Monitoring of crack length growth on welded specimens by applying square wave inductive thermography

The crack growth monitoring is an important task for the maintenance policies of steel structures subjected to cyclic loading, such as bridges, cranes, off shore facilities and wind energy towers. A reliable crack detection method allows to survey properly the crack initiation and growth in responsive details of these structures, so that, they can be repaired or restored in time in order to avoid services interruption, accidents or structural collapses. In this paper, a crack detection system, which is based on inductive thermography is applied to survey the crack growth on a SM490 steel welded specimen subjected to cyclic loading. The required thermal excitation of this system is based on the generation of eddy currents, which cause a temperature increase on the crack tips. This temperature rise can be observed and recorded by using an infrared camera. Afterwards, the crack tip and growth are established by analysing the infrared (IR) images. The mentioned system allows to detect cracks on steel structures in real time and in situ, characteristics that represent the efficiency and the potential of this method in the field of NDT.