Eiffel 101: The Basics of Drill Pipe
Drill pipe is a hollow steel pipe that’s used to connect the surface of drilling rig equipment to the bottomhole assembly and bit. Its purpose is twofold: drill pipe both pumps drilling fluid to the bit, and it also allows the bottomhole assembly and bit to be raised, lowered and rotated. Drill pipe comes in a variety of sizes and strengths, but the pipe typically spans between 27 and 45 feet in length.
Steel Drill Pipe Manufacturing and Design
When drilling into the earth, the steel pipe must be able to transfer the drilling torque across combined lengths of pipe that often extend several miles into the earth’s crust, all while resisting the pressure and friction that comes with such deep drilling. Steel drill pipe is designed with these challenges in mind.
Drill pipe comprises of three separate elements: a box tool joint, a pin tool joint and the tube. During the manufacturing process, the ends of the tube are “upset,” which is a forging process that makes the walls at the tube’s ends thicker and increases their cross-sectional area. After the ends have been upset, the tube then goes through a heat-treating process. Drill pipe steel is commonly quenched and tempered to achieve high yield strengths, which makes it more durable and less likely to crack, dent or break.
After the steel pipe is quenched and tempered, the tool joints are cut into box (female) and pin (male) threads. All drill pipe includes these threaded ends. When the pipe is fitted to a drill, this threading creates an effective connection that allows the pipe to hold firmly to the surface of the rig equipment, even under high pressure.
Finally, the tubes and tool joints are welded together using rotary inertia. To achieve a strong weld, the tube is held stationary while the tool joint is rotated at high RPMs. The tool joint is then firmly pressed onto the upset end of the tube while the tool joint is still rotating. When they come together, the heat and force of this combination weld the two ends to each other.
The Use of Steel in Drill Pipe
Though drill pipe is sometimes made of aluminum, steel is the favored choice, mainly due to its high capacity. Steel pipe is stronger than many other types of pipe and can be made larger or thinner without compromising its durability. The strength of steel makes it a great option for drill pipe since it can withstand vibrations, shock and high pressure. Unlike other materials, steel will bend rather than break in extreme conditions, which means it’s less likely to crack or leak. It has a high torque resistance, a relatively low repair rate, better hydraulic performance, and is sustainable for use in sour environments.
Similarly, the threading of drill pipe through heat treating is a vital element of its design. The threads and joints between the tube and end pieces can be vulnerable, which is why the joints are friction welded for maximum strength and heat treated for optimum durability. Steel pipe holds up well to both friction welding and heat treatment. This ensures not only a long service life for the pipe, but also the simplification of joining and breaking, therefore cutting cycle time. In the drilling industry, this durability, reliability and simplicity is what makes steel pipe a top choice.
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