Drill Pipe Size: The Short Answer
Regular drill pipe is made in a family of standard outside diameters from about 2 3/8 inches to 6 5/8 inches. Within that range the sizes that appear most often in rotary drilling programmes are 2 7/8 in, 3 1/2 in, 4 in, 4 1/2 in and 5 in. The tool joint outside diameter is always larger than the pipe body, so joint dimensions, not the tube, usually govern clearance in the hole.
Common Outside Diameters and Their Uses
| Outside diameter | Typical duty |
|---|---|
| 2 3/8 in and 2 7/8 in | Workover rigs, slim-hole and shallow exploration wells |
| 3 1/2 in | Medium-depth land drilling, common in workover and water wells |
| 4 in and 4 1/2 in | General land drilling, the most widely supplied sizes |
| 5 in | Deep land and offshore drilling with high torsional load |
| 5 1/2 in and 6 5/8 in | Heavy-duty deep wells and large-hole top-hole sections |
Wall thickness and nominal weight are not free variables: for every outside diameter, API 5DP fixes a set of weight designations with matching wall thickness, so a heavier pipe of the same diameter means a thicker wall and a smaller internal bore.
Standard Lengths and API Length Ranges
Joint length matters as much as diameter, because it determines the number of connections the crew must make on every trip. API 5DP groups drill pipe joints into three length ranges: Range 1 from 18 to 20 ft, Range 2 from 27 to 30 ft and Range 3 from 38 to 45 ft. Range 2 is the volume product and suits the derrick height of most land rigs, while Range 3 is chosen offshore where fewer connections shorten trip time. The two most common joint lengths quoted in metric units are 9 m for a 30 ft joint and 14 m for a 45 ft joint. Short pup joints are produced to make up the exact string length required.
How to Select the Right Size
Selection starts from the hole size and works back through tool joint clearance, torsional and tensile capacity, hydraulic capacity at the planned mud flow rate, and pressure loss along the string. A larger bore reduces circulating pressure loss but increases weight and make-up torque requirements, so the smallest pipe that satisfies the hydraulic programme is normally the most economic choice. Grade, upset type, tool joint and thread form are then fixed together with the diameter and weight.
Ordering and Inspection Points
Drill pipe should be ordered to API 5DP with the grade, outside diameter, wall thickness, weight designation, length range, upset and tool joint details stated in full. Receiving inspection covers wall thickness, straightness, thread gauging, internal and external surface condition, hardbanding and the legible stamping that links each joint to its mill test certificate.
FAQ
Q: What is the most common drill pipe size?
The most widely used outside diameters are 4 in, 4 1/2 in and 5 in, while the full standard range extends from about 2 3/8 in to 6 5/8 in.
Q: How long is a joint of drill pipe?
A common joint is about 30 ft or 45 ft long; these lengths belong to Range 2 and Range 3 of API 5DP, with Range 2 covering 27 to 30 ft and Range 3 covering 38 to 45 ft.
Q: How thick is drill pipe?
There is no single wall thickness. For each outside diameter, API 5DP defines several weight designations, and each designation corresponds to a specific wall thickness and internal bore, so the wall must be quoted together with the size and weight.
Q: What is drill pipe used for?
Drill pipe is the hollow tubular that connects the surface rig equipment to the bottomhole assembly and bit. It transmits rotation and weight, and it also carries drilling fluid down to the bit and back up the annulus.
Q: Does the tool joint affect the size I can run?
Yes. Tool joints are upset and have a larger outside diameter than the pipe body, so the joint diameter is checked against the hole and casing clearance before a size is confirmed.
Q: Can different sizes be mixed in one string?
Mixing is possible but is normally avoided, because a change of diameter creates a stress concentration and complicates handling. Where a tapered string is necessary, the transition is engineered and documented.
