Abstract
Over a five-year period, a series of fatigue crack growth experiments have been conducted in air and in a bubbling CO2 environment to induce diffusible hydrogen ingress. While the main objective of the hydrogen-charging research targeted characterization of near-neutral stress corrosion crack growth, many of the findings can inform emerging hydrogen transport crack threat management. Summarizing and highlighting these findings and trends could benefit the pipeline industry and accelerate research toward international net zero carbon objectives.
Crack growth retardation in X52 and X65 were found to be readily achieved with an overload cycle, both in air and with hydrogen charging. Subsequent underload cycles were shown to cause resumption of crack advancement: such underload cycles are typical of pipeline operations. Grade X65 pipe steel samples with hydrogen charging were found to be sensitive to underload cycles with significantly higher da/dN growth rates.
Crack retardation models currently available were evaluated using the AFGROW crack growth modeling software to determine and compare model performance to test results. Potential implications of these findings to mainline pipe integrity management are considered in light of crack threat management methods, specifically periodic hydrostatic test methodologies, including emerging hydrogen transport considerations.
