Tank car research

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Rail tank cars exposed to fire: Literature review of crude oil, condensate and ethanol behaviour

NRC technical report A1-005795-01.1

In an effort to better understand how tank cars carrying crude oil behave in fires, Transport Canada asked the National Research Council of Canada (NRC) to review related open literature. The NRC’s literature review focused on the following topics:

  • pool fires
  • large obstructions and large heat absorbing objects in fires
  • behaviour of crude oil, condensate and ethanol fires
  • fire modeling
  • behaviour and modeling of complex mixtures such as crude oil

The report describes general characteristics of pool fires including factors that influence the heat transfer to engulfed objects such as fuel type and wind. The report goes on to describe the characteristics of pool fires from a number of sources and some pool fire modeling work. The report found that it is very difficult to predict how complex mixtures containing many components (such as crude oil) change with temperature and pressure. To overcome this difficulty, a number of numerical methods based on experimental investigations have been developed.

The NRC also developed a research plan to address gaps in the available literature. This plan describes a series of testing from small flammable liquid pool fire tests to progressively larger tests of containers mimicking tank cars in flammable liquid pool fires. Investigation into how pressure relief devices meant to release gas behave when expelling viscous liquids are suggested. Fire modeling and crude oil behaviour modeling are also discussed as areas requiring further research.

Full report: Rail tank cars exposed to fire: Literature review of crude oil, condensate and ethanol behaviour

Please direct technical questions regarding the report to the NRC. If you would like other information regarding the full report, please contact the Safety Research and Analysis Branch, Transportation of Dangerous Goods Directorate, Transport Canada at TDG-RD-TMD@tc.gc.ca.

Risk evaluation of tank car top fittings breach in derailments

Transport Canada asked Sharma & Associates, Inc. to investigate how well various tank car top fittings protection strategies performed in derailments. Sharma & Associates, Inc. used a combination of models they originally developed for the United States Department of Transportation Federal Railroad Administration to analyse the performance of individual tank cars and the forces involved in whole train derailments.

Top fittings are devices mounted on the top of a tank car such as:

  • fill gauges
  • discharge pipes
  • thermometer wells
  • safety vents
  • other connections or valves

These fittings are strong but are typically not designed to survive a derailment. They are often covered by some form of protection. The strength of the protection depends on the risk posed by the material being carried in the tank car. Tank cars carrying products such as corn syrup or clay slurry will have fairly thin covers that only protect against vandalism or the weather. Tank cars carrying higher risk materials, such as some flammable liquids, use stronger covers to help protect against damage to top fittings in derailments. Tank cars carrying very high risk products, such as toxic gases, use the strongest covers which are designed to help prevent damage to top fittings in derailments.

Some of top fittings protection strategies investigated in this report include:

  • stronger covers
  • reducing train speeds
  • different train braking systems
  • shorter trains

For each of these cases, tank car performance models and derailment simulations were combined to estimate how many top fittings would be damaged. The results of these simulations were compared against real accident data. Reasonably good correlation was found between the simulation results and the accident data. Overall, the simulations found that slower trains, stronger covers, and faster braking systems reduced the number of damaged top fittings.

If you would like more information regarding the full report, please contact the Safety Research and Analysis Branch, Transportation of Dangerous Goods Directorate, Transport Canada at TDG-RD-TMD@tc.gc.ca.

Natural Resources Canada tank car steels literature reviews

At Transport Canada’s request, and with Transport Canada’s support, Natural Resources Canada’s (NRCan) Canmet MATERIALS group conducted reviews of existing literature on the properties of two common tank car steels. These tank car steels were TC128B and ASTM A516 Grade 70. TC128B is commonly used in the shells of tank cars that carry dangerous goods. ASTM A516 Grade 70 is used in the shells of general service tank cars though it is sometimes also found in the shells of tank cars that carry dangerous goods. The reviews were titled:

  • A Review of the Strength and Fracture Toughness Properties of Two Tank Car Steels: TC128B and A516-70
  • Mechanical Properties of Tank Car Steel at Flame Temperature and Modeling of Failure – A Review
  • Internal Corrosion of Rail Tank Cars

The literature reviews focused on the following steel properties, respectively:

  • The resistance of steel to cracking at various temperatures (fracture toughness)
  • How the strength of steel changes at elevated temperatures (including creep properties)
  • A primer on corrosion focusing on corrosion arising from transporting crude oil

The fracture toughness report summarizes the results of several studies investigating fracture toughness in both TC128B and ASTM A516-70 steels using a variety of standards and test methods. The report also describes some newer techniques to test the fracture toughness of steels. A number of the reports reviewed were older. Some of the data presented in these reports may not represent the performance of current steels produced using more modern steel manufacturing practices and with the composition of the steels that are currently found in the standards.

The review of the performance of tank car steels at elevated temperatures summarized the few high temperature studies conducted on TC128B steel. No such studies were found for ASTM A516 Grade 70 steel. The report also reviews some common software models of tank car fire performance at elevated temperatures.

The corrosion report describes the basics of corrosion with a focus on likely mechanisms found in tank cars. Some circumstantial evidence of corrosion in some tank cars carrying crude oil was found but a more thorough investigation is required to determine its prevalence and causes.

If you would like more information regarding the full reports, please contact the Safety Research and Analysis Branch, Transportation of Dangerous Goods Directorate, Transport Canada at TDG-RD-TMD@tc.gc.ca.

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