Abstract: Using the test methods of macroscopic observation, metallographic examination, electronic microscope and energy spectrum analysis, the perforation failure cause at the elbow of crude oil terminal pipeline was analyzed. The results show that the inner-wall at outer arc side of the elbow pipe was eroded by the oil and gas medium in the pipeline, leading to the decrease of the pipe wall thickness, which caused the perforation failure; the decrease of outer-wall thickness at outer arc side of the elbow pipe caused by corrosion also had some effects on the failure. In order to prevent the perforation failure, the weld reinforcement of the straight and elbow pipes join should be controlled carefully during the welding of pipeline, realizing the reduction of turbulence to reduce the erosion of elbow pipe. Also the external protection of the pipelines should be considered.