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I. What is non-destructive testing? Answer: Non-destructive testing is a testing method used to examine the surface and internal quality of components being inspected, without damaging the condition of the workpiece or raw material. II. What are the common flaw detection methods? Answer: Common non-destructive testing methods include X-ray testing, ultrasonic testing, magnetic particle testing, penetrant testing, eddy current testing, gamma ray testing, fluorescent testing, and dye penetrant testing. III. Explain the principle of magnetic particle testing? Answer: Its basic principle is as follows: when the workpiece is magnetized, if there are defects on its surface, the increased magnetic resistance at those defects causes magnetic leakage, resulting in a local magnetic field. Magnetic powder then indicates the shape and location of the defects at these areas, thereby allowing the detection of their presence. IV. Describe the types of magnetic particle testing Answer: 1. Depending on the magnetization direction of the workpiece, it can be divided into circumferential magnetization, longitudinal magnetization, combined magnetization, and rotational magnetization methods. 2. Based on the type of magnetizing current used, they can be divided into: direct current magnetization method, half-wave direct current magnetization method, and alternating current magnetization method. 3. Depending on the preparation method of the magnetic powder used for flaw detection, it can be divided into the dry powder method and the wet powder method. V. What are the defects in magnetic particle testing? Answer: Magnetic particle inspection equipment is simple to use, easy to operate, allows for rapid inspections, and possesses high sensitivity for detecting defects on the surface or near the surface of ferromagnetic materials such as nickel, cobalt and their alloys, carbon steel, and certain alloy steels ； It is suitable for inspecting thin-walled parts or surface cracks in welds, and can also reveal under-welding defects of certain depth and size ； However, it is difficult to detect pores, inclusions, and defects hidden deep within the weld. VI. Into how many categories can defect magnetic traces be divided? Answer: 1. Magnetic traces of various process-related defects. 2. Magnetic marks caused by slag in the material. 3. Spot-shaped magnetic marks caused by slag inclusions and pores. VII. Explain the reasons for magnetic leakage Answer: Since the magnetic susceptibility of ferromagnetic materials is much greater than that of non-ferromagnetic materials, based on the formula for magnetic flux density B = μH after the workpiece is magnetized, B magnetic lines pass through each unit area of the workpiece. However, a certain number B of magnetic lines cannot pass through each unit area in the defective region; this forces some of the magnetic lines to penetrate into the material beneath the defect, while the remaining magnetic lines are forced to escape from the surface of the workpiece, resulting in leakage magnetic field. Magnetic powder is attracted by this leakage magnetic field. VIII. Discuss the factors that contribute to magnetic leakage Answer: 1. Magnetic permeability of the defect: The lower the magnetic permeability of the defect, the stronger the magnetic leakage. 2. Magnification field strength (magnetizing force): The greater the magnetizing force, the stronger the leakage magnetic field. 3. Shape and size of the workpiece under inspection, as well as the shape, size, and depth of defects: When all other conditions are equal, the magnetic flux leakage caused by pores buried at the same depth beneath the surface is less than that caused by transverse cracks. IX. Why do certain parts need to be demagnetized after magnetic particle testing? Answer: The residual magnetism of certain rotating components can attract iron particles, causing frictional damage to those components during rotation, such as in shaft bearings and similar parts. The residual magnetism of certain parts can cause the nearby instruments to give incorrect readings. Therefore, why are certain parts demagnetized after magnetic particle inspection? X. What is the basic principle of ultrasonic flaw detection? Answer: Ultrasonic flaw detection is a method for detecting defects in parts by utilizing the property that ultrasonic waves can penetrate deep into metal materials; when they pass from one cross-section to another, they are reflected at the interface edges. When the ultrasonic wave beam travels from the surface of the part through a probe into the metal, it is reflected upon encountering defects or the bottom surface of the part, resulting in pulse waveforms on a fluorescent screen. The location and size of defects can