PSI - Issue 30

Nikolay I. Golikov et al. / Procedia Structural Integrity 30 (2020) 28–32 Nikolay I. Golikov / Structural Integrity Procedia 00 (2020) 000–000

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The residual stress was measured using x-rays on the outer and inner surfaces of the pipe. At each point located at a different distance from the center of the seam, residual stress was determined in the axial and circular directions. The chemical etching was applied to a depth of 0.2 mm before measurement to relieve mechanical stress, which appeared during the manufacturing of pipes. 3. Results and discussion After ten years of operation of the main gas pipeline, gas leaks were detected in two sections of the linear route. Inspection of defective pipe coils revealed a crack on the inner side of the longitudinal weld of the pipe No. 1 (Fig. 1, a). It develops along the weld from the inside of the pipe and is 26 mm in length with a maximum opening of about 0.4 mm. On the outside of the pipe (Fig. 2, a) opposite the cracked section, a corrosive attack is observed with signs of through holes (indicated by short arrows).

Fig. 1. Type of detected cracks in the longitudinal welds on the inner surface of the pipes No. 1 (a) and No. 2 (b)

Fig. 2. Sections on the outside of the pipes opposite to the places of detection of internal cracks: a - pipe No. 1; b - pipe No. 2. Short arrows indicate through holes

A crack was also detected in the longitudinal seam of the pipe No. 2 from the inner side. The maximum crack opening of about 0.5 mm is observed in the central part. The total length of the crack is 30 mm (Fig. 1, b). Cracks 7 and 9 mm long divide from the upper end of the central crack at an angle. Cracks 8 and 16 mm long extend down