Oil drill pipe connections are a critical part of the drill pipe, consisting of a pin and box connection at either end of the drill pipe body. To enhance the connection strength, the wall thickness of the pipe is usually increased at the connection area. Based on the way the wall thickness is increased, connections can be categorized into three types: internal upset (IU), external upset (EU), and internal-external upset (IEU).
Depending on the type of thread, drill pipe connections are divided into the following four main types: Internal Flush (IF), Full Hole (FH), Regular (REG), and Numbered Connection (NC).
1. Internal Flush (IF) Connection
IF connections are primarily used for EU and IEU drill pipes. In this type, the inside diameter of the thickened section of the pipe is equal to the inside diameter of the connection, which is also equal to the inside diameter of the pipe body. Due to relatively lower strength, IF connections have limited common applications. Typical dimensions include a box thread inner diameter of 211 (NC26 2 3/8″), with the pin thread tapering from the smaller end to the larger end. The advantage of the IF connection is its lower flow resistance for drilling fluids, but due to its larger outer diameter, it tends to wear out more easily in practical use.
2. Full Hole (FH) Connection
FH connections are mainly used for IU and IEU drill pipes. In this type, the inside diameter of the thickened section equals the inside diameter of the connection but is smaller than the inside diameter of the pipe body. Like the IF connection, the pin thread of the FH connection tapers from the smaller to the larger end. The box thread has an inner diameter of 221 (2 7/8″). The main characteristic of the FH connection is the difference in internal diameters, which results in higher flow resistance for drilling fluids. However, its smaller outer diameter makes it less prone to wear compared to REG connections.
3. Regular (REG) Connection
REG connections are mainly used for IU drill pipes. In this type, the inside diameter of the thickened section is smaller than the inside diameter of the connection, which in turn is smaller than the inside diameter of the pipe body. The box thread’s inner diameter is 231 (2 3/8″). Among the traditional connection types, REG connections have the highest flow resistance for drilling fluids but the smallest outer diameter. This provides greater strength, making it well-suited for drill pipes, drill bits, and fishing tools.
4. Numbered Connection (NC)
NC connections are a newer series that gradually replace most IF and some FH connections from the API standards. NC connections are also referred to as the National Standard coarse-thread series in the United States, featuring V-type threads. Some NC connections can be interchangeable with older API connections, including NC50-2 3/8″ IF, NC38-3 1/2″ IF, NC40-4″ FH, NC46-4″ IF, and NC50-4 1/2″ IF. The key feature of NC connections is that they retain the pitch diameter, taper, thread pitch, and thread length of older API connections, making them widely compatible.
As a crucial part of drill pipes, drill pipe connections vary significantly in terms of strength, wear resistance, and fluid flow resistance, depending on their thread type and wall-thickness reinforcement method. IF, FH, REG, and NC connections each have unique characteristics and are suited to different working conditions. With advancements in technology, NC connections are gradually replacing older standards due to their superior performance, becoming the mainstream choice in modern oil drilling operations.
Post time: Aug-22-2024
