By using Hertz theory, the location of yielding and the expression of contact center pressure are obtained after interference fit of the spherical/conical seal structure of premium threaded connections. Combined with the structural characteristics of premium threaded connections, the expression of contact pressure is calculated. The magnitude of contact length and contact pressure of spherical/conical seal for premium threaded connections are calculated by using the Herz theory and the results are compared with those obtained by the finite element method. According to the calculation results, a CBS4 premium threaded connections with a new spherical/conical sealing structure is designed, and finally a machining test is conducted to prove the feasibility of the method. New premium threaded structure is obtained with small errors compared to the results of Hertz theory and finite element simulations, which is similar to experimental tests. The research results are applicable to a certain range of tubing or casing premium thread connector.

Keywords: Premium thread connection, Metal to metal seal, Hertz theory, Contact pressure, Contact length.