Ssafety valve Installation

[omerada]

I need to install two safety valves on my bioler, but the valves are to be installed to a single vent pipe using a Y connection. I need your advice

 

[ApC2Kp]

omerada,

Ordinary power piping code recommends individual vent line for each safety valve outlet. It allows combined single vent line with requirement that the combined vent single line size have flow area equal or greater than the sum of the individual vent lines. Each individual vent line would have been sized to be equal or greater than the outlet of each safety valve for adequate flow from each safety valve.

Not sure about any different nuclear piping code requirement, if it would be a closed vent system to a blowdown tank. There could be some interaction between the safety valves discharging into vent line with backpressure, depending on the settings of the two safety valves.

If you are considering two safety valves mounted to same steam drum connection, then that would be another situation.

 

[omerada]

This is actually a safety valve connection to our 150,000 lbs/hr boiler at 150 psi. I am just wondering if anyone has done this type of installation before so that I don't have to re-invent the wheel. I am concerned with any further calculations regarding some back pressure problems at the Y connection.

 

[dcasto]

ApC2Kp is correct on the area part as a starting poit. Typically, if the relief valves is a 8 x 10, then the two lines would join into 14" to be safe, but a 50' 14" line has 11 psi drop and a 50' 12" line has 16 psi drop. So a 12" would work for that distance. A 10" line has a drop higher than 25% of the inlet pressure (this is just a quick analysis and not the final answer)

 

[omerada]

Hello dcasto, the phrase " if the relief valves are 8 x 10,..." are you referring to the areas of the valves? The internal diameters of the valves are 4" each. Can you explain further please. The height of the vent line from the valve to the roof is about 100 feet.

 

[dcasto]

8" inlet by 10" outlet. I did a quick sizing and came up with a R orifice (16 in^2). Looked up someones R orifice and saw a 8 X 10.

I then did some pressure drop calculation based on 300,000 lb/hr steam.

 

[omerada]

Are there any relationship between the ASME BPVC Section III and API 520 and 521 as regards MAWP for relief devices. These bodies have different formulas for calculating the minimum discharge area of the relief valves, do they give the same results?