Stress-corrosion failures of main pipelines

The basic peculiarities of stress corrosion fracture cases of main pipelines are analyzed. The authors consider structure, mechanical properties, Charpy energy, fracture toughness, corrosion fatigue, and fracture mechanisms of steel Kh70 (from transit gas pipeline “Urengoy–Pomary– Uzhgorod”) in three conditions: as received (archive), after 24 and 26 years of service. The service degradation of steel is revealed, which manifests itself in considerable drop of Charpy energy, fracture toughness and resistance to the corrosion fatigue crack growth. The analysis is performed of the resistance of the pipeline steels to the corrosion fatigue crack nucleation and growth and the respective recommendations are provided concerning the avoidance of the stress corrosion failure of transit gas pipelines.