Fractographic Signs of the In-Service Degradation of Welded Joints of Oil Mains

According to the results of inspection of the damaged elements of an oil pipeline with axial welded joints, we analyze the most probable sites of fracture initiation and the mechanisms of crack propagation in the course of long-term operation. As a result of hydrostatic-pressure tests of the pipe, it becomes possible to visualize the fractographic signs of the in-service degradation of the metal in the form of dispersed damages located along the grain boundaries and observe a decrease in the resistance of grains to brittle failure. We associate the dispersed damage to pipe wall with the hydrogenation of the metal from its inner surface in the course of operation.