Application of the magnetic leakage field method to investigate wire strands

The magnetic leakage measurement method is useful for the nondestructive investigation of the integrity of tendons used in prestressed concrete components [1, 2]. It is based on the fact that ruptures or sudden changes in the cross sections of prestressing steel can be detected by characteristic magnetic anomalies. Due to the fact that all ferromagnetic elements of the reinforcement cause magnetic signals, these anomalies have to be obtained by using a magnetization scheme adapted to the given geometrical conditions and according signal analysis. The measuring of the remanence magnetic leakage field, in combination with numerical methods, leads to the satisfactory suppression of unwanted signals from the mild reinforcement. Ruptures of prestressing steel of pretensioned concrete members can be reliably detected with good repeatability. In case of tensioning steel arranged as bundle, the detection limit becomes severely limited because the adjacent intact steels cause a considerable attenuation of the signal of a rupture. This paper shows different applications of the magnetic field leakage method for the investigation of wire strands