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The Brazilian offshore oil and gas industry uses flexible pipes to transport water, oil, and/or gas. Currently, the high concentration of acid gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S), in Brazilian pre-salt wells has been introducing new challenges to these pipes. The acid gases may migrate from the bore to the annulus of these structures, forming a corrosive environment that can induce the steel armors’ failure by SCC (Stress Corrosion Cracking) or HIC (Hydrogen Induced Cracking). Hence, predicting the gas composition in the annulus is of fundamental importance to ensure the safe operation of flexible pipes. However, this prediction involves complex gas permeation analyses through the layers of these pipes. For instance, the permeation rate depends on temperature, gases partial pressures, and the free volume distribution. Therefore, new tools are required to understand better the fluid permeation between the flexible pipes’ layers. Therefore, this paper presents and compares two finite element (FE) models to predict the annulus composition of flexible pipes. Both models consider the temperature gradient effects on the layers’ material properties. On the one hand, the first approach deals with a two-dimensional model that considers helical layers as rings. So, the shielding effect is simplified. On the other, the second develops a complete three-dimensional model of the cross-section geometry. The results indicate that, while being faster, the two-dimensional approach shows higher concentration results than the three-dimensional approach. Furthermore, the difference between the two approaches suggests that the shielding provided by the helicoidal wires is relevant. |
