[PipingDesign] interesting discussion Vibration

From: <Altech_m1>
Date: Sat Apr 07 2007 - 21:21:00 EDT

On Apr 7, 2007, at 8:33 AM, Jun Atibo wrote:

> And by the way, sway braces are not used to absorb vibration. And i can
back this claim with several > tech articles and books related to the use and mis-use of sway strut(s).

.. would you mind sharing the titles/sources of those articles and books. I would be very surprised if they categorically state dampers or snubbers CANNOT be used to fix vibration problems. IMHO its done all the time. If you change the restraint you change the response and thereby can damp or alter the mode shapes thereby making the vibration less offensive. Of course it ALWAYS better to locate and eliminate the source. Sometimes it's not possible and a band-aid is often all you can do. Often there are huge time, budget and client restraints.

However from Chris.

> Too many people see a piping span apparently vibrating and think that's
the problem. It may
> not the problem, only one of the symptoms. If the problem is an improperly
supported pump or flow > oscillations, bracing the span doesn't fix anything. It might even make things worse.

  .. so true. Too often they are just looking for a quick cheap and dirty solution to a significant and involved problem.

But Also.

I absolutely DO NOT agree that CII is NOT the right tool existing or in-service piping vibration .

>>"CII is not the right tool in performing vib analysis of piping already in-service. A call from Coade will easily validate what I have said.""

I don't believe Coade would say what you claim, in fact I have heard them say the opposite , on many occasions. I wouldn't attribute such a negative claim, and would let Coade speak for themselves. Refer to their forum or website or training.

Problems can be solved with reasonable caveats. Eg. It is not a "cure-all" and "fit-for-purpose" and experience are imperative.. They have (solved existing plant problems) , their clients have, many others on this forum and list have.

It may not always be the right tool but sometimes it is. Try to use multiple tools, ..an more expensive but I think prudent way to go, but what is the cost of getting ti wrong?

Very often it (CAESAR) has to be used in conjunction with other tools, often to the dismay and

rejection of clients (and bosses too) who think any one program has

"quick answers from a black toolbox". I once got reamed out by my boss because "a program" was found to have an error and somehow it was my fault the program wasn't delivering the "right" answer.

I always enjoy Chris's sage advice (albeit crusty at times).


From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com] On Behalf Of Jun Atibo
Sent: April 7, 2007 8:47 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Re: Vibration

And by the way, sway braces are not used to absorb vibration. Wrong application. And i can back this claim with several tech articles and books related to the use and mis-used of sway strut.

Imran,

How can you solve a vibration problem without knowing the forces and displacements applying to a piping system? First you must have an accurate & Real piping model which can be created by CAESAR II. Then adding some pipe supports i.e. X,Y,ZROD or sway-brace will absorb vibration.
Please refer to steps below that I've already posted.

Regards,
Farhad Salehi


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[Non-text portions of this message have been removed] Received on Sat Apr 07 21:21:00 2007

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