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#73203 - 04/29/19 03:19 PM Maintenance Pipe Lifts
cingold Offline
Member

Registered: 06/20/13
Posts: 14
Loc: TX, USA
My company needs to lift a pipe during operation to repair some supports. I'm looking for help in modeling this piping system.

I want to run some test cases to ensure a safe lift by varying the following variables: lift height, number of lift points, and lift contact area.

I have the system modeled geometrically, but I'm having trouble with the lift scenario. If I want to test a 10 inch lift, how would I model the lift (displacement, force, some other form)?

My goal is to not exceed the sustained stress during the lift, so I need to account for the additional displacement of the pipe during the lift. The pipe is too long to lift all of it at once, so there will be additional bending stresses near the lift points.

Any input on how to model this and how to adjust the load cases is appreciated. Currently, I'm checking (SUS) W+P+D, but the results do not look accurate.

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#73206 - 04/30/19 06:11 AM Re: Maintenance Pipe Lifts [Re: cingold]
anubis512 Offline
Member

Registered: 08/24/18
Posts: 79
Loc: USA
Applying a vertical external force until displacement = your desired lift may be a method

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#73211 - 04/30/19 07:54 AM Re: Maintenance Pipe Lifts [Re: cingold]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 814
Loc: Louisiana, US
Say you have 15 supports, and you're lifting at support 7.

Apply a displacement of 10" at support 7. Apply a CNODE that is otherwise unused to this support, and then apply a displacement onto the CNODE.

Fails?

Do the same for the 2 adjacent supports, but lift only say, 5 inches.

All will be D1.

Lifting multiple locations? Say you have dozens of places.

There will be some point where lifting at support N and N+X will not have demonstrable additive effects, so they can use the same displacement slot, and you can check multiple locations simultaneously.

If your supports are all in too close of proximity, I'm sorry, but that means you may have to maintain a library of CAESAR files as a result.

I'll note that if this is a one-time operation, and they're not going to prop it up for more than a few hours, then you could get away with OCC allowables. However, I won't dissuade you from being conservative with SUS allowables, either.

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