Application technology of the hottest ultrasonic t

2022-08-14
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The use technology of ultrasonic thickness gauge

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 and reaches the material interface, the pulse is reflected back to the probe. The thickness of the measured material is determined by accurately measuring the time of ultrasonic propagation in the material

the ultrasonic thickness gauge measures the thickness according to the wave pulse reflection principle. When the ultrasonic pulse emitted by the probe reaches the material interface through the measured object, the pulse is reflected back. At the same time, it can also be used for other low-temperature detection and experimental work. The head can determine the thickness of the measured material by accurately measuring the propagation time of the ultrasonic wave in the material. All kinds of materials that can make ultrasonic wave propagate inside at a constant speed can be measured by this principle. (provided by instrument world) ultrasonic thickness gauge adopts the latest high-performance and low-power microprocessor technology. Based on the principle of ultrasonic measurement, it can measure the thickness of metals and other materials, and measure the sound velocity of materials. It can measure the thickness of various pipes and pressure vessels in production equipment, monitor their thinning degree after corrosion in the process of use, and also accurately measure various plates and various processed parts

the thickness gauge designed according to the principle of ultrasonic pulse reflection can accurately measure all kinds of plates and all kinds of processed parts, and can also monitor all kinds of pipes and pressure vessels in production equipment to monitor their thinning degree after corrosion in the process of use. It can be widely used in petroleum, chemical industry, metallurgy, shipbuilding, aviation, aerospace and other fields

technology of using ultrasonic thickness gauge for measurement

I. clean the surface

before measurement, remove all dust, dirt and rust on the surface of the measured object, and remove paint and other covers

second, improve the roughness requirements

excessively rough surfaces will cause measurement errors, and even the instrument has no reading. Before measurement, try to make the surface of the tested material smooth. You can use grinding, polishing, filing and other methods to make it smooth. You can also use high viscosity couplant and choose coarse-grained probe sz2.5p

III. rough machined surface

regular fine grooves caused by rough machined surface (such as lathe or planer) will also cause measurement errors. The compensation method is the same as 2. In addition, adjust the angle between the probe crosstalk spacer plate (the thin layer passing through the center of the probe bottom) and the fine grooves of the measured material,

make the spacer plate and the fine grooves perpendicular or parallel to each other, and take the minimum value in the reading as the measurement thickness, which can achieve better results

IV. measuring cylindrical surface

measuring cylindrical materials, such as pipes, oil drums, etc., it is very important to select the angle between the probe crosstalk barrier plate and the axis of the measured material. Simply put, couple the probe with the tested material, the probe crosstalk isolation plate is parallel or vertical to the axis of the tested material, and slowly shake the probe vertically along the axis of the tested material. The reading on the screen will change regularly. Select the minimum value in the reading as the accurate thickness of the material

the standard for selecting the direction of the intersection of the probe crosstalk interlayer plate and the axis of the material to be measured depends on the curvature of the material. For pipes with larger diameter, select the probe crosstalk interlayer plate to be perpendicular to the axis of the pipe, and for pipes with smaller diameter, select two measurement methods, parallel and vertical to the axis of the pipe, and take the minimum value in the reading as the measurement thickness

v. composite shape

when measuring composite shape materials (such as pipe bends), the method introduced in 7.4 can be used. The difference is that the secondary measurement should be carried out, and the two values of the probe crosstalk barrier plate and the axis vertical and parallel should be read respectively. The smaller number is the thickness of the material at the measurement point

VI. temperature effect of materials

the thickness of materials and ultrasonic propagation speed are affected by temperature. If the measurement accuracy is high, test blocks of the same material can be used to measure respectively under the same temperature conditions, calculate the measurement error of temperature on the material, and provide parameters to correct it. For steel, high temperature will cause large errors, which can be compensated and corrected by this method

VII. Non parallel surface

in order to obtain a satisfactory ultrasonic response, the other surface of the tested material must be parallel or coaxial with the tested surface, otherwise it will cause measurement error or no reading display at all

the above content is the technology of using ultrasonic thickness gauge to measure. The thickness gauge designed according to the principle of ultrasonic pulse reflection can accurately measure all kinds of plates and all kinds of processed parts, and can also monitor all kinds of pipes and pressure vessels in production equipment to monitor their thinning degree after corrosion in the process of use

1. General measurement method:

(1) use the probe to measure the thickness twice at one point. In the two measurements, the dividing surfaces of the probe should be 90 ° to each other, and the smaller value is the thickness of the measured workpiece

(2) 30mm multi-point measurement method: when the measurement value is unstable, take a measurement point as the center and carry out multiple measurements in a circle with a diameter of about 30mm, and take the minimum value as the thickness value of the measured workpiece

2. Precise measurement method: increase the number of measurements around the specified measurement points, and the thickness change is represented by isopach lines

3. Continuous measurement method: use single point measurement method to measure continuously along the designated route, with an interval of no more than 5mm

