RR 22-36 | November 2022

EXPANSION OF RAIL FLAW LIBRARY AT THE

TRANSPORTATION TECHNOLOGY CENTER

SUMMARY

In 2017, Transportation Technology Center, Inc. 

(TTCI) began adding naturally occurring rail 

flaws to the Rail Flaw Library of Associated 

Defects (RF-LOAD) by acquiring defective rails

from the field with funding by the Federal 

Railroad Administration (FRA). Rail samples 

containing service induced flaws have varying 

rail profiles, such as different rail head profile 

wear, and different surface conditions. Since 

only so many of these natural/field defects can 

be collected every year, the goal is to continue 

this work and collect more rail flaw samples for 

the RF-LOAD every year.

TTCI characterized RF-LOAD and naturally 

occurring rail flaw samples collected with a high 

level of accuracy using available physical and 

non-destructive evaluation (NDE) measurement 

techniques. Physical measurements included 

dimensional and MiniProf profile measurements 

and analysis. This allowed researchers to 

calculate rail wear, align rails with the template 

profiles, and generate two- and threedimensional (2D/3D) Solidworks® models of the 

defective rails and calculate the cross-sectional 

head areas for different rail head profiles. 

Embedded reflectors and internal flaw 

characterization was done by using hand-held 

ultrasonic testing (UT) NDE methods, which 

include conventional UT and phased array UT 

(PAUT).

These rail flaw samples and 2D/3D Solidworks®

models of the rails with internal flaws are 

available to other rail researchers and industry 

service providers in the United States to support 

rail inspection research. Also, these rail flaw 

samples are useful to investigate how well

particular NDE techniques can characterize rail 

flaws under different rail head situations.

BACKGROUND

Ultrasonic NDE methods for rail flaw detection 

are the primary techniques employed by the 

railroads to monitor, detect and characterize rail 

defects. Although conventional ultrasonic 

inspection systems have proven effective at 

finding most of the critical rail flaws, inherent 

limitations leave some flaws undetected during 

periodic inspection [1]. Overall, ultrasonic 

detection greatly depends on the magnitude of 

the received/recorded ultrasonic reflection from 

the flaw. The physical shape, size, location, and 

orientation of flaws, and poor ultrasonic coupling 

can result in a low-amplitude reflection signal. 

Two limitations of existing conventional ultrasonic 

systems lie with the fixed-angled inspection 

approach and not automatically compensating the 

ultrasonic beam path in worn rail head profiles. 

Another inherent limitation with ultrasonic 

inspection is acoustic coupling. The detection of 

internal defects in the presence of surface flaws

as a result of rolling contact damage

(RCD)/subsurface shelling can be a challenge.

The rail integrity research efforts by FRA and the 

Association of American Railroads (AAR) aim to 

increase safety and reliability of rail 

transportation. One of the continued FRA-funded 

initiatives led by the research team involves 

expanding the RF-LOAD and characterizing it 

using UT NDE methods at the Transportation 

Technology Center (TTC), near Pueblo, CO [2–

3]. Standardized rail defect samples are important 

for qualifying NDE techniques used for rail 

inspection.

The RF-LOAD initially consisted of master 

gauge samples containing a variety of artificial 

reflectors, mostly flat bottom holes (FBHs) of 

differing cross-sectional area. FBHs were drilled 

at different orientations and locations relative to 

RR 22-36 | November 2022 

RESEARCH RESULTS 3 | Page

direction). Similarly, by scanning across the 

head of the rail (i.e., transverse direction), the 

width of the TD type defect can be measured.

Table 1 shows some of the wear measurements 

(i.e., W1, W2, and W3) and area (gained/loss) 

measurements for some of the master gauge 

samples.

Table 1. Rail profile measurement results

Figure 2 shows the SolidWorks® drawing for one 

of the RF-LOAD master gauge samples.

