RF vs RTJ Flange: Face Type Selection
Definition
RF (Raised Face) flanges have a raised sealing surface machined above the flange bolt circle. The gasket sits on this raised area and is compressed by the bolts. RTJ (Ring Type Joint) flanges have a machined groove in the flange face that accepts a metallic ring gasket. The ring is deformed into the groove under bolt load, creating a metal-to-metal seal.
When Each Is Used
RF flanges are the standard for ASME Class 150 and Class 300 services. They use soft gaskets (spiral wound, compressed fiber, or PTFE) and are suitable for most low-to-medium pressure applications in refineries, chemical plants, and utility services.
RTJ flanges are specified for high-pressure and high-temperature services, typically ASME Class 600 and above. The metal ring gasket provides a leak-proof seal under extreme conditions. RTJ faces are mandatory for wellhead equipment (API 6A) and most upstream oil and gas applications.
Specifications Table
| Feature | RF (Raised Face) | RTJ (Ring Type Joint) |
|---|---|---|
| Sealing mechanism | Gasket compressed on flat raised face | Metal ring deformed into machined groove |
| Gasket type | Spiral wound, CNAF, PTFE, graphite | Metallic ring (oval, octagonal, BX, RX) |
| Typical pressure classes | Class 150, 300 | Class 600, 900, 1500, 2500 |
| Raised face height (Class 150/300) | 1.6 mm (1/16”) | N/A (groove instead) |
| Raised face height (Class 600+) | 6.4 mm (1/4”) | N/A (groove instead) |
| Gasket cost | Low to moderate | High (precision-machined metal ring) |
| Reusability of gasket | Spiral wound: no; soft: no | Oval: no; Octagonal: limited reuse |
| Seal reliability | Good for moderate P&T | Excellent for high P&T |
| Fire resistance | Depends on gasket (PTFE melts) | Excellent (all-metal seal) |
| Standard | ASME B16.5, B16.47 | ASME B16.5, B16.47, API 6A |
| Face finish | 125-250 AARH (serrated or concentric) | Mirror finish in groove |
Comparison
Sealing integrity. RTJ provides a superior seal because the soft metal ring deforms plastically into the groove, creating two concentric seal lines. RF gaskets rely on compressive stress across the gasket face and are more sensitive to uneven bolt loading, flange misalignment, and thermal cycling.
Interchangeability. RF and RTJ flanges are not interchangeable. An RF flange cannot mate with an RTJ flange. If one side is RF and the other is RTJ, one flange must be replaced or a special adapter used.
Cost. RF flanges and their gaskets are significantly cheaper. RTJ flanges require precision groove machining, and the metallic ring gaskets cost 5 to 20 times more than spiral wound gaskets. However, for high-pressure services, the added cost is justified by improved leak prevention.
For details on face finish requirements, see the flange face finish guide.
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