Ultrasonic Thickness Gauge Indication Distortion And Their Causes - Ultrasound - Education Industry
Ultrasonic thickness in practical applications
, particularly monitoring equipment in service, if indications of distortion of the actual thickness of the phenomenon, resulting in pipeline (equipment) there is hidden, is based on wrong data to replace the pipe pieces, causing a lot of material waste. According to recent years ultrasonic thickness of the track usage, to show the value of distortion and the reasons as follows:
1, shows no indication or indications of instability because of flash: this phenomenon in the field equipment and pipe detection often occurs after a large number of phenomena and data analysis, summarized for the following reasons:
(1) through the large surface roughness, resulting in the probe contact surface coupled with the effects of poor echo low, can not even receive the echo signal. In-service equipment, most of the surface corrosion of pipes, the coupling effect of very poor.
(2) workpiece radius is too small, especially in small diameter tube thickness, because of the probe used for the flat surface, and surface contact with the point contact or line contact, the sound intensity transmission is low (poor coupling).
(3) detection of surface and bottom is not parallel to the scattering of sound waves generated bottom face, the probe wave signal can not accept in the end.
(4) casting, austenitic steels due to inhomogeneity or grain coarsening, in which the ultrasonic wave through the scattering attenuation when severe, were scattered along the complex path of ultrasonic propagation, has the potential to echo annihilation, result is not displayed.
(5) probe contact surface has some wear and tear. Thickness probe surface used acrylic resin surface roughness of long-term use will Qigongkangxian Sakura? Jia Lu aluminum lance fanny recognized worry? Commission? Fiji brake Sapporo allow the floating net razor?
(6) measured object on the back of a large number of corrosion pits. Because the other side of the measured object has rust, corrosion pits, resulting in attenuation, leading to changes in reading irregular and, in extreme cases, even without reading.
2, said value is too large or too small because of the actual test work, often encountered thickness and design of indication value (or expected value) are obviously too large or too small, the reasons as follows:
(1) the measured object (such as pipelines) within the sediments, when the acoustic impedance difference between the sediment and the workpiece is little, showed a value of wall thickness plus the thickness of sediment.
(2) when the material deficiencies in internal (such as inclusion, mezzanine, etc.) to show the value of the nominal thickness of about 70% (now use ultrasonic flaw detector further defect detection).
(3) temperature. General speed of sound in solid materials with the temperature decreased, and test data show that hot material for each additional 100 C, velocity decreased by 1%. High-temperature equipment in service for this situation is often encountered.
(4) layered materials, composite (non-homogeneous) materials. To measure the cascading material without the coupling is not possible, because ultrasound can not penetrate the space without coupling, and can not be in the composite (non-homogeneous) materials evenly spread. Made by the multi-layer bandaging material for the equipment (such as urea high-pressure equipment), special attention when measuring thickness, thickness of the indication that the probe only contacts of that layer thickness.
(5) the impact of coupling agent. Coupling agent is used to rule out the probe and the air between the measured object, so that ultrasound can effectively penetrate the workpiece to detect the purpose. If you choose to type or incorrect use will result in errors or coupled sign flashing, can not be measured. Actual use of coupling agent because of excessive use, causing the probe from the workpiece, the instrument showed a value of coupling agent layer thickness.
(6) speed of sound wrong choice. Measuring workpiece before, according to material type preset speed of sound or its block against the standard silent speed test. When, after instrument calibration with a material (used for the steel test block) went to measure another material, will produce erroneous results.
by: gaga
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Ultrasonic Thickness Gauge Indication Distortion And Their Causes - Ultrasound - Education Industry