There exist some atypical loads on pressure vessels during transportation. This is particularly true when the pressure vessel weighs over 500 tonnes. In this example vessel, the transportation was via rail on a “Schnabel car,” in which the vessel is suspended horizontally between the top nozzle and the skirt, and a significant axial compressive load is applied. During the evaluation of the stresses in the top head, a particularly novel situation was encountered which brought about some interesting issues with regards to the three design-by-analysis methods: elastic, limit load, and elastic-plastic. This paper discusses the comparison between all three of these design-by-analysis methods, and provides recommendations for which is most appropriate for this type of evaluation. Additional recommendations and warnings are provided for the use of the elastic and limit load methods as well.
General components such as pressure vessels, piping, storage tanks, and so on are designed in accordance with the construction codes based on the assumption that there are no flaws in such components. There are, however, numerous instances in which in-service single or multiple volumetric flaws such as local thin areas are found in the equipment concerned. Therefore, it is necessary to establish a fitness for service rule, which is capable of evaluating these flaws. The procedure for a single flaw or multiple flaws has recently been proposed for assessing the flaws in the p-M (pressure-moment) diagram, which is an easy way to visualize the status of the component with flaws simultaneously subjected to internal pressure p and external bending moment M due to earthquake, etc. If the assessment point (Mr,pr) lies inside the p-M line, the component with flaws is judged to be safe. In this paper, numerous experiments and finite element analysis for a cylinder with external multiple volumetric flaws were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic collapse load at volumetric flaws by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are much the same as those calculated under the proposed p-M line based on the measured yield stress.
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