Cracking Reason of 16Mn Steel Bent Pipe

Failure analysis of the hot-bended pipel in the gas gathering station of a gas field was carried out by macroscopic morphology observation, physical and chemical performance test, metallographic and energy spectrum analysis. The results show that the composition of the bent pipe was normal; but the structure was abnormal, contained a large amount of coarse-grained martensite, and the bending process was unreasonable, and there was residual tensile stress on the outer side of outer arc. Therefore, under the combined action of external load, residual stress and corrosive medium, the outer wall of outer side of the bent pipe generated cracks which expanded through the wall thickness, eventually leading to the leakage of pipeline.