be determined based on these pulse waveforms. XI. What are the advantages and disadvantages of ultrasonic testing compared to X-ray testing? Answer: Ultrasonic flaw detection offers advantages such as higher detection sensitivity, shorter inspection time, lower costs, flexibility and convenience, higher efficiency, and no harm to the human body, compared to X-ray flaw detection ； The disadvantages are that it requires a smooth working surface, experienced inspectors to identify different types of defects, and there is no visual indication of the defects ； Ultrasonic flaw detection is suitable for inspecting parts with greater thickness. XII. What are the main characteristics of ultrasonic flaw detection? Answer: 1. When ultrasonic waves propagate through a medium, they have the property of reflecting at different material interfaces. If they encounter defects whose size is equal to or greater than the wavelength of the ultrasonic waves, the waves are reflected back from those defects, and the flaw detector can display these reflected waves ； When the size of a defect is even smaller than the wavelength, sound waves will bypass it rather than being reflected ； 2. Sound waves have good directionality; the higher the frequency, the better the directionality, allowing them to be radiated into the medium as a very narrow beam, which facilitates the identification of defect locations. 3. Ultrasonic waves convey a large amount of energy; for example, the energy transmitted by an ultrasonic wave with a frequency of 1 MHz (100 hertz) is one million times that of an acoustic wave with the same amplitude but a frequency of 1000 Hz. 13. When the thickness of the ultrasonic flaw detection plate is 14 millimeters, what is the relationship among the three main curves on the distance-amplitude curve? Answer: The length measurement line is Ф1 x 6 –12dB; the quantitative line is Ф1 x 6 –6dB; the scale line is Ф1 x 6 –2dB. 14. What does it mean for a ray to be “soft” or “hard”? Answer: The ability of X-rays to penetrate materials is related to the wavelength of the rays themselves; the shorter the wavelength (the higher the tube voltage), the greater its penetrating power, which is referred to as \"hard\"” ； The opposite is called “soft”. 15. What could be the reasons for the disappearance of the bottom wave during ultrasonic flaw detection? Answer: 1. Major defects in the near-table. 2. Absorptive defects. 3. Large tilt defects. 4. The scale does not bond well to the steel plate. 16. What are the main factors affecting development? Answer: 1. Development time. 2. Developer temperature. 3. Shaking of the developing solution. 4. Formula type. 5. Degree of aging. 17. What is electromagnetic induction? Answer: The phenomenon in which the magnetic flux through a closed loop changes, thereby generating an electromotive force in that loop, is called electromagnetic induction ； The electromotive force generated in this way is called induced electromotive force. If the conductor forms a closed circuit, a current will flow through it, and this current is known as induced current ； Transformers, generators, and various inductors all operate based on the principle of electromagnetic induction. 18. Briefly explain what causes the attenuation of ultrasonic waves as they propagate through a medium in ultrasonic flaw detection Answer: 1. The propagation distance of ultrasonic waves increases, the beam cross-section grows larger, and the energy per unit area decreases. 2. Material attenuation is first caused by absorption due to the viscosity of the medium ； The second is the scattering caused by chaotic reflections at the medium interface. 19. What is the main purpose of the CSK-IIA test block? Answer: 1. Verify sensitivity. 2. Calibrate scan linearity. 20. What are the main factors affecting photographic sensitivity? Answer: 1. The size of the focal point of the X-ray machine. 2. The rationality of the selection of exposure parameters, with the main parameters being tube voltage, tube current, exposure time, and focal length. 3. Sensitization method. 4. Rationality of film selection. 5. Darkroom processing conditions. 6. Scattering obstruction, etc. 21. When using ultrasonic waves to inspect large disc-shaped forgings, what are the requirements for the working bottom surface when adjusting the initial sensitivity of detection using the bottom wave? Answer: 1. The bottom surface must be parallel to the inspection surface. 2. The bottom surface must be flat and have a certain level of smoothness. 22. What are the three principles for selecting the K value of a probe in ultrasonic flaw detection? Answer: 1. The beam scans the entire weld cross-section. 2. The sound beam should be as perpendicular as possible to the main defect. 3. It has sufficient sensitivity. 