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Drilled Threaded plug and Solid Threaded plug

Drilled Threaded plug and Solid Threaded plug

Drilled Threaded plug and Solid Threaded plug

(OP)
When looking at the P&ID , I was confused the use of drilled threaded plug or solid threaded plug at the end of drain or vent line. Please advise what occations are suitable for drilled plug. Thanks.

RE: Drilled Threaded plug and Solid Threaded plug

meanstone,
You asked:

"Please advise what occations are suitable for drilled plug."

I have the feeling that this is a trick question.  The answer is "None".  A plug is a plug.  A plug with a hole in it is NOT a plug.

You said you saw this on a P&ID.  
What is the process or what kind of plant is this?

RE: Drilled Threaded plug and Solid Threaded plug

The square ends of plugs could be drilled (or not), so as not to penetrate the sealing envelop of the drain, to allow attachment of a keeper chain or cable. (Wild guess)

RE: Drilled Threaded plug and Solid Threaded plug

We use drilled plugs in only one case.  If I have a leak-off line that would normally be passing a flow of steam, but I do not want liquid water to be carried along, I drill a weep hole in a plug at the low point of the line so the water can drip out onto the base but the majority of the steam is carried on to an elevated location to vent further away from personnel. We do this on leak-off lines from steam turbine carbon ring housings. We also do this on the drain ports of some mechanical seals if a steam quench might cause a buildup of liquid water on the atmosphere side of the seal.  In this case, I don't want to leave the port completely open in the case of a catastrophic seal failure.  The open port would allow greater leakage. The drilled plug forces most of the leakage to pass through the close clearance bushing (sometimes called a disaster bushing).  

Johnny Pellin

RE: Drilled Threaded plug and Solid Threaded plug

(OP)
Thanks all. I would like to add that the drilled plug is located at the end of 3/4" cryogenic globe valve.

RE: Drilled Threaded plug and Solid Threaded plug

A plug with the middle drilled out (picture a cup with threads on the outside) is more flexible and thus more forgiving of things like differential thermal expansion. Due to its reduced mass, it also responds more rapidly to temperature changes. This type of plug makes sense on some hot applications and some cold ones. Looks like you found a cold application...

jt

RE: Drilled Threaded plug and Solid Threaded plug

I use this type plug in hydraulic circuits as an inexpensive Flow Control that cannot be tampered with by an untrained person on midnight shift.

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

RE: Drilled Threaded plug and Solid Threaded plug

I have looked at your P&ID and I (with more than 45 years in piping) still do not have a reasonable answer for you.  After consulting with a colleague (with more than 34 years in piping) and we both recommendthe following.

You should find the process engineer that made the P&ID or was responsible for creating the P&ID and ask them what is the purpose of, and function of, the through hole drilled in the threaded plug.   

Good luck.

Please let us know what you find.

RE: Drilled Threaded plug and Solid Threaded plug

Since both the valves with that plug are shown closed, my guess is that it is a way for any leakage to vent itself rather than building up and rendering the valve inoperable.  Since no valve is 100% leakfree (some leak less than others) this would relieve any leakage and would also be a tell tale that the valve was not holding.

rmw

RE: Drilled Threaded plug and Solid Threaded plug

A very important question.
What is in this line?

If it is a "Toxic" gas (or fluid) then you would not want to do this.


A minor question.

What does the "P" in the "Box" tag mean and are these flange connections?

RE: Drilled Threaded plug and Solid Threaded plug

(OP)
Thanks, pennpiper and rmw. I will contact process engineer but may need time to get reply. Let you know once I have it.

The product is LNG at -265°F and 265psig. But the line highlighted is tank discharge line PSV inlet and outlet. NNF.

pennpiper, if you are asking the <P> at one side of valve, it means pressure preferred side.

Thanks again.

RE: Drilled Threaded plug and Solid Threaded plug

(OP)
3/4" Valve SW X Thd.

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