RTJ Raised Face to RTJ Flat Face 1

[YMech]

Hello,

I have an application that connects an API 6A Type 6B RTJ Raised Face flange to an API Type 6B RTJ Flat Face flanged choke valve.

Does any one have experience, or see an issue with mating a RTJ Raised Face to an RTJ Flat Face flange? I know that this is not recommended for typical RF/FF connections, but we would be using an RX type gasket and the RTJ faces are not meant for face-to-face makeup. My initial thought is that since the faces do not touch and both flanges are of the same material, that the mating between the two would be acceptable.

Thank you in advance!

 

[LittleInch]

Well API 6A 10.1.2.2.1 says

Type 6B flanges are of the ring joint type and are not designed for face-to-face make-up. The connection make-up
bolting force reacts on the metallic ring gasket. The type 6B flange shall be of the through-bolted or studded
design

There is an inherent mismatch, IMHO, between your statement "RTJ flat face flange". It's either an RTJ flange or it's a flat face flange. It cannot be both at the same time.

So no, IMHO, this would not be acceptable.

either get a different choke valve or get a 6B FF flange and a gasket able to handle the pressure.

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

 

[YMech]

LittleInch,

I have an older version of API 6A, but looking at 10.1.2.2.3 (Flange Face): "The flange face shall be flat or raised on the ring joint side and shall be fully machined."

We have these flanges in our shop (both a RTJ with a raised face and a RTJ with a flat face), so I know it is possible. It is the gasket that provides the space in between so that the faces do not touch, which is why I am thinking the different facings will not affect the integrity of the connection.

We plan to mock the connection up in our shop to verify, but wanted to see if anyone here had any first-hand experience to provide any suggestions/concerns.

 

[LittleInch]

Aaah, Ok, A drawing always helps!

What it means is that there is a groove for the ring, but it is machined into a flat face, not with a raised face?

My apologies for not realising what you meant.

For API 6A flanges this is acceptable as there is a machined groove and the two faces don't touch, unlike ASME B16.5 FF to RF flanges.

Interestingly type 6BX flanges require one of the flanges to be RF, but type 6B doesn't have this stipulation

See also

https://www.woodcousa.com/QandA/q_a-r_42.htm

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

 

[YMech]

LittleInch,

That was a good article. I think we are on the same page now. The ring groove is still there on both flanges - the flat face has the groove machined flush with the face and the raised face has the groove machined in the raised portion. The overall length (from neck to flange face vs. neck to raised face) are also the same, with the difference being made up in the flange thickness.

Anyway, thank you for your input. I'll try to follow up once we mock the connection to give this thread an update.

Thanks!