WATER HAMMER IN CHANGE OF MATERIAL

[CesarYalan]

Hello everybody

I have been designing a irrigation system, i shall install steel pipe for 20 first meters and the rest, 12 km, in GRP, so my doubt is: what happen in transition GRP-STEEL during a water hammer phenomen?

What's background for the majority of softwares for hydraulic transient analysis for this case?

The results seems no be real, because in the change of material the overhead up to 10 time the pressure, while in GRP is around 20%.

I'm not sure if i should use the concept: equivalent celerity.

I hope you can help me

Thanks in advance

César

 

[BrianCNTFM]

Cesar, the effect of water hammer will most likely be the same for steel and GRP.
Have you established how water hammer will occur?

It is best to design out or put in operation procedures to prevent occurence, though you cannot rely on people to follow procedures.

Regards Brian

 

[MortenA]

The wave speed is about 400 m/sec for GRP and 1200 for steel. But i have not seen that this in itself "amplifies" the surge to that degree? Is there something else? Column separation or something? What software are you using?

Best rgards

Morten

 

[MJCronin]

99654..

Can you prevent the watterhammer event ?

Installing "venting valves" at a high point...just downstream of the pumps wopuld help ???

-MJC

 

[CesarYalan]

Hello everybody

Thanks so much for your answers, i agree with your answers, but i want to know what happen with the overpressure behavior in this transition change material?, according with jokosky theory the change is very strong.....i mean in steel pipe the over pressure is around 100 psi and for GRP pipe si around 20, i bet that the radical change is not real.
Also i want to know, is anyone have ever ear about equivalent wave speed?

a=L1+l2`+....Ln / (L1/a1+L2/a2....Lnan)
where
L= pipe lenght
a=wave speed

I asked for that because in the pipeline that we have been analized i have around 13 km of grp pipe and 20 m for steel pipe, so for the transient analisys, it's important know the wave speed. may the wave speed is less. we have been used Hammer XM as software

If i use this equivalent wave speed the over pressure is reduced...

I hope you can understand me and help me

Thanks sou much

César

 

[BrianCNTFM]

Cesar if you Google "equivalent wave speed" you can get a link to a review of this book:- Hydraulics of pipeline systems By Bruce E. Larock, Roland W. Jeppson, Gary Z. Watters. You might find some assistance here. I took from it that it might be possible to establish an equivalent thickness in steel for a presstressed concrete pipe. If you did a simailar exercise for GRP it may assist.

On a slightly different note is your question really "what is the optimum transition design from steel to GRP?"

Regards Brian

 

[racookpe1978]

I'm not really sure you should expect water hammer: 12 km of plastic pipe is so flexible that the "sudden shock wave" itself (the symptom of water hammer as a valve opens/shuts quickly) is going to more likely "push" the bends of the pipe - and also expand it under the exposed temperatures ? of the open sun in a field - so that you don't get damaging results.

 

[BrianCNTFM]

Gents, if you consider the kinetic energy for the pipework in full flow and then equate it to potential energy, you can see at a quick glance the potential problem if valves are closed quickly. This is why it is imperative that valve closure is managed.

I have seen damage that can be done on systems with much smaller volumes but with higher speeds and this was largely atributed to extremely quick shutting times of valves.

 

[BigInch]

Since the plastic pipe expands more than metal, pressure wave amplitudes in the plastic piping are reduced.

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