Failure Analysis of AISI-304 Stainless Steel Styrene Storage Tank

Abstract

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler wire. The failed base plate was replaced with the new AISI 304 base plate of same thickness. After a short period of time, seepage was observed along the weld bead. Upon nondestructive testing cracks were found in the heat-affected zone and in the base plate. The failure investigation was carried out on welded and base plate samples using spectroscopy, optical and scanning electron microscopy, fractography, SEM-EDS analysis, microhardness measurements, tensile and impact testing. The results revealed transgranular cracks in the HAZ and base plate, and the failure was attributed due to stress corrosion cracking. Cracks initiated as a result of combined action of stresses developed during welding and the presence of a chloride containing environment due to seawater. It was further observed that improper welding parameters were employed for weld repair which resulted in sensitization of the structure and postweld heat treatment to remove weld sensitization and minimize the residual stresses was not done.

Measurement and analysis on the sensitization behavior of SS-304 welds using Nb-based stabilization through flux-coated gas tungsten arc welding

“…The investigations revealed that these cracks appeared because of IGC. 6 The austenitic SS was used as a tube material in steam generators for the purpose of increasing its lifetime instead of conventional materials. But after 6 months, corrosion takes place also in welded joints of SS, which results in the leakage of tubes.…”

“…This is because carbide precipitation requires some time, as adjacent to the fusion line material senses maximum temperature and cooling rate. 6,7 Various researchers have used many approaches to stop the IGC after welding.…”