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Pressure Control Devices

Pressure Control Devices

(OP)
Howdy All,

I have a bit of a value engineering problem, and would like to see what your thoughts are on my solution.

I'm dealing with a pipeline which is carrying high TDS seawater (lots of salt), at a pressure of around 75 barg. I have to take a sample from that line, so there's a branch connection with some sort of pressure-reducing device which will drop it down to about 15 barg.

My client (bless his heart) already has it in mind that I use a super duplex pressure reducing valve. This thing costs about as much as a new car. Meanwhile, my solution is to just go with a simple orifice plate to drop the pressure.

I think they will most certainly not go with my option, so I am trying to consider some other ideas. Here are some questions I want to run by you:
1. For those of you more familiar with PRV's: what are some downsides to using a PRV? I can thing of maintenance and replacement of wearable parts, but are there any other factors which make them undesirable?
2. Any foreseeable issues with the orifice plate idea? I think the liquid will most likely cavitate at the constriction, but this won't matter much as I plan to leave enough straight length of pipe downstream for the fluid to recover. Worst case is, I'll provide some spare plates in case they get damaged over time.
3. Are there any other ways to reduce pressure? I'm considering some other valve types which will serve the same purpose, please add to the list if something comes to mind:
-Check Valves: Super duplex body with a high-gauge Inconel spring. Still checking with supplier; I don't think they'll have a strong enough spring.
-Multi-Turn Valves: I can try for a needle or globe valve, but cost might still be too high.
-Sliding Gate Valve: I'm getting a quote for this, but basically I see it functioning same as an orifice plate. There would be no need for automatic actuation; do they even come in manual type?

Please let me know if you have any other ideas.

Thanks.

Aljosa Mitrovic
Mechanical Engineer

RE: Pressure Control Devices

A high quality engineered Pressure Control Valve has few downsides.

For a simple restriction device you really want a restriction orifice, not an orifice plate because of excessive velocity and cavitation. You can get these in ceramic so hopefully you won't have an issue with corrosion

Main downside is that you need flow to create the pressure drop so in the initial phase you get a spurt of high pressure fluid so your system needs to be able to cope with that before you get the lower pressure.

To drop that much pressure in any form of accurate pressure or flow you need a control valve of some sort - ball and gate are no good. Needle and globe should be Ok but all depends on how much volume / flow you need.

You could have a simple tube or try a long length of instrument tubing to get the pressure loss over a longer length?

What sort of flow / volume are we talking about here?

BTW you don't have a brother called Aleksander do you who plays football for Newcastle Utd do you??

LI

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure Control Devices

Foe a small sampling flow, a small bore connection with the tube and tubing valve, such as globe or needle valve, will meet your design purpose. If needed, a restricted orifice tube fitting can be added to limit the maximum flow.

RE: Pressure Control Devices

A pressure reducing valve steps pressure down no matter what the sample flow is (subject to turdown limits), while an RO cannot do this.

You may also have to install a blocked flow PSV downstream of the throttling device if the design pressure of the kit downstream of the throttling device is lower than that upstream of it.

If you are using this sampling PRV ocassionally only, then may be you could get away with a SS316L PRV and have it replaced whenever you see signs of internal pitting.

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