Torispherical heads pressure

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. 

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. 

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. 

BD = head blank diameter, inch c = corrosion allowance, inch D = inside diameter of shell or head, inch E = joint efficiency H.Fac = head blank diameter factor OD = outside diameter of head, inch P = internal design pressure, psig R = inside radius, inch R = crown radius of torispherical head, inch S = allowable stress, Ib/in ... 

The computer program PROG43 determines the vessel weight of the pressure vessel with hemispherical, elliptical, and torispherical heads. Table 4-7 gives input data and computer output for 2 ft 6 in.-diameter vessel. The output gives the shell and head thicknesses, the weights of the shell and head, and the total weight of the vessel with hemispherical, elliptical and torispherical heads. 

P = design internal pressure, psi P = allowable external pressure, psi Px = design external pressure, psi R = outside radius of spheres and hemispheres, crown radius of torispherical heads, in, t = thickness of cylinder, head or conical section, in. t, = equivalent thickness of cone, in. oc = half apex angle of cone, degrees... 

The MAP and MAWP for other components, i.e., cones, flat heads, hemi-heads, torispherical heads, etc., may be checked in the same manner by using the formula for pressure found in Procedure 2-1 and substituting the appropriate terms into the equations. 

CIRCUMFERENTIAL COMPRESSION STRESS IN KNUCKLE REGION OF TORISPHERICAL HEAD DUE TO INTERNAL PRESSURE... 

Eor an internal pressure P, the thickness of the torispherical head is given by... 

What is the required thickness of a torispherical head attached to a shell of diameter 6 mm, to have a crown radius of 6 mm and a knuckle radius of 360 mm (ASME head r/L = 0.06). The allowable stress is 120 MPa and the internal pressure is 345 KPa. 

A pressure vessel designer generally has flexibility in selecting head geometry. Most common is of course the torispherical head, which is characterized by inside diameter, crown radius, and knuckle radius. The designer selects a head configuration that minimizes the total cost of the plate material and its formation. 

Hohn analyzed all of the reliable test data Ih available on torispherical heads and performed many tests of his own. He noted that the yield point of the head matorial was first nKiched in the knuckle, and measured the pressure required to prodi such yielding. He then computed the stress in the center of the crown at this preMure by use of the equations for spherical sheik based upon membrane theory. Next he determined the ratio of the yield point to the stress in the center of the crown and used this-strw-intensilieation factor for correlation purpMes. After trying a number of raethcMls of correlation, he concluded that the resulte could best be correlated by comparing the computed stress ratios with the ratio of the knuckle radius to the crown radius rx/tc. 

Formed t losures under external pn ssure ai( subject to failur l y elastic insUibility as are shells. Equation 1.33 applies in the case of hemispherical or torispherical heads and gives the theoretical pressure at which collapse wouhl occur because of elastic insUibility. 

Ellipsoidal and Torispherical Heads under External Pressure... 

The governing equations for the design of ellipsoidal and torispherical heads are obtained from expressions 6.10 and 6.11. For internal pressure, = P, = 0, and the two equations give ... 

For external pressure, the knuckle area is subjected to a tensile stress. Hence the critical area that is necessary for consideration under external pressure is the spherical region. Thus the ASME criteria for all ellipsoidal and torispherical heads under external pressure are the same as those for spherical 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. 

Internal-pressure design rules and formulas are given for cylindrical and spherical shells and for ellipsoidal, torispherical (often called ASME heads), hemispherical, and conical heads. The formulas given assume membrane-stress failure, although the rules for heads include consideration for buckling failure in the transition area from cylinder to head (knuckle area). 

External-pressure failure of shells can result from overstress at one extreme or n om elastic instability at the other or at some intermediate loading. The code provides the solution for most shells by using a number of charts. One chart is used for cylinders where the shell diameter-to-thickness ratio and the length-to-diameter ratio are the variables. The rest of the charts depic t curves relating the geometry of cyhnders and spheres to allowable stress by cui ves which are determined from the modulus of elasticity, tangent modulus, and yield strength at temperatures for various materials or classes of materials. The text of this subsection explains how the allowable stress is determined from the charts for cylinders, spheres, and hemispherical, ellipsoidal, torispherical, and conical heads. 

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