Supports saddle

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. 

The longitudinal bending stress at the mid-span of the vessel is given by  

The resultant axial stress due to bending and pressure will be given by  

Ch = an empirical constant varying from 1.0 for a completely stiff shell to about 0.1 for a thin, unstiffened, shell. 

The ends of the vessels will stiffen the shell if the position of the saddles is less than D/4 from the ends. Ring stiffeners, located at the supports, are used to stiffen the shells of long thin vessels. The rings may be fitted inside or outside the vessel. 

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Single Wall. Single-wall tanks are usually cylindrical and may have either vertical or horizontal orientation. Horizontal tanks are generally supported by two saddle supports and use more space than vertical tanks. Horizontal tanks have an advantage in that leaks can be seen as they occur. 

Zick, L. P., Stresses in Large Horizontal Cylindrical Pressure Vessels on Two Saddle Supports, Welding Journal Research Supplement, 1951. 

Figure 13.22. Horizontal cylindrical vessel on saddle supports...

Figure 13.25. Saddle supports shaded area is ineffective against longitudinal bending in an unstiffened shell...

Procedures for the design of saddle supports are given by Brownell and Young (1959), Megyesy (2001), Escoe (1994) and Moss (2003). 

Zick, L. P. (1951) Welding J. Research Supplement 30, 435. Stresses in large horizontal cylindrical pressure vessels on two saddle supports. 

Ml2 Longitudinal bending moment at saddle support ML2T 2... 

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

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.

A vessel supported on two saddles can be considered as a simply supported beam, with an essentially uniform load, and the distribution of longitudinal axial bending moment will be as shown in Figure 13.22. Maxima occur at the supports and at mid-span. The theoretical optimum position of the supports to give the least maximum bending moment will be the position at which the maxima at the supports and at mid-span are equal in magnitude. For a uniformly loaded beam the position will be at 21 per cent of the span, in from each end. The saddle supports for a vessel will usually be located nearer the ends than this value, to make use of the stiffening effect of the ends. 

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

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 ... 

Moody, G. B., How to Design Saddle Supports, Hydrocarbon Processing, November 1972. 

Procedure 3-11 Design of Saddle Supports for Large Vessels, 177... 

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