New formula for predicting the plastic buckling pressure of steel torispherical heads under internal pressure

Thin-walled torispherical heads under internal pressure can fail by plastic buckling because of compressive circumferential stresses in the head knuckle. However, existing formulas still have limitations, such as complicated expressions and low accuracy, in determining buckling pressure. In this paper, we propose a new formula for calculating the buckling pressure of torispherical heads based on elastic-plastic analysis and experimental results. First, a finite element (FE) method based on the arc-length method is established to calculate the plastic buckling pressure of torispherical heads, considering the effects of material strain hardening and geometrical nonlinearity. The buckling pressure results calculated by the FE method in this paper have good consistency with those of BOSOR5, which is a program for calculating the elastic-plastic bifurcation buckling pressure based on the finite difference energy method. Second, the effects of geometric parameters, material parameters, and restraint form of head edge on buckling pressure are investigated. Third, a new formula for calculating plastic buckling pressure is developed by fitting the curve of FE results and introducing a reduction factor determined from experimental data. Finally, based on the experimental results, we compare the predictions of the new formula with those of existing formulas. It is shown that the new formula has a higher accuracy than the existing ones.