Applies To
Product(s):	AutoPIPE
Version(s):	ALL;
Area:	Reporting
Date Logged & Current Version	March 2025 24.00.02.243

Problem:

Why does the Center of Gravity report not match the Gr load case?

Example: 

Totaled up all of the forces from the gravity load on the supports in the y-direction and came up with an overall number. However, this number is about 4000 lb lighter than the overall weight of the piping and the contents

After adding all the support loads = 73032 lbs

difference of 4602.35 lbs

Why?

Solution:

There can be any number of reasons why the COG report is different from the sum of support reactions in the vertical direction. Some of those reasons to review for accuracy:

• • • Analysis Set
      • Contents
      • Fluid Density Factor
      • Soil Stiffness
      • Load case to include GR
      • Ignore Friction Gr
    • Distributed Loads
    • Concentrated forces
    • Support -
      • Gap Settings = As-built
    • Segment
      • Buoyancy 
    • Tee - internal branch piping weight and contents to surface of header pipe

      Consider the following modeling techniques to correct this weight issue (2-point Tee):

      1. Add a node point on the branch piping located at the imaginary surface of the header pipe.

      2. Select the internal piping, and Insert "Rigid Properties" over the length of this internal piping

      3. Set Rigid properties to consider thermal expansion but to ignore weight 

      

      4. As shown in the reference 2-point tee page, take care of the SIF value. 

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Scenario #1:

In this scenario, a particular model was used to generate the COG report (imaged above). The following list was compiled by taking a deep dive into modeling all of the component one at a time to understand how the weight is being reported to each report. For each component, calculate their weight in the COG report and Restraint report to find reasons for any disparities. 

1. Pipe

• • • • COG report - 2523.51 lbs.
      • Restraint report - 2524 lbs.
      • Diff = 0.49 lbs. (0.019%)

1. Bend

• • • • COG report - 3306.78 lbs.
      • Restraint report - 3303 lbs.
      • Diff = 3.78 lbs. (0.01%)

2. Tee

• • • • COG report - 7570.54 lbs.
      • Restraint report - 6519 lbs.
      • Diff = 1051.54 lbs. (13%)

3. Flange

• • • • COG report - 1000
      • Restraint report - 1000
      • Diff = 0.0

4. Valve

• • • • COG report - 2069.32
      • Restraint report - 2069
      • Diff = 0.32 lbs. (0.015 %)

5. Flexible Joint

• • • • COG report - 1758.17
      • Restraint report - 1758
      • Diff = 0.17 (0.009%)

6. Reducer

• • • • COG report - 1657.67
      • Restraint report - 1658
      • Diff = 0.32 lbs (0.019%)

7. Support

• • • • COG report - 1000.00
      • Restraint report - 1000
      • Diff = 0 (0%)

8. Added weight

• • • • COG report - 1000.00
      • Restraint report - 1000
      • Diff = 0 (0%)

9. Distributed weight

• • • • COG report - 0
      • Restraint report - 3000
      • Diff = 3000 (100%)

10. Concentrated force

• • • • COG report - 0.00
      • Restraint report - 1000
      • Diff = 1000.00 (100%)

11. Beam

• • • • COG report - 34.72
      • Restraint report - 35
      • Diff = 0.28 lbs.  (0.008%)

As mentioned above, the following component are not correctly accounted for across the 2 reports: Tee, Distributed Loads, and Concentrated forces. 

Conclusion

Most of all AutoPIPE's components are correctly accounted for across the various reports. Any discrepancies of weight between these reports can be attributed to these few items until they are addressed.