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Sizing PSV
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Hi Paul,
I would start by saying that the sizing of the relief is a very serious undertaking, and any sizing that you do should be confirmed with someone who has the experience that you currently do not have. The point to remember is that it is a life safety device and you should always treat the sizing and specification with the utmost reverence.
Now, having said that, the starting point is with our system review and defining what you are protecting and what is the limiting factor, and what is the worst case. If it is a vessel, if it is a pump, if it is a boiler, thermal expansion in piping, exothermic reactions, and so forth. There are hundreds of potential cases spanning all of the various industries in which pressure saftey valves are employed. You have to identify your case, and then have an understanding of the applicable codes regarding saftey valves. NFPA, API, ASME are the big three when it comes to relief devices. All of the codes have very specific sections on the calculation methods.
Go out and search around under these three codes, and you will find the applicable sections (I would give them to you, but I'm on the road this week). Perhaps someone else can direct Paul to the specifics, but again it does depend upon your application and worst case senerio.
Hope that this was of some help.
Best Regards,
TSeener
I would start by saying that the sizing of the relief is a very serious undertaking, and any sizing that you do should be confirmed with someone who has the experience that you currently do not have. The point to remember is that it is a life safety device and you should always treat the sizing and specification with the utmost reverence.
Now, having said that, the starting point is with our system review and defining what you are protecting and what is the limiting factor, and what is the worst case. If it is a vessel, if it is a pump, if it is a boiler, thermal expansion in piping, exothermic reactions, and so forth. There are hundreds of potential cases spanning all of the various industries in which pressure saftey valves are employed. You have to identify your case, and then have an understanding of the applicable codes regarding saftey valves. NFPA, API, ASME are the big three when it comes to relief devices. All of the codes have very specific sections on the calculation methods.
Go out and search around under these three codes, and you will find the applicable sections (I would give them to you, but I'm on the road this week). Perhaps someone else can direct Paul to the specifics, but again it does depend upon your application and worst case senerio.
Hope that this was of some help.
Best Regards,
TSeener
Advice,
I think relief valve manufacturers are a good bet. All the catalogs will have sizing formulas for fire, etc.
When I search the main suppliers (Dresser, Farris, Anderson Greenwood, etc) on-line, most even offer some sizing programs as well as documentation.
For example, check out the the Crosby Pressure Relief Engineering Handbook at bottom of this link
best wishes, sshep
I think relief valve manufacturers are a good bet. All the catalogs will have sizing formulas for fire, etc.
When I search the main suppliers (Dresser, Farris, Anderson Greenwood, etc) on-line, most even offer some sizing programs as well as documentation.
For example, check out the the Crosby Pressure Relief Engineering Handbook at bottom of this link
best wishes, sshep
sshep
Got to remember: There are two sides to psv sizing
1) The calculation of the orifice size - fairly basic stuff just a formula - the PSV will do this just fine
2) Determination of how much that need to be relieved. The setting up of the various relief cases (fire, blocked outlet etc). This is the job of the process engineer and no PSV manufactor will take responsibility for this (they may make a fire calc - but you must provide the input data).
Best regards
Morten
Got to remember: There are two sides to psv sizing
1) The calculation of the orifice size - fairly basic stuff just a formula - the PSV will do this just fine
2) Determination of how much that need to be relieved. The setting up of the various relief cases (fire, blocked outlet etc). This is the job of the process engineer and no PSV manufactor will take responsibility for this (they may make a fire calc - but you must provide the input data).
Best regards
Morten
Moreten,
That is exactly the point. The process engineer must review all possible cases, and make the determination of the worst case. Most vendors don't even want to by liable for your inability to identify a potential runaway reaction scenerio that could have the potential to far surpass the releiving requirements of the fire case. There are also materials that are not easily relieved in certain cases, like Styrene in a fire case... Once you understand that you need to identify all of the potential sources for an over pressure, then you can look at identifying the relieving capacities required. If you look at the fire case for a "flammable liquid", I would recommend that you look at NFPA 30. The heat and thus the total pounds calculated to be relieved are far greater than the API equivalent.
There are several hard backs dedicated to the sizing and selection of pressure relief devices and the systems. If you are serious about this task, I would suggest looking for one of them. They can give you chapter after chapter of the fundamentals. Even with a text book, use the eyes of someone who is very experienced with the process and the calculations you have prepared. As I mentioned, it is a very very serious undertaking.
Best Regards,
TSeener
That is exactly the point. The process engineer must review all possible cases, and make the determination of the worst case. Most vendors don't even want to by liable for your inability to identify a potential runaway reaction scenerio that could have the potential to far surpass the releiving requirements of the fire case. There are also materials that are not easily relieved in certain cases, like Styrene in a fire case... Once you understand that you need to identify all of the potential sources for an over pressure, then you can look at identifying the relieving capacities required. If you look at the fire case for a "flammable liquid", I would recommend that you look at NFPA 30. The heat and thus the total pounds calculated to be relieved are far greater than the API equivalent.
There are several hard backs dedicated to the sizing and selection of pressure relief devices and the systems. If you are serious about this task, I would suggest looking for one of them. They can give you chapter after chapter of the fundamentals. Even with a text book, use the eyes of someone who is very experienced with the process and the calculations you have prepared. As I mentioned, it is a very very serious undertaking.
Best Regards,
TSeener
It doesn't look like anyone has gotten specific with respect to references, so I would suggest starting with API Recommended Practices 520 and 521. In addition to the cautions of other folks who have responded, these references are the most direct route to a starting methodology.
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