Re: [PipingDesign] ->Nozzle loads on Rotating Equipments

From: <George>
Date: Tue Jul 05 2005 - 08:27:00 EDT

Guys:
Just a cautionary word on nozzle loads. Be sure you check all the loads involved, and that analysis runs at least to the closest significant piping anchor. We installed a couple of 6000 hp centrifugal compressors, with axial inlet/radial outlet piping (20", 1000 Psig rated). Had about 100 feet of unanchored piping on each side, and made up the piping with no load. When piping was pressurized, it shifted the compressor about 1/4 inch on its mounting. I assure, if it had been running, would have caused some vibration. Point in effect, look at what total loads on nozzles would be, and possible resulting misalignment. This can cause problems which are specific to a certain operating condition, as pressure or temperature on piping change force on nozzles.

George McKinney

   Somehow this view may be too generous for rotating equipments I feel. Some    rotating equipments are not that generous that they will permit high piping    loads.

   My personal experience has been that whats there in the model should    translate in the field. To find out that, we need a thorough audit. With all    due respect to our site counterparts, we should also ensure whether these    piping connections are freely aligned with the nozzles ? We should also run    a case for this (for free alignment) I believe. Even the first few supports    are also very crucial.

   Regards,
   Shreedhar.

> Rajesh,
>
> Most of machine vibrations I have encountered are not due to piping. Big
   machines like turbine, big pumps etc are too massive and piping loads in    itself are really trivial, considering the inertia of the machine (with    foundation). Of couse exception are bad piping design, but again, these are    really exceptions.
>
> I appreciate your concern regarding equipment vibration. I always believe
   that the root cause for these vibration is not stand-alone piping design but    the system in itself. Hence reducing static load in equipment nozzle may not    be the correct solution.
>
> Pankaj.
>
> Rajesh.Balapure@ril.com wrote:
>
> Dear Pankaj,
> Thanks for your reply,
> There are lot of theories ,hypotheses,conjectures,hunches,feelings on how
> the piping loads affect the rotary equipment performance for which keeping
> the vibration levels within limits is an absolute requirement.We do not
> want to have a theoretical discussion on this issue but we are looking
> for any real experience on the effect of piping loads on machine
> performance(i.e.Vibration levels of the machine ).
> If you are having such inputs please let us know.
>
> P.S.
> "Now, regarding piping load on rotating equipment nozzles, the real
   concern
> is casing distortion. Since these are precision equipment, gap between
> casing and impellers are small and a small local distortion in casing
   could
> result in performance failure. Also, overall stability of the equipment
> needs to be considered".---->Your statement in a way justifies the concern
> of vibration levels increasing with machine loads.
>
>
> Regards,
> Rajesh V Balapure
>
>
>
> Pankaj Mandal
> <man45039@yahoo.c To:
   PipingDesign@yahoogroups.com
> o.in> cc:
> Sent by: Subject: RE:
   [PipingDesign] ->Nozzle loads on Rotating Equipments
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>
> 07/02/2005 02:33
> PM

> Please respond to
> PipingDesign
>
>
>
>
>
>
> Rajesh,
>
> Your statement "There are concerns that the vibration levels of the
   machine
> can be increased with high piping loads"- is not fully correct. Piping
> loads on rotating equipment are mostly static in nature. Piping, in
   itself,
> do not vibrate. In some cases like pump cavitation, slug flow or other
   flow
> related issues causes vibration in piping. In extreme cases, due to poor
> design, eigen frequency of piping comes in proximity to the natural
> frequency of the rotating equipment (with foundation) and this causes
> vibration in the system.
>
> Now, regarding piping load on rotating equipment nozzles, the real concern
> is casing distortion. Since these are precision equipment, gap between
> casing and impellers are small and a small local distortion in casing
   could
> result in performance failure. Also, overall stability of the equipment
> needs to be considered.
>
> I agree that in some cases codes, specially API610, gives nozzle
   allowables
> that are hard to justify. Like pump allowable for a discharge pressure of
> 150psi is same as 1500psi. A higher pressure (discharge) pump should have
   a
> stronger casing and hence should be able to sustain higher load. But code
> has no such provision.
>
> That's it in a nut shell. You are right. Lots of literature is already
> available and one should go through it for further details.
>
> Best regards,
> Pankaj Mandal.
>
>
> Rajesh.Balapure@ril.com wrote:
>
> Dear group members,
>
> A lot has been said &discussed (& also huge amount of literature available
> ) about the piping loads on the nozzles of the rotary equipment.There are
> concerns that the vibration levels of the machine can be increased with
> high piping loads.We have come across many machine vibration problems
   which
> were supposed to be caused by piping loads on the nozzles but finally the
> problems were found to be else where.
> I would like to know from the team members about your "actual experience
> "on the effect of piping loads on the vibration of the rotary equipment.
>
>
>
> Regards,
> Rajesh V Balapure
>
> [Non-text portions of this message have been removed]
>
>
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[Non-text portions of this message have been removed] Received on Tue Jul 05 08:27:00 2005

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