3.1. Diagnostics of defects at the bearing level

The “bearing” level includes all defects in the support bearings of the units, and the support struts themselves. Since rolling and sliding bearings are most widely used in practice, this section discusses the features of diagnosing defects in these particular types of bearings.

Rolling bearings of various types and brands, ball and roller, radial and radial thrust, single and double row, etc. are widely used in rotating equipment for various purposes. Without exaggeration, we can say that most equipment repairs, especially of low and medium power, are carried out due to defects in the roller bearings. Therefore, issues of prompt assessment of the technical condition of such bearings, diagnosis of defects that arise in them, as well as forecasting the possibility of their further operation, occupy one of the most important places in the work of vibration diagnostic services.

This chapter provides a fairly brief overview of the main diagnostic methods used to assess the quality of bearings, identify defects at various stages of development, and calculate the residual life of rolling bearings. The reason for the brevity of the description is simple - each of the methods listed below requires a separate book for its complete description.

3.1.1.1. Main signs and features of the development of defects

The presence of a defect in a rolling bearing is easily detected in several ways. The defect can be diagnosed “by ear”, by the shape of the vibration signal, by the spectrum, by the RMS signal, by the spectrum of the vibration signal envelope, using the “crest factor”, “kurtosis”, and other methods.

In the introductory section, we will consider various features and signs of the occurrence, development and diagnosis of defects in rolling bearings, focusing on those features that we will need further to describe one or another method of diagnosing bearings. This will reduce the duplication of descriptive information that must be provided when describing each defect diagnostic method.

The characteristic shape of a vibration signal, in this case, recorded on a support with a rolling bearing, which has a fairly developed condition defect, is shown, for example, in Figure 3.1.1.1. This figure clearly shows the two most characteristic and important for diagnostics components of the vibration signal - background and pulse.

The background, or average value of the vibration signal level recorded on a rolling bearing, is characterized by some average value, for example, the root-mean-square value of the vibration velocity. This vibration value can be measured quite simply using conventional vibrometers.

At the moments when a rolling bearing, defective element or elements pass through the “carrying”, loaded area, a clearly defined amplitude peak, a certain energy pulse, appears on the vibration signal. The parameters of this impulse are determined by the type, location and degree of development of the bearing defect. Each such shock pulse has four main diagnostic parameters. This is the maximum amplitude of the pulse, the frequency of free (filling) oscillations, the rate at which the amplitude of these oscillations decays, and the pulse repetition rate.

The most important parameter characterizing the degree of development of a bearing defect is the amplitude of the shock pulse. To measure this pulse parameter, vibration monitoring devices must provide for the use of high-frequency vibration measurement sensors and the use of special peak detectors or sufficiently high-frequency ADCs. This is due to the fact that shock pulses have a relatively high frequency. The localization of the defect, its location, is usually specified by the pulse repetition frequency, for which spectral methods are used.

If the diagnostics of the state of rolling bearings is carried out using the parameters of temporary vibration signals, then the main attention should be paid to two. This is, firstly, the quantitative value of the general vibration background level and, better measured in the RMS dimension, and secondly, this is the relationship between the vibration background levels and the amplitudes of the peak values ​​in the vibration signal.

In the most general case, changes in the technical condition of a rolling bearing, the occurrence and development of defects in it, over the entire period of its service, can be divided into five main stages. These stages are shown schematically in Fig. 3.1.1.2. In this figure, the vibration level is plotted vertically in the dimension of vibration velocity (mm/sec), and the relative operating time of the bearing is plotted along the horizontal axis.

The general technical condition of a bearing, at each stage of its operation, is determined by the zone between two lines of vibration levels. The lower line corresponds to the value of the background vibration level, determined in the RMS vibration velocity dimension, and the upper line corresponds to the average amplitude of shock pulses arising during operation of the rolling bearing.

As we have already noted, five stages characterizing changes in the technical condition of rolling bearings can be distinguished. At the first stage, in the figure this is the zone up to the border marked “1”, we will consider the general technical condition of the bearing to be ideal. This zone can be considered not the zone of the presence of defects, but the zone of their primary occurrence. The defects do not yet affect the vibrations of the bearings; all the increase in vibration that occurs is due to the natural wear of the rolling surfaces of the bearings. At this stage, vibration peaks exceed the background level slightly, and the “background level” of vibration itself, in this case it is the RMS vibration velocity, is significantly less than the normalized values ​​of alarm and emergency levels adopted for this class of equipment.

Zone “1-2” in Figure 3.1.1.2. In this zone, starting from boundary “1”, a defect appears and begins to develop in the bearing, which is accompanied by shock vibration pulses, the amplitude of which quickly increases in magnitude. The “destructive energy” of the pulses is spent on “deepening” the defect in the working surfaces of the bearing, resulting in an even greater increase in the pulse energy. The level of background vibration in its magnitude remains almost unchanged for now, since the defect is local in nature and does not yet affect the general condition of the bearing. Let us repeat that this is the zone where a defect occurs during operation.

Zone "2-3". Starting from boundary “2”, the shock pulses in the bearing reach in their energy, in relation to the graph, this increase in amplitude, almost the maximum value. Further, the amplitude of the pulses increases slightly. The quantitative value of the maximum pulse energy is determined by the type of bearing and its operating conditions. The pulse energy released in the bearing is already so great that it is enough not only to “deepen”, but also to expand the defect zone. At this stage, the process of self-development of the defect begins to proceed more quickly. At the same time, the background level also increases quite monotonically. We can say that the defect is gaining strength, preparing for a decisive attack.

Zone "3-4". This is the zone of transition of a bearing defect from the “strong defect” stage to complete degradation. The process starts from boundary “3”. The geometric zone of defect development here is already so large that the bearing begins to “lose” its main purpose - to ensure rotation of the supported shaft with minimal friction. Losses in the bearing due to rotor rotation increase and, as a result, the energy released in the bearing increases and the background level increases. This is already the stage of self-destruction of the bearing.

Zone "4-5". This is the last stage of development of the defect, when it has already covered the entire bearing, or rather, everything that remains of the bearing. The background vibration level is almost equal to the level of the peaks; more precisely, the entire vibration signal consists of peaks. The operation of rolling bearings in this area should be avoided, although, more precisely, it is simply impossible.

