Method and arrangement for crack detection in a metallic material

摘要

It is presented a method of determining a crack depth of a crack (C) in a metallic material (M). the method comprises the steps: feeding a current with a first magnitude to a transmitter coil (3) for generating a magnetic field in the metallic material (1V1); controlling the current such that it obtains a second magnitude when the magnetic field is estimated to have penetrated deeper than a deepest crack depth desired to be measured in the metallic material (1V1); detecting the magnetic field by means of a receiver coil (5), which detected magnetic field thereby generates a signal in the receiver coil (5); determining a first characteristic value of the signal in a first time range, the first time range starting at a time: at which it has been estimated that any disturbances due to control of the current to obtain the second magnitude have ceased, and a current induced in the metallic material due to control of the current to obtain the second magnitude has penetrated deeper in the metallic material (M) than a depth corresponding to surface irregularities of the metallic material (1V1) and crack depths not desired to be measured, the first time range ending when the current induced in the metallic material (M) due to control of the current to obtain the second magnitude has penetrated to a depth in the metallic material corresponding to a deepest crack depth desired to be measured; determining a second characteristic value of the signal in a second time range after the first time range; and determining a possible presence of a crack and its crack depth based on the first characteristic value and the second characteristic value.