Office of Research and 

Development 

Washington, DC 20590

DOT/FRA/ORD-06/12 December 2005 

 

This document is available to the

U.S. public through the National

Technical Information Service

Springfield, Virginia 22161.

Federal Railroad

Administration

U.S. Department

of Transportation

DAMAGE ASSESSMENT OF RAILROAD TANK 

CARS INVOLVED IN ACCIDENTS: PHASE I 

LITERATURE SEARCH AND EVALUATION 
ii 

Notice 

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manufacturers. Trade or manufacturers’ names appear herein 

solely because they are considered essential to the objective of 

this report. 

Notice 

This document is disseminated under the sponsorship of the 

Department of Transportation in the interest of information 

exchange. The United States Government assumes no liability 

for its contents or use thereof. 
iii 

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 December 2005 

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Damage Assessment of Railroad Tank Cars Involved in Accidents: 

Phase I Literature Search and Evaluation 

6. AUTHOR(S) 

K. Scott Pieratt, Jeffery C. Davis, and Peter C. Conlon

Contract No. DTFR 53-93-C-00001, 

Task Order 115 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION 

REPORT NUMBERS

Transportation Technology Center, Inc. 

P.O. Box 11130 

Pueblo, CO 81001

9. SPONSORING/MONITORING AGENGY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY 

REPORT NUMBER 

U.S. Department of Transportation 

Federal Railroad Administration 

Office of Research and Development, MS 20 

1120 Vermont Avenue, NW 

Washington, DC 20590

DOT/FRA/ORD-06/12 

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

This document is available through National Technical Information 

Service, Springfield, VA 22161.

13. ABSTRACT

 Transportation Technology Center, Inc., a subsidiary of the Association of American Railroads, is conducting a 

research project titled, "Damage Assessment of Tank Cars Involved in Accidents." Phase I of the project 

evaluated the validity of guidelines currently used to assess the severity of damage to pressure tank cars caused 

by derailments. 

 A search of the technical literature was performed and subsequently evaluated to identify which of the guidelines 

can be validated and which require additional modeling and validation in the Phase II effort. This report and 

accompanying appendix present the results of the literature search and evaluation and make recommendations for 

the Phase II research.

14. SUBJECT TERMS 15. NUMBER OF PAGES

55 

16. PRICE CODE Tank cars, damage assessment, guidelines, hazardous materials 

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 

OF THIS PAGE 

19. SECURITY CLASSIFICATION 

OF ABSTRACT 

20. LIMITATION OF 

ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED 

NSN 7540-01-280-5500 Standard Form 298 (Rec. 2-89) 

Prescribed by ANSI/NISO Std. 

239.18 

298-102
iv 
v 

Table of Contents 

List of Figures............................................................................................................................ vii 

List of Tables ............................................................................................................................. vii 

1.0 Introduction..................................................................................................................... 1 

2.0 Objectives ........................................................................................................................ 3 

3.0 Procedures ....................................................................................................................... 5 

3.1 Guidelines ............................................................................................................. 5 

3.2 Survey ................................................................................................................... 7 

3.3 Literature Search Methods .................................................................................12 

4.0 Results............................................................................................................................13 

4.1 Analysis of the Literature ....................................................................................13 

4.2 Developments in Fracture Mechanics Relevant to Tank Car 

Damage Assessment ............................................................................................23 

4.3 Assessment of Guidelines and Their Degree of Validation .................................30 

4.4 Expert Review......................................................................................................34 

5.0 Conclusions and Recommendations ..............................................................................35 

List of References ....................................................................................................................37 

Appendix. Expert Review.......................................................................................................47 

Acronyms.................................................................................................................................51 

Glossary ...................................................................................................................................53 
vi 
vii 

List of Figures 

Figure 1. Slide-Graph Analysis ..............................................................................................16

Figure 2. Schematic of Dent in a Tank Car ............................................................................20 

Figure 3. Jappl versus Crack Length for a 4T A533B Steel Compact Tension Specimen 

Compared to a Material Resistance Curve .............................................................26 

Figure 4. Deformation and Fracture Behavior of Explosively Loaded Welded HY-130 

Steel T-Joints...........................................................................................................29 

List of Tables 

Table 1. Limiting Score Depths for 340W Tanks..................................................................... 6 

Table 2. Limiting Score Depths for 400W Tanks..................................................................... 6 

Table 3. Scope of Literature Review ......................................................................................13 
viii 
1 

1.0 Introduction 

Under Federal Railroad Administration (FRA) Contract No. DTFR 53-93-C-00001, Task Order 

115, Transportation Technology Center, Inc. (TTCI), a subsidiary of the Association of 

American Railroads (AAR), conducted a research project titled, "Damage Assessment of Tank 

Cars Involved in Accidents." Phase I of the project evaluated the validity of guidelines currently 

used to assess the severity of damage to pressure tank cars caused by derailments. 

In February 1993, AAR/TTCI produced a handbook on emergency response titled, Field Product 

Removal Methods for Tank Cars. AAR/TTCI developed the handbook for FRA under contract 

DTFR 53-82-C-00282, Task Order 31, and produced it for emergency response personnel who 

deal with tank cars carrying hazardous materials that have been damaged in accidents. The 

publication and subsequent use of this handbook has pointed to the need for a companion 

handbook that identifies proven and reliable damage assessment procedures. 

Since 1985, AAR/TTCI and other organizations have used a set of guidelines developed by AAR 

in the late 1970s to teach emergency response personnel how to make judgments in the field as 

to the severity of damage to tank cars involved in accidents. AAR developed these guidelines to 

help emergency responders decide when tank cars carrying hazardous materials shipped under 

pressure can be safely rerailed, unloaded in place, or whether nature should be left to take its 

course. 

Recently, AAR/TTCI reviewed the guidelines to determine how or if they were validated. After 

consulting with experts in the tank car, railroad, and chemical industries, TTCI has determined 

that the guidelines were developed by several individuals who are no longer available to 

substantiate them. To better ensure the safety of emergency response personnel and the publicat-large, responders need some sound, qualitative evaluation techniques which they can safely 

and reliably use to make these decisions. Compiling this information in an easy-to-understand 

handbook to assist emergency response personnel in making critical decisions is an important 

effort that will significantly improve the safety of such operations. 

Phase I of the project focused on evaluating the technical foundation for the guidelines. 

AAR/TTCI searched and evaluated the technical literature to identify which of the guidelines 

can be validated and which require additional modeling and validation in the Phase II effort. 

This report and appendix present the results of the literature search and evaluation and make 

recommendations for the Phase II research. 
2 
3 

2.0 Objectives 

In an attempt to gather pertinent information to assist in the assessment and validation of the 

current pressure tank car damage assessment guidelines, AAR/TTCI designed Phase I work to 

accomplish the following: 

• Compile current guidelines for pressure tank car damage assessment. 

• Survey individuals from various entities, including major railroads, chemical shippers, 

and government agencies, to acquire additional information that might aid in the 

evaluation of the current damage assessment guidelines. 

• Search the technical literature for previously published research, rules, regulations, 

guidelines, and recommended practices that are or may be applicable to pressure tank 

cars. 

• Review the relevant material identified in the literature search, and evaluate to determine 

if the literature can validate the guidelines. 

• Write a report that includes a technical discussion of the applicable portions of the 

literature that validate the current guidelines and identify areas where additional 

modeling and validation will be required. 

• Circulate the report for review and comments to selected individuals previously 

surveyed. 

• Prepare and submit to FRA a final Phase I report that documents the work performed 

under Phase I, identifies the conclusions drawn, and makes recommendations for 

modeling and work necessary to validate the guidelines. 
4 
5 

3.0 Procedures 

The following paragraphs will identify the procedures used to gather the information presented 

in this section. These procedures included the collection of current guidelines, administration 

and evaluation of an industry and government survey, and the identification of methods used to 

perform the literature search. 

3.1 Guidelines 

While pressure tank cars transporting compressed gases can sustain extensive damage in 

derailments without releasing their contents, delayed failures are possible and have occurred. 

During this delay, response personnel are likely to have begun derailment clearing operations 

and, consequently, risk death or injury should the tank fail. 

In the late 1970s, AAR developed damage assessment guidelines to help emergency response 

personnel make critical decisions whether tank cars damaged in derailments could be safely up 

righted and transported (either on their own trucks or on flat cars) for unloading or whether they 

must be unloaded in place. While these guidelines have been used safely for some years, no 

clear record exists of what methodology was used to establish the guidelines, and their primary 

author is no longer available to provide that information. 

The following information identifies the specific tools (guidelines), which were extracted from 

the AAR/TTCI Hazardous Materials Training Center Tank Car Safety Course Manual, as found 

in Reference 110. The Glossary contains definitions of key terms found in this section. 

• A crack in the tank base metal indicates serious damage. Cracks in welds used to attach 

brackets or reinforcement plates are not critical unless the crack extends into the base 

metal. 

• Any crack found in the base metal of a tank, no matter how small, justifies unloading the 

tank as soon as possible. If in a yard, however, the car may be carefully moved to a 

designated remote location in the yard for transfer. 

• When a crack is in conjunction with a dent, score, or gouge, the tank should be unloaded 

as soon as possible without moving it. 

• Scores or gouges crossing a weld and removing only the weld reinforcement are not 

critical. 

• Longitudinal scores are the most dangerous. Circumferential scores, however, cannot be 

ignored for at any given section such scores also constitute a longitudinal notch. 

• Longitudinal scores or gouges crossing a weld and affecting the heat affected zones are 

critical. Transfer the contents of the tank car immediately. 

• Unload in place tanks having scores or gouges when the internal pressure exceeds half of 

the allowable internal pressure listed in the following tables. Tables 1 and 2 show the 

allowable pressures for 340W and 400W tanks, respectively. 
6 

Table 1: Limiting Score Depths for 340W Tanks

Depth of Score Maximum Safe Internal Pressure, PSIG 

1/16 in 191 (89° F for commercial propane) 

1/8 in 170 (85° F for commercial propane) 

3/16 in 149 (76° F for commercial propane) 

1/4 in 127 (65° F for commercial propane 

Note: In no case should a tank containing a score in excess of 1/16 in for 340W tanks be 

shipped by rail, although the tank could be uprighted and even moved short distances for 

product transfer. 

Table 2: Limiting Score Depths for 400W Tanks

Depth of Score Maximum Safe Internal Pressure, PSIG 

1/16 in 228 (108° F for commercial propane) 

1/8 in 205 (99° F for commercial propane) 

3/16 in 188 (93° F for commercial propane) 

1/4 in 162 (82° F for commercial propane) 

Note: In no case should a tank containing a score in excess of 1/8 in for 400W tanks be 

shipped by rail, although the tank could be uprighted and even moved short distances for 

product transfer. 

While the values given in Tables 1 and 2 are conservative, they do not include the welded joint 

efficiency for tanks built before 1968. This amounts to an extra 10 percent safety factor. 

• If the maximum depth of a wheel burn exceeds 1/8 in, unload the tank as soon as 

possible. If the depth of the wheel burn is less than 1/8 in, empty the tank at the 

closest loading facility, provided it is moved with care and not in ordinary train 

service. 

• Sharp dents in the shell of the tank (cylindrical section), which are parallel to the long 

axis, are the most serious as these dents drop the rating of the tank by 50 percent. 

• For dents in the shell of tank cars built before 1967, unload the tank without moving 

it under the following conditions: 

 - A minimum radius of curvature of 4 inches or less 

 - Have a crack anywhere 

 - Cross a weld 

 - Include a score or gouge 

Dents with a radius of curvature more than 4 inches are not a problem by themselves. 
7 

• For dents in the shell of tank cars built since 1967, unload the tank without moving it 

under the following conditions: 

 - A minimum radius of curvature of 2 inches or less 

 - Have a crack anywhere 

 - Cross a weld 

 - Include a score or gouge 

 - Show evidence of cold work 

Dents with a radius of curvature more than 2 inches are not a problem by themselves. 

• Massive dents in heads of the tank are generally not serious unless gouges or cracks 

are present with the dents. 

