Linking microstructure to fracture morphology under hydrogen charging in L485MB pipeline steels
Published in The Energy Pipeline Innovation Conference (EPIC 2025), Cambridge, United Kingdom, 2025
Abstract
Hydrogen, a much sought-after option for a green energy carrier, affects the mechanical properties of pipeline steels. The underlying microstructure often governs the severity of hydrogen-assisted degradation. Understanding these microstructural effects is, therefore, critical for safe hydrogen transport. This work uses ex-situ quasi-static tensile tests to study the hydrogen performance of two cold-bent L485MB pipeline steels with different banding morphologies. Thorough microstructural characterization is done using light optical microscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy. For hydrogen characterization, samples are taken from the middle section of the pipe wall and electrochemically hydrogen-charged. Hydrogen content, diffusion coefficient, and trapping are measured using hot extraction, electrochemical hydrogen permeation, and thermal desorption spectroscopy, respectively. Ex-situ quasi-static tensile testing is conducted on smooth round bars under two conditions: in air as the reference condition, and after electrochemical hydrogen charging in a 0.5M H2SO4 electrolyte containing 1 g/L thiourea, using a constant current density of 0.8 mA/cm² for 18 hours. Fracture surfaces are analysed using scanning electron microscopy to link the observed hydrogen signatures with specific microstructural features. Both steels exhibit reversible traps, with banding morphology influencing hydrogen diffusivity and trapping. The presence of hydrogen leads to fisheyes and quasi-cleavage regions on the fracture surfaces, indicating hydrogen embrittlement. Banding characteristics affect hydrogen uptake, diffusivity and fracture behaviour.
Recommended citation: J. Jubica et al., "Linking microstructure to fracture morphology under hydrogen charging in L485MB pipeline steels," in Proceedings of the Energy Pipeline Innovation Conference 2025, Cambridge, United Kingdom, 2025.
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