A circulating joint is a specialized joint used to connect the drill pipe with the casing during or after casing operation, and to circulate drilling fluid. According to needs, it can be divided into drill pipe thread circulation joints, casing thread circulation joints, and union thread circulation joints. The upper part of the casing circulation joint is the thread of the drill pipe joint, which is used to connect the drill pipe or connect the pipeline with a union joint. The lower part is processed with API casing partial trapezoidal thread (or API casing long round buckle/short round buckle) to connect the casing coupling.