Apparatus and method for detecting defects in a metallic surface by moving an eddy coil along a scan path relative to the surface

A method of detecting defects in a metallic roll mill, the method comprising:

• receiving from an eddy coil an oscillating signal induced at the eddy coil as it is moved along a scan path between first and second positions along a longitudinal length of an underlying metallic surface of the metallic roll mill;
• recording the oscillating signal received along the scan path between the first and second positions;
• outputting to a display a representation of the oscillating signal for the scan path;
• and
• moving a defect indicator along the longitudinal length of the underlying metallic surface and responsive to user selection of part of the signal representation of a circumferential defect to indicate a position on the metallic surface of the metallic roll mill from where the selected part of the signal was received.

A non-transitory computer-readable storage medium having stored thereon computer-readable code, which, when executed by computing apparatus, causes the computing apparatus to perform a method comprising:

• receiving from an eddy coil an oscillating signal induced at the eddy coil as it is moved along a scan path between first and second positions along a longitudinal length of an underlying metallic surface of a metallic roll mill;
• recording the oscillating signal received along the scan path between the first and second positions;
• outputting to a display a representation of the oscillating signal for the scan path;
• and
• moving a defect indicator along the longitudinal length of the underlying metallic surface and responsive to user selection of part of the signal representation of a circumferential defect to indicate a position on the metallic surface of the metallic roll mill from where the selected part of the signal was received.

A method of detecting and locating defects in a metallic roll mill including the acts of:

• passing a test head incorporating an eddy coil circuit along a scan path over a metallic surface of the roll mill, the eddy coil circuit inducing an oscillating signal as it is passed along the scan path between first and second positions along a longitudinal length of the metallic surface of the roll mill;
• recording the raw oscillation data received from the oscillating signal along the scan path between the first and second positions for the longitudinal length of the metallic surface under test;
• outputting a representation of the raw data on a screen display for the scan path;
• displaying a location of the test head on the screen display;
• reviewing the screen display to identify potential defects, including circumferential defects;
• and
• moving the metallic surface with respect to the test head or the test head with respect to the metallic surface along the longitudinal length, to a position where the displayed location of the test head and a circumferential defect area identified in the act of reviewing overlap on the screen display.