Agreed. But sometimes or most of the times I found people deciding
supporting and stress analyzing are not sufficiently experienced. And
they think that they should provide guides and line stops only when they
think that this is required from stress analysis point of view. People
do not think that whenever some liquid flows through the pipe it hits at
every change in direction creating some forces. To restrain that proper
guides and line stops are to be provided otherwise as an obvious case
vibration problem will come. From George's mail I am anticipating that
similar kind of thing happened there. Support design was poor. Sometimes
you do not need to analyze even just looking at the routing and supports
selected can give you a feel of anticipated problem.
Tanmoy
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=4QYiMvc-j6TmCu-pkAyRX5phLXWY0MhL5qeUjeT6cfM88L81WBqDjnad_H6IhO5nbMzDbFftMy2euD52SV-t23Y0n2Y">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=4QYiMvc-j6TmCu-pkAyRX5phLXWY0MhL5qeUjeT6cfM88L81WBqDjnad_H6IhO5nbMzDbFftMy2euD52SV-t23Y0n2Y">PipingDesign@yahoogroups.com</a>]
On Behalf Of Pankaj Mandal
Sent: Thursday, July 07, 2005 10:59 AM
To: <a href="/group/PipingDesign/post?postID=4QYiMvc-j6TmCu-pkAyRX5phLXWY0MhL5qeUjeT6cfM88L81WBqDjnad_H6IhO5nbMzDbFftMy2euD52SV-t23Y0n2Y">PipingDesign@yahoogroups.com</a>
Subject: Re: [PipingDesign] Pump Nozzle loads
Tanmoy,
One cannot encounter bad workmanship in site with any amount of good engineering. So, it is impossible to take proactive measures if the pump itself is erected wrongly, the foundation is cast in wrong place or piping installation is not proper. In these cases, we need to do re-engineering and modify design as per actual situation.
What best we can do as design engineer is to ensure that our design is in line with all the data available with us, should be feasible to erect and operate and take care of limited site adjustments.
In case of rotating machinery, we used the concept of floating nozzles in cold. This ensured that in cold condition (erection phase for example) there is no residual dead weight on respective nozzles, thus ensuring perfect fit during installation.
Regards,
Pankaj Mandal.
"Saha, Tanmoy" <TSaha@mcdermott.com> wrote:
Rajesh
You asked that pump nozzle loads are cause of pump failure. Normally for any rotary equipment it is decided by agreement with the pump vendor how much load will be allowed to his nozzles. 2 times Nema/API allowable or more. By pipe stress analysis we are supposed to check how much load is coming to the nozzle due to piping. If it is more and cannot be reduced it has to be sent to the pump vendor for his checking. Nozzle loads are case of mutual agreement. Breaking that agreement from either side is not acceptable. Normally pipes are installed after installing of the equipment and piping field welds are provided accordingly. First support from the nozzle for pump piping is kept adjustable type to take care any vertical misalignment.
My personal discussion with some field construction guy and my experience gives a horrible picture. Sometimes they do not care about reasons for field welds or by mistaken FW has been missed in drawing. As a result there is a misalignment. In that case construction people will work in the middle of the night and pull the pipe to connect the flange to the nozzle. Actually that creates the problem. This gives more loading on the shaft than it is designed for. Since the shaft is a rotating object this will give an unbalanced force. Hence your bearings and shaft will fail. But things are changing now as QC are doing a better job nowadays and quite strong.
For compressors I feel they are relatively very sophisticated equipment and needs a lot of care. There piping loads may not be the main cause of failure. But it is advisable for few pipe supports adjacent to the compressor/turbine nozzles to be of spring support type.
Tanmoy Saha
Senior Mechanical Engineer
McDermott, Dubai
++971 4 8043132
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