23. What are the main components of an ultrasonic flaw detector? Answer: It mainly consists of components such as a circuit synchronization circuit, a transmission circuit, a reception circuit, a horizontal scanning circuit, a display, and a power supply. 24. What is the main function of the firing circuit? Answer: The synchronous pulse signal input by the synchronization circuit triggers the transmission circuit to operate, generating high-frequency electrical pulse signals that excite the crystal, resulting in high-frequency vibrations and the production of ultrasonic waves within the medium. 25. In ultrasonic flaw detection, what is the reason for using a coupling agent between the surface of the crystal chip and the surface of the workpiece being inspected? Answer: The air gap between the chip surface and the surface of the workpiece being inspected causes the ultrasonic waves to be completely reflected, resulting in inaccurate inspection results and an inability to conduct the inspection. 26. What are the three situations for identifying defects as specified in the JB1150 standard? Answer: 1. Without a bottom wave, there are only the multiple reflection waves of the defect. 2. There are no bottom waves; only multiple chaotic defect waves. 3. Defect waves and bottom waves exist simultaneously. 27. What is the purpose of the distance-amplitude curve specified in the JB1150 standard? Answer: The distance-amplitude curve is primarily used to determine the size of defects and to provide a basis for acceptance criteria; it consists of three curves: the rejection line, the quantification line, and the length measurement line ； Reject line – the maximum allowable equivalent for defect detection ； Quantitative line – a control line used to determine the size and length of defects ； Length measurement line – the sensitivity control line for starting flaw detection. 28. What is an ultrasound field? Answer: A space filled with ultrasonic field energy is called an ultrasonic field. 29. What are the main parameters that reflect the characteristics of an ultrasound field? Answer: Important physical quantities that characterize an ultrasound field include sound intensity, sound pressure and acoustic impedance, beam divergence angle, as well as the near-field and far-field regions. 30. What is the most important performance indicator of a flaw detector? Answer: Resolution, dynamic range, horizontal linearity, vertical linearity, sensitivity, signal-to-noise ratio. 31. How many types are there for the near-display methods of ultrasonic flaw detectors? Answer: 1. In Type A display, the horizontal axis of the oscilloscope screen represents the time (or distance) taken for the ultrasound to travel, while the vertical axis represents the amplitude of the reflected echo. 2. In Type B display, the horizontal axis of the oscilloscope screen represents the time (or distance) taken for the ultrasound to travel; this type of display provides a cross-sectional view in the direction of depth scanned by the probe. 3. The oscilloscope screen of a Type C display instrument represents the projection surface of the workpiece under inspection; this type of display can show the horizontal position of defects, but it cannot indicate the depth to which those defects are embedded. 32. What is the main function of an ultrasonic probe? Answer: 1. The probe is an electroacoustic transducer that can convert the returning sound waves into electrical pulses. 2. Control the direction of ultrasonic wave propagation and the degree of energy concentration. By changing the incident angle of the probe or the divergence angle of the ultrasonic waves, the main energy of the sound waves can be directed into the medium at different angles, or the directivity of the sound waves can be altered to improve resolution. 3. Achieve waveform conversion. 4. Control the operating frequency ； Suitable for different working conditions. 33. What are the safety operation requirements for magnetic particle probes? Answer: 1. When the workpiece passes directly through the magnetization process, be careful of poor contact between the chucks, or the use of an excessively high magnetization current that can cause arcing and sparks. Protective glasses should be worn, and this method should not be used in areas where flammable gases may be present. 2. When using the wet magnetic suspension continuously, a protective ointment can be applied to the skin. 3. When used in a water-magnetic suspension system, the equipment must be properly grounded to prevent electric shock. 4. When using cocoon fire magnetic powder, the ultraviolet light used must pass through a filter to protect the eyes and skin. 34. What is resolution? Answer: It refers to the minimum distance between recognizable images on a radiographic film or fluorescent screen, and is usually expressed as the number of recognizable lines per 1 millimeter. 