PSI - Issue 80

Sherif Ezzeldin et al. / Procedia Structural Integrity 80 (2026) 195–202 S. Ezzeldin / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 5: Evolution of average contact stress σ avg c

over logarithmic time with leakage threshold of 2.85 MPa.

against yielding ( SF y = S y /σ max vM ) decreases slightly after re-torqueing but stabilizes by the end of the service period due to relaxation. At 60 ◦ C (Fig. 6(b)), the first re-torque is required within 8 hours, followed by a second after 2 months. Two interventions are necessary to maintain sealing integrity due to accelerated HDPE relaxation at elevated temperatures. Despite multiple re-torques, SF y remains above the designated threshold, showing behavior similar to the 23 ◦ C case, with stabilization over time.

Fig. 6: Average contact stress σ avg c

and safety factor against yielding SF y for (a) 23 and (b) 60 ◦ C.

5.3.2. Annual Temperature Variation To simulate real-world conditions in the Arabian Gulf, an annual temperature cycle (23–60 ◦ C) Weather and Climate (2024) was applied. Fig. 7 shows that two re-torques—at 1 and 5 months—are su ffi cient to maintain σ avg c ≤ 2 . 85 MPa. Safety factor against yielding SF y ) drops slightly after each re-torque but remains above 2 through out the service year.

6. Conclusion

This study applied the Tetra-Parametric Assembly Method (TAM) to determine optimal initial bolt loads in an HDPE–steel flange connection. TAM was first verified against EICM, confirming its accuracy for hybrid joints. Using a calibrated viscoelastic TN material model, the long-term sealing performance under thermal loading was evaluated. Results show that flange integrity is strongly temperature-dependent, with earlier leakage at higher temperatures. Stress relaxation necessitates re-torqueing—multiple times at 60 ◦ C and under real-world thermal cycles, but only