Stress corrosion crack ing (SCC) was seriously imperilling the safety of a Japanese Industrial Standard JIS-SPV36 steel ammonia sphere of volume 5200 m3 and diameter 21.5m. Chemical composition of the corrosion products has been analyzed

a survey of the stress corrosion cracks propagation characteristics at welded joints has been made

and statistical analysis of the results based on the record of internal inspection of the sphere in open status and of experimantal studies have been worked out. Then the reliability of the sphere wasevaluated. An approach Spray metal coating to prevent the ammonia sphere from SCC has been proposed. Spray coating on the internal surface of the sphere during the period of annual regularmaintenance in December 1986 has proven to be effective on practical trial.