Deciding between a raised face flange vs. flat face flange comes up on nearly every piping project. Both faces do the same basic job of sealing a joint, but they handle bolt load and gasket compression differently, and that difference determines which one belongs on your system.
Learn more about gasket compression, bolt load, sealing performance, and equipment compatibility to choose the right one for your project.
What Is a Raised Face Flange?
A raised face flange has a small ring raised above the bolt circle, typically 1/16 in. for Class 150 and 300, and 1/4 in. for higher classes per ASME B16.5. That ring concentrates bolt load onto a narrower gasket area, increasing sealing pressure at the gasket. This makes the raised face flange the standard choice for higher-pressure, higher-temperature service, including most oil and gas, petrochemical, and power piping.
A raised face slip-on flange pairs the RF facing with a slide-and-weld attachment, providing a secure connection that handles concentrated bolt loads effectively.
Because the raised ring narrows the load path, this facing pairs well with metallic and semi-metallic gaskets, such as spiral-wound gaskets, that need concentrated pressure to seat properly.
What Is a Flat Face Flange?
A flat face flange has no raised ring; the gasket surface sits flush with the bolt circle, spreading bolt load across the entire gasket instead of concentrating it. This matters most when mating equipment cannot tolerate a concentrated load.
Flat face flanges are required when bolting up to cast iron valves, pumps, or fittings, since a raised face’s concentrated pressure can crack a brittle mating part. They’re also common in low-pressure water, fire protection, and HVAC piping, typically paired with a full-face soft gasket made of rubber or non-asbestos material.
Raised Face vs. Flat Face Flanges: Key Differences
When weighing raised flange vs. flat face options, the differences trace back to how each surface transmits load into the gasket:
Gasket compression & bolt load. A raised face concentrates both pressure and bolt load on a narrow gasket ring, which can overstress brittle parts if mismatched; a flat face spreads the same load evenly across the full gasket, protecting brittle equipment.
Sealing performance. A raised face supports higher pressure with metallic gaskets; flat face relies on a soft, full-face gasket.
Equipment compatibility. Flat face is required against cast iron and other brittle components; raised face is standard for steel-to-steel joints.
Which Flange Face Should You Choose?
The raised flange vs. flat face question usually comes down to the system’s pressure and temperature rating, and what’s on the other side of the joint. For steel piping in oil and gas, petrochemical processing, or high-pressure steam service, a raised face flange is usually specified. For water utility, fire protection, or any connection to cast iron equipment, a flat face flange protects the mating part from cracking and is typically required, not just preferred.
Raised Face vs. Flat Face Flange Comparison Chart
The table below summarizes the raised face flange vs. flat face flange comparison at a glance.
| Feature | Raised Face (RF) | Flat Face (FF) |
|---|---|---|
| Sealing surface | Raised ring above bolt circle | Flush with bolt circle |
| Typical pressure/temperature | Higher pressure and temperature | Lower pressure and temperature |
| Gasket type | Spiral-wound or metallic | Full-face, soft (rubber, non-asbestos) |
| Mating equipment | Steel valves, pumps, fittings | Cast iron or other brittle equipment |
| Common industries | Oil and gas, petrochemical, power | Waterworks, HVAC, fire protection |