This blog helps identify which materials work with the latest magnetic rollers for the 64- and 128-element WP2 models.
Not all steels respond equally to the magnetic rollers on Sonatest’s WheelProbe2 (WP2). The effectiveness of our magnetic traction depends on the ferromagnetic properties of the material being inspected.
Fig. 1 - Magnetic WP2 on a steel pipe for a circumferential scan
What Works?
Ferritic steels are ferromagnetic and ideal for magnetic coupling, making them suitable for pipelines, tanks, and other industrial assets. Other ferromagnetic materials include nickel, cobalt, and some rare-earth metals.
Fig. 2 - Wrench tooling that can attract WP2 rollers
Beware of Some Alloys
Materials that are diamagnetic or paramagnetic, like copper or aluminum, do not create a static magnetic attraction. While dynamic effects from the Lorentz force may appear when moving a magnet quickly over such materials, they do not provide the constant holding force required for WP2 operations.
Stainless Steels
Not all stainless steels are magnetic. For example:
- 304 and 316 series are generally non-magnetic
- 409, 410, 420, 430, 440 series are magnetic
If you have access to the alloy’s specification sheet, check for two key indicators:
- Iron content must be present
- The alloy must have a ferritic or martensitic crystal structure—these are responsible for the ferromagnetic behaviour
For more information, you can check out this article about magnetic vs. non magnetic stainless steel.
What About Coatings?
Yes, coatings matter. Paint, zinc, galvanization, or any added surface layer introduces a gap between the roller and base metal, reducing magnetic grip. Even a small air gap has the same weakening effect due to its low electromagnetic permeability.
The WheelProbe2 magnetic rollers are a powerful enhancement for steel inspections. Those accessories provide good contact that ensures optimal data quality.
Interested in videos about the Lorentz force by the popular Veritasium YouTube channel:
Check out the full video about our magnetic WheelProbe 2 accessory:
Video covering magnetic WP2 accessory
Please contact our Applications Team if you have any questions. You can also find more solutions on our website.
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