Authors: U.S. National Transportation Safety Board

Date of Publication:  December 1992

Sponsoring Agency:  U.S. National Transportation Safety Board

Performing Organization:  U.S. National Transportation Safety Board

Report No: NTSB/SIR-92/05

Abstract:

On January 18, 1992, a U.S. Department of Transportation (DOT) specification tank car containing 30,700 gallons of propane, a flammable gas, fractured and separated along a circumferential weld when the train it was in began to move at Dragon, Mississippi. The separation resulted in the sudden and complete release of the entire load of propane
from the dual diameter tank car. There was metallurgical evidence of a preexisting crack at the origin of the fracture. Postaccident testing and inspection of, 108 other dual diameter tank cars of the same design revealed that 40 tank cars had cracks in the same location; 25 of the 40 with cracks had been tested and inspected, since 1988, under DOT periodic testing and inspection regulations, including 13 that were retested and reinspected in 1991 and 1992.

On March 25, 1992; a DOT specification tank car containing about 13,000 gallons of sulfuric acid cracked circumferentially when the train it was in began to move. This crack resulted in the release of the entire cargo. There was also metallurgical evidence of a preexisting crack in the area of the failure. At the time of the accident, the tank car was transporting its first cargo since it had been retested and reinspected in February 1992.

In addition to these accidents, cracking and structural failure at stub sill-to-tank car attachments on various classes of DOT specification tank cars have been noted since the mid-1980s.
 

Because of the nature of these structural failures, the National Transportation Safety Board conducted a special investigation into the adequacy of the DOT regulations pertaining to the periodic testing and inspection of DOT specification tank cars. As a part of its special investigation, the Safety Board also examined current industry practices and standards
for testing and inspecting tank cars and the application of various methods of nondestructive testing for DOT specification tank cars.

The safety issue discussed in this report is:

• The adequacy of U.S. Department of Transportation regulations for the inspection and testing of DOT specification tank cars.

No. of Pages:  44