A pipe fitting welded to the end of a steel pipe to cover the pipe. Butt welding pipe cap is a pipe fitting welded to the end of the steel pipe to seal the pipe. It is also called a pipe cap, head, plug or pipe cap. The main materials include carbon steel, stainless steel and alloy steel, with specifications ranging from DN15 to DN1200, wall thickness from SCH10-SCH160, and compliance with various international and domestic standards such as ASME, DIN, JIS, GB/T . The appearance of butt welded pipe caps includes convex, conical shell, flat cover, etc. Among them, convex pipe caps are divided into hemispherical, oval, dish and spherical caps. It is fixed by welding to ensure pipeline sealing, and is widely used in petrochemical industry, nuclear power, machinery, medical equipment, shipbuilding, pipelines and other fields .