Double block and bleed valve
Double block and bleed valve
(OP)
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?
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?





RE: Double block and bleed valve
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.
RE: Double block and bleed valve
RE: Double block and bleed valve
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.
RE: Double block and bleed valve
It’s seems that we are not in the same page, I’m talking about the design not the work . I’m designing a caustic dosing system, do I need to provide DBB for the pump ( head=70ft).
RE: Double block and bleed valve
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.
RE: Double block and bleed valve
if it passseswhen it passes.If you try to adopt a standard that says over XXX deg C and YYY barg or ZZZ class of material shall always have DBB, you risk winding up with far more valves than you need (and have to maintain them, increase fugitive emissions etc), or even worse increase the risks to people because they don't have sufficient/proven isolation to do a job because 'the standard didn't require DBB'.
Matt
RE: Double block and bleed valve
I just finished a job in BC across the border in Canada and they updated their isolation requirements based on the line size, fluid, pressure and temperature but the end result is that a lot of equipment and instrumentation had to be provided with DBB. Much more than I'm used to seeing. I believe this was in response to BC government regulations.
RE: Double block and bleed valve
Basically, DBB is used for effective isolation when maintenance is required.
I am what I am by His grace
RE: Double block and bleed valve
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.
RE: Double block and bleed valve
When you want to take the CV out for maintenance, how do you isolate the line without a DBB?
I am what I am by His grace
RE: Double block and bleed valve
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.
RE: Double block and bleed valve
RE: Double block and bleed valve
I think you should read Davids posts and dont make very general statements in this subject.
Aside form this Hamood should also notice that practise varies and some companies have very stringent policies and other will rely more on engieering. Both has its more or less obvious disadvantages. Ihave developed a policy myself - but its a part of a total design phlosophy and consideres a number of other practises to be followed as well and may therefore not be right for everybody else. I will give it anyway
Any process design shall determine whether process isolation is appropriate. Entrance to any vessel/tank requires positive isolation (i.e. blinds or removal of spools). For other systems, positive isolation shall only be applied if the time to establish the positive isolation does not exceed the time required for the actual work to be performed.[positive isolation is not the same as DBB - its more]
The design shall ensure that isolation and depressurisation of pressurised systems can be performed in a safe and controlled manner. This process isolation shall be based on the Medium Ranking System, in which the requirement for system isolation is established from an individual risk assessment.
The risk score shall be determined from a tab1e based on the media type and system pressure and temperature. The isolation requirements are then determined from another table based on the risk score and activity. These tables are however impossible to reproduce here.
RE: Double block and bleed valve
I'm most familiar with DBB's on natural gas, which I assumed were installed so you could work downstream of the DBB safely.
RE: Double block and bleed valve
RE: Double block and bleed valve
That is the only non-safety related example that I can come up with as well.
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.
RE: Double block and bleed valve
RE: Double block and bleed valve
A bleed valve is incorporated between the 2 block valve to ensure that, the isolation is secure and men can work satisfactorily.
RE: Double block and bleed valve
In addition to this, ASME has defined a defacto "double block & bleed" as a required configuration on steam and feedwater systems when multiple boilers are manifolded
RE: Double block and bleed valve
My focus is on petrochemical valves for corrosive applications.
RE: Double block and bleed valve
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.
RE: Double block and bleed valve
RE: Double block and bleed valve
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"