Double Block and Bleed -> Requirements
Double Block and Bleed -> Requirements
(OP)
Hello,
I would like to know what are typical Double block and bleed requirements. On our project we have set the following requirements: Any pipe containing a substance at 40 degress celcius or higher and/or at 50 psi or higher shall have double block and bleed for any equipment or tank. Does this seem excessively stringent?
Can you share some requirements from your projects?
I would like to know what are typical Double block and bleed requirements. On our project we have set the following requirements: Any pipe containing a substance at 40 degress celcius or higher and/or at 50 psi or higher shall have double block and bleed for any equipment or tank. Does this seem excessively stringent?
Can you share some requirements from your projects?





RE: Double Block and Bleed -> Requirements
It does not seem very strict to me. We evaluate the neccesity for singel or double barriere according to the pipe pressure and medium. I do not see any reason for having a limit of 40 degrees C as we do have hazardious medium below this temp. By doing the correct valve choice you can easily obtain a double barriere with a single valve. Most of our requirements for double barriere is obtained with a single valve.
RE: Double Block and Bleed -> Requirements
The use of DBB has been creeping slowly further along the line from high pressure to low pressure and the quote above may be someone's attempt to eliminate the thinking part about whether it does or does not apply to different substances or particular projects. Usually written by someone without responsibility for the budget...
For natural gas / liquid petroleum products, if there is a normal it is at #600 you see DBB, normally no DBB at #150, but variable at #300. It is though very much substance dependant and risk averseness (if that is a word).
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Double Block and Bleed -> Requirements
If you want to be sure about seat tightness I would suggest you to specify all your valves with supplementary requirements of API 6D that ask the low pressure test with 5 bar air test and the low low air seat test with 0.5 bar. You will be slightly stric but correctly stric.