API 6A Weld Neck Flanges are pipe flanges attach by welding the pipes to the neck of the flanges. This transfers stress from the flange to the pipe instead. It also reduces the stress concentration from the base of the hub. Welding neck flanges remove stress concentration and allow full working pressure and they are often used for high pressure applications. The inside diameter of the flange is designed to match the pipe's inside diameter. Weld neck pipe flanges are typically provided with a raised face, flat face, or RTJ facing.