Common Drill Pipe Connection

According to the threaded button type drill pipe joints, there are four types: REG(Regular style connection), IF(Internal-flush style connection), FH(Full-hole style connection); NC(Numbered Connection).

The drill pipe joint is a component of the drill pipe, divided into a male joint and a female joint, which are connected to the two ends of the drill pipe body. In order to enhance the connection strength of the joint, the wall thickness of the pipe body needs to be increased at the joint. According to the method of thickening, it can be divided into three forms: internal thickening, external thickening, and internal and external thickening.

NC is a new series, gradually replacing all IF in the API standard and all FH connectors except 5 1/2" FH. There are several interchangeable with old API connectors, mainly NC50-2 3/8"IF, NC38-3 1/2"IF, NC40-4"FH, NC46-4"IF, NC50-4 1/2"IF.

REG(Regular Style Connection)

This type of drill pipe joint thread was used to connect the inner upset drill pipe so that drill pipe diameter is smaller than the inner diameter of the thickened and the inner diameter of the thickened is smaller than the diameter of the inner tube diameter. The main purpose of API design regular style connection is applied to the bit connection. Since the drill bit is located in the end of drill string, the stress concentration phenomenon of thread is not relevant, so API retained their all specifications.

IF(Internal-flush style connection)

This type of tool joint thread connects EUE or inside and outside thickened drill pipe, forming the inner diameter of the drill pipe joints, tube inner diameter and thick pipe inner diameter is equal to the inner diameter or approximate size. All specifications are used thread V-0.065 flat top and bottom triangular tooth type, which width is 0.065 inches (1.651mm). Because of this type easily lead to stress concentration, API has gradually replaced it.

FH(Full-hole style connection)

This type of joint screw connects inside and outside thickened drill pipe, forming the inner diameter of the drill pipe joint is equal to thickened end diameter and they are smaller than the inner diameter of the pipe. Although the thread specification is not much, but it has three models named V-0.065?V-0.05 and V-0.040 so that it has been widely used in kelly, drill pipe, drill collars and drill.

NC(Numbered Connection)

For drill pipe with a minimum yield strength of 75,000 PSI or greater (high-strength), the API recommends an additional designation, known as a numbered connection, or NC. NCs are designed to connect a pin and box with matching thread designations and are largely interchangeable if the grade codes match, meaning the thread pitch is the same and if the thread types are compatible. Numbered connections range from NC10 to NC77, at various intervals with corresponding inner and outer diameters. Again, it’s a good idea to check with the tool joint manufacturer to see if the NC and thread types are compatible.

Tips: Drill pipe buckles are generally REG and IF buckles, others such as FH are not found in tool shops. According to the master’s experience, REG buckle and IF buckle are generally 5 buckles/in and 4 buckles/in respectively, but more than 41/2" even 4 buckles/in are REG buckles, that is to say, larger than 41/2" are generally REG buckles., If it is less than 4-1/2", more IF buckle types are used.

Steel pipe industry practitioners at Permanent Steel Manufacturing Co.,Ltd, knowledge enthusiasts