Implementing API-5CT standard seamless pipe and API-5DP drill pipe are the pipes that connect the drilling motor and the drill bit during the drilling process. The outer diameter is generally 2-6.5 inches (50-165mm), and the length is generally between 5-14m. Casing serves as the structural wall or lining of an oil/gas well to protect the well or surrounding groundwater from contamination, and can be up to 26 inches in diameter. Casing accounts for more than 3/4 of the shipments of special oil pipes.