Guides / Process

How Shops Verify Non-Magnetic Tungsten Parts Before Shipping

September 21, 2026 · Reviewed September 26, 2026

A tungsten heavy alloy part specified as non-magnetic is only non-magnetic if someone actually measured it that way. The alloy choice sets the expectation, but the finished part is what has to perform near an MRI magnet, a magnetic sensor or an electron beam column. This article covers how shops actually check that, from a five-second magnet test to instrument-based permeability measurement, and what to ask for if you need it in writing. For background on what W-Ni-Cu is and when to specify it over standard W-Ni-Fe, see our guide to non-magnetic tungsten parts.

Why “should be non-magnetic” is not the same as “tested non-magnetic”

Tungsten heavy alloy in the W-Ni-Cu (tungsten-nickel-copper) system is formulated to be effectively non-magnetic, unlike the more common W-Ni-Fe system, which carries mild magnetism from its iron content. But formulation is a starting point, not a guarantee for a specific part. Two things can push a nominally non-magnetic alloy away from that behavior on an individual piece:

• Material variation. Sintering conditions, binder ratio and cooling rate affect the microstructure batch to batch. A mill’s typical permeability figure for W-Ni-Cu is a typical value, not a per-part promise.
• Processing effects. Machining, grinding, welding or even aggressive clamping can locally cold-work the surface and change its magnetic response in that spot, even when the bulk material is fine.

This is why a buyer who genuinely needs non-magnetic performance, not just a non-magnetic alloy on the drawing, should ask how the shop verifies it rather than assuming the grade selection alone covers it.

The simple check: magnet-pull testing

The most basic verification is a handheld permanent magnet brought close to the part, sometimes with a small sensitive indicator like a compass needle or a lightweight ferrous test piece to make weak attraction visible. A shop technician runs the magnet along the part surface and notes whether there is any perceptible pull.

This method is fast, needs no special equipment and catches the failure modes that matter most in production: a part accidentally made from W-Ni-Fe instead of W-Ni-Cu, a batch mix-up, or a ferrous fixture screw or pin left inside a bore. It is a reasonable baseline check on every part in a non-magnetic order.

What it cannot do is give you a number. A magnet-pull test tells you “no noticeable attraction,” which is a pass or fail judgment call made by whoever is holding the magnet. It will not reliably catch the kind of small, localized permeability increase that cold work or grinding can introduce, especially in a broad area check rather than point by point.

Instrument-based permeability testing

For a documented, repeatable result, shops use a magnetic permeability meter or susceptibility indicator that gives a numeric reading, typically expressed relative to the permeability of free space (mu, where 1.000 is perfectly non-magnetic). These handheld instruments are common in aerospace and medical device inspection, where non-magnetic material claims already have to be substantiated.

The process is straightforward:

1. Calibrate the instrument against a known reference standard before use.
2. Measure at multiple points on the part, not just one, since localized magnetism from machining stress or contamination can be missed by a single reading at the center.
3. Record the readings against a location map or reference numbers if the part has a complex geometry.
4. Compare against the specification, typically a maximum permeability value agreed with the buyer or a standard mill figure.

A permeability meter reading is what belongs on a test report if you need documented proof, not a description of a magnet-pull check. The two are not interchangeable, and a buyer who asks for “verification” without specifying which one will often get whichever is faster and cheaper for the shop to run.

Method	What it tells you	Limitation
Magnet-pull check	Pass or fail on gross magnetism	No numeric value, subjective, may miss localized spots
Permeability meter	Numeric mu value at each measured point	Needs calibrated instrument and a documented procedure

What to ask for before the parts ship

If non-magnetic performance is a hard requirement for your application, not just a preference, put the verification method in the RFQ rather than assuming it will happen by default. Useful things to specify:

• The grade, W-Ni-Cu specifically, not just “non-magnetic tungsten alloy,” since that phrase alone leaves room for interpretation.
• The test method, magnet-pull screening on every part versus instrument-based permeability reading on a sample or on 100 percent of parts.
• A maximum permeability value, if your application has a documented limit, so the shop knows what pass or fail means numerically.
• A written report, listing the instrument, the measurement points, the readings and the date, tied to your part or lot number.

Shops that regularly supply non-magnetic parts to medical imaging or sensor-adjacent industries will usually have this documentation as a standard offering. A shop that has never been asked before may need to source or borrow the instrument, which is worth knowing before you commit to a delivery date.

Where this fits in the overall order

Verification is one step in the broader quality process, not a replacement for it. Dimensional inspection, material certification and any density testing still apply the way they would to any machined tungsten heavy alloy part. Non-magnetic verification is an additional check specific to parts where field disturbance matters, and it is worth calling out separately in your RFQ and purchase order rather than folding it into a generic “inspect per standard practice” note that leaves the method up to the shop.

For the A342 methods and the report fields to ask for, see magnetic permeability tests to ASTM A342.

When you are ready to source a non-magnetic tungsten part, send your RFQ with the verification method and any permeability limit stated, and we match it with shops that can test and document it the way you need.

Frequently asked questions

Sources

• ASTM B777 - Standard Specification for Tungsten Base, High-Density Metal
• Wikipedia - Tungsten heavy alloy

Keep reading

• Thin Tungsten Plate and Foil: How Shops Machine It Without Cracks or Warp
• Grinding Tungsten Heavy Alloy: Which Wheel, What Finish, How Tight