Raised Face vs Flat Face Flange: 5 Checks Before You Order

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• Alt text: Raised face and flat face flange sealing surfaces compared beside a flanged gate valve

Quick Answer

A raised face flange has a ring around the bore; a flat face flange is level across the sealing surface. The ring concentrates bolt load on a narrow gasket for higher pressure. The flat face spreads load across a full-face soft gasket and protects brittle cast iron equipment. Match face, gasket and standard on both sides; they are not interchangeable. GOWIN offers both across its flanged ranges.

How Do You Identify a Raised Face vs Flat Face Flange?

Look at the gasket seating surface, not the bolt circle. A raised face (RF) flange has a shallow ring standing proud of the face, machined around the bore. A flat face (FF) flange is level from the bore to the outside edge, with no step.

Ring height follows the pressure class. For Class 150 and Class 300, the raised portion is about 1/16 in (1.6 mm). For higher classes it is commonly about 1/4 in (6.4 mm). A straightedge laid across the face shows the difference: it rocks on an RF ring and sits flat on an FF face.

A third pattern, the ring joint (RTJ), uses a grooved face and a metal ring gasket. It should not be confused with either face above.

Most flanged steel valves in oil and gas service arrive with a raised face unless the order says otherwise, which is why RF is often treated as the default. It is a common choice, not a rule. A gate valve order for a low-pressure water line may still have to match an FF pump casing at the other end of the spool, and the end connection decision covers more than the face alone. Pipeline valves ordered to API 6D follow the same logic: the face is one line on the specification, and it has to agree with the flange it meets.

How Do Gasket Contact and Bolt Load Differ?

Both faces use the same bolts. They differ in where those bolts put the load.

On a raised face, the gasket sits only on the ring. The contact area is narrow, so the same bolt load produces a higher unit pressure on the gasket. That is why RF suits higher pressure and temperature: the joint reaches sealing stress with a smaller, stiffer gasket, and the ring is less exposed to the process fluid.

On a flat face, the gasket covers the full face, from the bore to the outside diameter. The load spreads over a much larger area, so unit pressure is lower. The benefit is mechanical rather than hydraulic. The mating flange is supported across its whole face, which limits the bending that bolt torque can introduce. That bending is what cracks a brittle flange, and it is why flat face is specified against cast iron valves, pumps and fittings.

Neither face is stronger in every sense. Pick the one that matches the equipment on both sides, not the higher rating on paper. Body material matters too. A ductile steel body tolerates more local load than a brittle casting, and our guide to valve materials explains where the common grades sit.

Which Gasket Belongs With Each Face?

The gasket has to match the contact area, not just the fluid.

The three common faces differ in gasket and load path.

A raised face takes a ring gasket that covers the raised portion only. Spiral-wound gaskets are the usual choice for higher pressure and temperature. A spiral-wound gasket is a thin metal strip wound with a softer filler into a flat ring. Metal-jacketed and cam-profile metal-core gaskets are the other common semi-metallic options. They compress against the ring and are supported by it.

A flat face takes a full-face gasket that covers the whole seating surface, usually a soft sheet material such as rubber or compressed non-asbestos fiber. The gasket reaches from the bore to the bolt circle, so the bolts pass through it and the load is carried across the full face.

Mixing the two is a common order error. A full-face gasket on a raised face bridges the ring and sits partly over open space. A ring gasket on a flat face has no raised land to compress against and leaves the outer face uncovered.

The same rule reaches valves that sit between flanges rather than on their own flanged ends. A wafer butterfly valve is clamped between two mating flanges, so the gasket and the face on each side both affect the seal. GOWIN lists RF and RTJ faces on that range, with sizes from 2 to 120 in and Class 150 to 600. A GOWIN API 600 gate valve covers Class 150 to 2500 with RF, RTJ or butt weld ends. In both cases the face is a selected option, not an assumption.

Can Raised Face and Flat Face Flanges Be Mated?

No. An RF flange bolted to an FF flange puts the raised ring against a flat surface with no matching land. The ring load lands on a narrow band, the gasket cannot seat as designed, and the mating flange is loaded in a way it was not built for. On a brittle casting, that is the path to a cracked flange.

Some references describe machining the raised face flat to make the pair work. Treat that as a warning, not a workshop instruction: removing the ring changes the pressure boundary and the gasket seating geometry, so it needs engineering approval and a revised drawing.

The safe rule is simple: flat to flat, raised to raised. Both sides should share the face pattern, the gasket coverage and the governing standard. Material and finish should match as well, because a correct face with the wrong gasket or a damaged surface still leaks.

This is also why a wafer or lug butterfly valve needs its own check. It depends on the two mating flanges, the gasket on each side and the bolt set that pulls them together. Our comparison of lug vs wafer butterfly valves explains how the two mounting styles change that joint.

Why Does Pressure Class Alone Not Prove Compatibility?

