Pitting corrosion of austenitic and duplex stainless steels in dilute acids at elevated temperature: Effect of electrolyte chemistry and material microstructure
Andressa Trentin, Ahmad Mardoukhi, Aloshious Lambai, Pekka Pohjanne, Elina Huttunen‐Saarivirta
Abstract
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)