External Loads on Vertically Mounted Equipment

Abstract

Heat exchangers and pressure vessels are frequently mounted vertically to economize plant floor space. In some cases, the process function of the hardware requires vertical installation. For example, gravity driven boiling in a thermosiphon reboiler, or fractionation in a distillation column, can proceed only if the equipment is vertically installed. As discussed in Chapter 17, the supports may consist of a skirt, a set of lugs, or a ring-type structure at (or near) the bottom and a lateral restraint near the top. Photograph 20.a shows a skirt mounted unit with a lateral support at the top. Figure 20.1.1 shows a skirt mounted unit without a top lug. Preliminary design data on sizing supports for vertical mounting is given in Chapter 17. However, it is subsequently necessary to determine the adequacy of the preliminary design for external loads. The external loadings on such equipment arise from various sources such as from wind load, from seismic motion, and from reactions due to attached piping. In its most simplified form, a seismic loading is specified as a set of static inertial accelerations in three orthogonal directions (two horizontal and one vertical). A precise specification of loads on the vessel nozzles from inter-connecting piping is more problematic, since piping design is usually not complete at the time of equipment procurement. This problem is usually circumvented by postulating a set of loads for each nozzle and by requiring that the plant designer route the piping to maintain the loads on the equipment-piping interface to within these limits. Thus the process of equipment and piping design can proceed concurrently. The piping load can be prescribed in terms of six vectorial components; three forces and three moments. The sense of action of these loads is not specified.