All of these above stages of bearing deterioration are characteristic of almost all types of defects that occur in any type of bearing. Depending on a number of design and operational parameters of bearings, differences may be observed in the duration of the described stages and in the intensity of vibration processes in them, but the overall picture of the development of defects does not change.

There are other characteristic signs of defects in rolling bearings.

When a bearing with defects on the rolling surfaces operates, characteristic components, harmonics, with natural frequencies appear in the spectrum of the vibration signal, from which the location of the defect can be quite correctly identified. The numerical values ​​of the frequencies of these harmonics depend on the ratio of the geometric dimensions of the bearing elements, and of course are uniquely related to the rotational speed of the rotor of the controlled mechanism.

In a loaded rolling bearing, four main, characteristic frequencies used for diagnostics can be differentiated - harmonics. These harmonics (from the rotation frequency) are caused by specific processes on the outer race of the bearing, on the inner race of the bearing, are associated with the operation of the bearing cage, and with the frequency of rotation of the rolling elements - balls or rollers. Let us consider, for simplification without intermediate mathematical calculations, formulas for calculating these frequencies.

The frequency of rolling elements rolling along the outer race of the bearing, often referred to in the literature as BPFO:

Fн = Ntk / 2 x F 1 (1 - Dtk / Dc x cosj)

where: Ntk - number of rolling elements in one bearing row;

F 1 - rotor rotation speed;

Dtk - diameter of the rolling body;

Dc - average diameter of the separator;

j is the angle of contact of the rolling body with the cage.

Fв = Ntk / 2 x F 1 (1 + Dtk / Dc x cos j)

Fc = 1 / 2 x F 1 (1 - Dtk / Dc x cos j)

Operating frequency (rotation) of rolling elements - BSF:

Ftk = 1 / 2 x F 1 x Dtk / Dc (1 - Dtk 2 / Dc 2 x cos 2 j)

As can be seen from these formulas, to accurately determine the characteristic harmonics of a rolling bearing, 4 primary parameters are sufficient, three of which are structural, and the fourth is determined by the operating speed of the rotor.

These formulas for calculating characteristic bearing frequencies are quite simple, but not always convenient for practice. The difficulty is that they include the angle of contact of the rolling elements with the races. This parameter is not always known accurately and during the operation of the bearing, as the working surfaces of the bearing wear out, it may change its value.

In practice, it is more convenient to use simpler formulas that do not include this angle; as a result, they are naturally less accurate and are most often acceptable for practical diagnostics. Let us present these formulas:

Frequency of rolling elements rolling along the outer (outer) race - BPFO:

Fn = F 1 (Ntk / 2 - 1.2)

Frequency of rolling elements rolling along the inner race - BPFI:

Fв = F 1 (Ntk /2 + 1.2)

Separator operating frequency - FTF:

Fc = (1 / 2 - 1.2 / Ntk)

Rolling element rotation speed - BSF:

Ftk = (Ntk / 2 - 1.2 / Ntk)

The algorithm for using these formulas is quite simple - if harmonics with such frequencies appear in the spectrum of the vibration signal, then we can talk about defects in the corresponding bearing element. This can be interpreted theoretically, but in practice everything looks more complicated.

These formulas should be used very carefully based on the analysis of “direct spectra” (classical Fourier spectra of the entire signal); the reliability of diagnostics using them may not be high. Quite often, even if there is an obvious defect in the bearing, the characteristic frequencies in the vibration signal may be completely absent, have a frequency shift, or have a very low level.

3.1.1.2. Methods for diagnosing bearing defects

To assess the technical condition and diagnose defects of rolling bearings, various authors and companies have developed quite a lot of different methods. Naturally, all these methods, different in their theoretical premises, have different labor intensity, require different instrumentation and can be used for different purposes. Of course, the final information obtained as a result of using these methods has varying information content and reliability.

In this section we will try, very briefly and superficially, to review and compare the main methods most often used in practice. The comparison will be based on a parameter that we will call practical applicability and efficiency. At the same time, we will systematize these methods based only on the basic, basic, theoretical premises, the possibility of using them at various stages of the development of bearing defects.

In the most general case, assessment of the technical condition and search for defects in rolling bearings can be carried out using the four most common methods, using the following diagnostic parameters:

1. According to the value of RMS vibration velocity

This method makes it possible to detect bearing defects at the last stages, starting approximately from the middle of the third stage of defect development, when the overall vibration level increases significantly. This diagnostic method is simple, has a regulatory framework, requires minimal technical costs and does not require special training of personnel; it is used in the diagnosis of “mass” and relatively inexpensive rotating equipment.

2. Diagnostics of defects in rolling bearings using the spectra of vibration signals

This method is used in practice quite often, although it does not have high sensitivity, it allows identifying, along with bearing diagnostics, a large number of other defects in rotating equipment. This method allows you to begin diagnosing bearing defects approximately from the middle of the second stage, when the energy of resonant vibrations increases so much that it will be noticeable in the overall picture of the frequency distribution of the entire vibration signal power. To implement this method, you need a good measuring instrument of a sufficiently high level, and specially trained personnel.

3. Diagnostics of defects based on the peak/background ratio of the vibration signal

The basics of the method are illustrated in Figure 3.1.1.1. This method was developed by several companies and has many different practical modifications of approximately the same effectiveness. These are the HFD method (High Frequency Detection - a method for detecting a high-frequency signal), the SPM method (Shock Pulse Measurement - a method for measuring shock pulses), the SE method (Spike Energy - a method for measuring pulse energy), as well as several other, but less well-known methods. The best versions of this method make it possible to detect defects in rolling bearings at fairly early stages, starting approximately from the end of the first stage of development. Devices that implement this method of diagnosing defects are quite simple and cheap.

4. Diagnostics of defects in rolling bearings using the spectrum of the vibration signal envelope

This method makes it possible to detect bearing defects at the earliest stages, starting approximately from the middle of the first stage. Theoretically, this method for diagnosing defects in rolling bearings can be based on both the analysis of acoustic signals and the analysis of vibration signals. In the first case, the method is called SEE (Spectral Energy Emitted - analysis of emitted spectral energy), and for its work it uses a special acoustic radiation sensor. Most often, acoustic leak detectors of various modifications operating in the frequency range up to 100 kHz are used for such diagnostics. In this case, the measurement of acoustic parameters is carried out remotely, at some distance from the controlled bearing. If "conventional contact vibration sensors" are used to measure vibration signals, then this method does not require the use of special equipment. Russian diagnosticians have been involved in the development of this method; it is now considered a classic method for analyzing vibration signals from rolling bearings.

