Application of ultrasonic flaw detection technology in non-destructive testing

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1 Principles, advantages, disadvantages, and basic classification methods of ultrasonic flaw detection  1.1 Principles of flaw detection  When utilizing ultrasonic flaw detection technology in non-destructive testing, it is necessary to first understand the basic principles of this technology and master its operational techniques. Only then can the practical value of this technology be fully realized, ensuring that the accuracy requirements for the testing process are met. Generally speaking, ultrasonic testing primarily relies on the reflection and refraction of ultrasonic waves. By analyzing the changes in the waveform when the sound waves come into contact with an object, it is possible to determine whether there are any internal defects. It is also necessary to use visualization equipment to plot the sound wave patterns, thereby observing the amplitude and frequency of the sound wave vibrations and calculating the depth and length of the defects. Furthermore, it also needs to be applied in pulse-echo devices, which are the core components for ensuring detection efficiency and quality; therefore, staff must possess the ability to operate these devices. 1.2 Advantages and disadvantages of the technology
1.2.1 Description of advantages
Ultrasonic testing relies on ultrasonic waves for detection. Its characteristics include a compact and portable detection device. The reflection effects of sound waves vary in different media; it is frequently used for assessing the quality of objects. Additionally, it exhibits distinct directivity. It can not only determine whether there are structural defects in an object, but also identify the location and severity of those defects, estimate the object’s utility value, and provide a reference for subsequent repair work. In addition, the overall technical operation process has a high safety factor. 1.2.2 Analysis of drawbacks At present, ultrasonic testing technology still needs further optimization. The key issue is that there are several difficult problems yet to be resolved when it comes to the quantitative and qualitative analysis of defects. For example, if the surface of an item is uneven, too small, or too thin, it cannot be inspected non-destructively using ultrasonic testing methods. Furthermore, for objects with cavities, the detection accuracy needs to be further improved. 1.3 Type of technology: (1) The method of reflecting ultrasonic waves is a relatively common type of ultrasonic testing, which focuses on the time and waveform of the sound waves as they reflect back to the instrument after passing through an object. (2) Depending on the coupling method, flaw detection methods can be classified into those involving direct contact with the object, those in which the object being inspected is immersed in a liquid, and those that use electromagnetic waves or lasers for indirect flaw detection. Each method has its own application value and usage conditions. In practical applications, based on the type and quantity of the objects to be tested, a comprehensive analysis should be conducted in terms of cost, convenience, accuracy, etc., in order to select the most suitable non-destructive testing method. (3) Based on the display of the flaw detection results, during the process of pulse signal reflection, depending on the type, quantity, placement location, and usage method of the instruments, there are three types of flaw detection techniques: Type A, Type B, and Type C. Type A has good application effects; it primarily accomplishes flaw detection by placing two points on the working surface, emitting sound waves, and receiving the reflected signals. Since its overall shape during operation resembles the letter A, it is called the Class A detection method. (4) With the advancement of science, technology, and information technology, intelligent flaw detection methods have emerged within ultrasonic flaw detection techniques; this requires professionals to possess the skills to operate these technologies and to carry out innovative research. 2 Basic principles for applying ultrasonic testing technology in non-destructive testing 2.1 Standardize the work process. Ultrasonic testing technology features high detection efficiency and a wide range of applications, offering significant practical value and good prospects for further development. However, when actually applying this technology, it is essential to ensure that personnel have practical operating experience and understand its principles. They must carry out each step of the operation in an orderly manner according to the prescribed procedures. During operations, they should be cautious and attentive, carefully identifying any issues that arise. These factors are crucial in determining the accuracy of detection, and thus require great attention from the staff. Since the human ear cannot directly receive ultrasonic signals, it is also necessary to ensure that the infrastructure is well-developed and that equipment testing is carried out in advance, so as to provide a solid foundation for the safety and stability of the detection process. 