Table of content
Introduction
Flanges play an important role in industrial piping systems, connecting pipe fittings, valves and other settings. Flange production and installation process also requires some flange surface treatment and other dimensions and pressure.
Flange surface treatment refers to the removal of burrs and surface texture treatment. Not doing surface treatment may affect the tightness of the gasket and the sealing of the installation. What are the surface treatment types of flanges besides the above two? Let’s take a look.
What Is a Flange Face Finish?
The surface finish of the flange refers to whether there are burrs and stripe processing patterns on the sealing surface. It determines the tightness of the flange and the gasket.
The finish is expressed in AARH (arithmetic average roughness) to express the surface roughness. Common from 125 to 500 AARH. It depends on the specific use.
Common Flange Face Finish Types
The following are the surface treatment types of various standard flanges, including ASME B16.5 and ASME B16.47
1. Stock Finish
The most widely used surface treatment method.
Surface continuous spiral groove treatment.
Roughness range: 125–250 AARH
Gaskets are compatible with rubber, PTFE and fiber, etc.
2. Spiral Serrated Finish
Surface continuous spiral groove treatment.
The serrations are more obvious than the stock surface treatment.
Roughness range: 125–250 AARH.
The sealing performance under the grip force between the gasket and the flange.
3.Concentric Serrated Finish
The shape of the surface grooves is mostly concentric circles.
Roughness range: 125–250 AARH.
Can be used with high-pressure metal gaskets.
Can ensure uniform signboard.
4.Smooth Finish
The surface texture has minimal roughness and is almost flat.
Roughness range: 63–125 AARH
Can be used with metal sealing gaskets and has a tight seal.
High torque bolts are required to ensure sealing.
5.Cold Water Finish
Mainly suitable for metal gaskets with high sealing performance.
Roughness range: 30–55 AARH
Suitable for vacuum and aerospace industries.
What Are the Three Basic Flange Face Types?
There are three main types of flange surfaces, and each type has different treatment methods.
| Flange Face Type | Description | Common Finish |
|---|---|---|
| Flat Face (FF) | Fully flat surface | Smooth, Stock |
| Raised Face (RF) | Raised area for sealing | Stock, Serrated |
| Ring-Type Joint (RTJ) | Metal-to-metal groove | Cold Water |
Flange Face Finish Roughness Chart
| Finish Type | Roughness (AARH) | Recommended Gaskets |
|---|---|---|
| Stock Finish | 125–250 AARH | Soft gaskets (rubber, fiber, PTFE) |
| Spiral Serrated | 125–250 AARH | Metallic & composite gaskets |
| Concentric Serrated | 125–250 AARH | Metal & semi-metal gaskets |
| Smooth Finish | 63–125 AARH | Metal-to-metal sealing |
| Cold Water | 30–55 AARH | High-performance metal gaskets |
How to Choose the Right Flange Face Finish
The following factors need to be considered when treating the flange surface:
(i) Pressure: Consider whether higher pressure is required. High-pressure surfaces need to be treated with serrated or RTJ surface treatment.
(ii) Temperature conditions: Smooth surface treatment is required at extreme temperatures (high or low).
(iii) Gasket type: There are soft gaskets and metal gaskets, and different types are suitable for different surface treatments.
(iv) Industry standards: Flange surface treatment is different according to different production standards.
Common Mistakes to Avoid
Improper surface treatment, such as a smooth surface treatment when a serrated surface is required.
Improper selection of gasket material, such as choosing a plastic gasket instead of a metal gasket.
Improper flange surface, that is, improper treatment of the concave and convex surfaces.
Summary
The type of surface treatment of the flange is very important, which is related to the pressure and the sealing of the gasket. The surface treatment mainly includes spiral serration, concentric serration and smooth surface treatment. So you should know which surface treatment to use in what situation. I hope this article will be helpful to you.
