Perforation Cause Analysis of 90° Gas Transmission Elbow Pipe of Oilfield Wellhead

Perforation failure occurred in 90° elbow pipe at wellhead of an oil field. The causes of perforation failure were analyzed by macroscopic inspection, metallographic examination, scanning electron microscopy and energy spectrum analysis. The erosion model of particles on elbow pipe under the condition of gas-solid two phase flow was established by the finite element method. Also, the dangerous area and the main influencing factors of the elbow erosion damage were calculated. The results show that the erosion rate on the inner wall of the outer arc was the highest, and the erosion rate rose with the increase of diameter, mass concentration and flow rate of solid particles. The ductile-brittle transition and low temperature brittleness occurred on 20 steel at low temperature, and eventually the perforate failure happened under the continuous impact of solid particles.