High Temperature Corrosion By Catalytically Formed Hydrogen Sulfide

Organic sulfur compounds are known to be a major cause of high-temperature corrosion in refining processes. Chromium steels are widely used in such environments. The required chromium content for adequate resistance depends upon the chemical form of sulfur encountered. Surfaces of corroding metals can act as catalysts in forming hydrogen sulfide, either from hydrogen and sulfur or by decomposition of organic sulfur compounds. Catalytically formed H2S is more corrosive than the same concentration of other H2S and can be corn-batted by adding chromium to the steel. Because corrosion is proportional to the concentration of H2S, a surface concentration of H2S is postulated as proportional to the catalytic activity of the surface. Laboratory tests on sulfur vapor mixed with hydrogen and on amyl mercaptan mixed with nitrogen or hydrogen indicate that corrosion is proportional to the yield of catalytically formed H2S. Chromium additions to the steel, oxide scales on the metal surfaces, additions of chlorides to the stream, and increased velocity decreased both H2S yields and corrosion, whereas increased temperatures and addition of oxidizing agents caused increases. Further work should be done to develop practical methods to reduce the catalytic activity of corroding steel surfaces, thereby improving corrosion resistance to certain high-temperature streams that contain sulfur compounds. 3.4.2, 4.4.9, 3.5.9, 3.7.2, 8.4.3