PSI - Issue 80

Alok Negi et al. / Procedia Structural Integrity 80 (2026) 203–211

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AlokNegi / Structural Integrity Procedia 00 (2023) 000–000

Fig. 5: (a) Initial residual stress distribution in the notched pipe segment after mapping residual stresses of around 20% of the yield strength in the pipe geometry, (b) Phase-field simulation results showing crack evolution via the damage variable ϕ at a testing time of t = 18 . 76 hours, under the initial residual stress distribution illustrated in (a).

Fig. 6: Summary of fullscale-pipe test results: comparison of experimental and numerical final / failure pressure for C110 Steel considering residual stresses. Note that the failure / final pressure in Fig. 6 refers to the pressure at the time of failure for specimens that failed during numerical simula tions. In case of no failure, the pressure on the y-axis in Fig. 6 represents the final pressure.

4. Summary and conclusions

A coupled deformation–di ff usion–fracture phase-field framework is used to simulate SSC-driven burst failure in API 5CT C110 steel pipes under sour service conditions, with a particular focus on quantifying the role of as manufactured residual stresses. The modeling framework integrates elastoplastic deformation, stress-assisted hydro gen di ff usion, and hydrogen-induced fracture toughness degradation, calibrated using experimental data specific to C110 steel and representative NACE test environments. The model’s predictive capability was validated through sim ulation of a full-scale burst test from the API PRAC II Joint Industry Project. A key contribution of this work is the mechanistic and quantitative assessment of how residual stresses contribute to SSC-driven pipe failure via two cou pled e ff ects: (i) amplification of the e ff ective stress intensity at the notch tip, and (ii) enhancement of local hydrogen concentration through stress-assisted di ff usion, which accelerates material degradation. By incorporating numerically generated residual stress fields representative of as-manufactured conditions, the simulations revealed a strong sen sitivity of burst performance to residual stress magnitude. Importantly, a critical threshold was identified: residual stresses below 17.5% of the material’s yield strength did not result in failure within the 672-hour test duration, whereas