Design of premium threaded connections for oil casing based on Herz theory

Aiming to improve the sealing performance and optimize the sealing surface structure of premium threaded connections, a design method which parameterize the spherical sealing surface to tapered sealing surface of premium thread connections based on Herz theory is proposed. The multi-dimensional parameters of the sealing surface on the new premium thread connections are obtained, including the equivalent force, contact stress and equivalent plastic deformation, through finite element numerical simulation, and the accuracy of the simulation is proved by experiments. At the same time, extended wall thickness and increased tolerance fit methods were adopted to obtain a large amount of simulation data for the geometric models what verify the stability and excellent sealing performance of the designed structure. The results show that the premium threaded connections designed based on Herz theory have a good stress condition and elasticity in the sealing zone of the threaded connections, including high sealing contact pressure and equivalent force, and long sealing contact length. It provides a reference for sealing surface of tubular column thread connections in deep wells, ultra-deep wells, high temperature and high pressure wells conditions.