• Small dents in heads not exceeding 12 inches in diameter in conjunction with cold 

work in the bottom of the dent are marginal if they show a radius of curvature less 

than 4 inches for tanks built before 1967 or less than 2 inches for tanks built since 

1967. If at all possible, unload such tanks in place. In any case, move the tank as 

little as possible and promptly unload it. 

3.2 Survey 

AAR/TTCI designed, constructed, and administered a survey in May 1995 in an attempt to 

acquire additional information that might aid in the evaluation of the current damage assessment 

guidelines. The survey was sent to various representatives of FRA, the National Transportation 

Safety Board, Canadian Transportation Safety Board, National Research Council of Canada, 

Transport Canada, AAR, Railway Progress Institute/Association of American Railroads 

(RPI/AAR) Tank Car Safety Research Project, major railroads, chemical shippers, tank car 

manufacturers, and others who are or were previously associated with the railroad industry that 

may have knowledge pertinent to this project. AAR/TTCI sent 50 surveys to representatives of 

the above referenced entities. The 30 responses received represent a 60 percent return of the 

total surveyed. The following summarizes the survey administered and the responses received. 

At the request of several respondents, attribution is not given on direct quotes. 

1. Are you aware of any previously published research, rules, guidelines, or 

recommended practices which are, or may be applicable to, the evaluation of the 

current guidelines for assessing the severity of damage to pressure tank cars? 

The list of references provided to the subcontractor for review during the literature search 

incorporated the responses received. Below is a summary of the literature identified by 

survey respondents. 

• "Phase 18 Study: Integrity of Damaged Tank Cars," Association of American 

Railroads, Chicago, Illinois (publication date unknown). [Reference 20] 

• AAR Standards and Recommended Practices, Sec. C–-P Part III, Specifications 

for Tank Cars, Specification M-1002. [Reference 21] 

• L. S. Beller, J. D. Mudlin, W. G. Reuter, and M. A. Tupper, "Survey of 

Nondestructive Methods for Evaluating Derailed Tank Cars," U.S. Army Ballistic 
8 

Research Laboratory Contract Report BRL-CR-539 (November 1984) DOT/ 

FRA/ORD-84/11. [Reference 36] 

• J. L. Hechmer and G. L. Hollinger, "The ASME Code and 3D Stress Evaluation," 

Journal of Pressure Vessel Technology, 113, 481-487 (November 1991). 

[Reference 77] 

• National Transportation Safety Board, "Derailment of Burlington Northern 

Freight Train No. 01-142-30 and Release of Hazardous Materials in the Town of 

Superior," Hazardous Materials Accident Report NTSB/HZM-94/01, Notation 

5842B, Washington, DC (March 1994). [Reference 23] 

• National Transportation Safety Board, "Derailment of Louisville and Nashville 

Railroad Company's Train No. 584 and Subsequent Rupture of Tank Car 

Containing Liquefied Petroleum Gas, Waverly, Tennessee," Railroad Accident 

Report No. NTSB-RAR-79-1, Notation 2313B, Washington, DC (February 22, 

1978). [Reference 25] 

• National Transportation Safety Board, "Special Investigation Report: Tank Car 

Structural Integrity after Derailments," Bureau of Technology, Report No. 

NTSB-SIR-80-1, Washington, DC (1980). [Reference 26] 

• E. A. Phillips and W. A. Pellini, "Phase 03 Report on Behavior of Pressure Tank 

Car Steels in Accidents," Association of American Railroads, Report No. 

RA-03-6-48 (June 20, 1983). [Reference 13] 

• E. A. Phillips and H. Role, "Effectiveness of Shelf Couplers, Head Shields, and 

Thermal Shields on DOT 112 (114) and 105 Tank Cars," Association of 

American Railroads, Report No. RA-02-5-51 (AAR R-610), Chicago, Illinois 

(June 13, 1985). [Reference 27] 

• K. Rahka, "The Anatomy of a Break Before Leak Case," ASME PVP-Vol. 281, 

High Pressure Technology, ASME, 49-54 (1994). [Reference 78] 

• W. G. Reuter, J. D. Mudlin, R. L. Harris, F. M. Haggag, W. L. Server, and J. S. 

Epstein, "Evaluation of Damaged Tank Car Structural Integrity," Department of 

Transportation, Federal Railroad Administration, Office of Research and 

Development Report DOT/FRA/ORD-88/02 (January 1988). [Reference 37] 

• Z. Rosenberg, J. Mironi, A. Cohen, and P. Levy, "On the Catastrophic Failure of 

High-Pressure Vessels by Projectile Impact," Int. J. Impact Engng., 15(6), 

827-831 (1994). [Reference 86] 

• D. K. Shaver, and R. L. Berkowitz, "Guideline Manual, Post Accident Procedures 

for Chemicals and Propellants," Air Force Rocket Propellant Laboratory Report 

AFRPL TR-82-077 (January 1983). [Reference 34] 

• D. K. Shaver, R. L. Berkowitz, and P. V. Washburne, "Accident Management 

Orientation Guide," Air Force Rocket Propellant Laboratory Report AFRPL 

TR-82-0075 (October 1983). [Reference 35] 

• Tank Car Fatigue Crack Growth Test, DOT/FRA/ORD-93/10. [Reference 22]
9 

2. Do you have any knowledge of unexpected behavior of damaged pressure tank cars 

that would aid AAR/TTCI in evaluating the current tank car damage assessment 

guidelines? 

• Report RA-03-6-48, "Phase 03 Report on Behavior of Pressure Tank Car Steels in 

Accidents, 6/20/83." The reports cited delayed ruptures in two separate incidents 

at Cumming, Iowa, and Waverly, Tennessee. 

• Vinyl Chloride car exploded in Livingston, Louisiana, September 1982. 

• Vinyl Chloride car failed following accident in Flomaton, Alabama, May 1995. 

• Several other respondents indicated yes to the questions; however, no specific 

incidents were noted. 

3. Are you aware of any three-dimensional, finite element computer modeling work 

that has been done to simulate the behavior of damaged tank cars or pressure 

vessels (particularly under load)? 

• Transport Canada has developed a complete tank car finite element analysis 

(FEA) model. Other models have or are being developed as part of a stub sill 

study being performed in conjunction with the Tank Car Research Committee. 

• Battelle may have done an FEA of a tank car. 

• Specific packages or companies with capabilities included: NIKE2D, NASGRO, 

NASCRAC, CRACKS 94, FM, PFRAC, Failure Analysis Associates, and 

Transoft, Inc. 

4. Are you familiar with the methodology Roy Holden used to develop the current tank 

car damage assessment guidelines? 

• One respondent indicated that Mr. Holden developed the guidelines based upon 

coupon samples that were taken from damaged tank cars and from tank cars that 

had failed. 

• Several respondents indicated that Mr. Holden developed the guidelines primarily 

through the experience he gained attending derailments. 

• Another respondent indicated that Mr. Holden developed the guidelines from 

engineering calculations (conservative) with an added safety factor. 

5. Did you assist Mr. Holden in the development of the current guidelines?

• Several indicated that they had assisted Mr. Holden. Many of those indicated that 

they were involved in discussions with Mr. Holden regarding the guidelines. 

6. Did Mr. Holden consult with you during the development of the current guidelines?

• Response the same as in Question 5. 

7. Do you know of anyone that worked with Mr. Holden in the development of the 

guidelines?
10 

• Gene Kunz • E. A. Phillips 

• W. J. Ruprecht • Pat Student 

• George Binns • Ted Orr 

• Mike Miller 

8. Do you have any reason to suspect that the current tank car damage assessment 

guidelines published by AAR/TTCI may not be reliable?

• One respondent indicated that the guidelines were out of date. "No mention is 

made of normalized steels mandated in the mid-1980s, and it contains some errors 

and omissions." 

9. Do you have any reason to believe that the current guidelines may be too 

conservative? 

Only two respondents indicated that they felt that the guideline may be too conservative. 

Their responses are as follows: 

• "The descriptions of some of the damage types are not specific enough and to 

some extent are in error." 

• "In today’s environment, damaged tank cars are seldom moved when loaded, 

especially if hazardous materials are involved." 

10. In your opinion, do the current tank car damage assessment guidelines published by 

AAR/TTCI meet the needs of emergency response personnel?

Most respondents indicated that, in their opinion, the current damage assessment 

guidelines do meet the needs of emergency response personnel. The following comments 

were supplied by those who did not agree. 

• "Secure the advice of someone with tank car experience is vague. The 

appropriate contacts are the designated shipper and carrier emergency response 

personnel." 

• "The guidelines should be reviewed and definitions revised to meet the current 

regulations. Fractures and creases should also be discussed in greater detail." 

• "They point a direction, but if this is all emergency response personnel have to go 

on, people are going to get hurt." 

11. What other topics of concern to emergency response personnel would you like to see 

addressed by the guidelines?

• What lifting configurations can responders use to safely lift, roll, or drag a 

damaged pressure tank car considering different damage types and locations of 

damage. 

• Responders are concerned over the inability to apply the damage assessment 

guidelines to jacketed tank cars short of physically removing the jacket. By 

removing the jacket using a cutting torch or other mechanical means, the 
11 

responder may be introducing additional hazards that raise critical safety 

concerns. 

• "The guidelines should address what conditions responders should look for that 

may contribute to the delayed failure of a tank car." 

• Responders would like to see a means of remotely inspecting a damaged tank car 

to assess the criticality of damage (i.e., nondestructive evaluation (NDE) 

techniques). 

• "Responders need guidelines to perform damage assessment on general service 

tank cars." 

• "Engineering calculations and data verification must be performed on current 

guidelines, and then a statistical margin of safety must be added to the findings." 

• A concern was raised over the effect of damage to pressure relief systems and 

applicability of guidelines under these conditions. 

• Several comments identified a need within the guidelines for training 

requirements and available resources. 

• "The guidelines do not appear to address the current problem of fatigue in the stub 

sill tank cars." 

• "Fractures and creases are not discussed in great enough detail in the current 

guidelines." 

• What effect does the increasing age of the tank car fleet have with respect to 

application of the guidelines (i.e., double diameter tank cars built in early 1960s). 

Several respondents also identified concerns that may not be appropriate to cover within this 

handbook but more appropriately under the handbook titled, Field Removal Methods for Tank 

Cars. The comments are included here merely as information. 

• Responders need a tool or method to dislodge or move the excess flow check 

valve on pressure tank cars in order to allow responders to remove the liquid 

without moving a severely damaged tank car. 

• "Liquid flaring of liquefied petroleum gas (LPG )from tank cars should be 

addressed identifying the limitations, capabilities, and advantages of the 

technique." The Field Removal Methods for Tank Cars handbook covers this 

topic. More study, however, would be required to fully address this individual’s 

concerns. 
12 

3.3 Literature Search Methods 

The objective of the literature search was to identify technical literature from previously 

published research, rules, guidelines, and recommended practices which are, or may be 

applicable to, pressure tank cars or pressure vessels. The search employed several methods. 

These included searches of catalog files for applicable documents from AAR libraries in 

Chicago, Pueblo, and Washington; national and international computer searches of various 

libraries; technical information services; and professional organizations, as well as responses 

from surveys sent to various government and industry representatives. Both AAR and 

subcontract personnel hired to assist with the search and review of the information performed the 

search.

3.3.1 Institutions and/or Sources Investigated 

Using advances in computer technology to perform literature searches allowed AAR to search 

for applicable documents in numerous locations. The search included AAR libraries in Chicago, 

Pueblo, and Washington, DC, the University of Colorado, the Colorado School of Mines, 

Colorado State University, and other nationally known libraries. AAR did computer searches of 

the Technical Research Information Services, Engineering Index databases, National Technical 

Information Service (NTIS), Defense Technical Information Center (DTIC), ASME Journal of 

Pressure Vessel Technology, and conference proceedings of the ASME Pressure Vessel and 

Piping Division. Survey respondents were also a useful source of identifying technical literature 

and other contacts. 

