Buckling assessment procedure for large diameter vessel with local thin area subjected to combined pressure and external moment

The newly developed p-M diagram provides a means for readily evaluating the collapse and/or buckling load of pressure equipment with external flaws simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. In this paper, some FEAs for large diameter vessels with an external flaw were conducted under (1) pure external bending moment, and (2) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic collapse load by applying the twice-elastic slope (TES) as recommended by the ASME and to determine the buckling load. The p-M line adopted in the Ibaraki FFS rule based on the measured yield stress indicates that the safety margin for the TES loads at the LTA is about 1.2–1.8, and 1.5–2.0 for the buckling loads. The Ibaraki FFS rule that prevents buckling by applying Donnell's equation of FS = 2 can assure adequate levels of integrity and safety.