Ken,
Until you carry out an anlysis you do not know if it is a problem or not. The pipe size in question is DN1050. Any change in velocity will release a great deal of energy in the form of a pressure change. Vacuum may be the worst case and the pipeline could fail due to buckling.
Loss of power is likely to be the worst case. This will result in a nnegative pressure wave. However local situations can occur with multiple pumping. If one pump is tripped by a protection device or by the emergency stop the closing of its check valve can result in very high pressures at the pump discharge as the pressure from the adjacent pump closes the NRV.
Butterfly valves are notorious offenders in the world of waterhammer. When 20% open the flow can be 80% or more. So what you think is a slow opening valve can in fact be surprisingly quick.
The pump inertia and check valve characterisitics will have the biggest impact on the anticipated pressures.
I have sent you the two papers that appear on www.pipingdesign.com that cover this topic. Before you can establish your design pressure you need to determine the surge pressure. that is a standards and code requirement.
So your question is answered by the fact that to establish a design pressure your need to estabish the surge valve not the likelihood of an event occurring. You dont know what you dont know. Unless you are building an identical facility with proven performance how can you possibly tell if surge will occur or not?
Would you avoid sizing a relief or control valve? Guess where air release valve should be installed? Pick a pipe diameter on the basis of what the supplier wants to sell without regard to energy usage? Not look at fatigue, wind loading, earthquake, vibration etc in piping design.
Yes, surge analysis is a complex subject but one doesnt ignore it because its hard. If it was that easy there wouldnt be over a dozen different software packages for waterhammer analysis, BHRA wouldnt hold conferences every year or so on the topic, books wouldnt be published, university courses done away with and the Codes and Standards wouldnt refer to it.
Geoff
Ken Eppleston <keneppo@yahoo.com.au> wrote:
This mostly directed at Geoff but all advice is welcomed,
We have a large closed network utilising insulated steel pipe and I am trying to understand the likelihood or risk associated with a pressure surge.
This network is entirely buried and we have not been commissioned to undertake the pumping plant design- so we have little control of valve selection and/or control within the plants.
There will be 3 pumping stations each pump is variable flow and all valves in the network are manually operated large diameter butterfly valves. Roughly there will be 20 pumps in each pumping station.
My limited understanding of surge and water hammer is that it relies on a fast change in pressure (by valve closure or loss of pumps etc) in the network which propogates through out the system causing if not catastrophic failure then fatigue.
The overall system pressure will modulate in accordance with demand but this will be controlled by VSD's on the pumps, also given that the entire network is completely restrained by the soil and that there is no real risk that a valve can be shut quickly...Is surge and water hammer still a potential risk on the system and why?
The size of the network dictates that any ramping up or down of pumps will not induce a rapid change in the network pressure. And even if one pumping station goes down because of power failure the other two will be designed to pick up the slack. My thoughts are that this still may induce a rapid change in pressure??
Can managing the operation (including the event of a failure) of the network in such a way as to avoid any rapid pressure variations be used to eliminate the risk or surge and water hammer?
Any ideas or comments??
YAHOO! GROUPS LINKS Visit your group "PipingDesign" on the web.
To unsubscribe from this group, send an email to: <a href="/group/PipingDesign/post?postID=9fcMoZprDtxnIkdVAlOw__UDMiGLzQh-qLu_MWW3g3kEYgWY3gZ6m2rbYwGApr3_grWJvOy_lkwgO4Y1V5Ww-_oj7IvCtFsoxPBVac4_mA">PipingDesign-unsubscribe@yahoogroups.com</a>
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
Design Detail and Development (a division of Blenray Pty Ltd)
Mail Address PO Box 1351 Castle Hill NSW 1765 Australia Tel Mob 0402 35 2313
Office 02 8850 2313 AH 02 8850 2324
We specialise in pipe network and waterhammer analysis, pipe stress analysis,
the design of buried pipelines and thermoplastic pipe systems.
[Non-text portions of this message have been removed] Received on Thu Jan 12 23:04:00 2006
This archive was generated by hypermail 2.1.8 : Tue Mar 04 2008 - 11:40:46 EST