All of the above methods for diagnosing defects in rolling bearings differ not only in the theoretical premises underlying them. They differ in the type of diagnostic equipment used, its cost, the necessary training of personnel and, of course, their effectiveness. A simple rule is almost always true - the earlier and the more reliably it is necessary to detect bearing defects, the more expensive it is.

In addition, you should always remember and take into account that diagnosing the condition of bearings is only part of the overall equipment diagnosis. A complete analysis of the condition of equipment is usually carried out using the spectra of vibration signals, therefore, when choosing a method for diagnosing rolling bearings, preference should be given to diagnostics using envelope spectra, which makes this method almost universal. With this approach, the full set of technical tools designed to diagnose the condition of equipment will be minimal in volume and cost.

If standard spectral diagnostics of this type of equipment are not constantly carried out, then for early diagnosis of the condition of rolling bearings, the use of methods based on comparison of the background and peak levels of the vibration signal is very effective. These methods have sufficient reliability for the standard practice of vibration diagnostics specialists. A very great advantage of these methods is that for their implementation they do not require expensive and specialized vibrometers.

In order for there to be an obvious defect in a bearing, a number of different requirements must be met. These requirements are determined by the design, operational, and methodological features of diagnosing rolling bearings using various methods.

The main requirement for the design of the bearing assembly is the following - there must be good acoustic contact between the installation area of ​​the rolling bearing and the possible installation location of the measuring sensor. The term “acoustic contact” is used here for the reason that most of the vibration frequencies of interest to us are in the acoustic audibility zone. Of course, it would be more correct to talk about the transmission of vibration signals from the controlled bearing to the sensor, but in this case it is equivalent.

Measurement of the parameters of the technical condition of the controlled bearing must be carried out under certain conditions:

• The bearing being monitored must be loaded with sufficient force so that the “defect can appear” in the measured vibration signals. If this condition is not met, on-line diagnostics become meaningless.
• The defective area of ​​a rolling bearing must periodically pass through the load area of ​​the bearing.
• It is desirable that in the equipment being monitored there are no other sources of vibration signals with a frequency equal to the frequency of defects, or their influence is weakened in the control zone.

The measuring equipment used for diagnostics must have certain properties:

• The frequency parameters of the measuring sensor must cover the entire possible range of frequencies that may occur in the controlled bearing, and which is of “diagnostic interest”.
• The recorder and analyzer of vibration signals used to analyze the “direct spectra” of rolling bearings must, after processing, provide a vibration signal spectrum with a resolution of at least 1600 - 3200 lines.

These requirements apply to all methods for diagnosing rolling bearings using spectra and envelope spectra, which are based on the use of the above formulas for calculating bearing frequencies.

At the end of this general section concerning general diagnostic issues, I would like to touch upon an important methodological issue related to the diagnosis of “low-speed bearings”. Such bearings are used in large quantities in paper machines, various conveyor lines and lifting mechanisms.

The meaning of the issue under consideration is quite simple, it is to determine what frequency parameters the measuring instruments designed to diagnose such rolling bearings should have, and what are the features of such diagnostics. For example, if you need to diagnose a bearing whose rotation frequency is 0.2 Hz, that is, if the controlled bearing makes one revolution in five seconds, then what should be the frequency properties of the diagnostic device used, the measuring sensor? In what frequency range should measurements be made so that the information obtained is sufficient to carry out correct diagnostics of the bearing.

To answer this question, let us turn to Figure 3.1.1.3., which shows a time signal recorded on a defective bearing that has a cavity on the inner race.

The vibration picture shown in the figure is clear and visual. Once every five seconds, the defective zone of the inner race enters the loaded zone of the bearing, and when the rolling elements pass through the defective zone, dynamic shocks occur. After each impact, free damped oscillations with a frequency of about 2 kHz occur in the defective zone. In the example given, we have a “series” of three impacts, i.e., during the passage of the defective zone, three bearing rolling bodies “hit” it. This is a “refined” vibration picture of a real defect, which is quite common in practice.

The question is as follows: what frequency properties should a measuring sensor have, and in what frequency range should we carry out measurements in order, for example, to diagnose a defect in a given bearing using direct spectra.

First, let's decide which zone of our vibration signal is of interest to us; a lot depends on this. Obviously, if we are talking about repeating pulses, then we must include in consideration at least 2-3 revolutions of the controlled rotor, and ideally 4-5, so that we can confidently diagnose defects in the rolling bearing cage. This is due to the fact that the harmonic frequency of a defective separator is usually slightly less than 0.5 Hz, i.e. such a defect “runs in” once every two revolutions of the rotor. If we include 4 rotations of the rotor into consideration, we find that we must register a vibration signal whose duration is 20 seconds.

We have already said above that the frequency of free vibrations after dynamic impacts, in our example, is 2 kHz. To correctly register and diagnose this harmonic on the spectrum, we must record with a frequency of at least 5 kHz, and preferably more, for example, at least 6 kHz. This logically follows from the Nyquist rule.

Now it becomes clear that one registration of a vibration signal on a low-speed bearing should be carried out with a frequency of 6 kHz and a duration of 20 seconds. The total length of one sample must be at least 120 thousand ADC samples. Not all vibration signal recording devices, including the best ones, have such capabilities; this is a specific requirement. For 95% of the instruments available on the market today, the maximum signal sampling length does not exceed 8192 samples.

The second important question is, what is the frequency range of the measuring sensor designed for diagnosing low-speed rolling bearings? What is most paradoxical is that many argue that the lower this range, the better. What range is needed to diagnose the bearing, the signal from which is shown in our figure? When surveyed, 90% of specialists said that a sensor with a lower limit frequency of 0.05 Hz or even lower is needed.

When we focused on the fact that the main diagnostic frequency is 2 kHz, this is the frequency of free vibrations of structures “around the bearing” after dynamic shocks in the defect area, even after this, not everyone changed their requirements for the frequency properties of the measuring sensor. Let us emphasize once again that all these considerations are valid only for diagnosing rolling bearings; for diagnosing sliding bearings the requirements are different, more standard.

