Isolation procedures question 1

[Stonejaw]

I am trying to find some isolation procedures for using double block and bleed valves, when/where to use them and procedures for PSV isolation, when/where. I really would just like to be pointed in the right direction for some reading material. I have already tryed to go through ASME and CSA code, but it is not of to much help. If there are any good write ups on double block and bleed procedures and PSV isolation procedures I would really appreciate it.

Thanks!

 

[gr2vessels]

The best source is the actual manufacturer of DBB valves, who are suppose to comply with specific requirements ( corrosive, explosive environments, lethal service, etc..).
Cheers,
gr2vessels

 

[thalathb]

I dont think there is a specfic stander or code will give you a sufcient material for DBB, each company has its own isolation procedures for using double block and bleed valves.

 

[MortenA]

The NORSOK standards will give you some guidance. Look at this general process design:

http://www.standard.no/PageFiles/1134/P-001e5.pdf

Best regards

Morten

 

[ash9144]

The legal requirement is positive isolation from energy source. With energy source being pressure, chemicals, or other hazards. How you decide to accomplish that is a company decision.

 

[unclesyd]

Here is a little information that should help you with your problem in the OP. Dbl Block and Bleed is a part of the Tag/Lockout procedure.

http://siri.uvm.edu/ppt/powerpt.html

http://siri.uvm.edu/ppt/lockout/index.htm

 

[JLSeagull]

Some systems with standards that require automated double block and bleed valves include fuel gas to fired heaters and oxygen systems.

 

[HEC]

ash9144,
Correct the DBB is to provide positive isolation. The full intent is for positive and verifiable isolation. First block valve provides isolation, bleed is the point where isolation is verified (first valve is holding), second isolation is braces for the belt, if the first valve fails the energy source (pressure, chemical, electrical etc) is bled off through the bleed while the second valve holds.
For references try OHS authorities or pressure vessel inspection procedures.

Mark Hutton

 

[786392]

May I take the slight liberty on HEC words;The bleed valve is also a check of energy inflow from either side and thus care taking for safety's sake.

Definitely operationally Positive Isolation is the main duty of Double Block& Bleed system.
At times it's supplemented with sealing Or Chain-Lock system

Hope this helps

Best Regards
Qalander(Chem)

 

[AlexUser]

As far as I know, DBB isolations schemes and guidelines are extensively discussed in the following fundamental

"The safe isolation of plant and equipment"
Oil Industry Advisory Committee, HSE Books 1997

For PSV, if there are 2 PSV's and one is 100% spare, the spare one shall be locked closed in order to avoid error in leaving the spare operating (this would result in chattering of PSV's).

 

[VikingUK]

There is no standard for positive isolation. It is the responsibility of a company to prove it has it's own standards. However most North Sea oil companies have pretty similar procedures as they all work together.
These use a matrix that shows pressure, flammability, temperature etc and reads out a standard based on the criteria. For example a 6" oil line may require a higher level of isolation than a 48" water line