SURGE CALCULATION 1

[Buchi]

Hi guys,

i need explation on surge calculation in pipeline hydraulics.

what it is all about, why do we have to do it, how to go about e.t.c.

i will appreciate a very simplistic explanation.

cheers

Buchi

 

[MortenA]

Surge (or water hammer) is when you stop a liquid flow. The kinetic energy need to go somewhere.


Why do you have to calculate: Because the surge pressure might exceed your design specs incl margins. But you dont _have_ to calculate anything. You may just hope that you have left the company if something goes wrong!

A good simulation might tell you where to spend your money (more steel, surge relief valve, RV's whatever)

You can calculate the total kinetic energy in the volume of liquid moving in the pipeline. If you assume instant closure and no compressability then you should be able to calculate the resulting force easily.

However all liquid _can_ be compressed. This means a (much) lower surge pressure.

From Perry you get the most common "rule of thumb":

h(wh)=a*DV/gc

where

a=sqrt(1/(den/gc*(1/K+D/b*E)))
(velocity of wave propagation)

and
h(wh)= water hammer head
V=change in fluid velocity
gc: grav. constant
den: Fluid density
K: Bulk modulus
D= pipe inside diameter
b: Pipe wall thickness
E: Young modulus for pipe material

Some of these properties might be difficult to obtain

The formula is a conservative estimate of max. surge pressure.

Anyway its complicated stuff. I recommend that you contact a consultant if its critical work and your company dosnt have any inhouse knowledge

Best Regards

Morten

 

[ramamag]

MortenA has given the source from where you can get the necessary equations. Generally, water hammer or surge in liquid line occurs, when there is a sudden closure of a valve (mostly ESD valve) on the downstream end of a pipe. The parameters of critical importance are the length of the pipe, size, MOC(whether Metallic or Plastic), fluid flow and fluid type. The bulk modulus of compressibility for water is 2.2 E+09 Pa and oil is 1.5 E+09 Pa. The Modulus of elasticity of a CS pipe is 2.1 E+11 Pa and PVC pipe is 3.1 E+09 Pa. I have developed a spreadsheet for calculating water hammer in pipes. I am willing to work out the answer if you can give me more details of your requirement.

Alternatively, you can use "Google" as your search engine and type "Water hammer" and you would get a few sites which would offer a method to do the calculation.

 

[Samiran]

Try this site:

http://www.lmnoeng.com

 

[KernOily]

Strictly speaking there is a difference between 'surge' and 'fluid hammer'. It depends on the wave speed and the duration of the disturbance. The euqations used to calculate the magnitude of the pressure rise, and the magnitude and direction of the subsequent reactions on piping and equipment, are different depending on whether you have a surge or a real-live hammer event. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com

 

[whylie]

Gentlemen,

I have come across the simplified equation,based on (Pipelines Rules of Thumb) by Gulf Publishing 1978:

P= 0.8 x W x V

Where P surge pressure psi
W Fluid density lb/cu.ft
V Velocity change ft/sec

This equation gives < 5% deviation from the standard equation


Try it..

Whylie