The substrate is No. 20 steel and the surfacing layer is 304 stainless steel
The test block for surfacing layer side thickness measurement is designed according to the requirements of pressure equipment austenitic stainless steel, nickel alloy and other surfacing layer thickness measurement methods, which is suitable for calibration of ultrasonic thickness meter using twin crystal straight probe from the surfacing layer side measurement.
Test method: The twin-crystal straight probe is measured on the side of the surfacing layer
a) Adjust the horizontal linearity and scanning range of the instrument on a test block with the same or similar acoustic characteristics as the substrate;
b) Use the above test block, place the probe in the center of each step, adjust the instrument gain, so that the amplitude of the interface echo between the test block and the substrate is 50% of the full scale of the fluorescent screen, read out the displayed value of the thickness of each surfacing layer at this time, and compare it with the actual thickness of the surfacing layer;
c) Place the twin crystal probe on the surface of the workpiece surfacing layer, adjust the instrument gain, so that the amplitude of the interface echo between the test block surfacing layer and the substrate is 50% of the full scale of the fluorescent screen, and read the display value of the workpiece surfacing layer at this time;
d) The displayed value of the thickness of the workpiece surfacing layer is corrected according to the comparison result in b), that is, the thickness value to the workpiece surfacing layer.
