Hydrogen being sustainable and renewable energy source has become crucial to achieve net zero commitment worldwide by 2050-2070. Presently, efforts are being made to transport hydrogen in pure and/or blended form with natural gases [1]. Trucks and ships do not appear to be viable transporting options compared to pipeline systems (capacity of 100,000 kg per hour at a cost of 0.1–1.0 USD/kg/km) [1]. Interaction of pipeline steel with hydrogen can lead to serious issue of hydrogen embrittlement (HE), which has a serious deteriorating impact on the mechanical properties, such as elongation and fracture toughness [2]. Welding being a critical process for hydrogen transportation via pipeline has received less attention and the effect of HE becomes more detrimental in case of welded pipeline [3].

In the current study, X60 grade pipeline steel has been welded using Manual metal arc welding (MMAW) process and further subjected to hydrogen environment via electrochemical route. The microstructure and mechanical properties of as-received, welded and post-welded steels have been evaluated using SEM (including EBSD) and hardness/tensile tests, respectively. The hardness of the steel was found to increase after welding; however, heat treatment led to decline in the hardness of the steel. Hydrogen charging resulted in decrease in ductility of X60 steel by 40-50 % and 80-85 % before and after welding, respectively. However, post-weld heat treatment showed an improvement, with 60-70 % loss in ductility, after hydrogen charging as compared to welded condition. Fractography analysis confirmed the presence of cleavage features after hydrogen charging. This study establishes the relationship between the microstructure (phase fraction, grain size, etc) with mechanical properties of X60 steel before and after hydrogen charging and the same will be discussed.

References

[1] D. Mahajan, T. Kun, T. Venkatesh, P. Kileti, and C.R. Clayton, Energies, 2022, 10, 3582.

[2] G. Pluvinage, International Journal of Pressure Vessels and Piping, 2021, 190, 104293.

[3] H. Li, N. Ranming, W. Li, H. Lu, J. Cairney, and Y. Chen, Journal of Natural Gas Science and Engineering, 2022, 105, 104709.