Let us conclude this argument as follows. Diagnostics of low-speed rolling bearings should be carried out using “pulse” methods. Diagnostics using “direct” spectra is practically impossible, and using spectra of the vibration signal envelope is very doubtful.

3.1.1.3. Diagnostics of defects based on the general vibration level

This method of assessing the technical condition and diagnosing defects in bearings in general, and in rolling bearings in particular, is part of the widespread simple practice of assessing the general technical condition of rotating equipment based on the general level of the vibration signal. Such diagnostics are performed by technical personnel without special vibration training. To carry out such diagnostics of defects in rolling bearings, it is quite sufficient to use a simple vibrometer that measures the overall level of vibration.

As mentioned above, such diagnostics of defects in rolling bearings makes it possible to determine defects only at the very last stage of their development, when they already lead or have already led to degradation of the condition of the bearings and an increase in the overall level of vibration. Diagnostics of bearing defects based on the value of RMS vibration velocity, and only for this dimension of the vibration signal there are criteria for the technical condition of equipment, can be interpreted as pre-emergency.

The criteria for the technical condition and the degree of development of defects in this method are completely oriented towards the corresponding standard values ​​of vibration levels adopted for a given mechanism. In this diagnostic method, a rolling bearing is considered defective if its vibrations exceed the general norm for the unit; this is a sign of a defective state of the controlled rolling bearing. With such a threshold increase in the vibration level measured at the support bearing, maintenance personnel need to make a decision about the possibility of further operation of the unit or about stopping the equipment and replacing the bearing.

The first signs of a bearing defect using this diagnostic method are detected during equipment inspection by personnel quite late, approximately several months, weeks or even days, which depends on a number of operating features of a given bearing, until the moment the bearing completely fails. Despite this late detection of defects, and the somewhat skeptical attitude of experienced specialists to this method, this method of diagnosing the condition of rolling bearings is quite widely used in practice and gives good results in those cases.

The method has maximum advantages in cases where:

• The main task of conducting a diagnostic examination of equipment is only to prevent accidents and their consequences, even if diagnostic information about the presence of a defect will be obtained at a fairly late stage.
• Shutting down the equipment to replace a bearing can be carried out at any time, without any damage to the operation of the controlled installation and the technological cycle of the entire enterprise, without disrupting the overall process.
• If the cyclicity of repair work on the monitored equipment is such that the remaining service life of a bearing with a diagnosed defect, even minimal, always exceeds the remaining operating time before it is taken out for repairs for other reasons.

The advantage of this, the simplest method for diagnosing defects in rolling bearings based on the general level of vibration, is also that its use does not require virtually any additional training for maintenance, and often operating personnel. In addition, the cost of the technical equipment required for this diagnostic method is minimal.

If the enterprise has not previously carried out any work on vibration diagnostics, then this diagnostic method provides the greatest efficiency when implemented. The use of all other methods for diagnosing rolling bearings always requires large initial material costs, and provides an economic effect only at later stages of work.

In conclusion on this issue, it should be said that the diagnosis of defects in rolling bearings can be unexpectedly highly effective in the simplest way - “by ear”. To do this, you must have some kind of device for listening to the bearings, such as a stethoscope, or a vibration meter with plug-in headphones. If you don’t even have this, then you can use any dry wooden stick of sufficient size.

If you apply one end of it to the bearing being monitored, and the other end to your ear, then if there is a defect in the bearing, you can very clearly hear a high, quiet, pleasant ringing, sometimes called “bronze bells.” One has only to hear it once, and it will no longer be possible to confuse it with anything else. The reliability of diagnosing defective bearings using this method is very high.

3.1.1.4. Diagnostics of bearing defects using signal spectra

Most specialists in vibration diagnostics, if they start working on rolling bearings, expect the greatest reliability and the greatest effect when implementing diagnostics using classical spectra of vibration signals. Such spectra, in contrast to the spectra of the vibration signal envelope, also used for diagnosing rolling bearings, are often called “direct”, and we will also use this term.

Unfortunately, most often this is where their optimistic expectations will not come true. Not only is the diagnostic procedure itself quite complex and controversial, the reliability of most practical diagnoses on the condition of rolling bearings obtained using such “direct” spectra of vibration signals is unexpectedly low. A method designed to solve the most complex diagnostic problems of rotating equipment does not give good results when diagnosing “penny” rolling bearings!

The “unexpectedness” of such a paradox is programmed in advance and is inherent in the diagnostic features based on the spectra of vibration signals. Diagnosis errors are predictable in advance and lie in the fact that the classical spectrum is, by definition, the distribution of the power of the original temporary vibration signal in the frequency domain. For this reason, the appearance of characteristic harmonics of a particular element of a rolling bearing on the spectrum should be expected only when the defect develops to such an extent that the power of its harmonics is comparable to the power of “mechanical” harmonics associated with unbalance and misalignment. Only in this case can one confidently diagnose “bearing” harmonics on the spectrum when they have not only a large amplitude, but also significant power.

In order to increase the sensitivity of this diagnostic method to low-power “bearing harmonics”, various methods are used, for example, the harmonic amplitudes in the analyzed spectra are presented on a logarithmic scale. This certainly helps, but up to a certain point, when the harmonics are already beginning to be masked by the general “white noise”, which in vibration signals has a significant amplitude.

In accordance with the gradation of the development of rolling bearing defects into stages given at the beginning of the chapter, we can say that diagnostics using the spectra of vibration signals can confidently identify defects in rolling bearings, starting only from the end of the first stage of their development, and more often from the middle of the second zone. Moreover, even at this level, diagnostics using “direct” spectra of vibration signals is quite difficult and has a number of specific features.

Below we will try to consider these features, which significantly complicate the diagnosis of defects in rolling bearings using direct spectra.

Let's start with the requirements for instruments for recording and analyzing vibration signals. The measuring device used to diagnose rolling bearings must have a high frequency resolution, no less than 3200 lines in the spectrum. Otherwise, the power of the narrow impact peak of the defect will be “smeared” over a fairly wide spectral band, which will lead to a sharp decrease in the amplitude of the characteristic bearing harmonic, which will definitely distort the results of the diagnostics. As we wrote earlier, there are not many such devices in operation; usually the frequency resolution of the devices is much lower.

