AN EDDY-CURRENT ARRAY INSTRUMENT FOR APPLICATION ON FERRITIC WELDS

This paper describes a multi-element, eddy current array for the local testing of ferritic specimens including welds. A novel transient meth od is used to extract coil impedance parameters, and has the advantage of fast measurement, digital compatibility and a minimum of front-end components; a useful feature when large element numbers are involved. The problem of displaying lift-off and flaw information from an array is solved by using a novel 'volcano display', which provides a simple two-dimensional image of conditions under the array. However, to prod uce this display, the burden of interpreting the coil element response s must be left to the instrument. The resident analysis software conta ins a number of operating modes which provide options for single eleme nt and multi-element operation. The array has been applied to the dete ction of cracks in the HAZ of a weld, where the large surface area of the probe permits a coarser scanning pattern to be used whilst providi ng a high probability of detection due to the number of elements deplo yed.