35. What is geometric ambiguity? Answer: The blur caused by the penumbra depends on the focus size, focal length, and workpiece thickness. 36. Why is it necessary to strengthen the compilation and reporting of ultrasonic flaw detection work? Answer: After any workpiece is inspected using ultrasonic testing, an inspection report must be issued as proof of its quality. A proper inspection report relies not only on reliable testing methods and results but also to a large extent on the original records. It is extremely important to issue a proper inspection report; if we inspect a workpiece without taking any records or issuing a report, then such testing is meaningless. 37. Why are sensitivity test pieces used in magnetic particle inspection? Answer: The purpose of using sensitive test pieces is to evaluate the performance of magnetic powder and magnetic suspension, as well as to determine factors such as the effective magnetic field strength and direction on the surface of the test piece in the continuous method, and to check whether the operating procedures are correct. 38. What is fixing? Answer: The process in which, while the developed film is still in the developing solution, a fixing agent dissolves the undeveloped silver bromide on its surface while simultaneously protecting the black metallic silver particles is called fixing. 39. What is the basic principle of dye penetrant testing? Answer: The basic principle of colored (penetrant) flaw detection is to use capillary action to allow the penetrant to penetrate into defects; after cleaning, the surface penetrant is removed, while the penetrant remaining in the defects is drawn out using the capillary action of the developer, thereby enabling the detection of defects. 40. What are the main factors affecting the sensitivity of coloring (penetrant) flaw detection? Answer: 1. Influence of the performance of the penetrant. 2. Influence of the emulsifying agent’s emulsification effect. 3. Influence of the imaging agent’s properties. 4. Impact of the operation method. 5. The influence of the nature of the defect itself. 41. How are defects in welds classified in ultrasonic flaw detection? How to classify? Answer: In ultrasonic testing of welds, defects in the weld are generally classified into three categories: point defects, linear defects, and surface defects. In classification, defects with a length of less than 10 mm are referred to as point defects ； Generally, length is not measured; defects smaller than 10 mm are counted as 5 mm. Defects with a length greater than 10 mm are called linear defects. Defects with a length greater than 10 mm and a height greater than 3 mm are called planar defects. 42. How is the film developing process? Answer: Development, stopping, fixing, rinsing, drying. 43. What is conductivity? Answer: It refers to the property of metals to conduct electricity. 44. What is magnetism? Answer: It refers to the property of metals to conduct magnetism ； In practical terms, for example: magnetic materials (metals) can be used to manufacture permanent magnets and electrical materials, and magnetism can also be utilized to detect cracks in magnetic metals. 45. What is high pressure? Answer: Equipment with a voltage to ground of 250 volts or more is considered high-voltage. 46. What is low voltage? Answer: Equipment with a voltage to ground of 250 volts or less is considered low-voltage. 47. What is safe voltage? Answer: When a person comes into contact with a live conductor, a voltage below 36 volts, which does not pose a life-threatening risk, is generally considered a safe voltage. A safe voltage of 12 volts is used for electrical lighting in workplaces that are humid, or inside metal containers, tunnels, and mines. 48. What is the function of ultrasonic test blocks? Answer: The purpose of ultrasonic test blocks is to verify the performance of instruments and probes, determine the starting sensitivity for flaw detection, and calibrate the scanning linearity. 49. What is the correct value of the refraction angle β for an oblique probe? Answer: The correct value of the refraction angle for an angled probe is called the K value; it equals the ratio of the horizontal distance from the emission point of the angled probe to the reflection point to the corresponding depth. 50. What should be done when unacceptable defects are found in welds inspected by local non-destructive testing? Answer: Supplementary radiographic inspection should be conducted in the direction of the extension of the defect or at the suspected area. If doubts about the weld quality persist after additional inspections, the entire weld should be inspected. 