Guide to Flange Face Finish Types

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As a necessary component in various industries, flanges connect pipes, valves, and other equipment. The efficiency and reliability of these connections heavily depend on the surface finish of the flange face. This Guide to Flange Face Finish Types will explore the four standard flange face finish types as determined by the American Society of Mechanical Engineers (ASME) and America Water Works Association (AWWA):

Stock finish
Smooth finish
Spiral Serrated Flange Face Finish
Concentric Serrated Flange Face Finish

Understanding these surface finish types will aid engineers, manufacturers, and maintenance personnel in selecting the most appropriate flange face finish for their specific applications. It is important to note that different industry standards have unique tolerances and surface finishes. Also, any finish that isn’t machined is considered a mill finish, e.g., laser or plasma finish.

Average Surface Roughness Chart

1. Stock Finish (AWWA C207 & C228 / ASME B16.5)

The stock finish is the most basic and rough flange face finish type. It is the surface condition that flanges typically have when they are delivered from the manufacturing process. The stock radius finish is the most common surface because it’s easy to manufacture and suitable for various applications. AWWA standard tolerances support 24-55 grooves per inch and have an average roughness of 250/500Ra. ASME standard tolerances support 30-55 grooves per inch and an average roughness of 125/500Ra.

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Surface Roughness Conversion Chart

2. Smooth Finish

The smooth finish involves refining the flange face to create a smoother surface than the stock finish. This finish aims to improve the sealing performance and reduce the risk of leakage. It is achieved by using machining or grinding techniques to reduce surface roughness, making it suitable for various applications that require a reliable seal- dependent on gasket material, design, service conditions, and bolting procedure. These typically have an average roughness of 63Ra.

3. Spiral Serrated Flange Face Finish (Phonographic)

The Spiral Serrated Flange Face Finish is designed to improve the sealing performance significantly, making it suitable for high-pressure and high-temperature applications. This finish features a continuous spiral groove pattern cut into the flange face. The spiral serrations enhance the contact area between the flange and the gasket, providing a tight and reliable seal under demanding conditions.

Spiral Flange Face Finish

4. Concentric Serrated Flange Face Finish

Like the spiral serrated finish, the Concentric Serrated Flange Face Finish is intended for high-pressure applications, particularly those involving raised-face flanges. This finish type features a series of concentric grooves machined into the flange face. The concentric serrations ensure even distribution of the compressive force, leading to improved gasket seating and reduced chances of leaks.

Concentric Flange Face Finish

The appropriate flange face finish type ensures a reliable and leak-free connection in various industrial applications. The ASME standard surface finish types offer different levels of sealing efficiency to suit specific requirements. Engineers and manufacturers must consider factors such as pressure, temperature, and the nature of the fluid or gas being transported when choosing the optimal flange face finish for a given application. By doing so, they can maximize the performance and lifespan of the flange connections, promoting safe and efficient operations in their respective industries. If you can’t find the exact flange to suit your project, we can create custom solutions in our Custom Machine Shop.

API International’s experienced sales and engineering staff can answer your questions regarding flange face finish types or applications. Contact us and get connected with a dedicated account manager today!