Valve Pressure Ratings 4

[JABoomer]

Hello,

I am wondering how the different valve pressure rating systems work and also how they relate to each other.

I'm familiar with the standard ANSI pressure ratings: Class 150, 300, 600, and 900; but I believe there's also Class 125, 800, 1500, 2500. Is this correct (mostly is Class 800 really an ANSI class?)?

I I'm also familiar with the 2,000 CWP designation, and understand that there's also 1,000, 3,000, 6,000, and 10,000 CWP ratings.

I've read about a WOG pressure rating which is similar to the CWP rating. Similar, but different.

My question is basically how to these valve pressure rating systems correspond to each other? I am trying to write piping specifications and each valve manufacturer and engineering company seems to use different pressure ratings!

For instance when a needle valve is Class 6000, is that and ANSI Class 6000 or 6,000 CWP???

If anyone can shed any light on the subject I would be most appreciative !

 

[hsbcn]

CWP is cold working pressure, and WOG is simply Water, Oil, Gas. ANSI, in this sense, is a more comprehensive standard that takes into account more factors, which makes it unfeasible to try to match it up against WOG or CWP.

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[LittleInch]

Yeh, it's a bit of a mess really.

The ANSI ratings come from the ASME B 16.5 which is the flange rating code. This pressure rating changes by class (the 125, 150, 300 , 600 etc0, the material and the maximum working temperature. Betweeen -29 and +38 C the pressure rating doesn't change, but after that starts to gradually fall. This fall is dependant on your material.

Have a quick look at this..

http://www.globalsupplyline.com.au/pdfs/catalogues/apv/Valve_Suitability_ASMEB16.34.pdf

The CWP rating means Cold Working Pressure, i.e. below 38C and is in psi. Hence temperatures above this you need to check with the vendor. These tend to be instrument systems and hydraulics where having a high rating costs pennies more than a lower rated valve, but pressures of 3-5,000 psi are not uncommon.

WOG stands for Water Oil Gas and is essentially the same as CWP - see this thread

http://www.eng-tips.com/viewthread.cfm?qid=263386

You also have API 6A ratings which are wellhead ratings and go in psi rating, again at ambient temperature, but see API 6a for how this drops off or changes by material at temps above 60C. Ratings normally seen are 3,5,10, 15 and 20,000 psi. The sizes of the flanges and pipe is completely different to ASME B 16.5.

Your needle valve may have been designated as #6000, which can be used for flange class, but in this case means 6,000 psi

My motto: Learn something new every day

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

 

[JABoomer]

Starting to make a bit more sense. So I take it when you read "Class 800" or "Class 6000", they are actually referring to 800 CWP and 6,000 CWP respectively, because I can find no mention of an ANSI 800# class in B31.5.

 

[gerhardl]

I fully understand your frustration.

Working with US classifications in Europe, I have several times been forced to ask customers for exact specifications. Inquiries for class 800 is no real full described specification for a valve. This needs an addition, for instance ANSI CLASS 800# B31.5 and/or other norms.

Else 'class 800' (only) could easily be misinterpreted as 'part of normal specification valid, but other (unspecified!) parts not valid' or alternatively understood as 'full specification valid, without any diversion allowed' (and also perhaps inclusive additional 'norms' that the company normally uses but dont bother to mention, because it is assumed that 'everyone' already have a pre-knowledge of this.)

Normally class 800 is 'short hand' meaning full specification of latest issued norm.

 

[LittleInch]

Jaboomer.

No.

Class 800 is a class rating in 16.5 (I think, but it's late here and my laptop is turned off), though very rarely used and as far as I can tell only for small instrument valves.

Class 125 and 250 is another that is rarely used for steel but common in cast iron.

CWP 6000 is a pressure rating.

Lots of people misuse # to be both "class" and "pound" or psi. You need to be clear on the difference.

Pressure classes are in asme b 16.5, not 31.5, which is a piping spec, not a flange rating spec.

As I said it's a bit of a mess, but make sure you understand and then get it in writing from your customer, client, vendor etc.

Clear as mud??

My motto: Learn something new every day

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

 

[JABoomer]

Ya I meant B16.5 not B31.5, my bad. It is not mentioned in B16.5, but it is briefly mentioned (once) in B16.34 and all it says is "Class 800 is not a normally tabulated ASME B16.34 designation, but it is an intermediate class that is widely used for socket welding and threaded end valves."

 

[reverman]

To make it messier

API 602 has class 800 defined. however it can also be calculated through ASME B16.34 or B16.5. API 602 just does the math for you.

Many forged valve manufacturers use the odd limited class 1690 and 2680 for some valves. Limited class valves are not interpolated like most other in-between classes like class 200 but instead use a B16.34 appendix to do some calculations on cross sectional area ratios to justify a little higher ratings than a straight interpolated class.

For classes like 125, 250, 150, and 175 when dealing with bronze and Iron valves most refer back to MSS specs for the PT tables, MSS SP-80, SP-70, etc..

 

[uaepiping]

Class 800 is not from B16.50.

API 602 defines it "Class 800 is not a listed class designation, but is an intermediate class number widely used for socket welding and threaded end compact valves."

 

[LittleInch]

Correct - I did say I didn't have my main machine on. Turns up in table 4 of ASME 16.34, with socket welded design details up to 2 1/2". No idea what the pressure rating is though...

My motto: Learn something new every day

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