A primary component of drilling operations, a drill pipe is a seamless, hollow piping specially designed to withstand distortion, vibration, and bending during extractions. Tubular like these are thick-walled, enabling them to tolerate high stresses and pressures.
Drill pipes help circulate drilling fluid and transfer torque to the drilling bit during boring. Lifting the bottom hole assembly is the primary function of these components. A drill stem makes up 95% of the drill string - several pieces are often joined together in operations requiring longer lengths. To facilitate this, drill pipes have a threaded end on both sides that can be used to combine multiple stems. These thread ends are called tool joints.
Like the pipe stem/tube, manufacturers receive these joints as green tubes. From here, these items are sampled, inspected, and tested to manufacture tool joints that abide by standard specifications such as API.
Tool Joint: Important Terms to Know
Upset: Also called thread-end finish, the upset is the wall of the tool joint at its threaded connection. Depending on the product specification or client demand, drill pipes typically have an internal upset (IU), an external upset (EU), or an internal-external upset (IEU).
IU - Short for internal upset, an IU tool joint is thicker along the inside walls. This variation compensates makes up for the threading steel removed with a uniform, straight outside wall.
EU - An EU or external upset tool joint is thicker on the outside/along the outside diameter of the tubing, making up for the material removed in threading with a straight bore.
IEU - A tool joint with IEU or internal-external upset has increased thickness along the pipe's inside and outside walls, making up for the metal removed in threading.
Other important threaded ends terms (API + proprietary) include
- TPI: Threads per Inch
- REG: Regular
- FH: Full-Hole
- IF: Internal-Flush
Manufacture of Drill Pipes
Drill pipes are manufactured by welding several vital pieces together, including
- Central steel tube
- Pin tool joint
- Box tool joint
Manufacturers typically receive green tubes as the base fare directly from the steel mill. These drill stems are then worked to create the main body of the drill pipe. But, first, the tube ends are worked to enhance the cross-sectional area. This is done via upsetting of the ends - the tube end may be externally upset (EU), internally upset (IU), or internally and externally upset (IEU), depending on the order requirements.
Manufacturers also quench these tubes to increase yield strength. These pieces may also be tempered to achieve high strengths. However, the immediate step after end-upsetting is heating. The max dimensions and specifications for these steps are outlined in the API 5DP standards.
Manufacturing Tool Joints
Like the drill tube base, the tool joints also start as green tubes fresh from the steel mills. As connectors, these components are first quenched, tempered, and heat treated to increase their yield strength. Only after this step are the tool joints cut into box (female) and pin (male) threads.
Tool joints are typically stiffer than the drill tube. This quality increases the fatigue resistance of the connection, making the entire column more durable. However, tool joints using higher-strength steels are harder and, therefore, more brittle. Using such materials thus makes them more prone to cracking and stress.
Welding Tubes and Tool Joints
The final step in drill pipe manufacturing is welding together the most crucial components. For the drilling tubes and tool joints to be adequately fused, the former must first be held in place. So, manufacturers must hold the tube stationary while the tool joint is revolved at high speeds.
This process enables them to fix the joint onto the worked end of the drill stem. This may be achieved via direct drive friction welding or rotary inertia welding. The former is the more controlled method and creates a high resulting-quality weld. In fact, manufacturers using direct friction welding may not even need to make their drill pipes undergo a complete heat treatment, quenching, and temper regime.
Drill Pipe Sizing
Important standards like API generally dictate drill pipe sizes. Manufacturers use these guides to develop nominal sizes for drill pipes. Among the specifications, length and diameter requirements are among the most crucial.
The API has three distinct classifications for pipes of varying lengths that can be used when manufacturing drill pipes. These ranges are used to categorize the "single" pieces into segments of
- R1 - These are the shortest types of drill pipes, with lengths reaching a maximum of 22 feet. R1 pieces have a minimum length of 18 feet and are used in general operations, including casing and tubing.
- R2 - This range is the most commonly used category for drilling processes. The standard length for the R2 pipe is 27 to 33 feet. Most operations with wells below 15,000 feet use this type of drill pipe.
- R3 - Reaching lengths of 45 feet, R3 pipes are used to bore wells exceeding 15,000 feet in depth. The tool joints in each stand for these pipes are fewer compared to R2 pieces. Such a setup can exert more strain on the connectors, causing the drill pipe to wear faster. Drilling projects requiring such enormous lengths are mostly offshore and deep-water extractions. Additionally, R3 pipes are used in casing applications as well.
Drill Pipe Diameter
As a BHA component, the drill pipe diameter heavily depends on the borehole width. Typically, a drill piece's outer diameter (OD) ranges from 2 3/8" to 6 5/8". However, in non-nominal applications, the OD of the article should have a ratio of 0:6 to the borehole diameter. Such a design will help limit pressure loss and effectively circulate drilling fluid.