ASME B16.47 Series A and Series B Flanges: Design, Strength, and Application

The ASME B16.47 standard defines two common types of large flanges: Series A and Series B. These two types of flanges have significant differences in terms of design, thickness, strength, and application.

First, Series A flanges are typically thicker and stronger than Series B flanges and can withstand higher external loads. Due to their thicker design, Series A flanges are more suitable for high-pressure and complex piping systems. They are often used in new piping projects or in applications where higher operating pressures are involved. In contrast, Series B flanges are lighter, more economical, and are ideal for maintenance or replacement of existing piping systems. Due to their thinner design, Series B flanges are better suited for environments with lower pressure requirements.

In terms of fasteners, Series B flanges require a greater number of smaller fasteners (such as bolts and nuts) and typically feature smaller bolt hole diameters. This means that after installation, the flange faces of Series B flanges are more stable, as smaller bolt hole diameters result in less movement between the flange faces. On the other hand, Series A flanges use fewer but larger fasteners, which allows them to provide better sealing performance when subjected to higher pressure.

Additionally, Series A flanges include Ring-Type Joint (RTJ) flanges in their standard, suitable for pressure classes from Class 300 to Class 900, whereas Series B flanges do not include this type. As a result, Series A flanges have a broader application range and are more suitable for high-pressure applications with stringent requirements.

Finally, due to their heavier and stronger design, Series A flanges are more expensive, and thus are typically used in new construction projects. In contrast, Series B flanges are more cost-effective, making them ideal for replacement or maintenance of older systems.

In summary, Series A flanges are better suited for high-strength, high-pressure applications, especially in new piping projects, while Series B flanges are typically used for maintenance or replacement work due to their lower cost and adaptability. If you're unsure which series is right for your project, you can choose based on the specific requirements and pressure ratings, or consult a professional flange supplier for advice.