To identify the shortcomings of the internal structurestructures and details are applied methods of nondestructive testing. They allow us to fix defects of various kinds without intrusion into the basis of the material, determining their compliance with regulatory requirements. One of the most accurate methods of such inspection is eddy current monitoring, in the process of application of which electrotechnical equipment is involved. This method has significant drawbacks, but in certain areas it is used quite actively.
The control is based on an analysis of the parametersinteraction between the electromagnetic field of the flaw detector and its equipment and eddy currents, which are formed in the field of the object of investigation. As for the actuator generating the active electromagnetic zone, it is usually represented by an inductive coil, also called a transducer. Pulse currents, which excite the vortex currents, in the end and allow you to calculate the defective zones. The fact is that violations in the structure of the investigated object will inevitably lead to an uneven interaction of the material with the electromagnetic field throughout its area. It is the areas with current oscillations that reveal the eddy current method of non-destructive testing with the help of special analysis. The principle of operation is rather complicated in comparison with alternative methods of magnetic control, but again it is also one of the most accurate methods of detecting defects.
This method has two principalfeatures. First of all, this is the possibility of excluding direct contact with the target object. That is, it is not just about non-destructive testing, but about the technique of contactless examination. This allows, for example, to diagnose structures and elements in motion. But contact methods of analysis are not excluded. For comparison, the method of magnetic-powder analysis, which necessarily requires the application of indicator material to the surface of the object under investigation, can be cited. The second feature that distinguishes eddy current from the general group of methods of defects is the possibility of an additional analysis of the electrophysical properties of the material. But this functional already depends on the specific model of the device used and the quality of the auxiliary equipment.
Devices can have different formats of execution.Manual models, control stations, component and modular devices are common. They also differ in the way they process and present information: one can distinguish analog, digital and microprocessor-based modern control devices. Internal filling is usually an electrical basis with the same coils, and external organs are represented by sensitive elements of analysis.
Also, eddy current devicesequipped with nozzles for convenient placement of the converting device in front of the monitored surface. Although the devices provide for the possibility of contactless control, the position and direction of the sensing element are of great importance from the point of view of obtaining a qualitative result. With regard to power supply, the devices are powered by batteries or mains. In the first case, devices allow an independent diagnosis of structures and communications in remote areas.
As already mentioned, the defect is notthe only task that an eddy current method of material control can solve. The second most common function is to measure thickness. In this way, the parameters of plates, film products, walls of pipes and other objects are evaluated. For this purpose, special eddy current devices with a thickness gauge option are used. Often this is the main function that such devices solve. They are compact hand-held devices with a sensitive element, which also creates an electromagnetic field, but during the analysis not the presence of voids, but the thickness of the electrically conductive sheet, is fixed.
The main direction of the use of eddy currentDiagnosis is still a defect, which also provides for different options. In particular, absolute control allows measuring the deviations of the measured value from the previously established reference point, which is checked at the calibration stage of the apparatus. Also, eddy current monitoring performs a comparative measurement, in which the difference of two quantities is calculated, one of which is taken as the reference one.
A differential measurement is also used thatAlso calculates the difference between two fixed values in the process of monitoring. But in this case, the measurement path with the unchanged distance between the reference points remains the same. In each of the methods, eddy current testing can work with both surface and internal characteristics of the material structure. However, in-depth analysis provides for a small immersion of about 2-3 mm, which is the main drawback of this technology.
The device is tuned to the workflow bycalibration and setting the optimum sensitivity index in relation to the characteristics of the target object. Depending on the functionality of the device, the user can adjust the parameters of the electromagnetic filters, the phase and the value of the gap of the sensitive sensor. It is important to take into account that the external factors influence the quality of the eddy current method of nondestructive testing. To ensure convenient placement of the device, its installation, alignment and direction of the converter, the workplace must also be properly prepared. Also, the inspection site is thoroughly washed, cleaned of dirt and oil stains, then dried and, if necessary, additionally treated with chemical solutions.
At the first stage, the surface of the part is scannedelectromagnetic signal over the entire target area, which can capture a little and the area not subject to analysis. Based on the characteristics of the received feedback signal, a conclusion is drawn about the physical state of the object. The device with the help of computer analysis provides data on the wear of the object, the presence of defects and damages. A specific set of parameters will depend on what task was placed before the eddy current control. GOST 15549-2009 for this method also determines the mandatory set of signal characteristics, among which the phase, amplitude and their combination in the previously indicated spectra. Then the received information is entered in the technical control journal. Criteria for assessing the identified defects in advance are provided in the task for monitoring and in the future allow the decision to admit the product to the intended use.
This technology of diagnostics of structures andDetails on the presence of defects are widely used in construction and production. For example, multifunction stations are used on conveyor lines that produce metal products. Equipment in automatic mode checks the details for compliance with regulatory parameters. In the construction of this method, the quality of metal structures, ceilings, racks, fasteners, welding seams, etc. is evaluated. An eddy current control of pipes is widely used, which makes it possible to detect discontinuities of the metal and timely update the problem areas of the communication network. In the household sphere, thickness gauges are often used, which determine the parameters of the same pipelines or hulls of various techniques.
The eddy current defect can be calledone of the most technological and modern. It allows you to work with details of different shapes and purposes, fixing their physical parameters with high accuracy. But there are characteristics for which eddy current non-destructive testing is much inferior to alternative methods, including from a group of magnetic methods. This concerns not only the restriction in the depth of penetration of the signal. Electromagnetic currents can give information about the internal structure of the material only in the case of its electrical conductivity. The absence of this property makes the device useless in relation to such an article.
