Common Drill Pipe Connection

Drill pipe connections are crucial components in the drilling industry, providing the means to connect individual sections of drill pipe and form a continuous drill string. Several common drill pipe connections are used in the industry, each with its unique design and features. In this article, United Steel Industry will introduce some of the commonly used drill pipe connections.

Regular Style Connection (REG):

This drill pipe joint thread is utilized to connect inner upset drill pipes, resulting in a smaller outer diameter than the inner diameter of the thickened section, and the inner diameter of the thickened section being smaller than the inner tube diameter. The primary application of the API-designed regular style connection is for bit connections. As the drill bit is situated at the end of the drill string, stress concentration phenomena in the threads are not critical. Hence, API has maintained all specifications for this connection.

Internal-Flush Style Connection (IF):

This type of tool joint thread connects External Upset End (EUE) or inside and outside thickened drill pipes, forming a drill pipe joint with an inner diameter and tube inner diameter equal to or approximately the same size as the thickened pipe inner diameter. All specifications utilize the V-0.065 flat top and bottom triangular tooth type thread, with a width of 0.065 inches (1.651mm). Due to the potential for stress concentration, API has gradually phased out this type of connection.

Full-Hole Style Connection (FH):

This joint screw connects inside and outside thickened drill pipes, creating a drill pipe joint with an inner diameter equal to the thickened end diameter, both of which are smaller than the inner diameter of the pipe. Although there are not many thread specifications, three models named V-0.065, V-0.05, and V-0.040 are available, making it widely used in kellys, drill pipes, drill collars, and drills.

Numbered Connection (NC):

For drill pipes with a minimum yield strength of 75,000 PSI or greater (high-strength), the API recommends the use of a numbered connection, or NC. These connections are designed to link pins and boxes with matching thread designations and are largely interchangeable if the grade codes match, ensuring the same thread pitch and compatibility of thread types. Numbered connections range from NC10 to NC77, featuring various intervals with corresponding inner and outer diameters. As always, it is advisable to confirm compatibility with the tool joint manufacturer regarding NC and thread types.