Technique for measuring with an ultrasonic thickness gauge
The ultrasonic thickness gauge measures the thickness according to the ultrasonic pulse reflection principle. When the ultrasonic pulse emitted by the probe passes through the measured object to reach the material interface, the pulse is reflected back to the probe to accurately measure the time the ultrasonic wave propagates in the material to determine Measure the thickness of the material. The ultrasonic thickness gauge measures the thickness according to the ultrasonic pulse reflection principle. When the ultrasonic pulse emitted by the probe passes through the measured object to reach the material interface, the pulse is reflected back to the probe to accurately measure the time the ultrasonic wave propagates in the material to determine Measure the thickness of the material. Various materials that enable ultrasonic waves to propagate inside at a constant speed can be measured using this principle. (provided by Instrumentation World Network) Ultrasonic Thickness Gauge uses the latest high-performance, low-power microprocessor technology. Based on the principle of ultrasonic measurement, it can measure the thickness of metal and other materials, and can measure the sound velocity of materials. Thickness measurement of various pipes and pressure vessels in production equipment, monitoring of the degree of corrosion after corrosion during use, and accurate measurement of various plates and various machined parts The thickness gauge designed according to the principle of ultrasonic pulse reflection can accurately measure various plates and various processed parts, and can also monitor various pipelines and pressure vessels in production equipment to monitor their reduction after corrosion during use. Thinness. Can be widely used in petroleum, chemical, metallurgy, shipbuilding, aviation, aerospace and other fields. Technique for measuring with an ultrasonic thickness gauge First, clean the surface Before the measurement, all the dust, dirt and rust on the surface of the object to be tested should be removed, and the covering such as paint should be removed. Second, improve the roughness requirements Excessively rough surfaces can cause measurement errors and even the instrument has no readings. Before the measurement, the surface of the material to be tested should be as smooth as possible, and it can be smoothed by grinding, polishing, rubbing, etc., and a high-viscosity coupling agent can be used, and the coarse crystal probe SZ2.5P is selected. Third, rough machined surface Regular fine grooves caused by rough machined surfaces (such as lathes or planers) can also cause measurement errors. The compensation method is the same as 2, and the probe crosstalk spacer (thin layer passing through the center of the bottom surface of the probe) is adjusted and measured. The angle between the fine grooves of the material, The separator plate and the fine groove are perpendicular or parallel to each other, and the minimum value in the reading is taken as the measured thickness, and a good effect can be obtained. Fourth, measuring the cylindrical surface To measure cylindrical materials, such as pipes, oil drums, etc., it is important to choose the angle between the probe crosstalk and the axis of the material to be tested. Briefly, the probe is coupled to the material to be tested. The probe cross-talking plate is parallel or perpendicular to the axis of the material to be tested. The probe is slowly rocked perpendicularly to the axis of the material to be tested, and the readings on the screen will change regularly. Select the minimum value in the reading as the exact thickness of the material. The standard for selecting the direction of the crosstalk between the probe crosstalk and the axis of the material to be tested depends on the curvature of the material, the pipe with a larger diameter, and the pipe with the probe crosstalk plate perpendicular to the axis of the pipe, and the pipe with a smaller diameter, the pipe and the pipe are selected. The two parallel and vertical measurement methods take the minimum of the readings as the measured thickness. Five, composite shape When measuring the material of the composite shape (such as the elbow of the pipe), the method described in 7.4 can be used. The difference is that the second measurement is performed, and the two values ​​of the probe crosstalk plate perpendicular to the axis and the axis are read separately. Its smaller number is used as the thickness of the material at the measurement point. Sixth, the temperature influence of the material The thickness of the material and the propagation speed of the ultrasonic wave are affected by the temperature. If the measurement accuracy is high, the test piece of the same material can be separately measured under the same temperature condition, and the measurement error of the temperature is calculated, and the parameter is corrected. It, for steel, high temperature will cause a large error, this method can be used to compensate for the correction. Seven, non-parallel surface In order to obtain a satisfactory ultrasonic response, the other surface of the material to be tested must be