51. How many types of magnetic marks are there that are not caused by defects? Answer: 1. Local cold work hardening, resulting from the accumulation of magnetic marks caused by changes in the material’s magnetic permeability. 2. Magnetic powder accumulation at the interface between two different materials. 3. Segregation in the structure of the carbide layer. 4. Magnetic flaw at the sudden change in the cross-sectional dimensions of the part. 5. Excess magnetizing current, resulting in magnetic marks caused by metal flow lines. 6. Spotted magnetic marks caused by an unclean workpiece surface or oil contamination. 52. What does a magnetic particle inspection procedure include? Answer: 1. Scope of application of the regulations. 2. Magnetization methods (including magnetization specifications and surface preparation of the workpiece). 3. Magnetic powder (including particle size, color, and preparation of magnetic suspension and fluorescent magnetic suspension). 4. Test specimens. 5. Technical operations. 6. Quality assessment and inspection records. 53. What are the applicable scopes of magnetic particle testing? Answer: Magnetic particle testing is a method used to detect surface and near-surface defects in ferromagnetic materials. 54. What is the main function of the synchronization signal generator in an ultrasonic flaw detector? Which two main parts of the circuit does it control? Answer: Synchronization circuits generate synchronization pulse signals to trigger the various components of the instrument to operate in coordination; they primarily control the synchronization transmission and synchronization scanning circuits. 55. What is the purpose of non-destructive testing? Answer: 1. Improve the manufacturing process. 2. Reduce manufacturing costs. 3. Increase the possibilities of the product. 4. Ensure the safe operation of the equipment. 56. What are the various methods for adjusting the time scanning line of the instrument used for defect location during ultrasonic weld inspection? Answer: There are three methods: horizontal positioning, vertical positioning, and sound range positioning. 57. What are the advantages and disadvantages of visual inspection (VT)? Answer: Visual inspection is a primary method in the first stage of non-destructive testing, which is rarely used in China but is given great importance internationally. In accordance with international practices, visual inspection is carried out first to ensure it does not affect subsequent tests, after which the four standard tests are performed. For example, BINDT’s PCN certification includes specialized assessments at levels VT1, VT2, and VT3, as well as specific requirements for holding the certificate. Thanks to international-level training, its VT testing technology is quite professional and is highly valued by international organizations. VT is often used for visual inspection of welds. There are standard criteria for evaluating weld quality, and preliminary inspections can be carried out through visual inspection and direct measurement of dimensions. Any defective appearances such as undercutting must be polished or corrected first, before more in-depth instrumental testing is conducted. For example, VT is more commonly used on the surfaces of welded parts and castings, while it is rarely used in forgings; moreover, their inspection standards are basically similar. 58. What are the advantages and disadvantages of radiography (RT)? Answer: It refers to a non-destructive testing method in which X-rays or gamma rays are used to penetrate the test specimen, with film serving as the medium for recording information. This method is the most basic and widely used type of non-destructive inspection technique. 1. Principle of radiographic inspection: Rays can penetrate materials that are invisible to the naked eye, thereby exposing the film. When X-rays or gamma rays illuminate the film, they, just like ordinary light, cause silver halides in the film’s emulsion layer to develop latent images. Since materials with different densities have varying absorption coefficients for these rays, the energy of the rays reaching different parts of the film varies as well; thus, defects can be identified by examining the differences in darkness across various areas of the film after darkroom processing. 