Weld neck flanges are resistant to deformation, provide a good seal, and are widely used. They meet the requirements for both rigidity and elasticity, featuring a reasonable weld thinning transition. The weld joint is spaced far from the mating surface, preventing 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. Generally used for pipe and valve connections with PN over 2.5 MPa; also used in pipelines transporting expensive, flammable, and explosive media.