Equivalent Sensitivity Setting During Ultrasonic Inspection of Steel Butt Welded Joints

Introduction. The echo-pulse technique is commonly used for welded joints ultrasonic testing. The first step of the technique is setting the ultrasonic flaw detector sensitivity. For this purpose NDT-operators usually use calibration blocks with a flat cylindrical or hemispherical reflectors, which are to be manufactured and metrologically certified for every weld joint size and transducer angle. The objective of this work was to develop a sensitivity setting technique using the CO-2 reference block, which could take into account the equivivalent area of the flat cilindrical reflector (as a model of a point-planar flaw) and the equivivalent area of the hemispherical reflector (as a model of a point-bulk flaw). Method. The paper analyzes methods of ultrasonic flaw detector sensitivity setting while testing of butt welded joints with the use of samples and reference reflectors of different types. The theoretical studies using beam acoustics and the Kirchhoff method, were carried out. Results. The analytical dependences for calculation of the sensitivity correction factors have been presented for the equivalent sensitivity setting on a side cylindrical reflector of 6 mm in diameter with the center line location at a depth of 15 mm within the CO-2 reference block. For automation of calculations the NDTRT-20.01 software has been developed and implemented. The sensitivity setting procedures with the use of the NDTRT-20.01 software and without it are given. Discussion. The offered technique has the following advantages: for different thicknesses of welded sheets with different requirements to the minimum acceptable defect the only CO-2 reference block is needed; the sensitivity can be adjusted on both the flat cilindrical reflector and the hemispherical reflector; the NDTRT-20.01 software allows automating the calculations of sensitivity correction factors and flaw detector sweep parameters.