parallel or coaxial with the surface to be measured, otherwise it will cause measurement errors or no reading at all. The above content is the technique of measuring with an ultrasonic thickness gauge. The thickness gauge designed according to the ultrasonic pulse reflection principle can accurately measure various plates and various processed parts, and can also be used for various pipes and pressure vessels in production equipment. Monitor to monitor how thin they are after corrosion during use. 1. General measurement method: (1) Perform the thickness measurement twice with the probe at one point. In the two measurements, the split faces of the probes should be 90° each other, and the smaller value is the thickness of the workpiece to be tested. (2) 30mm multi-point measurement method: When the measured value is unstable, a plurality of measurements are made in a circle having a diameter of about 30 mm centering on one measurement point, and the minimum value is the thickness value of the workpiece to be tested. 2. Accurate measurement method: increase the number of measurements around the specified measurement points, and the thickness change is indicated by the thick line. 3. Continuous measurement method: continuous measurement along the specified route by single point measurement method, the interval is not more than 5mm. 4, grid measurement method: draw a grid in the specified area, according to the point thickness record. This method is widely used in corrosion monitoring of high pressure equipment and stainless steel lining. 5. Factors affecting the indication value of the ultrasonic thickness gauge: (1) The surface roughness of the workpiece is too large, resulting in poor coupling between the probe and the contact surface, low reflection echo, and even failure to receive the echo signal. For surface rust, in-service equipment, pipes, etc., which have extremely poor coupling effects, can be treated by sand, grinding, and frustration to reduce the roughness, and the oxide and paint layers can be removed to expose the metallic luster. A good coupling effect can be achieved by the coupling agent with the test object. (2) The radius of curvature of the workpiece is too small, especially when the small diameter tube is thick, because the surface of the common probe is flat, the contact with the curved surface is point contact or line contact, and the sound intensity transmission is low (coupling is not good). A small diameter probe (6mm) can be used to accurately measure curved materials such as pipes. (3) The detection surface is not parallel to the bottom surface, the sound wave encounters the bottom surface to generate scattering, and the probe cannot accept the bottom wave signal. (4) Castings and austenitic steels are unevenly distributed or coarse grains. When ultrasonic waves pass through them, they cause severe scattering attenuation. The scattered ultrasonic waves propagate along complicated paths, which may cause the echoes to annihilate, resulting in no display. . A low-frequency coarse crystal dedicated probe (2.5MHz) is available. (5) There is some wear on the probe contact surface. The surface of the commonly used thickness measuring probe is made of acryl resin. The long-term use will increase the surface roughness, resulting in a decrease in sensitivity, resulting in incorrect display. It can be sanded with 500# sandpaper to make it smooth and ensure parallelism. If it is still unstable, consider replacing the probe. (6) There are a large number of corrosion pits on the back of the object to be tested. Due to rust spots and corrosion pits on the other side of the object, the sound waves are attenuated, resulting in irregular readings and, in extreme cases, no reading. (7) There is sediment in the measured object (such as pipeline). When the sediment and the acoustic impedance of 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, interlayers, etc.), the displayed value is about 70% of the nominal thickness. At this time, the defect detection can be further performed by the ultrasonic flaw detector. (9) The effect of temperature. Generally, the speed of sound in solid materials decreases with increasing temperature. Test data shows that for every 100 °C increase in hot material, the speed of sound drops by 1%. This is often the case with high temperature in-service equipment. High-temperature dedicated probes (300-600 ° C) should be used. Do not use ordinary probes. (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. (12) The influence of the coupling agent. The couplant 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 a 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. (13) 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 instrument 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. (14) The effect of stress. Most of the in-service 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 slowed 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. (15) The effect of an ultrasonic thickness gauge on the 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. Table Legs,Folding Table Leg,Aluminum Table Legs,Adjustable Height Table Legs Wenzhou Zhaoxia Hardware Co.,Ltd , https://www.zhaoxiahardware.com