Figure 2. SolidWorks® drawing of RF-LOAD 

sample

Figure 3 shows the hand-held PAUT rail flaw 

characterization. From the UT characterizations 

of rail flaws, researchers demonstrated that 

hand-held PAUT was more accurate than the 

conventional UT measurements for sizing 

reflectors (i.e., 16–30 percent CSHA) in the 

gage and field faces that were oriented 5 

degrees and 10 degrees relative to the base. 

Table 2 shows results obtained from this 

exercise. In some cases, it was extremely 

difficult to observe signals for reflectors in the 

gage and field faces using conventional UT for 

the curve worn rails. Zero-degree oriented FBHs 

(0.25 and 0.50 inch diameter) on the gage and 

field faces as shown in Figure 4 were almost 

impossible to find using both PAUT/UT methods. 

However, the detectability for PAUT increased 

when the FBHs were about 1 inch in diameter.

Figure 3. Hand-held PAUT rail flaw characterization

Table 2. PAUT and UT characterization the RFLOAD master gauge samples

Figure 4. Zero-degree oriented FBH on gage side 

the rail head

The current status of the RF-LOAD is as follows:

• Artificial reflectors: 54

• Service induced flaws: 53

• No flaws: 32

• Broken weld samples: 8
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RESEARCH RESULTS 4 | Page

CONCLUSIONS

FRA and TTCI developed an extensive rail flaw 

library. The rail flaw samples collected so far are 

characterized with a high level of accuracy using 

available physical and NDE measurement 

techniques. RF-LOAD helps to meet current 

industry rail inspection challenges by providing 

flaw library access to rail researchers and other 

industry service providers so that they can 

optimize their inspection systems for better flaw 

detection and characterization.

FUTURE ACTION

Efforts will continue to collect and fully 

characterize a wide array of naturally occurring 

rail flaw samples from FAST, the TTC, and 

revenue service. This rail flaw library aims to 

meet future development needs by providing 

researchers open access to different kinds of rail 

flaw defects. FRA and TTCI expect that RFLOAD will be used for operator training and 

POD capability demonstrations for emerging 

NDE methods.

REFERENCES 

1. Witte, M., Poudel, A., & Kalay, S., 2016, 

“Rail Flaw Characterization Using Phased 

Array Ultrasound,” Proceedings of 25th 

ASNT Research Symposium, New Orleans, 

LA.

2. Garcia, G. & Zhang, J., “Application of 

Ultrasonic Phased Arrays for Rail Flaw 

Inspection,” Technical Report No.

DOT/FRA/ORD-06/17, Washington, DC: US

Department of Transportation, Federal 

Railroad Administration. 

3. Al-Nazer, L., & Welander, L., 2012, “Rail 

Flaw Sizing Using Conventional and Phased 

Array Ultrasonic Testing,” Research Results

No. RR 12-20, Washington, DC: US

Department of Transportation, Federal 

Railroad Administration. 

4. Poudel, A., Lindeman, B., and Wilson, R., 

2019, “Current Practices of Rail Flaw 

Inspection using Ultrasonic Methods – A 

Review,” Materials Evaluation, 77(7), pp. 

868–881

ACKNOWLEDGEMENTS

The authors would like to acknowledge the 

hard work of the TTCI project team: Brian 

Lindeman, Greg Giebel, Joseph Paseka, 

Bryan Morgan, Brandon Zane and his track 

crews.

CONTACT

Robert Wilson, Ph.D.

General Engineer

Federal Railroad Administration

Office of Research and Development

1200 New Jersey Avenue, SE

Washington, DC 20590

617-999-0061

Robert.Wilson@dot.gov

Anish Poudel, Ph.D.

Project Manager 

Association of American Railroads

Transportation Technology Center, Inc.

55500 DOT Rd, Pueblo, CO 81001

(719) 584-0581

Anish_Poudel@aar.com 

KEYWORDS

Rail, rail wear, rail defect, rail flaw library, 

ultrasonic testing, UT, phased array 

ultrasonic testing, PAUT, Miniprof, Rail Flaw 

Library of Associated Defects, RF-LOAD, 

non-destructive evaluation, NDE, track

CONTRACT NUMBER

DTFR5311D00008L