Low Profile Focused Array Probes
Angle beam probes with flat transducers on convex surfaces like tubes, suffer from the fact that the sound tends to become defocused. This is especially true if the transducer’s width is relatively large compared to the bending radius of the curved surface. Therefore, GE Inspection Technologies has developed laterally focused array probes with concave curvature in elevation (CCEV) for the use with the PALM Scanner, where the focus not only countervails the defocusing effect of the surface, but even increases lateral defect resolution compared to unfocused probes.
Why laterally focused arrays for small diameter tube inspection?
Angle beam probes with flat transducers on convex surfaces like tubes, suffer from the fact, that the sound tends to become defocused because of refraction at the interface between wedge and specimen. This is especially true if the transducer’s width is relatively large compared to the bending radius of the curved surface.
One application where this scenario becomes necessary to understand is the testing of welds of thin walled boiler tubes. This tubes normally have diameters in the range of 1,5 to 3,5 inch and wall-thicknesses of only a couple of millimeter. Flaws that normally have to be characterized in these welds are also only couple of millimeters in width and thus comparable to the width of the sound-field of commonly used probes. Since -6dB drop-down is the most prevalent sizing technique flaws will always be characterized larger than they are because the operator detects the overlap of sound-field and flaw. Thus, GE Sensing & Inspection Technologies’ new low-profile phased array probe for testing small diameter tubes have concavely curved transducers to reduce the width of the sound-field in the region of flaws of typical components. With curved transducers the width of the sound-field can be reduced significantly.