Influence of long-term operation of the 17H1S steel on the main gas pipeline on the change of the mechanical properties

The characteristics of strength, ductility and impact toughness of 17H1S steel in the initial state and after 31 years of operation on the main gas pipeline are analysed in terms of their sensitivity to degradation. It is shown that resistance to brittle fracture is the most sensitive of them to changes in the technical state of the metal. Ductile-brittle transition curves were plotted for both steel variants and fractographic features of specimen fracture at temperatures from +20 to –60 ° C. An increase in the temperature of ductile-brittle transition of steel from –40 to –30 ° C after its operation has been established. The ratio of the crystalline relief on the fractures of impact specimens is estimated. It has been established that the obtained data on the mechanical (brittle fracture resistance) and fractographic (fraction of the crystalline relief of the fracture) indicators correlate well with each other. In particular, with a decrease in the index of the mechanical state of the metal due to its operation, the fraction of the crystalline relief at the fracture increases. The data obtained from this study correlate with the previously obtained data for the steels of other gas pipelines.