What Is API 5DP Drill Pipe?
Drill pipe is the seamless steel tubular that forms the rotating column between the drilling rig and the bit. It carries the weight of the drill string, transmits rotary torque from the top drive or rotary table, and provides the internal passage through which drilling fluid is pumped down to the bit and returns up the annulus with the cuttings. Because it works under combined tension, torsion, internal pressure and cyclic bending in the doglegs of a well, drill pipe is specified to API 5DP with a very tight control of chemistry, tolerance and straightness.
The pipe body is supplied as a plain-end seamless tube and is then fitted with tool joints by friction welding. The tube ends are upset, that is thickened, so that the wall can accept the weld to the tool joint and so that the transition from the tube to the heavy tool joint does not concentrate stress. This is why a drill pipe string is described by grade, size, wall thickness and upset style rather than by a single dimension.
Grades and Mechanical Properties
| Grade | Yield strength, minimum | Tensile strength, minimum | Typical use |
|---|---|---|---|
| E75 | 517 MPa (75,000 psi) | 689 MPa (100,000 psi) | Shallow and medium depth wells, moderate loads |
| X95 | 655 MPa (95,000 psi) | 724 MPa (105,000 psi) | Deeper wells and higher tension requirements |
| G105 | 724 MPa (105,000 psi) | 793 MPa (115,000 psi) | Standard grade for demanding directional wells |
| S135 | 931 MPa (135,000 psi) | 1,000 MPa (145,000 psi) | Deep, high angle and extended reach wells |
Chemistry is controlled to protect toughness and resistance to cracking. Phosphorus is limited to 0.020 % maximum and sulphur to 0.015 % maximum, which keeps non-metallic inclusions low and protects the fatigue life of the tube in bending. Wall thickness tolerance is held to plus or minus 10 %, and full length straightness is controlled to a maximum of 1.5 mm per metre so that the pipe rotates without excessive bending stress at the tool joint.
Dimensions, Length Ranges and Connections
| Item | Range |
|---|---|
| Outside diameter | 60.32 mm to 168.28 mm |
| Wall thickness | 6.45 mm to 12.70 mm |
| Length range R1 | Approximately 18 ft to 22 ft |
| Length range R2 | Approximately 29 ft to 31 ft |
| Length range R3 | Approximately 38 ft to 42 ft |
| Upset style | Internal upset, external upset and internal-external upset |
| Connections | NC26, NC31, NC38, NC40, NC46, NC50, 5-1/2 FH and 6-5/8 FH |
| Heavy weight drill pipe | 2-3/8 inch to 6-5/8 inch, range 2 and range 3 |
Length range is measured on the finished joint with the tool joint fitted, so the tube cut length is shorter than the run length quoted on the tally. Range 2 is the most common in land operations, while range 3 reduces the number of connections to be made up on deep wells.
Tool Joints and Upgrades
Tool joints are friction welded to the upset tube ends and machined with the connection taper and thread required by the drilling programme.
Hardbanding is applied to the box and pin shoulders when the operator needs extra resistance to casing wear.
Internal plastic coating or a corrosion resistant liner can be added for wells with corrosive fluids.
Heavy weight drill pipe has a thicker wall and a longer upset for use in the transition zone, replacing part of the drill collar string.
Inspection and Handling
Ultrasonic inspection of the tube body and ends confirms wall integrity after upsetting and welding.
Tool joint threads are gauged and the shoulder faces checked for flatness before the string is made up.
Torque is applied to the manufacturer value for the connection and recorded joint by joint.
Pipes are handled with protectors on and are racked clear of the ground to avoid mechanical damage.
Retire pipe once wear, ovality or thread damage exceeds the limits of the applied inspection standard.
FAQ
Q: Which drill pipe grade should be chosen?
Grade selection follows the maximum tension, torsion and pressure expected in the well. E75 covers moderate loads, G105 is the common choice for demanding directional wells, and S135 is used where deeper wells or extended reach profiles impose higher loads.
Q: Why is the tube end upset before welding the tool joint?
Upsetting thickens the wall at the connection, restores the section lost when the weld and thread are produced, and smooths the transition from the light tube to the heavy tool joint so that stress is not concentrated.
Q: What do length ranges R1, R2 and R3 mean?
They are API 5DP length categories for finished drill pipe. Range 1 is the shortest, range 2 is the standard field length, and range 3 is the longest and reduces the number of make-ups in deep wells.
Q: How is straightness controlled?
Finished pipe is straightened and inspected to a maximum deviation of 1.5 mm per metre over the full length, which limits the bending stress imposed as the string rotates.
Q: Can drill pipe be used for casing or tubing?
No. Drill pipe is designed for repeated make-up, rotation and bending in the drilling phase. Casing and tubing are specified separately under API 5CT for permanent completion duty.
Q: What documents accompany a shipment?
Each shipment is supplied with a mill certificate giving chemical composition, tensile and yield results, dimensional records, straightness data and the results of the non-destructive examination of the tube body and ends.
