Pipeline surge pressure

[PTH001]

I have an equation for surge pressure from 'Mechanics of Fluids' - BS Massey, which gives
Ap = p.c.U
Where Ap is surge pressure
p is fluid density
c is speed of wave propogation
U is change of velocty

In my case the fluid is NATO F34 so p is 775 - 840 kg/m3 (I have used 800)
I have calculated c as 713m/s
and change of velocity is 3m/s to 0.

My problem here is with units as I was never very good with maths - I get my answer as kg/m/s2 which doesn't relate to a pressure or a force as far as I know. If I could get to kg.m/s2 I would have a force which would be OK.

Now, all the surge pressure equations that I can find on the web relate to water-hammer and are in the form Ap=c.U.g where g is gravity.

Can someone tell me what I am doing wrong?

 

[BigInch]

IMHO what you're doing wrong is attempting to do a "surge analysis" when you don't have any experience or training in doing so. You arn't the guy to be doing the surge analysis, if you're still struggling with units. Why are you even bothering doing a proper surge analysis by hand. There are computers that do this kind of stuff very easily, accurately and consider all variables, and do not make the idealistic assumptions that you must do when working with a pencil.

That said,

First: Use 840.

You don't really want force either. Force/area would be good, as would Head suffice, or its equivalent Pressure. Those are the units you need to arrive at the correct answer.

Lastly, do not use the total closure time of your valves. Use the effective time. Be aware of how much flow cutoff you are getting at various positions of valve travel and take the effective valve closure time accordingly.

It would be helpful if you would post the equation you are using to figure out why the units are going wrong. Can't say the same about the analysis.

Now find somebody who can give you some training and most importantly someone who can check your work.



Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[BigInch]

Actually I find it strange that NATO would allow you to do surge analysis by hand. Nobody else I know would let you.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[PTH001]

Thanks for that valuable information.

I've used both max and min values of density.
I'm not actually carrying out a surge analysis by your definition. I am attempting to quantify an 'order of magnitude' for anchor loads in unstable ground, not really the same thing and perhaps my query title was misleading.

I'll keep searching.

 

[BigInch]

Assuming that you are not putting wide cut jet fuel and diesel into a non-steel, and long pipeline, you're still looking in pretty much the wrong direction. Now that you mention it, surge has little to do with anchor loads on continuously welded pipelines. It has everything to do with axial anchor loads and thrust block loads for weak asphalt sealed jointed concrete pipelines and similar pipeline materials. You will find that anchor loads per say on welded steel pipelines are primariy dependent on internal pressure, temperature change between tie-in temperature and operating temperature and soil cohesion value. Surge pressures in welded steel pipelines are largely taken as a very small percentage of total axial load into the walls of the steel and and evenly distributed over many lengths of pipe into the soil through cohesion or by soil pressure at bends where they rarely become significant.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[25362]

PTH001,

kg/(m.s[sup]2[/sup]) is a unit of pressure. See, please,

[•] force : m.a = kg.m/s[sup]2[/sup]
[•] pressure = force[÷]area = (kg.m/s[sup]2[/sup])[÷]m[sup]2[/sup] = kg/(m.s[sup]2[/sup])

1 N/m[sup]2[/sup] = 1 Pa = 1 kg/(m.s[sup]2[/sup])​

 

[PTH001]

Thanks for the trouble that you have taken, however, I have found the information I need elsewhere.