Load bearing of corroded shells under external/internal pressure
Abstract
The paper examines the effects of axisymmetric, corrosion-induced, wall thinning on load bearing (buckling, collapse, plastic instability) of domed closures. It is assumed that the wall is corroded on inside only. Details are provided for torispherical closures with additional results for ellipsoidal heads. For torispherical domes, the ratio of corroded wall thickness, tc, to non-corroded thickness, t, is varied between 0.10 ≤ tc/t ≤ 1.0. Three modelling scenarios are considered: (1) corrosion confined to the knuckle, (2) corrosion spanning evenly the knuckle and spherical parts and (3) patch-type area positioned at the apex. The factors influencing load bearing capacity were found to be (1) meridional position of corroded area, (2) depth of corrosion itself and (3) meridional span of corroded wall. The largest drop of load bearing capacity is found when corroded wall is at the knuckle/crown junction (“buckling zone”). It is shown that assessment of load carrying capacity based on collapse mechanism is not only wrong but dangerous. Sensitivity of buckling strength to the amount of corrosion shows similar trends under internal or external pressure. Load bearing capabilities are also assessed for prolate and oblate ellipsoidal heads. Performance of the latter is compared with performance of Korbbogen dome – frequently found in industry.