Process vessels are normally supported by one of the following methods (See Figure 400-19):
• Support legs
• Support lugs
• Ring girders
Skirts are typically used for vertical vessels because they are the most economical. Leg-supported vessels are normally lightweight, and the legs provide easy access to the bottom of the vessel. A lug support system depends on the stiffness of the shell and its ability to adequately resist the bending moments. This capacity should be completely investigated. Cross-bracing on lug-supported vessels may be needed to minimize lateral and torsional movements.
Vessels supported by ring girders are usually placed within a structural frame. The ring girder has the advantage of supporting torsional and bending moments resulting from the transfer of loads from the vessel wall to the supports.
Horizontal vessels are normally supported by saddles. Stiffening rings may be required if the shell is too thin to transfer the loads to the saddles. Thermal expansion is typically accommodated by having one end of the vessel on a sliding support.
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