Corrosion of low carbon steel weldments at 600–800 °C in N2/H2S/H2O gases

A low carbon steel was arc-welded, and corroded at 600, 700 and 800 °C for up to 20 h in 1 atm of either N2/H2S-mixed gases or N2/H2S/H2O-mixed gases to characterize the effects of H2S and H2O gases on the high-temperature corrosion of welded joints. Corrosion proceeded fast and almost linearly. It increased with the increases in the corrosion temperature and with the addition of H2S and H2O. H2S formed FeS, while H2O formed iron oxides such as Fe3O4. Hydrogen and sulfur that were released from H2S and H2O made the scales fragile and nonadherent. Weld metals corroded faster than base metals because the former had coarser grains than the latter.