3.3.2 Bibliography of Literature Reviewed 

At the end of this report, the List of References contains a bibliography of literature reviewed 

during the Phase I portion of this project. AAR supplied the subcontract with References 1 

through 33. NITS and DTIC yielded References 34 through 37. The Technical Research 

Information Services and Engineering Index databases resulted in References 38 through 76. A 

review of the abstracts for these 39 references showed that the documents did not contain any 

substantially new information compared with the information in References 1 through 37. The 

ASME Journal of Pressure Vessel Technology provided References 77, 79 through 85, and 89. 

Reference 78 was from proceedings of a recent conference of the Pressure Vessel and Piping 

Division of ASME. A bibliography established by the subcontractor over the years provided 

References 86 through 88, 90 and 92 through 109. 
13 

4.0 Results 

TTCI retained a subcontractor with expertise in metallurgy, FEA, and fracture mechanics to 

assist in the literature search and review of relevant material. Upon completion of the review, 

Stanford Research Institute, International (SRI) prepared a report to document the methods by 

which materials were collected to discuss the applicable portions of the literature, to provide an 

assessment of the guidelines and the degree of validation, and to discuss their conclusions and 

recommendations for Phase II modeling and validation. Sections 4.1, 4.2, and 4.3 were extracted 

from the report titled, "Literature Search and Evaluation Pertaining to Damage Assessment of 

Tank Cars Involved in Accidents," prepared by (SRI). These sections discuss the findings of the 

SRI evaluation. 

4.1 Analysis of the Literature 

After searching the literature, AAR/TTCI sorted the identified references into five general 

categories, as indicated in Table 3. The table lists some references under more than one 

category. Although the largest number of references falls in the category, "Structural and 

fracture analysis methods," many of the references in this category do not deal specifically with 

tank cars. 

Table 3: Scope of Literature Review 

Category Total No. of 

References 

Specific References 

Structural and fracture analysis 

methods 35 1, 2, 6, 30, 36-42, 77, 79-81, 82, 85, 87, 88, 90, 92-105, 106 

Material properties and 

specifications 20 4, 5, 7, 11, 12, 21, 43-54, 83, 84 

Tank car accident reports 25 3, 8, 13, 15, 23, 25, 26, 27, 29, 55-70

Tank car failure analyses 17 2, 9, 10, 14, 16, 17, 18, 19, 20, 24, 

28, 31, 32, 76, 78, 86, 89 

Miscellaneous 10 33-37, 71-75 

After reading AAR/TTCI guidelines on "Tank Car Damage Assessment," SRI reviewed the 

identified references to: 

• Retrace the genesis of the guidelines and determine on what basis they were established. 

• Obtain physically accurate descriptions of the types of damage incurred by tank cars. 

• Establish the failure scenarios that have resulted from tank car damage. 

• Identify the analytical tools that have been used to explain tank car failures associated 

with accidental damage. 

• Identify the loading and stress levels to which damaged tank cars may be subjected. 
14 

• Assemble information from other engineering fields that may be useful in assessing tank 

car damage. 

4.1.1 Findings and Relationship to Guidelines 

The literature reviewed did not specifically mention the establishment of the guidelines or 

indicate the basis on which they were established. SRI’s review suggests that it may have been 

prompted by recommendations issued by the National Transportation Safety Board to AAR on 

August 30, 1978 (I-78-14, I-78-15, and I-78-16), and to FRA in the spring of 1979 (I-79-13) (see 

Reference 26). According to AAR personnel, Ray Holden, former AAR Bureau of Explosives 

engineer, developed the guidelines, which were based on experience gained attending 

derailments and the inspection of specimens from damaged or failed tank cars [91]. Reference 

35 discussed the guidelines in some detail, which indicates the rationale for a few specific 

recommendations. 

Most of the available fracture analyses for tank cars are based on the work of William S. Pellini, 

who, after a career at the Naval Research Laboratory, acted as a consultant to AAR for many 

years [References 2, 5, 6, 13, 17, 18, 19, 30, 40]. The guidelines appear to be based, at least in 

part, on these analyses. Mr. Holden reportedly interacted extensively with Mr. Pellini during the 

drafting of the guidelines [Reference 91]. References 2, 6, 17, and 30 give descriptions of 

Pellini's Slide Graph Fracture Analysis System (SGFAS) and of its use for the analysis of tank 

car failures and tank car safety. 

The approach applies to structures made of low to medium strength carbon steels and operating 

on the lower shelf or the low transition region. It combines experimental data and service 

experience accumulated since the late 1940s with Linear Elastic Fracture Mechanics (LEFM) to 

establish whether a freshly nucleated crack1 will arrest before unstable catastrophic failure 

occurs and whether a pre-existing crack will initiate and lead to unstable fracture [References 92-

94]. 

Pellini used SGFAS to develop guidelines for the fracture-safe and fatigue-reliable design of 

steel structures [References 18 and 19]. Reference 6 (pp. 51-53) presents the historical evolution 

of these fracture guidelines. Pellini used SGFAS to explain the good safety record of tank cars 

and the few occurrences of arrested or catastrophic brittle fracture (in particular, the two known 

cases of catastrophic delayed fracture in tank cars containing extensive rail burn damage) 

[Reference 2]. Because it underlies many of the more recent safety studies undertaken by AAR, 

the next section gives a short description of SGFAS. 

 

1 This report uses the terminology "nucleate a crack" to indicate formation of a sharp macroscopic crack in a 

material that was previously pristine. SRI refers to "initiate a crack" as the process of extending a pre-existing 

stationary sharp macroscopic crack (e.g., a fatigue crack) by increasing applied loads and/or displacements. 
15 

4.1.2 The Pellini SGFAS 

Figure 1 illustrates Pellini's SGFAS. The abscissa plots a relative temperature scale, and the 

ordinate plots the normalized applied stress. This graph is indexed with respect to the nil 

ductility temperature (NDT) of the steel considered for a specific structure. The concepts of 

NDT and fracture mode transition are the foundation for the crack arrest analysis. Below the 

NDT, fracture occurs entirely by brittle microscopic cleavage, with the steel behaving essentially 

elastically on the macroscopic level. In the temperature range for fracture mode transition 

defined by: 

 NDT < T < NDT + ΔT (1) 

two microscopic modes of fracture coexist (brittle cleavage and ductile void growth), with the 

proportion of brittle cleavage gradually decreasing and the extent of macroscopic plastic 

deformation increasing with increasing temperature. Above the transition range, fracture occurs 

in a microscopically, fully ductile (void growth) mode. The material undergoes extensive 

macroscopic, plastic deformation (that is, the fracture driving stress is equal to or higher than the 

yield stress). 

Standard fracture tests, such as the drop weight test performed over a range of temperatures 

bracketing the transition region, established the NDT [107]. Pellini selected 50° F (28° C) as the 

value of ΔT for shells of thickness corresponding to the thickness range of tank cars (0.5 to 0.75 

in or 12.7 to 19.1 mm), based on experimental data and service experience. The points L and 

YC in temperature versus applied stress space define the crack arrest line. 
16 

The index is located at the average NDT temperature for the old tank car steels. 

Figure 1. Slide-Graph Analysis (from Reference 8) 
17 

According to SGFAS, service conditions to the left of this line will lead to instability of a 

nucleated crack, whereas a crack nucleated for service conditions to the right will always arrest 

and lead to a leak-before-break situation. 

The crack initiation part of the analysis is a straightforward application of LEFM to the case of a 

semi-elliptical surface crack. The effect of dynamic loading has been approximately accounted 

for by a shift in the toughness versus temperature curve toward higher temperatures. 

Enter in the graph of Figure 1 the service temperature relative to the NDT and the normalized 

service stress to make fracture safety evaluations with SGFAS. This procedure is rather simple 

and requires very little stress analysis because, in most reviewed references, the service stress is 

taken as either the membrane hoop stress induced by the tank internal pressure or the yield 

stress. It also avoids the difficulties of dealing explicitly with fracture in the transition region 

and under elastic-plastic or fully plastic conditions. SGFAS is therefore a useful engineering 

design tool, even though it is somewhat qualitative and based on fracture experience and theories 

dating back to the early 1970s. Since then, the field of fracture mechanics made several 

significant advances that can apply to the assessment of damaged tank cars. The following will 

further address this point. 

4.1.3 Damage to Tank Cars 

The guidelines identify and define six types of tank car damage: 

• Cracks • Scores 

• Dents • Gouges 

• Rail burns • Wheel burns 

These types of damage can occur simultaneously and interact in derailments, as will become 

apparent in the following discussion. 

4.1.3.1 Cracks 

Welding during the fabrication process, fatigue during service, or deformation during an accident 

can introduce cracks in tank cars. 

Explosion bulge tests show that it is very difficult to nucleate a crack in the base metal of the 

tank (see for example Reference 6, pp. 78 and 79; or Reference 2, pp. 38 and 41). Plastic 

denting during accidents, however, can nucleate cracks at tank car welds. In particular, long rail 

burns can nucleate cracks at girth welds, which caused catastrophic delayed fractures in two 

instances. The guidelines also seem to recognize the possibility of initiating a crack at a sharp 

dent in the base metal. 

Longitudinal cracks (along the axis of the tank) are the most dangerous because they are oriented 

normal to the hoop stress, which is twice as high as the axial stress for normal-service 

conditions. SGFAS provides a rational method to assess the criticality of cracks in tank cars as 

long as the temperature and stress level allow a linear elastic analysis. The guidelines take a 

conservative approach and assume that any stationary crack discovered in the base metal of the 

damaged tank car always leads to catastrophic failure. 
18 

The reviewed literature did not contain any detailed fractographic information (for instance, 

scanning electron microscope photographs) for cracks found in tank cars. This lack of 

information is particularly unfortunate for failures triggered by rail dents because fractography 

could help establish whether the nucleated crack became immediately unstable or was extended 

first by stable ductile tearing and then switched to brittle cleavage (because of coupled rate and 

constraint effects). 

4.1.3.2 Dents 

The punching action of an external object forms dents in accidents, which causes a local 

decrease or reversal of the tank curvature. Rail burns, discussed below, represent a special type 

of long narrow dent. 

Dents have several effects on the structural integrity of the tank car; they change the mechanical 

properties of the material in the dent (increase in flow stress and decrease in ductility due to 

work hardening); they cause a redistribution of the stresses in the tank shell, which may 

significantly increase the stresses in the dent region; they can lead to nucleation of cracks (for 

instance, at a girth weld); and, in some cases, when dents occur near so-called hard points that 

constrain the displacement of the shell and induce large membrane strains, they may be 

associated with significant wall thickness reductions (see for example Reference 37, Figure 1, 

pp. 12 and 13). 

A decrease in the radius of curvature will make each of the first three effects associated with 

dents more critical. This is probably why the guidelines require that tanks be unloaded if (1) the 

radius of curvature of the dent is smaller than a certain limit value and (2) the dent crosses a 

weld. Further, a dent will be more threatening to the integrity of the tank if it contains other 

defect types (such as scores, gouges, or pre-existing cracks). Again, the guidelines recognize the 

risk associated with the interaction of two types of damage and mandate unloading. Small dents 

in tank heads <12 in ( <30 cm) are considered marginal if their curvature is below a certain 

radius. Unload the tank in place if at all possible. 

Pellini, in Reference 2, states that "...delayed fracture should not be expected for the cases of 

broad area dents." Here one must presume that a broad area dent is one with plastic deformation 

leading to a large radius of curvature and without additional damage in the deformed region. 

With this understanding, the statement of Reference 2 is consistent with the guidelines. Service 

experience (for example, hydroforming repairs) supports this assessment, although no analysis is 

available that would take into account lifting loads during rerailing. 
19 

4.1.3.3 Rail Burns 

Rail burns are a special type of long dent, oriented more or less longitudinally and caused by a 

rail impacting on the tank. Usually no material is removed in the process of forming a rail burn, 

except in girth weld regions where the weld reinforcement may be gouged away. Rail burns 

have the same effects as other dents (see discussion above). Rail burns, however, often have 

small radii of curvature and extend over a significant portion of the tank shell more or less 

normal to the hoop stress direction and magnify these effects. Therefore, Reference 2 considers 

rail burns as the most critical damage to tank cars short of a long through-crack in the shell. The 

following discussion will emphasize this point and indicate the parameters of a rail burn that 

control the weakening of the tank car. 

