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Any time you&#;re going to work on a valve, separator, or other piece of equipment on a well site, we highly recommend you use the practice &#;Double Block and Bleed.&#;
The Hiss
Maybe you&#;ve had this experience.
You&#;re going to repair a valve that&#;s in line. You know this means you need to block off and depressurize the section you&#;re working on. So you close off the ball valve upstream, open the bleed valve to vent pressure, and get to work.
You square up to the valve in need of repair and start unthreading bolts. Then you hear it: a hiss. You quickly snug the bolts back down.
I could have sworn I just isolated this valve, you think. What did I miss?
One possible cause of the hissing in this scenario is that the valve is getting pressure from downstream.
What is Double Block and Bleed?
Double block and bleed (DBB) is the practice of shutting in a section of pipe on both sides of the valve rather than just one.
It means you close the ball valves to block both the upstream and downstream sides of your working area, and then bleed any pressure that remains in the piping and valve.
The practice of double block and bleed reduces the risks of harm to people and the environment, which is why many oil and gas companies have adopted the practice as mandatory when working on field equipment.
Stay safe out there!
(Note: This article refers to the safety practice; double block and bleed may also refer to a specific kind of valve.)
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Ball vs Gate: Which Wellhead Valve is Right for You?To me, double block and bleed always sounded like a move out of the Cobra Kai karate dojo. Of course a double block and bleed valve has nothing to do with karate, it has more to do with controlling process flow to allow for maintenance, sampling, and flow diversion. This post describes the attributes of a double block and bleed valve, its function, and application.
What is a double block and bleed valve?
A double block and bleed valve is like having three valves in one.
API 6D defines a double block and bleed valve as a "single valve with two seating surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of vending/bleeding the cavity between the seating surfaces."
There are a couple different styles of double block and bleed valves. One style has two independently seating valves inside, with a bleed or drain valve. This configuration is referred to as a double isolation and bleed (DIB). The DIB valve can isolate either side of the valve (bi-directionally) to vent or bleed the cavity and isolate piping.
This trunnion style ball valve from Val-Matic provides double block and bleed in a single valve. This style can isolate piping on both sides of the valve (uni-directionally) to vent/bleed the valve cavity between the seats.
Using a single double block and bleed valve system versus 3 separate valves saves installation time, weight on the piping system, and space. It also cuts down the number of leak paths to the atmosphere, reducing the risk of hazards when transferring liquids dangerous to humans or the environment.
Which applications require a double bock and bleed valve?
Double block and bleed valves are most commonly used in the oil and gas industry, but can also be helpful in many other industries.
It's typically used where bleeding the valve cavity is required, where piping needs isolation for maintenance, or for any of these other scenarios:
- Prevent product contamination
- Remove equipment from service for cleaning or repair
- Meter calibration
- Liquid service near waterways or municipalities
- Transmission and storage
- Chemical injection and sampling
- Isolate instrumentation such as pressure indicators and lever gauges
- Primary process steam
What to look for when selecting a double block and bleed valve?
As with any valve, during selection, one should consider the fluid properties, pressure, temperature. Perhaps most importantly, however, is how the valve will be used. With a number of configurations offered, consider which of these will fit your process and needs best.
If you're unsure which double block and bleed valve is right for you process, talk to an engineer. They can help determine which one will achieve your objectives best.
Need help selecting a double block and bleed valve? Ask us about it! We gladly provide technical assistance to businesses in Wisconsin, Minnesota, Iowa, and upper Michigan.
For more information, please visit Double Block And Bleed Ball Valve.
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