4.1 Eddy Current Array for Crack Detection and Sizing in Carbon Steel Welds—Eddy current array allows for a fast examination of carbon steel welds for surface-breaking cracks located on the surface closest to the sensor. However, not all ECA probe designs allow for accurate depth sizing of such discontinuities over a significant range (several millimeters, for example). To achieve proper crack depth sizing, the system shall exhibit certain characteristics, such as: 1) a lift-off signal that allows monitoring that lift-off over an adequate range of values, 2) suitable phase separation between the lift-off signal and the defect signal, 3) the capability to make use of the lift-off monitoring for crack depth determination, 4) the capability to take into account material properties variations for crack depth determination along and across the weld and, 5) a uniform sensitivity across the sensing elements of the array in order to provide an effective single-pass examination, as it is expected when using an array sensor.
4.2 Array Sensors and Single Sensing Element Sensors—Depending on the weld geometry, it may be possible to use either a sensor array or a sensor with a single sensing element. The sensor array would provide a better spatial representation of the weld and an improved probability of detection. The size of the array, as well as the size and number of individual sensing elements within the array depend on the weld geometry and other factors such as target discontinuities. When a single-sensing element sensor is used, it shall produce signals that exhibit the characteristics listed in subsection 4.1 and the maximum distance from the scan line to a target discontinuity, potentially detectable at a specified probability of detection, is typically 58201;mm.
4.3 Conformable Sensors—Examining welds that are not ground flush typically requires a conformable array sensor, minimally along one axis. A conformable sensor is key to allow the individual sensing elements to follow the profile of the weld cap, and to provide a uniform response over the region of interest during the examination when the array is oriented transverse to the weld and scanned along the length of the weld.
4.4 Crack Depth Range—The crack depth sizing range over which the array sensor can provide accurate measurement depends on the sensor geometry, such as individual sensing element size and configuration. For example, larger sensing elements may provide the ability to size deeper cracks, but offer limited detection capability for shallow cracks. Appropriate array sensor selection and operating frequency is critical to ensure adequate performance for a given application. Typical operating frequencies range between 108201;kHz and 5008201;kHz.
4.5 Coating Thickness Range—The......