Let's also not forget the importance of making sure that the major stresses get concentrated where they can be directed and controlled by the proper use of guides and anchors.
I'm getting pretty convinced that we could come up with a quite nice book on piping design, just based on stuff that has been written here in this forum.
Paul
> >Too much flexibility in a piping system is not desirable since
it will have
> >difficulty in meeting the stringent allowable load imposed by
the equipment
> >(he's of course refering to the nozzle allowable loads per API
610 for
> >centrifugal pump, API 617 for compressor and NEMA SM 23 for
steam tubrine).
> Flexible pipe will decrease the nozzle loading from thermal
stress.
> Nozzle loading from external loads such as wind loads is a
little more
> complicated. If the pipe is soft (flexible) with respect to the
nozzle
> (think about a piece of pipe mounted to a very stiff support
which will
> be substantially clamped at the ends), the actual nozzle loads
will be a
> maximum but the stiffer vessel may be able to carry them more
easily. If
> the vessel is soft the end loads carried into the vessel may be
small
> (think about a piece of pipe supported by soft springs--almost
no end
> moment) be the vessel may not be strong enough to support the
loading.
>
> >The use of expansion loop makes the pipe prone to vibration
since it will
> >get easily excited by a small disturbing fluid force (normally
we term this
> >as focring function in vibration). In addtion it enhances the
internal fluid
> >diturbenace by creating cavities due to excessive delta P.
>
> The expansion loop makes the pipe more flexible so that thermal
> deformations can be absorbed with less force (A soft spring
requires less
> force to deform a given distance). It's correct that a softer
pipe run is
> more susceptible to vibration but that's because the pipe has
lower
> natural frequencies so that deformations are higher when
resonance
> occurs. A softer system deforms more under a given force than a
stiffer
> system and the bigger the deformation, the higher the stress.
>
> Sorry for the engineer-speak. I'm not really trying to split
hairs,
> Ralph, but sometimes it's easier using rules of thumb if the
physics is a
> little more solid. I find it's a lot easier thinking in terms of
stiff
> springs and soft springs rather than writing down a bunch of
equations or
> resorting to FEA.
Received on Sun Sep 30 20:40:00 2001
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