Anhydrous ammonia tank failure spurs safety advisory

Washington — Two federal safety agencies are urging owners of certain “nurse” tanks used to transport anhydrous ammonia to check the tanks for potential catastrophic failure.

The Federal Motor Carrier Safety Administration and the Pipeline and Hazardous Materials Safety Administration issued a joint safety advisory in February. The advisory warns that nurse tanks manufactured by American Welding and Tank between 2007 and 2011 “that are exempted from periodic inspection and testing requirements” may be prone to failure. 

Anhydrous ammonia is a hazardous chemical often used for farming applications.

The advisory comes after an August incident at a farm co-op in which an AWT nurse tank experienced a catastrophic failure, resulting in the release of anhydrous ammonia. “The failure caused the tank shell to ‘rocket’ over 300 feet from its original location,” the advisory states. Although no injuries were reported, “this event is an indicator of potential continuing problems with AWT nurse tanks that have now been in service for over a decade.”

Further corrosion and porosity testing of 142 AWT nurse tanks manufactured between 2007 and 2012 and owned by the co-op parent company found that 100 of the tanks failed. All the tanks manufactured in 2012 passed, however.

The advisory notes that nurse tanks that carry American Society of Mechanical Engineers identification plates and meet other requirements are exempt from periodic inspection and testing under hazardous materials regulations. Inspection and testing requirements apply when plates are missing or illegible.

FMCSA and PHMSA recommend owners of affected tanks who are unable to conduct voluntary pressure testing attempt either radiographic or ultrasonic testing. The agencies suggest testing at least once every five years.