Raised face (RF) and flat face (FF) flanges can share a nominal pipe size, bolt circle and material family, yet they use different sealing geometry. That difference changes the gasket selection, bolt-load distribution and, most importantly, whether two flanges should be joined at all. A reliable flanged joint is designed as a system: faces, gasket, bolts, material, pressure-temperature conditions and pipe alignment must all work together.
This guide explains raised face vs flat face flange construction in practical terms. It is written for engineering, purchasing and maintenance teams. The governing project drawing, applicable flange standard, gasket manufacturer data and site assembly procedure are always the final authority.
What is a raised face flange?
A raised face flange, often called an RF flange, has a small raised sealing land around the bore. The gasket is compressed on that raised area rather than over the entire flange face. The concentrated sealing area can help develop the intended gasket stress when the flange, bolts and gasket are matched to the service.
Raised face flanges are widely used in industrial piping, but “RF” does not by itself define a complete joint. Confirm the nominal size, pressure class or rating basis, face dimensions, surface finish, gasket type, bolt material and applicable standard. A raised face gasket is selected for the specific face and operating conditions—not only for the pipe size.
What is a flat faced flange?
A flat faced flange, also written as a flat face flange or FF flange, has its sealing surface at the same plane across the full face. It typically uses a full-face gasket that extends to the bolt holes. The gasket footprint and load path are different from an RF connection, so the joint should be evaluated as an FF system rather than as an RF joint with a different gasket.
Flat face flanges are common in systems where the equipment or piping specification calls for that arrangement. The correct flat face flanges gasket type depends on the medium, temperature, pressure basis, facing condition and project requirements. Gasket material must be compatible with the fluid and assembly method; “full face” only describes the gasket geometry, not its material suitability.
Raised flange vs flat face: the core differences
| Feature | Raised face (RF) | Flat face (FF) | Why it matters |
|---|---|---|---|
| Sealing surface | Raised annular land around the bore. | Full face lies in one plane. | The contact area and gasket compression path differ. |
| Typical gasket geometry | Ring-style gasket sized for the RF contact area. | Full-face gasket extending to the bolt holes. | Using the wrong gasket can compromise sealing and load distribution. |
| Joint behavior | Bolt load acts through the raised sealing area. | Bolt load is shared across the full-face gasket arrangement. | Fastener loading and stiffness must suit the intended construction. |
| Identification | Raised sealing land is visible when faces are clean. | No raised land; face appears planar across the sealing surface. | Visual checks help, but drawings and markings remain the authority. |
| Selection basis | Standard, rating, facing, gasket and service data. | Standard, rating, facing, gasket and service data. | Nominal size alone never proves compatibility. |
Can a raised face flange mate with a flat face flange?
In general, do not assume that a raised face flange can mate with flat face flange equipment. The raised land can concentrate load differently from an FF joint and may damage a less-rigid mating flange or produce an unverified gasket condition. This is especially important where cast materials or equipment flanges are involved. If a mixed-face joint is proposed, obtain an engineered project decision that defines any required facing modification, gasket arrangement, bolts and assembly method.
Field personnel should not solve an RF/FF mismatch by stacking gaskets, trimming a gasket, increasing bolt torque or “pulling” the faces together with studs. These workarounds can hide a face incompatibility while increasing the risk of leakage, uneven loading or component damage. Stop and verify the connection against the approved drawing.
RF flange vs FF flange: gasket selection
For a raised face vs flat face flange comparison, the gasket is not an accessory; it is the sealing element. Gasket material, thickness, dimensions, compressibility, chemical compatibility and tightening method should be reviewed as one package. A raised face gasket is normally dimensioned to the RF sealing area, while an FF connection commonly uses a full-face gasket designed for the flat face.
| Joint condition | Gasket approach | Checks before assembly | Common mistake to avoid |
|---|---|---|---|
| RF to RF | Use the project-approved gasket sized for the raised faces. | Face type, finish, gasket ID/OD, material, bolt load. | Selecting a gasket only by nominal pipe size. |
| FF to FF | Use the specified full-face gasket arrangement. | Full-face dimensions, material, bolt-hole alignment and face condition. | Substituting a ring gasket without engineering approval. |
| RF to FF | Do not proceed on assumption; obtain the engineered joint detail. | Mating material, face geometry, gasket plan and controlled assembly method. | Forcing the joint with extra torque or multiple gaskets. |
| Damaged or corroded face | Repair or replace only under approved procedure. | Surface condition, flatness, scoring, pitting and flange alignment. | Using a thicker gasket to conceal an unsuitable face. |
How to specify a flange face correctly
Terms such as flange flat face, flange face, flat face vs raised face flange and raised face flange vs flat face are useful search phrases, but a purchase order needs precise technical data. State the applicable standard and controlled edition, flange type, nominal size, pressure-temperature design basis, facing designation, material grade, gasket specification, bolts and inspection requirements.
- Identify RF, FF or another approved facing without relying on photographs alone.
- State the mating connection and any equipment manufacturer requirements.
- Specify gasket material, dimensions and compatibility with the actual process medium.
- Confirm bolt material, length, lubrication and project tightening procedure.
- Include requirements for markings, material traceability and dimensional inspection.
Installation checks for RF and FF joints
Correct installation is as important as correct selection. Qualified personnel should follow the project-approved isolation and assembly procedure. Before closing a joint, confirm that the flange faces are clean, undamaged and correctly identified; that the gasket is the specified type; and that the pipe is supported and aligned. Bolts should not be used to force a misaligned pipe spool into place.
| Check | RF connection focus | FF connection focus |
|---|---|---|
| Face inspection | Protect the raised land from dents, corrosion and scoring. | Confirm the full sealing plane is clean and even. |
| Gasket placement | Center the approved RF gasket on the raised area. | Align the approved full-face gasket and bolt holes without stretching. |
| Bolting | Use the specified cross-pattern and controlled load method. | Use the same disciplined pattern; avoid uneven full-face compression. |
| Alignment | Keep pipe loads off the face and gasket. | Keep pipe loads off the face and gasket. |
| Final record | Record gasket and flange-face details where required. | Record gasket and flange-face details where required. |
Frequently asked questions
Is “race face flange” a flange type?
Race face flange is commonly a spelling error for raised face flange. Confirm the actual face designation on the drawing, marking and applicable standard before ordering or assembling a joint.
Are all raised face gaskets interchangeable?
No. A raised face gasket must match the flange face, process medium, temperature, design pressure, bolt-loading method and project specification. Similar-looking gaskets can have different dimensions or materials.
Is flat face flange vs raised face only a low-pressure versus high-pressure choice?
No. Pressure is one factor, but the connection must also match the applicable standard, mating equipment, face geometry, gasket and bolting system. Treat RF and FF as distinct joint designs.
Final takeaway
The decision between raised face vs flat face flanges is a sealing-system decision. RF uses a raised gasket contact area; FF uses a full planar face and normally a full-face gasket arrangement. Specify the exact flange face, gasket and mating connection early, and do not assume that a raised face flange and flat face flange are interchangeable. Songhai can support flange-face selection, dimensional review and production documentation for industrial piping projects.