 

made to align the PNNL and Navy RT indications and with similar adjustments being applied to 

the PNNL UT data.

The X-ray system used at PNNL is composed of the X-ray vault (shielded enclosure), X-ray

machine, imaging media (whether film or digital), and the imaging software. These topics as 

well as the inspection protocols and data interpretation, are discussed below. 

5.1 X-ray Vault

PNNL performed the radiography for this project at a facility located in Richland, Washington. 

The facility is equipped with a lead-lined X-ray shielded enclosure (vault). A large sliding door to 

the vault allows forklift access for handling heavy components. Figure 5-1 shows the interior of 

the PNNL 2410 facility and X-ray vault.
5-2

Figure 5-1 PNNL Radiography Facility and X-ray Vault

5.2 X-ray Machine

The X-ray machine (shown in Figure 5-2) used for all of the work in this report was a Comet 

MXR-451/26, which has a 450-kilovolt, 10-milliamp generating tube with dual focal spots of 

2.5 and 5.5 mm (0.098 and 0.217 in.). The X-ray machine is mounted on a movable gantry and 

can be raised, lowered, and/or angled to accommodate optimum exposure positions. Pipe and 

plate specimens that are undergoing inspection are also placed on a lift/turntable that can be 

manipulated to facilitate exposure configurations. The X-ray controller (Figure 5-3) has 

functional capability to precisely set the desired voltage, current, and time elements. The 

system is completely interlocked and meets all PNNL safety requirements for operation.
5-3

Figure 5-2 X-ray Machine

Figure 5-3 X-ray Controller

5.3 X-ray Imaging Media

PNNL uses traditional film, phosphor storage cassettes, and digital detector plates for imaging 

media. As shown in Figure 5-4, for the case of these piping weld examinations, the cassette is 

loaded with a backing lead plate and either phosphor plate or film. When film is used, a 

0.125-mm (0.005-in.) lead screen is placed in front of the film and also on the back side of the 

film to filter out low background and scattered energies, which will increase signal-to-noise and 

enhance contrast. A vacuum cassette is employed to ensure adequate lead screen-to-film 

contact. The cassette is placed into the pipe section and compressed to conform to the inside 

diameter of the pipe. PNNL performed single-wall RT on all of the specimens because it 

produced the best detection and sizing capability. However, in field RT applications, doublewall RT is frequently performed as the piping system may be in operation or configured such 

that single-wall is not possible (i.e., no access to the pipe ID). However, because PNNL is using 

the RT as a method to establish true state, the best technique (single wall) available was 
5-4

implemented. During initial examinations of the carbon steel pipe samples, film radiography 

was used in addition to computed radiography (CR), to assess correlation between the two RT 

imaging methods. Limitations for film radiography include a lack of image filtering with no postimaging contrast enhancement capability. CR images are digital and can be readily enhanced 

to provide better flaw detection and characterization. Therefore, PNNL chose to employ CR for 

the bulk of the RT work because of the advantages it has over film RT. A more detailed 

comparison of digital versus film radiography can be found in Moran et al. (2010).

Figure 5-4 RT Imaging Media and Placement

5.4 X-ray Imaging Hardware and Software

The image analysis platform used by PNNL is SENTINEL Vision HR software, which combines 

icon-driven operation with single-button filters, brightness, contrast, and gamma adjustments. 

The software initiates the phosphor plate reader, which has a 14-micron laser spot size and 

offers full 16-bit imaging (65,535 gray levels) capability. The phosphor plates are fed into the 

scanning area by wrapping around the feed drum. PNNL utilized the Scan-X drum phosphor 

plate reader shown in Figure 5-5. Also shown in Figure 5-5 is a screen shot of the software as 

applied to an actual processed RT image demonstrating flaw measurement capability. The 

image shows an incomplete penetration in the root of a pipe weld and software cursors are used 

to measure the length of the flaw at 13.7 mm (0.54 in.).
5-5

Figure 5-5 Reader and Screen Shot of SENTINEL Vision HR Software Application

5.5 X-ray Inspection Protocols

The quality of X-ray images is based on the visibility of an “image quality indicator.” There are 

two types of indicators—a flat, rectangular plate with holes in it (commonly known as a 

penetrameter), or a wire indicator which has various wire diameters. For this study, the 

penetrameter image quality indicator was used (Figure 5-6). 

Figure 5-6 Penetrameter Image Quality Indicator

Penetrameters used in this study were fabricated in accordance with American Society for 

Testing and Materials (ASTM) E 1025 (2005). ASME Code examinations require specific 

penetrameter thicknesses with certain diameter hole sizes to be visible on a radiograph as a 

general measure of the quality of the radiographic process. Figure 5-7 shows the placement of 

a penetrameter on a pipe component. The thickness and material of the penetrameter is based 
5-6

on the thickness and material of the pipe wall that is being examined. In the case noted in 

Figure 5-7(a), a stainless steel penetrameter is placed directly on the pipe as there is no weld 

reinforcement (i.e., the weld crown has been ground flush). Note that it is acceptable to use a 

stainless steel penetrameter on a carbon steel weldment as the density and inherent material 

scattering attributes are nearly equivalent. In Figure 5-7(b), a shim (as required by ASME 

Code) has been placed under the penetrameter to account for the extra thickness of the weld 

reinforcement.

Figure 5-7 Placement of Penetrameter on Pipe

The radiography performed in this study was completed in accordance with ASME Code 

requirements. Because the requirements for repair and replacement activities in ASME Code, 

Section XI require acceptance criteria based on ASME Code, Section III, the Section III criteria 

were used for the PNNL RT. As an example, a pipe wall thickness greater than 25.4 mm 

(1.0 in.) to 31.8 mm (1.25 in.) would require the use of a penetrameter designation of 25 and the 

requirement would be to show the 2T [hole size of 1.27 mm (0.050 in.)] on the RT image. 

Therefore, the most current ASME Code, Section III, Article NB-5000 was used (2010 Edition

with 2011 Addenda) as the basis document for radiographic inspections and Table NB-5111-1 

was used for penetrameter selection.

Figure 5-8 provides examples of typical radiographs that demonstrate the sensitivity of the 

radiographic process. In these examples, the visibility of the penetrameter shape and 

associated holes provide assurance that the radiograph is of sufficient quality. The ASME Code 

specifies what penetrameter is used based on the thickness of the pipe wall and whether any 

weld reinforcement is present (if weld reinforcement is present, a shim is placed under the 

penetrameter). It also specifies which diameter hole must be visible to achieve a quality 

radiograph.
5-7

Figure 5-8 Typical Radiographs Displaying the Use of a Penetrameter

5.6 Interpretation of Flaw True State Results

The interpretation of weld defects using radiographic techniques is somewhat subjective and 

relies heavily on the skill and experience of the inspector. RT works very well for volumetric 

fabrication-type flaws such as incomplete penetration, slag inclusions, and porosity. It is less 

effective for planar defects such as lack of fusion and cracking. This understanding of RT 

limitations was considered when the first set of specimens used in this study were analyzed. 

The specimens were all fabricated with implanted flaws; that is, a manufacturer that specifically 

makes flaw standards was used to construct these specimens. Therefore, the manufacturer 

provided a drawing indicating exactly where the flaw was located, the dimensions of the flaw, 

and the characterization of the flaw (e.g., slag inclusion, crack, etc.). Because PNNL personnel 

may have been biased by this information, PNNL contracted with AREVA Federal Services to 

procure the services of a RT expert (American Society for Nondestructive Testing [ASNT] level 

III) with many years of experience with performing radiographic examinations and interpreting 

radiographs for weld defects. AREVA independently evaluated, with no prior knowledge of the 

flaws, one of the specimens containing multiple defects. Comparisons of AREVA’s analysis

(using film) with PNNL’s analysis (using CR) indicated only slight differences in flaw detection 

and length sizing. AREVA’s interpretations and guidance formed the basis for the rest of the RT 

characterizations made by PNNL using CR in this report.
5-8

5.7 PNNL RT Performed on the Navy Plates

Many of the sample protocols that were used for the carbon steel pipe welds were also used in 

conducting CR on the Navy plates. The plates were considerably thicker than the piping 

specimens; therefore, examination parameters such as X-ray voltage and amperage, and 

exposure times, were changed to accommodate this thickness variance. Figure 5-9(a) provides 

an example of the specimen set-up and labeling for Plate 18 during CR examination. 

Figure 5-9(b) is a digital image of a section of this plate.

Figure 5-9 (a) Example of the Specimen Set-up and Labeling for Plate 18 for CR 

Examination with the Radiographic Parameters. (b) Digital Image of a 

Section of Plate 18.
6-1

6 LABORATORY ULTRASONIC RESEARCH VARIABLES

The general use of the PA system and specific methods employed for evaluation of the carbon 

steel specimens are presented in this section. Section 6.1 reviews the system electronics and 

scanner. Section 6.2 covers the scanning protocol and, lastly, Section 6.3 briefly presents flaw 

characterization guidelines and results of a limited blind exercise.

6.1 PA-UT System

Phased-array ultrasonic examinations of the four, carbon steel pipe-to-pipe specimens and 

three, carbon steel Navy plate specimens discussed in Section 3 were conducted using a 

ZETEC DYNARAY system. This commercially available system is equipped to accommodate a 

maximum of 256 channels from PA probes and requires the use of UltraVision software. Its 

frequency pulsing electronics will drive probes in the 0.2–20 MHz range. Each probe is driven 

with a square wave having an optimized pulse width. The pulse width is set to approximately 

half of the probe’s design frequency (F) (one-half F in nanoseconds).

Set-up and laboratory configuration for PA-UT data acquisition on the pipe-to-pipe specimens 

used an automated scanner device on an adjustable guide ring supported by a customdesigned floor-to-ceiling brace. The scanning fixture includes a translation slide providing 

additional control and freedom for adjusting the specimens in both horizontal and vertical 

directions. This provides easy manipulation for fine-tuning the guide-ring position, relative to the 

pipe specimens. The laboratory configuration for the Navy plates used the same automated 

scanner system on a flat guide track. The plates were supported by blocks and the entire setup was placed in a basin to collect and recycle the water used for coupling the acoustic energy 

to the specimen.

The automated system consists of an ATCO dual-axis magnetic wheel scanner driven by a 

ZETEC motor control drive unit (MCDU-02). The scanning system linked directly to the 

DYNARAY unit via Ethernet and encoder cabling to allow control of scan motions by the 

UltraVision software package. Spatially encoded data were acquired in both the scan and index 

axes using this system. As with the Navy plates, acoustic coupling between the probe wedge 

and the piping specimen surface was performed using water pumped through nozzles 

embedded on both sides of the wedge harness. This set-up allowed water to flow evenly over 

the surface of the specimen. As the water couplant flowed off of the top of the specimen, it was

collected in a tray, channeled back to the pump, and recycled. The DYNARAY data acquisition 

system and laboratory workstation are shown in Figure 6-1. The automated scanner and 

scanning fixtures for both piping and plate specimens are depicted in Figure 6-2.
6-2

Figure 6-1 DYNARAY and Motor Control Drive Unit

Figure 6-2 Automated Scanner and PA-UT Probes on Piping Specimen (top) and Navy 

Plate Specimen (bottom)
6-3

6.2 Scanning Protocols

6.2.1 Calibration for Carbon Steel Pipe

Prior to scanning the welded region of the specimens, probe calibrations were conducted on the 

end of the specimen being evaluated (Figure 6-2). The response from the end of the specimen 

presents a 100% through-wall indication in the material. The probe was positioned near the end 

of the pipe specimen and the corner-trapped response signal at or near 45 degrees was 

maximized by moving the probe toward and away from the corner. The system hard gain was 

set such that the received signals from the corner were slightly unsaturated [just under 100% full 

screen height (FSH)].

6.2.2 Calibration for Navy Plates and Re-scan of Carbon Steel Pipe B1A

The probe was calibrated by finding the highest response from a corner-trapped reflection from 

the actual Navy plate being examined, or if the plate corners were too roughly cut, an innerdiameter corner-trap response from a carbon steel pipe of similar thickness was obtained. All of 

the angles (45–75 degrees) being generated were assessed for the highest response to ensure 

that none of the angles in this range would saturate during scans. The highest response value 

was adjusted to 80 percent FSH. All scanning of the plates was performed with a hard, or initial 

calibration, gain setting of 43.5 dB. During data analysis, 6 dB of soft, or digital gain was added 

to the data images for increased sensitivity to small flaws. A detection threshold was set to 50 

percent FSH. This effectively provides a detection sensitivity that is approximately 10 dB below 

the corner trap reference reflector response.

