Non-destructive testing

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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, which creates a local magnetic field. Magnetic powder then indicates the shape and location of the defects in these areas, thereby allowing the presence of such defects to be detected. IV. Describe the types of magnetic particle testing 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 classified into direct current magnetization method, half-wave direct current magnetization method, and alternating current magnetization method. 3. Depending on the formulation 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 inspection? 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 it 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 flux. Magnetic powder is attracted by this leakage magnetic flux. VIII. Discuss the factors that contribute to magnetic leakage Answer: 1. Magnetic permeability of defects: The lower the magnetic permeability of a defect, the stronger the magnetic leakage. 2. Magnitude of the magnetization magnetic field strength (magnetizing force): The greater the magnetizing force, the stronger the leakage flux. 3. Shape and size of the workpiece under inspection, as well as the shape, size, and depth of embedded defects: When other conditions are identical, the magnetic flux leakage caused by pores embedded 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 filings, causing frictional damage to those components during rotation, such as in shaft bearings and similar parts. The residual magnetism of certain parts can cause nearby instruments to give incorrect readings. Therefore, why are certain parts demagnetized after magnetic particle testing? X. What is the basic principle of ultrasonic flaw detection? Answer: Ultrasonic testing 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 surface 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 waves that appear on a fluorescent screen. The location and size of defects can be determined based on these pulse waves. XI. What are the advantages and disadvantages of ultrasonic testing compared to X-ray testing? Answer: Ultrasonic flaw detection offers advantages such as higher sensitivity, shorter inspection times, 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 larger thicknesses. 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 the defect is even smaller than the wavelength, sound waves will bypass the defect and not reflect ； 2. Sound waves have good directivity; the higher the frequency, the better the directivity, allowing them to be radiated into the medium as a very narrow beam, which facilitates the identification of defect locations. 3. Ultrasonic waves transmit a large amount of energy; for example, the energy transmitted by ultrasonic waves with a frequency of 1 MHz (100 hertz) is one million times that of sound waves 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 structure ； 2. Absorptive defects ； 3. Large tilt defect ； 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 electric current? Answer: Current refers to the regular movement of electrons under the action of an external force in a certain direction ； The direction of electric current is conventionally defined as flowing from the positive pole of the power source through the electrical device to the negative pole, which is in the opposite direction to the direction of electrons. 18. What is current intensity? Answer: Current intensity is the amount of electric charge that passes through the cross-section of a conductor per unit of time. Current is sometimes used as an abbreviation for current intensity, and it can be expressed as I = Q/T, where I represents current intensity, Q represents the amount of electric charge, and T represents time. 19. What is resistance? Answer: It refers to the resistance encountered by electric current as it flows through a conductor. At the same temperature, the resistances of different materials with identical length and cross-sectional area can differ significantly ； Resistance is denoted by “R”, with the unit being ohm, abbreviated as Ohm, represented by Ω. 20. What is voltage? Answer: It refers to the movement of positive and negative charges within a conductor under the influence of electrical power, to the ends of the conductor, thereby creating a potential difference. The unit of voltage is the volt, abbreviated as V, and is represented by the symbol “V”. 21. What is alternating current and what are its characteristics? Answer: Alternating current refers to a circuit in which the magnitude and direction of current, voltage, and electric potential are not constant, but rather change periodically. Its characteristic is that the magnitude and direction of current, voltage, and electric potential all undergo periodic changes over time ； AC motors used in industrial and mining enterprise equipment, as well as electrical devices for household lighting and everyday use, all rely on AC power as their power source ； Alternating current comes in three-phase and single-phase types, with voltages of 380 volts and 220 volts respectively. 22. What is direct current, and what are its characteristics? Answer: It refers to a current in which, at any given moment, the charge passing through the cross-section of a conductor per unit of time is constant, and its direction remains unchanged ； Its characteristic is that the magnitude and direction of current, voltage, and potential in the circuit do not change over time; they remain constant ； DC motors, electroplating, motor excitation, battery charging, semiconductor circuits, etc. 23. What is Ohm’s law? Answer: Ohm’s law reflects the interrelationship between resistance, voltage, and current in a circuit with a steady current flowing through it ； Ohm’s law states that the current flowing through a circuit is directly proportional to the voltage across the circuit, and inversely proportional to the resistance in the circuit ； That is, I = V / R. 24. 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, an electric 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. 25. Briefly explain what causes the attenuation of ultrasonic waves as they propagate through a medium in ultrasonic flaw detection Answer: 1. As the ultrasonic waves spread over a greater distance, their beam cross-section increases, resulting in less energy per unit area. 