Effect of thiosulphate/H2S on crevice corrosion behaviour of P110 carbon steel in CO2-saturated solution

The effect of thiosulphate/H2S on crevice corrosion behaviour of P110 carbon steel in the CO2-saturated 3.5 wt% NaCl solution was investigated. The results showed that crevice corrosion of P110 steel could not occur in the CO2-saturated solution, likely due to the inhibition of both anodic and cathodic reactions inside crevice. Further, the structure of corrosion product film along the crevice wall is influenced by the concentration of thiosulphate. Increasing the concentration of thiosulphate to 10(-2) mol L-1 promotes the formation of fine flake-like mackinawite outside crevice. In addition, crevice corrosion of P110 steel in the CO2-saturated solution is promoted by increasing the concentration of thiosulphate. This is because the dense and fine mackinawite film on the steel surface has a better protectiveness and could enhance cathodic reaction rate outside crevice.