Pyörrevirtitutkimus

Pyörrevirtitutkimus, known in English as eddy current testing, is a non-destructive testing method used to detect surface and near-surface flaws in electrically conductive materials. This technique relies on the principle of electromagnetic induction. A primary coil, energized by an alternating current, generates a time-varying magnetic field. When this field is brought near a conductive material, it induces circulating electrical currents within the material, known as eddy currents.

These induced eddy currents create their own magnetic field, which opposes the original magnetic field. The testing instrument measures the changes in the magnetic field caused by the interaction of the primary field and the induced eddy currents. Any discontinuity or flaw in the material, such as cracks, voids, or inclusions, disrupts the flow of eddy currents. This disruption alters the impedance of the primary coil, which is then detected and displayed by the instrument.

Pyörrevirtitutkimus is particularly effective for detecting surface cracks, which are often the most critical defects. It can also identify variations in material properties, such as heat treatment or hardness, as well as measure coating thickness. The method is versatile and can be applied to a wide range of conductive materials, including ferrous and non-ferrous metals. Its advantages include speed, sensitivity to surface defects, and the ability to perform testing without requiring direct contact with the material surface. However, its depth of penetration is limited, and it is only applicable to electrically conductive materials.