Assessment of Coatings in High pCO2 Environment for Pipeline Internal Coating Application

Offshore pipeline transportation of non-treated, high CO2-containing gas stream imposes significant challenges due to the anticipated high corrosion rate that could disqualify the economic use of the carbon steel material. Alternative solutions are required in order to find the most cost effective system in transporting CO2 over long distances particularly for offshore application. Several solutions exist which include application of corrosion resistance alloy (CRA), cladded or CRA- or non-metallic-lined pipes and internal coatings. This paper is focused on the assessment of the physical properties of internal coating for pipeline transporting high CO2 gas in the dense phase under the steady state operational condition. The performance of commercially available epoxy-based coatings exposed to high pCO2 has been studied as per NACE TM0185. Three coatings from different manufacturers were tested in an autoclave at temperature of 25°C and 80°C and partial pressure of CO2 (pCO2) 80 bar and 150 bar respectively for 28 days. The coatings were evaluated for the presence of blistering, adhesion to metal and between coats, hardness and resistance to undercutting and creep. The results have shown that all the 3 coating systems did not show significant physical degradation under the test conditions. However, one of the coatings showed a reduction in the pull off adhesion at high temperature which indicates some degradation of the coating under the imposed test conditions. The results from the lab testing have shown that commercially available coatings are able to perform well in dense CO2 phase within the defined test parameters. However, in order to reliably predict the service life of the coatings material, their performance when subjected to the variation in operation, e.g., decompression, as well the analytical methods that can give representative performance measures between laboratory test and service life, are critical and the subject of this review.