Calculation of the Damage Factor for the Hydrogen-Enhanced Fatigue in the RBI Framework

Hydrogen has been largely indicated as a promising long-term solution for energy transport and storage, thanks to its near-zero environmental impact at the end-use site. On the other side, it can permeate and embrittle most metallic materials, thus resulting in sudden component failures in the hydrogen industry. Maintenance activities have a prominent role in accident prevention. The risk-based inspection (RBI) approach aims at prioritizing the inspection of high-risk components to minimize the overall risk of the plant. Nevertheless, RBI has never been adopted for equipment operating in a hydrogen environment. The determination of the risk is based on the damage factor, a parameter accounting for the material degradation likely to occur. Hydrogen-induced damages are mostly neglected or generalized by the existing RBI standards. This study proposes a methodology to determine the damage factor for hydrogen-enhanced fatigue crack growth, normally caused by pressure fluctuations in pipeline systems. The environmental severity is based on the operating conditions, while the material's susceptibility depends on its microstructure, chemical composition, and presence of welds. The working conditions are considered through the frequency and the stress ratio. This methodology could allow the application of the RBI methodology for hydrogenrelated equipment. Hence, it will facilitate risk-informed managerial decisions, thus stimulating an increasingly widespread rollout of hydrogen as a clean and safe energy carrier.

Keywords: Risk-based inspection, Hydrogen damage, Fatigue crack growth, Material degradation, Loss of containment, Predictive maintenance, Maintenance planning.

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