Abstract: A 720×8 mm pipeline elbow of LunNan terminal station was exploded in February 1996. At that moment, the internal pressure of pipeline was about 0. 04 MPa, which could not make the welding crack explode. The Finite Element Method is employed to analyze the pipeline elbow of LunNan terminal station in this paper, showing that the bending hoop stress of elbow was induced on account of the effect of the temperature difference. Once the temperature difference was higher than a certain number, the bending hoop stress induced by it made the welding crack of pipeline elbow explode.