Torispherical head

Head attachment. UW-13. Fig. UW-13.1 Fillet welds. UW-18. UW-36 Table UW-12 Knuckle radius. UG 32. UCS-79 Torispherical head. Pressures. 

A shell of revolution is the form swept out by a line or curve rotated about an axis. (A solid of revolution is formed by rotating an area about an axis.) Most process vessels are made up from shells of revolution cylindrical and conical sections and hemispherical, ellipsoidal and torispherical heads Figure 13.3. 

Hemispherical, ellipsoidal and torispherical heads are collectively referred to as domed heads. They are formed by pressing or spinning large diameters are fabricated from formed sections. Torispherical heads are often referred to as dished ends. 

Standard torispherical heads (dished ends) are the most commonly used end closure for vessels up to operating pressures of 15 bar. They can be used for higher pressures, but above 10 bar their cost should be compared with that of an equivalent ellipsoidal head. Above 15 bar an ellipsoidal head will usually prove to be the most economical closure to use. 

A hemispherical head is the strongest shape capable of resisting about twice the pressure of a torispherical head of the same thickness. The cost of forming a hemispherical head will, however, be higher than that for a shallow torispherical head. Hemispherical heads are used for high pressures. 

This equation will only apply at points away from the cone to cylinder junction. Bending and shear stresses will be caused by the different dilation of the conical and cylindrical sections. This can be allowed for by introducing a stress concentration factor, in a similar manner to the method used for torispherical heads,... 

Torispherical and ellipsoidal heads can be designed as equivalent hemispheres. For a torispherical head the radius Rs is taken as equivalent to the crown radius Rc. For an ellipsoidal head the radius can be taken as the maximum radius of curvature that at the top, given by ... 

La = inside radius of hemispherical head or inside crown radius of torispherical head, before corrosion allowance is added, in. 

La = inside radius of hemispherical head or inside crown radius of torispherical head, in., see Table 4 Le = fictitious length of straight pipe with the equivalent resistance of a pipe fitting of same nominal diameter as pipe, ft M = molecular weight, lbm/lbmol... 

Table 6.1 Weld Joint Efficiencies for Ellipsoidal and Torispherical Heads (Source Adapted from Ref. 10). 

Select a vessel head. If the internal pressure is 150 psig (10.3 barg) or less, select a torispherical head. If the internal pressure is above 150 psig (10.3 barg), select a 2 1 ellipsoidal head. 

Now, calculate the head thickness following the procedure outlined in Table 6.4. From Table 6.1, with no X-ray inspection, the weld efficiency for the weld joining the head to the shell is 0.80. Because of the acetic acid present in the distillate, we select SS 316, which has an allowable stress of 15,200 psi (1.04x10 kPa). For the moment, neglect the corrosion allowance. From Equations 6.3.1 and 6.3.3 for a torispherical head, the head thickness... 

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