It is quite clear that since diagnostics of rolling bearings is most often carried out on the analysis of dynamic processes, then measurements must be carried out in the dimension of vibration acceleration, in which these processes are more significant. Although in some diagnostic methods it is necessary to analyze the energy component of vibrations, for which measurements in the dimension of vibration velocity should be used.

Next, let us turn to the main features of the manifestation of bearing defects in the original vibration signals and in the “direct” power spectra obtained from them. There are several such characteristic features.

Let us first consider the shape of the shock pulses that arise during shock impacts from bearing defects that appear in the vibration signal. To do this, let's consider the simplest example of a vibration signal, shown in Figure 3.1.1.4., recorded on a defective rolling bearing. After each impact, free resonant oscillations arise in the defective area of ​​the bearing, which usually decay exponentially.

The probability of the appearance of such periodic shock pulses, which have a very characteristic appearance, accompanying the process of rolling in a bearing defect, is close to 100%. To describe the form of these processes of features, a special term was even coined - “goldfish”. The presence of pulses of this shape in the vibration signal is a reliable diagnostic sign for identifying bearing defects.

The repetition frequency of these “goldfish”, or more precisely, their fins and tails, in the time signal should quite accurately correspond to the frequency characterizing the defect of a particular bearing element. The intensity of the “goldfish”, the degree of its severity, the excess over the general vibration background, depends on the degree of development of the defect. An example of such a vibration signal with two “goldfish” is shown in our figure. We immediately draw the reader’s attention to the fact that “per revolution of the rotor” there may be a different number of shock pulses; their repetition rate is determined not by the rotor’s rotation frequency, but by the calculated “bearing” frequencies.

In real vibration signals, the “goldfish” is not so beautiful; most often its shape is more “shaggy”. It has various “extra fins” located above or below. Shock impulses can follow one after another, often even layering on top of each other. All this depends on the actual frequency of impacts from defects, and on the intrinsic resonant properties of the mechanical structure or its individual elements.

The second, main diagnostic feature is the presence of a specific manifestation of defects in rolling bearings in the “direct” spectra of vibration signals. Directly during diagnostics, it is possible to identify three types of possible, most common types of vibration signal spectra, corresponding to different stages of development of defects.

Diagnostic stage 1

The first signs of defects in the spectrum of vibration signals appear when a bearing defect, having arisen, develops to such a level that the energy released by it (in goldfish) becomes relatively noticeable in the total vibration energy of the bearing, i.e. will be represented on the spectrum. In relation to the above-described division into stages of defect development, shown in Figure 3.1.1.1., this is approximately the end of the first stage - the beginning of the second. In terms of timing, this happens approximately several months from the moment the defect begins to develop. An example of the spectrum of the first stage is shown in Fig. 3.1.1.5.

In this spectrum, along with the first, mechanical, harmonics of the rotor rotation speed, a peak appears at the characteristic frequency of a defect in a particular bearing element. At this stage of defect development, the characteristic “bearing” harmonic is already clearly visible in the spectrum, which makes it possible to accurately identify the defective element, especially if the amplitude of the harmonics is represented on a logarithmic scale.

In terms of its amplitude, the peak of the characteristic harmonic is already comparable to the amplitude of the first or second harmonics of the rotor's rotation frequency, but in terms of its power it is still much inferior to them. This is reflected in the spectrum by the fact that the bearing harmonic peak is very narrow. The defect has appeared, but is not yet highly developed; there are dynamic shocks when the defect is rolled in, but their amplitude and energy are not yet very significant.

This stage, corresponding to the specific manifestation of bearing defects in the spectra of vibration signals, ends when the amplitude of the characteristic harmonic reaches its maximum, approximately equal to the amplitude of the reverse harmonic, and no longer grows. Even if it exceeds the reverse harmonic, it will not be by much, no more than 30%. The reason for this is simple - the energy of bearing harmonics is automatically “introduced” by the Fourier transform - FFT into the composition of the return harmonic. As a result, a logical rule is triggered, saying that one term cannot be greater than the total.

Diagnostic stage 2

The next stage in the development of a rolling bearing defect begins when the first pair of lateral harmonics, located on the left and right, appears on the spectrum next to the bearing harmonic, very close.

The appearance of lateral harmonics indicates that the stage of spatial expansion of the defect zone in the bearing along the rolling surfaces has begun, which is illustrated in Figure 3.1.1.6. In this zone, the defect already has such dimensions (depth) that when the rolling body “falls” into the defect zone, it shifts so much that the main load for supporting the mechanism shaft is already taken on by nearby rolling bodies. The “step” from which the rolling element “jumps” in the defect zone practically cannot be very large; its value depends on the overall degree of wear of the rolling bearing. As a result, the amplitude of dynamic pulses no longer increases. All the energy of these pulses is now spent not on deepening, but on expanding the defect zone, which occurs due to the gradual “coloring” of the boundaries of the defect zone.

At this stage of diagnosing bearing defects using the spectra of vibration signals, the “contribution of the defect” to the overall vibration of the controlled mechanism increases significantly. The bearing harmonic increases its power to such a value that it becomes comparable to the main mechanical harmonics - the first and second. The result of the presence in the vibration signal of at least two harmonics - synchronous and non-synchronous - of approximately the same power excites beat frequencies in the unit. These beat frequencies appear in the spectrum in the form of side bands near the characteristic bearing harmonic. As the power of the bearing harmonic increases with the expansion of the defect zone, the number of side stripes and their power gradually increases.

Further development of the defect leads to the emergence of new families of harmonics, starting from the most characteristic bearing frequency. Usually harmonics number two and three appear from the fundamental frequency of the bearing defect. Next to each such harmonic on the left and right there will also be side frequencies, the number of pairs of which can be quite large. The more developed the defect, the more side harmonics there are and the harmonics of the defect frequency.

Harmonics from bearing frequencies with a number greater than three are recorded quite rarely. This is due to the fact that although higher frequency harmonics occur, we cannot register them on the outer surface of the bearing supports. The higher the frequency of the oscillations that occur, the more intensely this oscillation will attenuate inside the bearing support, in the area from the place of origin to the place of installation of the primary measuring sensor.

An example of the vibration signal spectrum of a rolling bearing with this level of defect development is shown in Figure 3.1.1.7. This spectrum contains two harmonics from the characteristic frequency of a bearing defect, the first and second. Around each harmonic there are two pairs of side harmonics, located on the left and right.

