The corrosion behaviour of oil well casing steel in H 2 S saturated NACE solution (5 wt-%NaClz0?5 wt-%CH 3 COOH) was investigated by means of electrochemical methods, Xray photoelectron spectroscopy and scanning electron microscopy. It was found that the investigated oil well casing steel can react with hydrogen sulphide in the H 2 S saturated NACE solution at 25uC. During the reaction, corrosion films of mackinawite (FeS) form on the steel surface and the hydrogen atoms diffuse into steel matrix. The further corrosion of iron with H 2 S can be retarded, and hydrogen permeation flux decreased, by the presence of the mackinawite film, which acts as a protective barrier provided it remains intact.

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