A weld neck flange is a type of flange that has a long tapered neck, which allows it to be welded to a pipe. This design provides a strong connection and helps to minimize stress concentrations. Weld neck flanges are commonly used in high-pressure applications and are ideal for piping systems that require a strong, leak-proof seal.

Weld neck flanges offer several advantages, including high strength and reliability under pressure, reduced stress at the joint, and the ability to handle thermal expansion. They also provide a smooth transition from the flange to the pipe, which can minimize turbulence and enhance fluid flow.

Weld neck flanges can be made from various materials, including carbon steel, stainless steel, and alloy steel. The choice of material depends on the specific application, including factors like temperature, pressure, and the type of fluid being transported.

The primary difference is in their design and application. Weld neck flanges have a long neck that is welded to the pipe, providing a stronger joint and better stress distribution. Slip-on flanges, on the other hand, simply slide over the pipe and are welded on the outer edge. This makes weld neck flanges more suitable for high-pressure applications.