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Using most B31 and international piping codes, you can calculate the minimum pipe wall thickness ™ required for a piping system once you know the following pieces of data:

1. P = Internal design pressure
2. D = Outside dia. of pipe
3. S*E = Maximum allowable stress at design temperature * material joint factor
4. Y = Pressure coefficient from the piping code (usually 0.4)
5. A = Additional thickness to allow for threading corrosion

Most code equations are similar to the following:
tm = [(P*D) / 2 (Y*P + S*E)] + A, see equation 4 from B31.1, paragraph 104.1.2.

Model a few pipe elements after you put in materials, sections and loads into CAEPIPE. Analyze. Look at Code Compliance. The second column reports “Press Allow (psi).” “Press” stands for internal design pressure (P) you input. “Allow” stands for allowable pressure computed according to the equation above. The internal design pressure needs to be less than the allowable pressure. If not, then increase the wall thickness of the section and recalculate the pressure until you arrive at an appropriate wall thickness. If necessary, you might want to decrease the wall thickness too. Each change in the wall thickness will affect the stresses (SL, SE) and subsequently the stress ratios. A thicker wall increases the stiffness of the system.

For the sample model we provide with every copy of CAEPIPE (free and licensed), notice below how the allowable pressure changes with the wall thickness for an 8″ pipe. (Internal Design Pressure, P = 200 psi)

Schedule Thickness (in.) Allow. Pressure (psi)
80 0.5 2103
40 0.332 1332
20 0.25 1027
5S 0.109 442

Note: To account for A, you need to add it to the corrosion allowance field for Section in CAEPIPE.
You can arrive at an optimum wall thickness after just a few iterations.

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