In situ eddy current and ultrasonic monitoring of hydrogen diffusion in API X70 pipeline steel

Hydrogen embrittlement poses a risk to the integrity of pipeline steels used in hydrogen industries, and early signs of this degradation are often undetectable by conventional non-destructive testing methods. This work introduces a one-sided hydrogen charging and opposite side monitoring methodology that isolates the electrolyte-related surface-reaction artefacts, replicating the actual hydrogen permeation condition in API X70 steel pipelines. Multifrequency eddy current testing reveals frequency-dependent changes in electrical conductivity and magnetic permeability that correlate with hydrogen charging. Complementary high frequency ultrasonics testing confirms through thickness hydrogen diffusion via monotonic reductions in ultrasonic signal amplitude and increased acoustic attenuation. The agreement between electromagnetic and acoustic trends supports that the signal evolution is consistent with a three-stage kinetic response—incubation, rapid diffusion, and saturation—providing real-time, depth resolved insight into hydrogen diffusion and trapping behavior. The proposed monitoring approach supports hydrogen transport infrastructure by enabling early-stage monitoring of hydrogen exposure state in pipeline steels.