PSI - Issue 71

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

229

3.2 In-service condition

In the in-service condition, firstly, internal pressure was applied to the inner surface of the pipe. Subsequently, dents were imparted on the pipes using rigid indenter and the indenter is removed. Dent depth after removal of indenter is measured. Strain variations at different locations in the longitudinal direction and circumferential direction of the pipe are plotted and studied to understand the re-rounding behaviour of dent during in-service condition. Experimental studies were carried out on a piping component typically used in Indian oil and gas industry. The typical operating pressure used in the oil and gas industry is 9 MPa. Hence, internal pressure of 9 MPa is considered in this study. 4. Results and discussion From the numerical studies, for the combination of above parameters, various responses were obtained. From the dent formation studies, dent depth at specified indentation force and load vs displacement curves for different cases were obtained. From the re-rounding studies, dent depths at various stages of re-rounding, viz., dent formation, releasing of the indenter and internal pressurization, were obtained along with strain variation around the dent. 4.1 Dent formation studies Table 3 shows the summary of dent depths corresponding to indentation force from experimental and numerical studies. For the same indentation force, dent depth is higher for smaller indenter. For indentation force of 90 kN, dent depth for 89 mm and 142 mm diameter indenters are 11.1 mm and 10.2 mm respectively. For indentation force of 105 kN, dent depth for 89 mm and 142 mm diameter indenters are 13.9 mm and 12.9 mm respectively. Figure 2 shows load vs dent depths for both 89 mm and 142 mm diameter indenters from numerical analysis. From table 3, it can be observed that the dent depth obtained from numerical analysis for 89 mm diameter and 142 mm diameter indenters are found to be in close agreement with the corresponding experimental observations. Table 3. Summary of dent depths in dent formation study

Dent depth (mm)

Indentation force (kN)

89 mm diameter indenter

142 mm diameter indenter

Experimental

Numerical

Experimental

Numerical

90

9.6

11.1 13.9

9.8

10.2 12.9

105

14.0

10.0

120

90

60

30

89 mm indenter 142 mm indenter

Load (kN)

0

0

4

8

12

16

Dent depth (mm)

Fig. 2. Load vs dent depth from numerical analysis

4.2 Re-rounding studies Tables 4 and 5 show the summary of dent depths at different stages for both commissioning condition and in-service