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How to calculate the Hydrotest Hoop stress and Allowable in AutoPIPE?
Give the following information:
Piping code = B31.3 - 2014
Ambient temp = 21 deg C
Units = SI
Start by looking at the following AutoPIPE help section:
1. Help > Contents> Contents Tab> Reference Information> Code Compliance Calculations> select the proper piping code & year
2. Select the Hoop Stress section
3. Look for the appropriate equations for Stress and Allowable that AutoPIPE is using.
From the Pipe properties dialog find values for Do, Wall thk, Corrosion allow, Mill tol, W, and E.
From the Pressure Temp tab on the grids find the respective value for Pressure, Temperature, and SH as defined by the Hydrotest dialog (ex. P4 - T4)
Perform the Calculations
P = 4 N/mm^2
Do = 219.075 mm
tred = 7.036-.1.5-0.879 (Help> Definition of terms> Pipe Properties)
Y = 0.4
W = 1
E = 1
SH = 137.8951 N/mm^2
Compare to allowable documented for hydrotest case:
The hoop allowable matches exactly, however hoop stress hand calculation does not match AutoPIPE, why?
Question: What else can influence the code calculations.
Answer: Correct, the Results Model Options settings. If you do not already know about these settings, strongly suggest that you spend a little time getting to know them all because these settings will significantly affect your results.
As in this case, the results calculation was changed because of "Use nom. thk for hoop" setting was enabled.
Instead of Tred, use Tnom. in the hoop stress equation. Now, Hoop stress = 91.009 N/mm^2.
AutoPIPE results are correct.
Note: See WIKI here for method of setting a custom allowable value for the combination.