基于8年氢气输送服役条件的L245NS冷弯管与母管氢脆敏感性对比OA

To evaluate the long-term reliability of hydrogen transportation pipelines,the hydrogen embrittlement behavior of cold-bent pipes and straight pipes for L245NS pipeline steel after eight years of service was investigated.A comparative analysis was conducted using slow strain rate testing,metallography,transmission electron microscopy,and electron backscatter diffraction.Results show no significant difference in strength between the two;however,the cold-bent pipe exhibits a higher hydrogen embrittlement susceptibility index(HEI=6.1%),indicating greater hydrogen embrittlement risk.Microstructural analysis reveals that the straight pipe has a rolled ferrite-pearlite structure with an equiaxed grain size of 18 μm,low dislocation density,small-angle grain boundaries(2～5°)totaling 1 960 μm in length,and abundant low-energy coincidence site lattice(CSL)boundaries such as Σ13 and Σ15,resulting in fewer hydrogen traps and suppressed hydrogen aggregation.In contrast,after plastic deformation,the cold-bent pipe shows elongated grains with the minor-axis grain diameter of 15 μm,increased dislocation density forming tangles and networks,small-angle grain boundary length increased to 3 000 μm,and reduced fraction of low-energy Σ boundaries—generating numerous hydrogen trapping sites and promoting hydrogen enrichment.Fractography shows the straight pipe has large,deep dimples and a relatively flat fracture surface,while the cold-bent pipe exhibits fine,shallow dimples and pronounced necking due to strain hardening-induced ductility loss,indicating increased brittleness.The research results demonstrates that cold working significantly amplifies the hydrogen embrittlement susceptibility of L245NS steel,providing quantitative guidance for process optimization and in-service monitoring of cold-bent pipeline sections.