The failure mechanism of ammonia suction pipe bursting under fire environment

Abstract Liquid ammonia is widely used in the refrigeration industry, which brings serious challenges to the safety control of ammonia refrigeration systems due to its high danger, ease of exploding, and acute poisoning accidents. Current research on ammonia refrigeration equipment mainly focuses on accident hazard analysis, while the study on the failure mechanism of equipment under fire conditions is not deep enough. In this paper, the ammonia suction pipe with burst phenomenon was sampled, and the failure mechanism of the suction pipe under a fire environment was comprehensively studied by means of macroscopic examination, chemical composition analysis, metallographic examination, surface decarburization and fracture analysis, mechanical property test, and simulated heat treatment experiment. The results show that the failure mechanism of a suction pipe under a fire environment is a toughness overload fracture caused by the reduction of material strength. Affected by the high temperature of fire source combustion, the nitriding layer appears on the inner surface, and some decarburization occurs on the outer surface of the suction pipe. The microstructure of the fire-facing surface (the starting position of the tear) undergoes the pearlitic spheroidization phenomenon with the level of 3 grade, which reduces the strength and creep resistance of the material. The liquid ammonia in the pipe is rapidly expanded and gasified under a high-temperature environment, which produces high-pressure stress inside the pipe. Eventually, the pipe burst on the fire-facing surface, where the strength is the weakest.