Double Block and Bleed 1

[JABoomer]

Hi Everyone,

Question for you. What's more cost effective for a double block and bleed arrangement. Purchasing and installing a dedicated double block and bleed valve, or purchasing the separate components (two block valves and a drain valve) and fabricating the arrangement as part of your piping fabrication.

Any thoughts?

Thanks, Boomer.

 

[LittleInch]

You would think that a single unit would be more cost effective, but often not so. It is usually a space consideration rather than cost which drives these things. DBB valves (proper ones) are notoriously expensive, but if it is a manual situation (i.e. not valve and actuator times two), can easily be double two SPE ball valves, tee etc. The cost of welding and fit up is often difficult to accurately assess so the bean counters tend to count the no of beans for the materials alone.

Composite single body DBB valves are limited in size, but can be quite effective (two ball valves and a bleed valve in one body).

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[curtis2004]

Hi everyone,

I think installation of dedicated DBB valve is not based on cost effectiveness, but rather requirement of project specs.
What do I mean?
Even if you install single body DBB valve very often you will have another isolation valve before it. I worked in projects where specs split "piping" scope from "instrumentation" scope. When, for instance, you have pressure gauge installed in a line, piping spec requires 1/2" Nom x Sch 80 pipe with gate valve installed at the point. In some cases spec may allow using one end socket weld and the other end threaded gate valve.
After gate valve instrumentation scope starts and they can install DBB with 1/2" male NPT and 1/4" male NPT where pressure gauge is installed.

Regards,

Curtis

 

[LittleInch]

Kind of depends on the size the OP is talking about. Instruments - integral DBB are pretty standard - 6" + process piping, much less so.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Pipingeng100]

Dear All,

In Both Cases, the cost would be the same probably. But, As said by Littleinch,
the selection of DBB is purely depend upon the space provision and piping spec.

In other view, if we put DBB Twin type, how it will be done when it come for
Maintenance or Shut down. You have to replace with Pipe Spool or isolating the
first isolation valve in the same line.

The purpose of DBB is for Double Positive Isolation. It will be good providing
2 Ball Valves & 1 Drain Connection if there is no space constraint.

Regards
Pipingeng1