New to the PRV world 1

[badal]

I have been thrown into the world of ASME pressure vessels and PRV sizing. I am a PE, but my experience is in HVAC and plumbing consulting. Not process piping or pressure vessels. I've been asked by a local large manufacturing plant to size a PRV for a small chilled water system surge tank. I have zero experience doing this. I have read Tyco's and Crosby's guides and several other publications on how to do this over the past few days. I also have access to documentation that a previous engineer provided for sizing some valves. I at least know a few of the things that I don't know now, but I realize it is very involved and more then can be explained in a single post. I have not yet purchased ASME section VIII, API 520 or API 521 and realize those may answer all of my questions. I have my tank and system information. What I don't know is how to determine the worst case cause of failure or overpressure or when a rupture disk is required. I realize these are elementary questions and I may be in way over my head, but some guidance would be appreciated. What books/codes/references do I need to buy? Is there a course I can take to get my feet wet? Should I throw in the towel before I get too deep into this?

 

[Latexman]

[Φ] comes from mastery of the field of heat transfer. A whole other field.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

babal,

The intent of this site is so an engineer, knowledgeable in the subject, can ask peers questions, and so engineers, knowledgeable in the subject, can answer those questions so the "askee" can become a better engineer. If the "askee" is not knowledgeable in the subject, then what is the purpose. It just takes too long to teach the subject. I hope you don't intend to put your PE stamp on this relief design.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[badal]

Thank you.

 

[LittleInch]

I don't think you have sufficient data. You need to determine what system is that you're trying to calculate - just the tank or all the pipes as well. Each different diameter will have a different heat transfer rate from ambient air and if any is insulated then its different as well. This equation is really or when you have a large amount of heat going into a fixed volume which is then boiling or heating up gas, often from a fire or a runaway heat exchanger, both of which you can work out heat transfer rate.

This sort of thing is not what the calculation is for.

You probably need to just assume some sort of temperature rise over time and run a few cases which look reasonable. If this thing is insulated (as you know most chilled systems will be) then temperature rise of 5C per hour?, maybe 10 at a push.

whatever it is I can't see the volumes being enough to go bigger than the 3/4 x 1" TRV you quoted at the start.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[vladrath]

Badal,

If you read through API 520/521 you will find the calculation to find the heat input rate due to external fire.

You probably can fill the vessel with your pumps, you might have a blocked outlet while the pumps are running. Then you can over pressure the vessel that way.

After reading through the thread I do see that you probably should have contracted this out to an experienced PSV designer. They probably could do the design for you fairly quickly.

Aside from that, I would consider going through the 16 API scenarios again and double check that you've gotten everything correct. After you solve all the possible scenarios for flow rate and area you can select the correct orifice. Then you could find the appropriate inlet and outlet size, and complete your pressure drop calculations to ensure you meet the 3% inlet and 10% outlet rule.

But I would seriously consider getting an experienced designer to do this work in liu of you putting your stamp on a report that may not be done correctly as you've not had much experience in this subject.