Corrosion resistant materials in high-pressure high-temperature oil wells: An overview and potential application of complex concentrated alloys.

• Mitigation of external and internal corrosion behaviour in high pressure high temperature (HPHT) oil wells based on material design and selection. • Main challenges associated with structural and stainless steels used in HPHT are sweet and sour corrosion. • Hydrogen ingress in HPHT results in embrittlement, stress induced corrosion cracking and corrosion fatigue leading to metal dissolution and final material breakdown in conventional dilute alloys. • Equiatomic and non-equiatomic complex concentrated alloys and coatings have better resistance to hydrogen embrittlement, stress corrosion cracking and corrosion fatigue than most conventional alloys in simulated HPHT environments. • Implications of potential applications of complex concentrated alloys such as cost and scalability issues are imminent. This review discusses potential applications of complex concentrated alloys (CCAs) for mitigating sweet and sour corrosion in high-pressure, high-temperature (HPHT) wells with concentrated chlorides, carbon dioxide and hydrogen sulphide. The harsh oil and gas environments lead to severe components failures through sour corrosion, sweet corrosion, hydrogen induced cracking, stress corrosion cracking and corrosion fatigue. Many of these failures are material driven. Hence the domain of complex concentrated alloys are being explored to reduce the severity of failures in the oil and gas industry, especially in HPHT zones. The CCAs possess high thermal stability, the balance of strength and ductility resulting from complex deformation mechanisms, and high creep resistance due to sluggish diffusion. These properties are driven by the design philosophy: high entropy and enthalpy of mixing, severe lattice distortion, sluggish diffusion, chemical ordering, and the cocktail effects. These effects allow for greater flexibility and many degrees of freedom which is absent in conventional one principal element-based materials. Most CCAs have shown excellent and superior mechanical and corrosion properties in some of the environments of currently used corrosion-resistant alloys in the oil and gas industry. This review highlights recent literature on potential high entropy alloy chemistries, microstructural features and their effects on mechanical and corrosion properties, and areas for future research directions. [ABSTRACT FROM AUTHOR]