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Anhydrous ammonia is one of the most widely used and most dangerous agricultural chemicals. It is transported to farm fields in nurse tanks: steel pressure vessels towed behind tractors or trucks. Nurse tank failures have caused fatalities, injuries, and property damage. This document describes several problems commonly associated with nurse tanks that can lead to failure, including: stress corrosion cracking, residual stress in unannealed welds, improper welding methods, and metal fatigue. Special emphasis is placed on neutron diffraction measurements of residual stresses in and near welds; a side-angle ultrasound survey of a large population of used nurse tanks to determine the number, orientation, and size of cracks; analysis of welding flaws leading to pinhole failures; stress corrosion crack growth rate experiments; and tank lifetime estimation based on growth of existing stress corrosion cracks in nurse tanks.

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Alan Russell is Professor of Materials Science and Engineering at Iowa State University. His areas of expertise include mechanical properties of transition group metals, alloys, and intermetallic compounds; metal-matrix composites; stress corrosion cracking in steels; and processing and mechanical properties of metastable alloys.

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