The results of the analytical limit-state equations in DNV standard DNV-ST-F101 (2021), a prevailing design standard for submarine pipeline systems, are not always in line with those of detailed finite-element models. Under certain conditions, the predicted collapse pressures can be significantly different. This paper suggests an improved analytical framework. The proposed model reflects the underlying and interacting physics of material yielding and geometric instability; however, unlike the DNV model, it includes the effects of stress triaxiality and plastic bifurcation. The result is an elegant set of equations for predicting pipeline collapse that helps enable and economize pipeline projects whilst ensuring the required safety level.
One of the gaps identified in the research road map of the Design Committee of the European Pipeline Research Group (EPRG) is the lack of a valid formulation to evaluate the local-buckling limit state under combined loading for a thick-walled pipe. The formulations in DNVGL-ST-F101 (DNV GL, 2017), a prevailing standard for the design of subsea pipelines, were not valid for a diameter-to-wall-thickness ratio (D=t) less than 15.
