Method And Arrangement For Crack Detection In A Metallic Material

An arrangement for determining a crack depth of a crack in a metallic material, the arrangement comprising:

• a transmitter coil arranged to generate a magnetic field in the metallic material,
• a receiver coil arranged to detect the magnetic field,
• a signal generator arranged to feed a current having a first magnitude to the transmitter coil for generating the magnetic field in the metallic material,
• a control unit arranged to control the signal generator M such that the current 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, and
• a computing arrangement arranged to receive a signal created by the magnetic field detected by the receiver coil, and to determine 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 than a depth corresponding to surface irregularities of the metallic material and crack depths not desired to be measured,
• the first time range ending after the current induced in the metallic material clue 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,
• the computing arrangement being further arranged to determine a second characteristic value of the signal in a second time range after the first time range, and to determine a possible presence of a crack and its crack depth based on the first characteristic value and the second characteristic value.