Investigating the effect of microstructure difference on hydrogen embrittlement sensitivity of X80 pipeline.

This work aims to reveal the complex relationship between hydrogen embrittlement behavior and microstructure of X80 pipeline. The influence of the microstructure difference between X80 pipeline base metal and weld metal on the hydrogen induced damage and hydrogen permeation behavior of the material are investigated by fracture toughness testing, fatigue crack growth rate testing and hydrogen permeation testing. The metallographic structures are analyzed by scanning electron microscope and electron back scatter diffraction. The fatigue crack growth rate test results that fatigue crack growth rate of weld metal is slower than that of base metal in both hydrogen-containing and hydrogen-free environment. The metallography shows that this phenomenon is due to the action of fine-grain strengthening. However, the results of fracture toughness test and hydrogen penetration test show that the hydrogen embrittlement sensitivity of weld metal is higher than that of base metal. This is mainly caused by the more uneven microstructure distribution, the higher differences of local grain size, and the formation of micro-pores and microcracks in some areas for the weld. These results are expected to be used to avoid the risk of hydrogen induced embrittlement failure in the pipeline during hydrogen transportation.