Barlow's Formula is used to determine:

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

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

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