Figure 2a shows a cross section through a tank shell with a rail burn dent. The radius of 

curvature ρ of the dent controls the degree of plastic bending that the shell wall undergoes during 

the denting process. The sharper this radius, the higher the likelihood that a crack will be 

nucleated, particularly in the region of a girth weld intersected by a rail burn. The depth d of the 

dent controls, in part, the bending moment imposed by the pressure-induced hoop stresses on 

Section A-A at the bottom of the dent. The moment the section can support is limited to the 

fully plastic moment, which is reached rather rapidly as the dent depth increases. Beyond this 

level, the load must be transferred to the material surrounding the dent. 

In other words, the dent acts like a soft bellow or like a hole. If the longitudinal dimension L of 

the dent is small (Figure 2b), the stresses near the dent will increase, but the dent width W will 

not increase much because of this stress redistribution. Section A-A will see loading conditions 

approaching fixed displacement conditions. On the other hand, if L is large, the stress 

redistribution caused by the dent will induce significant opening of the dent width at the dent 

longitudinal mid-position (Figure 2c). Section A-A will then see loading conditions approaching 

fixed-load conditions. This distinction is important with respect to the nucleation of a crack at 

section A-A, delayed crack growth, and the stability of a nucleated crack. Clearly, a long, deep, 

rail burn is most detrimental for both crack nucleation and instability. 

Pellini recognized these aspects in References 2 and 6, albeit in a somewhat qualitative manner. 

His interpretation of the delayed fracture of tank cars with rail burns, however, is not completely 

satisfactory because it does not provide an analysis of fully plastic, stable, crack growth and 

instability, and it does not consider low (near room) temperature creep phenomena that occur in 

fully plastic, low-carbon, steel specimens. Pellini also states that "...it is not realistic to expect 

that the judgments can be made as to the possibility of delayed fracture initiation, for a tank car 

that has been involved in an accident that results in straight-line burn dents" [Reference 2]. The 

potential for delayed fractures, therefore, is a major risk of damaged tank cars. It should be 

thoroughly understood and mitigated. Advances in fracture mechanics, as well as improved 

monitoring of damaged tank cars, can serve to achieve these goals. 
20 

Figure 2. Schematic of Dent in a Tank Car. 
21 

The guidelines incorporate some of the knowledge drawn from Pellini's analysis discussed above 

by specifying unloading of dented tank cars with a dent radius of curvature below a certain 

value, or with a weld, a crack, a score, or a gouge in the dented region. The guidelines do not 

discriminate between long and short dents or deep and shallow dents, although these dent 

characteristics also critically affect the influence of the dent on the structural integrity of the tank 

car. In addition, they do not account for strain history effects (in particular, reversal of the 

bending moment when the denting loads are removed). 

4.1.3.4 Scores, Gouges, and Wheel Burns 

SRI obtained little information from the literature review concerning scores, gouges, and wheel 

burns. As discussed previously, Pellini comments in Appendix B of Reference 2 on the relative 

severity of rail burns on the one hand and scores, gouges, and wheel burns on the other hand (in 

the light of definitions given in the AAR Manual of Standards and Recommended Practices, 

Section C-Part III, Appendix R, Section R 13.00, "Repair of Deformation and Scoring" 

[Reference 21]. Pellini indicates that scores and gouges caused by sliding on a smooth rail are 

restricted to the crown of girth welds and do not normally result in cracks large enough to initiate 

delayed fracture. Wheel burns (defined by Section R 13.00 as circular cuttings into the shell 

surface by the wheel flange) are usually short and not associated with a deep dent. 

SRI only found geometric and metallurgical information regarding scores, gouges, and wheel 

burns in Reference 29. In a recent derailment in Bonfield, Ontario, a tank car sustained (1) a 56 

in (143 cm) long, 1.6 to 2.9 in (4 to 7.3 cm) wide, and at most 0.1 in (2.5 mm) deep wheel gouge 

(sic), and (2) a shorter, 5 in (13 cm) long, 0.12 in (3 mm) deep gouge of unknown origin with 

sharp edges. Both gouges intersected a girth weld. From metallographic cross sections, SRI 

estimated that the heat-affected zone and the deformed zone associated with the wheel gouge 

were approximately 25 to 100 μm (1 to 4 mil) and 100 μm (4 mil), respectively. Hardnesses rose 

as high as 62 Hardness Rockwell C Scale (HRC) in the untempered martensite layer of the heataffected zone, whereas the hardness dropped to 42 HRC in the deformed layer. The martensite 

layer was cracked, but the cracks were arrested at the interface with the deformed layer. The 

region where the smaller gouge intersected the girth weld showed longer cracks (0.6 mm or 24 

mil). This information indicates that rather superficial damage is associated with wheel burns 

and gouges, suggesting that the cold work and metallurgical changes may not be significant. 

Analysis and experiments should, however, validate these points. 

The guidelines consider scores and gouges to be dangerous, in as much as they constitute a notch 

or affect the heat-affected zone of a weld. In the first instance, recommendations for unloading 

the car are given in terms of damage depth and internal tank pressure. If the maximum wheel 

burn depth exceeds 1/8 in (3.2 mm), the guidelines mandate unloading of the damaged car. 

4.1.4 Stress Analysis of Tank Cars and Rerailing Loads 

This review provided pressure-temperature curves for various loadings from which the 

membrane hoop and axial stresses in the tank can be estimated. Appendix A-5 (Figures A-1 and 

A-2) of Reference 6 gives the pressure temperature curves, respectively, for carbon dioxide, 

hydrogen chloride, hydrogen sulfide, propane, ammonia, chlorine, vinyl chloride, and sulfur 
22 

dioxide. The hoop stress-temperature curves can then be calculated for various types of tank 

cars (and hence wall thicknesses) using the pressure-temperature curves. As an example, Figure 

A-2 of Reference 6 shows the resulting stress-temperature curve for the minimum wall thickness 

of an A-340W tank car made of TC-128B steel. For the ladings suitable for transport with A340 tank cars, the stress level is below 20 percent of the yield stress. 

Lupkner analytically and experimentally treated the denting and perforation of tank car heads 

and the collapse of the underframe [Reference 90]. He also analyzed collision accident 

scenarios. Wierzbicki and Suh modeled the indentation of cylinders using rigid-plastic analysis 

[Reference 106]. This type of analysis may provide estimates of the strains associated with 

specific dent dimensions and help assess the severity of the damage associated with the dent. 

Reference 38 reports on a stress analysis of the stub sill region and the effect of redesigns on 

fatigue cracking. 

A decade before Pellini's report Eiber et al. used LEFM to analyze tank car accidents predating 

1972 [Reference 2]. Using the model of References 87 and 88, they modified LEFM to account 

for the effect of plasticity and bulging. Eiber et al. also used their experience with the fracture of 

pressurized gas transmission lines to discuss dynamic aspects of pressurized tank fractures 

[Reference 16]. They showed the importance of the ratio of gas volume over liquid volume in 

the tank in the process of changing the (dynamic) propagation direction of a crack from axial to 

circumferential. No evidence exists that the work of Reference 16 influenced the drafting of the 

guidelines. 

References 28, 34, and 37 provide additional applications of LEFM to tank car safety analysis. 

These analyses consider semi-elliptical surface flaws and estimate critical flaw sizes. They are 

essentially the same as the analysis used by Pellini in SGFAS. 

Reference 81 presents the results of finite element simulations of tank cars supported at various 

locations along their axis. It shows how the stress distribution varies with the position of the 

support brackets. This information could prove useful in establishing guidelines on where to 

apply hoisting cables to lift damaged tank cars. In this context, Reference 34 lists procedures 

and recommendations for lifting and moving cars. 

Beyond the literature quoted here, SRI found little stress analysis relevant to damaged tank cars.2 

Reference 77 discusses methods to calculate membrane and bending stresses in threedimensional configurations for use with the design rules of the ASME Pressure Vessel Code. 

References 78 and 79 report on other applications of LEFM to analyze the structural integrity of 

gas tanks. Reference 80 is a recent application of Pellini's SGFAS. 

As is emphasized below, more extensive stress analysis is needed to support and augment the 

guidelines and their application. 

 

2 Just as this report was being completed, SRI became aware of a recent analysis of tank cars with circumferential 

throughwall cracks by Dr. Akram Zahoor, Zenith Corporation. The analysis uses the elasto-plastic fracture 

mechanics methodology discussed in the next section and is part of an investigation sponsored by the U.S. 

Department of Transportation through NIST in 1992. The report on this work is at present not publicly available. 
23 

4.1.5 Characterization of Tank Car Steels 

The literature search produced an extensive list of reports dealing with the characterization of 

tank car steels [References 4, 5, 7, 11, 12, 21, 43-54]. Many characterizations were associated 

with the analysis of tank cars that failed in accidents and included tensile tests, Charpy impact 

tests, and microstructural data [References 43-54]. SRI did not review these references in detail. 

The degradation in fracture properties caused by prior straining of the steel is an important 

aspect of damage assessment in tank cars and is addressed in References 4 and 37. For example, 

the -50° F (-46° C) Charpy V-notch energy of a TC-135A steel (proposed specification steel 

that was never approved) is reduced by 73 percent from 156 to 42 foot-pounds (6.8 to 1.8 kJ) by 

a 5-percent deformation [followed by a 1 hr stress relief treatment at 1150° F (621° C), see 

Exhibit 12B, p. 31 of Reference 4]. Similarly, prestraining ASTM A515 steel to a strain of 12 

percent can induce a 25 percent reduction in the static fracture toughness and a 65 percent 

reduction in the so-called tearing modulus3 [see Reference 37, Figure 13, and Table 2 on p. 32]. 

Reference 83 proposes a new correlation between Charpy energy and fracture toughness KIc

transition curves for pressure vessel steels. Review of this correlation could provide additional 

support for the definition of Pellini's arrest curve. 

4.1.6 Fractographic and Metallographic Information 

References discussing tank car steels and the analysis of tank car accidents present little 

fractographic information. In particular, the accidents involving delayed fracture showed no 

fractographic or metallographic results. Such information is essential to establish the 

mechanisms responsible for delayed fractures. Further, except for the data on gouges that was 

discussed above, SRI found little useful information about the extent of the zone affected 

thermally or by deformation at scores or gouges and about the geometry of these types of 

damage [Reference 29]. 

4.2 Developments in Fracture Mechanics Relevant to Tank Car Damage Assessment 

SRI’s review of the literature suggests that fracture analysis of tank cars is primarily based on 

LEFM and on engineering fracture assessment methods that use fracture transition temperature 

and crack arrest curve concepts.4 Over the last 20 years, however, the field of fracture 

mechanics made many significant advances. It is now feasible, with the J-based elastic-plastic 

fracture mechanics (EPFM) approach, to evaluate the conditions required to initiate and 

propagate a pre-existing crack in a partially yielded or fully plastic structure. It is also possible, 

using damage mechanics or so-called local fracture methods, to predict crack nucleation at blunt 

stress concentrations (such as gouges or scores) or in prestrained material. 

These new approaches apply to both the problem of the onset of cleavage fracture under 

conditions of extensive yielding (which is a situation often encountered in practice) and the 

problem of ductile tearing, which is, the initiation of a stable fracture by microvoid coalescence, 

followed by stable growth of the crack, and finally unstable propagation. 

 

3 The next section discusses the tearing modulus. 

4 The only known exception is the recent unpublished elasto-plastic fracture analysis by Zahoor mentioned earlier. 
24 

The following section gives a brief review of these developments, along with a discussion on 

how they can be applied to formulate more reliable and better documented guidelines for the 

assessment of damaged tank cars. For a more detailed treatment of these developments, refer to 

References 92 to 102. 

