Effect of hydrogen on corrosion damage of metal of the high-pressure energetic boiler drum

The causes and mechanism of initiation and growth of pointed and linear pits, separations and cracks of corrosion origin on the internal surface of the shell of high-pressure (15.5 MPa) steam boilers used at heat power plants were investigated by the LLMS, SEM, AES, SIMS and fractography methods. It was found as a result of comprehensive investigations that initiation and growth of the above damages were caused by hydrogenation and embrittlement of metal in the zones resulting from the simultaneous effect of an unfavourable local combination of several factors, such as formation of regions with a quenching structure and structural heterogeneity in the joining zone between dissimilar metals, many years of thermal cycling and corresponding thermal fatigue, local variations in chemical composition of metal in the intergranular and interface regions between the phases and corresponding variations in mechanical properties of given microvolumes of metal with a decreased crack resistance against the background of an increased sulphur content and decarburized surface layer of metal on the steam boiler drum shell.