Design of Process Vessels

Process design of vessels establishes the pressure and temperature ratings, the length and diameter of the shell, the sizes and locations of nozzles and other openings, all internals, and possibly the material of construction and corrosion allowances. This information must be supplemented with many mechanical details before fabrication can proceed, notably wall thicknesses. 

Allowable tensile stresses are one-fourth the ultimate tensile strength of the material of construction. Values at different temperatures are given in Table 18.5 for some steels of which shells and heads are made. Welded joint efficiencies vary from 100% for double-welded butt joints that are fully radiographed to 60% for single-welded butt joints without backing strips and without radiographing. The Code has details. 

Azbel and Cheremisinoff (1982) also presented formulas for the design of shells, vessel bottoms, heads, and appertenances. 

The ASME Code provides formulas that relate the wall thickness to the diameter, pressure, allowable stress, and weld efficiency. Since they are theoretically sound only for relatively thin shells, some 

The formulas are expressed in terms of inside dimensions. Although they are rarely needed, formulas in terms of outside dimensions, say Do, may be derived from the given ones by substitution of Do — 2t for D. For the 2 1 ellipsoidal head, for instance. 

Vertical tanks. Those supported above ground are made with dished or conicai bottoms. Flat bottomed tanks rest on firm foundations of oiled sand or concrete. Supported flat bottoms usually are 1/4 in. thick. Roof plates are 3/16 in. thick. Special roof 

In order to minimize hazards, storage tanks for inflammable or toxic materials may be buried. Then they are provided with an overburden of 1.3 times the weight of water that the tank could hold in order to prevent floating after heavy rainfalls. 

For safety reasons, the design and construction of pressure vessels are subject to legal and insurance standards. The ASME 

Air at lOOOcuft/sec and density of 0.075 lb/cuft contains particles with density 75 lb/cuft. 50% of the 10 pm diameter particles are to be recovered. Find the sizes and numbers of cyclones needed with inlet velocities in the range of 50-150 ft/sec. The inlet is rectangular with width D/4 and height 2.5D/4, where D is the diameter of the vessel. 

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Mechanical Design of Process Vessels 621 Design Pressure and Temperature 623 Shells and Heads 624... 

In addition to the ANSI/ASME Boiler and Pressure Vessel Code and the ANSI B31 Code for Pressure Piping, many other codes and standards are commonly used for the design of process vessels in the United States. Some of them are ... 

In the design of process vessels and pressure equipment, two basic modes of failure may be assumed elastic failure based on the theory of elasticity and plastic failure based on the theory of plasticity. Except for thick-walled vessels, elastic failure is usually assumed for the design of pressure vessels. It is considered to occur when the elastic limit of the material is reached. Beyond this limit, excessive deformation or rupture is expected. These limits are usually measured in terms of tensile strength, yield strength, and, to some degree, rupture strength. 

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