Can dents and gouges compromise the structural integrity of hydrogen transport pipelines?
This research is significant for pipeline operators and engineers considering the repurposing of natural gas pipelines for hydrogen transport, as it provides insights into the safety implications of external defects under hydrogen exposure. It is an incremental step in pipeline safety research.
This paper investigates the impact of dents and gouges on the structural integrity of hydrogen transport pipelines, particularly under hydrogen exposure. The study found that hydrogen generally does not significantly worsen the damage severity of these defects, except in a specific scenario where hydrogen egress is prevented in a pre-existing passive dent with a gouge under internal pressurization.
Repurposing natural gas pipelines for hydrogen transport requires understanding how external defects, like dents and gouges, affect structural integrity under H$_2$ exposure. To address this, we combine experiments with a new hydrogen embrittlement model aimed at large plastic straining scenarios, which integrates: (i) multi-trap hydrogen transport, (ii) finite-strain plasticity, and (iii) a hydrogen- and triaxiality-dependent damage law. Each constituent of the model is validated with experiments on X65 pipeline steel: (i) hydrogen permeation, (ii) full-scale pipe-indentation, and (iii) mechanical testing at different hydrogen and triaxiality levels. The validated model is used to study \textit{passive} (indent before H$_2$ exposure) and \textit{active} (indent with H$_2$) dents and gouges. Results reveal that hydrogen does not significantly increase the damage severity of those defects, unless hydrogen egress is completely precluded at the outer surface of a pipeline that is being pressurised internally and contains a pre-existing \textit{passive} dent with a gouge.