In recent years, steam injection wells, which are enhanced oil recovery wells, have been developed. Since well casings installed in steam injection well are subjected to excessive tensile loading during oil production, problems such as casing collapse, connection fracture and connection jump out (pull out) can occur during service life. However, the joint strengths for fracture and jump out have been calculated for cases of axial loading alone. Therefore, no formulas for estimation of the strengths under combined external pressure and axial tensile loading are available. We conducted jump out tests under conditions of biaxial loading with high axial stress close to the yield strength of the casing material and derived an empirical formula for estimation of the jump out pressure by regression analysis. This formula can be used for accurate estimation of jump out pressures under conditions of biaxial loading, since jump out pressures calculated using this formula agree well with ones determined experimentally.
