Pipe Pressure Calculator

Barlow's formula calculates the bursting pressure (or allowable working pressure) of a thin-walled pressure vessel or pipe: P = (2 x S x t) / OD, where P is the pressure (psi), S is the material allowable hoop stress (psi), t is the wall thickness (in), and OD is the outside diameter (in). Apply a safety factor by using the allowable stress rather than the ultimate tensile strength.

ASTM A53 Grade B carbon steel has a minimum tensile strength of 60,000 psi and a minimum yield strength of 35,000 psi. The ASME B31.3 allowable stress for this material at ambient temperature is approximately 15,000 to 20,000 psi, depending on weld efficiency and service classification.

Design pressure is the maximum operating pressure the system is designed for, set by the process engineer. MAWP (maximum allowable working pressure) is the maximum pressure that can be safely applied to the pipe based on its material, wall thickness, and code allowances. MAWP is typically equal to or greater than the design pressure.

Barlow's formula is accurate for thin-walled pipe where t/OD is less than about 0.1. For thick-walled pipe (t/OD greater than 0.1), more rigorous formulas such as the Lame equation should be used. ASME B31.3 and B31.1 provide the code-correct wall thickness calculation methods.

The safety factor is implicit in the allowable stress value used in the formula. ASME codes typically use an allowable stress equal to the lesser of (tensile strength / 3.5) or (2/3 of yield strength), providing safety factors of 3.5 and 1.5 respectively. Always use code allowable stresses, not ultimate tensile strength, in pressure calculations.