Raised Face vs Flat Face Flange: RF and FF Flange Selection Guide

Choosing between a raised face flange and a flat face flange is not just a catalog detail. The flange face controls where the gasket is compressed, how bolt load is distributed and how well the joint can resist leakage. For buyers and engineers, the question of raised face vs flat face should be answered before ordering flanges, gaskets or mating valves.

This guide explains raised flange vs flat face selection in practical terms, including RF flanges, flat face flanges, gasket style, pressure service, material compatibility and common installation mistakes.

What Does Flange Face Mean?

The flange face is the sealing surface where the gasket sits. A small difference in the face profile can change the gasket contact area and bolt load behavior. In industrial piping, the two common options are raised face flanges and flat face flanges.

When a purchase order says flange flat, flange flat face or flat faced flange, it should be clarified as flat face rather than raised face. Ambiguous wording can lead to the wrong gasket, wrong mating flange and leakage during commissioning.

What Is a Raised Face Flange?

A raised face flange, also called an RF flange, has a raised sealing area around the bore. The gasket sits on this raised ring instead of covering the whole flange face. Because the gasket contact area is smaller, the bolt load is concentrated more directly on the sealing surface.

RF flanges are widely used in oil and gas, petrochemical, power generation, steam, compressed air, process piping and other metallic piping systems. They are commonly paired with spiral wound gaskets, non-asbestos gaskets, PTFE gaskets or metallic gasket styles depending on pressure, temperature and fluid.

What Is a Flat Face Flange?

A flat face flange has a full flat sealing surface from the bore area to the outside face. A full-face gasket is normally used so bolt load spreads across a larger area. This helps protect brittle or softer mating components from high localized stress.

Flat face flanges are often used with cast iron valves, ductile iron fittings, plastic-lined systems, low-pressure water lines, HVAC, pump connections and utility piping. A flat faced flange is also common where the project specification requires full-face gasket support.

Raised Face Flange vs Flat Face Flange

The comparison of raised face flange vs flat face flange comes down to sealing load, mating material and operating condition. A raised face design gives stronger gasket compression in a smaller area. A flat face design spreads the load and reduces the risk of cracking a weaker mating flange.

Item	Raised Face Flange	Flat Face Flange
Face profile	Raised sealing ring around bore	Entire face is flat
Common name	RF flange, raised face	FF flange, flat face
Gasket style	Ring gasket or spiral wound gasket	Full-face gasket
Load behavior	Concentrated gasket compression	Wider load distribution
Typical service	Metallic piping, higher pressure and temperature	Lower pressure, cast iron, plastic or utility systems
Main risk	Wrong gasket or over-compression	Insufficient sealing load in demanding service

Flat Face Flange vs Raised Face: Which Is Better?

There is no single winner in flat face flange vs raised face selection. The better choice depends on the mating equipment and service condition. For carbon steel or stainless steel process lines, a raised face flange is usually preferred because it delivers reliable gasket compression. For cast iron valves or plastic components, a flat face flange is often safer because it spreads bolt load evenly.

If the system is low pressure water, drainage, HVAC or non-critical utility service, flat face flange vs raised face flange selection may favor a flat face design. If the line is steam, chemical, hydrocarbon, high temperature or pressure-sensitive service, raised face flange vs flat face comparison often favors RF flanges.

Can Raised Face and Flat Face Flanges Be Mated?

Mixing RF and FF flanges requires engineering review. Bolting a raised face flange directly against a flat face flange can concentrate stress on the flat face side, especially if the flat face component is cast iron, ductile iron, bronze, plastic or another material that can crack under uneven load.

In some field situations, an engineer may approve special gasket arrangements or machining the raised face off the RF flange. But this should not be treated as a casual site decision. The gasket, bolt torque, pressure rating and material strength must all be checked before installation.

Gasket Selection for RF and FF Flanges

For raised face flanges, the gasket usually fits inside the bolt circle and sits on the raised sealing surface. Spiral wound gaskets are common in demanding service, while compressed fiber, PTFE and graphite gaskets are selected based on fluid and temperature.

For flat face flanges, a full-face gasket with bolt holes is usually used. This gasket supports the entire face area and helps distribute load evenly. Using a narrow ring gasket on a flat face flange can reduce support and may create sealing or cracking problems.

Ordering Checklist Before Purchasing

Before ordering, confirm the standard, pressure class, material, nominal size, bore, face type, gasket material and mating equipment. Do not rely only on short wording such as flange flat or RF. Ask for the drawing, face finish and gasket recommendation when the service is critical.

• Confirm whether the required face is raised face or flat face.
• Check whether the mating valve, pump or fitting is cast iron, steel, stainless steel or plastic.
• Match gasket style to the face type and service condition.
• Use approved bolt torque values and tightening sequence.
• Do not mix raised face and flat face flanges without engineering approval.

FAQ About Raised Face and Flat Face Flanges

What is the difference between raised face vs flat face flange?

A raised face flange has a raised gasket seating area around the bore. A flat face flange has one continuous flat sealing surface and normally uses a full-face gasket.

When should I choose flat face vs raised face flange?

Choose flat face for low-pressure systems and cast iron or softer mating components. Choose raised face for metallic piping where stronger gasket compression and higher service capability are required.

Are RF flanges the same as raised face flanges?

Yes. RF flanges are raised face flanges. The term RF simply abbreviates the raised face sealing design.

Need Raised Face or Flat Face Flanges?

Songhai Flange supplies raised face flanges, flat face flanges and custom flange products for industrial piping, chemical equipment, marine projects, water treatment, pressure vessels and OEM systems. If you need help selecting raised face flange vs flat face flange products, our team can support material selection, machining, gasket matching and export packing.