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Custom Ring Joint Gasket: Specification, Materials, and Inquiry Guide

Quick Answer: A custom ring joint gasket is a metallic RTJ gasket produced to a non-standard ring number, dimension, material, or cross section. Buyers should confirm the flange standard, ring number, groove dimensions, material, and hardness before ordering. CORASEALS can quote a custom ring joint gasket once the flange standard, ring number, material, and required quantity are provided.

RTJ stands for ring type joint. A custom ring joint gasket is not a rubber or sheet gasket. It is a solid metallic gasket that fits into RTJ grooves on ASME, API, and other high pressure flanges. CORASEALS supplies custom ring joint gaskets within its industrial gasket range. Standard ring joint gaskets follow ASME B16.20, API 6A, or an equivalent flange specification. A custom ring joint gasket becomes necessary when a standard ring number does not match a non-standard groove, when the flange surface is worn or repaired, or when the service medium requires a special material.

When to Use a Custom Ring Joint Gasket

Most RTJ flanges accept standard R, RX, or BX ring numbers. A custom ring joint gasket is needed in several situations. The flange may be manufactured to a non-standard pitch diameter or groove width. The flange may have been remachined and no longer matches the original ring number. The service may require a material that is not easily available in a standard size. The gasket may need a special coating, a controlled hardness range, or a non-standard oval or octagonal section.

For these cases, the buyer should not guess the size. Send the flange standard, nominal pipe size, pressure class, and groove measurements. CORASEALS can cross-check the dimensions against ASME B16.20, API 6A, or the flange drawing.

R, RX, and BX Ring Types

R ring gaskets are used in ASME flanges and some API flanges. They have oval or octagonal cross sections. RX ring gaskets have a pressure-energized geometry and are used in some API high pressure flanges. BX ring gaskets are used in API 6BX flanges with pressure ratings up to 20,000 psi depending on the flange design. Each ring type has different dimensional rules and tolerances.

Do not assume that similar ring numbers are interchangeable. R, RX, and BX gaskets have different geometry. Always confirm the ring type from the flange drawing, flange marking, or groove inspection.

Material Selection for Custom Ring Joint Gaskets

Material selection depends on the fluid, temperature, pressure, and flange groove hardness. Common ring joint gasket materials include:

• Soft iron for general low pressure and non-corrosive service
• Low carbon steel for standard oil and gas flange connections
• Type 304 and Type 316 stainless steel for corrosive media
• Inconel 625 for sour gas, seawater, and elevated temperature service

ASME B16.20 defines material markings and hardness limits for standard ring joint gaskets. The gasket hardness must be lower than the flange groove hardness. The lower hardness allows the gasket to deform and seal without damaging the flange.

Dimensions and Cross Section

A custom ring joint gasket is not specified by ID, OD, and width in the same way as a rubber gasket. The critical dimensions are the ring number, pitch diameter, width, height, and oval or octagonal cross section. The pitch diameter is measured at the center of the gasket ring cross section. The groove dimensions must be compared with the gasket dimensions to confirm the correct fit.

If a ring number is unknown, provide the groove OD, groove width, groove depth, and pitch diameter from the flange drawing or a measurement report. A hand measurement of a used gasket alone is not enough because a crushed gasket may not reflect the original dimension.

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