2. Characteristics of radiography: The advantages and limitations of radiography are summarized as follows: a. It enables the acquisition of intuitive images of defects, with accurate qualitative assessment; quantitative measurement of length and width dimensions is also relatively precise ； b. The test results are directly recorded and can be preserved for a long time ； c. It has a high detection rate for volume defects (porosity, slag inclusions, tungsten inclusions, burn-through, undercutting, weld beads, pits, etc.), but for area defects (incomplete penetration, lack of fusion, cracks, etc.), it is easy to miss them if the photography angle is not appropriate ； d. It is suitable for inspecting workpieces with thin thicknesses but not those with thicker thicknesses, as inspecting thick workpieces requires high-energy radiation equipment, and its inspection sensitivity decreases as the thickness increases ； e. Suitable for inspecting butt welds, but not suitable for inspecting fillet welds as well as plates, bars, forgings, etc ； f. It is relatively difficult to determine the position and size (height) of defects in the thickness direction of the workpiece ； g. High detection costs and slow speed ； h. It has radiobiological effects; ultrasonic flaw detectors used for non-destructive testing are capable of killing biological cells, damaging biological tissues, and compromising the normal function of biological organs. In general, the characteristics of RT are – more accurate qualitative results, intuitive images that can be stored for long periods, relatively high overall costs, as well as the fact that radiation is harmful to the human body, which results in slower inspection speeds. Non-destructive testing X-ray machines: The industrial X-ray machines used in the manufacturing sector are typically non-destructive testing X-ray devices; such portable X-ray machines can be used to inspect various industrial components, electronic parts, and the interiors of circuits. For example, the inspection of internal wiring connections in socket plugs and plugs, as well as the welding inside diodes. Industrial inspection X-ray machines such as BJI-XZ and BJI-UC are those that can be connected to a computer for image processing; these portable industrial inspection X-ray machines offer excellent solutions for the field of home appliance repair in manufacturing industries. 59. Advantages and disadvantages of ultrasonic testing (UT): Answer: 1. Definition of ultrasonic testing: It is a technique that involves using ultrasonic waves to interact with the test specimen; by studying the waves that are reflected, transmitted, and scattered, it enables the detection of macroscopic defects in the specimen, as well as the measurement of its geometric properties and the identification of changes in its structural composition and mechanical properties. This technique also allows for an assessment of the specimen’s suitability for specific applications. 2. Principle of ultrasonic operation: It is mainly based on the propagation characteristics of ultrasonic waves within the test specimen. a. The sound source generates ultrasonic waves, which are then introduced into the test specimen in a certain manner ； b. Ultrasonic waves propagate through the test specimen and interact with the specimen material as well as any defects within it, causing their direction of propagation or characteristics to be altered ； c. The modified ultrasonic waves are received by the detection equipment, where they can be processed and analyzed ； d. Based on the characteristics of the received ultrasound, evaluate whether there are defects in the specimen itself and within it, as well as the characteristics of those defects. 3. Advantages of ultrasonic testing: a. Suitable for non-destructive testing of various materials such as metals, non-metals, and composite materials ； b. It has strong penetration capability, enabling the detection of internal defects in specimens with a wide range of thicknesses. For metal materials, it can detect thin-walled tubes and sheets with a thickness of 1–2 mm, as well as steel forgings several meters in length ； c. Defect location is relatively accurate ； d. Higher detection rate for area-type defects ； e. High sensitivity, capable of detecting defects with very small sizes inside the test specimen ； f. It features low detection costs and fast speed, lightweight equipment, no harm to humans or the environment, and is convenient for use on-site. 4. Limitations of ultrasonic testing: a. Further research is still needed to accurately characterize and quantify defects in the test specimen ； b. Ultrasonic testing of specimens with complex shapes or irregular outlines is difficult ； c. The location, orientation, and shape of the defects have a certain impact on the detection results ； d. Materials, grain size, etc., have a significant impact on the detection ； e. When detected using the commonly used manual Type A pulse-echo method, the results are not intuitive, and there is no direct documentation serving as evidence of the detection results. 