Drill Pipe Sizing

Drilling pipe sizes, also known as drill pipe sizes, refer to the diameter, wall thickness, and length of the pipes used in drilling operations, primarily in the oil and gas industry.  It is manufactured to withstand severe internal and external pressure, distortion, bending, and vibration as it both rotates and lifts the bottom hole assembly (BHA).  Drill pipe is threaded on each end in a section of pipe referred to as the tool joint.  It is manufactured, sampled, tested, and inspected in accordance with standard specifications such as the American Petroleum Institute (API).

Drill collars are a component of the drill string that makes up part of the BHA.  They are thicker-walled, heavier, and more rigid than drill pipes and are primarily used to weigh down the drill bit while dampening vibration and impact forces.

Drill Pipe has Two Main Functions

Torque Transmission  -  Drill pipes are designed to transfer drilling torque over long distances, often spanning several miles, from the drilling rig’s surface down to the drill bit.
Fluid Circulation  -  A drill pipe serves as a conduit for drilling fluid, also called "drilling mud," allowing it to flow down from the surface and back up the wellbore.  Drilling fluid is crucial for cooling the drill bit, carrying cuttings to the surface, and maintaining pressure in the well.

Given the substantial depths reached in drilling operations, which can extend up to nearly 15,000 feet, connecting different drill pipe sections is necessary.  This connection process typically involves welding together threaded tool joints, including the box tool joint and the pin tool joint, to create a continuous length of drill pipe.

These pipes are crucial for drilling boreholes into the earth, and they come in various sizes to suit different drilling conditions.  These dimensions and properties help to determine the drill pipe's suitability for different drilling conditions, such as the depth of the well, the type of rock formations, and the required load capacity.

Drill Pipe Inspection

Maintaining and inspecting drill pipes ensures their longevity and safe performance in drilling operations.  Regular maintenance involves cleaning, protecting against corrosion, and monitoring wear and tear.  Prior to each use, a thorough visual inspection is essential, checking for cracks, deformations, or other signs of damage.  Non-destructive testing (NDT) methods, such as magnetic particle testing (MPT) or ultrasonic testing (UT), can be employed to detect internal flaws.  Regularly inspecting the threaded connections for wear and ensuring they are properly lubricated is crucial. Additionally, monitoring the center upsets and wear pads can help prevent excessive friction and prolong the drill pipe’s lifespan.

How are Drill Pipes Measured

To determine the sizing of drill pipes, each individual joint is referred to as a "Single" and categorized further by its length, typically using a three-part API length range classification: one, two, or three.  The most common length for drill pipes is "range two,” a crucial factor when calculating drilling depth as it encompasses the entire drill string, including the drill pipe.

Common Drill Pipe Sizes

Outer Diameter (OD)  -  The most common outer diameters for drill pipes are:

• 2⅜ inches (60.3 mm)
• 2⅞ inches (73.0 mm)
• 3½ inches (88.9 mm)
• 4 inches (101.6 mm)
• 4½ inches (114.3 mm)
• 5 inches (127.0 mm)
• 5½ inches (139.7 mm)
• 6⅝ inches (168.3 mm)

Wall Thickness  -  Wall thickness varies depending on the specific grade and type of drill pipe.  The thickness is chosen based on the required strength and the conditions of the drilling environment.

Grade  -  Drill pipes come in different grades, which indicate the tensile strength of the material.  Common grades include E-75, X-95, G-105, and S-135.
Length  -  Drill pipes are typically manufactured in three standard lengths, referred to as Range 1, Range 2, and Range 3:

• Range 1 (R1)  -  18-22 feet (5.5-6.7 meters)
• Range 2 (R2)  -  27-31 feet (8.3-9.4 meters) – the most common length
• Range 3 (R3)  -  38-45 feet (11.6-13.7 meters)

Tool Joint  -  The tool joint is a thicker section at both ends of the drill pipe that connects to other drill pipes or downhole tools.  The dimensions of the tool joint can vary, but they are typically larger in diameter than the main body of the pipe.

Drill Pipe Classification

N-Class Pipe or New Pipe  -  The strongest, newest pipe available. Usually in pristine (or close to it) condition.
P-Class Pipe or Premium Pipe  -  A step-down from N-class pipe, premium pipe have endured some wear, but can still function very capably.
C-Class Pipe  -  C-class pipe, of which there are three classes (C-1, C-2, and C-3).  Depending on their rating, C-class pipes are either well-worn pipes, or nearing the end of their useful lives.

Drill Pipe Types

Drill String  -  This refers to the entire column of tools, essentially the drill pipe, shaft collar, tools, and the drill bit itself.  Generally, drill pipe used for the drill string is made from tempered steel.  For cost and transport reasons, sections of drill pipe rarely exceed ranges of 30 to 33 feet long.
Heavy-weight Drill Pipe (HWDP)  -  This pipe much stronger than regular drill pipes, because they are designed to deal with the added pressures and stresses arising from serving as transitions between drill collars and regular, thinner drill pipe.

Lifespan of a Drill Pipe