Safe tube pressure
Pressure formula for stainless steel & nickel tubes
Tubing specifications do not include any recommended service or burst pressure requirements. However, Barlow's formula is commonly used in the industry to approximate or predict the bursting pressures of ductile thin wall tubes. Working pressures or allowable pressures are calculated by using a safety factor (SF) to reduce the pressure from a level where bursting failure is very likely to an acceptable level of risk. This is a complex matter where many issues must be considered such as: personnel assessment and general safety, corrosion, fatigue, fabrication changes (bends, flares), codes and insurance, seismic stability and temperatures, to name a few.
Many engineers will use the ultimate tensile strength (UTS) to calculate a bursting pressure estimation and use the yield strength (YS) together with a safety factor (SF) when arriving at a working pressure estimation. Using the yield strength and no safety factor (SF=1) will calculate an approximate theoretical pressure at which the tubing will begin to plastically deform.
Actual wall thickness or conservative wall estimates should be used. For example 1.65 mm wall or 0.065" average wall tubing is likely to measure 0.060" thick, or near the low end of the allowable range. Actual tube ODs should be used rather than Nominal tube Sizes (1” OD, 25.40 mm is nominally 27.94 mm).
Barlow's formula can be used to estimate burst pressure of tubes.
P = max. working pressure (psi)
S = material strength (psi)
T = wall thickness (in)
OD = outside diameter (in)
SF = safety factor (in general 1.5 to 10)
The Barlow estimate is based on ideal conditions at room temperature.
The strength of a material is determined by the tension test which measures the tension force and the deformation of the test specimen.
- the stress which gives a permanent deformation of 0.2% is called the yield strength
- the stress which gives rupture is called the ultimate strength
Strength of our bright annealed tube materials with minimum requirements:
|Alloy||ASTM||Strength Yield (PSI)||Strength Ultimate (PSI)|