All sides of Plate 23 were flame-cut (Figure 6-3) and were therefore unusable for a cornerresponse measurement. Because all the Navy plates have very similar material properties, and 

there was no calibration block of the same thickness and materials available, the gain settings 

calibrated for the two thinner [38.1-mm (1.5-in.)] Navy Plates 10 and 18 were also used on the 

thicker [55.9-mm (2.2-in.)] Navy Plate 23.

Figure 6-3 Flame Cut Edges of Plate 23
6-4

6.2.3 Examination and Volume of Inspection

The current ISI examination volume specified in ASME Code, Section XI, IWB-2500, includes 

the inner surface 1/3 thickness of the weld plus an additional 6.4 mm (1⁄4 in.) [C-D-E-F in

Figure 6-4(a)] of parent material on both sides of the weld to include the heat-affected zones. 

However, examinations conducted in this study were aimed at detecting potential inservice 

flaws (ID-connected cracks), as well as fabrication flaws throughout the entire thickness of the 

weld. Therefore, the inspection volume was 100% of the weld volume plus 12.5 mm (1⁄2 in.) in 

the parent material on each side of the weld volume [A-B-C-D in Figure 6-4(b)], which is 

required by ASME Code, Section XI, IWA-4000, Repair/Replacement Activities. 

Figure 6-4 (a) ASME Code, Section XI, Inservice Inspection Volume – Inner 1/3 

Thickness and (b) Inspection Volume required for Repair/Replacement –

Entire Thickness

The examinations employed two types of scanning techniques—raster scanning and line 

scanning. Line scans are often used for initial screening/detection of weld volumes for any 

potential flaw responses. If responses from an area of interest are obtained, a raster scan of 

these reflectors will be conducted to fully characterize the indications. Line scanning in this 
6-5

study was done at several axial positions, and was used for only the initial detection of the flaws 

in the Navy plates and the re-scan of the pipe B1A. Raster scans acquire data over multiple 

axial and circumferential locations while line-scan data are acquired along a single, parallel-toweld circumferential line at multiple axial positions. As such, raster data presents a more 

thorough view of detected flaws from which an analyst may select optimum imaging to 

characterize flaw variables such as length and depth.

Figure 6-5(a) depicts an idealized pipe-to-pipe weld with an axial multiple-line scan plan. Data 

are collected along a line, while scanning parallel to the weld. The scanner is incrementally 

positioned further away from the weld in the axial direction for each line of data; this is repeated 

until all line scans are completed. Figure 6-5(b) shows an idealized pipe-to-pipe weld with an 

axial raster scan plan. Data are collected along a line scanning axially toward the weld, the 

scanner increments positively in the circumferential direction, returns the probe axially away 

from the weld to the next axial starting position, and then moves forward towards the weld 

collecting the next line of data. This pattern is repeated until the specified area has been 

completely scanned. This unidirectional collection method is specifically used for 

characterization of flaws oriented parallel to the weld (circumferential flaws). The examinations 

were conducted from both sides of the weld using a probe skew of 0 degrees (downstream) or a 

probe skew of 180 degrees (upstream). Because of the presence of an OD weld crown on most 

of the specimens, circumferential scanning for detection of axial flaws was not conducted. This 

is discussed further in the following section.
6-6

Figure 6-5 Axial Multi-line (a) and Raster (b) Scanning Looking for Circumferentially 

Oriented Flaws (parallel to weld centerline)

6.2.3.1 Examination of Carbon Steel Pipe with Weld Crown Present in the As-Welded 

Condition or Mechanically Conditioned

The weld crown presents an access restriction that prevents scanning directly over the top of 

the welded region. The leading edge of the probe wedge impacts the toe of the weld, which for 

the configuration of the piping welds in this study, was approximately 12.5 mm (0.5 in.) from the 

weld centerline. Therefore, in order to inspect the entire examination volume in the axial 

direction [Figure 6-4(b)], full-V and 11⁄2-V path examination techniques were used. Figure 6-6

displays the techniques of 1⁄2-V path (first leg of sound), and bouncing sound using full-V 

(second leg) and 1-1/2–V path (third leg of sound). The fine-grain microstructures of carbon 

steel parent and weld materials facilitated the use of shear waves. Shear waves ensure that 

minimum mode-converted signals will be produced during the skipping of sound off the ID/OD 
6-7

surfaces using the full- and 11⁄2-V techniques. Additionally, shear waves are more sensitive to 

potential flaws because of their shorter wavelengths (for the same frequency) than longitudinal 

waves.

A 4.0-MHz TRS PA probe was applied during initial pipe examinations using focal laws that 

produce a true-depth focusing method (see Figure 6.7 below) at the ID of the pipe for all angles 

being generated. True-depth focusing was selected for these examinations, which produced 

better results when sound was needed beyond the 1⁄2-V path (or first leg of sound). Azimuthally, 

the insonification angles were swept, from 30 to 75 degrees in 1-degree increments for the line 

scan configuration. Data were acquired in 1-mm (0.04-in.) increments in the scan axis and 10-

mm (0.40-in.) increments in the index axis away from the weld. Raster scan data were acquired 

incrementing the azimuthal sweep from 45 to 75 degrees at 5- or 10-degree increments, 

depending on the thickness. The decrease in steered beam angular resolution, as opposed to 

1–2 degrees, was necessary to maintain data file sizes to a reasonable level, as the skip path 

required an increase in the recorded time base to capture the responses from the full- and 11⁄2-V 

path techniques. In order to compare all piping weld data, the pipe (specimen B1A) with the 

weld crown ground flush was originally scanned as if having a weld crown present; this 

effectively kept the probe front edge to approximately 12.5 mm (0.5 in.) from the weld centerline. 

Scanning resolution for raster scans were 0.5 mm (0.02 in.) in the scan and 1.0 mm (0.04 in.) in 

the index axis.

Figure 6-6 Techniques for Scanning that Use 1⁄2-V (first leg of sound), Full-V (second leg 

of sound), and 1-1/2–V (third leg of sound)

6.2.3.2 Examination of Navy Plates

Examinations with the new 5.0-MHz array probe were performed using both 1⁄2-V and full-V 

beam paths, because the weld crown was not ground smooth on all the plate specimens.

Scans from both sides of the weld up to the edge of the weld crown were completed for those 

plates having existing crowns and up to a similar position on the plate without a crown to 

maintain consistency in acquisition protocol. This led to the use of a larger range of angles, 

including higher angles, in order to inspect the entire volume of the weld.
6-8

Two channels were set up for data acquisition to capture the entire volume of the weld in 1⁄2-V 

and full-V beam paths, respectively. The first channel used true-depth focusing at the lower 

surface of the plate, with an angle sweep of 45–75 degrees in 5-degree increments. This type 

of focusing fixes the focal point at the same depth for all specified angles, as shown in the 

schematic in Figure 6-7. The second channel used a half-path beam focus, and swept through 

refracted angles of 60–80 degrees, also with 5-degree increments. This type of focusing 

maintains a focal point at a constant part path for all specified angles and is also shown in 

Figure 6-7. The half-path focus was used for the higher angles required for PA-UT to reach the 

OD of the specimens. Sufficient part path was recorded to account for insonifying the bottom 

surface of the specimens with all angles up to 70 degrees and for a full-V beam path for angles 

up to 60 degrees.

Figure 6-7 True Depth, Focusing at a Fixed Depth, and Half Path, Focusing at a Fixed 

Part Path, Focal Styles are Demonstrated

Navy Plate 23 was marked and clearly stamped with a “0” (Figure 6-8) for alignment of the 

probe with the previously-defined reference point [0,0] used in the Navy inspection study. 

Plates 10 and 18, however, did not have a similar reference point, with only a faint etched line 

being observed perpendicular to the weld, and running down the middle of the plate.
6-9

Figure 6-8 “0” Stamp Shown for Navy Plate 23 (etched lines drawn over with marker for

scanning)

Because the meaning of this line was unclear, PNNL decided this etched line to be the 

coinciding end of the first station and start of the second station for both Plates 10 and 18, 

leaving a 25.4-mm (1.0-in.) buffer on each edge of the plate (see Figure 6-9).

Figure 6-9 PNNL’s Scanning Station 1 and Station 2 for Plate 10
6-10

6.2.3.3 Examination of Carbon Steel Pipe, B1A, with Weld Crown Ground Flush

With the weld crown being ground flush on this piping specimen, there were no access 

restrictions when examining the weld on B1A. This allowed for full coverage of the weld using 

only a 1⁄2-V inspection beam. The 5.0-MHz probe was used with two focusing methods, each in 

a separate data channel. The first used a 25.4-mm (1.0-in.) true-depth focus, targeted at the ID 

surface of the pipe. The angles employed for this channel were 30–60 degrees in 5-degree 

increments. The second focusing technique used a 35-mm (1.37-in.) half-path focus. This was 

applied for the use of higher angles to allow a focusing in higher regions of the weld because 

full-V path inspections were not being used. The angles used in this second channel were 

45–80 degrees, also in 5-degree increments. Data were collected with an encoded raster scan 

of the weld region. This was completed with 250-mm (9.84-in.) linear segments around the 

entire circumference of the pipe, with an overlap of 50 mm (1.96 in.) for each data segment. 

Scanning resolution for all raster data was 0.5 mm (0.02 in.) in the scan and 1.0 mm (0.04 in.) in 

the index axes, respectively. Similarly, line scan data were acquired using the same azimuthal 

sweep at 1 degree resolution. Scanning resolution for line scan data was 1.0 mm (0.04 in.) in 

the scan and 10.0 mm (0.40 in.) in the index axes, respectively.

6.3 Indication Characterization

Ultrasonic indications are typically characterized as either flaw responses (from volumetric or 

planar flaws) or as responses produced by geometrical surfaces (e.g., from weld root, counter

bore, etc.). General guidelines for distinguishing between a flaw and geometrical indications

have been used by multiple industry sectors for many years. A typical set of guidelines, as 

provided in PDI-UT-1 (PDI 2007) for ultrasonic examination of ferritic welds in the nuclear power 

sector, are shown in Table 6-1. PNNL applied this general set of guidelines during the detection 

and flaw characterization analyses for both the carbon steel pipes and the Navy plates. A 

separate, more focused flaw type characterization (i.e., to determine whether fabrication flaws 

are planar or volumetric), was also performed on the Navy plate welds. This will be discussed 

later in this report in Section 7.2.

Table 6-1 Characteristics of Flaw and Geometric Indications

Flaw Indications Geometric Indications

• Confirmation from opposite direction

• Multiple points of reflection (facets, tip, etc.)

• Higher angle provides comparable response

• Defined start/stop points

• Variance in time base position and/or amplitude 

across length

• Plots to ID at suspect area

• Good SNR

• Flaw type signal characteristics (inconsistent, 

facets, tips, etc.)

• No confirmation from opposite direction

• Single point of reflection

• Higher angle has reduced or no response

• Similar responses in other areas

• Consistent time base position and/or amplitude 

across length

• Plots to known geometry

• Geometry-type signal characteristics (consistent, 

contains multiples, smooth appearance, etc.)
7-1

7 ANALYSIS OF INITIAL DATA

This report section includes information and discussion for assessing and comparing the 

capabilities of UT and RT on fabrication flaws in carbon steel piping and plate welds. 

Section 7.1 assesses the detection and length sizing capabilities of RT and UT for carbon steel 

pipe specimens. Section 7.2 evaluates detection and flaw type characterization using Navy RT 

and PNNL PA-UT for the plate specimens.

7.1 Piping Weld Assessment

Replacement of one NDE method with another is a complex process. One of the key factors 

(Forli 1995) that must be considered before replacement should be approved is whether the 

flaw detection capabilities of the replacement method (i.e., ultrasonic testing in this case)

provide technically acceptable results when compared to the reference method (radiography).

In this section, a comparison of the detection and length sizing capabilities of RT and UT are

presented because (1) these are the primary flaw characteristics that can be readily compared

between UT and RT, and (2) most fabrication codes use flaw length (not through-wall depth) 

within their acceptance criteria. 

