RF Flange Face Types: Raised Face, Flat Face, and RTJ Explained

Flange Face Types: The Key to Leak-Free Connections

The flange face type determines the gasket selection, bolt loading requirements, and sealing performance of your flanged connection. Understanding the differences between RF (Raised Face), FF (Flat Face), and RTJ (Ring Type Joint) is essential for proper flange specification.

Raised Face (RF) Flanges: Industry Standard

Design Characteristics

Raised face flanges feature a raised ring around the bore where the gasket is compressed. The raised portion typically extends 1/16″ (1.6mm) for Class 150 and 300, and 1/4″ (6.4mm) for Class 400 and higher.

Advantages

  • Versatile: Compatible with most gasket types
  • Concentrated Load: Higher gasket stress with lower bolt torque
  • Widely Available: Most common flange face type
  • Cost-Effective: Standard manufacturing process

Gasket Options for RF Flanges

  • Non-Asbestos Sheet Gaskets: General service up to Class 300
  • Spiral Wound Gaskets: Class 150 to 2500, wide temperature/pressure range
  • PTFE Envelope Gaskets: Corrosive chemical service
  • Graphite Sheet Gaskets: High-temperature applications

Applications

  • Process piping in refineries and chemical plants
  • Steam distribution systems
  • Water and wastewater treatment
  • HVAC systems

Flat Face (FF) Flanges: Specialized Applications

Design Characteristics

Flat face flanges have a gasket surface in the same plane as the bolt circle. The entire face contacts the gasket.

When to Use Flat Face Flanges

  • Cast Iron Equipment: Prevents bending of brittle cast iron flanges
  • Class 125 and Below: Low-pressure applications
  • Full-Face Gaskets: When using gaskets that cover the entire face

Important Note

Never connect a raised face flange to a flat face flange without proper consideration. The mismatch can cause improper gasket compression and potential leakage.

Ring Type Joint (RTJ) Flanges: High-Performance Sealing

Design Characteristics

RTJ flanges have a machined groove that accepts a metal ring gasket. When bolts are tightened, the ring deforms into the groove, creating a metal-to-metal seal.

Advantages

  • Exceptional Sealing: Metal-to-metal contact for critical service
  • High Pressure: Suitable for Class 600 to 2500
  • High Temperature: Performance up to 1000°C+
  • Fire Safe: Maintains seal integrity during fire exposure

RTJ Ring Types

  • Type R: Standard oval or octagonal rings
  • Type RX: Pressure-energized rings for higher performance
  • Type BX: For API 6BX flanges (subsea applications)

Applications

  • High-pressure steam systems
  • Hydrogen service
  • Offshore oil and gas platforms
  • Critical process connections

Flange Face Surface Finish Requirements

Face Type Serration Ra Value Gasket Type
RF (Stock Finish) Spiral serrated 125-250 μin Soft gaskets
RF (Smooth) No serration 63 μin max PTFE, graphite
RTJ Machined groove 63 μin max Metal rings
FF Spiral serrated 125-250 μin Full-face gaskets

Gasket Selection by Face Type

For RF Flanges

  • Class 150-300: Non-asbestos sheet or spiral wound
  • Class 600-900: Spiral wound with inner ring
  • Class 1500-2500: Spiral wound or RTJ

For RTJ Flanges

  • Soft iron rings: General service
  • 304/316 stainless: Corrosive service
  • Inconel 625: High-temperature/corrosive

Bolt Torque Considerations

Proper bolt torque is critical for leak-free performance:

  • Use calibrated torque wrenches
  • Follow star-pattern tightening sequence
  • Apply torque in multiple passes (30%, 60%, 100%)
  • Consider hydraulic bolt tensioning for critical service

Quality Manufacturing Matters

Flange face finish quality directly impacts sealing performance. Songhai’s CNC machining centers ensure precise face finish and dimensional accuracy for all flange types.

Contact us for technical support on flange face selection and gasket recommendations for your specific application.