The raised face vs flat face flange question is not settled by the class number. Two flanges can share a Class 300 rating and still not mate. Class sets the pressure-temperature envelope and the dimensional family. It does not set the face.

A Class 300 RF flange and a Class 300 FF flange have the same nominal rating and different sealing surfaces. Bolting them together does not produce a Class 300 joint. The rating describes what each flange can hold when assembled correctly, not what happens when the faces disagree.

The standard behind the class matters as much as the number. ANSI/ASME flanges, AWWA flanges and other dimensional systems can share a pressure description and differ in bolt pattern, face detail or gasket coverage. A purchase order that says “Class 300 flanged” leaves the most important line open.

That is why the face belongs in the RFQ next to the class, the size and the standard. If the mating flange is unknown, ask for a photo of the face, the flange marking or the piping drawing. A supplier cannot build the right joint from a class number alone, and a buyer cannot inspect it later without the same information.

GOWIN’s globe valve line, for example, covers Class 150 to 2500 in sizes from 1/2 to 24 in with RF, RTJ or butt weld ends and a back seat. The range is wide, but the face still has to be named.

How Do You Check the Valve Drawing and Gasket Specification?

Read three documents together: the valve drawing, the gasket data sheet and the mating flange record. A mismatch between any two is easier to catch on paper than at the flange.

Start with the valve drawing. The end connection block should name the face, the standard and the size. On a GOWIN API 600 gate valve, the drawing also shows the back seat, the API 600 / GB/T 12234 basis and the Class 150 to 2500 range. The back seat matters at the joint only indirectly, but it shows the drawing is the controlled document for that valve.

Then read the gasket sheet. It should state the gasket type, the coverage (ring or full face), the material and the face finish it expects. A spiral-wound gasket listed for a raised face is not the same item as a full-face sheet gasket, even when both are described as graphite or PTFE.

Then read the mating flange record. Size, class, face, standard and material should all be present. If the record is a photo, check that the ring is visible and the bolt holes are not elongated. If it is a drawing, check the face callout rather than the title block.

Finish belongs in the same pass. A raised face may be smooth, serrated, mill-rolled or machined, and serrations may run continuously or as concentric rings. A common requirement is 30 to 55 grooves per inch at 125 to 500 microinches; AWWA references 24 to 55 serrations per inch. You do not need to measure them yourself, but the drawing and the gasket sheet should agree.

The same cross-check applies to other flanged valves. A bolted bonnet globe valve adds a body-bonnet joint that also uses a gasket, and that joint has its own face and finish. A control valve with a flanged body brings trim and actuation into the same datasheet, which makes the end-connection line easier to overlook. A cast steel check valve covers Class 150 to 2500 with RF, RTJ or butt weld ends, and its swing disc orientation has to be read from the drawing as well.

Which Interface Checks Belong in the RFQ?

Five lines settle the raised face vs flat face flange question before quoting. Put them in the inquiry and repeat them in the purchase order.

Face on the valve. State RF, FF or RTJ, plus the standard. “Flanged” is not enough.

Face on the mating flange. If the buyer does not know it, say so and supply a photo or drawing. A supplier who is told the mating face can flag a conflict before quoting.

Gasket family and coverage. Name ring or full face, the gasket type and the material. This is where most RF and FF errors become visible.

Class and standard together. Give the class, the dimensional standard and any project specification. Two Class 300 flanges from different standards are not automatically a pair.

Finish and material. State the required face finish and the body and flange material. A correct face in the wrong material is still a wrong joint.

Add the service data that affects the choice: fluid, pressure, temperature, size and flow direction. Our floating ball valve range lists DN15 to 250, Class 150 to 300, RF, BW or threaded ends, and -50 to +400 °C. A plug valve covers 1/2 to 24 in and Class 150 to 2500 with RF, RTJ, BW, threaded or socket weld ends. A needle valve runs from 1/8 to 1 in and Class 150 to 2500. In each case the face is one option among several, so the order has to name it.

Conclusion

The raised face vs flat face flange call follows the mating equipment, not the catalogue default. Specify the face the joint needs, then confirm it on both sides.

Choose raised face when the line runs at higher pressure or temperature and the mating flange is a steel flange built for a ring gasket. Choose flat face when the mating equipment is cast iron or another brittle material, or when the line is low-pressure water, fire protection or HVAC service where a full-face soft gasket is the norm. Choose RTJ when the project calls for a ring joint, and do not substitute it for either face without approval.

If the two sides disagree, change the specification, not the flange. Adding an adapter or machining a face moves the problem rather than solving it.

Within one product family the details still vary. A 2-piece ball valve covers 2 to 60 in and Class 150 to 2500, while a 3-piece ball valve covers 2 to 40 in and Class 150 to 4500. Both can be supplied with flanged ends, and both still need the face named. The same applies across the check valve range, where a swing disc and a flanged body do not remove the need to match the mating flange.

A face mismatch is cheap to fix on paper and expensive to fix after the valves are packed.

Send service media, size, pressure, temperature and the relevant drawing for a quotation.