Study on failure mechanism of rubber sealing rings for high pressure equipment in ultra high H2S gas fields

In this study, the failure mechanisms of fluoroether rubber (FM) and hydrogenated nitrile butadiene rubber (HNBR) seal rings employed in two feedstock gas coalescers operating within an ultra-high H₂S gas field were investigated. Both seal rings experienced breakage and failure after 30 days of operation. To analyze the failure mechanisms under ultra-high H₂S conditions, a high-temperature and high-pressure (HTHP) dynamic autoclave, along with an O-ring sealing fixture, was employed to replicate on-site conditions. Corrosion experiments were conducted on FM and HNBR under simulated conditions for 7 days. The progression of performance and failure behavior was assessed through comparative analyses of mechanical performance, fracture morphology, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric (TG) results. These analyses were carried out on samples in their initial state, after 7 days under simulated conditions, and following 30 days of field operation. Initial evaluations revealed ductile fracture characteristics for both FM and HNBR. After 7 days of simulated testing, no breakage was observed, and the thermal stability and mechanical properties of both materials remained largely unchanged. The tensile fractures maintained their ductile nature, although resistance to compression set declined, and porous defects were detected. Additionally, HNBR exhibited a slight increase in tensile strength. After 30 days of service, both FM and HNBR demonstrated brittle fracture failure accompanied by significant reductions in mechanical properties and thermal stability. The tensile strength decreased to 1.96 MPa for FM and 4.09 MPa for HNBR, while elongation at break declined to 46.2% and 59.9%, respectively. FTIR analysis indicated that the molecular chains of FM experienced breakdown and degradation, while those of HNBR underwent additional crosslinking. The deterioration in mechanical properties is primarily attributed to molecular chain degradation, crosslinking, and breakage, highlighting the impact of ultra-high H₂S exposure on these materials.