Flange Face Types Guide: RF, FF & RTJ Explained
The face type of a flange is the machined surface where it seals against the mating flange. Choosing the wrong face type — or the wrong gasket for it — is a common cause of leaks in piping systems. This guide explains the three main face types: Raised Face (RF), Flat Face (FF) and Ring Type Joint (RTJ), and when to use each.
1. Raised Face (RF) — the industry standard
The RF flange has a raised ring around the bore, slightly above the rest of the face. The gasket sits on this raised ring, so the bolt load is concentrated on a smaller area, producing a reliable seal. RF is the standard face type for most ANSI 150–600 lb flanges and works with soft gaskets such as spiral-wound or sheet gaskets.
2. Flat Face (FF) — for low pressure and cast iron
The FF flange has a completely flat, continuous face. It is used mainly at low pressure and with cast-iron equipment (pumps, valves, compressors). Because cast iron is brittle and can crack under bending stress, an FF joint distributes the load over the full face. FF flanges need a full-face gasket.
3. Ring Type Joint (RTJ) — for high pressure and temperature
The RTJ flange has a machined groove on the face that holds a metal ring gasket (style R, RX or BX). When the bolts are tightened, the ring is crushed into the groove, forming a metal-to-metal seal. RTJ is used for high-pressure and high-temperature service (typically Class 600 and above) where soft gaskets would fail.
4. Quick comparison
| Face type | Sealing surface | Gasket | Typical use |
|---|---|---|---|
| Raised Face (RF) | Raised ring around bore | Spiral-wound / sheet | Most ANSI 150–600 lb service |
| Flat Face (FF) | Full flat surface | Full-face soft gasket | Low pressure, cast-iron equipment |
| Ring Type Joint (RTJ) | Machined groove | Metal ring (R/RX/BX) | High pressure & temperature |
5. Matching face types and gaskets
Always match face types when bolting two flanges together. Mixing RF with FF can damage the gasket or create a poor seal. Choose the gasket to suit both the face type and the service: soft sheet gaskets for low pressure, spiral-wound for higher pressure and temperature, and metal rings for RTJ joints. Confirm the gasket is the right size for the face diameter.
6. How to specify the face type
When ordering flanges, always state the face type alongside the size and pressure class — for example “4” Class 150 RF Weld Neck”. Common additional notes include the raised-face height and surface finish (typically 125–250 µin for standard service). If you are replacing an existing flange, send a photo or drawing so the face can be matched exactly.
Frequently Asked Questions
What is the difference between RF and FF flanges?
RF has a raised ring where the gasket sits, concentrating the bolt load for a tighter seal — standard for most ANSI service. FF is completely flat, used at low pressure and with brittle cast-iron equipment to avoid cracking.
What is an RTJ flange used for?
RTJ flanges use a metal ring gasket crushed into a groove for a metal-to-metal seal. They are used in high-pressure and high-temperature service where soft gaskets would fail.
Can I mate an RF flange to an FF flange?
Generally no for pressure service. The different contact surfaces produce a poor seal and can damage the gasket. Always match face types.
Which gasket do I use with a raised face flange?
Use a soft flat or spiral-wound gasket sized to the raised face diameter. For RTJ flanges, use the correct metal ring (R, RX or BX) matching the groove.
Need flanges to a specific face type or standard?
Send your size, standard, pressure class and face type — we manufacture RF, FF and RTJ flanges in a wide range of materials.
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