Double block and bleed valves arrangements

[JohnBrittoUGL]

For the high pressure steam or high pressure fuel gas applications, I have been using a double block & bleed valves arrangements. During one of our HAZOP reviews, the facilitator asked me a question 'What was the definition of high pressure? and where was it mentioned in the code?'. My answer was 20 barg and above considered as high pressure based on general engineering practice.

Can anyone please clarify the following?
a) Is there a code requirement about this requirement?
b) If yes, above what pressure we need to apply double block & bleed arrangements?
c) Is it applicable for the main isolations or to be applied everywhere including the instrument isolations?

Thanks

JB

 

[TD2K]

I've seen this driven by client requirements. One client I'm working with requires double block and bleeds on new installations over 600 psig.

Another client had a matrix depending on the piping class and fluid. For example, a stream over 140F was a double block and bleed candidate even for class 150 piping. Double block and bleed requirement from the matrix included equipment and vessel isolation points, instrumentation (level gauges, pressure, pressure safety valves, etc) that they would have to maintain with the process remaining in service.

 

[pennpiper]

A). Some people use two line class block valves (Gate, Plug, Ball, etc) with a short spool piece (fitted with the bleed valve) between the two block valves.

B). Some people use two line class block valves (Gate, Plug, Ball, etc) with a Bleed Ring(fitted with the bleed valve) between the two block valves.

C). Some people use a one piece (monolithic) double Block and Bleed unit that encapsulates the same capabilities as A & B above.

You should investigate all three methods for application, cost, maintenance and replacement delivery time.

 

[Duwe6]

DB&B is a Sect 1 requirement for a boiler with a steam line connected to a common header. Boiler Inspectors won't enter a Boiler w/o this setup. .

Otherwise, what you install is up to the Owner. I won't make a Confined Space entry w/o everything blocked with 100% reliable closures. And these are a legal requirement for Confined Space Entry in the USA, per OSHA.

There are several 100% reliable ways to close off a line.
Double-block, and bleed. Fast method. $$ to buy, cheap to operate.
Spectacle Flange. Slow, may need 2 or 3 men and/or a crane, fairly cheap to buy.
"Hammer Blind" isolation valve. $$ to buy, fast & cheap to operate.
'Pancake' isolation blind inserted between a flange pair. Very cheap to buy. Slow, may need 2 or 3 men, expensive method to use, due to man-hours required.

 

[JohnBrittoUGL]

Thank you all of you for your valued feedback

JB