Corrosion and Cracking Performance of Stainless Steels and Nickel Alloys in CCS Environments

Carbon Capture and Storage (CCS) technology which involves capturing CO₂ and injecting into geological formations is seen as a focus area for reducing CO₂ emissions and sustainable future. One of the key challenges for CCS is material selection for construction of wells for injection and storage where the materials can be subjected to a complex environmental mix with various impurities present in the CO₂ stream along with different phases within the well. Knowledge and understanding of corrosion and cracking performance of various materials in different environmental conditions relevant to CCS wells can provide a basis for material selection. Being a relatively new field there is an effort to build up knowledge base via testing, characterizing materials suitable for long term well service.

In this study, martensitic, supermartensitic and super duplex stainless steels along with Age Hardenable (AH) Nickel Alloy were tested for both corrosion and cracking performance in different CCS type environments. The testing simulated exposure to injected fluid phase, interface between injected fluid and water phase and completely immersed in water phase. The details of testing performed results obtained along with discussions is presented so that it can provide guidance on material compatibility for some of the CCS environments.

Carbon Capture and Storage (CCS) is considered an important technology that can aid lowering CO₂ emissions especially with use of fossil fuels such as oil and gas. In this process, the CO₂ captured from industry sources are injected downhole into geological formations such as depleted oil and gas wells. To ensure safe long-term storage, the material selection for construction and design of CCS wells is very important.

The upstream oil and gas industry has lot of experience with selection and long-term equipment use in presence of CO₂ for different wells such as production, gas injection, Enhanced Oil Recovery (EOR) etc. However, one of the key challenges with CCS is the impurity content. Depending on the source from which the fluid stream is captured, it could have a range of impurities such as O₂, H₂S, NO_x, SO_x etc. Additionally, the same storage well could have multiple sources of capture with different concentrations of these impurities. Some of these impurities could react to form various byproducts including acids which can lead to a low pH environment increasing risk for corrosion including localized corrosion for CRA (Corrosion Resistant Alloys) materials.^1-4 This is quite different than the industry experience such as in gas injection or EOR where a known well controlled CO₂ composition would be used throughout the life of the well and typically impurities such as O₂, NO_x, SO_x are not encountered while in case of H₂S, the industry has good experience and testing, with material selection guidelines such as NACE MR0175/ISO 15156.⁵