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Description
Hydrogen transportation through pipelines has gained significant attention due to its low carbon footprint; however, hydrogen-assisted cracking (HAC) remains a major challenge. Therefore, this study investigates the effect of surface roughness on the HAC susceptibility of API 5L X52 pipeline steel under slow strain rate tensile (SSRT) testing with in-situ electrochemical hydrogen charging. Specimens were pre-charged for 24 h at a cathodic potential of -1225 mV in a 3.5 wt.% NaCl solution containing thiourea to simulate high-pressure gaseous hydrogen. HAC susceptibility was quantified using the susceptibility index (IHAC). Hydrogen charging significantly reduced ductility, with the as-machined specimens exhibiting the lowest reduction in area due to greater surface defects. Microscopic examination also revealed extensive surface cracking initiated from surface defects and stress concentration sites. Also, it is observed that the intensity of the surface cracking is reduced with decreasing SR (smoothing) of the specimen. However, further polishing beyond an average SR of 0.2 µm did not reduce the IHAC. Instead, IHAC increased, indicating that the highest resistance to HAC was achieved at an SR of 0.20 µm, identifying a distinct characteristic for HAC of API 5L X52 pipeline steel.
| Topic Area | Fatigue, Corrosion and Structural Integrity of Engineering Structures and Mechanical Systems |
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