Manufactured by non-standard flange manufacturers, non-standard flanges, also known as irregular flanges, serve as sealing and fastening components. They are widely used in large containers in aerospace, petrochemical, and other industries. Regardless of processing capabilities, due to their immense size, the overall manufacturing of non-standard flanges is impossible solely due to transportation constraints, and they must be manufactured in segments.

Typically, the odd-shaped flange is divided into several arcs for processing. First, the rough casting is forged into a square billet, then cold bent into arcs. After stress-relieving and heat treatment, the arcs are assembled into a complete circle and machined to the required shape and size on a vertical lathe. They are then transported to the construction site, where the arcs are welded together to form a complete odd-shaped flange and assembled with the pressure vessel.

Due to the difference in specific dimensions represented by the nominal diameter of the container shell and the nominal diameter of the pipe, container flanges and pipe flanges with the same nominal diameter are not interchangeable, as their sizes are also different.

Production and execution standards for non-standard flanges: National Standard, American Standard, Japanese Standard, German Standard, Italian Standard, Chemical Industry Department Standard, Mechanical Department Standard, Pressure Vessel Standard.