Top of Line Corrosion with High CO2 and Traces of H2S

Top of line corrosion has been studied in a flow loop where moist gas is circulated and water is condensed on 1.8 m long carbon steel pipes with external cooling. The condensed water is collected at the end of each test section. This setup enables meaurement of top of line corrosion on large surfaces with low water condensation rates. An experiment with high CO₂ partial pressure and traces of H₂S in the gas showed that most of the iron dissolved by corrosion precipitated as a porous iron sulphide film which did not offer good corrosion protection. Thin, protective iron carbonate films were formed close to the steel surface. This showed that the presence of even small amounts of H₂S can change the top of line corrosion mechanism considerably compared to pure sweet conditions.