Effect of high-temperature acid aging on microstructure and mechanical properties of PEEK

Polyether ether ketone (PEEK) has replaced some parts in downhole applications in the oil and gas industry, demonstrating a huge potential to eliminate the corrosion of metallic parts, especially those that are employed in acidic atmospheres and high temperatures, such as liners, impeller, and sealing applications. However, the performance of PEEK in real downhole conditions remains unknown. In this study, we therefore investigated the evolution of the microstructural, chemical, and mechanical properties of PEEK subjected to hydrochloric acid (HCl), which is the main acid used in downhole applications, at high temperatures. PEEK films with thicknesses of 250, 125, and 50 μm, were saturated in HCl at 100 °C. Moreover, the hardness, elastic modulus, yield, and ultimate strength for the samples with a thickness of 50 μm increased owing to the formation of new crystallites and enhanced chain mobility inside the PEEK microstructure. However, the changes in the mechanical response of the thicker samples were insignificant owing to the difficulty of HCl diffusion in their subsurface layers, especially with the increased crystallinity of the surface layer upon exposure to acids.