4.2.1 J-Based, EPFM 

It has been shown that, if certain specific conditions are met,5 the stress and strain fields in the 

neighborhood of a stationary crack in elastic-plastic or fully plastic material can be described in 

a form similar to the linear elastic solution, that is: 

 σ ≈ (J)( 1

n+1)

 r 

-( 1

n+1)

 Σ(θ) ε ≈ (J)( n

n+1)

 r 

-( n

n+1)

 Ε(θ) (2) 

where r and θ are polar coordinates centered at the crack tip, n is the strain hardening exponent, 

and Σ(θ) and Ε(θ) are nondimensional functions. In Equation (2), J is the so-called J-integral, 

which controls the amplitude of stresses and strains at the crack tip. By analogy with the elastic 

stress intensity factor K of LEFM, view J as a plastic stress intensity factor, which represents the 

influence of remote loading on the crack tip fields. In addition, estimate J from remotely applied 

boundary conditions and that, in the limit of pure elasticity and for plane strain conditions, it is 

related to K in the following way: 

 J = 

K2 (1 - ν2)

 E (3) 

where ν is Poisson's ratio and E is Young's modulus. 

It is argued that because the plastic crack tip stress and strain fields are controlled by the 

parameter J, it can be used to predict crack initiation under conditions of extensive plastic 

deformation. The criterion for initiation of a pre-existing sharp crack is then: 

 Jappl >

= JIc (4) 

where Jappl represents the loading applied to the crack tip and JIc is the material resistance to 

fracture (i.e., its fracture toughness), which can be measured in laboratory experiments. ASTMStandard E-813 gives procedures and size and geometric requirements for the determination of 

the material toughness JIc [Reference 108]. 

For ductile materials, a phase of stable crack growth in which an increase in Jappl (and the 

applied loading) is required to overcome an apparent increased resistance of the material to 

tearing and to propagate the crack by an amount Δa often follows the initiation of a tearing crack. 

Laboratory experiments can measure the curve Jappl versus Δa (the so-called J-resistance curve) 

[Reference 109] and is then considered a material property [Jmat (Δa)]. The resistance curve 

serves to predict the amount of crack growth using the relation: 

 

5 This includes among others: assumed small strain, small plastic deformation, and proportional loading. 
25 

 Jappl (Δa) = Jmat (Δa) (5) 

which states that, at any point Δa during the crack growth phase, the Jappl (Δa) applied by the 

external forces must be in equilibrium with the ability of the material to resist tearing Jmat (Δa). 

A comparison of the rate at which Jappl and Jmat increase with Δa determines whether the new 

increment of crack growth is stable or not, that is: 

 (

∂

∂

J

a

appl )fbc <(

∂

∂

J

a

mat ) => stable crack growth (6a) 

 (

∂

∂

J

a

appl )fbc > (

∂

∂

J

a

mat ) => unstable crack growth (6b) 

In Equations (6a) and (6b), the subscript fbc indicates that the rate of change of Jappl is 

estimated holding the boundary conditions fixed (for example, fixed load level for a loadcontrolled situation or fixed displacement for a displacement-controlled situation). The 

instability condition therefore depends on the loading configuration and more specifically on the 

compliance of the loading system. A compliant (soft) loading system promotes early instability, 

whereas a stiff system retards or precludes instability. This point is important in considering the 

safety of pressurized tank cars because the proportion of liquid to gas phase in the tank will 

affect the compliance of the system and hence the onset of instability. 

The parameter 

∂

∂

J

a

mat represents the slope of the experimental resistance curve. The derived parameter: 

J

a E mat

flow2

∂

∂ σ (7) 

(where σflow is the flow stress defined as the average of the yield and ultimate strengths) is 

called the tearing modulus and is often used to characterize the resistance of a material to tearing 

instability. 

Figure 3 shows how this method is applied to the fracture of a 4T, compact tension specimen of 

A533B pressure vessel steel loaded by testing systems of different compliances CM (fixed grip, 

CM = 0; soft loading system, CM x E = 1000; dead load, CM = ∞). For each case, the figure 

shows families of Jappl versus crack length loading curves, over which the material resistance 

curve has been superimposed. The point where loading and resistance curves are tangent 

represents the point of instability. The figure indicates that for CM = 0, crack growth is always 

stable, whereas for CM = ∞ instability sets in after only a limited amount of crack growth. The 

point of crack initiation, however, is independent of the compliance of the loading system. 
26 

Figure 3. Jappl versus Crack Length for a 4T A533B Steel Compact Tension Specimen 

Compared to a Material Resistance Curve. (Ref. 96) 

CRACK LENGTH (in)
27 

The elastic-plastic analysis method discussed here is valid for several applications, with 

established limitations. One of the main limitations is that the material resistance curve is not 

really a material property. Rather it is a structural property that depends on specimen geometry 

and dimensions. Therefore, measure the resistance curve with specimens simulating the specific 

application. Nevertheless, the method is now well accepted in the community and is used to 

characterize ductile materials, as well as to make structural integrity evaluations, particularly in 

the nuclear industry. Reference 93 is a handbook of solutions for Jappl. The Failure Assessment 

Diagram, discussed in Reference 79, is a convenient extension of the method for engineering 

applications. 

An elasto-plastic fracture analysis method based on the concept of crack-tip opening 

displacement (CTOD) has also been developed, mainly in Europe, and applied successfully to 

ductile engineering structures. One can show that the J-based elastic-plastic fracture analysis 

and the CTOD-based theory are essentially equivalent (see Reference 97 for a review). 

4.2.2 Fracture Predictions using Damage Mechanics/Local Fracture 

As pointed out in the preceding section, the J-based EPFM approach has limitations and cannot 

be used to predict fracture in the absence of pre-existing cracks. Therefore, it cannot be used for 

the analysis of scores, gouges, or dents in tank cars. 

To overcome the limitations of classical fracture mechanics approaches, new methods were 

developed that use continuum mechanics and focus on modeling the microstructural damage 

(such as cleavage or ductile void growth) induced in small volumes of structural materials. 

These models, although somewhat more complex in their use, present many advantages. They 

can handle more general fracture problems (multiaxial loading, no pre-existing cracks, 

microstructural gradients, large amounts of crack extension), and they can be calibrated using 

small notched and cracked tensile specimens, which are easy to fabricate, test, and analyze. 

An exhaustive review of developments in damage/local fracture mechanics is beyond the scope 

of this report. References 98 to 102 provide more details. Nevertheless, to illustrate the 

capabilities of these new approaches, SRI discusses a ductile fracture model proposed by 

MacKenzie et al. [Reference 103] that they have implemented in a finite element code and used 

in their own work on the fracture of weldments [References 104 and 105]. 

The local ductile fracture model [References 98 and 103] assumes that failure of a material 

location occurs when the damage within a surrounding characteristic volume VMIC exceeds a 

critical value that is: 

 D = ⌡

⎮

⌠ dε p

eq

εc(σ∗)

 = 1 over VMIC ≈ (RMIC)3 (8) 

where D is the normalized damage parameter, dε p

eq is an increment in plastic strain, and εc(σ∗) 

is the critical failure strain as a function of the stress triaxiality σ

*, defined as the ratio of the 

mean stress to the equivalent stress. A series of notched tensile tests with specimens of varying 

notch radii can determine this critical strain function. VMIC and RMIC are the volume and 
28 

radius of the process zone. These constant microstructural parameters introduce nongeometric 

scaling effects. A version of the explicit finite element code DYNA3D implements the fracture 

model, which contains a node release feature allowing the simulation of propagating cracks. 

The model of Equation (8) is equivalent to other local ductile fracture models based on the 

attainment of a critical void size or volume fraction [References 98 to 102]. SRI has used this 

model to successfully predict the dynamic fracture behavior of welded joints in HY-130 steel. 

Figure 4 compares the results of experiments and computations for a stiffened plate loaded 

impulsively by sheet explosive. The input to the calculation was the initial velocity imparted to 

the plate. The simulation models the deformation of the broken plate quite well. More 

importantly, the crack path through the plate, which was not prescribed a priori, resembles quite 

well the crack path through the metallurgical cross section of the weld. 

SRI suggests use of a local fracture model such as the one discussed here in conjunction with 

laboratory experiments on notched plates and round bars to analyze the effect of scores and 

gouges, as well as the effect of various amounts of cold work on the structural integrity of tank 

cars. SRI will discuss this approach further in this report. 
29 

Figure 4. Deformation and Fracture Behavior of Explosively Loaded Welded 

HY-130 Steel T-Joints. 
30 

4.3 Assessment of Guidelines and Their Degree of Validation 

Reading the guidelines brought to light several omissions, inconsistencies, or errors, which can 

in most cases be easily corrected. These are discussed below. 

Page numbers referenced in this section are in relation to Section G of AAR/TTCI’s Tank Car 

Safety Course Manual [Reference 110]. 

Section 1 (p. 2) of the guidelines discusses the four conditions affecting the ductility of tank car 

steels as: 

• The specification of the steel 

• Its service temperature 

• The amount of cold work it has received 

• The presence of heat-affected zones 

This list omits a fifth very important factor, namely the loading rate, which in steels can 

significantly reduce both ductility and fracture toughness and even induce a change in the 

microscopic mode of fracture from ductile void growth to brittle cleavage at a given temperature. 

On page 2, the discussion of the effect of pressure-induced stress on the stability of cracks does 

not recognize the possibility for slow, stable, ductile growth of a crack under conditions of 

gradually rising temperatures and pressures. Stable crack growth may play an important role in 

delayed fracture of damaged tank cars, as will be discussed below. 

The discussion of scores and gouges (p. 4) should mention that, in addition to reducing the tank 

metal thickness, these damage types induce a geometric stress concentration, locally workharden the steel, and possibly change its microstructure because of thermal effects. All these 

factors help make the tank car wall weaker at the damage location. These remarks also apply to 

wheel burns (p. 5). 

The terminology used for the damage induced by the contact of the tank car wall with a rail is 

ambiguous and should be clarified. If the tank car simply impacts the rail (for instance, because 

it overturned) without relative sliding motion between the rail and the wall, then the resulting 

damage is a relatively long and narrow dent. AAR Manual of Standards and Recommended 

Practices refers this type of damage as a rail dent [Reference 21]. If the rail slides relative to the 

wall while in contact with it, it may leave a region of reduced wall thickness with a surface 

microstructure affected by plastic deformation and frictional heating. This second type of rail 

damage is similar to a wheel burn and should be appropriately named rail burn. It is, of course, 

possible that a rail induces both a dent and burn in the tank wall. 

The criteria for assessing the limiting score depth for 340W and 400W tanks are not clear. On 

p. 8, the text mentions, "Tanks having scores or gouges should be unloaded in place when the 

internal pressure exceeds half of the allowable internal pressures listed in the tables below." The 

referenced tables list pressures associated with various score depths under the heading 

"Maximum Safe Internal Pressure." Should the tank car be emptied when the pressure reaches 

the full pressure or only half the pressure in the table? This ambiguity must be resolved. 
31 

Similarly, SRI identified an inconsistency in the criterion for unloading a tank car containing a 

wheel burn. The guideline text on p. 9, left column, requires that a tank containing a wheel burn 

deeper than 1/8 in (3.2 mm) be unloaded as soon as possible. On the other hand, Figure 10 

shows a major wheel burn requiring immediate unloading as one with a depth of 1/4 in (6.3 mm) 

or more, whereas cars with burns of less than 1/8 in (3.2 mm) can be transported. The text does 

not refer to Figure 10. 

On p. 9, introduce paragraph heading, "Dents, Rail Burns," before the second bulleted paragraph. 

In addition, SRI believes that if any one of the conditions listed at the bottom of the left column 

of p. 9 is fulfilled, state more clearly that the tank car should be unloaded without moving it. In 

addition, the last condition for tank cars built since 1967 requires unloading if the dent "shows 

evidence of cold work." By its very nature, a dent will always be associated with plastic 

deformation and hence cold work. Therefore, this requirement must be more specific. 

Finally, as indicated by Pellini and discussed earlier, a dent should be characterized not only by 

its radius of curvature but also its length and depth. In the following section, SRI suggests that 

more precise safety criteria involving these dent parameters should be formulated. 

4.3.1 Validation and Limitations of the Guidelines 

In discussing the degree of validation and the limitations of the guidelines, SRI focused 

primarily on Section 5, "Interpreting Tank Damage to Pressure Tank Cars," because it is the only 

part of the guidelines containing quantitative rules for assessing damage severity. 

First, given the available evidence, SRI found that the guidelines reflect good, overall, physical 

understanding of potentially dangerous damage to tank cars. However, recommendations are 

sometimes formulated in an ambiguous and qualitative way that could lead to misinterpretations. 

