Drill pipe joints are components of drilling pipes, consisting of pin and box connections attached to both ends of the pipe body. The joints have coarse threads for connecting individual pipes. During drilling operations, the joints are frequently assembled and disassembled, and their surfaces are subjected to significant clamping forces from tongs. Therefore, the joints have thicker walls, larger outer diameters than the pipe body, and are made of higher-strength alloy steel. Domestically produced joints in China typically use 35CrMo alloy steel.
Thread ConnectionsThread Connections
Thread connections must meet three conditions: identical dimensions, matching thread types, and compatible pin and box ends. Joint dimensions vary for different drill pipe sizes, and thread types may differ even for the same pipe size. To facilitate identification and engineering applications, API has standardized joint types, resulting in the widely adopted API drill pipe connections in the petroleum industry.
Three Types API Connections
API connections have old and new standards. The old API standard was developed for early fine-thread drilling pipes and includes three types: Internal Flush (IF), Full Hole (FH), and Regular (REG).
Internal Flush joints are mainly used for externally upset drilling pipes. They feature equal internal diameters, upset area, and joint, resulting in lower drilling fluid flow resistance and improved bit hydraulic horsepower. However, their larger outer diameter is prone to wear.
Full Hole joints are suitable for internally upset drilling pipes. They have two internal diameters: the joint's internal diameter equals the upset area's diameter but is smaller than the pipe body's diameter. Drilling fluid experiences higher resistance through these joints compared to Internal Flush joints, but their outer diameter is smaller.
Regular joints are used for internally upset drilling pipes. They have the smallest internal diameter, less than the upset area's diameter. Thus, Regular-connected pipes have three different internal diameters. Drilling fluid encounters the highest resistance through these joints, but they have the smallest outer diameter and higher strength. Regular joints are commonly used for small-diameter drill pipes, left-hand drill pipes, drill bits, and fishing tools. All three joint types use V-form threads, but thread forms (expressed by the width of the thread crest flat), pitch, taper, and dimensions vary significantly.
NC Type Joints
With the rapid development of friction-welded drill pipes, fine-thread drill pipes have been gradually replaced. Due to the complexity of old API Drill pipe joint standards, the American Petroleum Institute introduced a new series of NC (Numbered Connection) type joints, also known as digital-type joints. NC type joints are denoted by the letters NC followed by two digits, such as NC50, NC26, NC31, etc.
NC (National Coarse Thread) represents the American National Standard coarse thread. The two-digit number indicates the pitch diameter of the thread at the basic plane (using the first two digits of the pitch diameter). NC threads are also V-form threads with a 0.065-inch flat crest and 0.038-inch rounded root, represented as V-0.038R, which can connect with V-0.065 type threads. All Internal Flush (IF) and Full Hole (FH) connections in the old API standard use V-0.065 type threads, so there are plans to phase out the old standard and uniformly adopt NC type joints.
NC type joints have the same pitch diameter, taper, thread pitch, and thread length as old API standard joints, allowing for interchangeability. In addition to Drill pipe joints, drill strings also include various crossover joints and protector joints. Furthermore, kelly bars, drill collars, drill bits, and other downhole tools also use threaded connections (it should be noted that the thread types of these various joints and tools conform to the Drill pipe joint standards).
Vigor will provide you with a reliable solution, Please contact us at info@vigorpetroleum.com.
