Investigating Metallurgical Factors Affecting Corrosion of Pipelines used for Supercritical CO2 Transport

RIP2025-00118: To reduce greenhouse gas emissions, CO2 must be captured, transported, and stored, and this process is known as carbon capture, utilization, and storage (CCUS). Pipelines are the most feasible method for transporting large volumes of captured CO2 to storage facilities. Although the United States has an extensive pipeline network, an additional 110,000 km of new pipeline must be constructed by 2050 to achieve net-zero emissions goals. However, the captured CO2 stream may contain various impurities, such as SOx, NOx, and H2O, which can cause severe corrosion in carbon steel pipelines, posing significant challenges in pipeline design and operation.

While there is extensive literature on corrosion in pipeline steels related to CCUS applications, key gaps remain in understanding the role of metallurgical factors in CO2 corrosion. Many existing studies focus on the CO2 corrosion behavior of specific pipeline grades, such as API 5L X65, while neglecting variations in alloy composition and microstructure. However, it is known that microstructure and composition can have a significant impact on the corrosion response of a metal. In addition, there have been limited studies on pipeline weld corrosion in CCUS-relevant environments, even though welds may corrode preferentially due to variations in microstructure and local hardness.

The current project investigates the role of alloy composition and microstructure on the corrosion behavior of welded pipeline steels in CCUS-relevant CO2 environments. In this study, the base metal of an electric resistance welded X65 pipeline steel was corrosion-tested using a supercritical CO2 environment containing 385 mL of H2O. During corrosion testing, the steel samples were exposed to two extreme corrosive conditions within the test environment, i.e. some samples were submerged in the H2O while others were suspended above the H2O. The corrosion-tested samples were characterized through electron microscopy and diffraction techniques to reveal the effects of metallurgical factors on corrosion products, corrosion rate and the corresponding corrosion mechanisms. This work details the recently established CO2 testing capability and presents key lessons learned from CO2 corrosion testing performed thus far.