Factors affecting the detection accuracy of ultrasonic flaw detectors: detection object, temperature, surface roughness, magnetic field, attached substances, shape characteristics of defects, acoustic impedance of defects and surface characteristics of defects (such as whether it is smooth or not).
In such a detection object, even if it contains many different alloy components, its sound velocity is considered to be substantially constant. In many other materials, such as many non-ferrous metals or plastics, the variation of ultrasonic propagation velocity is very significant, which will affect the accuracy of the measurement.
If the material of the object to be detected is not isotropic, the speed of sound will be different in different directions. In this case the average value of the sound velocity in the detection range must be used for the calculation. The average value is obtained by measuring a reference block having a sound velocity comparable to the average sound velocity of the block to be tested.
The speed of sound in a material changes as the temperature of the material changes. If the calibration of the instrument is carried out in an environment with a relatively low temperature, but the instrument is used in an environment with a relatively high temperature, in this case, the detection result will deviate from the true value.
To avoid this effect of temperature, the method is to preheat the reference test block before calibrating the instrument to achieve the same temperature as the use environment; or multiply the measurement result by a temperature influence factor.
The surface roughness of the tested part has an influence on the flaw detection. The greater the roughness, the greater the impact. Rough surface will cause systematic error and accidental error, and the number of measurements should be increased at different positions for each measurement to overcome this accidental error.
Adhesive substances must be removed before flaw detection to ensure direct contact between the instrument probe and the surface of the test piece.
The strong magnetic field generated by various electrical equipment around will seriously interfere with the flaw detection work.
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