INFLUENCE OF THE LONG-TERM OPERATION OF GAS PIPELINES ON THE CYCLIC CRACK-GROWTH RESISTANCE OF 17G1S STEEL

摘要

We establish the kinetic regularities of crack propagation under low-, medium-, and high-amplitude cyclic tensile loads in 17G1S steel taken from the "Dashava-Minsk" gas main pipelines after 40 yr of operation and from the intact (original) pipes. 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.