Design Pressure

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 Design Pressure:

  • The design pressure is the maximum sustained pressure that a piping system must contain without exceeding its code-defined allowable stress limits.
  • In single-compartment systems the design prressure is the maximum differential pressure between the interior & exterior portions of the system.
  • In multi-compartment systems the design pressure is maximum differential pressure between any two adjacent compartments.
  • The design pressure is not to be exceeded during any normal steady-state operating mode of the piping system.
  • In formulating the design pressure, the designer  must consider all potential pressure sources.
  • Among the more common sources to be considered are:
  1. The hydrostatic head due to differences in elevation between the high and low points in the system.
  2. Back pressure effects.
  3. Friction losses
  4. The shutoff head of in-line pumps
  5. Frequently occurring pressure surges
  6. Variation in control system performance.
  • Design pressure should be determined accordingly to ASME B31.3 Standard, where Design Pressure P is
P = (2St/D)FT,  S is Yield Strength, t is Wall Thickness, D is Nominal OD of pipe, F is design factor, E is Longitudinal joint factor, T is Temperature derating factor.
  • Design factor F used in the calculation depends on the class location of where pipe is to be installed.



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