Re: Trunnions on Elbows
We agree that fittup and welding are really more important than analysis for every installation, (not just trunions on bends), but there are situations where analysis is required for contract requirements or to satisfy the PED, etc.and certainly there must be some reason for a pipe stress analysis in the general case. If the highest stressed point in the system occurs at a support on a bend, it could be that a bad design can be avoided by properly applying the potentially reduced "k" and modified sif at a bend with a trunion that is anchored at a control valve, for example.
It is speculated that the control valve installations do not fail because the major thermal loads do not often cycle in a Markl-piping sense, i.e. more than 7000 times in its life.
The situation is worse for large D/T pipe systems, but still many nuclear installations do not permit their use since they have never undergone evaluation by fatigue test.
More recently some clients are requesting that the round trunion be replaced by a coped structural element to facilitate inspection, and this further complicates the stress problem, since some structural sections in use take the form of a can-opener.
Other users also apply pads to these already analytically undefined junctions (because of the lack of correlating fatigue data), and produce fabricating difficulties or require the cutting-up of an oversized elbow to form the pad material.
> Hi Tom,
> Everyone are interested in Calc. Better you post the material on personal
ID
> of Paul (Moderator) and he will just Up-load the material on Group. I
think
> it will be convenient for you and all of also.
> Regards,
>
> -----Original Message-----
> From: tomcruz55 [SMTP:tomcruz55@yahoo.com]
> Sent: Thursday, March 27, 2003 12:10 AM
> To: PipingDesign@yahoogroups.com
> Subject: [PipingDesign] Re: Trunnion on an Elbow
>
> I have to disagree with comments made by Zope and Sachin. Trunnion
> is
> pretty much an industry accepted pipe support. As pointed out, even
> the guys at Kellogs ( avery long time ago) have done quite a
> detailed
> study on this very subject and recommend its use. The last book that
>
> ive read published by CASTI even has a an equation that deals
> specifically with its proper design. There are over a thousand of
> this type of pipe support installed in power plant, refinery and
> petrochem that to date is still around.
>
> And forget about the effect of the SIF, it rarely affect the result
> of your flexibility analysis. Instead focus on the details -
> welding,
> inspection and fitup if your designing one. If anyone is interested,
>
> i could post the equation for its design.
>
>
>
> --- In PipingDesign@yahoogroups.com, "Tushar, Zope"
> <zope_tushar@f...> wrote:
> > Hello Friends,
> >
> > Use of trunion on elbow is generally accepted practice. Some
> companies do not allow at all and some companies do allow on
> conditional basis.
> >
> > You can use it for temp. below 150 deg C (No problem at all.)
> > But it's not good to use it above 150 deg C. The reason is simple
> that we can take advantage of flexibility associated with the elbow
> in stress analysis.
> > Also I would suggest to avoid it above 60 deg C for Stainless
> Steel
> and Alloy Steel lines.
> >
> > Better go for a support at the pipe (horizontal or vertical as
> well).
> >
> > Thanks and regards.
> >
> > Tushar Zope
> > Piping Engineer
> > Foster Wheeler Eastern Pte. Ltd, Singapore
> > Ph: 6890 0837 Fax: 6223 2989
> >
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> >
> > ____________________Reply Separator____________________
> > Subject: Re: [PipingDesign] Trunnion on an Elbow
> > Author: Sachin_Bapat@r...
> > Date: 9/7/02 8:46 AM
> >
> >
> >
> >
> > If you go through piping design books you will find that
> > trunnion on elbow
> > reduces the flexiblity of trunnion & also it modifies the
> value
> > of sif &
> > flexibility factor . piping design book (M W kellogg)
> chapter 4
> > -local
> > components expilicitly derives relation for the same,
> thats
> > why most of
> > design companies dont prefer trunnion on elbows & use of
> pads
> > for trunnion
> > on elbow is highly discarded as all these reduce
> flexibility
> of
> > trunnion ,
> > which may be of concern in rigid layouts
> > hope this answers your query.
> > regards
> > sachin
> >
> >
> >
> >
> >
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> > Texas Flange - a good source for information on industrial
> > flanges, all they ask is for referrals for designs they
> help
> > with.
> > 877-610-8924.
> > www.texasflange.com
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Received on Sun Mar 30 06:39:00 2003
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