United States Department of Transportation
i
Testing and Recommended Practices to Improve Nurse Tank Safety, Phase I
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2013-10-01
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[PDF-6.04 MB]
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Abstract:This research project studied causes and possible remediation inspection strategies to prevent failures for anhydrous ammonia (NH3) nurse tanks. Nurse tanks are steel tanks used to transport NH3 locally over public roadways and farm fields. Many of the reportedly 200,000 nurse tanks in use in the United States are 3 to 5 decades old. Several tank failures have occurred in recent years. Nurse tank failures can injure workers and bystanders by way of chemical burns, frostbite, suffocation, and physical injuries caused by the catastrophic force of rupture. This research study addressed this problem by: surveying the technical literature on nurse tank properties and case studies of tank failures; examination of 20 used nurse tanks by metallography, glow discharge spectroscopy, neutron diffraction analysis of residual stresses, ultrasound, and fluorescent dye penetrant examination for cracks. It exposed 56 specimens of the commonly used tank steel, stressed in tension, while either immersed in liquid NH3 or exposed to pure NH3 vapor, for 7 months to study the initiation and growth of stress corrosion cracks. This research further confirms that stress corrosion cracking is the greatest threat to nurse tank integrity. Recommendations for best inspection practices are presented on how to reduce the risks associated with nurse tank failures.
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