Design pressure

Factors should be included to allow for variations in design pressure and material of construction ... 

Division 2. With the advent of higher design pressures the ASME recognized the need for alternative rules permitting thinner walls with adequate safety factors. Division 2 provides for these alternative rules it is more restrictive in both materials and methods of analysis, but it makes use of higher allowable stresses than does Division 1. The maximum allowable stresses were increased from one-fourth to one-third of the ultimate tensile stress or two-thkds of the yield stress, whichever is least for materials at any temperature. Division 2 requkes an analysis of combined stress, stress concentration factors, fatigue stresses, and thermal stress. The same type of materials are covered as in Division 1. 

Static Strength. Foi a straight pipe the internal design pressure, P, is given by... 

Pipe-Wall Thickness. Once the design pressure and temperature have been established and the pipe material and size selected, the wall thickness is calculated using the appropriate section of the code. In rare cases, a thin pipe must be made thicker to withstand handling. Occasionally the thickness is affected by external loads or vibrations. All codes prescribe essentially the same design formula for metallic hoUow circular cylinders under internal pressure ... 

For tank internal pressures that do not exceed the weight of the roof plates, most tanks have conical roofs because these are the simplest and most cost-effective. When the pressure is increased beyond the weight of the roof plates, the roof-to-sheU area goes into hoop compression. A small portion of the roof, the roof-to-sheU angle, and the top few centimeters of the sheU act as a compression ring to resist the unbalanced forces from internal pressure on the conical roof. The internal design pressure for this case may be... 

Service Diameter, m Height, m Type, tray/pack Design temp, °C Design pressure, kPa... 

IF design pressure is high THEN configure safety release valve... 

Design Pressure The design pressure of a piping system shall not be less than the pressure at the most severe condition of coincident pressure and temperature resulting in the greatest required component thickness or rating. 

P = internal design pressure or external design pressure S = applicable allowable stress... 

Impact testing is not required if the design temperature is helow —29 C (—20 F) hut at or above —46 C (—50 F) and the maximum operating pressure of the fabricated or assembled components will not exceed 25 percent of the maximum allowable design pressure at ambient temperature and the combined longitudinal stress due to pressure, deadweight, and displacement strain (see Par. 319.2.1) does not exceed 41 MPa (6000 Ibfiin ). 

The scope covers many other less basic exclusions, and inasmuch as the scope is occasionally revised, except for the most obvious cases, it is prudent to review the current issue before specifying or designing pressure vessels to this division. Any vessel which meets all the requirements of this division may be stamped with the code U symbol even though exempted from such stamping. 

Unfired steam boilers with design pressures exceeding 345 kPa (50 Ibftin") have restrictive rules on weided-joint design, and all butt joints require full radiography. 

Brittle fracture is probably the most insidious type of pressure-vessel failure. Without brittle fracture, a pressure vessel could be pressurized approximately to its ultimate strength before failure. With brittle behavior some vessels have failed well below their design pressures (which are about 25 percent of the theoretical bursting pressures). In order to reduce the possibility of brittle behavior. Division 2 and Sec. Ill require impac t tests. 

For an all-steel heat exchanger AAith mixed design pressures the total extra for pressure is 0.7 X pressure extra on shell side plus 0.3 X pressure extra tube side. 

For an exchanger AAith alloy parts and a design pressure of 150 Ibf/im, the alloy extras are added. For shell and shell cover the combined alloy-pressure extra is the alloy extra times the shell-side pressure extra/100. For channel and floating-head cover the combined alloy-pressure extra is the alloy extra times the tube-side pressure extra/100. For tube sheets and baffles the combined alloy-pressure extra is the alloy extra times the higher-pressure extra times 0.9/100. (The 0.9 factor is included since baffle thickness does not increase because of pressure.)... 

Base Bare-tuhe external surface 1 in. o.d. hy 12 B.W.G. hy 24 ft. 0 in. steel tube with 8 aluminum fins per inch V -in. high. Steel headers. 150 lh./sq. in. design pressure. V-helt drive and explosion-proof motor. Bare-tuhe surface 0.262 sq. ft./ft. Fin-tuhe surface/hare-tuhe surface ratio is 16.9. 

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