Flange Face Types and Gasket Selection: A Professional Guide

Understanding Flange Face Types in Industrial Piping

In high-pressure piping systems, the flange connection is the primary point of potential failure. Choosing the wrong combination of flange faces and gaskets can lead to catastrophic leaks, environmental hazards, and costly shutdowns. To ensure a leak-proof seal, a pipefitter must understand the different flange face types and their mechanical purpose. This guide covers the three most common faces: Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ), and how to select the appropriate gasket for each.

Featured Snippet: Quick Flange Face & Gasket Match

Use this quick reference table to ensure you are using the correct gasket for your flange configuration:

Flange Face Type	Common Gasket Type	Pressure Rating Style
Raised Face (RF)	Spiral Wound or Ring Gasket	Class 150 to Class 2500
Flat Face (FF)	Full Face Red Rubber/Non-Asbestos	Low Pressure (Class 150)
Ring Type Joint (RTJ)	Metal Ring Gasket (Octagonal/Oval)	High Pressure/High Temp

1. The Raised Face (RF) Flange

The Raised Face (RF) is the most common flange face used in industrial applications. It features a small area surrounding the pipe bore that is raised above the bolting circle face. This design concentrates more pressure on a smaller gasket area, increasing the sealing capability of the joint. RF flanges typically have a "serrated" finish—a series of concentric or spiral grooves that "bite" into the gasket material to prevent blowout under high pressure.

2. Flat Face (FF) and RTJ Configurations

Flat Face (FF) flanges have a surface that is in the same plane as the bolting circle face. These are typically used on cast iron equipment or low-pressure systems where the brittle nature of the material could lead to cracking if a Raised Face was used. NEVER bolt a Raised Face flange to a Flat Face flange, as the unequal pressure will likely break the cast iron component.

For extreme conditions, the Ring Type Joint (RTJ) is the gold standard. RTJ flanges have a deep groove machined into their face which accepts a solid metal ring gasket. The sealing happens as the bolts are tightened and the metal ring is compressed into the groove, creating a metal-to-metal seal that can withstand pressures exceeding 5,000 PSI.

3. Selecting the Correct Gasket

Gasket selection is as important as the flange itself. For standard RF flanges, Spiral Wound Gaskets (often called Flexitallics) are the industry standard. They consist of a V-shaped stainless steel strip wound with a filler material like graphite or teflon. For FF flanges, you must use a Full Face Gasket that covers the entire surface of the flange, including the bolt holes. Using a Ring Gasket on an FF flange is a recipe for disaster, as it causes the flange to lean inward under bolt load, potentially snapping the flange.

4. Installation Best Practices: The Star Pattern

Even with the perfect flange face type and gasket, a joint will leak if not torqued correctly. Always use a "Star Pattern" or cross-bolting sequence to ensure the gasket is compressed evenly. Start by hand-tightening all bolts, then use a torque wrench to tighten in increments (30%, 60%, 100% of target torque). For complex piping layouts that involve multiple flange connections and offsets, remember that PipeFit Pro can help you verify your spool lengths beforehand, ensuring that your flanges align perfectly before you even start the bolting process.

Conclusion

Mastering flange face types and gasket selection is fundamental to safe piping fabrication. By respecting the differences between RF, FF, and RTJ systems and following strict torquing procedures, you contribute to the overall integrity of the industrial plant. Always double-check your specs, keep your flange faces clean and free of scratches, and never compromise on gasket quality.