The wear of a bearing with such a set of characteristic harmonics in the spectrum is already obvious. Spatially, it can extend almost over the entire working surface of the bearing; it has already become a group, capturing several elements of the bearing. The bearing needs to be replaced or intensive preparation is required for such a procedure.

I would like to complete the description of this stage of development of a defect in a rolling bearing with a small but methodologically important comparison related to the use of a general approach to diagnosing defects in rotating equipment. Upon careful examination, it is clear that the composition of the harmonics of the bearing frequency, which is shown in Figure 3.1.1.7., if you do not take into account the side harmonics, is very similar to the composition of the harmonics of the rotor rotation frequency, which occurs in the presence of mechanical weakening in the rotor, also called backlash described in the corresponding section.

Such a coincidence of types of defects actually exists in reality. The appearance of bearing frequency harmonics in the spectrum indicates the development of mechanical weakening, since with such a degree of development of the defect, the fixation of the rotor in the defective bearing no longer becomes accurate enough. The consequence of this coincidence in the manifestation of defects is the approximate equality of the sets of fundamental harmonics that arise in both cases - with a general weakening of the rotor, and with weakening in the support bearing.

Diagnostic stage 3

This is the last stage in the development of bearing defects. At the end of this stage, the bearing has already completely degraded and ceased to perform its direct functions - to ensure rotation of the shafts with minimal friction costs. Friction losses in the bearing are high, and rotor rotation is difficult.

The development of a bearing defect at this stage, when diagnosing it using the spectra of vibration signals, proceeds as follows. Bearing wear reaches a stage where the characteristic frequency of the defect, due to the very large expansion of the defect zone, becomes unstable, and the same fate befalls the lateral harmonics. The superposition of many families of harmonics, each consisting of a fundamental frequency and side harmonics, creates a rather complex picture. If in these families the fundamental harmonics differ slightly in frequency, then the sum of all these frequencies represents a general rise in the spectrum, an “energy hump” that covers a frequency range that includes all the harmonics of all families from all existing defects in the rolling bearing.

Against the general background of the “energy hump”, individual harmonics can stand out, but usually they are all random in nature, both in frequency and amplitude, and practically do not reflect anything specific. They simply increase the power concentrated in that frequency range of the spectrum.

Almost all the power of the vibration signal is concentrated not in the zone of the most significant mechanical harmonics, from the first to the tenth, but in the zone of characteristic harmonics corresponding to the existing defects of the diagnosed rolling bearing. True, at this stage there are already a lot of such defects, and this is understandable, the bearing is practically gone, there is a “solid defect” of all elements of the bearing. To illustrate this stage, figure 3.1.1.8. The spectrum of the vibration signal is shown. The figure clearly shows all of the above features of diagnosing the third stage of development of the defect.

In addition, in the range of harmonics characteristic of mechanical weakening and increased clearance in the bearing, a forest of entire rotation frequency harmonics rises. All of them correspond in their parameters to the above-mentioned mechanical reasons. The reasons for the occurrence of such harmonics are quite clear; all the gaps in the controlled bearing are large, which we already wrote about a little earlier. Only at this stage do we have mechanical weakening not at the level of defects in the rolling elements, but at the level of increasing clearances in the support bearings. As a result, multiple harmonics of the rotor rotation frequency arise.

The diagnostic conclusion about the technical condition of such a rolling bearing is very simple - it needs to be replaced as soon as possible, since the possibility of an emergency with the controlled equipment is very high.

Here we come to the most important thing in diagnosing any equipment using any method. What are the final and intermediate criteria for assessing the technical condition of a rolling bearing? How to assess the level of development of an identified defect - based on a comparison of the amplitudes of specific harmonics, or by analyzing other harmonic parameters of characteristic bearing frequencies. Unfortunately, we are once again forced to disappoint our reader; there are no such practical meanings, or, to be even more precise, they are unknown to us.

In practice, diagnosticians most often have to operate with terms like “more - less”, or “more developed defect - less developed”. It all depends on many parameters - the type of bearing, the features of its installation, the magnitude of the technological load on the bearing, and much more. In other words, the level of bearing defects in each mechanism is different and unique. The threshold value for each defect is even affected by the chosen location for installing the sensor and the distance from the place where the defect occurs. For example, in the simplest case, a defect in the inner race of a rolling bearing is less noticeable in the vibration signal than a defect in its outer race.

Determining the true level of unacceptable development of a defect in rolling bearings, or more precisely, determining the true degree of development of each defect in each bearing, most often represents the greatest difficulty, and significantly increases the complexity of using the direct spectra diagnostic method. There is nothing more useful and important than practical experience gained from the results of diagnostic measurements and comparing them with the results obtained during repair work.

In conclusion, on this issue, I would like to repeat a little what has already been said, adding some specific features to it:

• All bearing frequencies are usually modulated by the rotor speed, which leads to the appearance of characteristic side harmonics around them. As the defect deepens, the number of lateral harmonics increases. The additional vibration power from the defect turns out to be concentrated not in the fundamental harmonic of the defect, but around it, and in a fairly wide frequency range.
• Quite often it happens that the actual frequencies of characteristic harmonics from individual bearing elements do not correspond to the calculated values, and as the defect zone “deepens and expands,” this difference may increase.
• Most often, with significant degrees of development of defects, “energy humps” appear on the spectrum - areas with a general increase in level, having a large number of random peaks. Such “humps” can appear both near the characteristic frequency and near the resonance frequency of the structure or its individual element. Often the “energy hump” occurs in two places on the spectrum, both at the characteristic frequency and at the resonant one. Quite often, with a developed defect, the very harmonic of the characteristic frequency, around which the “energy hump” appeared and grew, is absent on the spectrum. Sometimes the number of “humps” can be three or even more.

3.1.1.5. Diagnostics using peak factor

In this section, we will briefly consider those methods for diagnosing rolling bearings, which analyze the presence of bearing defects based on the ratio of peaks in temporary vibration signals and the general level of “background” vibration. One of the time dependencies by which such diagnostics can be performed is shown at the beginning of this section in Figure 3.1.1.1.

