Assessing the synergistic effects of hydrogen-induced damage, internal pressure, and corrosion on pipe elbow failure

The present study proposes a finite element method (FEM)-based framework to assess the synergistic effect of hydrogen-induced damage (HID), internal pressure, and corrosion effects on the failure behavior of elbows. The mechanical properties degradation of pipeline steel subjected to HID is incorporated into the FE modeling to model corroded pipe elbows serviced in a hydrogen-rich environment. Two dimensionless metrics (${\sigma }_{\max }/{\sigma }_y$ and ${\sigma }_{\max }/{\sigma }_u$) are proposed to quantify the parameter effects and sensitivity. The results demonstrate that 1) the combination of corrosion effects, internal pressure, and HID significantly reduces the load-bearing capacity at the pipe elbow; 2) ${\sigma }_{\max }/{\sigma }_u$ exceed 1 in all cases under a hydrogen-rich environment for more than 12 h, indicating that prolonged exposure to an environment abundant in hydrogen may promote elbow failure; 3) the critical defect length ($\varphi /\pi =9\%$) and neutral-line bend radius ($R/D=4.5$) are determined, exceeding which the elbow failure behavior is significantly affected; 4) ${\sigma }_{\max }/{\sigma }_y$ and ${\sigma }_{\max }/{\sigma }_u$ are lower than 1 when the defect occurs at the extrados, implying that the synergistic effects of HID and corrosion are unlikely to cause the elbow failure if corrosion occurs at the extrados, but it is not applicable to defects occurring at other locations, especially at the intrados; 5) The maximum von Mises stress exhibits the highest sensitivity to internal pressure, followed by defect location, defect depth, neutral-line bend radius, defect length, and hydrogen damage.