Wednesday, August 22, 2012

Fixing Acute Angle Pipe Deflection and other Piping Errors in Revit MEP

This tip comes straight from the top, from my buddy Dave Pothier...even though he's management now, he's still a geek at heart - gotta love it...

We had a recurring couple of problems with fittings we had defined for Ductile Iron pipe. When Autodesk brought their new versions out a short while ago for the AWWA standards, we were still having some issues, so we had a chat with Dave about it.

Problem 1 - some fittings at angles like 45 degrees could not be created, and we kept getting a "line too short" error - even though you could set the angle in the family, and it would work fine. As it turns out, my techs were modeling an existing plant on a project. To keep from getting crazy plant dimensions, they did what any good CAD tech would do - they set the units to 1/2" and 1".

Then we sailed in trying to place fittings that were accurate down to 1/16" - so when these fittings would try to fit under the higher scale, they couldn't be placed. We changed the project units down to 1/32" and everything works again. Go figure...

Problem 2 - this one was a doozy, and we had a lot of back and forth about it. When we finally did a web session with Autodesk, we were explaining how mechanical joint pipe connections have to be able to flex up to 5 degrees (2.5 each way) around a fitting, since all of this work is buried underground (and gasp, dirt does move). We also had ongoing problems where we could get pipe to deflect at angles great than 90 degrees (since the fitting angles were all between 0-90) but not at acute angles (when the deflection needed to occur, since these fittings don't exist as standard). Their fittings weren't doing deflecting, but then Dave noticed how we had the pipe connector set on the fitting. Here's part of his response:

"...Select the (pipe) connectors and temporarily change the system classification from “Fitting” to “Global”

Once you do that, you can turn On the Allow Slope Adjustments check box. After turning it on, set the System Classification back to Fitting. Do that for both connectors.

Now the fitting should allow the pipe to deflect without the fitting’s angle adjusting. I’m not sure how great of an angle you can have but it should work for what you are doing. Let me know if this works for you."

Now we when make the connection, we get piping deflecting the right way:

Sometimes it's just the simplest things - but thanks again to Autodesk for helping us out, and really get the most from this great package! I'll make sure we get this into the Revit MEP lab I'm teaching at AU, so you can see how do fix this first hand.

Have a great evening! David B.

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