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#41967 - 03/29/11 04:19 PM Trunnion supported elbows
Ferni2011 Offline
Member

Registered: 03/12/11
Posts: 13
Loc: Thunder Bay, Canada
I searched this specific question but found nothing in the Caesar II forum. I was curious as to where to get info to calculate the maximum allowable stress on an elbow from a lateral trunnion support with a large load. How does Caesar know that the elbow is less flexible? Can we calcaulate a new SIF?

It is near some equipment and the pipe system flexibility is important.

Thanks.
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"Just because you haven't done it doesn't mean it is impossible"

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#41982 - 03/30/11 08:18 AM Re: Trunnion supported elbows [Re: Ferni2011]
Crusader911 Offline
Member

Registered: 11/22/09
Posts: 25
Loc: Louisiana, USA
The way I was taught to do it by a Coade instructor is as follows. This will be difficult to do without a drawing, but picture a segment 10 to 20 with a bend at 20. Assuming the trunnion will be in line with this direction, model a rigid from node 20 going back into the straight length of pipe and having a length equal to the bend radius. Now attach a rigid of the same length going back toward the trunnion. Next, model the trunnion itself as pipe. The rigids connected to the elbow stiffen it. There are other methods in the Caesar manuals to change how the trunnion lines up with the pipe, and the manual does a good job on the pros and cons of each method.

I've seen other analysts just designate the elbow as having a flange attachment to stiffen it up.

My favorite method is to use FE/Bend, which is part of Paulin Research Group's FE/Pipe suite.

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#41998 - 03/30/11 03:17 PM Re: Trunnion supported elbows [Re: Crusader911]
runner Offline
Member

Registered: 12/11/08
Posts: 125
Loc: INDIA
hi to all Guru's
Can any one kindly suggest us your views while doing analysis considering support on Elbow as shown above two cases, which way we need to use to calculate trunnion support loads.
Why user use two different way to support on Elbow, as we are defining +Y restraint on both the cases.

Thank u for reading and replying.

Runner



Attachments
ELBOW SUPPORT.pdf (1290 downloads)


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#42004 - 03/30/11 10:38 PM Re: Trunnion supported elbows [Re: Crusader911]
Ferni2011 Offline
Member

Registered: 03/12/11
Posts: 13
Loc: Thunder Bay, Canada
Good points Crusader911.

I have modeled the trunions this way before, but I was wondering about the flexibility. As you mention, I can model the elbows with flanges at the ends that will stiffen them up. I know someone with FE Pipe so I will investigate this with them!

Thanks.
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"Just because you haven't done it doesn't mean it is impossible"

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#42024 - 03/31/11 06:59 AM Re: Trunnion supported elbows [Re: Ferni2011]
learner2011 Offline
Member

Registered: 01/14/11
Posts: 91
Loc: india
FE pipe has the real solution to this problem.Even calcuating the local stresss with Kellog method gives a conservative result.FE pipe calculates the Sif at trunion bend interface which we cannot do in Caesar

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#42078 - 03/31/11 04:45 PM Re: Trunnion supported elbows [Re: learner2011]
danb Offline
Member

Registered: 04/22/05
Posts: 1453
Loc: ...
Think so? I always succeded to comply with Kellog (I had indeed some hard time with 1.5" trunnions on 2" pipe) I do not like trunnions (but this is only my option smile )
It serve some skill to limit the loads on trunnions, nothing special.

Regards,
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#42523 - 04/19/11 11:11 PM Re: Trunnion supported elbows [Re: danb]
say Offline
Member

Registered: 10/16/08
Posts: 20
Loc: Manila
Just want to add some points on "why we model trunnion pipe as well"

Modeling trunnion pipe sometimes does not require any special reason.
Most of the time we just place Y restraint at support points and leave it as it is. Then we run the program, review the stress, loads etc.
When we encounter problems like large load on nozzles, high stresses at bends and high loads at support points. Then thats the time you do some tricks to your model by modeling the trunnion itself for your added flexibility and to make the system more real!

By the way, when we say more real doesn't mean its better, It's just a matter of being less conservative.

Cheers,
Say

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