Study on the sealing performance of the K-type metal sealing ring of the subsea Christmas tree

The Christmas tree tubing hanger serves as a channel for oil, gas, and electrical flow, supporting the tubing string and sealing the annular space. The sealing performance of the tubing hanger is important for ensuring the safe operation of the subsea Christmas tree. The effect of precompression load on the performance of the K-type metal seal was simulated and analyzed through two-dimensional and three-dimensional contact models, and the impact of oil and gas operating pressures, temperatures, and the elastic modulus on the sealing performance of the K-type metal seal was investigated. According to the results, the maximum error between the theoretical calculation and the finite element method for the contact stress on the exterior of the K-type metal seal was 4.72%. The contact stress of the sealing ring increased at higher precompression and internal pressure. Temperature had a minimal impact on the sealing performance of the seal, while reducing the elastic modulus of the sealing ring decreased its equivalent stress. Finally, static pressure and pressure cycling tests were conducted in compliance with the API 6A standard. The tests confirmed that the maximum sealing pressure of the K-type metal seal satisfied the requirement of a 1.5-fold working pressure and validated that the seal exhibited good sealing performance in oil and gas pressure-temperature cycling conditions. The K-type metal seal was self-tightening, where the pressure enhanced the sealing effect, Hertz contact theory can be used for preliminary parameter design in the early stage, and the sealing performance can be further verified through elastic-plastic finite element method and experiments.