Drill Collar (Slick & Spiral)
A drill collar is a thick-walled steel tube run at the bottom of the drill string to concentrate weight on the bit and keep the drill pipe in tension. Machined from AISI 4145H modified alloy steel and threaded per API Spec 7-2, drill collars are supplied in slick or spiral body styles in ODs from 3-1/8" to 11".
| OD range | 3-1/8" – 11" (79 – 279 mm) |
|---|---|
| Length | 30 / 31 ft standard |
| Body style | Slick or spiral (three-start groove) |
| Hardness | 285 – 341 HB |
| Impact toughness | ≥ 54 J (40 ft·lb) Charpy, per API 7-1 |
| Connections | API NC / REG series, stress-relief features optional |
| Optional features | Elevator/slip recesses, hardbanding, cold-rolled threads |
| Inspection | Full-length UT, MT on threads, hardness, MTC EN 10204 3.1 |
Materials
- · AISI 4145H Mod alloy steel
- · AISI 4140/4142 on request
RFQ Checklist
Include this in your inquiry for a fast, accurate quote
- 01OD × ID and length per joint
- 02Slick or spiral, elevator/slip recess requirements
- 03Connection type and stress-relief features (bore back, relief groove)
- 04Quantity and delivery schedule
- 05Hardbanding specification if required
- 06Certificates required (API monogram, MTC 3.1, UT chart)
Function in the drill string
Drill collars supply the axial load that keeps the bit cutting and hold the neutral point below the drill pipe, protecting pipe joints from compressive buckling. Wall thickness — not length — is what distinguishes a collar from heavy weight drill pipe.
Quality control
Every collar is ultrasonically tested along its full length, threads are magnetic-particle inspected and gauged per API Spec 7-2, and hardness is verified on both ends. Documentation ships as a package: mill test certificate, heat treatment record, dimensional report and thread gauge report.
- What steel grade is standard for drill collars?
- AISI 4145H modified chromium-molybdenum steel, quenched and tempered to 285–341 HB, is the industry standard. It meets the mechanical property table of API Spec 7-1 for drill stem elements.
- What is the difference between slick and spiral drill collars?
- A slick collar has a plain cylindrical body. A spiral collar has three helical grooves milled into the body, cutting wall-contact area by about 40% to reduce the chance of differential sticking — preferred in deviated wells.
- Can you supply API monogrammed drill collars?
- Yes — production follows API Spec 7-1 with threads gauged per API Spec 7-2. State the monogram requirement in your RFQ so certification documents are prepared with the shipment.
- What HS code applies to drill collars?
- HS 8431.43, parts for boring or sinking machinery, is the usual classification, consistent with published customs rulings for drill collars and stabilizers.