Microstructural Variation at Different Layers of API 5L X80 Pipeline Steel Thickness and Its Relation to Hydrogen Degradation




Abstract: The influence of microstructure on hydrogen embrittlement in API 5L X80 pipeline steel was investigated. Specimens from top surface and mid-thickness layers of pipeline steel were characterized before performing tensile and electrochemical corrosion test in hydrogen charging media. Microstructural examination showed mainly acicular ferrite phase at the mid-thickness, while the top surface was dominated by bainitic ferrite phase. Also, higher volume fraction of (111)||ND, (110)||ND, {123}〈634〉, {112}〈111〉, and {110}〈112〉 texture components featured at the mid-thickness region; unlike the top surface that contain more of (100)||ND, {001}〈100〉, {001}〈110〉 textured grains. Results showed that the mid-thickness layer has lower tensile properties with increased ductility, while the top surface displayed higher strength and reduced ductility. It was evident that microstructural evolution in the mid-thickness layer promoted resistance to hydrogen degradation in the region compared to the top surface.

Authors: Enyinnaya Ohaeri and Jerzy Szpunar

Keywords: Pipeline steel, Tensile test, X-ray diffraction (XRD), Crystallographic texture, Hydrogen embrittlement, Polarization

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8 pages


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