2.2 The principle of adaptability must be followed. Given the wide range of areas that require inspection, as well as the varying materials and sizes of the items to be inspected, and the fact that some items have complex structures, it is necessary to use ultrasonic inspection technology to carry out inspections without compromising the functional performance of those items; therefore, the principle of adaptability must be adhered to. A comparative analysis can be conducted based on the common types and characteristics of flaw detection techniques, allowing for the selection of the appropriate method; this is also a key prerequisite for reducing the difficulty of inspection work. 2.3 The object under inspection must not be damaged. When using ultrasonic testing techniques, it is necessary to comply with the regulations for non-destructive testing, ensuring that no irreversible damage is caused to the object. Given the characteristics of ultrasonic waves, many materials absorb sound waves; this is one of the key issues that technicians should pay attention to when optimizing detection methods and improving detection efficiency. Relevant work requirements should be integrated into the management system to ensure strict and comprehensive oversight of personnel’s technical skills and equipment operation practices. 3 Key Points of the Practical Application of Ultrasonic Testing Technology in the Non-Destructive Inspection of Tracks and Vehicles 3.1 Rail Inspection Rail transportation is one of the most commonly used modes of travel in people’s daily lives, and trains as well as high-speed trains are all types of rail vehicles that operate along pre-built tracks following predetermined routes. To reduce the maintenance costs of tracks and improve their durability, construction workers choose to use steel when carrying out track construction work. To prevent quality issues such as cracks and crushing in the rails during use, which could pose safety risks, it is necessary to carry out flaw detection without moving the rails or damaging their structural integrity. Taking the use of ultrasonic flaw detection technology as an example, it is necessary to bring the device’s probe into contact with the surface of the rail in order to transmit sound wave signals into the rail. Generally, when a signal encounters a location with internal defects, it will reflect the signal ； If there are no defects, the signal will pass straight through the rail without any reflection. Based on this, the staff only need to record the location where reflected signals appear on the working surface; by determining the time of reflection, they can calculate the distance between the internal defects and the detection surface. 3.2 Wheel Inspection Wheels are essential components for the stable and safe operation of vehicles. Moreover, as they are in constant contact with the ground, they wear out frequently. Therefore, when performing maintenance and repairs on vehicles, technicians need to pay special attention to inspecting the wheels for any defects. To ensure that the wheel can continue to be used after the inspection task is completed, non-destructive testing methods should be employed. Pay attention to testing the rim and the tire separately; taking the rim as an example, the main thing is to check whether cracks appear on this component. Generally, simulation tests are required, involving drilling and grooving on a sample wheel to simulate defect issues and study solutions. Furthermore, the probe of the ultrasonic detection device should be placed at the edge of the wheel, and an appropriate type of ultrasonic testing technique should be selected to detect various types of rim defects. For example, when performing phase compensation on acoustic wave signals, a phased array is required, which comes in two methods: longitudinal wave detection and transverse wave detection. Regarding circumferential and radial defects, it is not appropriate to use shear wave detection methods, and it is necessary to determine the placement position of the probe. For axial defects, it is possible to flexibly choose between using longitudinal waves or transverse waves depending on the actual situation; the key is to properly record the parameter information obtained during detection. 4 Key Points of the Practical Application of Ultrasonic Testing Technology in Non-Destructive Testing in the Construction Industry 4.1 Structural Strength After the construction of a building is completed, a comprehensive non-destructive testing should be carried out to determine whether the quality of the building meets the required standards and to identify any potential safety hazards. At the same time, during the regular daily use of buildings, non-destructive testing should also be carried out regularly to enable the early detection of safety risks in the buildings, allowing for timely implementation of effective measures to address those issues. Taking concrete structures as an example, during building construction, concrete is often used as the primary material for constructing walls, beams, and columns. During the inspection phase, the overall strength grade of the concrete structure should be tested in accordance with the building’s usage requirements. Ordinary workers are more concerned about the compressive strength of concrete. Based on work experience, it can be seen that when ultrasonic waves penetrate concrete, the elastic modulus of the concrete directly affects the speed at which these sound waves propagate.      Generally, the smaller the modulus, the slower the transmission speed; there is a direct proportional relationship between them. A mathematical model can be established to visually observe the changes in sound waves. Furthermore, to ensure that the coupling effect meets the requirements of non-destructive testing, the surface of the concrete structure should be cleaned first to maintain a smooth working surface. It is also possible to use a coupling agent to prevent the inspection results from being affected by other factors, thereby improving the accuracy of structural strength assessments. 