CONVENTIONAL DOUBLE BLOCK AND BLEED VALVES SYSTEM CONFIGURATON

[Pro409]

Dear members,
In the gas process plant, where must(or can)the conventional double block and bleed valve be used?
any comments is appreciated.

 

[PieterStander]

Please see attached, this might help

http://www.dlm.co.za:

Over Pressure Protection; Flow, Level & Density Measurement; Automation and Control.

http://www.metermatic.co.za:

Electronic Presets; Additive Systems.

 

[zdas04]

This comes up frequently. Please see faq378-1612 for my comments on the subject.

David

 

[JLSeagull]

People use double block and bleed where positive shutoff is required.

 

[Pro409]

thank you
but, In the offered matter it is reffered to the hot work for which the double block and bleed can be used for the isolation. but, some pepole consider other criteria required for considering double block and bleed. these criteria are:
1. in high pressure system, operating press. above or equal to 70 barg
2. H2S partial press. > 1 bara
3. all normally closed process lines connecting to drain.

what is your opinion?

 

[zdas04]

My opinion is that the term "positive energy isolation" comes from the realm of Health and Safety. Since the DBB concept lives in that realm, the only reason for it is personnel protection from energy sources (not even from poison gas, but that one would be hard to sell in court). If there are other applications that want two seating surfaces separated by a vent (for another example, if someone just HAS to have a bypass around a custody transfer gas measurement station I make sure that they have a way to verify that there is zero leakage around the meter), they will have their own criteria and limitations. The stuff you mention might be a reasonable place to put the equivalent of DBB, but as far as I know no one is going to jail for getting it wrong.

David

 

[Pro409]

thank all people for the comments

 

[MortenA]

I think the FAQ is pretty good!

Check with A) your company engineering standards, B) local and government regulations - then use you engineering sences.

Best regards

Morten

 

[Pro409]

OK.
Regards