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Question:

What is the meaning of the letter 'X' in the description for a ring joint gasket number?

Answer:

The various letters and numbers used to identify ring gaskets simply serve as names, much as a part number a company might assign to a product or part they manufacture.

The first standard ring gaskets, originally specified by ASA, now ANSI, had a number identification with the letter R placed in front to designate the item as a ring. Later manufacturers offered these "R" ring gaskets in 2 cross section configurations, Oval and Octagonal, but kept all identification designations the same, simply stating Oval or Octagonal as customers also designated when ordering.

Caution: Some early ANSI and API flanges have "Rounded" bottom ring grooves and can only seal with Oval "R" ring gaskets.

Cameron Iron Works offered an "improvement" to the first designs of "R" ring gaskets, offering a third "R" gasket profile or cross section "Xtra" to the original designs, but fitting all the same grooves. Hence "RX." All "R" ring gaskets fit flanges that have face separation when made-up, the use of "RX" ring gaskets increases this face to face separation or stand-off. All API 6B flanges with grooves to accept R ring gaskets will accept RX ring gaskets. API Spec 6A describes and specifies RX ring gaskets. For a further explanation, and the dimensions off stand-off between flanges, see Flange Make-up, Stand-off / No Stand-off and Drift between Flanges.

More recent flange designs, for higher pressure and greater resistance to bending, have a face to face make-up design. These flanges have come as a second generation and have Ring Gaskets designed to facilitate this face to face make-up. With the first generation of API flanges now called 6B flanges, it seems this second generation got called 6BX, again we suppose the X meant the now "Xtra" flanges introduced into the API 6A Specification. API gave the Ring Gaskets for these flanges the designation BX also.

For a detailed explanation of how ring gaskets of all types fit and seal in grooves, see Field Appraisal of Ring Grooves, and Ring Gasket Handling and Inspection.