Limit Load Capacity of Thick-Walled Pipe Loaded by Internal Pressure and Bending

Internally pressurised pipe behaves differently than externally pressurised pipe. DNVGL-ST-F101 [4], a prevailing standard for the design of submarine pipelines, provides limit-state equations for combined loading that are valid only if the diameter-to-wall-thickness ratio (D/t) is between 15 and 45. A recent study has shown that the results are increasingly conservative for lower values of this ratio if the nett pressure is acting on the pipe’s outside [8], especially if it is below 20. In this paper, the applicability of the limit-state equations for thick-walled pipe with D/t less than 15 and loaded by a nett internal pressure has been investigated. The first step was a fundamental review of the formulations. Next, the predicted capacities were compared with those estimated using a finite-element (FE) model. The results greatly coincided, which indicates that the conservatism underlying the formulations does not depend on D/t. Hence they can be used for design against local buckling under internal overpressure, too, when the ratio is below 15.