Feed water valve from de-aerator tank

[emanoelman]

Hi all.
I would like to ask you, is there any standard requirements for installing main valve on feed water line? On existing line, there are two valves on the branches leading to boiler feed pumps, but no valve on the main line. In case of changing/maintaning of any valve, feed water tank will drain.
Is there any common practice, or standard requirement where I can look for it?

 

[KiwiMace]

Valves can (should) be maintained during regular shutdowns. I wouldn't be too concerned with this. This is usually a very short pipe section too.

 

[emanoelman]

Yes, I am concerned. It is not a short section also, it has apoximatelly 15 m of lenght, but what worries me is emptying of the tank during maintanance. Could you help me with any standard that works with this matter?

 

[rmw]

There are no standards, just various practices based on experience and need. If you want to add a valve to be able to maintain the existing valves (which are there so you can maintain the pumps) then do you add a valve before it so you can maintain this new valve, and so on and so on...... Where do you draw the line.

Secondly, having lots of valves, fittings, bends, turns, etc. in suction piping to BFP's is not good practice. Best practice is to minimize head loss and that includes losses from piping and piping components in pump suction piping.

Do you have a history of having failures of these valves? Valves of this nature are usually serviced during plant shutdowns when you should be draining the deaerator tank anyway to inspect it anyway.

You are draining nad inspecting your DA tank, aren't you? I would be concerned about that, now.

rmw

 

[KiwiMace]

Expanding rmw's fine discourse on point #2:
Given the function of the deaerator tank is to promote the dissolution of gases, I would be concerned more with avoiding pump cavitation than maintaining the valves. My comment on such a design would be to ask if the pumps can be located closer to the DA.

 

[11echo]

My part of the world it's good practise to have a block valve at the tank! What if there is and issue with one of the two valves or the piping from the tank? You'd have to drain the tank to be able to deal with it. But with a block valve on the tank there would be no issue at all, any issue could be easily dealt with. As far as head loss ...use a full port block valve. My $0.02!

 

[emanoelman]

Thanks for your posts, guys.
But, I'll install the block valve, just in case. All of them will be normaly open, so problem expectancy should be minimum.

 

[Duwe6]

Additionally, API-510 and NBIC both strongly recommend magnetic particle - MT - testing and a visual Inspx of the inside of DA tanks every 5 years. There is a well documented stress-corrosion cracking mechanism of welds inside DA tanks. This Inspx will give you the time to clean and repack your valves.

Personally, I prefer to have a rebuilt valve instead of a new one. Who knows what grade of person built a new valve? Whereas a rebuilt one was done by a valve specialist.