RTJ Face Dimensions

Ring Type Joint (RTJ) flanges use a precision-machined groove that accepts a solid metal ring gasket to form a high-integrity seal. Three primary ring styles are used in industrial piping. The R-type ring is available in oval or octagonal cross-sections and is the most widely used for standard ASME B16.5 flanges. Octagonal rings are preferred over oval because they provide a higher contact stress and better seal, though both are interchangeable in the same groove. The RX-type ring has a pressure-energized design with a controlled interference fit that enhances sealing as internal pressure increases, making it suitable for higher-pressure applications.

The BX-type ring is designed specifically for use with API 6BX flanges rated at 5,000 to 20,000 psi working pressure. BX rings have a square cross-section with a pressure vent hole and are not interchangeable with R or RX rings. Each ring number (such as R-45 for 6-inch) corresponds to specific groove dimensions including groove pitch diameter, groove width, groove depth, and ring OD/ID. These dimensions are tightly toleranced, typically to +/- 0.002 inches on critical sealing surfaces, to ensure proper metal-to-metal contact.

Surface finish of the RTJ groove is critical for seal integrity. ASME B16.5 requires a groove surface finish of 63 micro-inches Ra (arithmetic average roughness) or better. The groove must be free of radial scratches, tool marks, corrosion pitting, and any other defects that cross the sealing surface. Before assembly, both the groove and the ring gasket should be inspected visually and dimensionally. Rings should be used only once; re-using a ring gasket that has already been compressed can result in leakage because the ring will not deform properly into the groove a second time.