Weld neck flanges are non-deformable, provide excellent sealing, and are widely used. They meet the requirements for both rigidity and elasticity, featuring a reasonable transition from weld thinning. The weld joint is far from the mating surface, protecting it from deformation due to welding temperatures. They adopt a more complex trumpet-shaped structure, suitable for pipelines subject to significant fluctuations in pressure or temperature, as well as for high-temperature, high-pressure, and low-temperature pipelines. Typically used for pipe connections and valves with PN ratings over 2.5 MPa; also used in pipelines transporting expensive, flammable, and explosive media.