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Subject: R and RX ring grooves


Can R ring gaskets work in ring grooves marked RX?


If you have flanges meeting API Spec 6A, 20th Edition requirements, the answer is YES, an R ring gasket can be used in a ring groove marked RX.  

All API Spec 6A, 20th Edition, 6B flanges, marked as using R, or RX ring gaskets, or perhaps marked R/RX, will have the same groove, and will seal properly with either an R or RX ring gasket.  

API Spec 6A, 20th Edition specifies R and RX ring gaskets/grooves. Interestingly the Specification has a Table B.63 titled “Type R ring gaskets,” and a Table B.64 titled “Type RX pressure energized ring gaskets.” These tables provide dimensions for both ring gaskets and grooves. The existence of these two specific tables might lead a person to believe that there are different dimensions for the ring grooves that accept R or RX ring gaskets, when in fact the grooves in the tables are identical. If you have access to a copy of API Spec 6A, 20th Edition you may want to compare the groove dimensions. For example, follow the line across R 31 on both tables, and note the dimensions in columns P, E, and F are identical, and the dimensions in Columns S show the resulting different Stand-off dimensions between flanges when choosing to use either an R or an RX ring gasket in the groove.  

We find no mention in API 6A that the grooves in the tables are actually the same, and it appears that the marking requirement will allow the flange to have marking that says R, or RX, or R/RX as the manufacturer chooses, or the customer requires.  

It may be possible to find some odd old flanges with deep ring grooves that National Oilwell manufactured in the late 1970’s, but there could only be a few examples of these in existence. We do not know how National Oilwell marked these flanges, but they probably were marked RX. We guess other manufacturers could have made other nonstandard flanges that seal only with RX ring gaskets, but we know of no examples. The unique flanges that had these deep ring grooves were typically made with raised faces that would pull together when made-up, much as 6BX Flanges.  

You can currently find ring grooves accepting only RX ring gaskets in API Spec 16A, 3rd Edition, in a few Clamp Hub connections.  API Spec 16A 3rd Edition calls these ring grooves, SR. R ring gaskets will not work in these Hubs, marked SR.   

We attempted to give you all the information we had on the subject because we could not tell, from your question, why you were asking the question and what you may have actually encountered.

Should you need any ring gaskets, studs, nuts, or complete pieces of equipment, please Contact Us.


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