A standard 10-inch flange requires 12 or 16 bolts depending on the pressure rating.

A 10-inch nominal pipe size flange most commonly uses 12 bolts for Class 150 ratings and 16 bolts for Class 300 through Class 900 ratings. These bolt counts are standardized to ensure uniform pressure distribution across the gasket surface, preventing leaks and maintaining structural integrity in industrial piping applications.

Bolt Configuration by Pressure Rating

The number of bolts in a flange is not determined by diameter alone, but by the pressure class assigned to the component. Higher pressure environments require more or larger fasteners to maintain a tight seal. For a 10-inch flange, the following configurations are standard:

• Class 150: 12 bolts with a 7/8-inch diameter.
• Class 300: 16 bolts with a 1-inch diameter.
• Class 600: 16 bolts with a 1-1/4-inch diameter.
• Class 900: 16 bolts with a 1-3/8-inch diameter.

Comparison of Flange Specifications

Installation and Tightening Procedures

To ensure the flange remains leak-free, technicians must follow a strict installation protocol. Using the correct number of bolts is only the first step in creating a secure connection during assembly.

1. Cleaning: Remove all debris and rust from the flange faces and bolt holes.
2. Alignment: Ensure the flange faces are parallel and the bolt holes line up correctly before inserting fasteners.
3. Lubrication: Apply industrial-grade lubricant to the threads and nut bearing surfaces to ensure accurate torque.
4. Sequence: Tighten bolts in a "star" or "criss-cross" pattern to apply even pressure across the gasket.
5. Torque: Use a calibrated torque wrench to reach the final specified tension in at least three incremental stages.

Always verify the specific engineering requirements for your piping system, as material type and temperature can influence the final torque values needed for these specific fasteners.