Although in the literature it is a common belief that electropolishing mitigates PWSCC, it is shown that electropolished Alloy 600 samples tested in hydrogenated steam undergo internal oxidation while mechanically polished ones oxidize externally. This has implications for SCC initiation, which has been tested with different surface preparations (electropolishing and mechanical polishing) using RUB and C-ring samples. The results showed a systematic trend that mechanically polished surfaces are more resistant to PWSCC than electropolished. The mechanism involved in this increased resistance is thought to be related to short circuit diffusion of Cr to the surface which promotes external rather than internal oxidation. The role of compressive stress induced by mechanical polishing is a much less likely explanation of the observed effects. Mechanical polishing does not suppress PWSCC completely because if the external oxide layer breaks, the exposed material continues oxidizing internally. These results suggest that the effect of electropolishing needs re-evaluation.

Subject
External surfaces, Metal surfaces, Polishing, Metal oxides, Partial pressures, Surface preparation, Oxide surfaces, Crack length, Cracking, Alloys, Cracks, Stress corrosion cracking, Oxidation
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2007
Association for Materials Protection and Performance (AMPP)
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