Second, the validation for the guidelines appears to be service experience and, possibly, analyses 

based on Pellini's SGFAS, taking only pressure loads into consideration. This degree of 

validation is not sufficient to guarantee safe handling of damaged tank cars. New experimental 

and analytical tools available today provide a means to refine and more thoroughly validate the 

guidelines. 

Third, to guarantee the safe handling of damaged tank cars, consider the effect of rerailing loads 

on pre-existing damage, particularly dents, and structural integrity more explicitly. The damage 

severity criteria included in the guidelines should take into account these loads. Provide specific 

lifting practices and load application locations, and validate the damage assessment guidelines 

for these conditions. 

Fourth, the safety-critical issue of delayed fracture has not been fully and satisfactorily explained 

by available analysis and should be reconsidered in the light of more recent understanding of 

ductile and ductile-brittle transition fracture processes. 

Finally, the qualitative character of the guidelines may contribute to very conservative 

assessments of damage in some cases and much less conservative assessments in others. 

No records exist of the method used to estimate the degree of conservatism assessed at the time 

the guidelines were drafted (as indicated by the footnotes in Tables 1 and 2), and no underlying 
32 

experimental or analytical results are available at the date of this report. Therefore, any 

proposed work on improving the guidelines should result in clear bounds on the safety margins 

associated with each recommendation, backed by a description of the method used to arrive at 

the estimates of the margins. The outcome will most likely show that, in some cases, the current 

guidelines are too conservative and in other cases not conservative enough. The following 

paragraphs will discuss the conclusions in more detail. 

The guidelines express the criticality of sharp dents, scores, and gouges in terms of dimensional 

and geometric features (radius of curvature of dents, depth of scores) and the type of material 

they affect (base metal of the tank shell, weld metal, or the heat-affected zone). The guidelines 

also consider interactions between several types of defects. The rationale behind using score 

depth and radius of curvature of dents is that these parameters relate respectively to a reduction 

in wall thickness and an associated increase in stress, as well as a certain level of plastic 

straining. Both stress and strain play a critical role in damaging the material and inducing 

fracture. In that respect, depth and curvature are good parameters to estimate the criticality of 

tank car damage, provided that a reliable correlation has been established (1) between them and 

the stress and strain distribution in the vicinity of the damage and (2) between stress and strain 

states and fracture. An analysis and some laboratory experiments can best establish these 

correlations. The analysis provides accurate values of stresses and strains in the damaged region, 

whereas experiments serve to establish the critical conditions for fracture and to validate the 

overall predictive approach. The power of such an approach is to allow analytical treatment of 

many situations without having to perform an excessive number of laboratory experiments. 

SRI suggests that the score depth-safe pressure specification in the guidelines was based on a 

requirement that net section stress at the score not exceed a fraction of the ultimate stress. 

Expressed in terms of pressures, this requirement is of the form: 

 Psafe = 

(t-dscore) Pburst

 t α Kt Pburst = 

σu t

 r (9) 

where r and t are the shell radius and thickness, respectively, dscore the score depth, Pburst the 

burst pressure (850 psi and 1000 psi (5.8 and 6.9 MPa), respectively, for 340W and 400W tank 

cars), Psafe the safe pressure cited in Tables 1 and 2 of the guidelines, α a safety factor, and Kt a 

stress concentration factor accounting for the score geometry. The data of Tables 1 and 2 indeed 

follow this linear relationship (see also Figure 3-3 on p. 3-25 of Reference 34) and indicate 

values of the product α Kt of around 4. Assuming that the required factor of safety is the same 

as for the undamaged tank car (2.5), then Kt is about 1.6. Dropping the value of α to 2 yields a 

value of Kt of 2, which is the value quoted in Reference 34. Testing small flat plates with 

simulated score damage and calculating from the load at failure the fracture stress and the 

corresponding tank pressure may provide validation for the depth specifications. No explicit 

provision is made in this analysis for changes in material properties due to heating or work 

hardening caused by the gouging or scoring process. 
33 

SRI further suggests, as also discussed in Reference 34, that the specification for the radius of 

curvature of dents is based on a comparison of the maximum strain εdent associate with a certain 

dent radius ρ and the elongation or strain at failure εfailure of typical tank materials: 

 εdent = 

t

2ρ

 < 

εfailure

β (10) 

where β is again a safety factor. For ρ = 2 in (5 cm) and 4 in (10 cm), the corresponding 

maximum strains are roughly 15 percent to 18 percent and 7 percent to 9 percent, respectively, 

depending on the thickness. For comparison, the room temperature failure elongations (2 in or 5 

cm gage length) for TC128 and TC135 steels must be at least 22 percent to 23 percent (from 

exhibit 6, Reference 4; see also Reference 7). Equivalent plastic strains at failure calculated 

from available reduction of area values exceed 50 percent. This comparison shows that the value 

of the safety factor underlying the recommendations depends on what experimental failure strain 

is used in conjunction with Equation 8. Using an (to the research team's knowledge) 

undocumented correlation between failure strain in pure bending and reduction in area in the 

tensile test, and a value of the reduction of area of 19 percent, Reference 34 estimates that the 

guidelines ensure a safety factor of 3. Laboratory bend tests with shell base metal may provide 

or validate the recommendations of the guidelines. 

The recommended curvature values may be less conservative than indicated above. The process 

of forming a rail dent involves pushing the shell wall inward to form the dent. If the dent is 

deep, once the rail load is removed, the dent will possibly be pushed and bent outward again 

under the action of the internal pressure and the associated membrane stresses (see earlier 

discussion). This process will tend to reduce the curvature. Thus, a dent may have accumulated 

more plastic strain (in a sense be more damaged by the deformation cycle) than simply indicated 

by its curvature. This point illustrates another deficiency of the guidelines. Although the 

guidelines acknowledge, in some cases, the possibility for deformation history effects (e.g., 

conditions on the presence of cold work in the dent), they do not indicate whether or how they 

account for these effects in specifying safe/unsafe conditions. In view of the important effect 

that prestraining can have on the fracture properties (see earlier discussion of References 4 and 

37), a validation of the guidelines requires an assessment of deformation history effects. 

As was discussed earlier, the criticality of a rail dent should also depend on its length and depth. 

Long deep dents are more dangerous than short ones in terms of delayed fracture and 

catastrophic failure after the accident. The guidelines should therefore specify limit values of 

these parameters on the basis of a structural and fracture mechanics analysis. 

The literature reviewed did not provide a satisfactory explanation of the phenomenon of delayed 

fracture of tank cars with large rail dents. The guidelines do not address this important safety 

issue; therefore, revisit this phenomenon, using developments in experimental and analytical 

elastic-plastic fracture made over the last 20 years. SRI believes that two mechanisms of slowcrack growth are possible for delayed fracture under either monotonically increasing loads or 

constant load in a creeping material. 
34 

Slow, stable, ductile growth of a small thumbnail crack can occur if the tank car pressure 

increases because of slowly increasing external temperatures. The growing crack then becomes 

unstable either because the applied (compliant) pressure loading overcomes the tearing 

resistance of the material (tearing instability) or because the stress state and the microstructural 

conditions at the tip of the growing crack are such that low energy cleavage is induced (cleavage 

instability). 

Low temperature creep deformation in carbon steels subjected to a constant, fully plastic load is 

a well-documented phenomenon. This type of fully plastic, dead weight, loading condition may 

prevail in the middle of a long-rail dent, so that if a crack is present, it can blunt and grow, 

driven by creep plasticity. The instability phase is then similar to that of a crack growing under a 

monotonically increasing load. In the future, give attention to these possible delayed fracture 

scenarios and to explaining unequivocally the conditions governing this dangerous failure mode 

of tank cars. 

Another area in which SRI believes the guidelines need improvement is in identifying 

recommended procedures for moving and lifting tank cars. By limiting these procedures to a 

few well-defined load application configurations (as suggested in References 34 and 35), 

quantitatively evaluate the effect of rerailing loads on damaged regions of the tank car. Only by 

truly taking into account the effect of these loads, will it be possible to reliably validate the 

damage severity criteria now proposed by the guidelines. 

Although this topic falls outside the scope of this project, seriously consider recommendations 

for using nondestructive techniques to evaluate damaged tank cars. The field of NDE has 

evolved rapidly since publication of References 36 and 37, and an update on NDE technologies 

that may be suitable to assess damaged tank cars should be obtained. 

4.4 Expert Review 

A number of individuals received for review and comment the report prepared by SRI. The 

individuals were selected because of their knowledge in the fields of tank car construction, 

metallurgy, fracture mechanics, and FEA. The individuals identified below participated in the 

review of the report, and with few exceptions they agreed that the report was sound. In general, 

the reviewers indicated that the report provided a good assessment of the literature and that the 

recommended approach for validation of the guidelines appeared to be reasonable. Appendix A 

lists the following reviewers’ specific comments: 

• J. Robert Sims, Exxon Research and Engineering, Chairman ASME Post 

Construction Committee 

• Dr. William J. Koves, UOP, Inc., Chairman ASME Flaw Analysis Subcommittee 

• Stephen Wong, Procor Limited 

• Paul Kinnecom, AAR 

• Diane Rocheleau, Transportation Safety Board of Canada 

• Edgar Ladouceur, Transport Canada 
35 

5.0 Conclusions and Recommendations 

Based upon the review of over 100 references, the subcontractor has identified the analytical and 

experimental work necessary to evaluate the criticality of the damage (cracks, scores, gouges, 

dents, and wheel burns). The subcontractor found that the guidelines reflect a good, overall 

physical understanding of potentially dangerous damage to tank cars. Quantitative specifications 

are generally expressed in terms of convenient parameters that can be related to the degree of 

structural and material weakening caused by the damage. The following presents the additional 

conclusions drawn by SRI regarding the relevance and validity of the guidelines: 

• The guidelines are often only qualitative and somewhat vague in their requirements. 

• No record of analytical or experimental work exists to directly support and validate 

the guidelines. The subcontractor was able to reconstruct some of the reasoning that 

must have led to the guidelines. It appears that the guidelines rely on 20-year or older 

analysis methods and do not reflect recent advances in computational and fracture 

mechanics. 

• The effect on damage of loads applied to move or lift the derailed tank car is not 

explicitly accounted for in the guidelines, even though these loads could be important 

in causing damaged areas to rupture. 

• The phenomenon of delayed fracture is not appropriately documented and 

understood. The guidelines do not adequately address this important safety issue. 

• The margins of safety associated with the current guidelines are not known. 

• The guidelines do not consider advanced NDE methods available to identify tank car 

damage and to monitor the damage during tank car handling at the accident scene. 

To alleviate these shortcomings and improve the reliability and usefulness of the guidelines, SRI 

and AAR/TTCI recommend that the following research be initiated: 

• Identify typical rerailing load scenarios. Calculate by FEA methods the stress and 

strain fields they induce in pressurized tank cars. Use these results as loading 

conditions to assess the criticality of various types of damage in tanks cars. 

• Assess the residual resistance of tank cars with large dents to buckling and plastic 

collapse when subjected to rerailing loads. 

• Refine and validate the severity criteria for scores, gouges, and wheel burns using 

recent advances in analytical and experimental fracture mechanics. 

• Assess the possibility for stable crack growth in fully plastic tank car steels and the 

implications for delayed fracture. 

• Evaluate the applicability of current NDE equipment, and recommend use of suitable 

NDE techniques in the guidelines. 

• Monitor and participate in the activities of the committee on Post-Construction 

Standards of ASME's Pressure Vessel and Piping Division. 
36 

SRI recommends that the structural and fracture mechanics analysis aspects of the proposed 

research be accomplished by combining nonlinear finite element simulations with advanced 

elasto-plastic fracture and local fracture theories to quantify the severity of various types of tank 

car damage. Perform this analytical effort in conjunction with an experimental effort using small 

laboratory specimens that will provide material properties data, as well as validation for the 

analyses. 

Use the results of this research to reformulate the guidelines in more precise and quantitative 

terms so that their use will contribute to increased safety at derailment sites. 
37 

List of References 

1. Tetelman, A. S. and D. H. Stone, "An Introduction to the Fracture Mechanics of Railroad 

Materials," Association of American Railroads, Report No. R-157, Chicago, Illinois (May 

1974). 