4. Grid measurement method: mark the grid in the designated area and measure the thickness by points. This method is widely used in corrosion monitoring of high-pressure equipment and stainless steel lining

5. Factors affecting the indication value of ultrasonic thickness gauge:

(1) the workpiece surface is too rough, resulting in poor coupling effect between the probe and the contact surface, low reflected echo, and even unable to receive the echo signal. For in-service equipment and pipelines with surface corrosion and poor coupling effect, the surface can be treated by sand, grinding, frustration and other methods to reduce the roughness. At the same time, the oxide and paint layer can be removed to expose the metallic luster, so that the probe and the tested object can achieve a good coupling effect through the coupling agent

(2) the curvature radius of the workpiece is too small, especially when measuring the thickness of small-diameter tubes. Because the surface of the commonly used probe is flat, and the contact with the curved surface is point contact or line contact, the sound intensity transmittance is low (poor coupling). Special probe with small diameter (6mm) can be selected, which can accurately measure curved materials such as pipes

(3) the detection surface is not parallel to the bottom surface, and the sound wave will scatter when encountering the bottom surface, so the probe cannot accept the bottom wave signal

(4) castings and austenitic steels have serious scattering attenuation when ultrasonic waves pass through them due to uneven structure or coarse grains. Scattered ultrasonic waves propagate along complex paths, which may cause echo annihilation and non display. A special coarse-grained probe (2.5MHz) with low frequency can be selected

(5) the contact surface of the probe is worn. The surface of the commonly used thickness measuring probe is propylene resin. Long term use will increase its surface roughness, resulting in a decrease in sensitivity, resulting in incorrect display. You can use 500 × sandpaper to polish it 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 tested object. There are rust spots and corrosion pits on the other side of the tested object, causing sound wave attenuation, resulting in irregular changes in readings, and even no readings in extreme cases

(7) there is sediment in the measured object (such as pipeline). When there is little difference between the acoustic impedance of sediment and workpiece, the displayed value of thickness gauge is wall thickness plus sediment thickness

(8) when there are defects inside the material (such as inclusions, interlayer, etc.), the displayed value is about 70% of the nominal thickness. This is when there is an arched frame lying on the base support, the ultrasonic flaw detector with a super 6.1 ear rate can be used for further defect detection

(9) effect of temperature. In general, the sound velocity in solid materials decreases with the increase of temperature. Experimental data show that the sound velocity decreases by 1% for every 100 ° C increase in hot materials. This situation is often encountered for high-temperature equipment in service. High temperature special probe (° C) should be selected, and ordinary probe should not be used

(10) laminated materials, composite (heterogeneous) materials. It is impossible to measure uncoupled laminated materials because ultrasonic waves cannot penetrate uncoupled space and cannot propagate uniformly in composite (heterogeneous) materials. For equipment made of multi-layer materials (such as urea high-pressure equipment), special attention should be paid to thickness measurement. The indication value of the thickness gauge only indicates the thickness of the layer of material in contact with the probe

(12) the influence of coupling agent. Couplant is used to eliminate the air between the probe and the measured object, so that ultrasonic can effectively penetrate the workpiece to achieve the purpose of detection. If the type is selected or the method of use is improper, it will cause error or the coupling mark will flicker and cannot be measured. Due to the selection of appropriate types according to the use situation, low viscosity couplants can be used when used on smooth material surfaces; When used on rough surfaces, vertical surfaces and top surfaces, couplants with high viscosity should be used. High temperature couplant shall be selected for high temperature workpiece. Secondly, the couplant should be applied properly and evenly. Generally, the couplant should be applied to the surface of the tested material, but when the measurement temperature is high, the couplant should be applied to the probe

(13) sound speed selection error. Before measuring the workpiece, preset its sound velocity according to the material type or measure the sound velocity according to the standard block. When the instrument is calibrated with one material (the commonly used test block is steel) and another material is measured, wrong results will be produced. It is required to correctly identify the material and select the appropriate sound speed before measurement

(14) effect of stress. Most of the in-service equipment and pipelines have stress, and the stress state of solid materials has a certain impact on the sound velocity. When the stress direction is consistent with the propagation direction, if the stress is compressive stress, the stress action will increase the elasticity of the workpiece and speed up the sound velocity; On the contrary, if the stress is tensile stress, the sound velocity slows down. When the stress is different from the propagation direction of the wave, the particle vibration track is disturbed by the stress in the wave process, and the propagation direction of the wave deviates. According to the data, the general stress increases, and the sound velocity increases slowly

(15) influence of oxide or paint coating on metal surface of ultrasonic thickness gauge. Although the dense oxide or paint anticorrosive coating produced on the metal surface is closely combined with the base material and has no obvious interface, the propagation speed of sound velocity in the two substances is different, resulting in errors, and with the thickness of the cover, the error size is also different. Open the experimental interface

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