7.1.1 Flaw Detection

Phased-array data were initially acquired and analyzed on the four carbon steel pipe-to-pipe 

specimens using a 4.0-MHz TRS probe. A ZETEC DYNARAY system was used to acquire the 

data, with the probe being driven at its optimum frequency. Raster scan data were collected 

from both sides of the weld as the refracted angles were swept from 45 to 75 degrees at

5-degree increments. The implanted or intentional flaws were located throughout the entire 

thickness of the weld and the adjacent parent material, thus covered by an examination volume 

consistent with Figure 6-4(b). During the analysis, the flaws were designated as far side (FS) or 

near side (NS) (Figure 7-1) depending on their relationship to weld centerline relative to the 

position of the probe. If the flaw was directly on the weld centerline as all LOP were located, the 

downstream side was arbitrarily designated as near side for analysis purposes and upstream 

side was designated as far side. The data were analyzed for flaw detection, signal-to-noise, 

and length.
7-2

Figure 7-1 Example of Near-Side and Far-Side Designation in UT Data Analysis

Ultrasonic data presented in this section of the report, regarding a comparison of detection and 

length-sizing with RT, were acquired with the 4.0-MHz TRS probe using the scanning protocols 

described in Section 6.2.3.1. This includes initial scans on specimen B1A (weld crown ground 

flush with the OD surface) where the probe was not closer than 12.5 mm (0.5 in.) from the weld 

centerline, simulating the inspection of a pipe with a weld crown present.

The manufacturer of the pipe specimens provided PNNL with as-built information in the form of 

drawings showing implanted flaw locations along with targeted length and depth of the flaws. 

The pipe owners wished to keep these specimens intact, so no destructive tests were 

performed to verify true-state flaw sizes and locations. As a result, PNNL used both film and 

computed RT techniques to validate the reported as-built information with true-state data. 

PNNL’s evaluation agreed with most of the information provided by the manufacturer; however,

there were a few flaws that PNNL characterized more accurately than the manufacturer, based 

on high-quality RT images. Additionally, certain “bonus” flaws were discovered as a result of 

the RT images that had not been accounted for in the manufacturer’s drawings. These were 

typically welding-related flaws not originally intended by the manufacturer. PNNL analyzed the 

bonus flaws using the same high-quality RT images, which provided a consistent sizing 

standard and reliable methodology for characterizing flaw type for these non-intentional flaws. 

For the carbon steel pipe study, if there were any fabrication flaws missed by RT, the flaw type 

was assigned LOF for any bonus flaws. LOF is the type of flaw typically missed by RT 

according to a recent PNNL literature study (Moran et al. 2010).

Figure 7-2 provides a diagram of typical image display features used to analyze PA-UT data. 

The UT raster scan data are presented with a C-scan (top view) in the upper right, B-scan (side 

view) in the bottom right, D-scan (end view) in the bottom left, and a Sectorial scan (multi-angle 

view) in the upper left portions of the analysis window. All UT images have the U-Sound, Scan, 

and Index scales intentionally covered as some of these specimens are intended to be used for

future procedure and personnel qualifications, so the specimen numbers and the flaw locations

are purposefully not revealed to maintain the integrity of the test set. Note that not all of the UT 

images that follow contain an echo-dynamic curve along the U-sound axis.
7-3

A total of 34 implanted, or intentional flaws, were evaluated using PA-UT. The planar flaws 

included eleven lack of fusion (LOF), four lack of penetration (LOP), and nine cracks. The 

remaining flaws were volumetric, consisting of six slag (SLG) inclusions and four porosities

(POR). Examples of each of the five fabrication flaw types assessed in this study are displayed 

in sets of images shown as Figures 7-3 through 7-17. Each set of figures includes a crosssectional schematic of the flaw type, a radiograph, and a PA-UT imaging screen for the reader 

to understand how each of the flaw types are manifested and displayed in both RT and UT 

images.

Figure 7-2 Description of a Typical PA-UT Analysis Screen Identifying Relevant 

Features and Locations of Weld Responses

Lack of fusion is a condition where the weld filler material does not properly fuse with the base 

material. Figure 7-3 depicts an idealized LOF condition on the side wall bevel of a single 

V-groove weld. PNNL performed RT of a typical area and the image is provided in Figure 7-4. 

The LOF as indicated on the image is to the right of the weld root along the side wall as was 

described by the weld fabricator. There were four implanted LOF flaws not detected by RT.
7-4

Figure 7-3 Weld Schematic for Lack of Fusion

Figure 7-4 Radiographic Image of Lack of Fusion

Figure 7-5 represents an ultrasonic PA analysis screenshot with images of the LOF shown in 

Figure 7-4. These data were acquired from the near side using a 1-V path examination. A

60-degree incident angle has been selected as it provided the highest amplitude response for 

this flaw. All D-scan end views show the flaw response maximized slightly below saturation 

(100% screen height) in the image. The LOF is indicated by a black contour box on the D-scan 

window. The other indication present is the weld root. The flaw SNR is 40.5 dB. These SNRs 
7-5

typically need to be on the order of 8-10 dB or greater for reliable detection of flaws. As an 

example, a 6 dB SNR represents a signal that is a factor of 2 times the ambient noise. The SNR 

was determined from the peak signal response and an average, or mean, noise value at the 

same metal sound path. The average SNR is higher for near-side than far-side inspection 

results due, in part, to the favorable refracted angle relative to the flaw orientation along the 

fusion zone. If the weld crown was not present, however, this flaw may have been higher in 

amplitude from the far-side using a 1⁄2-V path examination. All implanted LOF flaws in this study 

were detected by the 4.0-MHz probe used during the UT examinations from both the near and 

far side of the weld.

Figure 7-5 Ultrasonic Image of Lack of Fusion

LOP, or incomplete penetration, generally occurs in the root area when the weld material fails to 

penetrate the joint completely. A LOP condition has been depicted in the root of a single 

V-groove weld in Figure 7-6. An inside surface photograph and an RT image of a typical LOP 

area are provided in Figure 7-7. As can be seen in the image, LOP is easily identified and 

characterized by RT.
7-6

Figure 7-6 Weld Schematic of Lack of Penetration (incomplete penetration)

Figure 7-7 Photograph and Radiographic Image of Incomplete Penetration

Figure 7-8 represents the PA-UT analysis screen of the same LOP shown in Figure 7-7 when 

examined from the far side using a 1⁄2-V path examination technique and a 65-degree steered 

beam. The LOP is indicated by a black contour box on the D-scan window. The weld root is 

the only other indication present and is partially gated out in the D-scan view to facilitate

analysis. The SNR for this flaw is 30.3 dB. Because of the nature of LOP (that it occurs at the 

weld root), amplitude responses are nominally the same from either side of the weld. Thus, all 

LOP flaws in this study were detected during UT examinations from both the near and far side 

of the weld.
7-7

Figure 7-8 Ultrasonic Image of LOP

A crack is a fracture‐type discontinuity characterized by a sharp tip and high ratio of length and 

width to opening displacement. Figure 7-9 depicts an idealized crack emanating from the ID in 

the heat-affected zone near the side-wall bevel of a single V-groove weld. A radiographic image

of a crack is provided in Figure 7-10. The crack, as shown in the RT image, consists of several 

linear indications. Cracks are very challenging to identify using RT with detection being highly 

dependent on orientation relative to the penetrating radiation. The crack in Figure 7-10 has a 

large enough vertical dimension (through-wall depth) to provide sufficient density variation to be 

visible in the image. Cracks lying in non-favorable orientations (less parallel with regard to the 

interrogating beam) and of insufficient depth are nearly opaque to RT. The dark areas of this 

particular crack provide some depth information, but are difficult to quantify. Crack opening and 

morphology along the depth of the crack may account for the multiple linear indications. Based 

on industry-performed film RT using an Iridium92 source, six of the nine implanted cracks in the 

four piping specimens were detected. Computed RT, which can provide enhanced capability, 

detected an additional implanted crack that was not observed during film RT for the four piping 

specimens.
7-8

Figure 7-9 Weld Schematic of Crack

Figure 7-10 Radiographic Image of a Crack. Note: This image has been magnified 2X 

to enhance the visibility of the flaw for the reader.

Figure 7-11 represents the ultrasonic analysis screenshot for the crack shown in Figure 7-10

when examined from the near side using a 1-V path examination at 65 degrees. The crack is 

indicated by a black contour box on the D-scan window. The weld root is the geometric 

indication present (consistent time-base position across length that plots to known geometry). 

The SNR for the flaw represented here is 42.8 dB. The average SNR is higher for the near-side 

than far-side results. All cracks in this study were detected during the UT examinations from 

both the near and far side of the weld. 
7-9

Figure 7-11 Ultrasonic Image of a Crack

Slag inclusions are nonmetallic solid material (residue left on the weld bead from the flux)

entrapped in the weld material or between the weld and base materials. A slag inclusion 

condition exists in the weld region of a single V-groove weld as depicted by Figure 7-12. A 

radiographic image of slag is provided in Figure 7-13. The area of slag, as indicated in the RT 

image, consists of two separate inclusions. 

Figure 7-12 Weld Schematic of Slag
7-10

Figure 7-13 Radiographic Image of Slag Inclusions. Note: This image has been 

magnified 6X to enhance the flaw visibility for the reader.

Figure 7-14 shows an ultrasonic analysis screenshot for the slag shown in Figure 7-13 above, 

when examined from the near side using a 1-V path examination at a 60-degree steered angle. 

The slag is indicated by a black contour box on the D-scan window. The PA-UT applied did not 

have the resolution to separate the indication into two discrete responses, as shown by the RT 

image (Figure 7-13). The separation between the two slag inclusions is approximately 1 mm 

(0.04 in.), which is the scanning resolution used for UT. Other indications present in the UT 

images are weld root, counter bore, and other implanted flaws being examined in this study. 

The SNR for the slag represented here is 27.2 dB. The average SNR is higher for the near-side 

than far-side access data. All slag flaws in this study were detected during the UT examinations 

from both the near and far side of the weld.
7-11

Figure 7-14 Ultrasonic Image of Slag

Porosity is the result of gas entrapped in the weld, which is essentially a spherical void, or an 

area of voids, in the material. Figure 7-15 is a schematic depicting a cluster porosity condition 

in the weld area of a single V-groove weld. A radiographic image of cluster porosity is shown in 

Figure 7-16. The cluster porosity condition is easily identified and measured in the RT image. 

Depending on individual pore size and proximity to other pores, overall length sizing may vary.

Figure 7-15 Weld Schematic of Porosity
7-12

Figure 7-16 Radiographic Image of Cluster Porosity. Note: This image has been 

magnified approximately 2X to enhance the visibility of the flaw for the 

reader.

Figure 7-17 is an ultrasonic analysis screenshot with images of the porosity condition shown in 

Figure 7-16, when examined from the far side using a 1⁄2-V path examination technique at a 

70-degree steered angle. The porosity area is indicated by a black contour box on the D-scan 

window. Weld root or counter bore responses are not present in this image because higher 

refracted angles tend to reduce or provide no response for ID geometric indications. An

indication on the B-scan window (dark lines that are consistent throughout the scan) is an 

internal reflection within the wedge material. Internal wedge reflections are more apparent

when imaging higher refracted angles. In addition, the gain level needs to be higher in order to 

characterize porosity as the typical amplitude response is much lower compared to planar flaws. 

At higher angles, an internal reflection such as this has the possibility of interfering with a flaw

response, although it does not interfere with the flaw response in this particular analysis. The 

SNR for the flaw represented here is 17.7 dB. The average SNR is higher for the near-side 

than far-side data. With one exception, all implanted (larger) porosity conditions were detected 

during the UT examinations from both the near and far side of the weld.
7-13

Figure 7-17 Ultrasonic Image of Porosity

During UT and RT examinations of the piping specimens containing 34 implanted, or intentional,

fabrication flaws, other non-geometrical indications were observed. These bonus, or

unintentional, flaws were located predominately throughout the weld area, but some were 

observed to be in the adjacent parent material. A total of 90 bonus flaws were detected with a 

combination of both examination methods. Signal discrimination between intended and 

unintended flaws can be difficult because of masking of flaws in the same axial and 

circumferential positions, or if one flaw response gives a stronger response than others nearby, 

as can be seen in Figure 7-18. When analyzing the data from each of the specimens, UT

analysts relied on documentation provided by the manufacturer, and verified by PNNL 

radiography, to discriminate between implanted flaw responses and bonus flaw responses that 

were in close proximity. Flaw maps were created for each data set showing length and location 

of flaw responses, to compare detection capability of each technique applied. Relevant data 

were compiled to aid in this assessment, as exemplified by Figure 7-19, where red denotes 

PNNL RT data, blue is the PNNL PA-UT data, and green is as-built information provided by the 

flaw manufacturer (where applicable). Although not shown in the figures, a tolerance was used 

for making a valid detection assessment between RT, PA-UT, and as-built flaw information. 

