Pressure Class/Ratings for small, non-flanged valves 3

[hull6851]

I fully understand the pressure classes that are used for flanged valves (per ASME B16.5: Class 150, 300, 600, 900, 1500, 2500). It makes a ton of sense to me. You have a pressure and temperature of the piping system, you go to ASME B16.5, you look up the pressure class corresponding to the pressure/temperature in the appropriate table, and you specify a valve with that pressure class and it works for any flanged valve, no matter the type (ball, gate, globe, etc..). No ambiguity. No confusion.

For smaller, non-flanged valves (threaded and socket welded), I am VERY confused what the pressure classes are, who (what organization) determines/defines them, how an engineer determines the appropriate class for a particular valve, and which pressure classes apply to which types of valves. Can someone explain it to me? My company has options to specify smaller valves with the following pressure classes (please forgive nomenclature/symbology errors, I'm literally copying these from a company P&ID legend): 800# API, 1500# API, 2000# API, 3000# API, 5000# API, 10000# API, 15000# API, 1000# WOG, 1500# WOG, 2000# WOG, 3000# WOG, 3000# ANSI.

Some of these might apply only to ball valves, others only to gate valves (for example) and I just don't understand the rhyme or reason. I also don't understand at what pressure/temperature I need to switch from using a 2000# WOG ball valve to a 3000# WOG ball valve, for example. Or when I need to switch from a 800# API gate valve to a 1500# API gate valve. Is there a chart somewhere similar to what is found in B16.5 for flanged valves?

Any help would be appreciated!

 

[SPDL310]

I don't know about WOG flanges but API equipment is rated for full working pressure across its entire temperature range based on temperature class. If you have a #5000 API Temp class P-U flange it is good for 5000 PSI from -20F-250F. API temperature classes are listed in their respective API Standard, which for flanges is usually 6A.

 

[moltenmetal]

You need to go to the manufacturers' literature for each valve and look at the pressure-temperature rating curves.

Small socket welding and threaded gate and globe valves (i.e. 4" NPS and below, but typically 2" NPS and below per API 602) have ratings based on their body class- as long as the correct seals and packing are used. They start at 800# class. Yes, there's a P/T chart in API 602.

Ball valves have ratings entirely dependent on the soft goods used for their seats. Seat and seal materials determine the pressure rating at elevated temperature, and will determine when you must switch from a 1000 WOG to a 2000 WOG valve etc. at elevated temperature. Below about 100 F, the WOG rating is the safe allowable working pressure in psi irrespective of the seats and seals used.

 

[LittleInch]

I agree it's very odd and confusing, but there is some method.

The ASME flange and valve class ratings ( basically the same thing) are pretty clear.

The API ratings are similarly clear as they are psi ratings as defined in API 6A. I've never seen anything less than API 3000.

Small ball valves and screwed fittings are often seen as 3000 rated as cost difference is small and it means they are pretty meaty.

WOG is Water Oil Gas and is an older term not really well defined except in vendor literature, but commonly means that pressure in psi at ambient conditions up to about 50C.

3000# ANSI is a bit odd and doesn't really compute.

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

 

[KevinNZ]

Small socket and butt weld valves are usually to API602 class 800. API602 has a pressure/temp tables like the flanged valve codes do.

 

[dpValve]

I may be a little late to this rodeo; however, here is a FREE eBook on ANSI Class Ratings for Valves. I hope it helps. There is some valuable information in the eBook and there are some helpful ANSI charts for valves as well. Hope it helps; let me know.