Safety Pressure Relief Valve Installation 1

[boze]

Modifying existing an 8" dia 275 psig branch steam line reduced to 100 psi. A pressure relief valve is located on the 8" 100 psi side.

The restricted space for the relief valve from the 8" steam line requires that the branch to the relief valve is a minimum of 4'horizontal, then an elbow for the 6'vertical rise to the relief valve.

Basic rules require a 2 diameter pipe increase to the relief valve.
The existing relief valve inlet is 4" flange.

Two questions:
1. For the 4" valve, two pipe diameters (neglecting 5") would require an 8" line to the relief valve, reduced to 4" at the valve. I believe that I can use a 6" line.

2. Cannot slope the horizontal line due to other existing conditions. Slope is normally recommended to reduce the accumulation of debris such as sediment collection over time. I would like to consider a drip leg tee in place of the elbow.
If a valve is installed for drip leg for periodic drainage, then would expect to lock the valve, or at least use a plug. Plant operation is essentially 24/7, so the chance that the 6 month or annual shut down would include inspection to clean out is questionable. I am considering including this on the design notes, but realize the note could soon be forgotten.

Of course, over the long period of operation, debris can or will accumulate, so there is no sediment protection when needed the most.

Comments will be appreciated. The only option is to make some major modifications to the existing limitations in order to get a vertical installation.

 

[DLite30]

Use a rain cap, and drill a weep hole at the low point.

 

[CRG]

Whose "Basic rules" tells you the pipe diameter? Shouldn't you really be making a pressure drop calculation to ensure that the type of pressure safety valve you want to use will work? Is your concern chattering or set pressure? Pilot operated PSVs can be less prone to chattering; however, they can have some issues with condensates.

 

[boze]

"Basic rules" come from a Valve manufacturer's catalog showing comments and diagrams for the supply line to the valve, indicating that a long run,including horizontal and elbow(s) shall increase the supply line 2 sizes.
Although long run is not defined, judgement enters into the solution.

 

[BigInch]

Where'd that catalog go to school?

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Latexman]

1. Judgement should follow pressure drop calculations and not rely on rules of thumb from a catalog. You are probably right, IMO, but . . . in God we trust, all others bring data!

2. A y-strainer and steam trap piping arrangement at the drip leg would facilitate periodic cleaning, if needed.

Good luck,
Latexman