PD-T7 ultrasonic thickness gauge to use for measurement of technical notes using ultrasonic thickness gauge for measurement of technical notes
Ultrasonic thickness gauge is based on the principle of reflection of ultrasonic pulses to carry out thickness measurements, when the probe emits ultrasonic pulses through the object to be measured to reach the material interfaces, the pulses are reflected back to the probe through the precise measurement of ultrasonic propagation time in the material to determine the thickness of the material to be measured. The thickness of the material being measured is determined by accurately measuring the time it takes for the ultrasonic wave to travel through the material.
Ultrasonic thickness gauge is based on the principle of ultrasonic pulse reflection for thickness measurement, when the probe transmits ultrasonic pulse through the object under test to reach the material interfaces, the pulse is reflected back to the probe by accurately measuring the ultrasonic wave propagation time in the material to determine the thickness of the material under test. Where the ultrasonic wave can be made to a constant speed in its internal propagation of a variety of materials can be measured using this principle. (Provided by Instrumentation World Network)
Ultrasonic thickness gauge is the latest high-performance, low-power microprocessor technology, based on the ultrasonic measurement principle, can measure the thickness of metal and other kinds of materials, and can be the speed of sound of the material to be measured. It can measure the thickness of various pipelines and pressure vessels in the production equipment, and monitor the degree of thinning after they are corroded in the process of use, and also can make accurate measurement of various plates and various processed parts
Designed according to the principle of ultrasonic impulse reflection, the thickness gauge can make accurate measurement of various plates and various processed parts, and also can monitor the thickness of various pipelines and pressure vessels in the production equipment, and also can monitor the thickness of various pipelines and pressure vessels in the production equipment, and also can measure the thickness of metal and other materials based on ultrasonic measurement principle. Monitor their use in the process of corrosion after the thinning degree. It can be widely used in petroleum, chemical industry, metallurgy, shipbuilding, aviation, aerospace and other fields.
Using ultrasonic thickness gauge to measure the technology
One, clean the surface
Measurement should be cleared before the surface of the object to be measured all the dust, dirt and corrosion, eradicate paint and other coverings.
Second, improve the roughness requirements
Excessive roughness of the surface will cause measurement errors, and even the instrument does not read. Measurement should try to make the measured material surface smooth, can use grinding, throwing, filing and other methods to make it smooth, but also can use high-viscosity coupling agent, the choice of coarse crystal probe.
Third, rough machined surface
Rough machined surface (such as lathe or planer) caused by the regular fine groove will also cause measurement errors, make up for the same 2, in addition to adjusting the probe tandem spacer plate (through the center of the probe bottom surface of the thin layer) and the measured material fine groove between the angle of the
To make the spacer plate and the fine groove perpendicular to each other or parallel to the smallest value of the readings taken! As a measurement of thickness, can achieve better results.
Four, measurement of cylindrical surfaces
Measurement of cylindrical materials, such as tubes, oil drums, etc., the choice of probe tandem spacer plate and the measured material axis of the angle between the vital. Simply put, coupling the probe to the material being measured, the probe crosstalk spacer is parallel or perpendicular to the axis of the material being measured, slowly rocking the probe perpendicularly in the direction of the axis of the material being measured, the readings on the screen will change regularly, and selecting the smallest value in the readings as the exact thickness of the material.
Criteria for selecting the direction of the probe crosstalk spacer and the measured material axis intersection angle depends on the curvature of the material, the larger the diameter of the pipe, select the probe crosstalk spacer and the pipe axis perpendicular to the smaller diameter of the pipe, the choice of parallel and perpendicular to the axis of the pipe two measurements, take the smallest of the readings as a measurement of the thickness.
Fifth, the composite shape
When measuring the composite shape of the material (such as pipe elbow) can be used 7.4 method, the difference is to carry out the second measurement, respectively, read the probe crosstalk spacer and the axis of perpendicular and parallel to the two values of the smaller one as a number of the material in the measurement of the thickness of the point.
Six, the material's temperature
The thickness of the material and ultrasonic propagation speed are affected by the temperature, if the measurement accuracy requirements are high, the same material can be used in the same temperature conditions of the test block were measured, the temperature of the material to calculate the measurement error to provide the parameters to correct it, for steel, high temperatures will cause greater error, can be compensated for the correction of this method.
Seven, non-parallel surfaces
In order to get a satisfactory ultrasonic response, the other surface of the material to be measured must be parallel or coaxial with the measured surface, otherwise it will cause measurement errors or no readings at all.
The above is the use of ultrasonic thickness gauge measurement technology, according to the principle of ultrasonic pulse reflection thickness gauge can be designed for a variety of plates and a variety of processed parts for accurate measurement, but also for the production of a variety of pipelines and pressure vessels in the production equipment to monitor the monitoring of the degree of corrosion in the process of their use in the corrosion of the degree of thinning.
1, the general measurement method:
(1) at a point with a probe for two thickness measurement, in the two measurements in the probe split surface to each other 90 °, take the smaller value for the measured thickness of the workpiece value.
(2) 30mm multi-point measurement method: when the measurement value is not stable, a measurement point as the center, in a circle of about 30mm diameter for multiple measurements, take the minimum value for the measured thickness of the workpiece.
