Saddle supports for horizontal vessels

Figure 18.14. Methods of supporting vessels, (a) Saddle supports for horizontal vessels, usually of concrete, (b) Bracket or lug supports resting on legs, for either vertical or horizontal vessels, (c) Bracket or lug supports resting on steel structures, for either vertical or horizontal vessels, (d) Straight skirt support for towers and other tall vessels the bearing plate is bolted to the foundation, (e) Flared skirt for towers and other tall vessels, used when the required number of bolts is such that the bolt spacing becomes less than the desirable 2 ft.

Steel saddle supports for horizontal cylindrical vessels when they exceed 2 ft (0.6 m) height, measured at the center... 

Though saddles are the most commonly used support for horizontal cylindrical vessels, legs can be used for small vessels. A horizontal vessel will normally be supported at two cross-sections if more than two saddles are used the distribution of the loading is uncertain. 

For horizontal vessels with saddle supports, from the disposition of deadweight load (see Section 13.9.1). 

Stiffeners should never be located over circumferential weld seams. If properly spaced they may also double as insulation support rings. Vacuum stiffeners, if combined with other stiffening rings, such as cone reinforctunent rings or saddle stiffeners on horizontal vessels, must be designed for the combined condition, not each independently. If at all... 

Figure 7 shows nozzle locations and support arrangements for a typical horizontal vessel (7). The saddles used for support are sustained by concrete pedestals or steel stmctures. Sufficient clearance between the bottom nozzles and the support saddles needs to be provided for access to the nozzle flange bolts. The manway can be located on the end head of the vessel, the topside of the vessel, or the side of the vessel. The preference is for an end manway wherever possible for accessibiHty, except when it is limited by the level gauges and controls that are commonly mounted off the heads. 

The method used to support a vessel will depend on the size, shape, and weight of the vessel the design temperature and pressure the vessel location and arrangement and the internal and external fittings and attachments. Horizontal vessels are usually mounted on two saddle supports see Figure 13.20. Skirt supports are used for tall, vertical columns see Figure 13.21. Brackets, or lugs, are used for all types of vessels ... 

A methodology for the determination of the stresses in the shell and heads of a horizontal vessel supported on saddles was first published in 1951 by L. P. Zick. This effort was a continuation of others work, started as early as the 1930s. This procedure has been used, with certain refinements since that time, and is often called Zick s analysis, or the stresses are referred to as Zick s stresses. 

Figure 3-42. Typical dimensions for a horizontal vessel supported on two saddles.

Horizontal vessels supported by two saddles (Fig, 12. le) act as simply supported beams. For vessels with dished heads (Fig, 12,16o) the equivalent beam length is taken as L + AH 3 where L is the tangent-to-tangent length of the vessel and... 

Usually, horizontal pressure vessels and tanks are supported on two vertical cradles called saddles. The use of more than two saddles is unnecessary and should be avoided. Using more than two saddles is normally a stress-related issue, which can be solved in a more conventional manner. The reason for not using more than two saddles is that it creates an indeterminate structure, both theoretically and practically. With two saddles, there is a high tolerance for soil settlement with no change in shell stresses or loading. Even where soil settlement is not an issue, it is difficult to ensure that the load is uniformly distributed. Obviously there are ways to accomplish this, but the additional expense is often unwarranted. Vessels 40-50 ft in diameter and 150 ft long have been supported on two saddles. 

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