Hydrogen embrittlement of pipeline steels under gaseous and electrochemical charging: A comparative review on tensile properties

Hydrogen embrittlement (HE) has proven to be one of the most serious threats to the mechanical properties of gas pipeline steels, which are considered the primary means of hydrogen energy transportation. Despite many efforts to address this issue through various mechanical testing methods such as tensile, fatigue, and fracture tests, there is still a lack of studies comparing the results of such tests under different hydrogen charging conditions. This research focuses on comparing the slow and high strain rate tensile properties of pipeline steels in gaseous and electrolytic environments. To achieve this goal, various ex-situ and in-situ hydrogen charging setups, as well as adsorption and absorption processes in gaseous or aqueous medium, are discussed and illustrated. A comparison of different influencing parameters in two charging methods on tensile properties-including charging variables, strain rate, and microstructure-is made and summarized. Although the results of ongoing research up to now state that HE of pipeline steels should theoretically be independent of charging methods as long as equal hydrogen fugacity is obtained on the surface, due to the complexity of adsorption events in addition to mechanical loading, reaching such a condition seems to be challenging. Overall, it can be inferred that any alteration increasing the content of hydrogen in the steel microstructure would also enhance the degree of HE. Further studies on the effects of adsorption parameters and the initial microstructure of pipeline steels are still required to gain a clearer view of HE phenomena in the two charging approaches and in the presence of tensile loading.