Effects of O-ring defects on sealing performance of a pressure-testing valve assembly for seabed coring

This study focuses on two typical surface defects—back-cut defects and flow-mark defects—that occur frequently on O-rings used in the pressure-measurement valve assembly of a pressureretaining coring system for offshore drilling rigs. A nonlinear finiteelement contact model of the O-ring was developed based on the Mooney–Rivlin hyperelastic constitutive law. Under an assembly pre-compression ratio of 20%–30% and a working pressure of 8–22 MPa, the effects of defect length and depth on interfacial contact pressure, contact continuity, and the sealing pressure margin were investigated. In addition, a dimensionless leakage index J was proposed based on the area distribution of contact pressure. The results indicate that back-cut defects significantly reduce the contact pressure in the sealing region and promote the expansion of low-pressure zones. As the back-cut length increases from 0.94 mm to 4.71 mm, the overall P95 contact pressure decreases by 52.4%, while the proportion of the zero-pressure segment g0 increases by 15%. Increasing the working pressure amplifies the sensitivity of sealing performance to variations in back-cut length. By contrast, flow-mark defects mainly cause a localized reduction in contact pressure in the vicinity of the defect, whereas the contact region remains continuous. For this valve assembly, the O-ring assembly pre-compression ratio is recommended to be controlled at approximately 28%. This work provides a theoretical basis for evaluating defect-induced sealing-failure risk in practical applications and supports the establishment of critical criteria for sealing failure.