Study on the ultimate bearing capacity of high steel grade elbow with trench defects

Elbows are an important component of oil and gas pipelines. The force state and the medium flow state are more complex than that of the straight pipe. Once the defect occurs at the elbow, the elbow pipe is more prone to fail. The high steel grade pipeline is the development trend of the long distance oil and gas pipeline construction, and it is urgent to evaluate the residual strength of the high steel grade bending pipe. Through the establishment of the finite element model, the defect size, relative position, bending radius, pipe parameters and pipe performance influence were studied on the ultimate internal pressure of the elbow, and finally the prediction formula of the bending was established. The results show that with the increase of defect length and defect depth, the ultimate internal pressure of the elbow is significantly reduced. The trench defect affects the ultimate internal pressure when the trench defect is located in the inner arch of the elbow. The bending radius, the wall thickness and the pipe material will affect the ultimate internal pressure. The error analysis shows that the prediction formula is more accurate, which can provide the basis for the residual strength evaluation of high steel grade elbows with trench defects.