	Applies To
	Product(s):	AutoPIPE
	Version(s):	All
	Area:	Report
	Original Author:	Bentley Technical Support Group
	Date Logged & Current Version	May 2015 09.06.02.06

Problem:

Why are the HOOP stress results different throughout the AutoPIPE model?

Example, notice that the hoop stress is higher around the bends than any other part of the model:

Solution:

Please see the following AutoPIPE help section:

Help > Contents> Contents Tab> Reference Information> Code Compliance Calculations> select the correct piping code and year. Then select the Hoop Stress sub category, (ex. ASME B31.1- 2007, indicated below):

Notice the equation AutoPIPE uses to calculate the hoop stress values. Also notice the variable in the equation that could change from node point to node point that would results in a different calculated value. In this example above the only variables that would change are Pressure (P), Pipe OD (Do) and wall thickness (Tred) both of which are associated with the selected Pipe Properties used throughout the model. Therefore, verify all the values within the model related to the equation:

Example:

1. Confirm the Pressure is the exact same value across the entire model for this calculation to rule out the "P" variable.

2. Confirm Pipe properties are the exact same values across the entire model for the calculation to rule out "Tred" and "Do" variables.

3. If any changes were made, re-run the analysis and check the new Hoop stress results

4. Are the Hop stress values as intended now, If YES, stop here, If NO continue to next step.

5. If all the equation variables have all been determined to be correct, then maybe another Hoop Stress equations is being used, but why? Look back at the Hoop Stress Calculation in AutoPIPE help. There are 2 other hoop stress equations. Do these equations apply to a given model?

In the example above, yes, if the bend is assigned as a Close / Wide Miter bend. Review the Bend tab on the input grids.

6. Note that 4 bends were assigned as "Wide miter" bends., as a results equations 3 and 3b would be used to calculate the Hoop stress thus leading to different results.

As a test to prove this is the culprit, temporarily change the Bend Type from "Wide Miter" to "Elbow" run the analysis and check the results. In this case, the Hoop stress values are all the same now:

Conclusion:

Check the Hoop stress calculation used by AutoPIPE, confirm all variables in the equation related to node specific values, and check other Hoop stress equation criteria to be sure other equations are not being evaluated.

In the example above, because the bends had been set to Wide Miter, 2 different Hoop stress calculations were evaluated thus leading to different results for some node points in the model.

Also note that the bend equation for hoop stress would not be relevant because stress at always calculated at the centerline. Intrados and extrados are not calculated by AutoPIPE.

AutoPIPE's calculations are correct.

03. Why are the HOOP stress results different throughout the AutoPIPE model?

Problem:

Solution:

Conclusion:

See Also