One safety valve protecting multiple equipment.

[garfio]

I posted this case on other engineering forum and would like to have comment and advice from you.

Steam at 150psi if sent to a pressure vessel with a design pressure of 70 psi, through a control valve. There is no safety valve on the vessel, so if the control valve fails, there is a potential overpressure. Trying to understand the protection criteria used in the design, I thought that it might have been considered the vessel as part of "system" under the concept of ASME that allows a relief valve to protect interconnected equipment.

There are two potential paths for relief, one doesn't have any block valve, but goes through a condenser and into a third vessel, with a safety valve set at 70 psi.

The other goes through a pump and reaches a column with a safety valve set at 70 psi. In this case, we have more than one block valve (normally open).

For the first path, even without a valve, I believe that there are other conditions to be met. For instance, we have to assure that under relieving conditions, the pressure on the vessel been analyzed won't be above (70 psi +10%).

For the second case, I think that relieving through a pump would be totally unpredictable, thus, unacceptable.

I would like your opinion over the applicability of the "system" concept for these two possible paths.

One additional question that derives from the first path is, assuming that the flow rate and pressures (and any other additional requirement) is complied and we accept it as an adequate relief path, would the presence of a normally open manual valve (not car-sealed) void it? That is what I would understand from the code but, wouldn't it be another case of double jeopardy?

There are no hazardous products on this system and the existing safety valves are correctly vented to a safe area.

Thank you for your input.

 

[CJKruger]

lavals,

It is acceptable to have multiple vessels protected by a single relief valve provided:

- There are no intervening valves.
- The design pressures are such that vessels cannot be overpressured.
- Blockage/plugging of equipment and piping in the relief path is unlikely.

If you install a block valve in the relief path (not LO), then you would have to install a PSV on the first vessel.

The only exceptions to this is in ASME 8 App M, but they do not apply in your case (except if you lock open the valves).

 

[dcasto]

I would agree with all CJK says, but I would allow a block valve in the relief path with a car seal open, what is the difference between a valve under a relief valve and one a few feet upstream?