To sum up, since ultrasonic waves can pass through different wave types with different propagation speeds in metal media, the required ultrasonic wave type must be selected when performing flaw detection on metal welds. The above analysis is relatively good, so actual flaw detection is usually Choose shear wave, otherwise the echo signal will be confused and the correct flaw detection result will not be obtained.
4. Ultrasonic waves have the property of penetrating materials and attenuating in materials
This property of ultrasonic waves is similar to that of rays, but the energy of ultrasonic waves is very large, so it has stronger penetrating ability. When ultrasonic waves propagate in most media, especially in metal materials such as steel, the transmission loss is small, and the maximum propagation distance can reach several meters. Therefore, ultrasonic flaw detection can have a larger detection depth, which is an advantage that other flaw detection methods do not have.
When ultrasonic waves propagate in a medium, the phenomenon that their energy gradually weakens as the propagation distance increases is called the attenuation of ultrasonic waves. In ultrasonic flaw detection of metal materials, the main cause of ultrasonic attenuation is scattering, and its sound pressure attenuates according to a negative exponential law. The law is as follows:
PX=P0e-αx
In the formula, Px – the sound pressure at X point away from the surface of the piezoelectric crystal sheet (Pa); P0——Original sound pressure of ultrasonic wave (Pa); e——the base of natural logarithm; α——attenuation coefficient of metal material (dB/m); X——The distance of ultrasonic wave propagation in metal materials (m).