Double Block and Bleed Valves thread408-48267 4

[KenDing]

In thread408-48267 on 10Mar03, davefitz (Mechanical) posted a comment stating,"double block and bleed is required by code in section I (boiler) service if there are 2 or more boilers interconnected on a common steam line and the boilers have a manway in the steam drum. This is to avoid cooking the maintenance person that enters the steam drum on the idle boiler. A similar philosphy would be prudent for any pressure vessel that a person can enter , if the vessel is interconnected to another active system which has dangerous fluids."

What code is davefitz refering to? I ask this because at our facility we are currently installing a second boiler that will be connected to our existing boiler. I'm not the engineer over this project, but I would like to ensure that no one could potentially be hurt.

 

[jte]

Ken-

See also thread408-94849. If you are in the USA, Federal OSHA probably applies and its in their regulations that you'll find the energy isolation and entry requirements. Individual states and local jurisdictions may impose tighter restrictions. My state generally follows OSHA but is a bit tighter on some particular issues.

jt

 

[KenDing]

jt,

Thanks for your response. I am in the USA, North Carolina, and i'm familiar with OSHA and it's energy isolation requirements.
What I was trying to ask, is there a specific code, standard, or regulation that requires double block and bleed valves when there are 2 or more boilers interconnected on a common steam line or injector system? If so, can you let me know what that code is?
I'm definitely going to encourage the engineer in charge of this project to put double block and bleed valves on the interconnected boilers. Employee don't enter the steam lines because they are only 6" lines. But maintenance employees routinely enter the butterfly valves which is connected to the injector system used to vacuum seal the Vacuum Induction Melt tanks.

Thanks,

KD

 

[davefitz]

see ASME section I par PG-58.3.2. And don't cook the maintenance worker.

 

[HEC]

It is important to not forget why the regs are in place. In this case it is to ensure the area (tank, boiler or process equipment) can be positively isolated. The definition of positive isolation is stopped flow and a method of proving there is no flow past the isolation point. Hence the primary, secondary and bleed valves in the double block and bleed system. In bygone days a spade or blind was inserted into the line downstream of the primary isolation valve. Bleed past the primary isolation valve could pressurise behind the spade and create a hazardous situation for the person removing the spade. Hence the progression to double block and bleed. Having stated that rather than referring to legislation, apply safe operation guides and put the block and bleed valves in. A HAZOP would also identify this requirement.
Rant over.

Mark Hutton

 

[ww2]

Hello all,
A double bloc and bleed valve as security to enter would not be acceptable.
Complete isolation, of the concerning recipient, with blinds is the only secure and foolproof working practise.
this is a safety standard and should be implemented in your procedures.
cheers

 

[JWTweed]

Anyone,

I’m looking to find a DDB valve with the following specifications:

-1.00” NPT Inlet and Outlet.
-Rated for 3000 psi / 204 Barg
-¼” Vent
-316SS
I can't find any US manufacturers that make these. Any help inding one?

Thank you,
Justin W. Tweed

 

[mbt22]

Is there any reason you are looking for a DBB valve rather than using two block valves in series and one to a safe vent?

 

[JWTweed]

No reason why. I was instructed to look into this. Does what you suggest pass ASME & ATEX requirments?

 

[mbt22]

Being a mere chemical, rather than mechanical engineer, I couldn't say for ASME. I have however seen 1 all-in-one double block and bleed valve installed, as opposed to many hundreds of three valve sets.

 

[JWTweed]

mbt22

I did find one source for the DB&B valve unfortunately its made over seas and the shipping alone is $500. (Ouch!) I;m trying to find a US manufacturer, however that's not going very well.

 

[dcasto]

I'd specify two valves and a bleed. But for places that require isolation so as not to cook the worker, a specticle blind would be used.

 

[JWTweed]

dcasto

Gotcha. I'll check with the customer if this acceptable.
Thank you.

 

[Ashereng]

A double block and bleed valve is often cheaper than 2 valves and a bleed. That is why, say a Grove B4, is often used.

If it was me, I would prefer two valves and a bleed, and then a blind flanged before I stick my "behind" on the line, if you get my drift.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[utlandmah]

I agree with Asherang entirely on that!

JWTweed,
I believe you are intend to install the valve you are after upstream of an instrument devise; e.g PT,PIT! Is this right? If so, have you tried Swagelok?

Rgds,
Marcell

 

[utlandmah]

thread408-94849

Refered to the above thread, the gentleman has mentioned using gate valves as isolation valves in DB&B configuration; however I do not agree with him entirely on that. I prefer using Ball Valves. What do you think? Your feedbacks are welcome!

Rgds Marcell

 

[TRUT]

JWTweed

Did you ever find your 1" dbb valve? There are several manufacturers that make this valve for the instrumentation industry. I agree most of these are manufactured overseas, but are represented in the US. You might try going to

http://www.dbb-valves.com

and check on Alco Hi-Tek, or to

http://www.valves.co.uk

for the Oliver product line.

 

[ballvalveguy]

Hi JWTweed,

There are a few manufacturers out there who make DBB valves. The best know is probab ly Cooper Cameron's General twinseal valve.

http://www.saas.no/Portal/DesktopModules/ViewDocument.aspx?DocumentID=242

You could also contact Gosco valves.

http://www.goscovalves.com

 

[DF1971]

Hello there. Can Anyone explain to me the difference between double block and bleed with pressure proving and double block and bleed with position proving?
My application is two globe valves in series with a short section of pipe off of which a vent valve is taken.

Thanks
Dave

 

[Ashereng]

Dave,

You should start a new thread.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?