Heads, ASME dished

Solids suspension is usually carried out in mechanically agitated vessels with or without draft tubes, as shown in Figs. 5 and Dished heads (ASME dished, elliptical, or torispherical heads) are preferred. A single impeller is usually sufficient for off-bottom solids suspension in vessels with dished heads and 7 < 1.3. Dual impellers are recommended for vessels with 13 < H/T < 2.5, which are used for uniform suspension of fast-settling solids. Three or more impellers... 

Referring to the wetted surface, A , the surface areas of ASME flanged and dished head, ASME elliptical heads, hemispherical heads, etc., are often the end assemblies on... 

Type of bottom head ASME flange-dished head... 

The volumes of heads must be calculated separately and added to the volume of the cylindrical portion of the tank. The four types of heads most frequently used are the standard dished head, torispherical or ASME head, ellipsoidal head, and hemispherical head. Dimensions and volumes for all four of these types are given in Luken.s Spun Heads, Lnkens Inc., Coatesville, Pennsylvania. Approximate volumes can also be calculated by the formulas in Table 10-65. Consistent units must be used in these formulas. 

The standard dished head does not comply with the ASME Pressure Vessel Code. 

Faetor for determining the eapaeity (gal) for the bottom head = 0.606 for ASME Standard flanged and dished heads Total heat transfer surfaee area, ft ... 

Using ASME flanged and dished heads (F D) from Appendix Tables of Blanks, the circle size is 152 in. for a 12-ft diameter tank. Then add 3-in. straight flange which becomes 158 in. which is 158/12 = 13.166 ft diameter. Area of this diameter for surface area of head = 136.14 sq ft equivalent surface area of one head. For a horizontal vessel there are two heads possibly exposed to fire. 

These supports will not make a rectangular or square vessel suitable for pressure or vacuum service. If such a vessel is to receive a masonry lining, it must be designed as a cylinder with dished or hemispherical heads, both top and bottom or as a sphere. (Reference 8, p 80). Such vessel must also be designed in accordance with the ASME Code For Unfired Pressure Vessels, Section VIII. 

Figure 4-3. Various types of more common formed heads a, flanged only b, flanged and shallow dished c, flanged and standard dished d, ASME Code flanged and dished (torispherical) e, elliptical dished (ellipsoidal) f, hemispherical g, flanged and conical dished (toriconical).

The ellipsoidal dished head with a major to minor axis ratio of 2 1 is popular for economic reasons, even though the theory for thin-walled vessels predicts that the head of this shape should have twice the thickness of a hemispherical head where the major and minor axes are equal. Such an ellipsoidal head used for vessels under internal pressure has the same thickness as the cylindrical shell if the same allowable stresses and joint efficiencies are applied to both parts. The 1962 ASME Code Section VIII, Division 1 gives the following equation for the thin-walled ellipsoidal dished heads with a 2 1 major to minor axis ratio ... 

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. 

Construction In accordance with ASME Code U 68 for Unfired Pressure Vessels all-welded with flanged and dished heads shell thickness 4 iu., head thickness... 

The test tank, as shown in Fig. 2, is made of two flanged and dished 48 in. OD by l-in. wall, type-304 stainless steel ASME heads separated by a 7-in. long by -in. thick, type 304 stainless-steel cylindrical section. A 1 -in schedule-5S stainless steel neck tube was centered on one head for liquid fill, withdrawal, and instrumentation. This shape approximates that proposed for storage of fluids in space. Double curved surfaces provided an excellent test of the insulation-application technique. 

Fig. 5.7. Voriowi types of more common formed heads (a) flonged only, b) ftonged and shoitow dished, (c) Ranged and standard dished, (d) ASMS and API-ASMf code Ranged and dished (torisphericol), (e) elliptical dished (ellipsoidal), (f) hemispherical, (p) Ranged and conical dMsed (lorieonicai) (105). (Courtesy of tukens Steel Co.)...

Table 5J- Dimensions of ASMS Code Flangeci and Dished Heads (Courtesy of Lukeus Steel Company)...

Cowmoit Types of Formed Heads ond Their Selection Table 5.7. Dimensions of ASME Code Flonged and Dished Heads (Continued)... 

Fig. 5.10. Approximote 1955 cost of forming per head For ASMS code flonged and dished heads if two to four heads are purdiosed.

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