Coating thickness gauge and ultrasonic thickness gauge use methods and techniques Coating thickness gauge using methods and techniques: When using coated wave thickness gauge attention to the instrument's operating procedures and tips, you can greatly increase the coating thickness gauge life and measurement accuracy. Ultrasonic Thickness Gauges Use Note Four Items: Ultrasonic thickness gauge use methods and techniques: Transition Idler,Transition Idler Belt Conveyor,Transition Idler Frame,Transition Idler Type NINGBO TANSUO MACHINE MANUFACTURING CO., LTD. , https://www.tsjxidler.com
(1) When measuring with a coating thickness gauge, the probe must be perpendicular to the surface of the measured object;
(2) Do not drag the probe while measuring, because it will not only cause the probe to wear, but also will not get accurate measurement results;
(3) The position of the probe line at the point where the probe is connected must not be excessively bent or dithered (for split coating thickness gauges). This will affect the test results and will result in inaccurate and stable measurement results.
(4) Try to ensure that the coating thickness gauge is used and stored by a person; if you feel that the deviation of the measurement results is relatively large, please use a randomly allocated five plastic calibration patches to make a round of tests. If the deviation is far from the allowable error, it may be It is a problem with the instrument itself that needs to be returned to the factory for repair. Remember that it is not possible to disassemble and repair by yourself.
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 flat, contact with the surface is point contact or line contact, and the sound intensity transmittance is low (coupling is not good). Small-diameter special probes (<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 sound wave encounters the bottom surface to scatter, and the probe cannot receive the final wave signal.
4: castings, austenitic steel due to uneven microstructure or grain size, ultrasonic waves in which to pass through when there is a serious scattering attenuation, scattered ultrasonic waves along a complex path, it may cause echoes annihilation, causing no display. A coarse crystal dedicated probe (2.5MHz) with a lower frequency can be used.
5: There is some wear on the probe contact surface. 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 (eg pipeline). When the acoustic impedance of the deposit and the workpiece are not much different, the thickness gauge shows the wall thickness plus the thickness of the deposit.
8: When there are defects inside the material (such as inclusions, sandwiches, etc.), the displayed value is about 70% of the nominal thickness. At this time, flaw detection can be further performed by an ultrasonic flaw detector or a thickness gauge with a waveform display.
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. This is often the case for equipment that is in service at high temperatures. High-temperature special probes and high-temperature coupling agents (300-600°C) should be used. Do not use ordinary probes.
10: Laminated, 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 of the thickness gage only indicates the thickness of the material in contact with the probe.
11: Effect of couplant. 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.
12: The speed of sound is wrong. 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.
13: 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, if the stress is a compressive stress, the stress will increase the elasticity of the workpiece and accelerate the sound speed; If the stress is tensile stress, the speed of sound will slow 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.
14: Effect of metal surface oxide or paint coating. 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.