Hi all!

I have a query regarding pressure rating of 150lb A350 LF2 flanges.

I am looking at ASME/ANSI B16.5 and looking at table 2 pressure temperature ratings.

We are planning to use 150lb flanges on a job that has a design pressure of 225 psi. ASME 16.5 says an LF2 150lb flange is rated for 285 psi up to 100 deg F. However the problem I have is that although the rating of the flange is acceptable for the design pressure (225 psi), the rating is too low for our test pressure (the test pressure is anticipated to be circa 315 psi).

Can anyone advise if a 150lb flange is acceptable in this circumstance - or will we have to go to a 300lb flange for this application?

Many thanks for you help.

Andy Potts.

ASME B16.5-2003 addresses testing of flanges in Paragraph 8. Paragraph 8.1 states that "flanges are not required to be pressure tested." Paragraph 8.2 specifies a pressure test for "flanged fittings" (tees, crosses, etc). Some idea of the pressure capacity at test of the flange may be found by using the test pressure specified in 8.2.

Paragraph 8.2 states that the test pressure is to be no less than 1.5 times the pressure rating at ambient (100° F), rounded up to the next higher 25 psi increment.

The class 150 A-350 LF2 flange has a rating of 285 psi at the test temperature. Multiply by 1.5 = 427.5 psi. Round up to next 25 psi increment equals 450 psi test pressure. Since this is greater than your actual vessel test pressure of 315 psi you are probably "good to go" (assuming that there is no more than 450 - 315 = 135 psi of test liquid static head acting on the flange).

ASME Section VIII Division 1 accepts B16.5 flanges as a standard pressure component. This includes the testing rules of B16.5, so you do not have to worry about additional requirements under the vessel code.

Tom,

Thanks very much for that - it has made it a lot clearer!

Cheers.