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NatGas (Mechanical) (OP)
5 Nov 08 10:16
I work in the natural gas industry.  We have 150, 300, and 600# ANSI flanges in our system.  Some of our old documentation has the old maop for these flanges.  I believe in 1988 ANSI raised the ratings for these three flange classes.  Is there a directive anywhere in the ANSI standards, or elsewhere, that tells us if these "new" ratings are retroactive?  In other words do our old 600# valves have to be limited to 1440 psi, or can they, like our newer valves, be subjected to 1480 psi?  Thanks for any help you can give me on this.
Helpful Member!(2)  jte (Mechanical)
5 Nov 08 11:34

A good question. There are also several changes to the ratings from the 1996 ed to the 2003 ed. For example, at 200 deg F the rating of a CL-600 flange in material group 1.1 was raised from 1350 psi to 1360 psi while at 300 deg F the rating dropped from 1315 psi to 1310 psi.

The direct answer to your question is in B16.5 2003 (and at least as far back as the 1977 ed) in the last sentence of 1.3:

Quote (B16.5):

Where such components were installed in accordance with the pressure-temperature ratings of an earlier edition of this Standard, those ratings are applicable except as may be governed by the applicable code or regulation.

Another reference is Interpretation 2-38:

Quote (Int-2-38):

Subject: Use of Earlier Editions of B16.5
Question: According to B16.5-1988, can flanges manufactured in accordance with an earlier edition of B16.5 be rated at the higher pressure-temperature ratings in the current edition?
Reply: No. Se para. 1.3

Now, have I seen flange rating "cherry picked" by edition. Yes. Is it hazardous? Maybe. I guess the bottom line is that if the joint seals - no problem! But make sure you are in a ethically and legally defensible posture (e.g. you verified that the material spec didn't change, the manufacturing requirements didn't change...) if it leaks and causes a problem.

When referring to the Code, you have to recognize that the committee does not have infinite volunteer resources (material spec's change, B16.5 requirements change...), and is really not in a position to retroactively change flange ratings. You really wouldn't want to be told that your line at 300 deg F now has to be derated since the flange rating changed, would you? So, the same applies to increases in ratings.

NatGas (Mechanical) (OP)
6 Nov 08 14:28

Thank you for the answer and those references.  Those are very useful to me.   
UW1981 (Mechanical)
6 Mar 09 13:55
Can somebody confirm when the change in ANSI B16.5 pressure ratings for flanges occured....we are looking at confirming documentation for process safety info and need to ensure the pressure ratings are appropriate for the code under which they were built.

jte (Mechanical)
17 Mar 09 22:51
Well, each edition is different. Its a continuing process, not some sudden change like you might see with VIII Div. 1 from '98 to '99. They really don't just publish new editions to make a buck. If you have ANSI B16.5 then that's a clue since the more recent ones have been ASME B16.5.


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