Two flanges can share the same size, class and material and still be incompatible — because of the sealing face. Face type is one of the five details every flange order must confirm.
The Three Common Faces
RF — Raised Face. The industry default. A raised ring (1.6 mm high for Class 150/300; 6.4 mm for Class 600+) concentrates bolt load onto a smaller gasket area, improving the seal. Used with flat, spiral-wound or soft gaskets across oil & gas, water and process service.
FF — Flat Face. The entire face is flush. Used where the mating flange is flat — typically cast iron valves and pump bodies that would crack if bolted against a raised face — and in many low-pressure water systems. Rule: never bolt an RF flange directly to an FF cast iron flange.
RTJ — Ring Type Joint. A precision-machined groove holds a solid metal ring gasket (R, RX or BX type) that deforms to create a metal-to-metal seal. Specified for high pressure and high temperature service — wellheads, Class 900/1500/2500 piping, API 6A equipment.
| RF | FF | RTJ | |
|---|---|---|---|
| Typical service | General purpose | Cast iron mating, low pressure | High pressure/temperature |
| Gasket | Flat / spiral wound | Full face soft gasket | Metal ring (R/RX/BX) |
| Pressure classes | 150 – 2500 | 125 / 150 | 600 – 2500 |
| Relative cost | Base | Similar | Higher (machining + ring) |
How to Order Without Mistakes
A complete flange specification confirms five things:
Weld Neck Flange, 6”, Class 300, RF, ASTM A105, ASME B16.5, bore to match SCH40 pipe
- Type (WN/SO/BL/SW/TH/LJ)
- Size and pressure class
- Face type (RF/FF/RTJ)
- Material and standard
- Bore schedule (for weld necks)
European inquiries add one more trap: EN 1092-1 face types (Type A, B1, B2…) don’t map one-to-one onto ASME faces, and PN ratings are not interchangeable with ASME classes. If your project mixes standards, send us the data sheet — we’ll confirm the correct combination before quoting.
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