Hi Pankaj,
As u said, it is always correct that no one can put more than one axial stop in a straight pipe run. If any one wishes to put more than one axial stop, then they must go for expansion loop to absorb the thermal expansion and also to avoid overstressing of pipe line due to axial thermal stresses. However, the idea of limit stop with some gap is not new in stress analysis field, this is only a tool to avoid partial axial displacements and also limiting loads to the maximum possible allowable limits.
It is a common practice to use actual stiffness values near the equipment nozzle to avoid over rigidity fixing conditions in flexibility analysis. However, flexible limit stops are not common in the practical industrial stress analysis field, but if one is having time and money then they can do this kind research on this subject.
Cheers
Phani
Mandal Pankaj <Pankaj.Mandal@siemens.com> on 19/04/2002 09:10:28 PM
Please respond to <a href="/group/PipingDesign/post?postID=rQxUB38cbfX4_rqthPp5U1L8rX7uHPlrD8Zaax0RIeIDeR65rVf0BNh7gIXpPtHGltEredOO4aOFcdaWz64084BtthkAwg">PipingDesign@yahoogroups.com</a>
To: "'PipingDesign@yahoogroups.com'" <PipingDesign@yahoogroups.com> cc: (bcc: S V S PHANIKUMAR/L&T-CHIYODA) Subject: AW: [PipingDesign] Limit stop in Piping stress analysis
Dear Steve,
We are now into a deeper topic. What should be the stifness at the point
where we connect our support with steel or concrete. We can of course
calculate individual stifness. The range will vary (very flexible if we
have
a cantilever steel supporting arrangement to very stiff if we connect to a
concrete column, for example). The point here is to what depth we should
perform an analysis.
I know that people with nuclear background calculate stifness for all these points. But they have the time and money to do so. And the risk involved in case we end up in a failure is also too high.
So to sum up the story, I advise all to follow conventional solutions for simple problems to save time and money. In case you have critical problems, do all that is necessary.
By the way, axial stop with a gap was a new idea for me. I never used the
same in any projects. Could work since guide with gaps are used
extensively.
But please remember that in that case we will deal with gaps correct to
last
decimal in mm (not the case for guides). Again time and money involved in
erection.
One last recommendation for horizontal spring installations. Please
remember
that we are deling with siesmic forces also at least in most sites. In that
case we will have tension force compomemt in the spring (Spring is never
designed for tension). This is the specific reason why we normally never
use
horizontal spring installations.
Pankaj Mandal.
-----Urspr
üngliche Nachricht-----
Von: Steve McKenzie [mailto:Mechproj@xtra.co.nz]
Gesendet am: 19 April 2002 14:56
An: <a href="/group/PipingDesign/post?postID=rQxUB38cbfX4_rqthPp5U1L8rX7uHPlrD8Zaax0RIeIDeR65rVf0BNh7gIXpPtHGltEredOO4aOFcdaWz64084BtthkAwg">PipingDesign@yahoogroups.com</a>
Betreff: Re: [PipingDesign] Limit stop in Piping stress analysis
Dear Kaustubh
We think the same. However nothing is perfectly rigid. If a bit of
flexibiity will overcome the problem, why not use it? A "stop" is never a
stop; it always moves. The problem, as I see it, is to constrain the
movement of a long, straight pipe to within limits. If springs on the
"stops" will do it then why not? The calulations will show. However I
totally agree that the use of three hard stops on a single straight run is
a
recipe for fracture. So build in some flexibility by springs or cables and
counterweights.
By the way, there has been a lot of talk about coefficients of friction on
flat shoes, using teflon and the like. If I have a pipe that simply has to
move, I always use rollers. Do the sums and you will find the resistance is
very small. And they cannot tip and jam.
I repeat I am not an expert on this subject, but I do like a debate, and thats what I bvelieve is part of the purpose of discussion groups.
Cheers
Steve McK
> Dear Steve,
>
> I did not get you exactly.
>
> What I think, it can not be possible with rigid restraints. In case of
rigid restraints the line would be overstressed due to not allowing thermal
expansion. In case of multiple restrictions in a straight line, The
supports
can be sheared off or it can damage the pipe as well.
>
> With rigid supports, we can achieve the distribution of load
theoretically, as suggested by Tushar, but this system will be very very
difficult to be implemented at site. And more over, the performance of the
system could not be evaluated exactly due to deviations at site.
>
> I case of springs, being the low stiffness, supports absorb the thermal
expansion of the line and reduce the thermal stresses. But this certainly
can not work with conventional rigid limit stops.
>
> Regards,
> Kaustubh
>
>
>
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[Non-text portions of this message have been removed] Received on Fri Apr 19 23:45:00 2002
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