Pipe Tools & Calculators

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Barlows Formula

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


<form action="" method="POST" name="barlow" onsubmit="return false"><!-- [et_pb_line_break_holder] --><p><span class="main">P = Pressure</span> <input type="text" name="val0" size="4" /> <span class="main"> psig</span><br /> <span class="main">t = Nominal Wall Thickness</span> <input type="text" name="val1" size="4" /> <span class="main">in. </span><br /> <span class="main">D = Outside Diameter</span> <input type="text" name="val2" size="4" /> <span class="main"> in. </span><br /> <span class="main">S = Allowable Stress</span> <input type="text" name="val3" size="4" /> <span class="main"> psi. </span><br /> <input onclick="return calculateBarlow();" type="button" name="button" value=" Calculate " /></p><!-- [et_pb_line_break_holder] --></form>

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