Heads hemispherical

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. 

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. 

Flat face flange. Appendix Y. Fig. UA-111Q Welded connection. UW IS. UW 16. Fig. UW 15.1 Opening. UG 35to UG 42, UA 7. UA 280 Multiple openings. UG-42 Non pressure parts. UG-6, UG-22. UG-SS. UG-82 Hemispherical head. Pressures. 

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... 

Total volume or length of shell in cylindrical tank with ellipsiodal or hemispherical heads ... 

So for a cylinder closed by a hemispherical head of the same thickness the difference in dilation of the two sections, if they were free to expand separately, would be ... 

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. 

It can be seen by examination of equations 13.7 and 13.9, that for equal stress in the cylindrical section and hemispherical head of a vessel the thickness of the head need only be half that of the cylinder. However, as the dilation of the two parts would then be different, discontinuity stresses would be set up at the head and cylinder junction. For no difference in dilation between the two parts (equal diametrical strain) it can be shown that for steels (Poisson s ratio = 0.3) the ratio of the hemispherical head thickness to cylinder... 

Fig. 8(a) shows the design of a rotating hemisphere electrode used in the author s laboratory [14], It is composed of a hemisphere electrode, an arcylic support rod, and a tappered brass holder to be attached to a high speed rotator [Fig. 8(b) ]. The electrode is machined into the form of a metal screw with a hemispherical head, and is threaded into the inert acrylic support rod of a larger radius. The design has the advantages that... 

In the field — ion microscopy, the emitter usually is a thin single-crystalline wire with a hemispherical head, see Fig. 5. The diameter 2r of this head generally is between 10-s and 10-4 cm. Thus capillary pressure 2 yjr reaching, say, 5 x 108 g/cm sec2 may be expected. When the emitter is at work, an intense electrostatic... 

Hong, Sungmin, Jean-Pierre Candelone, Clair C. Patterson, and Claude F. Boutron. Greenland Ice Evidence of Hemispheric head Pollution Two Millennia Ago by Greek and Roman Civilizations. Science 265 (September 23, 1994) 1,841-1,843. The researchers analyzed an ice core from Greenland that covered a period from 3,000 to 500 years ago and found the concentration of lead was four times higher than natural conditions during the Roman era. 

Recently spherical separators have gained considerable popularity. The shell consists of two hemispherical heads with appropriate internal construction. They have operating versatility comparable to the horizontal separator and are very compact and easily hooked up. 

Because of the size and the pressure of the vessel, austenitic stainless steel could not be used throughout, but must be applied on the inner surfaces of the ferritic material. This has been done by explosion plating of a 4 mm cladding on the base material prior to rolling the cylinder and forming the hemispherical head. For the flat cover and the sealing faces weldcladding was applied. 

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. 

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

For torispherical (spherically dished) 0.885 PL, = SEj - 0.1 P + Cc For hemispherical head Same as for spherical shells with head n = La r a knuckle radius = 6% of inside crown radius and is not less than 3t... 

For high-pressure vessels, hemispherical heads are usually the most economical. 

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... 

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