A Damage Evolution Approach in Fracture Mechanics of Pipelines

Abstract

The paper concentrates on perspectives of the damage evolution approach in fracture mechanics of oil and gas pipelines. This approach is based on the generalised concept of damage. It is postulated that deformation and fracture processes in solids are determined by some general functional law related to the accumulation of damage. Fracture mechanics parameters are accepted as the controlling parameters for the failure processes. The approach leads to a description of fatigue crack growth, stress corrosion cracking, a correlation between hydrogen redistribution in the vicinity of a crack tip and the stress intensity factor during crack propagation under cyclic loads. The damage evolution approach has been also employed to quantify the shift of the ductile-to-brittle transition temperature of gas pipelines due to physical-mechanical damage of the steel during long-term operation of pipelines. The ductile–brittle transition curve of the steel pipeline shifts to higher temperature which decreases operation margins in both the temperature and pressure. The methodology of the above-mentioned approach and the failure assessment diagram has been employed for the structural integrity analysis including assessment of the ductile-to-brittle transition temperature and allowable sizes of surface longitudinal crack-like defects in gas pipelines.