Barlow’s Formula Calculator for Pressure

Barlow’s Formula is a calculation used to show the relationship between internal pressure, allowable stress, nominal thickness, and diameter.

The Formula is Expressed as P=2St/D, Where:

• P = pressure, psig
• t = nominal wall thickness, in inches (i.e. .375)
• D = outside Diameter in inches
• S = allowable stress in psi, which depends on the pressure being determined utilizing Yield or Tensile depending on what is trying to be determined

For Example:

• Internal Pressure at Minimum Yield:
  S= SMYS – minimum yield for grade of pipe

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Barlow’s Formula is Used to Determine:

• Internal Pressure at Minimum Yield
• Ultimate Bursting Pressure
• Maximum Allowable Operating Pressure
• Mill Hydrostatic Test Pressure

Ultimate Bursting Pressure:

• S = SMTS – minimum tensile strength for grade of pipe

Maximum Allowable Operating Pressure:

• S = SMYS – reduced by a design factor

Mill Hydrostatic Test Pressure:

• S = SMYS – reduced by a design factor depending on OD and grade