5. Scope of application for ultrasonic testing: a. In terms of the material being tested, it can be used for metals, non-metals, and composite materials ； b. In terms of the manufacturing process of the components to be inspected, it can be applied to forgings, castings, welded parts, bonded parts, etc ； c. In terms of the shape of the object to be inspected, it can be used for sheets, bars, tubes, etc ； d. In terms of the size of the object to be inspected, the thickness can range from as low as 1 mm to several meters ； e. In terms of the location of the defect, it can be either a surface defect or an internal defect. 60. Magnetic Particle Testing (MT) Answer: 1. Principle of magnetic particle testing: When ferromagnetic materials and workpieces are magnetized, the presence of discontinuities causes local distortions in the magnetic field lines on the surface and near the surface of the workpiece, resulting in a leakage magnetic field. This leakage field attracts magnetic particles applied to the surface of the workpiece, forming magnetic traces that are visible under appropriate lighting; thus, the location, shape, and size of the discontinuities can be identified through magnetic particle testing. 2. Applicability and limitations of magnetic particle testing: a. Magnetic particle inspection is suitable for detecting discontinuities on the surface and near the surface of ferromagnetic materials that are very small in size and have extremely narrow gaps – such as cracks that are 0.1 mm long and only a few microns wide – discontinuities that are difficult to detect visually. b. Magnetic particle testing can be used to inspect raw materials, semi-finished products, finished components, as well as components in use. It can also be applied to sheets, profiles, tubes, bars, welded parts, cast steel parts, and forged steel parts. c. Defects such as cracks, inclusions, grain boundaries, white spots, folds, cold shuts, and porosity can be detected. d. Magnetic particle testing cannot be used to inspect austenitic stainless steel materials or welds made with austenitic stainless steel electrodes, nor can it be used to inspect non-magnetic materials such as copper, aluminum, magnesium, and titanium. Shallow surface scratches, deeply buried holes, as well as delaminations and folds with an angle of less than 20° to the workpiece surface are difficult to detect. 61. Advantages and disadvantages of penetrant testing (PT) Answer: 1. Basic principle of liquid penetrant testing: After a penetrant containing fluorescent or colored dyes is applied to the surface of a part, under capillary action, it penetrates into any surface defects after a certain period of time ； After removing the excess penetrant from the surface of the part, a developer is applied to that surface. Once again, due to capillary action, the developer attracts the penetrant remaining in the defects; this penetrant then returns into the developer. Under certain light sources (ultraviolet light or white light), the traces of penetrant in the defects become visible, appearing as yellow-green fluorescence or bright red, thereby allowing the shape and distribution of the defects to be detected. 2. Advantages of penetrant testing: a. It can detect various materials, metal and non-metal materials ； Magnetic, non-magnetic materials ； Processing methods such as welding, forging, and rolling ； b. It has high sensitivity (able to detect defects 0.1μm wide). c. It provides intuitive display, is easy to operate, and has low detection costs. 3. Disadvantages and limitations of penetrant testing: a. It can only detect surface-opening defects ； b. Not suitable for inspecting workpieces made of porous, loose materials and workpieces with rough surfaces ； c. Penetrant testing can only detect the surface distribution of defects; it is difficult to determine the actual depth of these defects, which makes it hard to provide a quantitative assessment of them. The detection results are also greatly affected by the operator. 62. Advantages and disadvantages of eddy current testing (ET). Answer: 1. Basic principle of eddy current testing: A coil carrying alternating current is placed on the metal plate to be inspected or wrapped around the metal tube to be inspected. At this point, an alternating magnetic field is generated within the coil and in its vicinity, which induces an eddy-current-like alternating current in the test piece; this current is known as an eddy current. The distribution and magnitude of eddy currents depend not only on the shape and size of the coil, as well as the amplitude and frequency of the alternating current, but also on the electrical conductivity and magnetic permeability of the test piece, its shape and size, the distance from the coil, and the presence of cracks or defects on its surface. Therefore, by measuring the magnetic field changes induced by eddy currents using a detection coil while keeping other factors relatively constant, it is possible to determine the magnitude and phase changes of the eddy currents in the test specimen, thereby obtaining information regarding changes or defects in conductivity, defects, material condition, and other physical properties such as shape and size. However, since the eddy current is an alternating current with a skin effect, the information detected can only reflect the conditions on the surface or near the surface of the test piece. 