On the comparative degradation of selected Cr2O3-forming alloys by high-temperature carburization with a case study involving 310 stainless steel

摘要

A shroud plate of a heat exchanger made of 310 stainless steel plate about 5 mm in thickness has prematurely failed in a methanol production plant. The function of the heat exchanger is to reduce the temperature of steam reformed gaseous hydrocarbons from 850 degrees C to 325 degrees C. It is shown that the plate has been severely damaged as indicated by considerable metal wastage combined with massive precipitation of carbide phases, coke deposition at the inner surface as well as metal dusting associated with pitting. Based upon these observation failure of the plate is correlated with exposure to carbonaceous gases and the relatively low carburization resistance of the Cr2O3-forming 310 stainless steel. Experiment shows that other competitive Cr2O3-forming alloys particularly alloy 800H and alloy 556 grades are more suited for such applications. The carburization resistance of the two alloys in comparison with that of 310 stainless steel is explained in terms of alloy composition particularly the (Ni Co)/(Cr + Fe) ratio. A correlation is found to exist among this ratio and the activation energy of the carburization reaction, the amount of carbon absorbed by the alloy during exposure to carburizing environment as well as the retained room-temperature tensile ductility after the respective exposure. On the other hand, the results indicate that alloys most resistant to oxidation are also most resistant to carburization. It is concluded that either Incoloy 800H or Haynes alloy 556 would have been a better selection for the shroud plate application.