2. Pellini, W. S. "Analysis of Tank Car Failures Related to Rail Burn Dents," Association of 

American Railroads, Report No. R-551, Chicago, Illinois (June 1983). 

3. Phillips, E. A. and H. Role, "Analysis of Tank Cars Damaged in Accidents, 1965 through 

1986, Documentation Report," Association of American Railroads, Report No. RA-02-6-55 

(AAR R-709), Chicago, Illinois (January 30, 1989). 

4. Phillips, E. A. "Evaluation of New Steels for Tank Cars, Phase II," Association of 

American Railroads, Report No. RA-03-9-59 (AAR R-773), Chicago, Illinois (May 2, 

1991). 

5. Pellini, W. S. "Feasibility Analysis for Tank Car Applications of New Microalloyed and 

Controlled Rolled Steels—Description of Fracture Properties and Comparisons with Steels 

in Present Use," Association of American Railroads, Report No. R-543, Chicago, Illinois 

(April 1983). 

6. Pellini, W. S. "Guidelines for Fracture Mechanics Analysis of Pressure Tank Car Structural 

Integrity Factors," Association of American Railroads, Report No. R-586, Chicago, Illinois 

(June 1985). 

7. Phillips, E. A., R. J. Eiber, S. A. Coughlin, P. B. Heideman, and M. C. Fec, "Evaluation of 

New Steels for Tank Cars," Association of American Railroads, Report No. RA-03-7-53 

(AAR R-643), Chicago, Illinois (April 29, 1987). 

8. Phillips, E. A. and W. B. Krauskopf, "Phase 01 Report on Summary of Ruptured Tank Cars 

Involved in Past Accidents," Addendum-Report of Association of American Railroads, 

Report No. RA-01-2-7 (AAR R-130), Chicago, Illinois (May 1, 1973). 

9. Phillips, E. A. and L. L. Olson, "Phase 03 Report on Metallographic Examination of 

Specimens Removed from Sections of Tank Cars in Crescent City Derailment," 

Association of American Railroads, Report No. RA-03-1-2 (AAR R-125), Chicago, Illinois 

(October 15, 1970). 

10. Phillips, E. A. and L. L. Olson, "Phase 03 Report on Metallographic Examination of 

Specimens Removed from a Section of Tank Car in South Byron, New York Derailment," 

Association of American Railroads, Report No. RA-03-2-4 (AAR R-127), Chicago, Illinois 

(March 10, 1971). 
38 

11. Phillips, E. A. and L. L. Olson, "Phase 03 Report on Fracture Properties of Tank Car 

Steels-Characterization and Analysis," Association of American Railroads, Report No. 

RA-03-4-32 (AAR R-192), Chicago, Illinois (August 20, 1975). 

12. Eiber, R. J. and L. L. Olson, "Final Phase 03 Report on Material Study on Steels Used in 

Current and Former Tank Car Construction and from Cars Involved in Accidents," 

Association of American Railroads, Report No. RA-03-5-33 (AAR R-193), Chicago, 

Illinois (August 21, 1975). 

13. Phillips, E. A. and W. S. Pellini, "Phase 03 Report on Behavior of Pressure Tank Car Steels 

in Accidents," Association of American Railroads, Report No. RA-03-6-48 (AAR R-553), 

Chicago, Illinois (June 20, 1983). 

14. Phillips, E. A. and H. Role, "A Review of Pressure Car Shell Puncture Vulnerability," 

Association of American Railroads, Report No. RA-09-6-52 (AAR R-628), Chicago, 

Illinois (January 23, 1987). 

15. Reedy, C. E. and E. A. Phillips, "Phase 12 Report on Tank Car Accident Investigation 

Guide," Association of American Railroads, Report No. RA-12-1-6, Chicago, Illinois 

(revised April 26, 1973). 

16. Eiber, R. J., W. A. Maxey, and A. R. Duffey, "Analysis of Fracture Behavior of Tank Cars 

in Accidents," Association of American Railroads, Report No. RA-12-2-20 (R-143), 

Chicago, Illinois (September 1972). 

17. Pellini, W. S. "Slide Graph Fracture Analysis System," Association of American Railroads, 

Report No. R-552, Chicago, Illinois (June 1983). 

18. Pellini, W. S. "Guidelines for Fracture-Safe Design of Steel Structures," Association of 

American Railroads, Report No. R-455, Chicago, Illinois (November 1980). 

19. Pellini, W. S. "Guidelines for Fatigue-Reliable Design of Steel Structures," Association of 

American Railroads, Report No. R-490, Chicago, Illinois (September 1981). 

20. Association of American Railroads. "Phase 18 Study: Integrity of Damaged Tank Cars," 

Chicago, Illinois (pub. date unknown). 

21. Association of American Railroads, Manual of Standards and Recommended Practices, 

Sec. C-Part III, "Specifications for Tank Cars," Specification M-1002. 

22. Tank Car Fatigue Crack Growth Test, DOT/FRA/ORD-93/10. 

23. National Transportation Safety Board, "Derailment of Burlington Northern Freight Train 

 No. 01-142-30 and Release of Hazardous Materials in the Town of Superior," 

 Hazardous Materials Accident Report NTSB/HZM-94/01, Notation 5842B, Washington, 

 DC (March 1994). 
39 

24. Phillips, E. A. and W. A. Pellini, "Phase 03 Report on Behavior of Pressure Tank Car 

Steels in Accidents," Association of American Railroads, Report No. RA-03-6-48 (June 20, 

1983). 

25. National Transportation Safety Board, "Derailment of Louisville and Nashville Railroad 

Company's Train No. 584 and Subsequent Rupture of Tank Car Containing Liquefied 

Petroleum Gas Waverly," Railroad Accident Report No. NTSB-RAR-79-1, Notation 

2313B, Washington, DC (February 22, 1978). 

26. National Transportation Safety Board, "Tank Car Structural Integrity After Derailment," 

Special Investigation Report No. NTSB-SIR-80-1, Notation 3062, Washington, DC 

(October 16, 1980). 

27. Phillips, E. A. and H. Role, "Effectiveness of Shelf Couplers, Head Shields, and Thermal 

Shields on DOT 112 (114) and 105 Tank Cars," Association of American Railroads, Report 

No. RA-02-5-51 (AAR R-610), Chicago, Illinois (June 13, 1985). 

28. Wright, W. P. "Tank Car Damage Assessment Procedure Study," Ballistic Research 

Laboratory Final Report, Aberdeen Proving Ground, Maryland, to Federal Railroad 

Administration of the Department of Transportation, Washington, DC, Contract No. 

DTFR53-82-X-00275 (May 1984). 

29. Bryson, W. "Tank Car Wheel Gouge, PROX 80665, Bonfield Derailment," Report of the 

Transportation Safety Board of Canada, Gloucester, Ontario, to the Association of 

American Railroads, Pueblo, Colorado, Contract No. 580-3 R95H0003 (February 1995). 

30. Pellini, W. S. "Guidelines for Fracture-Safe and Fatigue-Reliable Design of Steel 

Structures-Applications of Fracture Mechanics and Structural Integrity Technology," 

Welding Institute, Abington, Cambridge, England (1983). 

31. Phillips, E. A., H. Role, and L. L. Olson, "Phase 02 Report on Analysis of Non-Pressure 

Tank Car Behavior in Accidents," Association of American Railroads, Report No. 

RA-02-4-47 (AAR R-541), Chicago, Illinois (March 24, 1983). 

32. Johnson, M. R. and E. A. Phillips, "Study of Railroad Tank Car Thickness Minimums," 

Association of American Railroads, Report No. RA-12-3-56 (AAR R-726), Chicago, 

Illinois (May 5, 1989). 

33. Conlon, P. C. L. "Exhaust Emission Testing of In-Service Diesel-Electric Locomotives 

1981 to 1983," Association of American Railroads, Publication No. R-688, Washington, 

DC (March 1988). 

34. Shaver, D. K. and R. L. Berkowitz, "Guideline Manual, Post Accident Procedures for 

 Chemicals and Propellants," Air Force Rocket Propellant Laboratory Report 

 AFRPL TR-82-077 (January 1983). 
40 

35. Shaver, D. K., R. L. Berkowitz, and P. V. Washburne, "Accident Management Orientation 

Guide," Air Force Rocket Propellant Laboratory Report AFRPL TR-82-0075 (October 

1983). 

36. Beller, L. S., J. D. Mudlin, W. G. Reuter, and M. A. Tupper, "Survey of Nondestructive 

Methods for Evaluating Derailed Tank Cars," U.S. Army Ballistic Research Laboratory 

Contract Report BRL-CR-539 (November 1984). 

37. Reuter, W. G., J. D. Mudlin, R. L. Harris, F. M. Haggag, W. L. Server, and J. S. Epstein, 

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Institute, Report No. FRA/ORD-89/01, NTIS Report No. PB90-161456/WTS (March 

1989). 

39. Phillips, E. A. "Designing for Damage Prevention in the Railroad Tank Car Industry," 

Proceedings of the 34th Meeting of the Mechanical Failures Prevention Group (National 

Bureau of Standards, Special Publication 652, Washington, DC, 1983), pp. 181-212. 

40. Pellini, W. S., D. H. Stone, and W. J. Harris, Jr., "Applications of Structural Integrity 

Technology in the Railroad Industry," Structural Integrity Technology, American Society 

of Mechanical Engineers, 125-143 (1979). 

41. Phillips, E. A., R. L. Wenk, R. R. Fessler, and R. J. Eiber, "Analysis of Fracture Behavior 

of Tank Cars, Phase 12 Report," Association of American Railroads, Report No. 

RA-12-2-20 (AAR R-143), Chicago, Illinois (1972). 

42. Phillips, E. A. "Report on Analysis of Tank Car Tub Rocketing in Accidents," Association 

of American Railroads, Report No. RA-12-2-23 (AAR R-146), Chicago, Illinois (1972). 

43. Early, J. G., C. G. Interrante, S. R. Low, and B. A. Fields, "Dynamic Mechanical Properties 

of Two AAR M128 and One ASTM A212-B Steel Tank Car Head Plates," National 

Institute of Standards and Technology, Report No. NBSIR-88/3690 (June 1988). 

44. Early, J. G. and C. G. Interrante, "A Metallurgical Evaluation of Two AAR M128 Steel 

Tank Car Head Plates Used in Switchyard Impact Tests," National Bureau of Standards, 

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45. Early, J. G. "Elevated-Temperature Mechanical Behavior of a Carbon-Manganese Pressure 

Vessel Steel," Journal of Engineering Materials and Technology, 99(4), 359-365 (October 

1977). 
41 

46. Early, J. G. "Mechanical Properties of AAR M128-69-B Steel Plate Samples Taken from 

Insulated Fire Tested Tank Car RAX 202," National Bureau of Standards, Report No. 

FRA/ORD-76-74, Contract No. DOT-AR-40008 (NBSIR 75725), Washington, DC (1976). 

47. Interrante, C. G. "Impact Properties of Steels Taken from Four Failed Tank Cars," National 

Bureau of Standards, Report No. FRA/ORD-75-51 (NBSIR 75656), Washington, DC 

(1976). 

48. Hicho, G. E. and C. H. Brady, "Hazardous Materials Tank Cars-Evaluation of Tank Car 

Shell," National Bureau of Standards, Report No. FRA/ORD-75-46, Washington, DC 

(1975). 

49. Interrante, C. G., G. E. Hicho, and D. E. Harne, "A Metallurgical Analysis of Eleven Steel 

Plates Taken from a Tank Car Accident Near Callao, Missouri," National Bureau of 

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Anhydrous Ammonia in Quenched-and-Tempered Steel Cargo Tanks," Southwest 

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Antonio, Texas (1976). 

51. Interrante, C. G. and G. E. Hicho, "Metallurgical Analysis of a Steel Shell Plate Taken 

from a Tank Car Accident Near South Byron, New York," National Bureau of Standards, 

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52. Early, J.G. and C. G. Interrante, "A Metallurgical Investigation of a Full-Scale Insulated 

Rail Tank Car Filled with LPG Subjected to a Fire Environment," National Bureau of 

Standards, Report No. FRA/ORD-75-52 (NBSIR 75657), Washington, DC (1975). 

