Destruction Patterns of X70 Steel Sample, Possessing Cracks of Corrosion-Mechanical Origin, under Cyclic Loading

Abstract

Most of the structures, parts of machines in the process of operation are subjected to the action of cyclically changing loads, such changes can be judged by the fatigue of the metal. In addition to the influence of mechanical stresses during the service, corrosive environment affects metal structures, machine parts, which leads to the process of gradual accumulation of damage. Corrosive media leads to a decrease in durability. The paper presents results of fatigue tests on a sample of steel X70, selected from the focal zone of destruction of the main gas pipeline. The sample under investigation had numerous cracks typical for corrosion-mechanical destruction. It is shown that with an increase in the number of loading cycles, the electrode potential of the metal decreases, which leads to a decrease in its thermodynamic stability. With the growth of the crack, there is a decrease in the potential, which is not compensated by the relaxation processes. Results of the regression analysis showed that the correlation coefficient is r = 0.99, using the three-parameter logarithmic function.