Introduction

When you choose flanges for industrial pipeline, the critical reference aspect is the face of flanges are raised (RF) or flat (FF).

There is a main differences between them. Raised face flange has a raised sealing surface, which can help gather the pressure of gasket to achieve better sealing. Flat faced flange has a flat surface, which is suitable for low pressure industries.

In this article, we can learn the differences, applications,of these two kinds of flange.

What Is a Raised Face Flange?

A raised face (RF) flange has a upper sealing face around the hole of flange. This upper face can gather the pressure in a little gasket, to create a tighter and safer seal.

Key Features of RF Flanges:

✅ Designed for higher pressure and higher temperature systems

✅ Available in ASME B16.5 pressure classes (150, 300, 600, 900, 1500, 2500)

✅ Apply to Spiral winding, circular and soft gaskets

✅ Reduces risk of leaks due to compress the gasket

Where Are RF Flanges Used?

RF flanges are always used in:

• Oil & gas pipelines
• Power factories
• Chemical processing industries
• High-temperature steamsystem

What Is a Flat Face Flange?

A flat face (FF) flange needs a full face gasket to ensure the distribution of pressure, because it has a completely flat sealing face.

Features of FF Flanges :

✅ Always used in low-pressure and low-temperature applications

✅ Prevents flange from becoming bent when connecting ductile iron and cast iron components

✅ Need bolted to firm to create sealing

✅ Can work with rubber, fiber, and soft gaskets

Where Are FF Flanges Used?

FF Flanges are always used in:

• Water systems
• Low-pressure systems
• Ductile iron piping applications
• Fire protection pipe line

Main Differences Between Raised Face and Flat Face Flanges

When to Use Raised Face vs. Flat Face Flanges

You can choose a Raised Face Flange in the conditions as below:

✅ Projects operating under high pressure and high temperature

✅ Matching smaller gaskets to achieve better compression effect

✅ spiral-wound or metal gaskets are needed in this project

You can choose a Flat Face Flange in the conditions as below:

✅ Match ductile iron or cast iron components

✅ Used in the projects which is at low pressure (below Class 150)

✅ choose full-face gaskets to evenly distributed pressure

Can You Connect a Raised Face Flange to a Flat Face Flange?

No, you can’t. it not allowed to bolted together raised face and flat face flanges directly.

• Reason:The raised face makes it hard to contact evenly, to increase the risk of gasket failure and leakage
• Solution:Use a adapter between flat face and raised face or process the raised surface into a flat surface.

Choosing the Right Gasket for RF and FF Flanges

The choice of gasket depends on the type of flange:

• RF Flanges:Cooperate with RF Flanges, spiral-wound, ring gaskets, or metal gaskets can enhance the ability of seal.
• FF Flanges:In order to distribute pressure more evenly among the subjects, you can choose full face gaskets to cover the surface.

Cost Comparison: Raised Face vs. Flat Face Flanges

Summary

How to choose the flange? That depends on the use environment, including pressure, temperature and the material compatibility.

• RF flange is more stable, better sealed, which is always used in high pressure applications.
• FF flange is morc cost effective, is more used in low pressure application or nodular cast iron connections.
• Without adapter or modification, it’s not allowed to connect RF flant with FF flange.

To ensure the safety and leak-free of the pipeline, we must know the differences between RF flange and FF flange.