Dear All,
I have this question regarding effect of Surge pressure during Pump Start up.
As you see in attachment, it is a Foam Generator Pump that use to mix water and foam solution for Fire Fighting purposes.
New line is Tie in into existing line using Split TEe 8"x8" with Hot tapping pressure.
The consideration is effect of Surge Pressure at the Split Tee 8" x8" at the discharge side.
As we know for pump shutdown (pump trip), the suction side will experience Delta P = Fluid Density x Sonic Velocity x Velocity differential.
and the discharge side will experience Delta P = P discharge - Pvapour.
and we can calculate the Surge Pressure by = Delta P x A x DLF

That is for pump shutdown, Now the case is for pump start up, where the discharge line initially is empty, the suction line is filled with water. When the Pump start up the empty discharge line will be filled by Foam solution Plus water.

My question:

Can i consider Delta P at the discharge side = Fluid density x Sonic Velocity x Velocity differential....?
or doest the Delta P at discharge side is only equal to the operating pressure of pump discharge?
And does the Surge Pressure significant in the suction side??
Pleas enlighten me........

Please see attachment...

Anyone can give a comment or input, meanwhile i try to simulate it using AFT Impulse....

Dylan,

Your approach is not correct. When the pipe is empty, applied loads are slug loads not hammer loads. In fact, there's no liquid to propagate pressure surge.
Slug flow loads develop because of the momentum change at elbows or intersections. Slug loads are proportional to (ρ)(A)(V^2). Slugs travel at flow velocities.

Dylan, sometimes guides and stops on pumps discharge lines, as per normal practice, do miracles. I had one situation when the designer ignored this (on a FRP line). One elbow kicked the wall. He learned the hard way.

Regards,

Dear Farhad i disagree with you...
This phenomena has been Research by Kolp (1968), Andrews (1970), and others.
If we filling an empty lines, particulary in pumped system, there will be a change in velocity that can lead to Pressure rise. As the pump start up and comes on line, Pressure surge will be developed in the downstream line. The magnitudes is depend on the sudden increase in velocity when check valve is forced open and the liquid in pipeline begin to move. If there is no air in the line, the pressure rise will not so large and will not exceed pump shutoff head, but if there is an air in the line, the when the liquid start to fill the empty line, and the line ends at any devices whic act as flow obstruction, then a serious pressure surge case will happen....why?? because when the last air leaves the segment of the pipe and water hit the obstruction, it will cause the velocity of the fluid decrease and this will lead to large increase of pressure.
Please find paper of research by Kolp, or research by Martin CS : "Entrapped Air in Pipelines, Second international Conference On Pressure Surge", and also "Concept of Waterhammer and Air Entrapment in the Filling and Testing of Pipelines" Tech. Report by John-Manville Corp.

Danb,
Yes i Agree with you Guide and stop will have important role, but i think it will not work for this configuration, (But i still work on it, who knows?), client only concern in the split tee strength whenever the force slam the split tee. Well is till check and work on it....thanks for you comment anyway..

Thanks in Advance.


Best Regards

T. Syahdilan
PFCE Indonesia

Dear Dylan,

If you think that you can come to a good conclusion out of those papers, go ahead, otherwise consult with an expert. Calculation of those theories are too complicated and may be out of reach. So it's better to do things that are feasible and recommended by today's practices.

Thanks Farhad, i'm going to use recommended practices also, because as you know as Engineer offcourse we can't rely 100% on Theory, Theory only for basic for our understanding. If Theoryly we mistake in intrepretation something offcourse it will lead to a mistake.
I appreciate your input. Thanks.

Best Regards

TS

Dear all,
Which one is more conservative or more likely to happened when pump is being start up and filled and empty pipe ?
There is two phenomena that will happened: 1. Slug Flow
2. Surge
I am trying to simulate it using Bossfluid, and when i consider both two phenomena happened, the unbalanced forced causes by this condition is to big, but if i only considered only slug flow then the load is not to big.

With system as i attached before, the unbalanced force causes by Slug and surge event at the first elbow is 67203 N. But if i only considered slug then the load at the first elbow is 264 N.

If i perform stress analysis using value from Slug+Surge pressure, i will ended up with some anchor and snubber in then system.
But if i only use the slug case alone then, my previuos configuration are still safe.

So, if any of you have several experience with pump start up filling empty pipe or maybe firewater pump start up, please share your experience, which phenomena is likely more to occur? Slug flow + Surge or just Slug Flow?
Thanks.

Rgrds
TS

I guess you need to make the concept right. Surge is preventable, use slug catchers for the slug, and I suggest you had better work on it instead of looking for the solution by the stress analysis. This makes everything simpler for all parties. You need to talk to the process engineers to reduce/eliminate the problems.

Regards,

Ibrahim Demir

Thanks Ibrahim, but the case like my first post is client ask to do stress analysis due to this pump start up because they are worry about the load effect to The "SPlit Tee" they are using after Tie in Process. Yes indeed they are right, load at the Split Tee connection is very high.
I have finished the simulation using Boss Fluid and perform stress analysis using CAESAR II. and i have this 2 scenario as i mentioned above, that is:

1. First, there will be Slug phenomena and Surge.
2. Second, only Slug phenomena that will be considered.

Some of engineer that i met, told that they have experienced with this case also and they are usually will only considered slug flow that will occur in these condition.
In Boss Fluid Manual also there is an example of this pump start up filling an empty pipe and it suggest to considered only slug flow.
But there are few papers and experiment by Kolp and Martin CS that mentioned that surge will also likely yo occur in these event.

So, my point here just to make justify whether there is among of Our Fellows here that have an experience with Pump Start Up case, and which approached that they usually used.
Thanks.

Rgrds
TS