Effect of Acetic Acid and Trace Amounts of H₂S on the Corrosion Behavior of Martensitic Stainless Steel in Natural Gas CO₂ Corrosion Environment

Abstract

Corrosion behavior of 13%Cr SS and modified 13Cr martensitic stainless steels were investigated in CO₂ solution with trace amounts of H₂S in presence of acetic acid. Conventional 13%Cr SS observed pitting corrosion in 2.0 MPa CO₂ with 20,000 ppm chloride solution at 40°C. However, pitting corrosion of 13%Cr SS was inhibited by presence of trace amounts of H₂S. The pitting corrosion was initiated on modified 13Cr SS in CO₂ solution with 0.002 MPa H₂S and number of pits was increasing with increasing acetic acid concentration. At 180°C, maximum corrosion rate of 13%Cr SS was observed in presence of 0.0005 MPa H₂S and decreased corrosion rate in higher H₂S partial pressure with 7.8 MPa CO₂ solution. Corrosion rate of modified 13Cr SS was independent of acetic acid concentration without H₂S partial pressure however, corrosion rate was increased with increasing acetic acid concentration with trace amount of H₂S. Effect of acetic acid was concluded that, decreasing pH, increasing solubility of Fe²⁺ and weaken passivation film and significantly affected corrosion behavior by coexistence of H₂S and acetic acid in CO₂ solution.