Vessel design ellipsoidal head

The ASME design formula from UG-32 for ellipsoidal heads having a major-to-minor axis ratio of 2 1 and being subjected to pressure on the concave side is t = PD/ 2SE — 0.2P), where t is the minimum thickness of the head (in.), P is the MAWP (psi), D is the internal diameter of the major diameter of the ellipsoid (in.) (and equal to the inside diameter of the vessel), S is the allowable stress of the material, as listed in ASME Section II, and E is the weld joint efficiency. ... 

Input Data and Computer Outputs for Vessel Design with Hemispherical, Ellipsoidal and Torispherical Heads... 

FORMAT (//,25X, VESSEL DESIGN WITH ELLIPSOIDAL HEADS, ... 

As the size or the pressure goes up, curvature on all surfaces becomes necessary. Tariks in this category, up to and including a pressure of 103.4 kPa (15 Ibf/in"), can be built according to API Standard 620. Shapes used are spheres, ellipsoids, toroidal structures, and circular cylinders with torispherical, elhpsoidal, or hemispherical heads. The ASME Pressure Vessel Code (Sec. TII of the ASME Boiler and Pressure Vessel Code), although not required below 103.4 kPa (15 Ibf/in"), is also useful for designing such tanks. 

Since this failure, most designers have used only ellipsoidal or hemispherical heads that require a minimum temperature, typically 80° F (27° C), for hydrostatic tests of field-erected vessels. 

If the hemispherical dished head is not feasible, the ellipsoidal dished should be preferred over the torispherical dished head for tall vertical vessels, since the cost of the top closure is only a small part of the total cost of the vessel. For a battery of horizontal storage tanks or small vertical vessels, the torispherical dished head may be the more economical choice. Closures with conical, tori-conical, flanged and dished (not ASME) or flat shapes have no place in the design of tall vertical towers unless the process requires such special shapes for some particular reason. 

A common type is ellipsoidal. Vessels made from this design are more compact and so take less space. For an ellipsoidal end cap (head), the height is just one quarter of the diameter. So its radius is not constant - it varies between the major and minor axis. 

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