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?

 

[zdas04]

Take a look at faq378-1612 and then we can talk.

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.

 

[Hamood101]

Thanks Zdas04 for the replay, I gone through attached doc. But still not clear to me what determining the need for DBB. Is the pressure or the fluid type.

 

[zdas04]

Neither. It is the work being performed.

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.

 

[Hamood101]

Zdas04,

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).

 

[zdas04]

Sorry, but the positive energy isolation regulations apply to activities, not systems.

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.

 

[mbt22]

Or to put it another way, why is the valve there and what are the consequences if it passses when 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

 

[TD2K]

Where is this equipment located? Could it be a client requirement?

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.

 

[asade]

You need double block and bleed valves around control valves. This allows the isolation of the CV from both the upstream and downstream section of the piping netwok.
Basically, DBB is used for effective isolation when maintenance is required.

I am what I am by His grace

 

[zdas04]

I must call BS on that one. You sometimes need isolation around a control valve, but unless you regularly do hot work on the control valve then DBB is not required or even slightly desirable.

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.

 

[asade]

zdas,
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

 

[zdas04]

Shut the block valves if they are there. If not, find the nearest block valves and blow down more pipe. Working on a control valve is not hot work and does not require positive energy isolation. Read the FAQ I referenced above.

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.

 

[atayto]

Generally DBB is not required only for non-hazardous fluids at the pressure below 1o barg. For all other cases DBB is required. In your case, caustic can be determined as hazardous. and in this case even if it is operating below 10 barg, DBB is required. About work requirement: every company have their own minimum standards. Isolation standard axeptable for one company can be not axeptable in other. Before isolation of any equipment all valves integrity needs to be proven and only when it is done tags and lock can be applied as a part of ICC. I beleive in all companies hot work requires positive isolation. valve isolation can used only if risk assesment level 2 is done. But in all case Positive isolation(not valve isolation) is preffered. thre some units where valve doesnot have any isolation valves. In order to replace the trim of the valve whole unit or equipment needs to be stopped. This reduces possibility to operate equipment in manual( by means of hand valves)and much safer design, but different people have different opinions.

 

[MortenA]

atayto

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 Its a little difficult to get the formatting right though:

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.

 

[macmet]

We have a number of control valves in our systems without DBB. If we need to work on the valve we close the upstream block valve and drain the line.

I'm most familiar with DBB's on natural gas, which I assumed were installed so you could work downstream of the DBB safely.

 

[dcasto]

About the only time I require a DBB valve is on measurement systems that have a bypass or need to go through a prover.

 

[zdas04]

dcasto,
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.

 

[maddocks]

Unfortunately, we're seeing a lot more of this DBB mentality and it's knee-jerk response is to install a DBB valve everywhere. Since some owner companies do not accept the DBB valves, we're into multiple manifolds, vents and drains for every valve that has upstream energy. A lot of producer companies are now re-examining their work procedures to remove CV block valves and just force the facility into a blowdown/de-energize state to fix the valve. So, we're moving back to DBB's only on equipment like lead/lag pumps, filters, and some heat exchangers that may require online maintenance.

 

[Aamir3354]

DBB are recommended when you require 2 independent ball valves for positive Isolation during Hot work or downstream works.

A bleed valve is incorporated between the 2 block valve to ensure that, the isolation is secure and men can work satisfactorily.

 

[MJCronin]

My experience has been the same as "macmet"..... DBB is required for natural gas fuel systems.

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