Acoustic emission of pipelines is the occurrence and propagation of elastic vibrations in the process of deformation of the studied structure. Quantitatively, it acts as an indicator of the integrity of the material under various loads. Acoustic emission control can be used to identify defects at the initial stage of structural failure. The main diagnostic method is the passive collection of information and their subsequent processing.
general characteristics
Acoustic emission is used to detect and establish coordinates, monitor deformation sources on surfaces or in the volume of walls, welded joints and structural elements. Diagnostics is performed only when creating a stress state. It initiates the operation of vibration sources in the object. Acoustic emission occurs when exposed to pressure, force, temperature field, and so on. The choice of a specific load is determined by the design features, the conditions in which it is used, and the specifics of the tests.
Acoustic emission method
To determine the reliability indicator of a structure, it checks its parameters and properties, in which its integrity and suitability for use and operation must not be violated. Traditional methods (ultrasonic, eddy current, radiation, and others, popular in practice) make it possible to identify geometric heterogeneities by emitting a certain energy into the structure of an object. Acoustic emission suggests a different approach. First of all, the material itself acts as a signal source, and not an external object, since this is a passive verification method, and not an active one, as mentioned above. In addition, acoustic emission makes it possible to detect not static inhomogeneities, but the movement of a defect. Accordingly, with its help it is possible to identify developing and, therefore, the most dangerous destruction. This method allows you to quickly detect the growth of small cracks, leaks of liquid or gas, faults and other processes that cause the occurrence and propagation of vibrations.
Nuances
In theoretical and practical terms, any defect is able to produce its own signal. It can cover quite large distances (several tens of meters) until it is detected by an acoustic emission sensor . Moreover, destruction can be detected not only remotely. Defects are also established by calculating the difference in the time of arrival of the waves to the pickup sensors located in different areas. Crack growth, delamination, inclusion fracture, friction, corrosion, fluid / gas leakage are examples of oscillating processes that can be detected and effectively investigated.
Features
The main advantages of the method over traditional non-destructive testing methods are:
- Integrality It consists in the fact that, using one acoustic emission transducer , motionlessly mounted on the surface of the structure, it is possible to check it all out. This property is especially relevant when studying hard-to-reach or inaccessible areas.
- No need to conduct thorough preparation of the surface of the investigated object. It follows that the control process itself, as well as its results, will not depend on the state of the structure and the quality of its processing. If there is an insulating coating, then it must be removed only at the installation sites of catching devices.
- Identify and record only developing damage. This allows the classification of defects not by their size or other indirect indicators (position, shape, orientation), but by their level of danger (degree of influence on the strength of the object).
- High performance. It is many times higher than the corresponding indicators for traditional (radiographic, ultrasonic, magnetic, eddy current, etc.) control methods.
- Distance Verification of the strength of the object can be performed at a considerable distance from the operator. This feature allows you to apply the method to monitor the condition of large-sized, especially dangerous, extended structures without decommissioning and threats to personnel.
Another advantage is the ability to monitor various technical processes and assess the state of the structure in the current time mode. This prevents accidental destruction of the object. It should also be noted that the acoustic emission method optimally combines quality and cost parameters.
Additionally
Monitoring using acoustic emission provides huge amounts of information, allows you to quickly adjust and extend the life cycle of critical industrial installations with minimal costs. The results of the tests are used to predict emergency damage. This control method can be used in the study of various properties of materials, structures, substances. Today, without its use it is impossible to create, as well as the reliable operation of many critical facilities in the industry.
Minuses
The acoustic emission method also has some disadvantages. The main disadvantage is the difficulty of decoding the indicators obtained during verification. This disadvantage significantly limits the widespread use of the method in practice. The complexity is due to the fact that the so-called spurious indicators of repeatedly reflected noise, waves from the operation of equipment, a loading object, and the environment are superimposed on wave processes during acoustic emission. The use of protection systems and various filters can only partially reduce the impact. In addition, the uniqueness of the equipment used in the control is considered a disadvantage. In industry, it is not mass produced. It also does not allow to extend the method beyond the field of experimental use.
Fields of application
As mentioned above, at present, various companies engaged in various economic fields use the acoustic emission method. The main ones include:
- Chemical and oil and gas industry.
- Metallurgy and pipe production.
- Thermal and nuclear energy.
- Railway transport.
- Aerospace complex.
The method is widely used by enterprises working with lifting, bridge structures, concrete and reinforced concrete structures.
Conclusion
The acoustic emission method is today considered one of the most effective ways to perform non-destructive testing and assess the condition and properties of materials. It is based on the identification of elastic waves generated when a sudden deformation of a structure under load occurs. The resulting oscillations depart from their source and are sent directly to the sensor, where they are transformed into electrical signals. Special instruments measure them. After that, the processed information is displayed. On its basis, a subsequent assessment of the state and behavior of the structure of the studied objects is carried out.