Non-Magnetic Drill Collars and Downhole Tools for Coal Drilling | API Spec 7-1
Non-magnetic tools for coal drilling are precision drill string components used to house Directional Drilling and MWD (Measurement While Drilling) instruments. They are made from premium austenitic stainless steel or copper-free alloy bars. These tools isolate sensitive sensors from the magnetic interference of the steel drill string. Each part goes through radial cold working and strict testing to ensure relative magnetic permeability under 1.010 and high mechanical strength for harsh underground conditions.
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Product Types
Non-Magnetic Drill Collars (NMDC): Solid bored tubular bars used as housing units for directional survey equipment.
Non-Magnetic Stabilizers: Integral-blade and welded-blade tools that provide directional control while keeping magnetic isolation.
Non-Magnetic Heavy Weight Drill Pipe (HWDP): Transitional components that offer flexibility and weight-on-bit control between drill collars and drill pipes.
Non-Magnetic Crossover Subs (X-Over): Specialized connection subs that bridge different API thread sizes without causing magnetic distortion.
Applications in Coal and Directional Drilling
Underground Gas Drainage Boreholes:
Guiding long horizontal holes along coal seams to relieve methane pressure before mining.
Directional Exploration Drilling:
Mapping geological structures and fault lines ahead of underground mining faces.
MWD/LWD Tool Housing:
Protecting downhole electronic tools from shock, vibration, and magnetic interference.
Geothermal and Trenchless Boring:
Providing non-magnetic sensor housing for utility installation and shallow directional bores.
Material and Technical Specifications
|
Property |
Specification |
|
Material Grades |
Low-Carbon Austenitic Stainless Steel (P550 equivalent); Copper-Beryllium (CuBe) for special low-magnetic applications |
|
Relative Magnetic Permeability |
Maximum 1.010, tested and certified according to MIL-STD-281 and ASTM A342 |
|
Yield Strength |
Minimum 100–140 ksi (689–965 MPa), depending on diameter |
|
Tensile Strength |
Minimum 110–150 ksi (758–1034 MPa) |
|
Hardness |
284–341 HBW (Brinell Hardness) |
|
Available Outer Diameter (OD) |
73–203 mm (2-7/8–8.0 inch), designed for coal mine drilling rigs |
Drill Pipe, Joint and Stabilizer Configuration
Thread Connections:
API Regular, API IF (Internal Flush), API FH (Full Hole), and custom rotary shoulders with cold-rolled root threads.
Stress Relief Features:
Pin stress relief grooves and box bore back-relief features standard on all connections to reduce bending fatigue stress.
Hardbanding:
Optional tungsten carbide chip hardbanding applied to stabilizer blades and collar ODs to resist wear in abrasive sandstone and coal-measure strata.
Bore Finish:
Gun-drilled and honed inner diameters with a surface finish under 1.6 um to prevent fluid turbulence and wireline catching.
Manufacturing and Processing
Forging and Radial Hot Rolling:
Raw alloy billets undergo heavy rotary forging to refine grain structure and remove internal micro-porosity.
Cold Working (Hammer Peening / Stretch Forging):
Specialized cold-working processes add uniform mechanical strength and deep hardness across the whole cross-section.
Deep-Hole Gun Drilling:
Precision boring using multi-axis CNC gun-drilling machines to keep concentricity and wall thickness tolerances within 0.5 mm over full-length bars.
Thread Machining:
CNC lathe threading done with single-point carbide inserts, followed by thread gauging and optical profile checks.
Quality Inspection
Magnetic Permeability Testing:
100% testing of each bar and finished part using a Förster fluxgate magnetometer (Hot Spot Test) to verify permeability under 1.010 along the full length and end faces.
Non-Destructive Testing (NDT):
Full-length ultrasonic (UT) testing for internal flaws and wet fluorescent magnetic particle inspection (MPI) on all finished thread roots.
Mechanical Property Tests:
Tensile testing, Charpy V-notch impact testing, and Brinell hardness testing done on test pieces from representative production lots.
Dimensional and Thread Metrology:
3-axis CMM and API certified thread ring and plug gauges to check pitch diameter, lead, taper, and standoff.
Custom Sizes and Connections
OEM and ODM Engineering:
Custom outer diameters, inner diameters, and overall lengths engineered to match specialized underground coal drill rigs (such as Atlas Copco, Zefang, or custom hydraulic rigs).
Specialized Connections:
Non-standard metric threads, high-torque connections, and lifting recess designs machined to client technical drawings.
Surface Treatments:
Phosphate coating, zinc-nickel plating, or anti-corrosion thread compound application for extended shelf life in humid underground environments.
How to Choose the Right Coal Drilling Tool
Match Rig Specifications:
Check the spindle torque, pullback capacity, and mast clearance of your underground drilling rig to pick the correct OD and length.
Verify MWD Sensor Requirements:
Check the magnetic clearance needs of your directional survey tools to find the required length of the non-magnetic collar.
Select Connection Types:
Choose standard API connections that match your current drill string inventory to avoid needing extra crossover subs.
Evaluate Formation Abrasiveness:
Choose tungsten carbide hardbanding on stabilizer blades if drilling through abrasive sandstone layers within the coal measure strata.
FAQ
As one of the most professional non-magnetic tools for oil manufacturers and suppliers in China, we also support customized service. With abundant experience, we warmly welcome you to buy high quality non-magnetic tools for oil for sale here from our factory. Contact us for more details.
Drill String Stabilizer, Non Magnetic Drill Collar Material, Stabilizers in Drilling