PNNL used an allowable deviation of ±25 mm (1.0 in.) from the ends of each flaw in the X, or 

horizontal direction, and ±5 mm (0.19 in.) from the center of the flaw depth position in the Y, or 

vertical direction. The detection tolerance for the X direction was adapted from performance 

demonstration criteria found in ASME Code, Section XI, Appendix VIII, while the detection 

tolerance for the Y direction was based on notable shifts of several flaws when comparing the 
7-14

RT, PA-UT, and the flaw manufacturer’s information. Because three of the specimens are

intended to be used for future industry procedure and personnel qualifications, specimen 

numbers have been changed and specific flaw locations have purposefully not been revealed in 

this report to maintain the integrity of the test set.

Figure 7-18 Example of Bonus Flaws

Figure 7-19 Example of a Radiograph Being Converted into a Flaw Map Which is Used 

to Aid in Interpretation of Detection Capability of UT (blue) and RT (red)
7-15

Figures 7-20 and 7-21 are Venn diagrams that represent a summary of the detection results for 

all fabrication flaws (implanted and bonus, respectively) examined in this study. These

diagrams provide the types and numbers of flaws detected by UT and RT alone, or by both UT 

and RT. A detection table combining both the implanted and bonus flaw results is located in 

Appendix B. The table includes flaw types, flaw length (as determined by PNNL RT, or PNNL 

UT when RT did not detect), whether the flaw was detected by RT or UT, and if the flaw was 

only detected from one side of the weld (UT only). Flaw types are identified as to whether they 

are volumetric (SLG or POR), or planar (LOF, LOP, or CRK), in nature. The flaw types listed in 

the Venn diagrams were determined by PNNL RT true-state characterization for anything 

detected by RT alone, or detected by both UT and RT. In the case where fabrication flaws were 

missed by RT, the flaw type was determined using the flaw manufacturer information for 

implanted flaws and for bonus flaws, assigned a designation of LOF. Based on a recent 

literature review, LOF is the type of flaw typically missed by RT (Moran et al. 2010); this was 

also confirmed by the implanted flaws missed by RT in this study. The detection and nodetection calls are made based on flaw maps created by UT and RT flaw analysts that mapped 

the circumferential and axial positions (distance from weld root or counter bore) for each flaw 

detected.

Figure 7-20 RT and UT Detection Results for All Implanted (intentional) Fabrication Flaws
7-16

Figure 7-21 RT and UT Detection Results for All Bonus (unintentional) Fabrication Flaws

In Figure 7-20, which summarizes results for implanted flaws, UT detected all flaws except for 

one area of porosity that was 5.3 mm (0.2 in.) in length. RT missed 5 out of the 24 planar flaws. 

The 5 flaws missed by RT ranged from 5.7 mm (0.22 in.) to 21.1 mm (0.83 in.). A commonly 

held standard for reliable ultrasonic detection of both volumetric and planar flaws has been that 

the signal response should, at a minimum, be twice the amplitude of ambient noise signals over 

some finite time interval. Thus, minimum SNR for reliable UT detection is two-to-one (2:1), or 6 

dB, and this flaw signal must have some minimum screen persistence for this detection to 

reliably occur. The average SNR (UT only) for the planar flaws (CRK/LOF/LOP) was 29.1 dB 

and the average SNR for the volumetric flaws was 22.6 dB, indicating that for the PA-UT applied 

in this study, both type of flaws are clearly distinguished from background noise in the carbon 

steel materials tested. 

An advantage of using encoded PA-UT is the ability to resolve flaws that may be aligned or 

close together in one plane, but separated in others. For example, the LOF displayed in 

Figure 7-22 is a flaw that RT was unable to detect because of the presence of a concave root 

condition. The LOF is observed at the mid-wall along the weld centerline directly above the 

root. If UT was limited to only a top, or plan, view (image in upper right corner of the figure), the 

flaw may have been obscured by the concave root condition, as is the case with RT. However, 

perspectives from the end-view and side-view (bottom images), clearly provide capability to 

detect other indications in the same circumferential location and plane as the concave root, but 

located at a different through-wall position. 
7-17

Figure 7-22 Example of LOF that was Not Detected by RT

Figure 7-23 is a schematic providing location and geometry for this LOF and concave root 

condition. LOF are planar flaws that require nearly parallel alignment with the incident 

penetrating radiation to be capable of being imaged by the RT detection media. Therefore, the

LOF in this example could potentially be difficult to discern, even if the concave root condition 

had not been present. Figure 7-24 is an RT image of the incomplete penetration area. 

Tangential RT examinations may have provided evidence of this LOF indication, but these were

not performed as part of this study.

Figure 7-23 Schematic of LOF and Concave Weld Root as Shown in Figure 7-22 PA-UT 

and Figure 7-24 RT Images
7-18

Figure 7-24 RT Image of Concave Weld Root

As previously shown, compiled bonus flaw detections are displayed in Figure 7-21. Twenty 

flaws were detected that were considered to be the same flaws using both UT and RT. There 

were, however, 38 flaws found only by RT and 32 flaws found only by UT. The flaw length 

histogram in Figure 7-25 was developed to help explain why there were numerous flaws 

detected by only one method. Of the flaws detected by RT only, 31 were less than 4 mm 

(0.15 in.) in diameter, which is smaller than the focal spot size of the 4.0-MHz PA-UT method 

applied; these 31 flaws were considered acceptable when applying ASME Code, Section III 

acceptance criteria. The two largest flaws found only by RT were a string of porosity and a 

convex root. These two flaws were masked by implanted flaws in the same region when 

examined with UT. The implanted flaws were both relatively large, unacceptable planar flaws, 

clearly more critical than either the porosity or convex root. The main advantage of RT over UT 

is the ability to discretely image flaws that are in close proximity in planes perpendicular to the 

incident radiation direction as RT has better spatial resolution, a benefit for imaging flaws that 

are closely spaced. Figure 7-26 is a radiograph of an in-line porosity that is adjacent to a LOF 

indication. The UT analysis may not be able to isolate or spatially separate independent flaws 

when they are relatively close together, such as shown in this figure.
7-19

Figure 7-25 Bonus Flaws Missed by UT (38) or RT (32)
7-20

Figure 7-26 Adjacent Flaws Easily Discernible with RT

RT missed 32 flaws that were detected by UT. All of these flaws were assumed to be LOF as 

this type of flaw is typically missed by RT (Moran et al. 2010). Furthermore, this assumption is 

supported by the fact that the majority of implanted flaws missed by RT in this study were LOF. 

RT had difficulty detecting LOF flaws because of the relative orientation of the radiation beam,

and flaws being masked, or over-layered with other flaws, at the same axial and circumferential 

positions. Unlike RT, which cannot detect through-wall extent, UT is capable of detecting these 

“stacked” flaws at different depths. Figure 7-27 is an enlarged D-scan (end view) and C-scan 

(top view) image of Figure 7-5. UT clearly provides evidence that this flaw is not connected to 

the ID surface when using the depth information provided in the end view. Further, by looking at 

the top view, it is clear that this flaw is not along the weld center line, and more likely may be 

located along the fusion line. By using X- and Y-spatial cursors, and both C- and D-scan 

images, the flaw can be precisely located in a three-dimensional fashion, thus allowing an 

analyst to determine if it is a fusion zone flaw.
7-21

Figure 7-27 Example of Side Wall LOF (D-scan view on left and C-scan view on right)

During the examinations, it was noted that all intended flaws detected by UT were not always 

detected from both sides of the weld; this is also true for the 32 bonus flaws detected only by 

UT. When a combined set of flaws (both intended and bonus) are considered, they were

detected by UT from only one side of the weld approximately 46 percent of the time. Therefore, 

if welds were to be examined from only one side of the field, it is quite possible that many flaws 

could go undetected. It should be noted that this was a very limited study in terms of weld 

types, geometries, and numbers/sizes of varied welding flaws. Thus, for statistical purposes,

the reader is cautioned with regard to the use of this single-sided detection result. During this 

limited study, it was not possible to fully assess fundamental causes for one-sided UT flaw 

detection; however, one would expect that a primary reason is the flaw location and orientation 

relative to the UT propagation beam(s) used for examining the weld. In a simple example, a

flaw may not be detectable in the interrogated volume by only using the first leg of sound at a 

single inspection angle, as shown for the 60-degree beam in Figure 7-28. This flaw, however, is 

detectable at 70 degrees or with the second leg of sound at a 45-degree inspection angle. 

A related concern is whether full insonification of the weld can be adequately performed with a 

scan-restricting weld crown present. In this study, PNNL used second and third legs of sound 

being skipped into the regions of interest to accommodate the presence of weld crowns. 

However, phased array is most effective when the sound beams can be controlled in the area of 

interest. Focusing and steering of sound using PA-UT can only be accomplished in the near 

field of the probe (the near field is related to the active aperture length). The near field of 

industrial PA probes, and common focal law development algorithms, generally allow this beam 

forming to occur only in the first leg of sound. Therefore, optimum sound beams are not being 

produced by skipping them into the weld volumes to ensure coverage. Figure 7-29 shows an 

example of a planar flaw on the fusion zone within the inner one-third of the weld volume. 

When a weld crown is present, one method using shear waves would be to bounce the sound 

using a full-V approach from the near side of the weld. However, if this is not possible because 

of geometry or obstruction, or insufficient angles for an optimum V-path to be performed, a 

planar flaw may be missed from the near side, but based on inspection angle, can be easily 

detected from the opposite side when inspecting through fine-grained materials such as carbon 

steel. The best method would be to remove the weld crown, and apply PA-UT from both sides 
7-22

of the weld using multiple sound beams focused and steered within the first leg of sound. 

Detection of the flaws in this study with full- and 11⁄2-V techniques provides a testimony to the 

robustness of the phased-array probes applied; this may also be positively influenced by the 

relatively fine-grained, easy to insonify, carbon steel materials assessed. Conventional singleprobe examinations cannot replicate the phased-array capability and would not be expected to 

perform adequately without the application of many scans at multiple angles.

Figure 7-28 Schematic of a Phased-Array Multiple Angle Inspection

Figure 7-29 Schematic of Phased-Array Inspection from Near and Far Side of the Weld

In summary, PA-UT detected all planar flaws that were detected by RT except for two small 

LOF that were approximately 1.8 mm ( 0.07 in.) and 3.8 (0.14 in.) in length. Further, UT 

detected five implanted and 32 bonus planar flaws that were missed by RT and all but one of 

the volumetric flaws that RT detected. However, 35 small [nominally less than 4-mm (0.15-in.)] 

volumetric flaws were not detected with UT, as well as one implanted flaw. All of these 

volumetric flaws undetected by UT were smaller than the focal spot size of the probe. Only one 

of the porosities in this set of volumetric flaws was large enough to be unacceptable by the 

acceptance criteria in ASME Code, Section III.

Among other issues when applying RT, such as the difficulty of application and related safety 

concerns, is a primary disadvantage in its inability to locate flaws within the three-dimensional

volume of the material being examined. The ability to assess through-wall flaw depth 

information and, a related attribute, to discriminate flaws stacked throughout the thickness in the 
7-23

same circumferential location, provide primary technical advantages for UT. In this study on 

relatively thin-walled carbon steel, and using advanced PA techniques, UT could detect many 

flaws using the second or third legs of sound, when the first leg of sound could not be applied

because of the presence of weld crowns. It should be noted that this ability to use the second 

or third legs of sound may only be possible in fine-grained carbon steel welds, using largeaperture PA probes; however, this may not be true for coarse-grained weldments in stainless 

steel materials. The effectiveness of UT examinations for these materials remains to be 

determined.

7.1.2 Flaw Sizing

When applying RT, length-sizing of indications is fairly straightforward because the flaws being 

sized are simple projections and are visually apparent on the RT image. Correct sizing is 

affected by the geometrical unsharpness (lack of clarity or sharpness) of the RT image. Thus, 

PNNL maintained the necessary distance between the X-ray source and the pipe/imaging plate 

to meet all of the requirements specified in the ASME Code for geometrical unsharpness.