Due to an established practical habit, we call these, in many ways quite different, methods of diagnosing rolling bearings, the general name - “diagnostics by peak factor”, although the developers of many companies have come up with other names for variations of this method. The diagnostic sign “peak factor” that we use is not the only one and is completely generally accepted in practice, but due to the fact that it well reflects the physical meaning of this method, we use it predominantly.

As mentioned above, this method of diagnosing rolling bearings has several fairly well-known varieties. These varieties were developed by different companies; they compare the peak and background levels of the vibration signal in slightly different ways. In one method, the peak amplitude is taken for comparison; in another, the energy; the background level can also be calculated differently.

We have already named the main varieties of this method:

• Diagnostics using RMS vibration signal and peak values ​​is a classic diagnostic method using the peak factor.
• Diagnostics using the ratio of the kurtosis of the vibration signal and the general level.
• HFD method (High Frequency Detection - a method for detecting a high-frequency signal).
• SPM method (Shock Pulse Measurement - method of measuring shock pulses).
• SE method (Spike Energy - method of measuring pulse energy).

The best versions of this method make it possible to detect defects in rolling bearings at fairly early stages, starting approximately from the end of the first stage of development. Devices that implement this method of diagnosing defects are quite simple and cheap.

Taking a more general look at all these methods, it is clear that they, due to the same theoretical, methodological and even instrumental approach to solving the problem, have approximately the same labor intensity and almost the same reliability of the diagnoses. These methods require approximately the same technical base - specialized portable vibrometers with built-in two types of vibration signal detectors - an average vibration signal level detector and a peak detector.

The use of a generalized quantitative relationship between two values ​​of the “average level – peak” type allows the diagnostician to identify bearing defects at fairly early stages of their development, which is an undoubted advantage of using this approach to diagnostics.

Each of the companies known to us that develop diagnostic methods, in their own way, using their own experience, solved the problem of normalizing the stages of development of diagnosed defects, but the practical presentation of these developments is approximately the same - these are special tables or nomograms that are quite convenient for practical use. There is no generalizing study comparing these methods with each other, and obviously there cannot be. All of them are used in practice with approximately equal success.

Issues of methodology for practical vibration measurements in these methods do not have a sufficiently detailed description. This is a result of the fact that these fairly simple diagnostic methods are intended for use by personnel who do not have special diagnostic training. Therefore, the measurement technology itself should be very simple, not “clouded” by complex theoretical calculations.

We will not compare all these methods for diagnosing rolling bearings by “peak factor” with each other; we will not look for the advantages and disadvantages of both the methods themselves and the development companies. This is a special, one might even say commercial, issue that goes beyond the main tasks solved by this methodological guide.

It will be better when each specific user makes his own decision on this issue, which method of diagnosing rolling bearings using the “peak factor” he likes best, and successfully uses it in practice. Moreover, such diagnostics are most often carried out by non-specialists who, we hope, are reading this book.

3.1.1.6. Diagnostics of bearing defects using envelope spectra

The method of diagnosing the condition of rotating equipment using vibration signal envelope spectra has received maximum applied development due to its use specifically for early diagnosis of the technical condition of rolling bearings. The basics of the method for diagnosing rolling bearing defects using the envelope spectrum and the features of its practical application are described in sufficient detail above, and therefore we will not repeat it all here.

To put it briefly and very simply, the essence of this method is to detect the high-frequency tails of the “goldfish” (see Figure 3.1.1.4), and obtain a spectrum from the resulting envelope of the high-frequency signal. The resulting curve, which envelops the original vibration signal, is more informative for diagnosing defects in rolling bearings than the original signal, since it is forcibly “removed” from unnecessary high-frequency information. For this reason, the harmonics corresponding to the characteristic bearing frequencies are more clearly represented in the spectrum of this curve; the mathematical formulas for calculating them are also given above, at the beginning of this section.

The procedure for recording the envelope of a vibration signal is quite complex. It must take into account several specific features to increase the sensitivity of the method.

• Firstly, registration is not carried out in the entire frequency range in which the measuring device can operate, but only in its narrow band. Since the first applications of this method most often took place using equipment from the Brühl & Kjær company, which, along with the creation of vibration monitoring devices, was engaged in acoustic measurements, octave definitions were used to determine the parameters of frequency bands. The current standard for calculating the signal envelope is to use one-third octave filters, or close to them.
• Secondly, it is quite difficult to select the required frequency band, the tuning of which is carried out using controlled high-order filters. On the one hand, in this frequency band there should be maximum high-frequency oscillations that occur after dynamic shocks in the bearing defect area. On the other hand, in the selected frequency band there should be minimal vibrations associated with other reasons leading to increased vibrations in the area of ​​the support bearings.

As you may have guessed, for almost every controlled bearing this issue has to be resolved separately. It depends on too many design and operational parameters.

We describe this issue in sufficient detail because the accuracy and reliability of the diagnostics of rolling bearing defects largely depends on its correct solution.

Next we present, in final form, in a general table, an almost complete list of defects that can be diagnosed in rolling bearings using spectral methods - using classical spectra and envelope spectra. In total, this table shows 15 of the most common causes of increased vibration - bearing defects with different localizations.

All defects in the table are presented in a certain chronological order, associated with the stages of the “life cycle” of a rolling bearing in equipment. First there are defects associated with the installation of bearings, which have to be encountered already at the stage of putting the equipment into operation. Next come defects in lubrication, i.e., in the operation of bearings. They are followed by problems associated with wear of the working surfaces of bearings. The table is closed by clearly expressed and already highly developed defects of bearing elements such as “chip” and “sink” on the rolling surfaces.

The “signal type” column indicates the parameter with which it is most effective to diagnose each defect. This may be the “direct” spectrum, the signal envelope spectrum, or a combination of both. In the “fundamental frequency” column, either the return harmonic or bearing harmonics, which are the main ones for diagnostics, are indicated. The next column indicates which harmonics from the fundamental frequency should be focused on. And in the last column “threshold” the level of modulation of the vibration signal by the main diagnostic harmonic is indicated. This parameter is calculated using standard signal processing formulas, which should be taken from the theory of analysis of modulated radio signals.

