RE: SIF on elbow weldolet

From: <Al>
Date: Tue Mar 30 2004 - 15:19:00 EST

Chris,
I agree with some of your remarks with some caveats A well applied FEA tool eg. Fepipe or similar , even ANSYS or the others will give you a much better local stress and hence SIF value than just a "WA Guess" or a beam element program. I dont beleive that a beam element analysis is the right tool in this sort of situation.

Such more modern tools have also been demonstrated to give good prediction of the effect on stiffness and flexibility of such geometries eg when applied to branch connections or trunnions or other attachments (far better than WRC107 or other older tools). The difficulty is what value to ascribe other than as you say by testing. However these program results when properly applied can be better predictors than guesswork. In one of many instances experienced, work done some time ago on "Promat" (weldolet style assemblies) fittings that were fatigue and strain tested proved the efficacy and prediction accuracy of the tools when properly applied.

al

-----Original Message-----
From: Christopher Wright [mailto:chrisw@skypoint.com] Sent: Tuesday, March 30, 2004 11:40 AM
To: ?
Subject: Re: [PipingDesign] SIF on elbow weldolet

> Elbolets (I assume you are referring to an elbolet) are odd creatures
> and I doubt that any programs cover this fitting.
>
> Do you *really* need an elbolet (or if I am misunderstanding, a WOL on
> an elbow)?

I've been followingthis discussion for a while, and I suspect that all that's needed is a value for the classical stress intensification factor used in all classic piping analysis. Like the value associated with tees and laterals. The SIF is usually built into the element formulation along with the stiffness correction. Given that the fitting includes a fillet reinforced butt weld I really don't think FEA is going to tell you anything valuable after you have made all the necessary guesses about the weld contour, metallurgy and residual stress. A SIF value obtained from testing will take all of this into account. I've been doing FEA for about 30 years, and I think trying to model a welded connection like that explicitly is an exercise in futility.

Looking at the construction at the Bonney Forge web site (Elbolet is a Bonney trade mark, not a generic name, BTW.) <http://www.bonneyforge.com/specs/branch/elbolet.cfm> it looks to me that the stress distribution is pretty much the same as a single welded coupling welded into a larger pipe. You can probably get guidance from the manufacturer or perhaps from a good handbook on piping stress analysis.

Do a Google search on Elbolet and get in touch with some distributors.   This web site has some chatter on the subject <http://www.eng-tips.com/gviewthread.cfm/lev2/16/lev3/58/pid/378/qid/71234>

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw@skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)

http://www.skypoint.com/~chrisw

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