Effect of the Operating Temperature of a Steam Methane Reforming Furnace on Structural Changes and Crack Susceptibility in Welding 800HT Nickel Alloy

The long-term operation of 800HT nickel alloy parts of a steam methane reforming furnace at temperatures above 800°C leads to significant embrittlement of the metal, sharp grain growth, and precipitation and coagulation of metal carbides along the grain boundaries. The operation of equipment at lower temperatures (400–420°C) does not lead to significant changes in the microstructure of 800HT nickel alloy; hence, no embrittlement. It was found out that the cause of the cracking of the welded joint after repair is the degradation of the base metal during operation at temperatures above 800°C.