Application of Acoustic Emission Detection Technology in Water Conservancy and Hydropower Engineering

Application of Acoustic Emission Detection Technology in Water Conservancy and Hydropower Engineering

Acoustic emission detection technology is a dynamic detection technology that can provide real-time information on the defects in the components that generate acoustic emission sources under the influence of external loads and other factors. It is suitable for online monitoring, safety assessment and early warning of dangerous situations. It can solve problems that conventional non-destructive testing methods cannot solve. Through application examples in water conservancy and hydropower projects, it has been proved that acoustic emission detection technology is an effective means for online monitoring and safety assessment of metal structures and electromechanical equipment in water conservancy and hydropower projects.
The phenomenon that materials generate transient elastic waves due to the rapid release of energy from local sources under the influence of external loads and other factors is called acoustic emission (AE for short). Acoustic emission is a common physical phenomenon, such as seismic waves, rock crushing, metal cracking and broken lead cores. The frequency range of acoustic emission signals of various materials is very wide (from several Hz to several MHz), and the amplitude range of acoustic emission signals is also very large. Some acoustic emission signals can be heard by the human ear, while some acoustic emission signals cannot be heard by the human ear. The acoustic emission signal intensity of many materials is very weak and requires the help of special detection instruments to detect them. The deformation and cracking of materials under stress are important mechanisms of structural failure. This source directly related to the deformation and fracture mechanism is called an acoustic emission source. The technology of using instruments to detect, record, analyze acoustic emission signals and use acoustic emission signals to infer the acoustic emission source is called acoustic emission testing (AET) technology.
As a means of non-destructive testing, the main purpose of AET technology is: ① determine the location of the acoustic emission source; ② analyze the nature of the acoustic emission source; ③ determine the time or load size of the acoustic emission; ④ assess the severity of the acoustic emission source according to the relevant acoustic emission standards. On the other hand, acoustic emission testing technology also has certain shortcomings and deficiencies. Acoustic emission testing needs to be carried out under specific load conditions. Acoustic emission testing can only give the location, activity and intensity of the acoustic emission source, but cannot give the nature and size of the defects at the acoustic emission source. For excessive acoustic emission sources, other conventional non-destructive testing methods (such as ultrasonic testing, X-ray testing, magnetic particle testing, penetration testing, etc.) need to be used for local re-inspection to comprehensively determine whether it is dangerous and whether it is allowed to exist.
AET technology has the following characteristics, which show its superiority compared with other non-destructive testing methods in many cases.
AET technology is suitable for real-time dynamic monitoring and detection, and only displays and records the extended defects, which means that it has nothing to do with the defect size. Instead, it displays the most dangerous defects that are expanding. AET
technology has a high sensitivity to extended defects. Its sensitivity is much higher than other methods. For example, the acoustic emission method can detect crack increments of the order of a few tenths of a millimeter under working conditions, which cannot be achieved by traditional non-destructive testing methods.
The characteristic of AET technology is integrity. The entire object can be inspected by using several acoustic emission sensors fixed on the surface of the object. When locating defects, it is not necessary to scan the sensor on the surface of the inspected object (positioning method: regional positioning method, time difference positioning method). Therefore, the inspection and its results are independent of the surface state and processing quality. It is particularly useful when it is difficult to contact the surface of the inspected object or it is impossible to contact it completely. For example: insulated pipes, containers, volutes; objects buried underground and components with complex shapes; when inspecting welds of large and long objects (such as bridge machine beams, overhead gantry cranes, etc.), this advantage is more obvious.
An important feature of AET technology is that it can detect different process and material properties and state change processes.
For most nondestructive testing methods, the shape and size, location and direction of the defect are very important, because these defect characteristic parameters are directly related to the defect missed detection rate. For AET technology, the location and direction of the defect are not important. In other words, the location and direction of the defect do not affect the detection effect of acoustic emission.
AET technology is less affected by the performance and organization of the material. For example, it can be successfully used to detect composite materials, which is difficult or impossible to detect with other nondestructive testing methods.
It is relatively simple to use AET technology. On-site acoustic emission detection monitoring and testing are carried out simultaneously, and the test period will not be extended due to the use of acoustic emission detection technology. The detection cost is also low, especially for the overall detection of large components, the detection cost is much lower than that of X-ray or ultrasonic detection. And the detection and result evaluation can be carried out in an integrated and real-time manner.
AET technology can detect defects, determine the location of defects and evaluate the danger level (safety) of the structure. Combined with other conventional nondestructive testing methods, the use of acoustic emission method will achieve the best results.
It can be expected that in China's water conservancy and hydropower projects, the use of acoustic emission detection technology for metal structures and electromechanical equipment for detection and safety assessment will become more and more common. The social and economic benefits of using acoustic emission detection technology will become more and more significant.