PNNL uses a software program (discussed in Section 5.4) for measuring lengths and diameters 

of indications on the RT screen image. The radiographic image is essentially a two-dimensional

plan view of the part being examined combining, or merging, each thickness of the part. 

Unfortunately, conventional RT does not allow examination of each of the cross-sectional areas

over the part thickness; rather, the result is a composite over all of these areas, which provides

a projection of the flaw onto a plane perpendicular to the incident X-ray incident beam. So, a 

small volumetric indication can only be measured by its widest cross section in that plane. 

Thus, a measurement in the vertical or thickness direction cannot be made from this image, 

resulting in the inability of RT to directly locate and size flaws in the through-wall volume of the 

part being examined. 

The flaw-sizing measurement accuracy of the RT software depends on a calibration technique 

for each of the images analyzed. A known dimension of an object in the image is applied to 

calibrate the software; this measurement value is then saved and used as a basis for all other 

measurements on that image. PNNL used measurements from penetrameters that were placed 

as image quality indicators on each of the RT images for this size calibration. The 

penetrameters are designed to a very tight tolerance and the dimensions of each are known, or 

easily measured. Figure 7-30 shows how the software is used to set a known penetrameter

width, and then used to make a measurement of a flaw in the weld on the RT image. This 

method of measurement is very accurate for flaw length-sizing. Figure 7-31 is an image of 

incomplete penetration and the flaw measurement performed on the RT image.
7-24

Figure 7-30 Example Radiograph Showing Sizing Methods Using RT Software

Figure 7-31 Length Measurement of Incomplete Penetration Flaw
7-25

Ultrasonic length-sizing presented in this section was performed on all detected flaws 

(previously presented in Figures 7-20 and 7-21) using the 4.0-MHz TRS phased-array probe. 

Flaw length was measured at both the −6 dB (half amplitude) and −12 dB points on each flaw 

response in order to determine the most accurate method of sizing for each flaw type. 

Length sizing techniques used on the piping specimens provide an OD length dimension that is 

longer than the actual length dimension because of the curvature of the piping material. The 

UT-corrected length is defined as:

Diameter at Flaw Depth Measured Flaw Length = Flaw Length at Depth of Flaw OD

×

Measurements for a majority of the data were straightforward and easily sized at −6 dB and 

−12 dB levels, but certain data required interpretation because of noncontiguous signals or 

interference from other reflectors that could not be gated out. This interpretation is likely to add 

subjectivity and human error into the measurement. As previously stated, three of the piping 

specimens will be used in the future for blind procedure and personnel qualifications, so their

numbers have been changed and the flaw lengths and locations are not directly presented in 

the report to maintain the integrity of the test set.

A benchmark used to determine the effectiveness and value of the UT measurement approach 

is to compare length-sizing results from the evaluation against ASME Code, Section XI 

acceptance criteria for a successful ultrasonic performance demonstration. The ASME Code 

length-sizing criterion calls for a root mean square error (RMSE) of less than 19.05 mm 

(0.75 in.). Table 7-1 presents a summary of the UT length-sizing results in terms of RMSE 

values for combined implanted and bonus flaws from all four carbon steel specimens as a 

function of being scanned from either the near- or far-side of the flaws. Radiographic results are 

used as the true state.

When sizing porosity, slag, and LOF, −6 dB was typically better than −12 dB as a sizing 

method. However, the opposite was true when sizing LOP and cracks, where −12 dB sizing 

fared better than −6 dB. Many factors influence sizing results such as size of flaw, surface 

connectedness, flaw type, insonification angle, use of second and third leg of sound, etc. These 

factors were not fully investigated. All results met the current ASME Code, Section XI, 

Appendix VIII RMSE length-sizing performance acceptance criterion of being less than 

19.05 mm (0.75 in.). However, it is very important to note that this criterion is applied during 

performance demonstration processes for service-induced cracking, and may not necessarily 

translate to acceptable error for fabrication flaw sizing. Thus, this remains a technical gap that 

will need to be addressed. The plus and minus sign after the RMSE values in Table 7-1 are 

indicators of tendencies for UT to over (+) or under (-) size the flaws, but does not mean each 

flaw within each type was over or undersized. The significance of over and under sizing these 

flaws relates to the potential to determine whether to accept or reject (repair) a flaw when 

appropriate fabrication criteria is applied.
7-26

Table 7-1 RMSE Length Sizing Summary: (-) indicates typically under sizing and (+) 

indicates typically over sizing

UT Length 4.0 MHz (mm/in.)

Flaw Type Near Side Far Side

6 dB RMSE 12 dB RMSE 6 dB RMSE 12 dB RMSE

Porosity 3.18 / 0.13 (-) 7.08 / 0.28 (+) 3.45 / 0.14 (+) 6.89 / 0.27 (+)

Slag 5.41 / 0.21 (-) 8.96 / 0.35 (+) 8.70 / 0.34 (-) 8.99 / 0.35 (+)

LOP 8.46 / 0.33 (-) 5.44 / 0.21 (-) 6.40 / 0.25 (-) 2.30 / 0.09 (-)

LOF 8.24 / 0.32 (+) 10.45 / 0.41 (+) 6.03 / 0.24 (+) 8.26 / 0.33 (+)

Crack 11.08 / 0.44 (-) 7.31 / 0.29 (+) 9.46 / 0.37 (-) 7.45 / 0.29 (+)

In summary, UT is more likely to oversize porosity and LOF. While LOF of any length is 

typically a cause for rejection, this tendency has a potential to classify certain benign 

(acceptable) porosity assessments as unacceptable because of their size. On the other hand, 

UT tended to undersize cracks and LOP, which could cause an unacceptable structural flaw to 

be accepted and remain inservice. For all fabrication flaws evaluated, the RMSE values were 

within ASME Code, Section XI, Appendix VIII acceptance criteria of 19.05 mm (0.75 in.). 

7.2 Navy Plate Assessment

Historically, the U.S. Navy inspected structural welds such as those in submarine hulls with 

radiography. The use of radiography was favored for many years as it provided a hard-copy 

record of the inspection in the form of the radiographic image, and it was thought to be a very 

accurate inspection method. Radiography, however, had many shortcomings, not the least of 

which was the disruption of work in the vicinity of the radiographic source and the time delay 

between inspection and availability of results due to film processing. Thus, in the mid-1980s, 

the U.S. Navy began a program to assess the use of UT as an alternative to radiography for 

submarine hull weld inspection. The successful demonstration of ultrasonic inspection was 

desired as implementing UT for weld inspection would result in reduced cost of inspection, 

increased productivity, more immediate inspection results including knowledge of the depth of 

the discontinuity, and potentially more accurate sizing of the discontinuity. As such, the 

objective of the Navy “UT/RT” program, which took place over several years, was to determine if 

structural welds could be ultrasonically inspected with repeatability and reliability comparable to

that obtained with radiographic inspection.2

The Navy program compared standard practice manual UT and radiography by inspecting 

36 welded test plates with each inspection technique. Eighteen of the test plates were 

fabricated with purposely induced discontinuities from 38-mm (1.5-in.) thick steel plate welded 

with double-V-groove joints. Shielded metal arc welding and automated and semi-automated 

 2 DeNale R and C Lebowitz. 1990. Ultrasonics as an Alternative to Radiography for Submarine 

Hull Weld Inspection. DTRC-SME-90/30, Office of the Assistant Secretary of the Navy, Naval 

Sea System Command, David Taylor Research Center, Bethesda, Maryland. Available only by 

request to the Commander, Naval Seas Systems Command (SEA 05M2).
7-27

gas metal arc welding processes were used to fabricate these plates. The other 18 welds were 

removed from service. The 36 test plates contained a total of 212 discontinuities including slag, 

lack of fusion, incomplete penetration, cracks, slugs, clustered porosity, and scattered porosity

(Lebowitz and DeNale 1991).

The Navy’s conclusions included: “a) Ultrasonics has a higher probability than radiography of 

detecting and consistently rejecting planar discontinuities. A review of literature has shown that 

planar flaws are considered to be more detrimental to weld quality than volumetric flaws,

b) Ultrasonics and radiography have comparable capacities for detecting and rejecting 

volumetric discontinuities, and c) Ultrasonics is an acceptable alternative to radiography for weld 

inspection”.

3

 

PNNL examined three of the remaining Navy “UT/RT” test plates to determine if today’s PA-UT

examination methods would support the Navy’s conclusions, and to expand the weld thickness 

range performed for carbon steel on piping specimens under the current NRC project. Another

objective was to confirm industry assertions that individual flaw types (e.g., cracks, LOF, LOP, 

slag, porosity) can be differentiated using phased-array UT methods. In this section, a 

comparison of the detection and flaw typing characterization on the Navy plate specimens will 

be presented.

7.2.1 Navy Flaw Detection and Characterization Protocol

In terms of the Navy inspections, eight shipyard inspectors, with qualifications equivalent to 

ASNT Level II, performed manual UT, and eight radiographic interpreters, with qualifications 

equivalent to Level II, reviewed all of the radiographs. The manual ultrasonic inspections were 

performed with a Krautkramer-Branson USL-48 ultrasonic flaw detector using a 2.25-MHz 

transducer mounted on a wedge that produced a 60-degree effective angle in steel. The 

radiography was performed with three different sources (X-ray, cobalt-60, and iridium-192) and 

two types of film (Kodak types AA and M). Consensus discontinuities, or those that were 

detected by a majority of inspectors or interpreters using at least one of the inspection methods, 

were identified by reviewing all of the inspection results, classified as to type, and a sample set 

verified by sectioning and metallography. Discontinuities were given one of four labels: crack 

(CRK), lack of fusion (LOF), slag (SLG), or porosity (POR). For purposes of the PNNL study, 

the Navy consensus detection and flaw typing results were used, but if a discontinuity was only 

detected by Navy UT, the discontinuity is not reported here.

7.2.2 PNNL UT Flaw Characterization Study

With amplitude and image analyses being more straightforward than sizing and characterization, 

PNNL UT detection data was recorded by only one analyst; however, because of the level of 

subjectivity inherent to this process, the flaw typing characterization study was performed by 

 3 DeNale R and C Lebowitz. 1990. Ultrasonics as an Alternative to Radiography for Submarine 

Hull Weld Inspection. DTRC-SME-90/30, Office of the Assistant Secretary of the Navy, Naval 

Sea System Command, David Taylor Research Center, Bethesda, Maryland. Available only by 

request to the Commander, Naval Seas Systems Command (SEA 05M2).
7-28

three independent personnel designated as Analysts A, B, and C. First, phased-array line scan 

data was used to detect and locate indications on Navy Plates 10, 18, and 23. Line scans are

used mainly for initial detection purposes as they can be performed in a fraction of the time 

needed for raster scanning, and line scan file sizes are much smaller than raster scan data. 

Merged line scan images are a much more efficient method of detecting, or screening,

responses within large areas of examined materials. Indications were recorded into an Excel 

worksheet if the amplitude of the signal exceeded the established detection threshold, described 

in Section 6.2.2. After the initial detection was recorded, raster scan data was acquired for each 

flaw location in order to allow a more thorough characterization of the indications. Analysts A, B,

and C were provided with the −6 dB start and stop positions (length) and the depth location for 

each of the detected indications. From this information only, all three analysts reviewed the 

raster scan data to evaluate and characterize the flaw type using a flaw-type decision matrix.

The flaw-type decision matrix (Table 7-2) was created from materials presented at an industry 

workshop on Phased Array UT Analysis in Breezy Point, Minnesota, during the summer of 

2012. Discussions at the workshop centered around the idea that ultrasonic testing could 

consistently and reliably detect and characterize embedded fabrication flaws as seen with 

carbon (low-alloy) steel weld configurations where typically RT had been the NDE method of 

choice. Presentations were given for part of the workshop, with the other portion of the 

workshop aimed at hands-on data analysis methods focusing on understanding of field 

techniques used to identify and characterize a variety of flaw types using PA-UT imaging (B, C, 

and D views), and various A-scan parameters.

The “echo-dynamic travel” and the “rise and fall response” columns in the flaw type decision 

matrix (Table 7-2) were based on A-scan methodologies. While examining an A-scan signal, if 

a quick rise and fall of the indication is observed, along with short echo-dynamic travel time, the 

matrix would characterize the flaw to be more volumetric (SLG/POR) in nature. When multiple 

peaks are observed with longer echo-dynamic travel time, the indication is characterized to be 

more planar (CRK/LOF). Echo-dynamic travel increases with increasing refracted angle,

making this characteristic of the matrix more subjective than some of the other signal variables.

