PSI - Issue 59

V. Makarenko et al. / Procedia Structural Integrity 59 (2024) 385–390 V. Makarenko et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 2. Values of parameters of the α -Fe crystal lattice, micro-stresses and carbon distribution in steel of sewer pipe structures. Steel grade Term of operation, years α, А0 σ, МPа Amount of carbon, % In ferrite In cementite

10 20 30 40 10 20 30 40

2.8671 2.8679 2.8690 2.8695 2.8770 2.8703 2.8723 2.8785

111 149 192 214 124 171 225 267

0.021 0.029 0.039 0.041 0.028 0.042 0.053 0.058

0.082 0.070 0.065 0.062 0.082 0.073 0.070 0.082

09G2S

17G1S

Fig. 2. Change in the amount of cementite in steel depending on the service life of pipe structures of sewer structures. 1 – Steel 20, 2 – steel 10, 3 – Steel 3.

Thus, the above data indicate intensive metal degradation during the long-term operation of hydrotechnical equipment and engineering structures in conditions of corrosion-aggressive working environments of sewer systems. 4. Conclusions Using X- ray diffraction analysis methods, the parameters of the crystal lattice of the α -matrix were measured, and the level of elastic lattice curvatures (microenvironments of curvatures) and the distribution of carbon in ferrite and steel were estimated. As the data obtained showed, an increase in the service life of steel sewer pipe structures leads to an increase in the parameter values of the volume- centred cubic crystal lattice of an 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 boundary of the α -matrix. The second part, apparently, remains on dislocations, passing into microcracks, and also goes to the formation of new finely dispersed carbide particles; relatively large carbide particles are formed at the grain boundaries between perlite and ferrite. It is shown that over time, with an increase in the service life (up to 40 years), the surface layers of the metal is enriched by hydrogen, oxygen and sulfur. This is especially evident in the area of a corrosion defect. As a result, this negatively affects the corrosion and mechanical properties and, in general, the crack resistance of the metal.