Minimum shell thickness

This indicates that circumferential stresses are more important, and they determine the minimum shell thickness for this tank. The BHP steel plate available and closest to this specification (Ref. T2) is... 

NACE Publication 6K-157 also recommends a minimum shell thickness of 74" (6.4 mm) for vessels four feet or more in diameter and a minimum thickness of %" (9. 5 mm) for bottom plates. 

Shell and baffles. Shell diameters are standardized. For shells up to and including 23 in. the diameters are fixed in accordance with American Society for Testing and Materials (ASTM) pipe standards. For sizes of 25 in. and above the inside diameter is specified to the nearest inch. These shells are constructed of rolled plate. Minimum shell thicknesses are also specified. 

Minimum shell thickness for columns and vessels is as follows ... 

In the case of a long cylindrical outer vessel, the minimum shell thickness is given by... 

Tank Shell. Another example of where thickness is set by minimums for fabricabihty but not for strength is in small-diameter tanks. For example, a water storage tank built using a steel of an allowable stress of 20,000 psi (138 mPa), 9 ft (3 m) in diameter by 21-ft (7-m) high, requires a shell thickness to resist hoop stress of only 0.023-in. (0.58-mm) thick. However, if built to API Standard 650, the shell would be fabricated at least 0.1875-in. (4.76-mm) thick. The code requires this thickness so that when fabrication, welding, and tolerances are considered, a tank of acceptable quaUty and appearance meeting the requirements of most services in most locations is provided. 

The mechanical design of the idler roUs is a function of the particular service under which the conveyor operates. Minimum industrial standards for roU dimensions, bearings, and appHcation criteria for different service conditions have been estabHshed (14). Idler life is deterrnined by a combination of factors such as bearings, seals, shell thickness, load density, and the operating environment. 

Industry sets limits that bound our degrees of freedom and thus tend to shorten our design case study load. We are all aw are of such limits and this last category is included primarily for completeness. Examples include minimum industrial thickness for carbon steel plate, and maximum baffle cut for shell and tube heat exchangers. 

The wall thickness of the pipe or plate used for the shell is normally determined from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. TEMA standards also specify some minimum wall thicknesses for the shell. 

Tst = equilibrium temperature at which Cst exists over liquid in dry air at one atmosphere, °C or °F Tu = equilibrium temperature at which the upper flammable limit composition exists over liquid in dry air at one atmosphere, °C or °F Tw = vessel wall temperature, °R Ti = gas temperature, °R, at the upstream pressure, determined fromTt = (Pi/P,) (T,) t = minimum required thickness of shell of vessel, no corrosion, inches... 

For pressure applications the shell thickness would be sized according to the pressure vessel design standards, see Chapter 13. The minimum allowable shell thickness is given in BS 3274 and the TEMA standards. The values, converted to SI units and rounded, are given below ... 

The analysis of the membrane stresses induced in shells of revolution by internal pressure gives a basis for determining the minimum wall thickness required for vessel shells. The actual thickness required will also depend on the stresses arising from the other loads to which the vessel is subjected. 

Design procedures for tube-plates are given in BS PD 5500, and in the TEMA heat exchanger standards (see Chapter 12). The tube-plate must be thick enough to resist the bending and shear stresses caused by the pressure load and any differential expansion of the shell and tubes. The minimum plate thickness to resist bending can be estimated using an equation of similar form to that for plate end closures (Section 13.5.3). 

Thus, the shell wall thickness is essentially the same as the head thickness. According to Table 6.2, the minimum wall thickness is 3/32 in (2.38 mm) for high-alloy steels. The application of this rule-of-thumb more than doubles the wall thickness, which should be an adequate corrosion allowance. The selection of a corrosion allowance in the final design must be based on past experience or from laboratory and pilot plant tests. 

Figure 1. Effective area of two grazing incidence mirror systems. Both contain four modules, each with a 24cm diameter, 10m focal length and 80 cm long gold reflectors. The shell thickness is 0.7mm and the minimum spacing between reflecting surfaces is 1.2mm. One type (dashed line) is a conventional two reflection conical (or Wolter Type I) system of 45 shells. The other is a four reflection conical mirror that contains 58 shells.

Figure 2-1 f. Chart for determining shell thickness of components under external pressure when constructed of cartxjn or low-alloy steels (specified minimum yield strength 24,000 psi to, but not including, 30,000 psi). (Reprinted by permission from the ASME Code, Section VIII, Div. 1.)... 

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