Hydrogen Attack of 1020 Steel: Influence of Hydrogen Sulfide^*

The influence of gaseous hydrogen sulfide in a hydrogen environment on the mechanical degradation of plain carbon steel exposed to elevated temperatures was examined. Hydrogen attack of SAE 1020 carbon steel was investigated at room temperature after exposure to 525 C at a pressure of 3.5 MN/m² (500 psi) for times up to 240 hours. Exposure to pure hydrogen resulted in a reduction in the yield strength of 57% and the ultimate strength of 34% with a very marginal reduction in elongation. Methane fissures and bubbles were observed. The interiors of the fissures were found to contain many manganese sulfide particles and some indication of aluminum and silicon. In the hydrogen/hydrogen sulfide blend, hydrogen attack was not observed—no fissure or bubble formation occurred, and the room temperature tensile properties were unchanged. The influence of a FeS surface layer on the susceptibility of carbon steel to hydrogen attack and its applicability to coal gasification systems are discussed.