How does EMAT – ultrasound generation work
Which physical principle is effected for EMAT
Two physical principles are responsible for the generation of ultrasound waves:
A) Lorentz force
Works in all conductive materials
Works in magnetisable materials. In magnetisable metals, the generated and received ultrasound using magnetostriction is approximately up to ten times stronger than the effect of Lorentz force, depending on the alloy
Can external and internal faults be distinguished
No, every discontinuity in the material is detected as an ultrasound echo. The position in the material (surface/inside) plays almost no role in this respect. You can distinguish between inside and surface faults through combination with an eddy current test instrument which only detects surface faults.
How well can faults be located on site
Faults can be located in the longitudinal direction to about 5 cm. No locating is possible in the radial direction.
How big is the maximum test diameter
The maximum test diameter is not physically limited. Since the detection limit for faults scales with the cross-sectional area of the test object, an effective test is possible up to approx. 15 mm rod or wire diameter.
How big is the minimum test diameter
The minimum diameter of a test object is approx. 1 mm.