Study of Hydrogen Embrittlement of steels for the Oil & Gas sector through Electrochemical Methods

Introduction The objective of this study is to investigate hydrogen embrittlement in steels used in the Oil & Gas sector, with the aim of ensuring the safe transportation and storage of hydrogen gas within existing infrastructures. The materials examined are T95 and P110 steel grades manufactured according to the API 5CT specification for casing and tubing applications. These low-alloy and micro-alloyed steels exhibit a tempered martensitic microstructure and high resistance to severe service environments due to their low impurity content. Understanding their susceptibility to hydrogen-assisted damage is essential for the transition toward hydrogen-based energy systems and for assessing the compatibility of current infrastructure with hydrogen service. Material and Methods A comprehensive characterization of the steels was performed, including microstructural analysis, hardness measurements, tensile testing, and fracture mechanics characterization. Hydrogen diffusion was measured using the Devanathan–Stachurski electrochemical permeation method. The experimentally determined hydrogen diffusion coefficients were implemented in a Finite Element Model to define the optimal pre-charging conditions required to achieve a uniform hydrogen concentration prior to mechanical testing. Subsequently, tensile and J-integral tests were conducted on hydrogen pre-charged specimens to evaluate the influence of hydrogen on strength and fracture toughness. Fractographic analyses were carried out to correlate mechanical performance with fracture morphology and microstructural features. Results Hydrogen diffusion coefficients were successfully determined for both steel grades, enabling the identification of suitable charging conditions. Mechanical testing revealed a reduction in ductility and fracture toughness in hydrogen pre-charged samples compared to uncharged conditions. The extent of degradation differed between T95 and P110, reflecting microstructural and compositional variations. Fractographic observations highlighted a transition toward more brittle fracture features in the presence of hydrogen. The experimental findings demonstrated a clear correlation between hydrogen content, microstructure, and mechanical response. Discussion The results confirm the susceptibility of tempered martensitic steels to hydrogen-assisted degradation, with differences attributable to microstructural characteristics and alloying content. The integration of experimental diffusion data with numerical modelling proved effective in defining reliable pre-charging procedures. A comparison with X60 steel, characterized by a different microstructure and widely employed in the Oil & Gas sector, further emphasized the role of microstructure in hydrogen embrittlement resistance. This study provides insights into the mechanical behaviour of pipeline steels in hydrogen environments, supporting the assessment of structural integrity and contributing to improved safety and reliability of oil and gas infrastructures.