Drill Collars

Improve your drill string design with Grant Prideco drill collars.


Designed to place weight on the drill bit and pump drilling fluids, our drill collars are integral heavy-wall joints manufactured from a solid bar of modified alloy steel. The solid bars are quenched and tempered to obtain the required mechanical properties and then trepanned, drifted, and threaded. Our drill collars are furnished as slick or spiraled; spiraled drill collars have grooves machined in the outside surface that promote the even flow of drilling fluid around the drill collar diameter, equalizing pressure and reducing the occurrence of differential sticking.

Drill collar materials

Grant Prideco™ drill collars are manufactured from AISI 4145H modified steel and supplied in the as-rolled surface finish condition (alternative surface finishes can be provided). Drill collars are trepanned and drifted to API Spec. 7-1. Full-length heat-treatment processes ensure mechanical properties meet or exceed API Spec. 7-1 requirements. A hardness range of 285-341 Brinell hardness and Charpy “V” notch minimum impact strength of 40 ft-lb at 70 °F are guaranteed 1 in. below the surface. 

Drill collar material and process traceability are maintained from receipt of mill-certified raw material to completion of all manufacturing. Serial numbers are die-stamped on drill collar bodies.

We inspect all our drill collars to comply with API standards and Grant Prideco specifications. These inspections include visual dimensional checks as well as ultrasonic inspections over the entire length of the drill collar.

Drill collar connection features

  • API connections – All API connections (regular, NC, H90, and PAC) comply with dimensional requirements specified in API Spec. 7-2 and guidelines presented in API RP7G. Other connections are available to meet specific needs.
  • Phosphate coating – All connections are phosphate-coated to improve resistance to galling.
  • Stress relief features – API pin stress relief groove and API box boreback decrease the frequency of fatigue failures. These features increase connection flexibility and reduce high-stress concentrations that normally occur adjacent to the end of engaged threads. Stress-relief features are machined in compliance with API Spec. 7-2.
  • Cold rolling – Drill collar thread roots are cold-rolled. Cold rolling creates a compressive stress condition that increases fatigue life by minimizing crack initiation.

Slip and elevator recesses

We offer optional slip and elevator recesses to improve handling efficiency and safety. The upper radius of the elevator recess is cold-rolled to increase product fatigue life. Slip and elevator recesses can be used together or separately. Unless otherwise specified, slip and elevator recesses are machined in compliance with API Spec. 7-1.


Drill Collars Specifications

Drill Collar Material Mechanical Properties
Drill Collar Diameter (in.) Minimum Yield Strength (psi) Minimum Tensile Strength (psi) Minimum Hardness (BHN)
3⅛ through 6⅞ 110,000 140,000 285
7 and above 100,000 135,000 285

Tensile properties are determined by tests on cylindrical specimens conforming to the requirements of the current ASTM A370, 0.2% offset method. Hardness tests are performed on the OD of drill collars in compliance with current ASTM standards.

Slip and Elevator Recess Dimensions
Drill Collar Diameter (in.) Elevator Recess Diameter (in.) Slip Recess Diameter (in.) Elevator Recess Radius (in.)
4⅛ 311/16
5 4⅝
6 5⅜
5⅞ 6
6 3/16
7 3/16
7 3/16
8 3/16
9 8⅛ ¼
8⅝ 9 ¼
8⅞ ¼
10 9⅛ ¼  
11 10⅛ 10½ ¼
Grant Prideco drill collars overhead view

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