Pipe Pressure Rating Calculator (Barlow Formula)
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Pipe pressure rating calculator using the Barlow formula: P = (2 x S x t) / D. Pipe Pressure Rating Calculator (Barlow Formula) Applies to thin-wall pipe where the wall thickness is less than about 10% of the outside diameter. Covers common UK carbon steel and stainless grades with preloaded allowable stresses at ambient temperature per ASME B31.3 / BS EN 13480.
Pipe burst and working pressure (Barlow)
Barlow formula: P = (2 x S x t) / D. This is a first-order estimate for thin-wall pipe (t/D < 0.1). For thick-wall pipe (t/D >= 0.1), use Lame or Boardman formulas. Always apply the correct ASME B31.x design code factor for your service.
How to use the Barlow formula
S is the allowable stress of the pipe material at operating temperature. Values drop significantly above 200C for carbon steel and above 400C for stainless. For elevated service always use the stress values from ASME Section II or BS EN 10216. The design factor adjusts for service severity: 0.72 is standard for ASME B31.3 process piping, 0.60 for cyclic or vibratory service, 0.50 for severe hot or cold applications.
For thick-wall pipe (D/t under 10) Barlow under-estimates the pressure capacity and you should switch to the Lame thick-cylinder formula. For high-pressure hydraulic lines or specialised high-pressure gas pipe, manufacturer-specific design codes take priority.
References
- ASME B31.3-2022 - Process piping design code
- BS EN 13480 - Metallic industrial piping
Frequently Asked Questions
What is the Barlow formula for pipe pressure?
P = (2 x S x t) / D, where P is the burst pressure, S is the allowable stress of the material, t is the wall thickness, and D is the outside diameter. Apply a design factor (typically 0.72 for ASME B31.3) to get the maximum allowable working pressure.
What is the maximum pressure of 2-inch schedule 40 pipe?
2 inch SCH 40 carbon steel pipe (A106 Grade B) has an outside diameter of 60.3 mm and wall thickness 3.91 mm. Using Barlow: burst = (2 x 138 x 3.91) / 60.3 = 17.9 MPa (179 bar). With ASME B31.3 design factor 0.72, MAWP is about 129 bar.
When should I use the Barlow formula?
Barlow works for thin-wall pipe where wall thickness is less than about 10% of outside diameter (D/t greater than 10). For thicker pipe use the Lame formula. Barlow is also only valid for internal pressure; external (vacuum) pressure needs different analysis.
What does the Pipe Pressure Rating Calculator (Barlow Formula) calculate?
The Pipe Pressure Rating Calculator (Barlow Formula) calculates the burst pressure and working pressure of thin-wall pipes using the Barlow formula, P = (2 x S x t) / D.
Which materials are covered by the Pipe Pressure Rating Calculator (Barlow Formula)?
The Pipe Pressure Rating Calculator (Barlow Formula) covers common UK carbon steel grades and stainless steel grades with preloaded allowable stresses at ambient temperature per ASME B31.3/BS EN 13480.
How do I choose the correct material for my pipe based on the calculator?
When choosing a material, consider the operating conditions such as temperature and pressure. The Pipe Pressure Rating Calculator (Barlow Formula) provides allowable stresses for different materials at ambient temperatures to help select an appropriate grade of carbon steel or stainless steel.
What are the standards followed by the Pipe Pressure Rating Calculator (Barlow Formula)?
The calculator adheres to ASME B31.3 and BS EN 13480, which provide guidelines on allowable stresses for pipes at ambient temperatures.
Are there different types or variants of the Barlow formula used in this calculator?
This Pipe Pressure Rating Calculator (Barlow Formula) is specifically designed for thin-wall pipes where the wall thickness is less than about 10% of the outside diameter, making it suitable for most common pipe applications in UK engineering.
Where can I find UK suppliers who provide materials compatible with the Pipe Pressure Rating Calculator (Barlow Formula)?
UK engineers can consult local steel and pipe suppliers or distributors that stock carbon steel and stainless steel grades compliant with ASME B31.3/BS EN 13480 for use in conjunction with the Pipe Pressure Rating Calculator (Barlow Formula).
What is the cost and availability of using this calculator for my project?
The Pipe Pressure Rating Calculator (Barlow Formula) itself is typically free to use online, but the actual material costs vary based on market prices from suppliers. Availability of materials depends on stock levels at steel distributors across the UK.