Update of DNV Recommended Practice RP-J202 with Focus on CO2 Corrosion with Impurities

Abstract

Abstract This paper presents results from experimental testing program designed to fill knowledge gaps identified during the process of making a recommended practice for design and operation of CO2 pipelines. This testing program has been executed as part of the second phase of the CO2PIPETRANS Joint Industry Project (JIP). The objective of the corrosion work package was to determine the mechanism and corrosion rate in dense phase CO2 for various impurities including O2, SOx, NOx, and H2S with and without free water. The experimental work was carried out using a specialised rotating autoclave for carrying out CO2 corrosion experiments, which gives a good mixing and disturbed flow around the test specimen. The test specimens used in the set-up were selected grades of carbon steel and stainless steel, typically used as pipeline materials. The experiments were carried out at two different temperatures, that is 4 °C and 50 °C, at a pressure of approximately 100 bar. Different combinations and concentrations of the impurities O2, SO2, H2S, NO, NO2 were added to the pure CO2 with water concentrations of 50 and 500 ppmv. Published quality recommendations from the DYNAMIS were used as a starting point to decide the concentrations of the impurities to be tested. After the corrosion testing the metal loss was determined and the corrosion rates were calculated. The effect of the impurities on the solubility limits of water, which results in increased corrosion rates, are presented. Further, how to use the results in order to define a safe operating window for dense phase CO2 containing various impurities is discussed. Based on the experimental results, there are still uncertainties related to water solubility and the corrosion mechanisms in the presence of impurities. Further work is required to narrow the uncertainty, however, the uncertainty can be overcome with an appropriate design philosophy. The results are a step in the refinement of the operational limits for different impurities found in pipelines carrying anthropogenic CO2 and the moisture content. The results serves as input for updating DNV-RP-J202 “Design and Operation of CO2 pipelines” [1] to provide improved guidance on safe and reliable design, construction and operation of pipelines intended for large scale transportation of CO2. Increased understanding of corrosion mechanisms furthermore leads to more cost effective pipeline design and design of CO2 conditioning processes.