Numerical analysis of brittle strength of welded pipelines with corrosion metal loss in transportation of blends of natural gas with hydrogen

Abstract As part of the analysis of the possibility of using the Ukrainian gas transportation system for transporting blends of natural gas and hydrogen, the peculiarities of the influence of hydrogen degradation of pipe steel on the brittle strength of girth welds and local corrosion metal losses were considered. For this, they were used the methods of finite-element modeling of the stress-strain state of structures during welding and subsequent operation loading along with advanced criteria of macroscopic fracture of a body with a crack. The results of predicting the safety factor for a typical welded part of a main gas pipeline with postulated surface cracks during the transportation of gas-hydrogen blends of various compositions showed that the most susceptible to brittle fracture are the weld metal and heat affected zone. But with regard to the fatigue strength of welded joints under the action of cyclic loading by internal pressure or bending moment, larger stress intensity factor ranges in the heat affected zone cause a more significant reduction of the residual safety factors. Local corrosion damage during the transportation of gas-hydrogen blends had a considerable negative impact on pipeline reliability, particularly when material properties experienced hydrogen degradation and a decrease in fracture toughness. However, this effect could be mitigated by adjusting the operating load accordingly.