Eddy Current
Eddy Current is a non-destructive testing technique used for the inspection of conductive materials without the need to remove non-conductive coatings. An alternating current is passed through a coil in order to create an alternating magnetic field which is used to induce a localised current (eddy current) into the material under test.
Discontinuities such as fatigue cracks will interrupt the flow of eddy currents and alter the terminal impedance of the test coil. The amplitude and phase of the received signal can be interpreted to ascertain the severity and exact location of any discontinuities found. Eddy current is routinely used to inspect a wide range of different materials and components across several fields of engineering including oil and gas, nuclear, rail, marine, manufacturing, power generation and aerospace.
Eddy current testing is based on the physics phenomenon of electromagnetic induction. In an eddy current probe, an alternating current flows through a wire coil and generates an oscillating magnetic field. If the probe and its magnetic field are brought close to a conductive material like a metal test piece, a circular flow of electrons known as an eddy current will begin to move through the metal like swirling water in a stream. That eddy current flowing through the metal will in turn generate its own magnetic field, which will interact with the coil and its field through mutual inductance.
Changes in metal thickness or defects like near-surface cracking will interrupt or alter the amplitude and pattern of the eddy current and the resulting magnetic field. This in turn affects the movement of electrons in the coil by varying the electrical impedance of the coil. The eddy current instrument plots changes in the impedance amplitude and phase angle, which can be used by a trained operator to identify changes in the test piece.
Testa can provide PCN qualified technicians to carry out eddy current testing. The benefits of eddy current include (but are not limited to) that test piece requires little pre-cleaning, the technique can detect defects through several layers of surface coatings and it is very portable.
At Testa all of our NDT technicians are qualified to industry recognised PCN (personnel certification in non-destructive testing) in accordance with BS EN ISO 9712.