Stability of ring stiffened steel liners under external pressure

External pressure is often the decisive load case for empty hydraulic pressure shafts for calculation of the wall thickness of the steel liner. Due to large diameters and thin wall thicknesses the steel liner is susceptible to shell buckling under external pressure. Therefore, the steel liner is often stiffened with circular rings having a rectangular cross section. In the Sixties of the last century comprehensive research activities started, including tests, and analytical formulae were developed for the design. Basically, these formulae are still used nowadays for the dimensioning of the ring stiffened steel liner. This paper sums up the analytical design rules for ring stiffened steel liners, which are very complex and not easy to handle. Two different verifications for buckling of the ring stiffener and for buckling of the cylindrical shell between the rings are necessary. The combined buckling behaviour of the ring stiffeners and the cylindrical shell between the rings can only be performed with a 3D-FEM analysis, which is also presented in the paper for different steel liner geometries used in practice. The distance of stiffeners e _ring is also varied. The results of the FEM analyses are compared with the current design rules. Due to the lack of accuracy of the analytical design rules, a new design model is presented in detail, using the results of the numerical analyses.