Pipe Wall Thickness

Pipe Wall Thickness

Barlow´s Formula is used to calculate the pipe pressure considering its diameter, wall thickness, and hoop stress (in the pipe material). Thus, it can be used to calculate whichever one of those parameters as a function of the other three.
In addition to some other simplifications, an important theoretical assumption made for the use of Barlow´s formula is that the pipe wall behaves like a membrane (or thin wall pipe), meaning the hoop stress in the pipe wall is distributed uniformly in all its thickness. There are no moments of any type within the pipe wall.One parameter to ensure that the membrane behavior happens in the pipe wall is the diameter over thickness ratio (D/t) to be bigger or equal to 20 ^{1 2}, although some authors consider 16 ³.
However, the decision of using or not of the formula is usually not based on its section geometry (D/t ratio), but on the service of the pipe, considering the type of fluid, industry, and physical conditions, like for instance, the ASME (American Association of Mechanical Engineers) does.

• P: Pipe pressure
• S: Hoop stress
• t: Pipe wall thickness
• D: Outside diameter

Calculations using Barlow's formula

Pipe wall thickness, (in)

Hoop Stress, (psi)

Outside Diameter, (in)

Pipe internal Pressure, (psi)

Calculation precision

Digits after the decimal point: 3

calculateD P S t

Calculate

calculated t, (in)

 

calculated S, (psi)

 

calculated D, (in)

 

calculated P, (in)

 

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Following that service criteria, the ASME B31.4 code (Pipeline Transportation Systems for Liquids and Slurries) applies the formula in this manner:

• A: Allowance for threading, grooving, corrosion

Wall Thickness by Barlow's Formula as applied by ASME B31.4

Pressure, (psi)

Diameter, (in)

Hoop Stress, (psi)

Sum of Allowances, (in)

Calculation precision

Digits after the decimal point: 3

Calculate

Pipe wall thickness, (in)

 

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ASME B31.8 code (Gas Transmission and Distribution Piping Systems) applies it in this manner:

and to calculate the minimum wall thickness including an allowance:

it should be expressed like this:

• F: Design Factor
• E: Longitudinal Joint Factor
• T: Temperature Derating Factor
• A: Allowance for threading, grooving, corrosion

Pipe Pressure by Barlow's Formula as applied by ASME B31.8

Hoop Stress, (psi)

Pipe wall thickness, (in)

Outside Diameter, (in)

Design Factor, (dimensionless)0.80 for Location Class 1, Division 1 0.72 for Location Class 1, Division 2 0.60 for Location Class 2 0.50 for Location Class 3 0.40 for Location Class 4

Longitudinal Joint Factor (dimensionless)1.00 for ASTM A53 Seamless pipe 1.00 for ASTM A53 Electric Resistance Welded pipe 0.60 for ASTM A53 Furnace Butt Welded: Continuous Weld pipe 1.00 for ASTM A106 Seamless pipe 0.80 for ASTM A134 Electric Fusion Arc Welded pipe 1.00 for ASTM A135 Electric Resistance Welded pipe 0.60 for API 5L Furnace Butt Welded pipe 0.80 for ASTM A139 Electric Fusion Welded pipe 0.80 for ASTM A211 Spiral Welded steel pipe 1.00 for ASTM A333 Seamless pipe 1.0 for ASTM A333 Electric Resistance Welded pipe 1.00 for ASTM A381 Double Submerged-Arc-Welded pipe 0.80 for ASTM A671 Electric Fusion Welded Classes 13,23,33,43,53 pipe 1.00 for ASTM A671 Electric Fusion Welded Classes 12,22,32,42,52 pipe 0.80 for ASTM A672 Electric Fusion Welded Classes 13,23,33,43,53 pipe 1.0 for ASTM A672 Electric Fusion Welded Classes 12,22,32,42,52 pipe 1.00 for API 5L Seamless pipe 1.00 for API 5L Electric Resistance Welded pipe 1.00 for API 5L Electric Flash Welded pipe 1.00 for API 5L Submerged Arc Welded pipe

Temperature Factor, (dimensionless)1.000 (for 250 ºF or less) 0.967 (for 300 ºF) 0.933 (for 350 ºF) 0.900 (for 400 ºF) 0.867 (for 450ºF)

calculateP t

Allowance A (in)

Internal Pressure P, (psi)

Calculate

Calculation precision

Digits after the decimal point: 3

calculated P (psi)

 

calculated t (in)

 

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ASME B31.9 code (Building Services Piping) applies it in this manner:

• E: Longitudinal Joint Factor
• A: Allowance for threading, grooving, corrosion

Pipe wall thickness by Barlow's formula as Applied by ASME B31.9

Pipe Internal Pressure, (psi)

Outside Diameter, (in)

Hoop Stress, (psi)

Lomgitudinal Joint Factor, (dimensionless)0.6 (for Furnace butt weld or continuous weld pipe) 0.75 (for ASTM A211 spiral joint pipe) 0.8 (for Single butt weld pipe) 0.85 (for Electric resistance weld pipe) 0.9 (for Double butt weld pipe) 1.00 (for butt weld with 100% radiography examination pipe)

Sum of all Allowances, (in)

Calculation precision

Digits after the decimal point: 3

Calculate

Pipe wall thickness, (in)

 

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On the other hand, as opposed to the thin wall assumption or membrane theory, there is the curved plate or thick wall pipe formulas derived from Lame´s theory whose use is more complicated, sometimes with iterations, and requires a careful approach like, for instance, in ASME B 31.1 code (Power Piping), ASME B 31.3 code (Process Piping), and ASME B 31.5 (Refrigeration Piping and Heat Transfer Components).