Preferred Weld Corrosion of Stainless Steel in Caustic Solution with Impurities-Case Study

Abstract The “18-8” type stainless steels perform well with lower corrosion rates in caustic at all concentrations up to approximately 65°C. However, literature shows that it is likely that the corrosion performance of such stainless steel, especially the welds are influenced by the contaminants in the caustic soda. The low-carbon grades perform marginally better than the high-carbon grades, including welds, because of their resistance to sensitization. A case study showed that in the presence of sulfuric acid impurities in caustic solution greatly influenced the corrosion performance of 308H stainless steel welds due to preferential delta-ferrite attack. Sample exposed to caustic (NaOH) with sulfuric acid impurities corroded preferentially by attacking the delta-ferrite phase in the interdendritic spaces. Such delta-ferrite phase attack was not seen on the specimens exposed to caustic solution without sulfuric acid presence.