Study of Hydrogen Embrittlement of steels for the Oil & Gas sector through electrochemical methods

The objective of this study is to investigate the phenomenon of hydrogen embrittlement in steels used in the Oil & Gas sector, with the aim of ensuring the safe transportation and storage of hydrogen gas in existing infrastructures. The materials under investigation are T95 and P110 steels, according to the API 5CT specification, which sets the requirements for pipes used in oil wells. These steels are low-alloy and micro-alloyed, with a tempered martensitic microstructure, offering high resistance to extreme operational environmental conditions due to their low impurity content. Firstly, a comprehensive characterization of the steels was performed, focusing on aspects such as microstructure, hardness, tensile mechanical properties, and fracture mechanics. Additionally, hydrogen diffusion in the steels was measured using the Devanathan-Stachurski method. The determined hydrogen diffusion coefficient was then used in combination with Finite Element Methods to predict the optimal pre-charging conditions necessary to achieve a uniform distribution of hydrogen concentration within the samples later subjected to mechanical testing. Tensile and J-integral tests were performed on the hydrogen pre-charged samples to evaluate the HE on toughness related mechanical properties. The macroscopic variation in mechanical properties, namely toughness, was correlated with the microstructure and the different fracture morphology in the samples exposed pre-charged with hydrogen. In light of this, the obtained results were compared with those of two X60 steels with different microstructures, also used in the O&G sector. This study provides valuable insights into the effects of hydrogen on material properties, which are crucial for improving the safety and efficiency of O&G infrastructures.