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#73336 - 06/12/19 07:37 AM Reinforcement pad
vik Offline
Member

Registered: 04/08/09
Posts: 31
Loc: Bangalore
Hi,

I have a case of Header-branch piping with connection type "Reinforced",

I Understand that CAESARII does not consider Reinforcement pad thickness to calculate stresses at this Header-branch connection (Unlike how we do in trunnion calculation).


What are the pros-cons of considering increased wall thickness, due to added pad/reinforcement thickness, while calculating stresses.

Thanks in advance.

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#73337 - 06/12/19 08:53 AM Re: Reinforcement pad [Re: vik]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 709
Loc: Louisiana, US
I think you need to define by what you mean by "reinforced."

In B31.3 and CAESAR, the "reinforced" type is a hole cut into the header pipe, the end of another pipe trimmed to fit the hole, and then a reinforcement pad is added and all components welded together.

Edit to add: B31.3 and CAESAR absolutely do take into account repad thickness and diameter.

You may be referring to a different kind of "reinforced" tee, which may be just a welding tee, but is just thicker.

If this is the case, then I would recommend you place nodes at the ends of the tee, and increase the thickness and diameter of the tee, unless you know for certain there's more than adequate safety factor built in.

Not doing so would would be inaccurate, and will lead to some conservative AND non-conservative results. Yes, stresses in the tee will be overstated, but flexibility of the tee will also be overstated, as well, and resultant forces and moments everywhere else will likely be understated.

The degree by which these values are over/understated will depend on what fraction of the total system length these extra thick tees take up, and various aspect ratios of the system.


Edited by Michael_Fletcher (06/12/19 08:54 AM)
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#73338 - 06/12/19 11:07 PM Re: Reinforcement pad [Re: vik]
vik Offline
Member

Registered: 04/08/09
Posts: 31
Loc: Bangalore
Thanks Mr. Michael_Fletcher.

My case is of "Header-Hole-Branch-Re-Pad".

I was under the assumption that CAESARII considers only the SIF of such Re-Pad branch connection and not the additional thickness to calculate stress.

I hope the Intergraph Spiders too agree with you.

Thanks again.

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#73340 - 06/13/19 07:15 AM Re: Reinforcement pad [Re: vik]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 5933
Loc: Houston, Texas, USA
CAESAR II stress computations are based on 3d Beam Element theory using nominal pipe dimensions. (If corrosion is being considered, then the corroded section modulus is used).

The pipe cross section used for the stress computation is not adjusted for the presence of a reinforcing pad. If this is what you're after you will have to perform a true FEA evaluation of the tee (using the forces and moments from the CAESAR II local element report).
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Richard Ay
Hexagon PPM (CAS)

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#73341 - 06/13/19 07:46 AM Re: Reinforcement pad [Re: vik]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 709
Loc: Louisiana, US
Perhaps I missed nuance of the question, but yes, I was referring specifically to the tee's SIF.

In CAESAR's eyes, the stresses are associated with points along the pipe's centerline, and generally not stresses on arbitrary points around the piping's circumference.

So in the case of an elbow, the code provides SIFs to emulate stress at the highest stress point between the intrados and extrados, between inlet and outlet. CAESAR dutifully estimates this highest stress point, too, and reports such.

The same can be said of custom fabricated tees. Based on the B31.3 algorithm, it estimates the highest stress point for the configuration at hand through the SIF and labels the entire connection as either passing or failing.

This SIF can be estimated through FEA, as well in order to outperform the code, but we can all agree that if you want to know stress levels at specific points, we have to construct that geometry somehow and calculate it.

But if you can back out the math do it on pencil and paper, I'll be impressed.
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