Weld decay failure of a UNS S31603 stainless steel storage tank

A brine storage tank was reported to have visible and severe localized corrosion 1 year after installation. The material used for this tank was UNS S31603 stainless steel. The corrosion was mainly noticeable at various points/areas along the welded joint, and there was also some pitting on the base metal at the bottom of the tank. Corrosion was also found at the welded joint at the hatch wall. Indications of severe corrosion that resulted in deep metal loss were found at some points along the welded joint. The results of an oxalic acid etch test in the heat-affected zone (HAZ) showed the interdendritic ditches, which are considered to be prone to intergranular corrosion/weld decay. The results of a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test and 3D multiscale images were in agreement with the results of an oxalic acid etch test that indicated the intergranular corrosion susceptibility of the HAZ. The base metal, in contrast, did not show any intergranular corrosion.