Amplitude-based characteristics are used in matrix columns labeled “amplitude from same 

side,” “detection angle effect on signal response,” “amplitude from opposite side of the weld,”

and “relative amplitude from other flaw types.” Signal amplitude tends to be higher for planar 

flaws (CRK/LOF/LOP) than volumetric flaws (SLG/POR). Volumetric (SLG/POR) flaws and 

LOP display similar amplitude responses from either side of the weld. Lack of fusion and

certain cracks (depending on orientation) generally display a higher amplitude response when 

scanning from the opposite side of the weld, and a lower, or non-existent, response when 

scanning from the same side of the weld using 1⁄2-V (first leg of sound) examinations. This 

applies to single-V or the upper half of double-V welds (Navy Plates 10, 18, and 23). If an

indication is located on the lower half of a double-V weld, then the opposite amplitude response

conditions would be true. The key factor is whether the beam is hitting the planar flaw 

broadside (good response) or at a glancing angle (poor response). 
7-29

Table 7-2 Flaw Type Decision Matrix

Echo 

Dynamic 

Travel 

"Walk"

Evidence 

of Tip 

Signals

Amplitude 

Signal 

from 

Same 

Side(a,b)

Evidence 

of Mode 

Converted 

Signals

Detection 

Angle Effect 

on Signal 

Response

Absent 

Root 

Response

Rise and 

Fall 

Response

Amplitude 

from 

Opposite 

Side of 

Weld(a,b)

R

Am

fro

Fla

General 

Flaw Type

Specific 

Flaw 

Type

Short/Long Yes/No Similar/ 

Lower or 

No 

Detection

Yes/No No effect/ 

Lower 

angles better 

signal 

response

Yes/No Multiple 

Peaks/ 

Quick

Lower/ 

Higher/ 

Similar

H

Planar

CRK(c) Long Yes similar Yes (d) No(e) --- (f) 

LOF Long Yes Lower or 

No Detect --- No effect(g) No Multiple Peaks Higher 

ICP ---

Split Signal 

Response -

similar to tip

Similar ---

Lower angles 

better signal 

response

Yes --- Similar 

Volumetric

SLG Short No Similar --- No effect No Quick Similar 

POR Short No Similar --- No effect No Quick Similar 

(a) Applies to single V welds and upper half of a double V weld.

(b) For lower half of double V weld - switch LOF responses from same and opposite side of weld in the table.

(c) These are typical responses from ID-connected cracks.

(d) Higher angles mean that amplitude can be similar or higher if the same reference sensitivity criteria are applied to each angle.

(e) Yes, if flaw is in base material on same side access.

(f) Can be higher in carbon steel based on flaw orientation.

(g) Based on bevel angle/flaw orientation.
7-30

Certain image characteristics are the bases for information in columns “evidence of tip signals,”

“absent root response,” and “location of signal.” When determining the location of a signal on 

the Navy plates, the analysts overlaid a weld profile in the data that matched the actual plate 

thickness and weld geometry (similar to Figure 3-4). When a signal plotted on the sidewall of 

the weld joint, it was more likely to be labeled as LOF. A signal was more likely to be 

characterized as LOP if the response showed up just short of where the weld root response 

should have been. A flaw that had connections to the ID had a higher possibility of being 

labeled a crack. When the indication showed up anywhere else in the weld volume, the 

indication was more likely to be classified as a slag or porosity. The crack-typing information 

used in this matrix is more representative of an ID-connected, service-induced crack, so if the 

indication was at mid-wall or an OD-connected response, the probability of the matrix classifying 

it as a crack was greatly reduced. Each of the different flaw types will not display each of these 

characteristics all of the time, making flaw characterization via the industry matrix highly analystdependent.

Before PNNL began the independent data analysis study, the three analysts held a brief training 

session to discuss the flaw-type decision matrix, what each of the characteristics meant when 

assessing the phased-array data, how to consistently record the data, and how to remain 

independent until all data could be reviewed. The analysts also viewed and discussed a few 

examples of different fabrication flaw types from data provided at the industry workshop in order 

to assist each of the analysts in understanding how to consistently distinguish between different 

flaw types while using the flaw-type decision matrix. After this training session, the three 

analysts worked independently. Characterization results were compiled into one Excel 

spreadsheet to facilitate an assessment of using the industry matrix. The flaw types were 

generalized as planar for any LOF, CRK, or LOP and volumetric for any SLG or POR. This type 

of characterization complies with the ASME Code, Section III acceptance criteria, where all 

planar flaws are deemed rejectable, regardless of length, and all volumetric flaws are either 

acceptable or rejectable, based on their length.

Figure 7-32(a and b) provides results for the independent analyses when using the flaw-type 

decision matrix for each of the indications found in Navy Plates 10, 18, and 23. The Venn

diagram [Figure 7-32(a)] indicates that all three analysts determined that 21 flaws (16 planar 

and 5 volumetric) were the same flaw type out of 50 total recorded indications. Therefore, only 

42 percent of the flaws were consistently characterized using the industry decision matrix. 

When comparing the results for pairs of analysts, the consistency in flaw characterization

increased to between 54 and 68 percent, depending on which two analysts were being 

compared. Clearly, flaw characterization based on the decision matrix is highly subjective and 

dependent on analyst experience. When using the matrix, indications did not display all of the 

“ideal” characteristics for each of the different column variables. This required each of the 

analysts to weigh flaw characteristics and provide more weight to features they considered more 

significant and less to others when making their assessments. One analyst chose amplitude as

the most important characteristic, so more reliance on the matrix columns that use amplitudebased measurements was shown. Another analyst made decisions based on a majority basis

such that if a majority of characteristics (A-scan response, amplitude, and image variables)

indicated a planar flaw, the flaw characterization was planar. The amplitude and signal 

responses varied depending on what angles were used in the analysis, which also contributed 
7-31

to flaw characterization discrepancies. The use of the weld profile overlay in the data was 

helpful in locating the flaw within the weld volume, but there was analyst subjectivity in 

placement of the weld overlay, which may also affect the flaw typing.

Figure 7-32 Results of Independent Flaw Type Analysis
7-32

7.2.3 Comparison of Navy RT with PA-UT for Flaw Detection and Characterization

PNNL compared the indications found by PA-UT to the Navy consensus data. Flaw maps were 

created in MATLAB for each examination station on Plates 10, 18, and 23. As mentioned 

previously, unlike Plate 23, which had a low stress stamp marking a zero reference, no clearly 

identifiable zero position existed on Plates 10 and 18. Therefore, PNNL created a new

reference point for these plates. However, a notable shift in locations of flaws was observed 

between the PA-UT data and the Navy data during the initial comparison. PNNL performed 

computed radiography on Plates 10 and 18, specifically targeted for resolving disagreements 

between locations of flaw responses between PA-UT and Navy consensus data, and to identify

all indications that could be clearly detected in these digital images. The PNNL RT information 

(position, length, and flaw type) was recorded in a spreadsheet and added to the flaw maps for 

Plates 10 and 18. When comparing PA-UT, PNNL RT, and Navy data, it was evident that the 

PA-UT data had been scanned from the opposite side of the weld than the original Navy 

reference point. This information was used to reverse the PA-UT about the horizontal axis for 

Plates 10 and 18, thus bringing the Navy and PNNL results into better alignment. 

Final flaw maps are shown in Figures 7-33 through 7-37. As noted in the legend, green 

indications correspond to PA-UT data, blue to Navy RT data, and red to PNNL digital RT data 

(for Plates 10 and 18 only). A blue box outline has been generated to represent the tolerance 

used for making a valid detection assessment. PNNL used an allowable deviation of ±25 mm 

(1.0 in.) from the ends of each flaw in the X, or horizontal direction, and ±7 mm (0.28 in.) from 

the center of the flaw position in the Y, or vertical direction. The detection tolerance for the 

X direction was adapted from performance demonstration criteria found in ASME Code,

Section XI, Appendix VIII, while the detection tolerance for the Y direction was based on notable 

shifts of specific flaws in the PNNL digital RT and phased-array UT data as compared to the 

Navy consensus flaws. The figures provide information pertaining to scans performed from 

either side of the weld (labeled skew 0 and skew 180). Other important symbols on the flaw 

maps are dashed lines that represent volumetric flaws, and solid lines with circle endpoints 

denoting planar flaws. The flaw characterizations made by PNNL PA-UT are simple majority

calls, meaning two or more of the analysts made the same interpretation on a particular flaw. 

The numbers listed in the boxes represent PNNL’s calculations of the detection percentages for 

each of the Navy RT-called flaws based on information provided to NRC/PNNL by the Navy.

The percentage is calculated from number of interpreters that called the flaw out of the possible 

48 calls (48 possible calls from 8 radiographic interpreters and 6 radiographic methods). These 

percentages are presented here to represent the level of radiographic detection that resulted 

during the Navy study.

The PNNL analysts considered a flaw to be detected, compared to the Navy RT results, when it 

fell within the tolerance “box” as described above. When the PA-UT only detected the flaw from 

one side of the weld, the flaw was still considered to be detected. When there were multiple 

flaws located within the tolerance box, only the closest UT indication to the Navy RT indication

was called the flaw (the others indications were listed as additional findings by PNNL UT).
7-33

Figure 7-33 Flaw Map of Plate 18 Station 1, Axes Units are in mm

Plate 18, station 1 (Figure 7-33), displays two volumetric Navy consensus flaw, with Navy RT 

detection rates of 72.9 percent and 81.3 percent, respectively. PA-UT only detected one of 

these volumetric flaws (81.3 percent Navy consensus) when scanned from skew 180 side of the 

weld. PNNL digital RT confirmed both of these indications. PA-UT detected an additional 

planar flaw at 100 mm (3.9 in.) in the horizontal axis as scanned from the skew 180 side of the 

weld. This planar flaw was not detected by Navy or PNNL RT.
7-34

Figure 7-34 Flaw Map of Plate 18 Station 2, Axes Units are in mm

Navy Plate 18, station 2 shown in Figure 7-34, displays four Navy consensus flaws. Navy RT 

characterized two flaws as volumetric with detection rates of 60.4 and 75 percent, and the other

two flaws as planar with detection rates of 60.4 percent and 97.9 percent, respectively. PA-UT

detected three of the four Navy consensus flaws, although only one of the flaws was correctly 

characterized (the 60.4 percent planar flaw). PA-UT missed a small volumetric flaw that could 

also not be confirmed using high-resolution PNNL digital RT. PA-UT detected an additional 

planar flaw and two volumetric flaws when scanning from the skew 180 side of the weld. These 

flaws were not detected by any of the Navy RT interpreters.
7-35

Figure 7-35 Flaw Map of Plate 10 Station 1, Axes Units are in mm

Navy Plate 10, station 1 (Figure 7-35), displays only one planar flaw identified as consensus by 

the Navy, with an RT detection rate of 47.9 percent. Both PA-UT and PNNL digital RT detected 

this flaw, although both methods characterized this flaw as being volumetric in nature. PA-UT 

detected five additional planar flaws that were not identified by Navy RT; three scanning from 

skew 0 and two scanning from skew 180 side. 
7-36

Figure 7-36 Flaw Map of Plate 10 Station 2, Axes Units are in mm

Navy Plate 10, station 2, shown in Figure 7-36, displays four flaws identified by Navy 

consensus. Two of the flaws were volumetric indications with detection rates of 72.9 and 79.2

percent, and the other two indications were planar flaws with detection rates of 6.3 percent and 

8.3 percent, respectively. PA-UT detected two planar flaws identified by Navy consensus;

however, PA-UT characterized one of the flaws (6.3 percent) as volumetric. The flaws that were 

missed were both volumetric flaws; one is considered to be rejectable, based on the analyses 

by 57 percent of the Navy RT interpreters using Navy acceptance standards of that time.

