Problem

The following is displayed in model consistency check report:

W726-8: Kink in straight run of 179.9 deg at point XX

TR Number: none
Product: AutoPIPE
Version: n/a
Area:
General
Problem ID#: 71944

Solution

This is an error in your modeling, AutoPIPE's results would be incorrect. All locations were the kink = 179.9 deg must be fixed before analyzing the model. See the following:

Scenario #1:

Bend Radius has a -ve value

Avoidance:

 Change -ve bend radius (ex. -4) to a +ve value or set to one of the drop down selections (i.e. Short, Long, 3d, 5d)

Scenario #2:

In AutoPIPE, open the model and select the "Points" tab on the input grid.

Navigate to the location in the warning message, by highlighting the Run, the following may be displayed in solid model view:

Notice how the selected pipe is colored both red and grey, this is a clear indication of this warning. The pipe is folded back on itself. Further evidence is shown on the points tab of the input grid.

The segment is shown to be progressing along a +ve X-axis direction, however from F682 to F680 the run is in the -ve X-axis direction, then directly back to a +ve X-axis direction with no bend specified. Here lies the problem, there should only be a progression in one direction along this part of the piping, thus the warning is displayed.

Another technique to locate the issue is by using the keyboard arrows (Left, Right, up, & down), move the current point in the positive direction along the segment and then back in the negative direction of the segment, passing the point identified on the message.

Each run, bend, component added to a segment in AutoPIPE should progress in a direction away from the point from its previous point. The warning message " W726-8: Kink in straight run of 179.9 deg at point XX" alerts the user that at some point, the direction of the segment was modeled directly back in the direction of a previous point, creating a 180 deg turnaround on the pipe, or Kink (bend with no bend component).

The common mistake is that a node point was added in the wrong direction without utilizing the Insert "Add Point Before/After" command correctly.

Note: Some codes have an allowance for size of angle alignment along a pipe (ie. Kink angle), while individual companies may have procedures on how to deal with kinks (see project Piping Spec or Design Spec documents), In regards to AutoPIPE, analytically, kinks would simply be two connected straight pipes and would be analyzed as such. The analysis results may calculate lower stresses as compared to applying a bend where a stress intensification factor would have been applied. Ultimately it is up to the user to decide what size kink angles are acceptable in a model. Otherwise, suggest to model kink locations as a smooth radius bend or miter bend to account for any SIF factors. 

Avoidance:

Example, Segment A00, A01, A02, A03...A20 each 10 feet apart in the +x-axis. A new point A21 was inserted between A02 and A03, 1 ft in the -x-axis from point A03.

1. Determine exactly what point was inserted incorrectly (ex A21)

2. Measure from the bad point to a proceeding point (ex. A02 to A21 = 9ft)

3. Delete bad point (ex. A21)

4. Review points tab to confirm segment does not have a kink of 180 deg

5. Choose one of the following: 

a. Make A02 the current point, insert Run dx= 9ft

OR

b. Make A03 the current point, set "Add Point Before/After" = before, dx = 1 ft.

6. Perform Model consistency check to confirm 180 deg kink warning was removed from report.

Example:

Using AutoPIPE's Tools> Model Consistency Check you may encounter the following warning message "W726-8: Kink in straight run of 179.9 deg at point xxxx". One cause for the warning message is a segment of pipe overlapping an existing pipe run. Another words, the pipe segment has section of pipe bent back into itself. Navigate to the point in question for inspection and to correct the warning message.

AutoPIPE segments should flow in one direction as AutoPIPE relies on the previous point to establish the next node point. See the following for complete explanation and steps to repair this modeling warning:

Step 1: The screen shot shows a segment that appears to be correct.
Step 2: However using Tools> Model Consistency Check shows the following
Step 3: Navigate to the node points for inspection. One clear indicator of a problem can be seen on the input grid, Points tab.
Step 4: As previously stated the segment should progress is a single direction and not directly back on itself. Notice the Offset Dx column; +dx, -dx, +dx.
Step 5: This can further be demonstrated with selecting the run section: A00 - A01 A01 - A02 A02 - A03 Notice A01 - A02 selection is hidden. And the A02 - A03 overlaps
Step 6: This may or may not be true in all cases but another indicator is the Segment numbering sequence. A00, A02, A01, A03.
Step 7: This is very easy to fix. After the inspection, determined which node point, if removed, will allow the segment to progress is a single direction. In this case, that would be A01. Take a measurement from A00 to A01.
Step 8: Select node point A01 and Delete it.
Step 9: Move cursor to A00, Insert > Run> length = enter calculated distance measured.
Step 10: Finished. The offset is progressing in one direction instead of overlapping back onto itself. In this case, the node points name sequence is correct (A00, A01, A02, A03). Also, when selecting the run sections, they are shown correctly. Verify the warning has been fixed, Tools> Model Consistency Check.

See Also

"Warnings" Messages

Bentley AutoPIPE