On August 27, 2016, about 8:26 a.m. eastern daylight time, a railroad tank car sustained a 42-inch long crack in its tank shell shortly after being loaded with 178,400 pounds of liquefied compressed chlorine at the Axiall Corporation Natrium plant in New Martinsville, West Virginia. Over the next 2.5 hours, the entire 178,400-pound load of chlorine was released and formed a large vapor cloud that migrated south along the Ohio River valley. The railroad tank car, AXLX1702, built in June 1979 by ACF Industries, Incorporated, was a 17,388-gallon US Department of Transportation specification-105J500W tank car, also known as a class DOT-105 tank car, with a stenciled load limit of 178,400 pounds and a maximum gross rail load of 263,000 pounds.
The tank car was equipped with an ACF Industries, Incorporated ACF-200 stub sill underframe design, which the Federal Railroad Administration has previously noted in a 2006 safety advisory as being prone to defects such as tank head cracks, pad-to-tank cracks, sill web cracks, and tank shell buckling that in some instances has led to release of hazardous materials.
Rescar Companies received the tank car in January 2016 to conduct a 5-year interior inspection required on chlorine tank cars in accordance with Axiall Corporation maintenance instructions. Inspectors revealed many corrosion pits across the bottom of the tank shell. AllTranstek (Axiall Corporation’s maintenance administration contractor) approved repairs that were made at that time. The tank shell crack and chlorine release occurred following its first postrepair loading.
We determined that the probable cause of the chlorine release was an undetected preexisting crack near the inboard end of the stub sill cradle pad, that propagated to failure with the changing tank shell stresses during the thermal equalization of the car after loading with low temperature chlorine. Contributing to the failure was Axiall Corporation’s insufficiently frequent stub sill inspection interval that did not detect the crack, the low fracture resistance of the nonnormalized steel used in the tank car construction, and the presence of residual stresses associated with Rescar Companies’ tank wall corrosion repairs and uncontrolled local postweld heat treatment.
We made recommendations to the Pipeline and Hazardous Materials Safety Administration, the Association of American Railroads, and American Railcar Industries, Inc.