4.2 Structural Thickness Construction work not only involves strict management of the quality of use of building structures, but also entails scientific control of the structural thickness in accordance with the requirements specified in the design plans. In thickness measurement tasks, ultrasonic testing technology can also be used. Based on the principles of this technology, the simplest method is to accurately determine the thickness of the structure by analyzing the reflection of sound waves. Generally, when sound waves pass from one solid into another, the waveform of the sound waves changes. During actual operation, it is necessary to fully take into account the changes in sound impedance values. A common practice is to install two probes at different locations on the same working surface of the building structure. The sound wave signals emitted by one probe are sent to the other probe through refraction, reflection, and other mechanisms. By applying the principles of trigonometry, along with the distance between the two probes as well as the length and angle of sound wave refraction, it is possible to calculate the vertical height. This allows for an accurate determination of the structure’s thickness. By comparing the actual values with the design specifications, construction errors can be identified. 4.3 Welding Joints Many metal materials are used in the construction of building structures, and depending on the design characteristics of the building framework, cutting and welding processes for these materials are also required. Therefore, the connection condition of each weld point is a key issue that construction workers need to pay attention to in quality management. In the new era, ultrasonic flaw detection technology can be used to effectively detect welding gaps. First, staff need to understand the common types and characteristics of welding quality issues. Secondly, an appropriate choice of ultrasound technology is necessary. For example, pulse-echo methods can be used to detect whether there are gaps at the welding points, while phased arrays combined with imaging techniques can be employed to identify defects at the welded areas. Especially in the installation of underground pipelines, this method can be used to comprehensively inspect whether there are any cracks or leaks in the pipes; it is necessary to conduct a thorough analysis of the resulting images. After completing the detection tasks, it is possible to estimate the service life of materials, providing reference data for the timely replacement of new materials and ensuring that the utility value of building frame structures and underground pipelines can be fully utilized. 5 Key points regarding the practical application of ultrasonic testing technology in non-destructive testing in other fields. 5.1 Inspection of composite materials. In the process of material production and manufacturing, relevant enterprises produce composite materials based on the market’s demand for various types of materials. Taking composite bars as an example, when non-destructive testing is carried out during the production process, electromagnetic ultrasonic testing is a technique that is used quite frequently. Compared to pulse-echo methods, this technique relies on the principle of electromagnetic induction to divide the material’s surface and interior into different areas, thereby enabling defect detection in each of those areas. Serpentine coils can be used to control the winding direction and current direction at both ends. When defects are detected, the resulting electromagnetic waves are scanned, and the specific characteristics of these defects are analyzed visually through graphs, thereby enabling systematic repair of the defects. 5.2 Inspection of high-temperature equipment: Electromagnetic ultrasonic testing technology can be used for high-temperature inspections, and it also yields good results when inspecting certain high-temperature pressure pipelines. Therefore, in many applications related to the storage and transportation of new energy sources, this inspection technology can be utilized to address quality issues of equipment containers. Its advantages include the fact that it does not require direct contact with the equipment, and it has no stringent requirements regarding the surface smoothness of the objects being inspected. However, electricity is required for operation, so the issue of conversion efficiency should be given due consideration. 6 Conclusion The common ultrasonic testing methods involve using pulse-echo devices to transmit sound waves into an object, and completing the testing process based on the refraction and reflection of these sound waves; electromagnetic ultrasonic testing technology can also be employed. When conducting tests on the quality of rails and wheels, as well as on the strength, thickness, and welding seams of building structures, as well as testing composite materials and high-temperature equipment, it is necessary to ensure that the infrastructure is in good condition, to determine scientifically the placement of the testing probes, and to keep the work area clean. In most cases, the proper use of coupling agents is an effective way to improve detection performance. Pay attention to enhancing talents’ innovation awareness and professional skills, so as to ensure they can use equipment and technologies flexibly to achieve the objectives of non-destructive testing.