Cracking Causes of Stainless Steel Right Angle Elbow of Buried Pipline in a Gas Field

The stainless steel right angle elbow of the buried pipeline of gas gathering station incoming valve group in a gas field was cracked. The reasons for the cracking of right angle elbow were analyzed by macroscopic observation, chemical composition analysis, metallographic inspection, scanning electron microscopy and energy spectrum analysis. The results showed that the cracking form of right angle elbow was chloride ion stress corrosion cracking. During the forging process of right angle elbow, incompatible deformation occurred between the alumina inclusions in the forging and the matrix, forming a banded structure, resulting in stress concentration. In an environment containing chloride ions, stress corrosion crack was formed in the area, and crack expanded gradually along the inclusions and penetrated the entire elbow wall, eventually causing right angle elbow to crack.