Unraveling effects of CO2 and H2S on the corrosion behavior of electroless Ni-P coating in CO2/H2S/Cl- environments

Generally, various materials and structural components are susceptible to failures. For example, corrosion is a cause of failure in carbon steel, which is used in most steam-assisted gravity drainage operations. This can be attributed to the presence of corrosive species in the well, such as carbon dioxide, hydrogen sulfide, and chlorine compounds. This has led to the deployment of various anti-corrosion measures like corrosion-resistant alloys. Unfortunately, application of these measures is limited considering the high initial investment required. Therefore, developing cost-effective corrosion prevention measures is highly desirable.

Among the available anti-corrosion coatings, electroless Ni-P coating has attracted significant attention from researchers, owing to its favorable mechanical and corrosion resistance properties. Corrosion performance of Ni-P coating has been investigated in various environments. For example, in acidic environments, high-phosphorous Ni-P coating exhibits superior corrosion resistance. However, most of the previously conducted research concerning the corrosion performance of Ni-P coating relied mainly on the presence of chlorine, acids, carbon dioxide, and hydrogen sulfide mostly at room temperature. Therefore, assuming the same results for corrosion performance at an elevated temperature may not give the desired outcome. As such, understanding the corrosion performance of Ni-P at high temperatures is highly desirable.

To this note, University of Alberta researchers Dr. Chong Sun, Professor Hongbo Zeng, and Professor Jing-Li Luo studied the corrosion mechanism in Ni-P coating, specifically in harsh environments. Their main objective was to ascertain the feasibility of using Ni-P coating as a corrosion-preventive measure in high-temperature and -pressure environments. Generally, their work was based on both theoretical and experimental approaches for analyzing the corrosion behaviors of Ni-P coatings. Consequently, it was necessary to investigate the defects in Ni-P coatings and their influence on corrosion resistance.

Various methods (i.e., weight loss test, water chemistry analysis, and surface characterization) were used to investigate the effects of carbon dioxide and hydrogen sulfide on the corrosion behavior of Ni-P coating. This entailed conducting laboratory scale and on-site corrosion tests under varying environmental conditions. Eventually, they proposed a corrosion model to analyze the degradation effects of Ni-P coatings in harsh environments.

The authors observed that the Ni-P coating exhibited significant corrosion resistance in a carbon dioxide environment as compared with hydrogen sulfide and H₂S-CO₂ environments. On the other hand, the coexistence of H₂S-CO₂ resulted in remarkable effects on the degradation of the coating. This was attributed to blocking the formation of the protective oxide film by the sulfide species. Alternatively, hydrogen sulfide significantly enabled electrolyte penetration in the micro-defects, thus resulting in the corrosion of the substrate.

In summary, the Canadian scientists reported the effects of carbon dioxide and hydrogen sulfide on the corrosion behavior of electroless Ni-P coatings in different environments. Considering the obtained results, the study provides vital information that will advance corrosion prevention in structures and materials, thus ensuring durability and excellent functionality.

The work was published in March 2019 in the Corrosion Science journal. The samples were provided by RGL Reservoir Management Inc., an international oil and gas engineering, manufacturing, and service company specializing in sand control and flow control technologies. RGL Reservoir Management Inc. also provided industrial insight for the research project and testing material and condition. Research funding was provided by Natural Sciences and Engineering Research Council of Canada/RGL Reservoir Management Inc. Collaborative Research and Development Grants.