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.)
