Double block and bleed valve 2

[Hamood101]

I have question : when is the double block and bleed valve is must or required, what is the reference API, OSHA ..etc?

I know that for more than 10 bar it’s required but what about corrosive chemical handling for less than 10 Bar is it required a double block and bleed valve?

 

[hsbcn]

Yes, indeed, Double Block and Bleeds are generally required for natural gas fuel systems.

My focus is on petrochemical valves for corrosive applications.

 

[zdas04]

"Generally" is a word that covers a lot of ground. What do you base that on?

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[maddocks]

David's got a good point. We spend a lot of time and energy looking at isolation planning, shutdown philosophy, on-line maintenance, and on and on. You just can't generalize on these issues - every pump, filter, and compressor needs to be reviewed for the DBB requirements.

 

[zdas04]

maddocks,
You have gone straight to the crux of the problem I keep having with discussions like these--we need Engineering Judgement applied to isolation and what we get is policies.

I can find a legitimate exception to every policy I've ever had to review (too many to count). I saw one last year (actually it was a "regulation" which I define as "a policy with the force of law") that said "... every gas well will be equipped with a downhole plunger...". Well, about half of the gas wells in North America have some sort of surface drive downhole pump. I asked the EPA if we had to purchase "donut plungers" to go around the rod, and if so did they have a recommendation on getting past rod couplings. This was the EPA being stupid, but OSHA has done the same magnitude of stupid.

Company policies on DBB are among the dumbest things that I come up against. The worst I've seen is a requirement to have DBB on both sides of an orifice meter--but the company refused to put it on the meter station buy-back bypass (where it is required by Onshore Order 6 which is the law of the land).

We need Engineering Judgement, not Policies.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"