PA-UT detected an additional planar flaw and two volumetric flaws when scanning from the 

skew 0 side of the weld. These flaws were not identified by any of the Navy RT interpreters.
7-37

Figure 7-37 Flaw Map of Plate 23, Axes Units are in mm

Navy Plate 23, shown in Figure 7-37, was the only plate taken directly from a decommissioned 

submarine hull and only had one station that was 304.8 mm (12-in.) long. The plate thickness 

was 55.9 mm (2.2 in.) whereas Plates 10 and 18 were 38.1-mm (1.5-in.) thick. There were four

flaws identified by Navy consensus. Two of the flaws were volumetric indications with detection 

rates of 12.5 and 50.0 percent, and the other two indications were planar with RT detection 

rates of 4.2 and 18.8 percent, respectively. PA-UT detected all four of the flaws that were 

detected by Navy consensus. In terms of flaw characterization, of the four consensus flaws, 

only the planar flaw (4.2 percent) characterization was in agreement with Navy RT. The 

characterization of other flaws differed from that called by Navy RT. As PNNL did not perform 

high-resolution RT on this plate, there was no ability to independently characterize the flaws. 

PA-UT detected a total of 16 additional planar flaws and 6 additional volumetric flaws when 

results from skew 0 and skew 180 scans of the weld are considered. These flaws were not 

identified by any of the Navy RT interpreters.
7-38

In summary, PA-UT detected only 11 of 15 (or 73 percent) of the Navy RT consensus 

indications existing in Plates 10, 18, and 23. All four indications missed by UT were volumetric 

flaws, of which two were reported as being rejectable by only 57 and 40 percent consensus, 

respectively, of Navy RT film interpreters using Navy acceptance standards. However, PA-UT

detected 34 flaws that were not detected by Navy RT. 

During this analysis, the UT detection threshold was set at 50 percent of the full screen height, as 

described in Section 6.2.2. This allowed for an efficient screening method that resulted in many 

small, typically irrelevant, indications to be eliminated from being analyzed, but could have also 

allowed a small, potentially relevant flaw, such as LOF or a crack, to remain undetected. The 34 

flaws missed by Navy RT were classified as 10 volumetric and 24 planar flaws by PA-UT. This

result is comparable to that observed in the carbon steel piping results discussed previously, in 

which UT tends to miss small volumetric flaws while RT tends to miss planar-type flaws. 

One observation during this study was that PA-UT does not always provide a readily detectable

response for all flaws when scanning from both sides of the weld. Thus, single-sided examination 

would not be expected to detect all potentially significant flaws, depending on flaw location and 

orientation. In addition, to improve flaw detection, the weld crown should be ground flush with 

surfaces of adjacent parent materials allowing PA-UT scans to be performed over the weld from

four orthogonal directions. This approach would also allow zero-degree, longitudinal wave scans 

to be acquired over the area of interest for enhancing flaw detection and characterization. More 

importantly, weld crown removal would result in enhanced scan area coverage and optimization of 

flaw responses using 1⁄2-V (first leg of sound) PA-UT methods. 

The flaw detection and characterization (volumetric versus planar) results comparing Navy RT 

and PA-UT on Plates 10, 18, and 23 are summarized in Table 7-3. A review of this data shows 

that PA-UT and Navy RT called only four out of the fifteen indications as being the same flaw 

type (volumetric or planar). The Navy flaw typing information was provided by the Navy to NRC 

and can be found in Appendix B of the report provided to PNNL by the Navy.

4

 The Navy RT 

flaw characterizations were consensus data, meaning not all interpreters called each flaw as the 

same type, nor did all interpreters detect all of the flaws, as can be seen in the detection 

percentages presented in Table 7-3. The flaw characterizations made by PA-UT are based on 

two or more of the analysts making the same interpretation (volumetric or planar) on a particular 

flaw. The PNNL RT flaw characterizations were made by one ASNT Level III RT analyst.

The results from the PNNL independent characterization analysis, as mentioned earlier in this 

section, exhibited only 42 percent consistency among three analysts using the same decision 

matrix to make flaw type calls. It was noted that, when using the matrix, indications did not 

display all of the “ideal” characteristics for each of the different column variables. This required 

each of the analysts to consider varied flaw characteristics and provide more weight to features 

they considered more significant and less to others when making their assessments. These 

 4 DeNale R and C Lebowitz. 1990. Ultrasonics as an Alternative to Radiography for Submarine 

Hull Weld Inspection. DTRC-SME-90/30, Office of the Assistant Secretary of the Navy, Naval 

Sea System Command, David Taylor Research Center, Bethesda, Maryland. Available only by 

request to the Commander, Naval Seas Systems Command (SEA 05M2).
7-39

conditions clearly illustrate the subjective, analyst-dependent nature of using PA-UT (even with 

a decision matrix) to differentiate varied fabrication flaw types. The amplitude and signal echodynamic responses varied as a function of the beam angle being used for the analysis. This 

alone could change the characterization result. The use of a weld cross-sectional profile 

drawing overlaying the PA-UT images was helpful in locating a flaw within the weld volume, but 

there is analyst subjectivity in placement of this weld overlay, which could also affect the flaw 

type characterization.

Further assessment of the flaw type characterization matrix was performed by applying the 

matrix to data from one of the carbon steel pipes used previously in this study. Specimen B1A, 

which had the weld crown ground flush, was used for this analysis. The pipe was re-scanned 

as discussed in Section 6.2.3.3 with the 5.0-MHz probe, with scans allowed over the weld. 

PNNL analyst B was selected to analyze the data as this examiner had not previously evaluated 

any B1A data. Only the 13 implanted flaws were assessed in this study. The PNNL analyst 

applied the flaw decision matrix (Table 7-2) on these flaws and correctly characterized 9 of the 

13 flaws for a 70 percent rate. These results are clearly much better than was observed with 

the initial use of the flaw characterization matrix on the Navy plate data. The nine flaws

correctly identified were four volumetric flaws and five planar flaws. A significant contribution to 

the improvement in flaw type characterization performance is believed to be the continuous 

acquisition of data via scans over the entire weld region. This allowed for analysis of the entire 

echo-dynamic (full peak responses) from each flaw. Previously on Navy plates, the data were 

clipped when limited by the presence of a weld crown, thus the peak response was cut off (not 

fully captured). 

The remaining four misidentified flaws were labeled as planar by the flaw manufacturer (and 

corroborated via PNNL digital RT); these were characterized as volumetric by PA-UT. These 

particular planar flaws did not display any tip signals. The through-wall depth of these flaws was

small, and their locations within the weld, with one exception, were not in typical planar flaw 

locations as presented in the decision matrix. In addition, the amplitude responses were much 

lower than the other flaws in this pipe. These results again illustrate the subjective analystdependent nature of using only the flaw type decision matrix, and will most likely lead to 

incorrect flaw type characterization with the potential to allow detrimental flaws to remain in 

these welds.

Additional items for consideration:

No “true state” (only consensus) information was available for the three Navy plates. Also, two 

of these plates did not have clear reference markings. Therefore, PNNL performed computed 

radiography to help establish detection tolerance, to better understand how the plates were 

originally scanned, and to confirm certain Navy consensus results. PNNL performed a singlewall CR technique on these specimens for high quality RT detection and sizing capability.

Further, the digital images can be enhanced for superior flaw detection and characterization 

over a standard film method. This laboratory quality RT, which helped to influence true 

conditions and locations of flaws, would not be expected in the field.
7-40

Finally, in order to make PA-UT data analysis more efficient, a detection threshold was 

established to primarily assess the targeted, or intended, flaws of this study while minimizing 

responses from very small welding anomalies (bonus indications) deemed of less importance. 

This type of detection threshold eliminates analyses of typically irrelevant indications, but could 

potentially allow a small, albeit significant, flaw to remain undetected if applied in the field. The 

detection threshold could have been set lower, which would have enabled very small reflectors 

to be analyzed while allowing more of the targeted Navy consensus flaws to be detected. 

Table 7-3 Flaw Detection/Characterization Analysis between Navy Consensus Calls, 

PNNL UT, and PNNL RT Calls

Plate ID

Navy 

Flaw 

Number

Navy RT 

Detection 

Percentage

Detection/Flaw Type (ND/Volumetric/Planar)

Navy 

Consensus PNNL UT(a) PNNL RT(b)

Plate 10-1 1 47.9% Planar Volumetric Volumetric

Plate 10-2

1 79.2% Volumetric ND Volumetric

2 72.9% Volumetric ND Volumetric

3 8.3% Planar Planar ND

4 6.3% Planar Volumetric ND

Plate 18-1 1 72.9% Volumetric ND Volumetric

2 81.3% Volumetric Volumetric Volumetric

Plate 18-2

1 60.4% Volumetric Planar Planar

2 97.9% Planar Volumetric Planar

3 75.0% Volumetric ND ND

4 60.4% Planar Planar Planar

Plate 23

1 50.0% Volumetric Planar Not Examined

2 12.5% Volumetric Planar Not Examined

3 18.8% Planar Volumetric Not Examined

4 4.2% Planar Planar Not Examined

(a) Based on ≥ 2 of 3 PNNL PA-UT analysts.

(b) Based on 1 PNNL Level III RT interpreter.
8-1

8 CONCLUSIONS AND RECOMMENDATIONS

This report is intended to provide an objective technical evaluation of the capabilities for

advanced ultrasonic testing to detect and characterize flaws in carbon steel piping and plate 

welds when compared to radiographic techniques. A set of four carbon steel pipe-to-pipe 

specimens containing a number of implanted fabrication and simulated service flaws (cracks) 

distributed throughout the volume of the welds was examined using both phased-array UT and 

digital RT techniques. In addition, three carbon steel plates on loan from the Navy containing 

multiple fabrication flaws, as determined by consensus radiographic interpretation, were 

similarly examined using PA-UT. Five different types of fabrication conditions have been 

evaluated, including planar (LOF, LOP, and cracks) and volumetric (POR and SLG) flaws. This

assessment provides a comparison of PA-UT and RT flaw detection, length-sizing, and flaw 

type characterization. Based on the results of this analysis, the following conclusions and 

observations can be made for carbon steel piping and plate welds in a range from 19.1 mm 

(0.75 in.) to 55.8 mm (2.2 in.) in thickness:

Flaw Detection: Phased-array UT detected all planar flaws in the piping specimens that were 

observed using digital radiography, except for two small LOF that were approximately 1.8 mm 

(0.07 in.) and 3.8 (0.14 in.) in length. PA-UT also detected five implanted and 32 bonus (nonintentional) planar flaws that went undetected using RT. Further, UT was shown to be capable 

of detecting all but one of the intended volumetric flaws observed in radiographic images. 

However, UT did not provide adequately detectable responses for 35 bonus (non-intentional) 

volumetric flaws imaged by RT; most (31 of 35) of these were nominally less than 4 mm 

(0.15 in.) in size. This value is smaller than the theoretical focal spot size of the probe at these 

metal paths and the non-detections may be a result of the amplitude threshold set to eliminate 

many very small reflectors. Only one of the porosities was large enough to be unacceptable per 

ASME Section III criteria, which states that any group of aligned indications having an 

aggregate length greater than t (26.1 mm [1.03 in.]) in a length of 12t (313.9 mm [12.36 in.]) 

unless the distance between successive indications exceeds 6L in which case the aggregate 

length is unlimited, L being the length of the largest indication.

Phased-array UT detected all planar flaws identified by the Navy and an additional 24 planar 

flaws that had not been identified by the Navy RT on the plates examined in this study. PA-UT

failed to detect four of the volumetric flaws identified by Navy, of which two were determined to 

be unacceptable by 57 and 40 percent, respectively, of Navy radiographic interpreters, based 

on Navy acceptance criteria at that time. However, PA-UT detected ten volumetric flaws that 

were not identified by the Navy. 

During plate weld analysis, a detection threshold was set. This level of amplitude was 

established to primarily assess the targeted, or intended, flaws in this study while minimizing 

responses from very small welding anomalies (bonus indications) deemed less important. This 

type of detection threshold eliminates analyses of typically irrelevant indications, but could 

potentially allow a small, but significant, flaw to remain undetected if applied in the field. 
8-2

Considering overall detections/non-detections for the piping specimens, as well as the Navy 

plates, it appears that PA-UT, based on the techniques applied in this study, provides an equally 

effective examination for identifying the presence of fabrication flaws in carbon steel welds. The 

PA-UT parameters applied were shown to be more effective for planar flaws, but slightly less 

effective for small volumetric flaws, than RT. This is most likely a function of the acoustic 

wavelength (based on the frequencies applied) and focal limitations from the sound V paths 

employed.

