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The pitting behavior of seven stainless steel grades with austenitic and duplex microstructures in varying acids (HCl, H 2 SO 4 , HCOOH), chloride concentrations (500–5000 mg/L), and pHs (2.5, 4.0) was investigated at 90°C. Low- and intermediate-PREN grades were prone to pitting under the test conditions. The electrolyte ranking by pitting susceptibility was HCl > H 2 SO 4 > HCOOH, while the progress of pitting attack in materials followed the reverse order: HCOOH > H 2 SO 4 > HCl. The presence of lacy cover prevents repassivation favoring a concentric "Russian doll" structure and high loss rates. The mechanisms of pitting propagation are presented in this paper. • High SS PRENs (>43) do not undergo pitting under the studied environments • In lower pH (2.5) there are higher material losses and reduced pitting potential • While chlorides lower pitting potential, formates cause greater material losses • Lacy cover hinders repassivation favoring a “Russian doll” pit structure • Preferential phase attack of duplex grades is absent with low PRENs (25, 26)
Trentin et al. (Wed,) studied this question.