Investigation of crack propagation in 17G1S steel of gas main pipelines after 40 years of operation.

What is it about?

gas pipeline, 17G1S steel, long-term operation, kinetic diagram of fatigue fracture, characteristics of cyclic crack-growth resistance, stress ratio, threshold value of the stress intensity factor, degradation of materials

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Why is it important?

The kinetic diagrams of fatigue fracture are plotted for various stress ratios of the loading cycle within the range of fatigue crack growth rates covering up to six orders of magnitude. The near-threshold regions of the kinetic diagrams are investigated for the material of different zones of the walls of the intact pipes and pipes after operation. The characteristics of fatigue crack-growth resistance are determined on the basis of the constructed plots. We reveal a significant decrease in the threshold value of the stress intensity factor of the material after operation as compared with the intact material caused by the degradation of its structure and the decrease in its fatigue-fracture resistance. It is demonstrated that the characteristic most sensitive to the stress ratio and to the structural degradation of 17G1S steel from the pipeline is the threshold value of the stress intensity factor, which decreases by 16–23% as a result of long-term operation depending on the ratio of the minimum and maximum stress intensity factors in the loading cycle. It was discovered that, from the viewpoint of fatigue fracture resistance, the material of the median section of the wall of gas pipeline has the highest strength.

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