2. Applications: Depending on the shape of the test specimen and the purpose of the inspection, different types of coils can be used; typically, there are three types: through-type, probe-type, and insert-type coils. A through-type coil is used to inspect tubes, bars, and wires; its inner diameter is slightly larger than that of the object being inspected. During use, the object in question is passed through the coil at a certain speed, allowing defects such as cracks, inclusions, and pits to be detected. Probing coils are suitable for local inspection of test specimens. When in use, the coil is placed on metal plates, tubes, or other components to detect fatigue cracks on the inner tubes of aircraft landing struts and on turbine engine blades. An insert-type coil, also known as an internal probe, is placed inside the holes of pipes or components to inspect their inner walls; it can be used to determine the degree of corrosion on the inner surfaces of various pipes. To improve detection sensitivity, probe-type and insert-type coils are mostly equipped with magnetic cores. The eddy current method is primarily used for the rapid inspection of metal tubes, bars, and wires on production lines, as well as for flaw detection of large quantities of parts such as bearing balls and valve components (in which case, in addition to eddy current instruments, mechanical devices for automatic loading, unloading, and transportation are also required). It is also used for material sorting and hardness measurement, and can be employed to measure the thickness of coatings and films. 3. Advantages and disadvantages: During eddy current testing, the coil does not need to be in direct contact with the object being inspected, which allows for high-speed testing and facilitates automation. However, this method is not suitable for parts with complex shapes; it can only detect surface and near-surface defects in conductive materials. Moreover, the test results are prone to being affected by the material itself and other factors. 63. Conventional non-destructive testing methods include: Answer: Ultrasonic Testing (abbreviated as UT) ； Radiographic Testing (abbreviated as RT) ； Magnetic particle Testing (abbreviated as MT) ； Penetrant Testing (abbreviated as PT) ； Eddy current Testing (abbreviated as ET) ； 64. Unconventional non-destructive testing techniques include: Answer: Acoustic Emission (abbreviated as AE) ； Leak Testing (abbreviation: UT) ； Optical Holography ； Infrared Thermography ； Microwave Testing. 65. NDT stands for Non-destructive testing. Answer: NDT refers to a testing method applied to materials or workpieces without damaging them or affecting their future performance or intended use. By using NDT, it is possible to detect defects existing inside and on the surface of materials or workpieces, to measure their geometric characteristics and dimensions, and to determine the internal composition, structure, physical properties, and condition of the materials or workpieces. NDT can be applied in various areas such as product design, material selection, manufacturing, final product inspection, and in-service inspection (maintenance), playing a key role in optimizing quality control and reducing costs. NDT also helps to ensure the safe operation and/or effective use of products. NDT encompasses a variety of methods that can be effectively applied, with the most commonly used NDT methods including radiographic testing, ultrasonic testing, eddy current testing, magnetic particle testing, penetrant testing, visual inspection, leak detection, acoustic emission testing, and fluoroscopic testing. Since various NDT methods each have their own scope of application and limitations, new NDT methods are continually being developed and applied. Generally, as long as it meets the basic definition of NDT, any physical, chemical, or other possible technical method can be developed into an NDT method. In our country, the term \"non-destructive testing\" was initially referred to as \"flaw detection\" or \"non-destructive flaw detection.\" The various methods used for this purpose were also called flaw detection methods, such as radiographic testing, ultrasonic testing, magnetic particle testing, penetrant testing, and so on. This term or notation has been widely spread and is still in use to this day; its frequency of use is no less than that of the term \"non-destructive testing\".