What Drill Pipe Is and What It Does
Drill pipe is the tubular member that transmits rotary torque and axial load from the surface to the bit while providing a conduit for drilling fluid. It is made from high-strength alloy steel so that it can carry combined tension, torsion and internal pressure, and resist the abrasion of the borehole. Drill pipe is supplied in defined ranges of length so that a string can be assembled to the depth required, and both ends carry forged tool joints with tapered, shouldered threads.
Pipe Body Grades and Dimensions
| Parameter | Typical range |
|---|---|
| Product specification | API 5D |
| Common steel grades | E75, X95, G105, S135 |
| Outside diameter | 60.3 mm to 168.3 mm (2-3/8 in to 6-5/8 in) |
| Range 1 length | 6.1-7.0 m |
| Range 2 length | 8.8-9.8 m |
| Range 3 length | 12.2-13.7 m |
| End connection | Forged tool joint, friction welded |
Grade designations use the letter and number convention in which the number is the minimum yield strength in thousands of psi. E75 covers moderate loads, while G105 and S135 are chosen where greater tensile capacity is needed in deep or extended reach wells.
Upset Configurations and Tool Joints
The pipe body wall is thickened at each end by upsetting so that a tool joint can be welded on. Three configurations are used: internal upset, external upset, and internal and external upset. External upset and internal and external upset are the most common for oil drill pipe because they provide a stronger weld neck and a more favourable wear profile.
Tool joints are the forged connectors welded to the pipe body. Each joint has a male pin half and a female box half. Make-up is made on a tapered thread plus a shoulder; the shoulder faces tighten against each other to seal, while the thread carries the load. The outside diameter of the tool joint is larger than the pipe body, so the box is fitted with a hard-faced anti-wear band to limit wear against casing and borehole wall. Without that band the joint wears rapidly, which can lead to washouts, twist-offs and fishing operations.
Thread Types and Connection Matching
Internal flush (IF) - smallest internal restriction and low flow resistance, used mainly on externally upset pipe; the larger outside diameter makes it more prone to wear.
Full hole (FH) - used on internal and external upset pipe; greater flow resistance than the internal flush design but a smaller outside diameter.
Regular (REG) - used on internally upset pipe, bits and fishing tools; the smallest outside diameter and greatest strength, but the highest relative flow resistance.
Numbered connection (NC) - a standardised series that is interchangeable with several older designs at the same nominal size.
A connection will only make up correctly when three conditions are met together: the two joints are of equal nominal size, the thread form is identical, and the pin and box are a matched pair. V-type threads are used on the IF, FH and REG families, but the thread form, pitch, taper and dimensions differ between them, so mixing families is not permissible.
Inspection, Hard Banding and Handling
New drill pipe is dimensioned and inspected in accordance with API 7-1 and API 7-2 for rotary shouldered connections. Inspection covers thread gauging, magnetic particle or ultrasonic examination of the weld neck, and verification of straightness, wall thickness and drift. Hard banding is applied and dressed within specified limits so that both the rotating string and the casing are protected.
In service, pipe is inspected at planned intervals for fatigue cracks, washouts, thread wear and required tool joint recuts. Make-up torque records, rotating hours and inspection results decide when a joint is downgraded, re-cut or withdrawn from the string.
Frequently Asked Questions
Q: What material is drill pipe made from?
High-strength alloy steel, produced in grades such as E75, X95, G105 and S135 under API 5D, with a yield strength indicated by the number in the grade designation.
Q: What is the difference between drill pipe and drill collar?
Drill collars are thick-walled, stiff components placed just above the bit to provide weight on bit. Drill pipe is the long tubular string that transmits torque and rotation and carries drilling fluid down the hole.
Q: What is a tool joint?
A forged connector friction welded to each end of the pipe body, made up of a pin and a box with a tapered thread and sealing shoulder that transmits tension and torque.
Q: Why is the pipe body upset at the ends?
Upsetting increases the wall thickness locally so that the weld neck can match the tool joint strength and reduce the risk of failure in the connection zone.
Q: What is the difference between IF and FH connections?
Internal flush connections have one internal diameter and low flow resistance with a larger outside diameter, while full hole connections suit internal and external upset pipe and have a smaller outside diameter.
Q: How is drill pipe length classified?
It is supplied in Range 1, Range 2 and Range 3 lengths of roughly 6 to 7 m, 9 to 10 m and 12 to 14 m, so a string can be built to the required depth.