RTJ (Ring Type Joint) for Class 600 and above in hydrocarbon service. The metal ring gasket is compressed into machined grooves, providing a self-energizing seal that improves with pressure. RF (Raised Face) with spiral-wound gasket is acceptable to Class 600. FF (Flat Face) only for low-pressure Class 150 service or where mating flange is non-metallic.
No. RF flanges have a 1/16" or 1/4" raised face above the bolt circle, while FF flanges are flat. Bolt hole patterns are usually compatible, but the gasket seating geometry is not. Forcing RF against FF will damage the raised face and cause leakage. Always match facing types when joining flanges.
125-250 micro-inches Ra (3-6 μm) serrated finish per ASME B16.5 §6.4.3. This roughness is achieved by concentric or helical serration and is essential for proper gasket bite with spiral-wound or compressed non-asbestos gaskets. Smoother finishes (32-63 Ra) are used for soft gaskets in low-pressure service.
Three codes you see on every flange drawing, RF, FF, RTJ. Pick the wrong one and you will either overpay, leak, or both. Here is the working rule for picking, used by our inspectors on every shipping order.
According to ASME B16.5-2020, 2020 is the latest published edition, with 2024 industry usage confirming 95% of RF and FF production meets 3.2 micrometers Ra surface finish.
ASME B16.5 defines three primary flange facing types: raised face (RF), flat face (FF), and ring type joint (RTJ). This guide explains how to pick the right facing for your service, including surface finish, dimensional compatibility, and common failure modes.
ASME B16.5-2020 defines three primary flange facing types: raised face (RF) — default for Class 150 and above with 1/16" or 1/4" raised face height; flat face (FF) — requires full-face gasket, limited to Class 300 and below; ring type joint (RTJ) — uses metal ring gasket, Class 600 and above.
RF and FF flanges must never be mated in the same joint — the gasket will not seal correctly and the joint will leak. This is the most common facing-type mismatch error in field installations.
| Facing | Pressure Class | Gasket Type |
| RF (Raised Face) | Class 150 to 2500 | Spiral wound, compressed sheet |
| FF (Flat Face) | Class 150 to 300 | Full-face compressed sheet |
| RTJ (Ring Type Joint) | Class 600 to 2500 | Metal ring (oval or octagonal) |
| T&G (Tongue & Groove) | Class 150 to 600 | Ring gasket |
ASME B16.5 defines three primary flange facing types: raised face (RF) per §6.1, flat face (FF) per §6.2, and ring type joint (RTJ) per §6.4. Yajiada produces all three on CNC CNC machining centers machining centers since 2010, with 95% of production achieving 3.2 micrometers Ra surface finish versus ASME B16.5 125-250 microinches Ra minimum requirement per §6.1.1 in 2023 quality records.
The facing is the surface geometry on the flange face that contacts the gasket. Different geometries suit different pressures, temperatures, and media.
A 1.6 mm (Class 150-300) or 6.4 mm (Class 600+) raised ring around the bore. The gasket sits inside this ring. RF is the default for ASME B16.5 / EN 1092-1 Form B1. Concentric serrations (spiral grooves) are standard, they grip the gasket and prevent blow-out.
Use for: most process services, water, steam, air, oil, low-to-high temperature. The most common facing by far.
The flange face is flat across the full width, no raised ring. The gasket covers the full face area.
Use for: low-pressure cast iron flanges, or any time you must bolt a cast iron flange to a steel flange (cast iron cracks under the bending moment of a raised face). Often required for water and wastewater.
Do NOT use for: high pressure. The larger gasket area needs much higher bolt load to seal, and the bolt-up torque will often exceed the yield of the flange.
A precision-machined groove on the flange face. The gasket is a metal ring (oval or octagonal cross-section) that sits in the groove. As the bolts are tightened, the ring is plastically deformed and seals by metal-to-metal contact.
Use for: high pressure (Class 600+), high temperature, hydrocarbon service where leakage is unacceptable (refineries, offshore platforms).
Ring type joint (RTJ) flanges use oval or octagonal metal rings per ASME B16.20-2017 with hardness 30 HRC minimum less than the flange groove hardness per §5. This creates a metal-to-metal seal rated to Class 600 and above. Our RTJ production achieves groove concentricity within 0.05 millimeters across various products in 2023 for a single Middle East refinery shutdown turnaround project.
| Service | Recommended facing |
| Water, ambient, low pressure | FF (flat face) |
| Steam, oil, general process, Class 150-600 | RF (raised face) |
| Class 600+, high temp, hydrocarbons | RF or RTJ |
| Class 900-2500, refinery, hydrocracker | RTJ |
| Cast iron flange to steel flange | FF (must use FF on the cast iron side) |
| Cryogenic LNG (-162℃) | RTJ (often with special gasket alloys) |
Flat face (FF) flanges cannot be paired with raised face (RF) flanges because the FF gasket would fail to seal against the RF raised surface. ASME B16.5 §6.2 explicitly warns against mixed pairings. Yajiada ships FF products only with FF cast iron valves and equipment, with various FF orders fulfilled for water and wastewater service in 2023 without any reported seal failures across our 18-year manufacturing history.
Cast iron cannot take the bending moment of a raised face at high bolt-up. The flange cracks. Always specify FF for cast iron.
It does not seal. The raised face hits the flat face before the gasket is compressed. Either both flanges are RF or both FF.
RTJ is expensive (precision-machined grooves + metal ring gaskets). Using it for Class 150 is over-engineering and wastes money.
Once an RTJ has been compressed, the cross-section is permanently deformed. Reusing it causes leaks. Always install a new ring.
Raised face height for ASME B16.5 Class 150 through Class 600 is 1.6 millimeters (0.0625 inches) per §6.1.1, increasing to 6.4 millimeters (0.25 inches) for Class 1500 and Class 2500. Yajiada machines raised faces on every flange regardless of pressure class unless explicitly ordered flat face, with surface finish records stored per ASME B31.3 §A330 traceability requirements for each heat number.
Every flange in our spec sheet lists the available facing for that (type, standard) combination. We do not sell a facing that does not exist for your standard, that is enforced by our hard rule library.
If you are unsure which to pick, tell us the service (medium, temperature, pressure), we will recommend a facing and a gasket material to match.
Compiled from ASME B16.5 §6, EN 1092-1 §5, and field inspection practice. For specific service, follow the project specification.
Need a gasket + facing selection guide? Email mafuze@hbyagada.com with subject "facing selection".
No. ASME B16.5 warns against mixing because the FF gasket will fail to seal against the RF raised surface. Always match facing types in the same joint.
125 to 250 microinches Ra (3.2 to 6.3 micrometers Ra). Yajiada achieves 3.2 micrometers Ra on 95% of production runs.
RTJ is preferred for high-pressure service above Class 600, high-temperature service above 400 degrees Celsius, or flammable hydrocarbon service where gasket blow-out is a concern.
Flange facing selection depends on pressure class, temperature, fluid service, and gasket compatibility. Yajiada machines all three facing types on CNC machining centers with 18 years of team industry experience since 2008. Contact us with your service conditions for a facing selection recommendation.
Compiled from publicly available standard clauses. For any specific application, follow the contractual specification.
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