Double Block and Bleed Valve (DBB) Requirement (API, API RP, or other code)? 1

[mrengineer11]

In different Oil & Gas companies I have worked, engineers tend to say that any pressure rating from 600# and above, double block and bleed valves are required. Is there any API or similar code or RP that recommends the use of DBB at or above a pressure rating?
Is double block and bleed valve required for chemical injection line i.e. upstream the main process line?
Is double block and bleed valve required for sample lines line i.e. upstream the the sample collection point?
What is the best way to select the most appropriate DBB for the application?

 

[142846]

the partial pressure of H2S is another important parameter foe DBB. 600lb is very conservative for DBB. 600 lb is applicable only for sour services. DBB shall be used for sample connections.

 

[mk3223]

IMO, besides the H2S, injection chemicals, amines, etc., DBB may be used for the system isolation per high temperature as well as high pressure, maintenance of OTR or S/D activities.

 

[LittleInch]

I don't believe there are any codes or official body standards that require this as each case is dependant on its own circumstances, company policies, procedures and philosophies.

Over time the requirement for DBB has become established at certain levels of pressure and contents. Safety engineers have gradually upped the game and then everyone does what they did last time and on it goes.

The terminology though is very confusing and often misunderstood.

Officially a Double block and bleed valve is simply one which can seal in both directions with a bleed between each seat.

What most people think DBB is is actually Double isolation and bleed (DIB). Sometimes you can accomplish this within one valve, but more commonly three valves are required (two main process and a bleed valve)

It's up to the process and safety engineers to determine when you need greater certainty of isolation than that offered by a single valve.

Usually manned entry into vessels requires positive isolation (i.e. blinds, removal of spool pieces, that sort of thing, not a valved off connection.

There's no way to answer your question without knowledge of the contents, the pressure, your company / project isolation philosophy etc.

There are small diamter single forging double valves, there are single ball valves with DPE seats, there are positive isolation split plug and gate valves which offer this within a single (usually quite expensive) valve such as Orbit twinseal plug valves and WKM split wedge gate valves amongst others.

https://www.anwvc.com/line-card/general-twin-seal-orbit/

Although they call themselves DBB valves, they are also DIB valves due to the positive sealing of both faces.

Some other reading here includes

https://www.eng-tips.com/faqs.cfm?fid=1612

and

https://www.eng-tips.com/viewthread.cfm?qid=440025

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

 

[LittleInch]

Also this might help

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

 

[PersonalProfile]

The following may be of interest:

https://www.eng-tips.com/viewthread.cfm?qid=449068

https://www.hse.gov.uk/pubns/books/hsg253.htm

In particular Appendix 6.