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.

Subject
Scanning electron microscopy, Weld attack, Materials, Materials performance, Sulfuric acid, Acid attack, Corrosion testing, Impurities, Sodium hydroxide, Corrosion protection, Corrosion resistance, Stainless steel, Samples
Keywords:
AWS 5.9 ER308H, corrosion, Delta ferrite, preferential attack, caustic solution, sulfuric acid, and stainless steel
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2025
Association for Materials Protection and Performance (AMPP)
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