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DOT warns of potential ‘nurse tank’ failures

Feb. 26, 2024
New FMCSA/PHMSA safety advisory spotlights possible ‘catastrophic failure’ of certain AWT hazmat tanks, outlines recommendation for periodic testing

The Federal Motor Carrier Safety Administration (FMCSA) and the Pipeline and Hazardous Materials Safety Administration (PHMSA) recently issued a safety notice on the possibility of “catastrophic failure” of “nurse tanks,” or heavy duty trailers used to transport various types of hazardous materials and liquids.

The advisory pertains to nurse tanks manufactured by American Welding and Tank (AWT) at its Freemont, Ohio plant between Jan. 1, 2007, and Dec. 31, 2011, the agencies reported. AWT nurse tanks made from 2009 to 2010 were the subject of a prior FMCSA investigation in response to improper manufacturing procedures.

On Aug. 23, 2023, a 2009 AWT nurse tank containing anhydrous ammonia experienced a catastrophic failure in a farm co-op lot, resulting in the release of all product, FMCSA said. The failure caused the tank shell to “rocket” over 300 ft. from its original location. While no injuries were reported, the event is an indicator of potential continuing problems with AWT nurse tanks that now have been in service for over a decade.

As a result of the incident, the nurse tank’s owner contracted with a third-party testing company to examine their AWT tanks manufactured between 2008 and 2012. Radiographic testing showed seven of  the eight nurse tanks tested had extreme stress corrosion cracking, porosity, and inclusions/voids in the welds where the heads and shells of the tanks were joined. Only the 2012 tank passed. The nurse tank owner submitted these results to engineering experts who were involved in previous research funded by FMCSA into similar issues with this series of AWT tanks.

Based on the test results and the review by the experts, the owner voluntarily placed the nurse tanks out-of-service. The parent company of the farm co-op subsequently conducted similar radiographic testing on 142 AWT nurse tanks manufactured between 2007 and 2012, and 100 failed the test. All 2012 tanks passed.

Agency recommendation

Current Hazardous Materials Regulations (49 CFR Parts 171-180) don’t necessitate periodic inspection and testing of nurse tanks with attached American Society of Mechanical Engineers (ASME) identification plates that meet all requirements in 49 CFR §173.315(m)(1). The requirements only apply when the ASME plate is missing or illegible.

However, FMCSA and PHMSA “strongly recommend” that owners of AWT nurse tanks manufactured between Jan. 1, 2007, and Dec. 31, 2011, periodically conduct visual inspections, thickness testing, and pressure testing. The agencies further recommend radiographic or ultrasonic testing when pressure testing isn’t possible.

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