Ring type joint (RTJ) flanges have a precision-machined groove in the flange face that holds a solid metal ring gasket. When the bolts are tightened, the softer ring is compressed into the harder groove and forms a metal-to-metal seal that holds at very high pressures and temperatures, which is why RTJ facings are specified on high-pressure oil and gas lines, wellhead and manifold piping, and high-temperature refinery and power service.
Raaj Fittings machines RTJ grooves on weld neck, blind, long weld neck and other flanges at our two plants in India, to ASME B16.5 and B16.47 and in stainless, duplex, nickel alloy, carbon, low-temperature and alloy steel, for projects across the Middle East, Europe and the Americas.
The groove is cut with a 23° angle on both walls. The metal ring gasket, oval or octagonal in section, sits in the grooves of both flanges. Bolt load deforms the ring plastically against the groove walls, so the ring must always be softer than the groove. Unlike a raised-face joint, the flange faces do not touch after make-up; a gap remains between them.
| Type | Section | Used with |
|---|---|---|
| R | Oval or octagonal | ASME B16.5 and B16.47 RTJ flanges; API 6B flanges |
| RX | Pressure-energised octagonal | API 6B flanges and higher-pressure wellhead connections; fits the same groove as the matching R ring |
| BX | Pressure-energised, for face-to-face make-up | API 6BX flanges for very high pressures |
Rings are identified by number (for example R-37 for a 4" Class 600 flange), and the groove dimensions for each ring are fixed by the flange standard.
ASME B16.20 limits the hardness of each ring gasket material so that it is softer than the flange groove:
| Ring gasket material | Max. hardness |
|---|---|
| Soft iron | 90 HBW |
| Low-carbon steel | 120 HBW |
| 4–6% chrome, ½% moly | 130 HBW |
| Stainless steel 304, 316, 347 | 160 HBW |
| Stainless steel 410 | 170 HBW |
The flange should be harder than the ring. With stainless steel or nickel alloy flanges, softer ring materials are chosen or the groove is hardened or overlaid. Tell us the ring material and any groove hardness requirement when you order.
Every RTJ flange is made from PMI-verified material, machined and dimensionally inspected, including the groove, and marked with the material, class, size, heat number and ring number. Flanges are supplied with EN 10204 3.1 certificates; EN 10204 3.2 certification and third-party inspection by the buyer's nominated agency are available on request.
The seal is made by the ring deforming plastically into the groove. If the ring were harder, the groove would deform instead and the flange could be damaged and leak. ASME B16.20 limits ring hardness for this reason.
An RX ring fits the same groove as the R ring of the same number on API 6B flanges and gives a pressure-energised seal. BX rings are only for API 6BX flanges. Follow the flange and equipment specification.
RTJ facings are available in ASME B16.5 from Class 150, but are mainly specified from Class 600 upwards and in high-pressure oil and gas service.
No. With R-type rings, a gap remains between the flange faces after make-up. BX rings on API 6BX flanges are designed for face-to-face contact.
Yes, in stainless steel, duplex and super duplex, nickel alloys, carbon, low-temperature and alloy steel. The ring gasket material and any groove hardness requirement should be stated on the order.