VALID? 3/4 double block and bleed valve as a drain 1

[monirri]

Hi

Is it valid to use a 3/4 DOUBLE BLOCK AND BLEED BALL VALVE as a drain? (I mean, with one of the ends directed to the atmosphere. From what I've read, these valves are used where there is flow or in a instrument, not in drains)

In which case one of these valves can be used in a drain?

Thanks
Carlos Molina

http://www.apiexam.com

Carlos F Molina

 

[pennpiper]

monirri.
The major issue on your question is:
- the Commodity?
- the Operating Pressure?
- the operating Temperature?

If these issues are not in the high risk zone, then I would not buy a single unit "Double Block and Bleed Ball Valve" (Price them out).
Consider purchasing three simple Line Spec. Ball Valves and a "Tee" fitting.

Sometimes its possible to do all the right things and still get bad results

 

[monirri]

Operating pressure: 2500psi
Temperature:50 celsius
Service: injectión water

Why would be needed to use a DBBV in a drain? Or 3 valves anda TEE fitting?

Thanks


Carlos F Molina

 

[mk3223]

Need to clarify the purpose of the DB&B piping on the HP injection water system. It could be a safety or contamination issue while draining the water through the bleed valve, the HP water leaking to the other process piping through the "single" isolation valve.

 

[Danlap]

Hi,

Aside from the classic tug-war between mechanical and instrumentation over DBB, PSV and actuated valves, you can assess by yourself whether the DBB concept suits your operational philosophy
You’re still missing some details though

DBB concept in general is:
-More compact in face to face dimension, and less leakage path. Shall compared with your proposed configuration
Except for gland, for non- integrated DBB concept you will have extra leakage path between Ball A and bleed/tee as well as between Ball B and bleed/tee
-Extra assurance that minimum to non-leakage shall pass through Ball B (downstream)
-Whenever deemed required, prior open Ball B the bleeder can be used to reduce the pressure surge or Delta P between Ball A and B

Need some details over your situation:
-2500 psig, is this the class rating, or maximum Delta P prior opening one of or two of the valves?
-Assumed the Seats are metal seated?
-Water?? Brackish, brine, with salt in some concentration, or with other components??
-The DBB concept that you’re using:
The bleed goes to close and pressurized loop? What is the pressure
For what purpose the bleed is used? Is it mounted to a pressure gauge so that one can check whether there is pressure between two Ball? Is it with “sight glass” so that if there is water then one of the valve is passing? Etc.
-Draining it with the downstream valve or with the bleed?
-What is the downstream pressure?
-If upstream always “wetted”, is the bleed and downstream also always wetted?

Some justification that I can think of:
Water + air (since water is not always presence) + some ideal condition will lead to corrosion
-Space constraint, the shorter the better
-Assuming bleed sometimes filled with water and sometimes air, shall you have extra leakage path (1 ball valve + tee + 1 ball valve) then the connection is susceptible for crevice corrosion.
-The general concept itself (shall you mount the bleed with pressure gauge or even just a simple sight glass), provide some “convenience” for the operator to understand the level of pressure/leakage inside the DBB prior opening one of the valve

Not a big fan of blow down 2500 Psi to atmospheric level just using one ball valve. It will have premature consequence over the ball vs seat. But indeed, some people do this, the fact that it is water makes it ALARP??

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[LittleInch]

I'm not really following your question.

Is the 3/4" valve really a Double block and bleed ball valve? - Some details would be interesting to see unless you mean the integrated double valve body type thing?

Can it be used as a drain? - Depends on your isolation philosophy / rules.

Having DBB for drains can seem a bit OTT, especially if you've got positive isolation (Blind flange) on the end. I personally think the double isolation thing has gone a bit far, especially for non hazardous fluids at low pressure. The point is how you ensure that there is no pressure in the system before opening the drain valve??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.