What are the factors that affect the measurement of the ultrasonic thickness gauge?(2)

(10)Laminated materials, composite (heterogeneous) materials. It is impossible to measure uncoupled laminates because ultrasonic waves cannot penetrate uncoupled spaces and cannot propagate at a constant rate in composite (non-homogeneous) materials. For equipment made of multi-layer materials (like urea high-pressure equipment), special care should be taken when measuring thickness. The thickness gauge indicates only the thickness of the material that is in contact with the probe.

(11) The influence of the coupling agent. The ultrasonic coating thickness gauge is used to remove the air between the probe and the object to be measured, so that the ultrasonic wave can effectively penetrate the workpiece for inspection purposes. If the type is selected or the method of use is improper, it will cause an error or the coupling mark will flash and cannot be measured. Since a suitable type is selected depending on the use, a low viscosity coupling agent can be used when used on the smooth material surface; a highly viscous coupling agent should be used when used on a rough surface, a vertical surface, and a top surface. High temperature couplings should be used for high temperature workpieces. Secondly, the coupling agent should be used in an appropriate amount and evenly applied. Generally, the coupling agent should be applied to the surface of the material to be tested, but when the measurement temperature is high, the coupling agent should be applied to the probe.

(12) The sound speed selection is incorrect. Before measuring the workpiece, preset the speed of sound according to the type of material or reverse the sound speed according to the standard block. When the aluminium sheet thickness gauge is calibrated with one material (commonly used for steel) and another material is measured, erroneous results will result. It is required to correctly identify the material before measuring and select the appropriate speed of sound.

(13) The effect of stress.Most of the surface ultrasonic thickness measurement equipment and pipelines have stresses. The stress state of solid materials has a certain influence on the speed of sound. When the stress direction is consistent with the direction of propagation, if the stress is compressive stress, the stress will increase the elasticity of the workpiece and the speed of sound will increase. If the stress is tensile stress, the speed of sound is slow down. When the stress and the wave propagation direction are different, the vibration trajectory of the particle is disturbed by the stress during the wave process, and the wave propagation direction deviates. According to the data, the general stress increases and the speed of sound increases slowly.

(14) The effect of metal surface oxide or paint overlay. The dense oxide or paint anti-corrosion layer produced on the metal surface, although tightly combined with the matrix material, has no obvious interface, but the speed of sound propagation in the two materials is different, resulting in errors, and the thickness of the cover varies with the thickness of the cover. It is also different.

Our common measurement methods are as follows:

General measurement method: