Influence of Cl^- Concentration on Corrosion Rates of Duples Stainless Steels and Ni-based Alloys

Aimed high temperature high pressure at HTHP corrosive environments with simultaneous existence of H2S/CO2/Cl-, 22Cr/25Cr duplex stainless steels, i.e., (DSS) and 028 Fe-Ni-based alloy/G3 Ni-based alloy were selected to conduct comparative tests. Under the same conditions other than Cl- concentration, i.e., (H2S/CO2 partial pressure, temperature and liguid flow were the same, only Cl- concentration was different, the influence of Cl- concentration on corrosion rates of general corrosion and pitting corrosion of corrosion resistant alloys was analyzed. The experimenal results show that under the corrosive conditions of temperature 160 ℃, CO2 partial pressure 4.13 MPa, H2S partial pressure 2.66 MPa and flow rate 3 m/s, with the increase of Cl- concentration(25 g/L, 100 g/L, 120 g/L, 250 g/L), the general corrosion rates and localized corrosion rates of two kinds of duplex stainless steels(UNS S32205 and UNS S32750) increased. The general corrosion rates of 028 and G3 Ni-based alloys had a little change and localized corrosion did not happen. The main compostion of passivation film on the surface of DSS specimen(UNS S32205/UNS S32750) was Cr2O3 and/or Cr(OH)3. The main compostion of passivation film on the surface of Ni-based alloy specimen(028/G3) was NiO/Cr2O3 and/or Cr(OH)3.