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. 26. What is the main function of the CSK-ⅡA test block? Answer: 1. Verification sensitivity ； 2. Calibrate scanning linearity. 27. 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. 28. When using ultrasonic waves to inspect large disc-shaped forgings, what requirements are there for the working bottom surface regarding the adjustment of the initial sensitivity using the bottom wave? Answer: 1. The bottom surface must be parallel to the flaw detection surface ； 2. The bottom surface must be flat and have a certain level of smoothness. 29. 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. 30. 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. 31. What is the main function of the transmitting 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, causing high-frequency vibrations and thus producing ultrasonic waves within the medium. 32. 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. 33. What are the three situations for identifying defects as specified in the JB1150－73 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. 34. What is the purpose of the distance-amplitude curve specified in the JB1150–73 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. 35. What is an ultrasound field? Answer: A space filled with ultrasonic field energy is called an ultrasonic field. 36. 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. 37. What is the most important performance indicator of a flaw detector? Answer: Resolution, dynamic range, horizontal linearity, vertical linearity, sensitivity, signal-to-noise ratio. 38. How many types are there for the near-display mode 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 projected 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. 39. 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 diffusion 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 operating frequency ； Suitable for different working conditions. 40. 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 excessive magnetization current that can cause arcing and sparks. Protective glasses should be worn, and this method should not be used in environments 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. 41. 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. 42. What is geometric ambiguity? Answer: The blur caused by the penumbra depends on the focus size, focal length, and workpiece thickness. 43. 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. 44. 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. 45. What is fixing? Answer: The process in which, while the developed film is in the developing solution, a fixing agent dissolves the undeveloped silver bromide on it while simultaneously protecting the black metallic silver particles is called fixing. 46. What is the basic principle of colored (penetrant) flaw detection? Answer: The basic principle of dye penetrant testing 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 those defects. 47. What are the main factors affecting the sensitivity of dye (penetrant) testing? Answer: 1. Influence of the properties of the penetrant ； 2. Influence of the emulsifying agent’s emulsification effect ； 3. Influence of imaging agent performance ； 4. Impact of operating methods ； 5. The influence of the nature of the defect itself. 48. 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. 49. What is the film developing process? Answer: Development, stopping, fixing, rinsing, drying. 50. What is conductivity? Answer: It refers to the property of metals to conduct electricity. 51. 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; magnetism can also be utilized to detect cracks in magnetic metals. 52. What is high voltage? Answer: Equipment with a voltage to ground of 250 volts or more is considered high-voltage. 53. What is low voltage? Answer: Equipment with a voltage to ground of 250 volts or less is considered low-voltage. 54. 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. 55. 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. 56. 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. 57. What should be done when unacceptable defects are found in welds inspected by local non-destructive testing? Answer: Supplementary radiographic testing should be conducted in the direction of the extension of the defect or at the suspected area. If doubts about the weld quality remain after additional inspections, the entire weld should be inspected. 58. 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 particle accumulation at the interface between two different materials ； 3. Microstructural segregation in the carbide layer ； 4. Magnetic marks at the sudden changes in the cross-sectional dimensions of the parts ； 5. Excessively high magnetizing current, resulting in magnetic marks caused by metal flow lines ； 6. Spotted magnetic marks caused by an unclean workpiece surface or oil contamination. 59. 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 the preparation of magnetic suspensions and fluorescent magnetic suspensions). 4. Test specimen ； 5. Technical operations ； 6. Quality assessment and inspection records. 60. What is the scope of application for magnetic particle testing? Answer: Magnetic particle testing is a testing method used to detect surface and near-surface defects in ferromagnetic materials. 61. 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 mainly control the synchronization transmission and synchronization scanning circuits. 62. What is the purpose of non-destructive testing? Answer: 1. Improve manufacturing processes ； 2. Reduce manufacturing costs ； 3. Increase the possibilities of the product ； 4. Ensure the safe operation of the equipment. 63. 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. 64. Compare the main advantages and disadvantages of the dry powder method and the wet powder method for testing? Answer: The dry powder method has a high ability to detect near-surface defects, making it particularly suitable for large-area or field flaw detection ； The wet powder method has a high ability to detect small surface defects, and is particularly suitable for bulk flaw detection of small parts with irregular shapes.