A Novel Comparison of Design-by-Analysis Methods

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.