14 replies to this topic

[justcrazy85]

Hello to all the forum.... I am writing to ask for your support

I am developing a project to replace a motor operated gate valve on a 12 '' Pipeline with a twin seal valve. Does anyone know how can i evaluate the correct valve closing time to avoid the "Fluid HAmmer" Effect?

Thanks for your support

Antonio

[kkala]

I believe previous thread http://www.cheresour...-relief-system'> http://www.cheresources.com/invision/topic/13890-pipeline-surge-relief-system can be of some help (introduction, clarifications, references). Post No 23 may be of particular interest. I suppose the pipe contains liquid. You can estimate water hammer effect by some formulas (or software) for several closure times of the valve, then select valve closure time to produce an effect that is acceptable. Detailed estimation is laborious, yet a rough quick estimate is much easier.
In my opinion, recommendations on valve closure time are of quite little value, so you should do the calculation to estimate increase of pressure due to water hammer effect.

[ankur2061]

justcrazy85,

A closure time of 30 to 60 seconds is considered to be more than adequate for the purpose of minimizing a pressure surge wave.

Surge analysis for single-phase can be done using TLNET for liquid and TGNET for gas. The software is supplied by PIPELINE STUDIO and is quite popular for single phase.

For two-phase or multi-phase surge analysis can be done by OLGA from SPT Group. This is one of the best software for pipline modeling but also quite expensive.

A spreadsheet for calculating instantaneous pressure rise due to valve closure and wave velocity can easily be generated. The calculations are quite simple and can give a preliminary estimate for pressure rise or surge pressure due to valve closure without having to do any modeling.

Hoe this helps.

Regards,
Ankur.

[justcrazy85]

Kkala, Ankur

thanks to both of you for your support.
Just one more question for you Ankur:

For my porpouse a preliminary estimate should be enough and I don't think I need a detailed modelling. You said that a spreadsheet for calculating pressure rise due to valve clousure and wave velocity can be easily generated. Should I generate it referring to links provided by Kkala or should i use other references?

Moreover, Currently a gate valve is installed on the P/L I am talking about. Obviously I already know current closing time. Now I want to replace it with a twin seal valve. Do you think that closing time (to minimize water hammer) is strongly affected?

Thanks in advance

Regards

Antonio

[ankur2061]

Antonio,

I already have a spreadsheet for surge pressure and wave velocity calculation based on instantaneous valve closure using the Joukowski equation. I am contemplating putting it on my blog in "Cheresources". Meanwhile you can try building your own calculation sheet using the following link:

http://help.intellis...papers/6020.pdf

Hope this helps.

Regards,
Ankur.

[breizh]

Consider this resource , it might help you


http://www.ajdesigne...ad_equation.php

Breizh

[vikramltv]

As per my knowledge..
Valve closing time is fixed by valve vendors.(say 10 sec.)
We calculate the time for the pressure to reach an unwanted high value at source (say pump) due to sudden valve closing witn the help of process softwares like OLGA or Natasha Plus.
Now we check whether this calculated time (say 15 min ) is sufficient for remove the cause of pressure upset or take some corrective measure to reduce the pressure (overcome the water hammer effect).

But we can back calculate to find the valve closing time once the responce time for corrective measures are known...
I Hope this little bit information will help and invites other process experts to cast some more light on this..

[Shivshankar]

Just Crazy,

A piping failure due to water hammer because of which system upsets can develop high piping loads.

When a valve is closed quickly, a dynamic condition sometimes called water hammer can occur. This

phenomenon may be noticed when a home faucet is suddenly closed. When the water lines are loosely

supported, the pipes may rattle or a loud thud is heard. The cause is a pressure wave that can accelerate to the speed of sound in a liquid due to the velocity change. The resulting pressure differential, Δp, (lb/in.2) can be determined by considering the change in linear impulse and fluid momentum

Δp = 0.028 X V X L/t

where V is fluid velocity in the pipe (ft/sec), L is pipe length (ft) and t is time for the valve closure (sec).

The average force, F, (lb) exerted at valve A, is due to this Δp times the pipe flow area, A (in.2).

F = Δp X A = 0.028 X V X L X A/t

References:

1 Design of Piping Systems, Hydraulic Hammer, M.W. Kellogg Company, Wiley, 1956, p. 283.

2 Sofronas, A., Engineering Methods With Applications to Industry, 4th edition, EP Press, pp. 4 - 6.

Hope this references will help you more.Good Luck!

Regards
Shivshankar

Attached Files

•  Water Hammer.pdf   191.74KB   118 downloads

Edited by Shivshankar, 03 May 2012 - 02:57 AM.

[Shivshankar]

Also refer to this paper

Consider the destructive force of water hammer by Heinz P Bloch (Hydrocarbon Processing)

Regards
Shivshankar

[justcrazy85]

Thanks for your support...

Just one question more.... is there any simplified method to estimate the change in water hammer effect due to the replacement of a valve with another one? Let me explain it better below.
On a P/L there is a gate valve installed. When it was installed, it was estimated the proper valve closing time to reduce water hammer effect..and it works!
Now the scope of the project is to replace this gate valve with a twin seal one. So i would like to know if current closing time is enough or if it is too high due to a possible increase in water hammer effect. Do you know if a rough estimate considering valve typology is available? Or should i run a detailed analysis with a proper software?
Thanks again

Antonio

[justcrazy85]

Thanks to all of you for your support...All references were very interesting and they made me understand better water hammer effect...

Just one question more.... is there any simplified method to estimate the change in water hammer effect due to the replacement of a valve with another one? Let me explain it better below.
On a P/L there is a gate valve installed. When it was installed, it was estimated the proper valve closing time to reduce water hammer effect..and it works!
Now the scope of the project is to replace this gate valve with a twin seal one. So i would like to know if current closing time is enough or if it is too high due to a possible increase in water hammer effect. Do you know if a rough estimate considering valve typology is available? Or should i run a detailed analysis with a proper software?
Thanks again

Antonio

[Shivshankar]

Antonio,

Please upload your sketch of pipe line and valve installed and calculations document, so the members can help you more effective manner.

Regards
Shivshankar

[Stefano]

Antonio, I think that the characteristic of the valve will affect the water hammer. The more rapid the variation of the flowrate in pipeline the bigger will be the pressure wave. So the closure speed should be considered in conjunction with the valve tipology.
For the evaluation of water hammer in pipeline I used the software "AFT Impulse", and it worked very fine.

[justcrazy85]

Ok...

Stefano I absolutely agree...this is the reason I asked for that. I think that a detailed modelling should be considered.

Thanks for all your contribution.... I think that info provided on this topic are enough for my porpouses... Thanks again

Antonio

[kjvenky]

I have a MOC code written by me which does a detailed solution of the same.I can help you . I am a engineering freelancer from IITM