Screw Air Compressor,Small Screw Air Compressor,Small Rotary Screw Air Compressor,Screw Type Air Compressor Hangzhou Zhongju air separation equipment manufacturing Co., Ltd , https://www.hzzjkfzz.com
(1. Laminated materials, composite (non-homogeneous) materials. It is impossible to measure uncoupled laminates because ultrasonic waves cannot penetrate uncoupled spaces and cannot be uniform in composite (non-homogeneous) materials. Propagation. 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 in contact with the probe.
(2. Sound speed selection error. Before measuring the workpiece, preset the sound speed according to the material type or reverse the sound speed according to the standard block. When the instrument is calibrated with one material (the common test block is steel) and the other material is measured. Will produce incorrect results.
(3. Effect of temperature. Generally speaking, the speed of sound in solid materials decreases with increasing temperature. Test data shows that the sound velocity drops by 1% for every 100 °C increase in hot materials. This is often the case for high temperature in-service equipment. Happening.
(4, the influence of the coupling agent. The coupling agent is used to exclude the air between the probe and the measured object, so that the ultrasonic wave can effectively penetrate the workpiece for the purpose of detection. If the type is selected or the method of use is improper, it will cause errors or coupling signs. Blinking, unable to measure. In actual use, due to the excessive use of the couplant, the instrument indicates the value of the couplant layer thickness when the probe leaves the workpiece.
(5. 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 sediment thickness.
(6. The effect of metal surface oxide or paint coating. The dense oxide or paint coating produced on the metal surface, although tightly combined with the matrix material, has no obvious interface, but the speed of sound travels differently in the two materials. , causing errors, and the magnitude of the error varies with the thickness of the cover.
(7) When there are defects inside the material (such as inclusions, interlayers, etc.), the displayed value is about 70% of the nominal thickness (in this case, the ultrasonic flaw detector is used for further defect detection).
(8. Influence of stress. Most of the in-service equipment and pipelines have stress. 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 acts on the workpiece. When the elasticity is increased, the speed of sound is increased. Conversely, if the stress is tensile stress, the speed of sound is slowed down. When the direction of propagation of the stress and the wave is different, the vibrational trajectory of the particle is disturbed by the stress and the direction of propagation of the wave is deviated. Generally, the stress increases and the speed of sound increases slowly.
Reasons for the measurement error of ultrasonic thickness gauge
In the actual inspection work, it is often encountered that the thickness gauge value is significantly larger or smaller than the design value (or expected value). The reasons are as follows: