Wall Thickness Calculator

Pipe & Pressure Vessel Wall Thickness Calculator

Calculate the minimum required wall thickness based on Barlow's formula for pipes and cylindrical vessels under internal pressure.

in PSI
in Inches
in PSI
0.0 to 1.0 (1.0 for seamless)
in Inches

Results will be displayed here.

function calculateWallThickness() { var pressure = parseFloat(document.getElementById("internalPressure").value); var diameter = parseFloat(document.getElementById("outsideDiameter").value); var stress = parseFloat(document.getElementById("allowableStress").value); var efficiency = parseFloat(document.getElementById("jointEfficiency").value); var corrosion = parseFloat(document.getElementById("corrosionAllowance").value); var resultDiv = document.getElementById("result"); if (isNaN(pressure) || isNaN(diameter) || isNaN(stress) || isNaN(efficiency) || isNaN(corrosion)) { resultDiv.innerHTML = 'Error: Please enter valid numbers in all fields.'; return; } if (pressure <= 0 || diameter <= 0 || stress <= 0) { resultDiv.innerHTML = 'Error: Pressure, Diameter, and Stress must be positive values.'; return; } if (efficiency 1) { resultDiv.innerHTML = 'Error: Joint Efficiency must be between 0 (exclusive) and 1.0 (inclusive).'; return; } if (corrosion < 0) { resultDiv.innerHTML = 'Error: Corrosion Allowance cannot be negative.'; return; } // Using a common simplified version of Barlow's formula: t = (P * D) / (2 * S * E) var minThickness = (pressure * diameter) / (2 * stress * efficiency); var totalThickness = minThickness + corrosion; var resultHTML = '

Calculation Results:

' + 'Minimum Required Thickness (t): ' + minThickness.toFixed(4) + ' inches' + 'Total Recommended Thickness (t + C): ' + totalThickness.toFixed(4) + ' inches'; resultDiv.innerHTML = resultHTML; }

Understanding Pipe Wall Thickness Calculations

The wall thickness of a pipe or pressure vessel is a critical design parameter that ensures its structural integrity and safety under operational pressure. An insufficient wall thickness can lead to catastrophic failure, while an overly thick wall results in unnecessary material cost and weight. This calculator helps determine the minimum required thickness to safely contain a specified internal pressure.

The Formula Explained

This calculator uses a widely accepted formula derived from Barlow's formula, commonly used in piping and pressure vessel design codes (like ASME B31.3 for process piping). The formula to find the minimum pressure design thickness (t) is:

t = (P * D) / (2 * S * E)

Where:

  • t = Minimum required wall thickness (in inches) before adding allowances.
  • P = Internal design pressure (in pounds per square inch, PSI).
  • D = Outside diameter of the pipe (in inches).
  • S = Allowable stress of the pipe material at the design temperature (in PSI). This value is specific to the material (e.g., Carbon Steel, Stainless Steel) and is often derated for higher temperatures.
  • E = Weld joint quality factor or efficiency. This accounts for the strength of a welded seam compared to the base material. For a seamless pipe, this value is 1.0. For welded pipes, it can range from 0.60 to 1.0 depending on the weld type and inspection level.

After calculating the minimum thickness, we add any required allowances to get the final recommended thickness. The most common is the corrosion allowance (C).

Total Thickness = t + C

Worked Example

Let's calculate the required wall thickness for a seamless carbon steel pipe used in a process plant.

  • Internal Design Pressure (P): 600 PSI
  • Outside Diameter (D): 10.75 inches (for a nominal 10″ pipe)
  • Allowable Material Stress (S): 20,000 PSI (for ASTM A106 Grade B Carbon Steel at moderate temperature)
  • Weld Joint Efficiency (E): 1.0 (since it's a seamless pipe)
  • Corrosion Allowance (C): 0.0625 inches (1/16″)

Step 1: Calculate the minimum required thickness (t).

t = (600 PSI * 10.75 in) / (2 * 20,000 PSI * 1.0)

t = 6450 / 40000

t = 0.1613 inches

Step 2: Add the corrosion allowance.

Total Thickness = 0.1613 in + 0.0625 in

Total Thickness = 0.2238 inches

Based on this calculation, a pipe schedule with a nominal wall thickness greater than 0.2238 inches should be selected (e.g., a 10″ Schedule 20 pipe has a thickness of 0.250 inches, which would be suitable).

Key Factors Influencing Wall Thickness

  • Pressure: The primary driver. Higher internal pressure requires a thicker wall.
  • Material Strength (S): Stronger materials (higher allowable stress) can have thinner walls for the same pressure and diameter. Note that 'S' decreases as temperature increases.
  • Diameter (D): For the same pressure, a larger diameter pipe experiences greater hoop stress and thus requires a thicker wall.
  • Corrosion: If the fluid is corrosive, an extra thickness (corrosion allowance) must be added to account for material loss over the design life of the pipe.

Disclaimer

This calculator is intended for educational and preliminary estimation purposes only. The calculation of wall thickness for real-world applications is complex and must adhere to specific design codes (e.g., ASME B31.1, B31.3, Section VIII) which may include additional factors like temperature coefficients, manufacturing tolerances, and bending stresses. Always consult a qualified professional engineer for the design and verification of any pressurized system.

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