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 measurement 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
sulfide 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.
Keywords: CO2 corrosion, H2S corrosion, top of line corrosion, condensation, gas pipeline