Influence of the Degradation of 17G1S Steel on its Properties After Operation in the Gas Main

We compare the mechanical and corrosions characteristics of 17G1S steel in the intact state and after its operation for 40 yr in a gas main. The low sensitivity of the strength characteristics of steel and its modulus of elasticity and much higher sensitivity of its plasticity characteristics to in-service degradation is confirmed. It is established that the corrosion resistance of the degraded steel is lower (as compared with the intact steel) and that the corrosion rate K m has gradients both across the thickness of the pipe wall (the value of K m is maximum near the inner surface of the pipe) and along its perimeter (the corrosion rate is maximum in the bottom part of the pipe). On the fracture surfaces of the specimens of degraded pipe near its inner surface, we detected local areas with fuzzy fractographic profiles, which are usually caused by the presence of surface films. They are regarded as signs of dispersed damage caused by the formation of corrosion defects inside the pipe wall.