This standard specifies the basic requirements for the design, manufacture, inspection and acceptance of factory-made carbon steel and low alloy steel seamless and welded butt weld pipe fittings. This standard applies to steel butt welding pipe fittings with a nominal diameter of no more than DN120Omm for oil and gas transmission pipelines. This standard includes the specifications, materials, chemical composition, mechanical properties, heat treatment, manufacturing inspection and marking of butt welded pipe fittings. This standard includes standard elbows (90° elbow, 60° elbow, 45° elbow, 30° elbow), non-standard elbows, return elbows, pipe caps (heads), tees, and drawn headers , reducer joints and factory-welded extensions and transition sections. Upon agreement between the supplier and the buyer, steel pipe fittings with special sizes, shapes, and tolerances can be manufactured; when materials other than this standard are used, they should comply with the corresponding material specification requirements. When such fittings meet all other provisions of this standard, they shall be considered to be partially compliant with this standard, but they shall be appropriately marked.