Pressure Ratings and Allowable Stresses
The allowable internal pressure for any copper tube in service is based on the Barlow formula for thin-walled, hollow
cylinders used in the ASME B31 Code, for Pressure Piping.
The value of ‘S’ is the allowable design strength for continuous long-term service of the tube, as determined by the
ASME Boiler and Pressure Vessel Code, Section 1 - Materials.
Allowable stresses for annealed and drawn temper copper tube are shown in the table below. They are only a small
fraction of copper’s ultimate tensile or burst strength. In system design, joint ratings must also be considered,
as the lower of the two ratings (tube or joint) will govern the installation. The rated joint strength in soldered
tube systems often governs design. However, annealed ratings must be used in brazed systems since the brazing
operation may anneal the tube near the joints.
Allowable stresses for Copper
Tube as a Function of Temp.
Barlow formula for thin
walled, hollow cylinders
P = Allowable Pressure
S = Allowable Stress
t = Wall Thickness
D = Outside Diameter
Psi x 0.006895 = MPa
MPa x 145.04 = Psi
F = [(F - 32) / 1.8]C
C = [(C - 1.8) / 32]F
National Standards Authority of Ireland - Irish Standard - I.S. EN 1057:1996
Copper and copper alloys - seamless, round copper tubes for water and gas in sanitary and heating applications.
This Irish Standards adopts CEN European Standard EN 1057 as an Irish Standard.
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