A long welding neck flange, also known as a long weld neck flange or LWN flange, is a type of flange that has a long, extended neck or hub. The hub provides reinforcement and facilitates smooth transition from the flange to the pipe.
The key features of a long welding neck flange include:

1. Long Neck: The neck of a long welding neck flange is longer compared to regular weld neck flanges. This longer neck provides added strength and reduces the stress concentration at the flange-pipe junction.

2. Smooth Transition: The long neck of the flange allows for a gradual transition from the flange to the pipe. This ensures a smooth flow of fluid and minimizes turbulence, which can be beneficial in high-pressure or high-velocity applications.

3. Welding Capability: The extended neck of the flange provides ample space for welding. It allows for stronger and more secure welds between the flange and the pipe, ensuring a leak-tight connection.

Long welding neck flanges are commonly used in high-pressure and high-temperature applications, such as in the oil and gas, petrochemical, and power generation industries. They are often used in situations where the pipe requires insulation or needs to be elevated from the ground.

It’s important to note that the dimensions and specifications of long welding neck flanges may vary depending on the standard being used, such as ASME B16.5 or API 6A. It’s recommended to consult the appropriate standards and guidelines, as well as work with qualified engineers or piping specialists, to ensure the correct selection and application of long welding neck flanges.