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Working Pressure Calculator for API 5L Line Pipe

(Jump down to:    Calculator for Pipe Working Pressure)

Field welding of Weld Neck flanges to Line Pipe has occurred for years and as long as the joined assemblies of pipe and flanges has service pressure well below flange rated pressure, the assemblies give little trouble. As the oilfield has matured and higher pressures have become a prominent issue, all potentially pressurized assemblies should now receive pressure tests to 1.5 times working pressure when first weld assembled, and to full rated working pressure with each movement of the assembly.

API Flange Specifications prescribe strength of material and chemistry limits for flanges, but leave the operators choice of pipe strength unspecified.

API Specification 5L specifies pipe of various sizes and wall thicknesses, many of which will match up to Flange Weld Necks, and this line pipe has many strength grades (see API 5L Line Pipe Physical Properties) but API Spec 5L does not designate working pressures for any sizes or strength grades.

WOODCO USA uses a formula consistent with API Spec 6A 20th Edition, Para. Distortion energy theory. Our formula makes no allowance for defects in material, variation in wall thickness, etc. You can use the calculator below, inputing your pipe wall and yield strength for the pipe selected. Users will have to determine the safety factors they want to use for the variation they expect to encounter in practice including considerations for corrosion, internal erosion, and welding variation.

The calculator provided below, will allow users to estimate the working pressure of selected sizes and strength grades of pipe, (see Carbon Steel Pipe Dimensions and Weights for Pipe O.D.'s, I.D.'s, and wall Thicknesses).

Calculator for Pipe Working Pressure *

Pipe O.D.

Enter Pipe Outside Diameter in Inches

Pipe I.D.

Enter Pipe Inside Diameter in Inches

Pipe Yield
Strength psi

Enter Pipe Yield Strength in psi
(Use no comma)


Working Pressure - psi
Test Pressure - psi

This calculator uses formulas consistent with API Spec 6A, 20th Edition, described as the Distortion Energy Theory, also known as the Von Mises Law. This calculator does not allow for pipe wall variation or material defects of any kind. Users will have to determine the safety factors they want to use for the variation they expect to encounter in practice, including considerations for corrosion and welding variation.

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