Ring type joint (RTJ) flanges
At high pressure and temperature, a soft gasket can blow out or creep. A ring type joint replaces it with a solid metal ring seated in machined grooves, and it has been the standard high pressure joint in oil and gas for decades.
A ring type joint (RTJ) flange has a groove with sloping sides machined in its face that holds a solid metal ring gasket to ASME B16.20. When the bolts are tightened, the ring is squeezed into the grooves of both flanges and seals metal to metal, which holds high pressure and temperature where a soft gasket could blow out. RTJ facing is most common in Class 600 and above. We machine RTJ grooves to ASME B16.5 on weld neck, blind and the other flange types in Class 150 to 2500, in A105, A350 LF2, stainless and duplex, with an EN 10204 3.1 mill test report for every heat.
How the joint seals
The groove dimensions and the ring number for each size and class are set in ASME B16.5, and the rings themselves in ASME B16.20. The ring is made softer than the groove, so that it deforms to fit while the flange does not. Once made up, the flange faces do not touch: a gap remains between them, and the ring carries the bolt load. A ring that has been used is not used again, because it has already been deformed to fit one pair of grooves.
| Style | Shape | Notes |
|---|---|---|
| R, oval | Oval cross section | The original style; fits the standard groove |
| R, octagonal | Eight-sided cross section | Seals on the groove flanks with a larger contact area; also fits the standard groove |
| RX | Pressure-energized octagonal profile | Internal pressure pushes the ring harder against the groove; used where the joint sees vibration or pressure swings |
BX rings belong to API 6A wellhead flanges, which are a different product with their own dimensions. We make ASME B16.5 flanges, not API 6A equipment.
Where RTJ flanges are used
- Oil and gas gathering, compressor discharge and pump station piping in Class 600 to 2500. See flanges for oil and gas.
- Refinery high pressure units, such as hydrotreaters and hydrocrackers.
- Steam and boiler feedwater piping in power plants, where specifications call for them.
- Orifice meter runs in the higher classes, with angled taps that clear the groove. See orifice flanges.
Groove hardness and finish
Because the seal depends on the ring being softer than the groove, many specifications set a maximum hardness for the ring and a minimum for the groove, and some ask for hardness readings in the groove on the certificate. The groove surface must be smooth and free of scratches across the sealing flanks. Tell us any hardness or surface finish requirement on the line list, so we confirm it in the quotation and record the results.
How to order
A typical line reads: "Weld neck flange RTJ, ring R-37, NPS 4, Class 900, bored for Sch 80, ASTM A105, 12 pcs". Send the type, size, class, facing, bore or schedule, material and quantity for each line, and we quote every line as specified. Every order ships from our works in Gujarat, India, with an EN 10204 3.1 mill test report for every heat; ordering from India explains the documents, marking, packing and customs.
Frequently asked questions
Can I use a spiral wound gasket on an RTJ flange?
No. An RTJ flange is grooved for a metal ring; a spiral wound gasket needs a flat raised face. Specify one facing per joint and order both flanges to match.
Which ring number do I need?
ASME B16.5 lists the ring number for each size and class, and ASME B16.20 gives the ring dimensions. The same ring number can serve more than one class, so check the table for your size and class.
Do RTJ flanges need special bolting?
The number and diameter of bolts are the same as for raised face flanges of that class, but the studs are longer, because the flanges stand apart on the ring; ASME B16.5 lists ring joint stud lengths separately, and our flange bolt chart gives both. Tighten the joint evenly so the ring seats all round, following your bolting procedure.
Sources
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24 Metric/Inch Standard
- ASME B16.20, Metallic Gaskets for Pipe Flanges
- API Specification 6A, Wellhead and Tree Equipment (BX rings, for comparison)