Ti-6Al-4V and Ti-6Al-4V-0.1Ru alloys in oil and gas exploration: A review of performance and hydrogen embrittlement

Titanium alloys are essential structural materials for advanced engineering applications. Among these, Ti-6Al-4V stands out as the most widely used titanium alloy for aerospace, biomedical and chemical industries. Nonetheless, these alloys are susceptible to hydrogen embrittlement in the harsh environments of offshore oil and gas exploration, characterized by high pressure, temperature, acidity, and exposure to chlorides, CO2, and H2S. Since hydrogen diffusion in beta-Ti phase is significantly higher than in the alpha-Ti phase, the impact of hydrogen on the mechanical properties of Ti-6Al-4V is strongly dependent on its microstructure. The hydrogen embrittlement effect is further more pronounced, under both monotonic and cyclic loading, in microstructures with a higher volume of continuously distributed beta-Ti phase. Drastic reductions in ductility, a lower fatigue crack growth threshold, and higher fatigue crack propagation rates are the primary consequences of hydrogen embrittlement. Ti-6Al-4V-0.1Ru has emerged as a promising alternative to overcome the challenges of applications in oil and gas exploration due to its enhanced corrosion resistance, specifically against crevice and stress corrosion cracking, which can mitigate the effect of hydrogen embrittlement. The primary objective of this review is to comprehensively assess the electrochemical and mechanical behavior of Ti-6Al-4V and Ti-6Al-4V-0.1Ru alloys, including the ELI versions, under harsh conditions, particularly those involving hydrogen exposures. Given the growing use of titanium alloys in deep water oil and gas exploration, a comprehensive understanding of their performance is essential for ensuring secure exploration.