How to calculate steel pipe allowable pressure?
Calculating Steel Pipe Allowable Pressure According to ASME B31.3
Calculating the allowable pressure for a steel pipe involves considering various factors such as material properties, design temperature, and pipe dimensions. According to the ASME B31.3 Code for Process Piping, Formula is:
P = 2SEt / (D - 2t)
Where:
P = Internal design pressure
S = Allowable stress for the material at the design temperature
E = Weld joint efficiency factor
t = Nominal wall thickness of the pipe
D = Outside diameter of the pipe
How to Calculate Steel Pipe Pressure Rate:
1. Determine the Material Allowable Stress (S):
The allowable stress depends on the material and the design temperature. Refer to the ASME B31.3 tables (Table A-1) to find the allowable stress value for the specific material at the design temperature.
2. Determine the Weld Joint Efficiency (E):
The weld joint efficiency factor accounts for the type of weld used. Typical values are:
- Seamless pipe: E = 1.0
- Longitudinally welded pipe: E = 0.85 (or as specified in the code)
3. Measure the Nominal Wall Thickness (t):
The nominal wall thickness should be determined, and corrosion allowance should be considered if applicable.
4. Measure the Outside Diameter (D):
The outside diameter of the pipe must be known.
5. Insert Values into the Formula:
Substitute the values for S, E, t, and D into the formula to calculate the internal design pressure P.
Example Steel Pipe Allowable Pressure Calculation:
Lets assume the following values for a steel pipe:
- Material: Carbon steel (A106 Gr.B)
- Design Temperature: 200°C (392°F)
- Allowable Stress (S) from ASME B31.3 for A106 Gr.B at 200°C: 20,000 psi
- Weld Joint Efficiency (E): 0.85
- Nominal Wall Thickness (t): 0.5 inches
- Outside Diameter (D): 10 inches
P = (2 x 20000 x 0.85 x 0.5) / (10 - 2 x 0.5)
P = 17000 / 9
P ≈ 1888.89 psi
Thus, the allowable internal design pressure for the specified steel pipe is approximately 1888.89 psi.
Important Notes:
- Ensure all measurements are accurate and all necessary factors such as corrosion allowances and additional code requirements are considered.
- Always refer to the latest version of the ASME B31.3 Code for any updates or changes in the allowable stress values or other parameters.
