PSI - Issue 71

V. Thondamon et al. / Procedia Structural Integrity 71 (2025) 226–232

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condition of re-rounding study through numerical analysis. For the same indenter diameter, higher dent depth shows lower percentage re-rounding. For 89 mm diameter indenter in commissioning condition, percentage re-rounding for dent depth of 35.6 mm and 44.5 mm are 74.7% and 67.9% respectively. For the same dent depth, higher dent diameter exhibits higher percentage re-rounding. For 142 mm diameter indenter in commissioning condition, percentage re rounding for dent depth of 35.6 mm and 44.5 mm are 75.3% and 69.2% respectively. For the same dent depth and indenter diameter, higher percentage re-rounding is observed without internal pressure. For 89 mm diameter indenter in in-service condition, percentage re-rounding for dent depth of 35.6 mm and 44.5 mm are 56.7% and 55.3% respectively. For 142 mm diameter indenter in in-service condition, percentage re-rounding for dent depth of 35.6 mm and 44.5 mm are 66.9% and 65.2% respectively. Figures 3 and 4 show the cross-section of dent depth at indentation and after removal of indenter for case RR5. Figure 5 shows the typical stress distribution in the pipe during indentation of the dent. Figures 6 and 7 show typical strain variation vs duration of re-rounding along longitudinal and circumferential directions. From figures 6 and 7, it is observed that the strain in longitudinal direction of the pipe, decreases with distance from the indenter but in the circumferential direction, strain values are maximum at around 80 mm distance from the indenter. The strain at indentation decreases after the removal of indenter. The residual strain indicates the plastic component of strain and the elastic component of strain can be evaluated. In longitudinal direction at distance more than 80 mm from the center of the indenter, the total strain is equal to the residual strain indicating plastic deformation. In circumferential direction, the total strain decreases after removal of the indenter. At a distance of 80 mm from the center of the indenter, the percentage of elastic component of strain is highest. Hence, the dented region at 80 mm from indenter in circumferential experienced highest range of deformation with repeated pressurization cycles. Table 4. Summary of dent depths in commissioning condition RR1 RR2 RR3 RR4 Indenter diameter 89 89 142 142 Dent depth at dent formation 35.6 44.5 35.6 44.5 Dent depth after removal of indenter 9.0 14.3 8.8 13.7 Percentage re-rounding 74.7% 67.9% 75.3% 69.2% Table 5. Summary of dent depths in in-service condition RR5 RR6 RR7 RR8 Indenter diameter 89 89 142 142 Dent depth after applying internal pressure -0.2 -0.2 -0.2 -0.2 Dent depth at dent formation 35.6 44.5 35.6 44.5 Dent depth after removal of indenter 15.4 19.9 11.8 15.5 Percentage re-rounding 56.7% 55.3% 66.9% 65.2%

Fig. 3. Cross-section showing the dent depth at indentation for the case RR5

Fig. 4. Cross-section showing the dent depth after removal of indenter for the case RR5