Brief overview of the steps in ultrasonic testing for non-destructive inspection

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The leak detection system of ultrasonic detectors differs from specific gas sensors, which are limited to the specific gases they are designed to detect, as it uses sound for detection. By scanning with an ultrasonic detector leak detection system, a leak sound can be heard through the headphones or changes in the digital signal can be observed. The closer to the leak point, the more obvious it is. 1 Principle of ultrasonic testing: Ultrasonic flaw detection is a non-destructive testing method that utilizes the differences in the acoustic properties of materials and their defects to examine internal defects in materials, by analyzing changes in the reflection pattern of ultrasonic waves and their penetration time. Pulse reflection testing uses longitudinal waves for vertical inspection and shear waves for oblique inspection. Pulse reflection testing includes longitudinal wave testing and transverse wave testing. On the oscilloscope screen of the ultrasonic instrument, the horizontal axis represents the propagation time of the sound waves, while the vertical axis indicates the amplitude of the echo signal. For the same homogeneous medium, the propagation time of pulse waves is proportional to the distance traveled. Therefore, the presence of defects can be determined by the appearance of defect echo signals ； The distance of the defect from the detection surface can also be determined by the position where the echo signal appears, thereby enabling defect localization ； The equivalent size of the defect is determined based on the echo amplitude. 2 Characteristics of ultrasound: 1) The ultrasound beam can be focused in a specific direction and travels in a straight line through the medium, exhibiting good directivity. 2) As ultrasound propagates through a medium, it undergoes attenuation and scattering. 3) Ultrasonic waves undergo reflection, refraction, and wave pattern transformation at the interface between different media. By utilizing these properties, the reflected waves coming back from the defect interface can be obtained, thereby enabling the detection of defects. 4) The energy of ultrasonic waves is much greater than that of sound waves. 5) Ultrasound suffers little transmission loss in solids, allowing for a large detection depth. However, ultrasound is reflected and refracted at heterogeneous interfaces, and in particular, it cannot pass through the gas-solid interface. If the metal contains defects such as pores, cracks, delamination (with gas within these defects), or inclusions, ultrasonic waves will be reflected entirely or partially when they reach the interface between the metal and these defects. The reflected ultrasonic waves are detected by the probe, processed by the circuits inside the instrument, and waveforms of different heights and at certain intervals are displayed on the instrument’s fluorescent screen. The depth, position, and shape of defects in the workpiece can be determined based on the characteristics of the waveform changes. 6) Disadvantages: The advantages of ultrasonic testing include the ability to detect thick components, high sensitivity, fast speed, low cost, and no harm to humans; it also enables the localization and quantification of defects. Ultrasonic testing does not provide an intuitive display of defects; it is a complex technique that is susceptible to both subjective and objective factors. Moreover, the test results are difficult to preserve. Ultrasonic testing requires a smooth working surface, and it needs experienced inspectors to identify different types of defects. It is suitable for inspecting parts with greater thicknesses, which are also the limitations of this testing method. 3 Ultrasonic Testing Steps 3.1 Preparation before testing ① Familiarize yourself with the workpiece to be tested (workpiece name, material, specifications, groove type, welding method, heat treatment status, surface condition of the workpiece, testing standards, acceptable quality level, testing ratio, etc.) ； ②Select the instrument and probe (determine the flaw detector, probe, test block, scanning ratio, detection sensitivity, and detection method based on standard requirements and site conditions). ③ Calibration of the instrument (measure the horizontal and vertical linearity of the instrument at the time it is first used). ) ④ Probe calibration (perform calibration for the front edge, refraction angle, main beam deviation, sensitivity margin, and resolution.) ) ⑤ Instrument adjustment (the time baseline scale can be adjusted proportionally to represent the horizontal distance, depth, or sound range of the pulse echo. ) ⑥ Adjustment of sensitivity (the sensitivity is verified using reference blocks or other equivalent test blocks. ) 3.2, Inspection Procedures ① Inspection of the base material: Before inspection, the wall thickness of the tube should be measured, with a measurement taken at least every 90° to serve as a reference during the inspection. Adjust the secondary bottom wave at the defect-free area to the full scale of the fluorescent screen as the detection sensitivity ； ②Inspection of welded joints: The scanning sensitivity should be no lower than that of the evaluation line (EL line); the scanning speed of the probe should not exceed 150 mm/s, and at least 10% overlap should exist between successive movements of the probe during scanning. 3.3 Test Results and Rating: The rating is determined based on the nature and severity of the defects, as well as the indicated length, in accordance with relevant standards. 3.4 Conduct calibration and re-inspection of instruments and equipment. 3.5 Issue a test report. Note: For welded joints with defects exceeding the specified limits, both the areas that require repair and the regions affected during the repair process must be re-inspected under the original inspection conditions. 4 Standard methods for non-destructive ultrasonic testing of metal materials JB/T 4730.3-2005 Non-destructive testing of pressure equipment – Ultrasonic testing GB/T 11345-1989 Methods for manual ultrasonic testing of steel welds and classification of test results CB/T 3559-2011 Ultrasonic testing procedures and quality classification for ship steel welds