Pressure Vessels – Determining Wall Thickness
The following formulas are used in the ASME Code Section VIII, Division 1 for determining wall thickness:
Wall thickness—cylindrical shells
Figure 12-1 defines the various types of heads. Most production facility vessels use ellipsoidal heads because they are readily available, normally less expensive, and take up less room than hemispherical heads. Cone-bottorn vertical vessels are sometimes used where solids are anticipated to be a problem. Most cones have either a 90° apex (a = 45°) or a 60° apex (a = 30°). These are referred to respectively as a “45°” or “60°” cone because of the angle each makes with the horizontal. Equation 12-4 is for the thickness of a conical head that contains pressure. Some operators use internal cones within vertical vessels with standard ellipsoidal heads as shown in Figure 12-2. The ellipsoidal heads contain the pressure, and thus the internal cone can be made of very thin steel.
Table 12-4 lists joint efficiencies that should be used in Equations 12-1 to 12-4. This is Table UW-12 in the ASME Code. Table 12-5 lists some of the common material types used to construct pressure vessels. Individual operating companies have their own standards, which differ from those listed in this table.