Shell vessel design

Ship-shaped FPSOs must be designed to weather vane i.e. must have the ability to rotate in the direction of wind or current. This requires complex mooring systems and the connections with the well heads must be able to accommodate the movement. The mooring systems can be via a single buoy or, in newer vessels designed for the harsh environments of the North Sea, via an internal or external turret. Figure 10.33 shows a schematic of the Shell-BP Foinaven FPSO. 

Cyclone Separator with Integral Catch Tank This type of containment system, depicted in Fig. 26-19, is similar to the ore-mentioned type, except that the knockout drum and catch tank are combined in one vessel shell. This design is used when the vapor rate is quite high so that the knockout drum diameter is large. 

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 ... 

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

The cylindrical shell is frequently used in pressure vessel design. For initial designs, it is useful to calculate the stresses in a thin-walled cylindrical shell that is uniformly loaded with internal pressure. For thin-walled pressure vessel calculations to be valid, the radial stresses in the shell need to be negligible. This is usually taken to be a valid assumption when the ratio of the vessel inner radius to the wall thickness (R/t) is greater than 10. "... 

Wind, seismic and vibrational stresses and accumulated dead weight compression loadings primarily affect the axial stress and produce only a small effect as a result of Poisson s relationship on the circumferential stress. Therefore, the shell thickness of the upper portion of a tall vertical vessel designed to operate under either internal pressure or vacuum is determined by the circumferential stress. 

Ev = modulus of elasticity of vessel shell at design temperature, psi... 

In order to understand the equations in pressure vessel design, it is important to go over some of the basics of solid mechanics. Although it is essential primarily to learn these concepts developed in the classical theories of plates and shells, for the sake of completeness we shall include the concepts of stress, strain, and constitutive relationships and move over to the theories of elasticity and plasticity. 

A hemispherical closure will be designed for the vessel des< ribed in the section entitled Example Design t)f a Shell. The design is a successive approximatit)n bt cause the tangent modulus of elasticity at this tenqH ralure (750° F) is also a functi()n of the stress, /. 

A torispherical closure will be deigned for t he vessel descril)eExample Design of a Shell. This design is.alm> a successive approximation. 

Various theories have been formulated in which the above stresses are used to compute worst stresses Ov within given structures (such as cylindrical shells). These theories have been taken into account in the formulation of the national codes for pressure vessel design, as indicated in Table 8.4. This table lists several relationships for calculating minimum permissible wall thickness for cylindrical shells as a function of internal radius and pressure. Geode in these... 

Based on the selected vessel design pressure (P) and temper ure (T), vessel shell wall thickness (dts, in inch) and head wall thickness (dth, in inch) can be calculated as follows ... 

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