Relative permeability, magnetic-field variation and localized magnetic hot spots.
DRILL STRING PRODUCTS
Non-Magnetic Drill Collars
Non-magnetic components for directional drilling and measurement-sensitive bottom-hole assemblies.
StandardAPI 7-1 dimensional references where applicable · API 7-2 connection references
Size / supply rangeOD, ID, length and unit weight coordinated to the BHA · Slick and spiral configurations
Grades / materialsAustenitic non-magnetic drill-collar materials · Material route selected by strength, corrosion and magnetic requirements
Connections / optionsAPI NC and selected project connections · Stress-relief and cold-rolling options where applicable
MEASUREMENT-SENSITIVE BHA COMPONENT
Weight and stiffness with controlled magnetic interference.
Non-magnetic drill collars provide structural weight and stiffness near MWD, LWD and directional-survey instruments while reducing magnetic disturbance around the measurement package. They are produced from selected non-magnetic austenitic alloy material and precision-machined as critical bottom-hole assembly components.
OAK’s existing drill-collar portfolio identifies non-magnetic material, slick and spiral forms, and an overall published drill-collar size range of 3⅛–14 in. Each non-magnetic collar is reviewed separately for material, magnetic properties, dimensions, connection and inspection.
Weight, stiffness, bending, torque, connection loading and fatigue-sensitive features.
Concentric bore, straightness, surface finish and accurate connection geometry.
OAK SUPPLY BASIS
Typical non-magnetic drill collar specifications.
OAK’s published drill-collar information provides the base product envelope. Final non-magnetic capability is confirmed against material and magnetic-property requirements.
| Product | Non-Magnetic Drill Collar (NMDC) for directional-drilling and measurement-sensitive BHA applications |
|---|---|
| Reference standards | API Spec 7-1 for applicable drill-stem-element requirements; API Spec 7-2 for rotary-shouldered connection dimensions where specified |
| OAK published drill-collar size envelope | 3⅛ in to 14 in OD for the overall drill-collar portfolio; NMDC availability is confirmed by size and material |
| Product forms | Slick and spiral drill collars; other machined BHA configurations reviewed from drawings |
| Material family | Non-magnetic, corrosion-resistant austenitic alloy steel selected to the purchaser’s property specification |
| Outside / inside diameter | API-related or drawing-specific OD and bore, with tolerances defined by the order |
| Length | Standard or project-specific length, subject to bar availability, machining route and transport |
| Connections | API rotary-shouldered or specified proprietary geometry, subject to authorization and detailed review |
| Optional features | Spiral grooves, slip recess, stress-relief features, thread-root cold rolling and surface treatment where specified |
| Protection & marking | Connection treatment, thread protectors, serial identification and traceable export packing |
The 3⅛–14 in range is retained from OAK’s existing drill-collar information; it is not presented as unconditional availability for every non-magnetic material and connection.
MATERIAL & MAGNETIC PROPERTIES
Specify the property envelope, not only “non-magnetic.”
Different purchasers and tool systems may use different proprietary or project material specifications. The required values and test methods should therefore be stated in the enquiry.
| Property group | What should be specified | Why it matters |
|---|---|---|
| Magnetic permeability | Maximum relative permeability, measurement method and test location | Limits distortion around directional and formation-evaluation instruments |
| Magnetic-field uniformity | Allowable field variation / gradient and scanning procedure | Identifies localized magnetic anomalies along the collar |
| Strength | Minimum yield, tensile strength and elongation | Supports BHA load capacity and structural design |
| Hardness | Required range, locations and test method | Helps control material consistency and service behavior |
| Impact toughness | Temperature, specimen orientation and acceptance value | Supports low-temperature or impact-sensitive requirements |
| Corrosion resistance | Environment, H₂S / chloride conditions and any qualification test | Material suitability cannot be inferred from low permeability alone |
| Grain structure | Purchaser requirement and examination method where applicable | Supports consistent mechanical and corrosion performance |
PRODUCT CONFIGURATION
Machine the collar around its BHA function.
Configuration affects annular flow, differential sticking, handling, fatigue and compatibility with adjacent tools.
Slick
Slick NMDCFull outside-diameter body for maximum section properties within the selected geometry.
Spiral
Spiral NMDCMachined spiral grooves can improve pressure equalization and help reduce differential-sticking tendency.
Connection
Pin & BoxExact connection designation, OD, bore, bevel and stress-relief requirements are reviewed together.
Features
Handling & FatigueSlip recesses, lift arrangements, boreback, stress-relief grooves and cold rolling are order-specific.
BHA APPLICATIONS
Positioned where magnetic cleanliness matters.
The required collar length and property level depend on the survey instrument, BHA layout, inclination, local magnetic field and directional-drilling program.
MWD Assemblies
Supports measurement-while-drilling tools while limiting magnetic interference near sensors.
LWD Assemblies
Provides structural placement for logging tools and formation-evaluation packages.
Directional Surveying
Used around magnetometer-based survey systems for wellbore-position measurements.
Geosteering BHAs
Supports measurement placement and BHA stiffness in complex well trajectories.
Non-Magnetic Subs
Shorter or drawing-specific components for tool spacing and connection transition.
Special Machined Components
Non-magnetic bars or components produced to approved drawings and property requirements.
TECHNICAL REVIEW
Magnetic performance is a measured acceptance requirement.
“Non-magnetic” should never be treated as a visual material description. The material certificate, magnetic test method, scanning interval, mechanical tests and acceptance values should be agreed before manufacturing.
Material specification reviewPermeability verificationFull-length magnetic scanningMechanical-property testingConnection compatibilityDrawing-based machining review
MANUFACTURING & INSPECTION
Trace the bar, machining and magnetic result.
A complete plan follows the component from incoming non-magnetic bar through trepanning, machining, connection inspection and final magnetic verification.
01Specification, drawing and material review
02Bar identity, chemistry and incoming UT
03Trepanning, bore and outside-diameter machining
04Connection machining and stress-relief features
05Dimensions, straightness, NDT and mechanical tests
06Permeability / magnetic scan, marking and final release
Typical available documents
Material Test Certificate · Chemical and mechanical results · Incoming / final UT report · Dimensional inspection · Connection and gauge report · Magnetic permeability report · Full-length magnetic scan record when specified · Surface / NDT records · Certificate of conformity · Third-party inspection records
NMDC RFQ CHECKLIST
Send the BHA drawing and magnetic acceptance criteria.
The right starting point is the complete component and property specification, not only OD and connection.
Request an NMDC Quote- 01Outside diameter, inside diameter, length, quantity and slick / spiral form
- 02Material specification or required chemical / mechanical properties
- 03Maximum permeability and magnetic-field-gradient acceptance criteria
- 04Pin and box connections, bore, bevel and make-up requirements
- 05Slip recess, stress relief, cold rolling and other machining details
- 06NDT, dimensional, magnetic and third-party inspection documentation
PRODUCT & PROCESS VIEWS
Product views and manufacturing context.
Representative product, production and inventory views support preliminary identification. Final supply details are confirmed against the quotation.
START A CONVERSATION
Have a specification or product list?
Send it to OAK PIPE for technical and commercial review.