Non-Magnetic Drill Collar
A non-magnetic drill collar is a drill stem element machined from austenitic stainless steel with very low magnetic permeability. Installed around MWD/LWD instruments in the bottom hole assembly, it isolates directional survey sensors from magnetic interference caused by steel drill string components, allowing accurate azimuth measurement while providing weight on bit.
| OD range | 3-1/8" – 11" (79 – 279 mm) |
|---|---|
| Length | 30 ft (9.14 m) standard; others on request |
| Magnetic permeability | μr ≤ 1.010 |
| Yield strength | ≥ 110 ksi (758 MPa), size-dependent |
| Connections | API NC series, threaded per API Spec 7-2 |
| Surface options | Slick or spiral (spiral reduces differential sticking) |
| Inspection | UT, PT, dimensional & thread gauging, permeability test, MTC EN 10204 3.1 |
Materials
- · P550 austenitic stainless steel
- · P530 austenitic stainless steel
RFQ Checklist
Include this in your inquiry for a fast, accurate quote
- 01OD and ID, or the MWD/LWD tool series the collar must house
- 02Overall length and connection type (e.g. NC50 box × pin)
- 03Material grade (P550/P530) and required permeability limit
- 04Slick or spiral body
- 05Quantity and target delivery date
- 06Required certificates (API 7-1 monogram, MTC 3.1, UT report)
Where it sits in the drill string
Non-magnetic drill collars are run directly above, below, or around the directional survey instruments in the bottom hole assembly (BHA). Ordinary steel collars would distort the Earth’s magnetic field around the magnetometers; the austenitic body of a non-mag collar keeps that interference below survey tolerance so the MWD azimuth reading stays valid.
Manufacturing sequence
Forged bar → rough machining → deep-hole boring → heat treatment and cold working for strength → finish machining → API 7-2 thread cutting → permeability survey, UT and PT inspection → phosphating and marking. Every collar ships with a mill test certificate and a dimensional/inspection report.
- What material is used for non-magnetic drill collars?
- Most non-magnetic drill collars are machined from P550-class austenitic stainless steel (a chromium-manganese alloy). It combines low magnetic permeability (μr ≤ 1.010) with the yield strength and galling resistance required for rotary shouldered connections.
- What HS code applies to non-magnetic drill collars?
- Drill collars are generally classified under HS 8431.43 — parts for boring or sinking machinery. Confirm the national subheading with your customs broker; several administrations publish rulings placing drill collars and stabilizers under 8431.43.
- How is magnetic permeability verified?
- Each collar is checked with a calibrated permeability meter along the body and near the connections. Values are recorded on the inspection report; typical acceptance is μr ≤ 1.010 with hot spots individually flagged.
- Slick or spiral — which should I order?
- Slick collars are standard for vertical wells. Spiral-grooved collars reduce wall contact area by roughly 40%, lowering the risk of differential-pressure sticking in deviated or high-angle wells.