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Hydrogen is of great significance for replacing fossil fuels and reducing carbon dioxide emissions. The application of hydrogen mixing with natural gas in gas network transportation not only improves the utilization rate of hydrogen energy, but also reduces the cost of large-scale updating household or commercial appliance. This paper investigates the necessity of a gas mixing device for adding hydrogen to existing natural gas pipelines in the industrial gas network. A three-dimensional helical static mixer model is developed to simulate the mixing behavior of the gas mixture. In addition, the model is validated with experimental results. Parametric studies are performed to investigate the effect of mixer on the mixing performance including the coefficient of variation (COV) and pressure loss. The research results show that, based on the, the optimum number of mixing units is three. The arrangement of the torsion angle of the mixing unit has a greater impact on the COV. When the torsion angle θ = 120°, the COV has a minimum value of 0.66%, and when the torsion angle θ = 60°, the COV has a maximum value of 8.54%. The distance of the mixing unit has little effect on the pressure loss of the mixed gas but has a greater impact on the COV. Consecutive arrangement of the mixing units (Case A) is the best solution. Increasing the distance of the mixing unit is not effective for the gas mixing effect. Last but not least, the gas mixer is optimized to improve the mixing performance.

The high‐temperature creep–fatigue (CF) interaction on the service damage of P92 welded joint was uncovered based on the evolution of local creep behaviour by nanoindentation. The creep resistance and high‐angle grain boundary (HAGB) distributions of the different regions of welded joint were investigated for the specimens under individual creep (stress relaxation [RS]), fatigue and CF loadings interrupted at lifetime fractions of 10%, 20%, 30%, 60% and 100%. According to structure evolution including the changes of HAGB and dislocation densities during high‐temperature deformation, the local variation mechanism of creep behaviour at different microstructural zones was systematically discussed.

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