THE CORROSION OF THREE COMMERCIAL STEELS IN REDUCING ATMOSPHERES CONTAINING HCL AND H2S AT 600°C

摘要

The corrosion behavior of three commercial steels with different Cr contents (NF616, 12CrMoV and SS304) at 600 °C in a gas mixture of (vol. %) 2 H2, 0.5 HCl, 0.005 H2S, balance CO2, has been studied to examine the effect of a minor addition of H2S to a reducing HCl-containing atmosphere on the corrosion of the same materials, studied previously under similar test conditions in the absence of H2S. The presence of sulfur accelerated the corrosion of the two steels with lower chromium contents, but not of the stainless steel SS304. Both NF616 and 12CrMoV formed duplex external scales plus a zone of internal attack rich in oxygen and chromium with little sulfur (up to 2 at. %). Little or no chlorine could be detected in the internal attack zone and in the scale. The stainless steel SS304 corroded much more slowly, forming a protective chromia scale as in the H2S-free atmosphere. The mechanism of "active oxidation", based on the formation, diffusion and re-oxidation of volatile chlorides of both Fe and Cr, has been adopted to interpret the results obtained.