PSI - Issue 2_B

H. M. Nykyforchyn et al. / Procedia Structural Integrity 2 (2016) 501–508 H. M. Nykyforchyn et al. / Structural Integrity Procedia 00 (2016) 000 – 000

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Extensive delamination revealed in the pipe elbows walls was marked on real lateral pipe elbows (Fig. 2). The scheme of delamination in the pipe elbow А is given in Fig. 6 а and the scheme of delamination in the pipe elbow B – in Fig. 7 а . The cross-sections of the pipe elbow А with a defect and that of the pipe elbow B are shown in Fig. 6 b and Fig. 7 b , respectively. Catastrophic spurious thinning of the pipe wall of the elbow А (Fig. 6 а ) was found at a large area of the tensioned pipe elbow segment between 4 and 8 hours. The dimensions of delamination were 380 mm along the longitudinal direction and 240 mm in the circumferential direction. The delamination propagated to about one-third of the pipe circumference.

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b

Fig. 6. Scheme of delamination in the wall of lateral pipe elbow А of a natural gas transmission pipeline system ( a ) and cross-section of the pipe elbow А with a defect ( b ).

Extensive delamination of the pipe elbow B having dimensions of 800 mm along the pipe axis and 450 mm along the circumferential direction (Fig. 7 а ) was found in the tensioned section of the pipe elbow between 7 and 12 hours. In Fig. 7 а the growth of the defect area ID for the period of 5.5 months between examinations was also marked. According to the data obtained by the non-destructive examination, the delaminations revealed in the body of the pipe elbows A and B had the dimensions significantly exceeding the acceptable defects limits, set by the standard of defects detection (for example, API 5L, and others). Thus, such defects should not be considered as acceptable defects.

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b

Fig. 7. Scheme of delamination in the wall of lateral pipe elbow B of a natural gas transmission pipeline system ( a ) and cross-section of pipe elbow B with a defect ( b ). In Fig. 7 a area ID corresponds to the increased defect area for 5.5 months.

The revealed delamination of the pipe body of elbow A was placed closer to its external surface. Therefore, the