RTJ gaskets ASME B16.5 vs API 6B 2

[GvanB]

Who can help me out?
My client is asking for: RTJ gasket, R31, 3 inch, API 3000#.
Acc. to API 6B the R31 is indeed suitable for 3000#
But my suppliers come up with R31 ASME-ANSI B16.5 in 900#
If I check the tables, both pressure classes are correct, but 900# or 3000# is a hell of a big difference.
Is a R31 RTJ always suitable for API 3000#??
Thanks in advance for any help!

 

[franen]

As you said the gasket is suitable both for ANSI B16.5 and API 6B, and for the classes you have mentioned.
The difference is between the dimensions of flanges ( for a valve 3000# you must use API 6A flange dimensions and not B16.5, or you must calculate the flange with a code-as ASME VIII ).
The reason of the different pressure classification are the different values considered in API and ASME for allowable stresses.

Bye
Francesca

 

[rneill]

The correlation of API flanges to ASME flanges is basically as follows:

ASME 600 equates to API 2000 (bolt together)
ASME 900 equates to API 3000 (bolt together)
ASME 1500 equates to API 5000 (bolt together)
ASME 2500 equates to API 10000 (do not bolt together due to different bolt circle diameter and gasket groove profile)

As mentioned by franen, the reason for the difference in pressure ratings is not the ring gasket but the fact that API flanges use higher strength steels and have different QA/QC requirements so API gives them higher ratings.

 

[GvanB]

Thanks for your answers France and Neill.
It helped me solve one and another!
Brgds
GvB