Hydrogen Embrittlement Sensitivity of low alloy and micro-alloyed steels for Oil & Gas applications

The safe transportation and storage of hydrogen in existing Oil & Gas infrastructures require a thorough understanding of hydrogen embrittlement (HE) in materials employed for these purposes. This study investigates the effects of hydrogen on the mechanical behaviour of steels widely used in the Oil & Gas sector, including two API 5CT grades for casing and tubing applications (T95 and P110) and two API 5L X60 pipeline steels characterised by different microstructure and produced in different periods. The investigated materials are low-alloy and micro-alloyed steels with distinct mechanical properties and microstructures, systematically characterized through microstructural analysis, hardness measurements, tensile testing, and fracture mechanics evaluation in inert environment. Hydrogen diffusion coefficients were determined by means of electrochemical permeation tests based on the Devanathan Stachurski method at 20°C and 40°C. Steel specimens were pre-charged with hydrogen by means of galvanostatic polarisation in solution with “poison” of hydrogen recombination using two different values of cathodic current density. The results of hydrogen diffusion tests were implemented into Finite Element Modelling to simulate hydrogen concentration profiles and define optimal pre-charging conditions for mechanical testing. J-integral fracture toughness tests were performed on hydrogen pre-charged specimens under two different hydrogen contents to assess the impact of hydrogen embrittlement on mechanical performance. The resulting degradation in toughness was correlated with microstructural features and fracture morphologies, highlighting the role of microstructure in governing hydrogen transport and embrittlement behaviour. The combined experimental–numerical approach provides a consistent methodology for identifying alloys more susceptible to hydrogen exposure, revealing a markedly higher sensitivity of the P110 steel compared to the other investigated grades, while one of the API 5L X60 steels exhibited comparatively higher resistance to hydrogen-induced degradation.