Effect of supercritical CO2 permeation on Poly(vinylidene fluoride) at high temperatures and pressure applied to offshore flexible pipes

ABSTRACT Flexible pipelines (FP) are widely applied in the offshore oil and gas industry and can operate with high pressures and temperatures, often with high CO 2 content, such as in the Pre-salt fields. In this scenario, one of the main polymeric materials employed in the internal sealing barrier is the Poly (vinylidene fluoride) due to its high chemical resistance and thermal stability. Therefore, the objective of this study was to assess the influence of supercritical CO 2 permeation through PVDF, considering the material's thermal stability and its suitability for high-temperature applications. The tests were performed at 80, 100, and 120 °C, all at 200 bars of pressure feed, from which permeability, diffusivity, and solubility (P, D, S) data were obtained. The samples were characterized via macrography, hardness tests, FT-IR and DSC analysis to evaluate mechanical and thermal properties, and phase composition before and after the permeation tests. The temperature influence on the transport coefficients is correlated with the material microstructure and a comparison with literature data is presented. The results showed an increase of almost 72% on the values of P and D coefficients with an increase of 30 °C on the permeation temperature test. In contrast, there was a decrease of 13% for the S coefficient, where CO 2 density played a key role. A reduction on the degree of crystallinity from 68% for untested samples to a minimum of 55% was also observed, showing that the sc-CO 2 affects the polymer barrier properties negatively.