Abstract
The causes and character of the fracture of a section cut from a main gas pipeline 530 mm in diameter made of low-alloy 17GS steel have been investigated. The length of a longitudinal main crack in the base metal is 12 m. The gas pipeline failed due to stress corrosion cracking according to a hydrogen mechanism. Cracks originated on the outer surface of the pipe near corrosion pits. Preferred crack propagation along the boundaries of ferrite grains and pearlite colonies is revealed. The fraction of intergranular fracture is 6–9.5%. An anomalously high anisotropy of impact toughness is found in the place of plastic corrugation formation, Ka = 3.2–3.9.
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