Sizing Relief Valves Using ASME Codes 2

RJB32482,

There are quite a few ASME codes that cover relief system requirements and they are not all the same. For example...
ASME Section VIII, Div 1
ASME Section I
ASME Section IV
ASME B31.3
ASME B31.1

The relief valve orifice (actually nozzle) flow equations can be found in ASME Section VIII or API RP-520 which is intended to supplement the information in ASME Section VIII. In ASME Section VIII, Div 1 look at UG-125 through UG-136, Appendix 11 and Appendix M. The Crosby Pressure Relief Valve Engineering Handbook includes the pertinent sections from ASME Section VIII.

Applicable sizing codes:
OSHA 29 CFR 1910 subpart H
ASME Section VIII (Rules for construction of Press Vessels)
Compressed Gas Association . Pamphlets S-1.3, S-8.1
NFPA 30, Flammable and Combustible Liquids Code
NFPA 58, Std for Storage % Handling of LPG
API RP 520, Recommended practices for design and installation of pressure relieving systems in refineries
API RP 521, Sizing, selection, and installation of pressure relieving devices in refineries
API RP 2000, Venting atmospheric and low pressure storage tanks

For relief valves that are not ASME code certified for liquid service, I understand that they are sometimes used in liquid service but the resulting overpressure required to fully open the valve is 25% for the non-certified valve vs. 10% for the certified valve. Our valve supplier says it is OK to use non-certified valves in liquid service. When is this acceptable?....only on non-ASME vessels?

I did not see the sizing equations in the ASME Boiler and Pressure Code. Is there a specific section I need to look in? Also, is there a section for orfice sizes in the ASME codes?

Thanks

Does anybody know what is the appropiate code/standard to follow for sizing PSVs for vessels used in the process ( not storage vessels)Most of the information I've found is about storage vessels and it refers to API520 and NFPA30. I'll appreciate any light on this matter

Natita,

For the efficient and courteous use of this site, Forum policies would suggest starting your new discussion in another thread. That way your question would get more exposure and would not interrupt the current thread. See faq731-376 for more details regarding forum policies.

RJB32482,

Regarding the sizing equations, you should find everything you need in the references I've cited above and in the Crosby Handbook.

As for orifice sizes, the ones frequently referenced are the API orifices usually designated as a letter and of a size as defined in API Standard 526. The API orifice areas are considered the effective areas. The ASME (actual) areas for a given manufacturer can be found in the National Board publication NB-18 otherwise known as the Redbook...

Alternately, you can contact the valve manufacturers directly. They will obviously have the API/ASME orifice area information specifically for their valves.

RJB32482:

I apologize for interrupting your thread. Thank you for the information.

EGT01,
I could not find the orifice sizes in the redbook. Where in it is the sizes?

Thanks

Well I hope I've not offended Natita, my comments were intended as an encouragment to start a new thread.


RJB32482,

To find the ASME orifice areas you will need to look in the certification tables.
1. go back to the NB-18 table of contents, click the "Listing of Manufacturer and Assembler Certifications".
2. at the Listing of Manufacturer and Assembler Certifications table of contents, look in the left window pane and select the manufacturer of interest, for example Farris Engineering (TFO).
3. at the listing of devices designed by the manufacturer, find the device type in which you are interested and click on that device, for example "2600 & 2600S".
4. at the device details page, find the API orifice in which you are interested and read the Flow Area as the ASME area.

While on this page, you should also read the Certified Value listed which is the ASME discharge coefficient for the device. You must use the ASME discharge coefficient when using the ASME area. You must not mix the API and ASME values in the sizing equations, either use all ASME data or use all API data.

An example and brief description of the certification listings and tables can be found by going to the NB-18 table of contents and clicking the "Listing of Certified Device Types by Manufacturer".

Alternately, you can get the orifice information from a manufacturer. For example...
download the series 2600 catalog and look on page 10 of the catalog (that's 12 of 94 in the document).

Just remember, the API orifice designation is a defined standard, the ASME areas are not and vary somewhat between manufacturers for a given API orifice.