2, precise measurement method: in the specified measurement point around the increase in the number of measurements, thickness changes expressed in equal thickness line.
3, continuous measurement method: single-point measurement method along the specified route of continuous measurement, the interval is not greater than 5mm.
4, grid measurement method: in the specified area on the grid, according to the point of the thickness measurement record. This method is widely used in high-pressure equipment, stainless steel lining corrosion monitoring.
5, factors affecting the ultrasonic thickness gauge value:
(1) the surface roughness of the workpiece is too large, resulting in poor coupling between the probe and the contact surface, low reflection echo, or even unable to receive the echo signal. For surface corrosion, coupling effect is very poor in-service equipment, pipelines, etc. can be sanded, grinded, thwarted and other methods of surface treatment, reduce the roughness, but also oxides and paint layer can be removed, revealing the metal luster, so that the probe and the object being examined through the coupling agent can achieve a good coupling effect.
(2) the radius of curvature of the workpiece is too small, especially when the small diameter pipe thickness measurement, because of the commonly used probe surface for the plane, and the curved surface contact for the point contact or line contact, the sound intensity transmittance is low (coupling is not good). Can choose a small diameter pipe special probe (6mm), can be more accurate measurement of pipeline and other curved materials.
(3) Detection surface and the bottom surface is not parallel, the sound wave encountered in the bottom surface scattering, the probe can not accept the bottom wave signal.
(4) castings, austenitic steel due to uneven organization or coarse grain, ultrasonic waves in which the passage of serious scattering attenuation, the scattered ultrasonic waves along the complex path propagation, may make the echo annihilation, resulting in non-display. A special probe (2.5MHz) for coarse crystals with a lower frequency can be used.
(5) probe contact surface has some wear. Commonly used thickness probe surface for acrylic resin, long-term use will increase its surface roughness, resulting in decreased sensitivity, resulting in incorrect display. Optional 500 # sandpaper grinding, so that it is smooth and ensure parallelism. If it is still unstable, consider replacing the probe.
(6) the back of the measured object has a large number of corrosion pits. Due to the other side of the measured object has rust spots, corrosion pits, resulting in acoustic attenuation, resulting in irregular changes in readings, and in extreme cases, even no readings.
(7) the object under test (such as pipe) within the deposit, when the deposit and the workpiece acoustic impedance difference is not large, the thickness gauge display value for the wall thickness plus deposit thickness.
(8) when there are defects within the material (such as inclusions, interlayers, etc.), the display value of about 70% of the nominal thickness, this time the ultrasonic flaw detector can be used for further defect detection.
(9) the effect of temperature. General solid materials in the speed of sound with its temperature increases and decreases, there are test data show that the hot material every increase of 100 ° C, the speed of sound decreased by 1%. For high-temperature in-service equipment often encountered this situation. High-temperature special probes (300-600°C) should be used, do not use ordinary probes.
(10) laminated materials, composite (non-homogeneous) materials. It is impossible to measure uncoupled laminated materials because ultrasonic waves cannot penetrate uncoupled space and do not propagate uniformly through composite (non-homogeneous) materials. For equipment made from multiple layers of material wrapped together (like urea high-pressure equipment), special care should be taken when measuring thickness, and the value of the thickness gauge only indicates the thickness of the layer of material in contact with the probe.
(12) the influence of the coupling agent. Coupling agent is used to exclude the air between the probe and the object to be measured, so that ultrasonic waves can effectively penetrate the workpiece to achieve the purpose of detection. If the choice of type or use method is not appropriate, will cause errors or coupling sign flicker, can not be measured. Due to the use of selecting the appropriate type, when used in the smooth surface of the material, you can use a low viscosity coupling agent; when used in the rough surface, vertical surface and the top surface, you should use a high viscosity coupling agent. High-temperature workpiece should be selected high-temperature coupling agent. Secondly, the coupling agent should be used in the right amount, coated evenly, the coupling agent should generally be coated on the surface of the measured material, but when the measurement temperature is high, the coupling agent should be coated on the probe.
(13)Wrong choice of sound speed. Before measuring the workpiece, according to the type of material preset its speed of sound or back-measure the speed of sound according to the standard block. When calibrating the instrument with one type of material (commonly used test block is steel) and then go to measure another type of material, it will produce erroneous results. It is required that the material must be correctly identified and the appropriate speed of sound selected before measurement.
(14) the effect of stress. In-service equipment, most of the pipeline stress exists, the stress condition of the solid material has a certain effect on the speed of sound, when the direction of stress and the propagation direction is the same, if the stress for the compressive stress, the role of stress to make the elasticity of the workpiece to increase the speed of sound; Conversely, if the stress for the tensile stress, then the speed of sound slows down. When the stress and wave propagation direction is not the same, fluctuations in the process of mass vibration trajectory by stress interference, wave propagation direction deviation. According to the data, the general stress increases, the speed of sound increases slowly.
(15) ultrasonic thickness gauge metal surface oxides or paint covering layer of influence. Metal surface produced dense oxide or paint anti-corrosion layer, although the combination of close to the base material, no obvious interface, but the speed of sound in the propagation of the two substances is different, resulting in error, and with the thickness of the cover different, the size of the error is also different.