Failure Analysis of the High Nitrogen Austenitic Stainless-Steel Boiler Tank Weldments

The paper investigates the reason for the cracking and leaking of stainless-steel (SS) tanks used to store processed hot water in rice boiling and husking plants. A detailed analysis of tank specimen samples using radiography, optical metallography, scanning electron microscopy, EDAX reveals that stress corrosion cracking (SCC) is the prime reason for the failure. The presence of favorable microstructure, environment and stress promoted the nucleation and propagation of SCC in the tank weldment. The evolution of the microstructure in the selected stainless grade was studied and discussed using Scheffler-Delong diagram. The formation of martensite in low nickel, high nitrogen austenitic stainless steel was observed to significantly influence the mechanical properties and promote SCC. The decreased pitting corrosion resistance of the material compared to SS 316 alloy was an important factor in the initiation of pits which acted as nucleation sites for SCC.