Cryogenic Tank Cars and Liquefied Natural Gas Hazards

The DOT-113 tank car family transports cryogenic commodities. All of the tank cars in this family have inner and outer tanks, the former wrapped with insulation to maintain the low temperature of its cryogenic cargo. The inner tank is constructed of stainless steel to withstand cryogenic temperatures, while the outer tank is constructed of carbon steel. The insulation around the inner tank consists of alternating layers of aluminum foil and a non-conducting spacer material, such as fiberglass or ceramic fiber paper. The annular space between the wrapped inner tank and outer tank is maintained as a vacuum, which is a key part of the insulation system. A PRD system is designed and set to activate when desired temperatures are not maintained. These systems must function under high-temperature conditions in the event of an incident and must be made from materials suitable for the temperature of the cargo in liquid and vapor phases.In authorizing the LNG’s shipment by tank car, PHMSA established new requirements for a DOT-113C120W9 tank car design that specified an outer tank made with a stronger and thicker carbon steel. The new design did not include changes to the requirements for insulation materials or the PRD system. The upgrades to the DOT-113’s outer tank were intended to make it more resistant to impact damage. The results of impact tests conducted by PHMSA and FRA suggest that the DOT-113C120W9’s outer tank is more resistant to puncture than the outer tank of a standard DOT113 tank car. However, questions remain about the resistance of the outer tank’s steel to brittle fracture from a potential exposure to cryogenic LNG. A matter that warrants consideration is that the temperature of cryogenic LNG is lower than the temperature at which the outer tank steel can become embrittled. Uncertainties also remain about the PRD’s capacity to release sufficient product when the tank car is engulfed in a high-temperature LNG fire and whether the materials used for insulating the inner tank can withstand the intense heat flux of the fire. © 2022 National Research Council. All rights reserved.