Study of the degradation of steel sewer structures of long-term operation

Experimental studies of the influence of harmful elements (hydrogen, sulphur, oxygen) on the degradation of structural steels of underground sewer systems and the nature of their distribution in the metal of pipelines operated for a long time in aggressive environments have been carried out. It is shown that with an increase in the service life, the surface layers of the metal are enriched by hydrogen, oxygen and sulfur, adversely affecting the metal’s corrosion-mechanical properties. Combined with structural transformations, this leads to local metal embrittlement and, under favourable conditions (under alternating cyclic loads), to the formation of micropores, the coagulation of which leads to crack formation. An increase in the service life of sewage steel pipe structures leads to an increase in the values of the parameter of the body-centred cubic crystal lattice of the α-solid solution and an increase in microstresses in the structure. At the same time, part of the carbon from the decomposed cementite passes to the interface of the α-matrix. The second part, apparently, remains on dislocations, turning into microcracks, and also goes to the formation of new finely dispersed carbide particles; relatively large carbide particles form at the grain boundaries between pearlite and ferrite.