Failure mechanism of sealing rubber exposed to supercritical CO₂ during rapid depressurization based on equivalent thermo-mechanical coupling damage model

The widespread application of supercritical carbon dioxide (S-CO₂) in carbon capture, utilization, and storage (CCUS) technologies imposes increasing requirements on pipeline sealing materials. As crucial sealing components, rubber O-rings are prone to damage during the rapid depressurization process due to the high permeability of S-CO₂ and sudden pressure changes, leading to sealing failure. However, the synergistic mechanism regarding deformation, diffusion, and material damage in rubber O-rings with cavity defects when permeated by S-CO₂ during rapid depressurization has not been thoroughly investigated. To address this issue, this study develops an equivalent coupled thermo-mechanical damage model by utilizing the similarity between Fick’s diffusion law and Fourier’s theory of heat conduction. This model systematically investigates the diffusion-deformation coupling behavior of cavity-containing rubber O-rings, considering the effects of the cavity position, orientation, depressurization rate, and material properties on the internal strain of the cavity. The results reveal that centrally positioned cavity in the compressive stress field exhibits lower strain compared to the cavity offset by 0.4 mm. A relatively fast depressurization rate gives rise to a greater transient pressure difference, inducing elevated strain levels that escalate the failure risks of the O-ring with a cavity. Material selection plays a critical role: NBR shows better sealing performance than EPDM and SBR, with EPDM experiencing cavity rupture under S-CO₂ rapid depressurization. These findings provide theoretical breakthroughs and methodological innovations for sealing system design in S-CO₂ based CCUS infrastructure, advancing both sealing reliability and operational robustness to facilitate CCUS technology development.