An important capability for UT, as opposed to RT, is an ability to identify through-wall depth and 

volumetric location information for detected flaws. This can be a significant advantage when 

one considers that UT can assess and discriminate the presence of over-laying, or stacked, 

flaws located through the thickness of a weld. In carbon steel, PA-UT was found to detect flaws 

using the second (full-V) or third leg (11⁄2-V) of sound when the first leg (1⁄2-V) could not insonify 

the entire weld volume because of the presence of a weld crown. It should be noted that the

use of second or third legs of sound was made possible in carbon steel because of the finegrained, essentially isotropic, nature of the material; this may not be effective for application on 

coarse-grained materials such as austenitic stainless steels. More importantly, this “skipping of 

sound” is not a best practice for PA-UT, which is most effective when optimal beam forming can 

be accomplished to properly focus and steer the acoustic energy; this is only available within the 

near field of the probe, generally in the first leg of sound. 

During this study, it was observed that UT does not always provide a detectable response when 

insonifying flaws from both sides (opposing propagation directions). Therefore, single-sided

examinations would not be expected to detect all potentially significant flaws, depending on flaw 

location and orientation. In order to improve flaw detection, it is recommended that all weld 

crowns be ground flush with surfaces of adjacent parent materials allowing UT scans to be

performed over the weld. This approach will increase the probability of detecting flaws along all 

fusion zones and throughout the weld volume by enabling scanning to be accomplished from 

opposing parallel and perpendicular directions to the weld, as well as allowing zero-degree data

to be collected for assisting flaw characterization. Weld crown removal will result in enhanced 

scan area coverage and optimization of PA-UT flaw responses using the first legs of sound,

thus improving overall flaw detection and characterization. 

Flaw Sizing: Phased-array UT has been found to be more likely to oversize porosity and LOF. 

Because volumetric flaws are assessed based on length, or diameter, as applicable, this could 

mislead evaluations of detected porosity by making these flaws appear larger than they are in 

reality, thus causing fabrication acceptance criteria (such as found in ASME Code, Section III) to 

be falsely exceeded. Furthermore, this study indicates that PA-UT tends to undersize cracks 

and LOP, which, in opposition to the above, could cause a potentially structurally significant flaw 

to be found acceptable when repair is warranted, if one is applying fitness-for-service 

acceptance criteria as would be found in ASME Code, Section XI. However, this tendency to 

undersize planar flaws is not as important when applying fabrication acceptance criteria 

because all of these type flaws (LOP, LOF, and cracks) are unacceptable regardless of length. 

While the cumulative sizing error for all fabrication flaws evaluated in this study did not exceed 

the length-sizing values required for ASME Code, Section XI UT performance demonstration,

this criterion is typically meant for service-induced cracking, so this level of sizing capability may 

not be applicable to fabrication flaws. PA-UT sizing error, or capability, for fabrication flaws 
8-3

remains as a technical gap. It should be noted that the length-sizing analysis conducted during 

this study included only those flaws detected in the carbon steel piping specimens.

Flaw Type Characterization: PNNL performed a flaw characterization study using three 

independent UT analysts. When using a flaw-typing decision matrix founded upon industry 

protocols, only 42 percent of the flaws were consistently characterized by all PNNL UT analysts. 

Further, when comparing PNNL UT characterizations to the Navy consensus calls, only 4 out of 

the 15 indications in the Navy plates were similarly characterized for flaw type. During use of

the decision matrix (Table 7-2), it was determined that few indications would display all of the 

“ideal” characteristics for each of the flaw attributes being assessed; this required the analysts 

to choose which flaw attributes were more valued, or weighted, over others when characterizing 

flaws. In addition, amplitude and signal echo-dynamic responses varied as a function of the 

beam angle being used for analysis. The use of a weld cross-sectional profile drawing overlaying the UT images was helpful in locating a flaw within the weld volume, but there is analyst 

subjectivity in placement of this overlay, which could also affect flaw typing. These conditions 

clearly illustrate the subjective, analyst-dependent nature of using PA-UT (even with a decision 

matrix) to differentiate varied fabrication flaw types. It is recommended that all performancebased methods developed to demonstrate personnel capability include sufficient variability of

flaw types for assessing these characterization skills.

PNNL applied the flaw decision matrix on 13 implanted flaws in one of the carbon steel piping 

welds with a weld crown that had been ground flush. The UT analyst in this case was able to 

correctly identify flaw types for 9 of the 13 (~ 70 percent) flaws, which displays improvement 

from initial use of the matrix on Navy plate data. A significant contribution to this improved 

characterization performance was continuous acquisition of data via scans over the weld, 

allowing analysis of the entire echo-dynamic (full peak responses) from each flaw. This full flaw 

response is typically not available when scans are limited by the presence of a weld crown, 

causing a peak response to be clipped (not captured) in the data. This result provides further 

evidence to support weld crown removal to support UT methods that examine over the weld 

area, thereby greatly improving not only detection, but flaw type characterization as well.

As was previously discussed, in the nuclear industry, radiography has historically been the 

primary NDE method for fabrication flaw acceptance, while UT has widely been the volumetric 

method of choice for detecting service-induced degradation. Per ASME Code, fabrication 

examinations must include the entire volume of the weld and adjacent base material, and are 

aimed at detecting welding flaws that may occur anywhere within this defined volume of interest.

Conversely, inservice examinations typically only interrogate material volumes subject to service 

degradation, such as at the inner one-third of piping welds, including the heat-affected zone and 

limited adjacent base material surrounding this area. Ultrasonic techniques for piping weld 

examinations have evolved to provide sound fields that focus near the ID for detection of 

surface-connected cracks, because this is where the preponderance of service-induced

degradation has occurred. As a result of these differences, as well as in consideration of the 

inherent strengths of each of the methods, the two methods are not considered to be 

interchangeable, rather they are complementary.
8-4

Thus, in order for the NRC to consider UT as a viable alternative to RT for repair and 

replacement activities in nuclear power plants, many issues remain to be addressed. These 

were identified in Section 2 of this report, and several were addressed by this work. For 

instance, it is clear that PA-UT has the ability to successfully detect flaws in carbon steel welds 

to performance levels comparable to, or even greater than, that achievable with RT when

examinations are performed from both sides of the weld and the weld crown is removed.

However, the PA-UT detection capability is degraded when only single-side weld access is 

available; even more so if weld crowns remain in place. In terms of sizing capability, PA-UT

both under-sizes and over-sizes, depending on flaw type. Overall, sizing of the fabrication type 

flaws in carbon steel piping welds fell within the acceptance standards of ASME Code, 

Section XI, Appendix VIII. However, the applicability of this acceptance standard, having been 

derived from performance demonstrations on planar crack-like flaws, to welding fabrication 

flaws is questionable. Further, in terms of characterization of flaws required for the application 

of ASME Code, Section III-type acceptance criteria, the results of this study indicate that the 

ability to adequately characterize flaws as either planar or volumetric is very analyst subjective.

Thus, whether it be may appropriate to apply current welding fabrication acceptance criteria,

which is highly dependent on UT characterization, also remains questionable.

An area outside the scope of the work reported here is the industry-proposed use of established 

standards for UT performance demonstrations for service-induced flaws (cracks) to UT 

performance demonstrations for full-volume weld examinations aimed at detecting welding 

fabrication flaws. It is unclear whether direct application of these existing standards will result in 

acceptable and reliable performance results. As such, an assessment of appropriate 

performance demonstration requirements for fabrication UT remains to be performed.

Additionally, because the PA-UT method is being used in lieu of RT applied for piping 

replacements in limited systems at operating nuclear power plants (i.e., ASME B31.1 

examinations), only PA-UT was assessed in this study. Whether conventional UT methods 

could be successfully applied for these applications remains unknown at the present time.

Finally, this work was limited to fine-grained, carbon steel butt welds. No conclusions should be 

drawn regarding the applicability of UT in lieu of RT for other nuclear power plant weld materials 

or configurations.
9-1

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APPENDIX A

ANALYSIS SUMMARY – FROM INDUSTRY QUESTIONNAIRE

A-1
A-2
A-3

APPENDIX B

RT AND UT DETECTION RESULTS FOR ALL 

IMPLANTED AND BONUS FABRICATION FLAWS 

IN THE CARBON STEEL PIPING

B-1

APPENDIX B

RT AND UT DETECTION RESULTS FOR ALL IMPLANTED AND BONUS 

FABRICATION FLAWS IN THE CARBON STEEL PIPING

RT UT

Flaw Type Length* (mm) Detection 

(Y/N)

Detection 

(Y/N)

Single Sided 

(Y/N)

Volumetric

Slag 1.2 Y N **

1.4 Y N **

2.5 Y Y Y

2.5 Y N **

3.1 Y N **

3.7 Y N **

6.2 Y Y Y

6.9 Y Y N

7.4 Y Y N

8.0 Y Y N

9.8 Y Y N

18.8 Y Y N

23.7 Y Y Y

29.1 Y Y N

52.3 Y Y N

Porosity 0.3 Y N **

0.3 Y N **

0.4 Y N **

0.5 Y N **

0.5 Y N **

0.5 Y N **

0.6 Y N **

0.6 Y N **

0.6 Y N **

0.6 Y N **

0.6 Y N **

0.7 Y N **

0.7 Y N **

0.7 Y N **

0.7 Y N **

0.8 Y N **

0.8 Y N **

0.8 Y N **

0.8 Y N **

0.8 Y N **

1.2 Y N **

1.4 Y N **

1.5 Y N **

2.0 Y N **
B-2

RT UT

Flaw Type Length* (mm) Detection 

(Y/N)

Detection 

(Y/N)

Single Sided 

(Y/N)

3.7 Y Y Y

4.1 Y Y Y

4.2 Y N **

4.5 Y N **

4.6 Y Y Y

5.3 Y N **

6.9 Y N **

8.1 Y Y N

9.4 Y N **

10.6 Y Y N

10.7 Y N **

11.9 Y Y Y

12.1 Y Y N

47.0 Y N **

Planar

LOF 1.8 Y N **

3.0 Y Y N

3.8 Y N **

5.0 N Y Y

5.0 N Y N

5.4 Y Y N

6.0 N Y Y

6.0 N Y Y

6.0 N Y N

6.0 N Y N

6.6 Y Y N

7.0 N Y Y

8.0 N Y Y

8.0 N Y Y

8.0 N Y Y

8.0 N Y Y

9.0 N Y Y

9.0 N Y Y

9.0 N Y Y

10.0 N Y Y

10.0 N Y Y

10.0 Y Y N

10.0 N Y N

10.2 Y Y Y

10.5 Y Y N

10.8 Y Y N

11.0 N Y Y

11.0 N Y Y

11.0 N Y Y

11.0 N Y Y

11.0 N Y N

11.0 N Y N
B-3

RT UT

Flaw Type Length* (mm) Detection 

(Y/N)

Detection 

(Y/N)

Single Sided 

(Y/N)

11.1 Y Y N

12.0 N Y Y

12.0 N Y Y

13.0 N Y Y

13.0 N Y Y

14.0 N Y Y

14.0 N Y Y

14.9 N Y Y

15.0 N Y Y

17.0 N Y Y

17.0 Y Y N

18.0 N Y Y

18.0 N Y Y

19.0 N Y Y

22.1 Y Y Y

32.2 Y Y N

47.0 N Y Y

53.6 Y Y N

LOP 5.7 Y Y N

8.8 Y Y N

9.6 Y Y N

14.1 Y Y N

24.3 Y Y N

31.1 Y Y N

39.1 Y Y N

CVX-RT 28.5 Y Y N

29.8 Y Y N

30.2 Y N **

33.8 Y Y N

Crack 5.4 Y Y N

14.0 N Y N

17.8 Y Y N

18.7 Y Y N

21.3 Y Y N

25.3 Y Y N

25.3 Y Y N

33.5 Y Y N

33.7 Y Y N

41.0 Y Y N
B-4

RT UT

Flaw Type Length* (mm) Detection 

(Y/N)

Detection 

(Y/N)

Single Sided 

(Y/N)

% Single Sided 

Detection

All Flaws 45.9%

POR 57.1%

SLG 30.0%

LOF 66.7%

LOP 0.0%

CVX RT 0.0%

CRK 0.0%

* The length was determined by PNNL RT. When RT did not detect, PNNL UT length 

was used.

** When UT did not detect the flaw, single-sided detection is not applicable.




NUREG/CR-7204 Applying Ultrasonic Testing in Lieu of Radiography for Volumetric

Examination of Carbon Steel Piping