Pressure surge(water hammer issue)
Pressure surge(water hammer issue)
(OP)
Can anybody help me with issue descibed below.
During introducing of seawater from 14barg pressurized system to another system which at this time is at 1barg, damage to downstream equpment was observed. Our suspect is that damage is created by water hammer. I found a lot of formulas to calculate water hammer effect if discharge valve is closed. But in my case is backwards, isolation valve is opened. My quiestion is can I use the same formulas. If not can anybody suggest right formula for this.
During introducing of seawater from 14barg pressurized system to another system which at this time is at 1barg, damage to downstream equpment was observed. Our suspect is that damage is created by water hammer. I found a lot of formulas to calculate water hammer effect if discharge valve is closed. But in my case is backwards, isolation valve is opened. My quiestion is can I use the same formulas. If not can anybody suggest right formula for this.





RE: Pressure surge(water hammer issue)
1) Surge arises from abrupt change of velocity of a fluid
2) Cavitation (column separation) may make things worse - these often occur at the same time
When you have a flowing stream and closes a downstream valve you have a classic water hammer - this can be estmitated by use of the Joukowsky equation. Check this article at wikipedia - look OK:
http://en.wikipedia.org/wiki/Water_hammer
It could also occur if you have a dry pipe that you prime - the downstream end terminates in a valve. This valve will have a very high capacity for air compared to water. So once the water hits the valve it will slow down considerable and you have a water hammer - even though you don't close a valve.
2) can arise eg. from tripping a pump or closing an upstream valve. But other circumstances must also apply - so that the pressure increase sufficiently for the cavity to collapse.
Best regards
Morten
RE: Pressure surge(water hammer issue)
I haven't heard of water hammer working the other way, but it may be possible, in which case (this may be stupid question) can't you just open the isolation valve slowly? Therefore introducing the high pressure water at a much slower rate.
Or use a pressure regulator therefore actively controlling the pressure rather than just opening up a valve?
RE: Pressure surge(water hammer issue)
RE: Pressure surge(water hammer issue)
In a closed conduit, when in normal operation a valve or wicket gate is open, the flow of water is increased, energy is supplied to set the water in motion, with a consequent reduction or drop in the hydrostatic pressure.
atayto (and specially SEP87), in order to get a better idea regarding this subject, you can read the book "Waterhammer Analysis" by John Parmakian.
RE: Pressure surge(water hammer issue)
Here you can see the effects of a sudden opening of a valve or gate in a hydroelectric power plant.
RE: Pressure surge(water hammer issue)
The equations calculating pressur increase based on valve closure, OR OPENING, time are not based on a F = M A concept as above, but on Bernoulli's change in pressure is inversly proportional to change in velocity relationship. V^2/2g. That assumes that the initial velocity or final velocity is constant whereas with F=MA, V = A dt. You'd be better off figuring the Acceleration on the fluid column with an instant introduction of 14 bar on one end, and the Force in which that would result. Its more like hitting the 1 bar system pipe on one end with a real hammer with a total force of 14 bar * the cross sectional area of the pipe, or something like a 22,000 lb smack on the end of a 12" pipe. Ya. You might expect a bit of damage from that.
The valve formula would essentially divide that blow (or something like it) into an impulse lasting for the valve closing time, say 22 seconds, which is only 1000 lbs a second or so. Maybe the same 22 K lb hit through a 2 meter thick hard rubber mat. Much different than a hammerlike hit of 22K lbs right on the "bean".
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Pressure surge(water hammer issue)
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Pressure surge(water hammer issue)
Thank you for your valuable input.
I will endeavour to read said book, to ensure I can provide equally valuable information as yourself in future. Perhaps I could even attempt to answer the question posed. I would, at least, be able to direct the person asking the question to some useful information.
RE: Pressure surge(water hammer issue)
RE: Pressure surge(water hammer issue)
When you open the "gate valve on the bottom" is there another valve on the other side of the heat exchanger that is also being opened?
If you have a system that is full of water (which is relatively incompressible) and you open a valve and try to inject more water at a higher pressure, the water has to go somewhere. If there's nowhere for the water to go to, the pressure in the system will go up until it's at equilibrium (like BigInch said). It sounds like the equilibrium pressure was higher than the heat exchanger (which was the weakest point) could take -- so the heat exchanger broke.
A general rule that I like to keep in mind with water is "what goes in, must come out. If you're adding water to a full system, then you need to have somewhere for the water to go -- an open exit valve, a relief valve -- or a leak in the piping somewhere where you don't want it.
Patricia Lougheed
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RE: Pressure surge(water hammer issue)
If you only have a system 100 m long, most of that pressure increase will happen in 100 m /1000 m/s, or about 2/10th of a second.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Pressure surge(water hammer issue)
Thanks for comments. Could you please also advise how can i prevent this issue fro reoccuring. Will be bucking pin PSV be appropriate for this. I looked through option of installation of surge vessel(similar design to pulsation damper) but size required is became enormous. I am currently looking through option of replacing gate valve with equal persentage globe valve.Could you please advise what is the most reliable method in your opinion?
Thanks
RE: Pressure surge(water hammer issue)
I think it would be appropriate to place a downstream pressure control valve (set to the 1 bar system's MAOP) between the 14 bar source and the 1 bar system. I would also put an automatic closure valve just downstream of that PCV set to close at the 1 bar system's MAOP +5% or so, and a relief valve downstream of that set to MAOP + 10%.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus