Ultrasonic Thickness Gauge is based on the principle of ultrasonic pulse reflection thickness measurement, when the ultrasonic pulse emitted by the probe through the measured object reaches the material interface, the pulse is reflected back to the probe through the accurate measurement of ultrasonic propagation time in the material to be determined The thickness of the material is measured. Any material that allows ultrasound to propagate inside it at a constant speed can be measured using this principle.
Ultrasonic thickness gauge tips
General measurement
1. Use a probe to measure thickness at one point. In the two measurements, the split faces of the probes are 90° apart, and the smaller one is the thickness value of the measured workpiece.
2.30mm multi-point measurement method: When the measurement value is not stable, take a measurement point as the center, perform multiple measurements in a circle with a diameter of about 30mm, and take the minimum value as the measured workpiece thickness value.
Accurate measurement
The number of measurements is increased around the specified measurement point, and the thickness variation is represented by a constant thickness line.
Fold continuous measurement
Continuous measurement along the specified route using a single point measurement, the interval is not more than 5mm.
Fold Mesh Measurement
Mark the grid in the specified area and press the thickness measurement record. This method is widely used in high pressure equipment, stainless steel lining corrosion monitoring.
5, the factors that affect the measurement indication
(1) The surface roughness of the workpiece is too large, which results in poor coupling between the probe and the contact surface, low reflection echo, and even failure to receive echo signals. For surface corrosion, the in-service equipment and pipelines with poor coupling effect can be treated with sand, grinding, and contusion to reduce the roughness. At the same time, the oxides and paint layers can be removed to expose the metallic luster. Coupling agent can achieve a good coupling effect with the test object.
(2) The radius of curvature of the workpiece is too small, especially when the small-diameter tube measures thickness, because the surface of the commonly used probe is a plane, contact with the surface is point contact or line contact, and the sound intensity transmittance is low (coupling is not good). Small-diameter special probe (6mm) can be used to accurately measure curved surface materials such as pipes.
(3) The detection surface is not parallel to the bottom surface, and the acoustic wave encounters scattering on the bottom surface, and the probe cannot receive the final wave signal.
(4) castings, austenitic steel due to uneven tissue or coarse grain, ultrasonic scattering in it when there is a serious scattering attenuation, scattered ultrasonic waves along a complex path, may cause echoes annihilation, causing no display . The coarse crystal special probe (2.5MHz) with lower frequency can be used.
(5) The probe contact surface has a certain amount of wear. The commonly used thickness measurement probe surface is acrylic resin, and its long-term use will increase the surface roughness, which will result in a decrease in sensitivity, which may result in incorrect display. Optional sanding with 500# sandpaper makes it smooth and parallel. If it is still unstable, consider replacing the probe.
(6) There are a large number of corrosion pits on the back of the measured object. Due to rust and corrosion pits on the other side of the test object, sound waves are attenuated, resulting in random readings and no reading in extreme cases.
(7) There are deposits in the measured object (such as pipelines). When the acoustic impedance of the deposits and the workpiece are not much different, the thickness gauge shows the wall thickness plus the thickness of the sediment.
(8) When there are defects inside the material (such as inclusions, interlayers, etc.), the displayed value is about 70% of the nominal thickness. At this time, flaw detection can be further performed with an ultrasonic flaw detector.
(9) The effect of temperature. The sound velocity in general solid materials decreases as their temperature increases, and experimental data shows that the sound speed drops by 1% for every 100°C increase in hot material. For high temperature equipment in service
Often encountered this situation. Should use high-temperature special probe (300-600 °C), do not use ordinary probe.
(10) Laminated and composite (heterogeneous) materials. It is not possible to measure uncoupled laminates because ultrasonic waves cannot penetrate the uncoupled space and cannot propagate uniformly in composite (heterogeneous) materials. For devices made of multi-layered materials (such as urea high-pressure equipment), special attention should be paid to the thickness measurement, and the value indicated by the thickness gage only indicates the thickness of the material in contact with the probe.
(12) Coupling agent effects. Coupling agent is used to eliminate the air between the probe and the measured object, so that the ultrasonic energy can effectively penetrate the workpiece to achieve the purpose of detection. If you choose a type or use it incorrectly, it will cause the error or coupling symbol to flicker and cannot be measured. Depending on the type of application, a low viscosity couplant can be used when used on a smooth material surface, and a high viscosity couplant should be used on rough, vertical, and top surfaces. High temperature parts should use high temperature couplant. Secondly, the couplant should be applied in proper amount and evenly applied. Generally, the couplant should be coated on the surface of the tested material, but when the measuring temperature is high, the couplant should be coated on the probe.
(13) The speed of sound is incorrect. Before measuring the workpiece, preset its sound speed according to the type of material or reversely measure the speed of sound according to the standard block. When a material is used to calibrate the instrument (usually the test block is steel) and another material is measured, it will produce erroneous results. Requirements must be correctly identified before the measurement of materials, select the appropriate speed of sound.
(14) The effect of stress. Most of the equipment and pipelines in service have stress, and the stress state of the solid material has a certain influence on the sound speed. When the stress direction and the propagation direction are the same, the stress is the pressure.
Stress, then the role of stress to increase the elasticity of the workpiece, the speed of sound acceleration; the other hand, if the stress is tensile stress, the speed of sound slows down. When the propagation direction of stress and wave is not the same, the vibration track of the particle in the wave process is disturbed by the stress and the wave propagation direction is deviated. According to the data, the general stress increases and the speed of sound increases slowly.
(15) Effects of metal surface oxides or paint overlays. Although the dense oxide or paint coating produced on the metal surface is tightly bound to the matrix material and has no apparent interface, the speed of sound propagation in the two materials is different, resulting in errors, and the error size varies with the thickness of the cover. Also different
Related applications
Related applications
Due to the convenience of ultrasonic processing and good directionality, ultrasonic technology measures the thickness of metal and non-metal materials, which is fast and accurate, and free from pollution. Especially when only one side can be touched, it can show its superiority. , Widely used in various plate, pipe wall thickness, boiler container wall thickness and local corrosion, rust, so the metallurgy, shipbuilding, machinery, chemicals, power, atomic energy and other industrial sector product inspection, the safe operation of the equipment And modern management plays a major role.
Ultrasonic cleaning and ultrasonic thickness gauges are only part of the application of ultrasound technology, and there are many areas that can be applied to ultrasound technology. Such as ultrasonic atomization, ultrasonic welding, ultrasonic drilling, ultrasonic grinding, ultrasonic level gauge, ultrasonic level gauge, ultrasonic polishing, ultrasonic cleaning machine, ultrasonic motor and so on. Ultrasound technology will be applied more and more widely in all walks of life.
Sonic drilling, ultrasonic grinding, ultrasonic level gauge, ultrasonic level gauge, ultrasonic polishing, ultrasonic cleaning machine, ultrasonic motor and so on. Ultrasonic technology will be applied more and more widely in all walks of life.
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