Hello Stressers,

I'm curious about the process of filling up an empty firewater line thru pump start-up case. Is the pressure gradually developed during filling up (say if my operating pressure is 10 bar is it developing from 1 bar, 2 bar, 3 bar...etc. until the line is filled-up). Or the other case where a pressure head of 10 bar has been developed already while some parts of the line is still empty. If this is the case a big unbalanced force will experience in elbow-elbow pairs where one elbow is at 10 bar while the other is at 0 bar developing a huge force of around 200KN for an 18" line...For an underground firewater line this is not a concern for a buttwelded CS pipe because the soil it self will serve to restrain this huge force..But for an aboveground piping this a huge force to design a structure for this magnitude.

Anyway, I want to know from those with operation experience how the pump startup is being done or from process engineers also.

And I was thinking also for aboveground piping since the length of elbow-elbow pairs is not so long compared to underground pipe this huge force will not be developed.

Please share your experience with this type of phenomenon. Just want to have a peace of mind while designing a firewater line...:)

Cheers!!!!!!!

Hi Borzki,

Slugs can exist due to firewater pumping systems. (Firewater is pumped into an empty system.) Slug flow loads develop because of the momentum change at elbows or intersections. Slug loads are proportional to (ρ)(A)(V^2).
Slug loading on an individual elbow is generally only a single application load that can be readily treated in mechanical piping system analysis by the application of a Dynamic Load Factor, usually equal to 2.

This link may be useful:
http://www.whatispiping.com/static-analysis-of-slug-flow

Thanks Farhad for the advice. In this case my given load to Civil of 20KN is sufficient enough to withstand this slug load because the velocity given to me by process is not so high giving me a load of 7KN with DLF=2.

Cheers!!!!