Methodology Proposal for Assessing SCC-CO2 Susceptibility in Flexible Pipe Armor Wires

Abstract Oil and gas exploration in ultra-deep waters imposes several challenges for the equipment and materials employed due to the extreme pressure and temperature conditions, as well as the presence of CO2 and contaminants (H2S). In Brazil, oil is extracted mainly in the pre-salt layer (under a massive water depth), and the production is transported mostly through flexible pipes (FP), which connect the wells to the processing units. Considering the specific challenges of the Brazilian pre-salt and the extreme conditions faced by the tensile armors of these flexible pipes, it is crucial to carry out detailed studies on their limits of use. Additionally, new methodologies that provide faster and more assertive responses are required to assess the susceptibility to stress corrosion crack (SCC) induced by carbon dioxide (CO2). Accelerated small-amplitude cyclic loading or ripple loading test is a well-consolidated methodology applied to corrosion-resistant alloys (CRAs), which naturally have a passive oxide layer that protects them against general corrosion. The rupture of this layer exposes the metal substrate to the environment, enabling the phenomenon of SCC-CO2. In contrast to CRAs, carbon steels do not have this passive layer, so to assess the susceptibility to SCC-CO2, it is necessary to form a corrosion film through the natural corrosion process of the steel-H2O-CO2 system. This work aims to describe a methodology for assessing the susceptibility to SCC-CO2 of high-strength carbon steels (material used in the FP’s tensile armors) using accelerated tests applying small-amplitude cyclic loadings. The proposed methodology proved to be a satisfactory method for assessing susceptibility to CO2 cracking, showing results like traditional tests (such as four-point bending, 4PB) but with a significantly shorter test time.