Allowable design pressure is calculated when we already have a pipe of particular thickness in stock and we want to find out upto what pressure we can use it for a particular temperature. Following input is required to calculate allowable pressure for such pipe.

Input Required

1. Pipe material of construction.
2. Pipe NPD.
3. Pipe construction type : Seamless, EFW, ERW etc.
4. Design temperature.
5. Available nominal pipe thickness.
6. Corrosion allowance for material and operating conditions.
7. Mechanical allowance.
8. Mill tolerance.

Allowable design pressure is calculated using ASME B31.3 formulae as specified in section 301.1.1 and 304.1.2

P : Allowable Design Pressure to Calculate

t : Pressure design thickness of pipe. It can be calculated by subtracting from nominal wall thickness various allowances such as :

1. Miill Tolerance,
2. Corrosion Allowance,
3. Mechanical allowance for Threading and Grooving.

D : Outside diameter of pipe. In this calculator, outside diameter is taken from American Pipe Standards for the selected nominal pipe diameter :

1. ASME B36.10 : Welded and Seamless Wrought Steel Pipe.
2. ASME B36.19 : Stainless Steel Pipes.

S : Allowable Stress value for material from Table A-1 : These are allowable stress values for different materials at different temperatures. Provided in Table A-1 of ASME B31.3. This app includes commonly used pipe materials.

E : Longitudinal Weld Joint Quality factor

1. Applicable as per ASME B31.3  Table A-1A or A-1B .
2. 1 For Seamless Pipes.
3. 0.60 for Furnace Butt Welded Pipes.
4. 0.85 for Electric Resistance Welded Pipes.

W : Weld Joint Strength Reduction Factor

1. Applicable as per Para 302.3.5(e) of ASME B31.3
2. It is applicable only for Welded pipes.
3. W is Take as 1 for Seamless Pipes.
4. Value of W is taken as 1.0 at temperatures of 510°C (950°F) and below, and 0.5 at 815°C (1500°F) for all  materials.
5. Value is linearly interpolated for intermediate temperatures.

Y : Coefficient from Table 304.1.1 : Valid for t < D/6 and for materials shown. The value of Y may be interpolated for intermediate temperatures.