Steel Flange Face Types: RF, FF, RTJ Explained
Flange face type is one of the most critical yet often overlooked specifications in piping system design. The face type determines how the flange seals against its mating gasket, directly affecting leak prevention, pressure rating, and maintenance intervals. We break down the three primary flange face types: Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ).
Raised Face (RF) Flanges
Raised Face flanges are the most common type in process piping. The gasket sits on a raised surface extending above the bolt circle, typically 1/16 inch for Class 150-300 and 1/4 inch for Class 400+. This concentrated sealing area allows higher bolt loads on a smaller gasket surface, creating reliable seals at pressures up to Class 600. RF flanges work with spiral wound, composite, and non-metallic flat gaskets.
Flat Face (FF) Flanges
Flat Face flanges have a gasket surface flush with the bolt circle. They are typically used with cast iron and other brittle materials where uneven bolt loading could cause cracking. FF flanges are common in low-pressure water systems, HVAC piping, and fire protection systems below 150 PSI. They must always mate with another Flat Face flange.
Ring Type Joint (RTJ) Flanges
Ring Type Joint flanges feature a machined groove accepting a metal ring gasket. When bolts tighten, the ring deforms into the groove creating a metal-to-metal seal for extreme pressures and temperatures. RTJ is mandatory for wellhead equipment, subsea pipelines, and high-temperature refinery piping. They operate reliably above Class 1500 and 1000 degrees F.
How to Choose the Right Flange Face
Selection depends on: operating pressure, temperature, media corrosiveness, and flange material. For Class 150-600 with non-hazardous media, RF is the default. For brittle materials or very low pressure, FF is appropriate. For high-pressure, high-temperature, or hazardous media, RTJ provides the most reliable sealing. Always consult ASME B16.5 for dimensional requirements.
Common Flange Face Finishes
Stock finish (125-250 AARH) is standard for RF flanges with non-metallic gaskets. Spiral finish (250-500 AARH) provides better sealing for metal gaskets. Smooth finish is required for RTJ grooves. CoreMetal supplies all flange face types in carbon steel, stainless steel, and alloy materials.
Conclusion
Understanding these technical details helps you make better purchasing decisions and ensures your projects meet all quality and safety requirements. At Xi’an Coremetal Steel Co., Ltd., we’re here to support your material selection needs with expert advice and premium products.
Need expert guidance on your next steel project? Contact Tracy at tracy@coremetalsteel.com or call +86 18291910632 for personalized recommendations.