Eddy current nondestructive testing

Eddy current nondestructive testing

This technology provides non-contact and quick testing of metal objects. Modern devices using eddy current testing method are able to: detect and estimate the size of surface and sub-surface flaws, under specific conditions detect flaws located on the inside of the monitored object, measure the gap between the meter and monitored object, measure the thickness of the monitored object, including objects made of steel.

Operating principle

A variation of attachable transducer is shown in Picture 1. It comprises one coil in the shape of a ring or a spiral. The AC source generates alternate current in the coil, which produces primary alternating magnetic field. This field partially penetrates the monitored object for some depth and generates eddy current there. Distribution of eddy current depends on frequency of the primary alternating field, magnetic permeability of the material, its electrical resistivity and object configuration in the area where the meter is placed.

Рисунок 1. Вариант накладного вихретокового преобразователя
Picture 1. A variation of attachable transducer.

If there are any flaws in the area of eddy current flow, the course of current changes. Consequently, there is a change of the secondary field determined by eddy current. By analyzing the shape, range and phase of the eddy current secondary field, a conclusion of presence or absence of flaws is made. Apart from the flaws, the gap and the thickness of the monitored object can influence the distribution of the eddy current secondary field, that’s why the method allows not only detect flaws, but also measure the thickness of the monitored object. Our company developed a hand-held device ED1370, which allows thickness testing of the monitored object using the eddy current testing method with gap up to 15mm.

Main advantages of eddy current nondestructive testing technology

  • Non-contact testing with big working gap. For example, ED1370 thickness meter has working gap up to 15mm
  • High productivity of this method: testing speed is estimated at meters per second
  • In case of measuring the object thickness, low sensitivity to the object shape, corrosion and rust.