are there any problem in the PSV design 6

[navycaptain]

Dear engineers:

Attached is an installed pressure safety valve? are there any problem in the design? In my view, the discharge pipe is directly connected with elbow, is it necessary to conncet a spool and then connect with the pipe?

what do you think of it? thank you!

Youth is not a time of life, it's a state of mind.

 

[Dhurjati Sen]

The inlet (bottom) orifice does not match with the discharge piping size.

DHURJATI SEN
Kolkata, India

 

[LittleInch]

I can't see much wrong with this other than there is no way to test the set point by means of inlet isolation valve and tee.

So to test it you will need to remove the valve and take it away to be tested.

Otherwise looks Ok.

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

 

[Latexman]

Good catch, Dhurjati Sen, the inlet piping does look smaller than the PSV inlet.

navycaptain, if the installation is in a jurisdiction where Code is law, you may have some issues. 1 - too high inlet pressure drop, and 2 - the law/Code. I refer you to thread1203-198350.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[Dhurjati Sen]

Thanks Latexman Sir.

DHURJATI SEN
Kolkata, India

 

[georgeverghese]

For safety valves discharging to a common header, it is standard design practice is to install a locked open full bore valve and drop out spool downstream of the PSV to allow for safe removal while the rest of the plant is still in operation. Installing a block valve here is subject to good safety in operations culture in the OpCo. If there is no such established culture ( which is verified by Operations Management audit every now and then), do not install this block valve.

 

[navycaptain]

Hi, Sen, thank you for your comments, it's helpful.

Youth is not a time of life, it's a state of mind.

 

[navycaptain]

Hi, LittleInch, thank you for your comments. it's true that we normally take away the PSV when we'd like to have a test. it's normaly

done offline test.

Youth is not a time of life, it's a state of mind.

 

[navycaptain]

Thank you Latexman, yes, the inlet valve size is smaller than the PSV valve size which could cause high pressure drop. Is it also a problem that the elbow directely connected with a straigh pipe? is it allowable? thank you!

Youth is not a time of life, it's a state of mind.

 

[navycaptain]

thank you georgeverghese, so you mean it should be connected with a straight spool at the discharge of PSV, right?

Youth is not a time of life, it's a state of mind.

 

[DGrayPPD]

A picture of the whole inlet/outlet piping might be a little more helpful to advise on. I agree with the above comments about the inlet pipe size and the lack of isolation valves (from what I can see in the picture), but I don't have any issue with the elbow welded directly to the outlet flange.

I'm curious as to what your concerns are with the elbow to flange connection? You see it all the time with PSV's that discharge to atmosphere. See below.

"Those who know, do. Those that understand, teach."

-Aristotle

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[navycaptain]

Hi DGRayPPD, thank you for your comments, I made a wrong explanation above, what I mean is the PSV outlet flange directly welded with

elbow, which I believe it should first welded with a spool and then with an elbow

Youth is not a time of life, it's a state of mind.

 

[georgeverghese]

The dropout spool can be either straight or an elbow, I would prefer the elbow as it is easier to remove and reinstall. The block valve is not to be installed if your plant operators dont have the required training to manage such block valves in PSV isolation service.

 

[navycaptain]

Hi George, thank you for your reply, I'm not meaning the block valve, I want to say the PSV flange welded directly with elbow, I'd

prefer to first weld with a short spool, and then connect with pipe.

Youth is not a time of life, it's a state of mind.

 

[DGrayPPD]

Hi navycaptain,

I understand what you're meaning about welding a pup piece of pipe in between the elbow and the flange. My question to you is, why do you think that this is necessary? What benefit do you think it gives to have a pup piece of pipe between the elbow and the PSV outlet flange?

"Those who know, do. Those that understand, teach."

-Aristotle

Feel free to connect with me on LinkedIn:

https://www.linkedin.com/in/dustin-...base_contact_details;YhTBIuX1Sz6q+FbtQVa8CQ==

 

[navycaptain]

Hi DGRayPPD, thank you for your reply. My concern is there could be a "welding stress" at the connection of elbow and flange, the

stress could not be evenly distributed during welding, and this could possible cause corrosion after many years, and it's not good for

mechanical integrity. it can improve the stress issue if there is a pup piece of pipe between the PSV flange and elbow.

Youth is not a time of life, it's a state of mind.

 

[DGrayPPD]

navycaptain,

Although I'm not saying that this should not be a concern, I can't say I've ever heard of it being one before when welding two fittings together.

If you have a beveled LR 90 and a beveled WN flange, then you should be able to weld them together same as you would a beveled LR 90 and beveled piece of pipe. That's sort of the purpose of having butt weld fittings and flanges. They can weld directly to the pipe or to each other. If you begin adding pup pieces of pipe between every fitting unnecessarily, then you'll start really increasing the time and cost of the project. Increased costs could come from extra cutting of pipe, extra end preparations of the pipe, extra welding, extra NDE, extra labor costs to do all the work, etc.. Of course there's always going to be certain exceptions to the rule, but I think for the most part you shouldn't really have any concerns welding two beveled fittings together.

Just my opinion though.

"Those who know, do. Those that understand, teach."

-Aristotle

Feel free to connect with me on LinkedIn:

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[LittleInch]

navycaptain,

I believe you're seeing potential issues which don't exist.

Biggest issue I see is that you need to de-pressurise the system to remove and test the valve.

The actual installation of the device and piping needs to be done properly or you can get some piping stress with such an arrangement if they don't build it right, but that's the same with any piping set up.

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

 

[MortenA]

Isnt it quite normal to specify the outlet piping class to e.g. #150 also for say a #300 valve (inlet flange). So if the vendor puts the same flange on both ends you match that with a #150 flange - because its a #150 system? Of course the holes might not match up but you could have asked for the PSV flange holes to be drilled to your #150 flange?

 

[The Obturator]

Despite all the comments, the issue raised about the inlet piping size has not be addressed. This is of great importance.

In any case, is the query real as the picture is identical to the the 'Relief Valve' entry listed in 'Wikipedia'! See here

https://en.wikipedia.org/wiki/Relief_valve

Per ISO-4126, only the term Safety Valve is used regardless of application or design.