Instrument root valve - isolation criteria

[mmonti0]

Good morning everyone,

In a project of a boiler according to ASME BPVC Section I, Ed 2017, we have to define the criteria to place root valves of instrument (see attachment for details). The criteria I am talking about is if we shall place single isolation root valve or double isolation root valve

I had a memory that ASME BPVC or ASME B31.1 was including a design pressure threshold above which double isolation valves are required. However, I can't find such requirements right now

Can you please inform me if the requirement are present in the code, and (if yes), where are they specified?

Thank you

Matteo

 

[CGonsalves]

I would also like to see the criteria for it. At my place of work, we just consider it as standard work to use double isolation for taps.

The closest I could find was ASME BPVC Section 1 Part PG-60.6.1:
"Each boiler shall have a pressure gage so located that it is easily readable. The pressure gage shall be installed so that it shall at all times indicate the pressure in the boiler. Each steam boiler shall have the pressure gage connected to the steam space or to the water column or its steam connection. A valve or cock shall be placed in the gage connection adjacent to the gage. An additional valve or cock may be located near the boiler providing it is locked or sealed in the open position. No other shutoff valves shall be located between the gage and the boiler..."

Even though this spec only outlines Pressure gauges, I think PTs would also apply to this req'ment.