What Is a Quantitative Ultrasound?

Ultrasonic Testing (Ultrasonic Testing) is abbreviated as UT, also called ultrasonic testing. It uses ultrasonic technology to perform the testing work, and is one of five conventional non-destructive testing methods.

Non-destructive testing is a non-destructive testing method that inspects the surface and internal quality of the inspected component without damaging the workpiece or the working condition of the raw material.

At present, the relevant domestic ultrasonic testing standards are JB / T4730.3, GB / T11345-1989, CB / T3559-2011, etc. JB / T4730.3 is a relatively comprehensive standard, while the latter two standards are weld testing standards. There are other testing standards for steel plates, castings and forgings, and users can make corresponding inquiries as needed ^[1]

Ultrasonic detector leak detection system is different from the specific gas sensor is limited to the specific gas it is designed to sense, but to detect by sound.

Any gas passing through the leakage hole will generate eddy currents, and there will be a part of the ultrasonic wave band, so that the ultrasonic detector leak detection system can sense any kind of gas leakage.

Scan with the ultrasonic detector leak detection system, you can hear the leakage sound or see the digital signal changes from the headphones. The closer the leak is, the more obvious it is. If the scene environment is noisy, you can use a rubber tube to narrow the receiving area and shield the ultrasound.

In addition, the frequency adjustment capability of the ultrasonic detector leak detection system also reduces background noise interference. Check pneumatic systems, test pressure cables used by telecommunications companies, etc. Tanks, pipes, and hoses can be tested by pressurization, as well as vacuum systems, vortex exhaust, diesel engine fuel intake systems, vacuum chambers, ship cabins, watertight doors, material handling systems, pressure vessels and pipelines. Internal and external gas-liquid leakage, etc. ^[2]

The propagation process of mechanical vibrations in the medium is called waves. The human ear can feel elastic waves with frequencies higher than 20 Hz and lower than 20,000 Hz. Therefore, elastic waves in this frequency range are also called sound waves. Elastic waves with a frequency less than 20 Hz are also called infrasound waves, and elastic waves with a frequency higher than 20,000 Hz are called ultrasonic waves. Neither infrasound nor ultrasound can be felt by the human ear ^[1]

1. Ultrasonic sound beam can be concentrated in a specific direction and propagate along a straight line in the medium with good directivity.

2. During the propagation of ultrasonic waves in the medium, attenuation and scattering will occur.

3. Ultrasound will generate reflection, refraction and wave mode conversion at the interface of heterogeneous media. By using these characteristics, the reflected wave reflected from the defect interface can be obtained, so as to achieve the purpose of detecting defects.

4. Ultrasonic energy is much larger than sound waves.

5. The transmission loss of ultrasonic waves in solids is small and the depth of detection is large. Due to the reflection and refraction of ultrasonic waves on heterogeneous interfaces, especially the inability to pass through gas-solid interfaces. If there are defects (including gas in the defects) or inclusions in the metal such as pores, cracks, delaminations, etc., when the ultrasonic wave is transmitted to the interface between the metal and the defect, it will be totally or partially reflected. The reflected ultrasonic waves are received by the probe and processed by the internal circuit of the instrument, and waveforms of different heights and a certain distance will be displayed on the fluorescent screen of the instrument. The depth, position and shape of defects in the workpiece can be judged based on the changing characteristics of the waveform ^[3]

The advantages of ultrasonic flaw detection are large detection thickness, high sensitivity, fast speed, low cost, harmless to the human body, and the ability to locate and quantify defects. Ultrasonic inspection of flaws is not intuitive, the inspection technique is difficult, subject to subjective and objective factors, and the inspection results are not easy to save. Ultrasonic inspection requires a smooth working surface. Experienced inspectors are required to discriminate the type of defect and be suitable for thickness. Larger parts inspections also make ultrasonic flaw detection a limitation.

There are many types of ultrasonic flaw detectors, but pulse reflection ultrasonic flaw detectors are the most widely used. Generally in a homogeneous material, the existence of defects will cause material discontinuities. Such discontinuities often cause inconsistencies in acoustic impedance. From the reflection theorem, we know that ultrasonic waves are reflected at the interface between two media with different acoustic impedances. The amount of reflected energy is related to the difference in the acoustic impedance of the medium on both sides of the interface and the orientation and size of the interface. Pulse reflection ultrasonic flaw detector is designed based on this principle.

Most of the pulse reflection type ultrasonic flaw detectors are of the A-scan type. The so-called A-scan display mode, that is, the abscissa of the display is the propagation time or distance of the ultrasound in the tested material, and the ordinate is the amplitude of the ultrasonic reflected wave. For example, there is a defect in a workpiece. Due to the defect, the interface between the defect and the material forms a different medium. The acoustic impedance between the interfaces is different. When the emitted ultrasonic wave encounters this interface, After that, reflection will occur, and the reflected energy will be received by the probe again. A certain position of the abscissa in the display screen will show a waveform of the reflected wave. This position of the abscissa is the defect wave in the inspected material. depth. The height and shape of this reflected wave are different for different defects, reflecting the nature of the defect ^[1]

Ultrasound

1. Preparation before testing

Familiar with the picked workpiece (name of workpiece, material, specifications, bevel form, welding method, heat treatment status, surface condition of the workpiece, testing standards, qualification level, testing proportion, etc.);

Select instruments and probes (determine flaw detectors, probes, test blocks, scanning ratios, detection sensitivity, detection methods according to standard regulations and site conditions)

Calibration of the instrument (When the instrument is used, the horizontal linearity and vertical linearity of the instrument are measured.)

Calibration of the probe (calibrate the leading edge, refraction angle, main beam deviation, sensitivity margin and resolution.)

Instrument adjustment (the baseline scale can be adjusted proportionally to represent the horizontal distance, depth, or sound path of the pulse echo.)

Sensitivity adjustment (Check the sensitivity on a comparison test block or other equivalent test block.)

2. Detection operation

Inspection of base material: The thickness of the pipe wall should be measured before inspection, at least every 90 °, for reference during inspection. Adjust the secondary bottom wave at the defect-free area to the full scale of the fluorescent screen as the detection sensitivity;

Inspection of welded joints: the scanning sensitivity should not be lower than the sensitivity of the evaluation line (EL line), the scanning speed of the probe should not exceed 150mm / s, and the interval between the two adjacent probes should be at least 10% during scanning. overlapping.

3. Inspection results and ratings: Ratings are based on the nature, extent, and length of the defect, and according to relevant standards.

4. Check and recheck the equipment.

5. Issue a test report.

Note: Welded joints with over-standard defects shall be re-examined in accordance with the original inspection conditions and their affected areas during re-work ^[3]

Compared with X-ray flaw detection, ultrasonic flaw detection has higher flaw detection sensitivity, shorter cycle, low cost, flexibility, convenience, high efficiency, harmless to the human body, etc .; the disadvantage is that it requires smooth working surfaces and requires experienced inspectors to identify the type of defect There is no intuition for defects; ultrasonic flaw detection is suitable for inspection of thick parts ^[3] .