Role of alloyed copper on corrosion resistance of austenitic stainless steel in H2S–Cl− environment

• The alloyed Cu reduces SCC and pitting corrosion susceptibility in the H2S–Cl− environment.
• The surface film indicates double layer consists of the copper sulfide and the chromium oxide.
• The stability of copper sulfide was estimated using thermodynamic calculation.
• A possible role of alloyed Cu is proposed.

Corrosion test, surface analysis and thermodynamic calculation were carried out in the H2S–Cl− environments to clarify the role of alloyed Cu on the corrosion resistance of austenitic alloys. The alloyed Cu improved pitting corrosion resistance in the H2S–Cl− environment. The surface film of Cu-containing alloy indicated double layer consists of copper sulfide and chromium oxide, and the copper sulfide was able to exist stably compared to iron sulfide and nickel sulfide. It is concluded that the copper sulfide would enhance the formation of chromium oxide film which improve the pitting corrosion resistance in the H2S–Cl− environment.