The Peculiarities Of Fatigue Failure For Pipe Steels Of Different Strength Classes (pipes With Welds)

Variable loads, as compared with static loads, have a greater impact on the condition of pipelines. They lead to the degradation of metal and significantly reduce the service life of pipelines. This paper considers the mechanism of fatigue crack development in steels of different strength classes (K50, K60 and K62), which helps to specify the fracture mechanism and evaluate the residual life of a pipeline material. The number of cycles to failure of specimens with no visible weld defects was reduced by more than 40%, as compared with seamless specimens. The tests allowed the authors to establish the peculiarities of K60 steel failure and to calculate regression equations of the second order between the number of cycles to failure of the specimen, the maximum tensile stress and the stress range during fatigue tests. Knowing the number of pressure fluctuations in the pipeline, which are registered in the control room, one can use the equations to predict the residual life of a particular section of the pipeline.