|Title||Tank car fire failure assessment using combined models|
|Licence||Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences.|
|Author||McKinley, J; Xue, J; Williams, B W; Xu, S|
|Source|| 2021, 49 pages Open Access|
|Alt Series||Transport Canada Publication (TP) TP 15493E|
|Subjects||Science and Technology; Transport; Health and Safety; models; temperature; software; finite element method; pressure; stress analyses; deformation; creep; Rail transport; Materials technology; Fire;
Railway accidents; Engineering; Public safety; Railway safety|
|Illustrations||time series; plots; schematic diagrams; flow diagrams; 3-D models; 3-D diagrams; tables|
Advanced Materials Porcessing|
|Released||2021 09 01; 2022 05 13|
An accident involving a rail tank car transporting flammable liquids such as crude oil, natural-gas condensates, or ethanol creates the potential for a pool fire. There have been a
number of rail incidences in which flammable liquids have been involved. This presents a safety risk to the public and the environment. TDG would like to better understand the fire performance of rail tank cars to evaluate the applicable safety
standards and regulations and to ensure that they provide a high level of safety.
In order to investigate these concerns, TDG initiated research projects to investigate tank car failure at high temperature. From FY 2016/17 to 2018/19
CanmetMATERIALS (CMAT) conducted tensile and creep-rupture tests of TC 128B and ASTM 516 Grade 70, two of the most common steels used in manufacturing tank cars. During FY 2018/19 a constitutive material model that includes temperature-driven (25 °C
to 800 °C) material softening and creep was implemented in finite element (FE) analysis software to enable detailed analysis of tank cars and tank car failures at high temperatures. CMAT then developed an FE model using specific tank car geometry to
predict tank car failure under various pool fire conditions in 2018/19 and 2019/20.
CMAT had three main objectives for the 2020/21 fiscal year. These were to 1) Develop a simpler and faster engineering model for calculating material failure and
validate it against the existing FE model. 2) Run a series of pool fire scenarios using temperature and pressure data from CanmetENERGY using both Models. 3) Complete a comparison between AFFTAC, an established program for predicting tank car failure
in pool fires, and CMAT's models.
CMAT developed an effective and time efficient engineering method for calculating the time to failure of a tank car in a pool fire scenario and validated it against their FE model. This model can be run in excel
or other computational software. CMAT simulated 34 realistic pool fire scenarios in both their FE and engineering models. All cases survived at least 100 minutes. Only two cases resulted in failure within the 716 minutes run time. One failed due to a
blocked PRV and one failed because it lacked thermal protection. These results demonstrate the importance of these key rail tank car safety systems.
Preliminary comparisons between CMAT's models and AFFTAC demonstrated some differences. Both
AFFTAC and CMAT's models describe the high temperature behaviour of tank car materials. They both can predict two failure modes; yield (plasticity) and creep. Both models are temperature dependent. As the temperature increases the yield stress
decreases. At higher temperatures creep deformation occurs more rapidly at a given stress level than at lower temperatures. The realistic fire scenarios presented above did not provide sufficient data for comparing CMAT's models with AFFTAC. CMAT and
AFFTAC produced different results in synthetic scenarios that were run for the purpose of comparison. Further investigation is recommended.
|Summary||(Plain Language Summary, not published)|
This report summarizes the results of the evaluation of current TC128B steel tank car welds. The sample coupons were received from a DOT-117J tank car.
The experimental work in this report included the determination, from a longitudinal weld, of (i) chemical composition, microstructure and micro-hardness (ii) tensile strength and failure locations in the temperature range of 23°C to -60°C, and (iii)
Charpy transition curves. Typical fracture features of low Charpy strength weld metal samples and volume fractions of acicular ferrite (AF) were characterized and discussed. The results of the longitudinal weld were compared to those from a
circumferential weld characterized previously from the same tank car, including updated Charpy testing at -34°C, and the main conclusions are provided.