53. Olson, L.L. "Data Display Report on Results of Tests on Mill Plate Samples and Samples 

Removed from Tank Cars Involved in Accidents, Phase 03 Report," Association of 

American Railroads, Report No. RA-03-3-13 (AAR R-136), Chicago, Illinois (1972). 

54. Wisnowski, M. J. "Coupler Steel Study," Association of American Railroads, Report No. 

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55. Brown, S. J. and T. J. Brown, "Explosion Failure of a Pressurized Railroad Tank Car 

Initiated at a Nozzle: Forensic Investigation," Proceedings of the 1994 Pressure Vessels 

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56. National Transportation Safety Board, "Railroad Accident Report: Louisville and 

Nashville Railroad Company Freight Train Derailment and Puncture of Hazardous 

Materials Tank Cars," Bureau of Accident Investigation, Report No. NTSB-RAR-79-11, 

Washington, DC (1979). 
42 

57. Rice, J. "3 LPG Blasts Follow Derailment of Tankers, Evaluation of Area," Fire 

Engineering Journal, 132(3), 24-26, 1979. 

58. National Transportation Safety Board, "Railroad Accident Report: Derailment of a 

Burlington Northern Freight Train at Belt, Montana, November 26, 1976," Bureau of 

Accident Investigation, Report No. NTSB-RAR-77-7, Washington, DC (1977). 

59. National Transportation Safety Board, "Railroad Accident Report: Derailment of Tank 

Cars with Subsequent Fire and Explosion on Chicago, Rock Island, and Pacific Railroad 

Company, Near Des Moines, Iowa, September 1, 1975," Bureau of Surface Transportation 

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60. National Transportation Safety Board, "Railroad Accident Report: Hazardous Materials 

Accident at the Southern Pacific Transportation Company's Englewood Yard in Houston, 

Texas, September 21, 1974," Bureau of Surface Transportation Safety, Report No. 

NTSB-RAR-75-7, Washington, DC (1975). 

61. National Transportation Safety Board, "Railroad Accident Report: Hazardous Materials 

Accident in the Railroad Yard of the Norfolk and Western Railway at Decatur, Illinois, 

July 19, 1974," Bureau of Surface Transportation Safety, Report No. NTSB-RAR-75-4, 

Washington, DC (1975). 

62. Weston, R.A. "Report on Accident Review, Phase 01 Report," Association of American 

Railroads, Report No. RA-01-4-16 (R-139), Chicago, Illinois (1972). 

63. Phillips, E. A. "Overall Project Summary Report," Association of American Railroads, 

Report No. RA-00-1-22 (R-145), Chicago, Illinois (1972). 

64. Reedy, C.R., L. L. Olson, and R. A. Weston, "Sequence of Events Following Crescent City 

Derailment," Association of American Railroads, Report No. RA-01-1-1 (R-124), Chicago, 

Illinois (1970). 

65. National Transportation Safety Board, "Railroad Accident Report: Southern Railway 

Company Train 154 Derailment with Fire and Explosion Laurel, Mississippi, January 25, 

1969," Department of Transportation, Washington, DC (1969). 

66. National Transportation Safety Board, "Railroad Accident Report: Derailment and 

Subsequent Burning of Delaware and Hudson Railway Freight Train at Oneonta, New 

York, February 12, 1974," Report No. NTSB-RAR-74-4, Washington, DC (1974). 

 67. National Transportation Safety Board, "Railroad Accident Report: Pennsylvania Railroad 

Train PR-11A, Extra 2210 West and Train SW-6, Extra 2217 East Derailment and 

Collision, Dunreith, Indiana, January 1, 1968," Report No. SS-R-2, Washington, DC 

(1968). 
43 

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47 

Appendix. 

Expert Review 

Several individuals sent comments after their review of the draft final report titled, Literature 

Search and Evaluation Pertaining to Damage Assessment of Tank Cars Involved in Accidents,

prepared by SRI. The list below identifies the reviewers along with the company and/or 

organization they represent and their comments. Several of the comments were not received 

before the SRI report was finalized and therefore were not incorporated. Those comments will 

be taken into consideration when Phase II modeling and validation efforts are planned and 

during the drafting of the handbook. 

• J. Robert Sims, Exxon Research and Engineering, P.O. Box 101, Florham Park, 

NJ 07932; ASME Pressure Vessel and Piping Division, Post Construction 

Committee Chairman. 

 (1) "The document is an excellent summary of the problem and gives good 

 guidance for the future work which is needed." 

(2) "The discussion of dents and delayed fracture appears to be well reasoned. 

 Slow, stable crack growth due to time dependent behavior of materials is a 

 very real possibility and should be studied if additional work is undertaken 

 in this area." 

 (3) "The proposed work should be of interest for other applications such as 

 pipelines and other pressure vessels." 

• Dr. William J. Koves, UOP, Inc., 25 East Algonquin Road, Des Plaines, IL 

60017-5017; ASME Pressure Vessel and Piping Division, Chairman of the Flaw 

Analysis Subcommittee to the Post Construction Committee. 

 (1) "The procedures for evaluating dents is a simple, field expedient method 

and the radii of curvature appear somewhat arbitrary." 

 (2) "Limiting the radius of curvature is a good practical method, since the 

 influence of global damage, out of roundness, etc. on the stress at the local 

 critical regions is not evaluated." 
48 

(3) "Loads other than internal pressure do not seem to be addressed. Support 

 attachment stresses as well as those due to lifting the car should be 

 evaluated. High local compressive stresses could cause buckling in 

 low pressure applications." 

(4) "Scores, gouges, and wheel burns could be evaluated as local thin areas, 

using some of the information already published." 

(5) "The use of NDE should be considered in critical applications since cracks 

 in a cold work region may behave in a brittle manner." 

 (6) "The effect of damage on material properties must also be considered. 

 The effect of cold work or heat due to friction should be evaluated." 

 (7) "The ASME Subcommittee on Flaw Evaluation will be addressing some 

 similar issues and would like to cooperate with the AAR in any way." 

• Stephen Wong, Chief Engineer, Rail Car Division, Procor Limited, 2001 Speers 

Rd., Oakville, Ontario L6J 5E1. 

 (1) "We feel the report achieved its objective of gathering information relating 

 to damaged tank cars and pressure vessels, and their residual structural 

 integrity, thus providing a good assessment of the validity of the current 

 AAR guidelines." 

 (2) "The report revealed omissions, inconsistencies, and/or errors in the 

 guidelines that should be resolved. The findings appear to be sound." 

 (3) "The approach SRI recommends to validate the criteria and to 

 improve the reliability and usefulness of the guidelines appears 

 reasonable." 

 (4) "Any revisions to the guidelines should maintain a significant factor 

 of safety to allow its use under field conditions." 

 (5) "The existing guidelines are direct, simple, easy to understand, and 

 use. Any revisions should also be easy to understand and use." 

• Paul Kinnecom, Assistant Director of Tank Cars, Customer Operations, 

Operations and Maintenance Department, Association of American Railroads, 

Washington Headquarters, 50 F Street, N.W., Washington, DC 20001. 

(1) "Page 15 of the report makes reference to a TC-135A steel specification. 

 TC-135A was a draft steel specification that was proposed, but never 

 implemented for tank car construction. It is not representative of tank car 

 steels, and conclusions based upon a study of TC-135A should be made 

 with care." 
49 

(2) "On Page 13, reference is made to an "A-340" tank car, and it is implied 

that such a car may transport carbon dioxide, hydrogen, chloride, or 

hydrogen sulfide with associated tank stresses (due to commodity 

pressure) of up to 60 percent of the tank material yield stress. The 

referenced commodities are required by DOT to be transported in -500, 

-600, and -800 lb tanks, respectively. The logic of this paragraph needs to 

be revisited." 

• Diane Rocheleau, Superintendent, Materials Engineering, Engineering Branch, 

Transportation Safety Board of Canada, 1901 Research Road, Gloucester, Ontario 

K1A 1K8. 

 (1) "Page 23: rail burn versus rail dent. I see a burn as resulting in 

 metallurgical changes in the metal, for example the creation of an 

 untempered martensitic layer. A dent would not have such a 

 microstructural change. If a rail impacts the tank car, yes, a rail dent, 

 but if the tank car slides along the rail and the material is blued or if a 

 significant gouge appears and localized heating of the microstructure took 

 place, I would call this a rail burn." 

 (2) "Page 28, I fully agree that NDE methods should be considered, since 

 stresses can be measured using methods such as infrared thermography, 

 acoustic emission, etc." 

• Edgar Ladouceur, Chief of Response Operations, Transport Canada, Canada 

Building, 344 Slater Street, Ottawa, Ontario K1A ON5. 

 (1) "The report does a good job of providing background information 

 regarding the origin of the guidelines, as well as identifying the 

 shortcomings of the guidelines." 

 (2) "The recommendations put forth in the report regarding future 

 research appear reasonable and appropriate." 

 (3) "The only caution flag that I would raise is that it will be important 

 to ensure that the final product be something useful at the field level. 

 A small pocket guide would be helpful for responders in the field. 

 The margins of safety associated with using the "rule of thumb" 

 information contained in the pocket guide would also need to be well 

 identified." 
50 
51 

Acronyms 

AAR Association of American Railroads 

ASME American Society of Mechanical Engineers 

ASTM American Society for Testing and Materials 

CTOD crack-tip opening displacement

DTIC Defense Technical Information Center 

EPFM elastic-plastic fracture mechanics 

FEA finite element analysis 

FRA Federal Railroad Administration 

HAZ heat affected zone 

HRC Hardness Rockwell C Scale 

LEFM Linear-Elastic Fracture Mechanics 

LPG liquified petroleum gas 

NDE nondestructive evaluation 

NDT nil ductility temperature 

NTIS National Technical Information Service 

RPI/AAR Railway Progress Institute/Association of American Railroads 

SRI Stanford Research Institute 

SGFAS Slide Graph Fracture Analysis System 

TTCI Transportation Technology Center, Inc. 
52 
53 

Glossary 

Below are definitions of key terms used in this document [Reference 110]: 

Cold Work: Cold work is deformation of steel when it is bent at ambient temperatures 

without benefit of heat treatment or suffers an impact or static load (i.e., a 

tank sliding over a solid object with a rounded point). 

Crack: A crack is a narrow split or break in the tank metal which may penetrate 

through the tank metal. 

Dent: A dent is a deformation that changes the tank contour from that of original 

manufacture as a result of impact with a relatively blunt object (coupler or 

end of an adjacent car). 

Gouge: A gouge is removal of the tank or weld metal along the line of contact 

with another object. This causes a reduction in tank metal thickness. 

Heat Affected Zone: The heat-affected zone is an area in the undisturbed tank metal next to the 

actual weld material. This zone is less ductile than either the weld or the 

plate due to the effect of the heat on the welding process. 

Internal Pressure: Internal pressure is the force against the internal surfaces of the tank 

caused by the vapor pressure of the contents. 

Jacket: The jacket is the first thin steel outer shell that holds the insulation or 

thermal protection in place and protects the tank from the elements. The 

jacket is not designed to hold the leaking contents of the car. 

Radius of Radius of curvature is used to describe the sharpness of a curve (dent). 

Curvature: A small radius of curvature indicates a small circle and a sharp bend, 

whereas a larger radius of curvature indicates a larger circle and a more 

gentle bend.

Rail Burn: A rail burn is a long dent, usually parallel to the length of the tank that 

crosses a weld and causes cold work. It may be caused by the tank 

passing over a section of rail. 

Score: A score is a relocation of tank or weld metal so that the metal is pushed 

aside along the line of contact with another object. This causes a 

reduction in tank metal thickness. 

Tank: Tank in this document refers to the actual tank car tank. 

Transition Transition temperature is the point where the properties of steel change

Temperature: from ductile to brittle.

Wheel Burn: A wheel burn is similar to a gouge but is caused by prolonged wheel 

contact with the tank. 
54