N	Bearing defect	Signal type	Fundamental frequency	Harmonics	Threshold
1. Problems with installing rolling bearings
1	Distortion of the outer ring during landing	Spectrum + envelope	2 x Fn	k=1.2	16 %
2	Uneven radial interference	Spectrum + envelope	k x F1	k=1.2	13 %
3	Slippage in the seat	Envelope	k x F1	k=1,2,3	9 %
4	Loose bearing	Range	k x F1	k=0.5,1,2,3	13 %
5	Contact with bearings and seals	Range	k x F1	k=0.5,1,1.5, 2,2.5,3	13 %
6	Rolling the outer ring	Spectrum + envelope	F1		16 %
2. Lubrication problems
7	Lubrication problems	Vibration background	-	-	20 dB
3. Wear problems of rolling bearings
8	Increased bearing clearances	Range	k x F1	k=1,2,3,4,5,6...	13 %
9	Outer ring surface wear	Envelope	Fн	-	16 %
10	Wear of the surface of rolling elements	Envelope	Fc or F1-Fс	k=1,2,3	15 %
11	Inner ring surface wear	Envelope	kxF1	k=1,2,..6	13 %
12	Defect of a group of friction surfaces	Envelope	Fн + Fв Fн+F1	k=1,2,...	16 %
4. Critical defects in rolling bearings
13	Sinkholes (chips) on outer ring	Envelope	k x Fн	k=1,2,3	16 %
14	Sinkholes (chips) on the inner ring	Envelope	k x Fв	k=1,2,3	15 %
15	Sinkholes (chips) on rolling bodies	Envelope	k x Ftk	k=1,2,3	15 %

Problems in the manufacture and installation of bearings can be attributed to the zero stage of development of bearing defects, when the operation of the bearing has not even begun. Lubrication problems and the initial stages of wear correspond to the first stage, when defects on the rolling surfaces are just beginning.

Severe wear and an area of ​​deepening physical defects in bearings belong to the second stage of development of defects in bearings. As mentioned above, the third stage of the development of defects in bearings, the beginning of their degradation, can be diagnosed by any method.

To illustrate the possibilities of diagnosing defects in rolling bearings, we present several characteristic spectra of the vibration signal envelope characteristic of several of the most characteristic defects.

In Figure 3.1.1.9. The spectrum of the envelope of a vibration signal from a rolling bearing with a significant cavity on the outer ring is shown. The given spectrum may contain quite a lot of harmonics, sometimes even more than ten. All of them, in their frequency, are multiples of the rolling frequency of the outer ring of the rolling bearing, i.e., they are its harmonics. There are simply no other significant, characteristic harmonics in this spectrum, so vibration diagnostics of this defect in rolling bearings does not cause significant difficulties; the diagnostic picture of the defect here is quite simple.

On the following spectrum of the vibration signal envelope, shown in Figure 3.1.1.10., a shell-type defect on the inner ring should be diagnosed. Here there are also harmonics of a characteristic frequency - the frequency of the inner ring, but there is a significant difference. Characteristic harmonics have sidebands shifted to the rotor speed. The appearance of side bands was explained above from a physical point of view.

One more explanation can be given for the reasons for the appearance of lateral harmonics, from a different point of view. A defect on the inner ring is not permanently located in the loaded area of ​​the bearing. During one rotation of the rotor, it is either in or out of the loaded zone. Thus, the defect in the inner ring is modulated by the rotor speed. A careful examination of the spectrum in Fig. 3.1.1.10. it seems that the defect is modulated by a sinusoid, along which the amplitudes of the main and side harmonics are located. This defect is also quite easy to diagnose.

We will not give examples of envelope spectra for other defects in rolling bearings. All of them are quite simple and can be easily differentiated after a little reasoning. The whole difficulty of diagnosing defects using the envelope spectrum lies in obtaining these spectra, and then everything is quite simple.

The level of the defect in the diagnostic spectra of the envelope is determined by the amount of modulation of the envelope of a given vibration signal by a characteristic harmonic. Diagnosed defects are usually characterized in this diagnostic method by levels - weak, medium and strong. The threshold of a strong defect is subject to normalization, in fractions of which the thresholds of medium and weak levels are subsequently calculated. The threshold for a moderate level of defect is most often considered equal to half the value of the threshold for a strong defect. The threshold for a weak defect level is usually set at 20 percent of the threshold level for a strong defect.

The most important thing is to correctly determine the threshold level of a strong defect. In this case, you have to take into account three aspects of the operation of the bearing and the method of vibration measurement:

• The larger the bearing size, the higher the severe defect threshold level should be. The larger bearing “rings” louder.
• The higher the operating speed of the rotor of the mechanism, the higher the threshold level for a strong defect should be. When rotating quickly, the bearing makes more noise.
• The measuring sensor should be located as close as possible to the bearing being monitored. When the sensor is removed, some of the useful information is lost in the structure and the threshold level for a strong defect must be lowered.

For each new specific type of equipment, more precisely, even for each bearing in each equipment, the threshold level of a strong defect actually has to be selected each time purely individually, not calculated, but selected.

The threshold value for a strong defect largely depends on the distance of the element with the defect from the measuring sensor. The defect thresholds for the inner ring of a bearing are always lower than the defect thresholds for the outer ring. This is explained by increased attenuation of the useful component of the vibration signal over a longer transmission path, including additional clearances in the bearing.

For reference, let us recall that, as an example, the averaged, most common, values ​​of the threshold levels of strong defects are given above in the table, which lists the defects diagnosed in rolling bearings. Depending on the method used for diagnosing bearing defects, the table contains two types of units in which the level of the strong threshold is normalized.

When using classical spectra of vibration signals to diagnose a bearing defect, the threshold level of a strong defect can be set in fractions of the normalized permissible vibration velocity value for a given bearing or also in percentage modulation. When comparing with the norm, it is necessary to use not the full, absolute value of the vibration velocity on a given bearing, but only that part of it that is caused by the diagnosed defect. It's a little more complicated, but ultimately more accurate.

When determining the quality of a lubricant, the general level of “background” vibration of a serviceable bearing with good lubrication is taken as a basis for comparison. When the overall level of “background” vibration increases tenfold, i.e. by 20 dB, the quality of the lubricant is considered unsatisfactory.

Once again, I would like to remind you that the table shows only general, average values ​​of threshold levels for strong defects. For specific bearings, these values ​​may vary by ±40% or even slightly more. It all depends on the type of bearing and its operating conditions.

The very fact of diagnosing a particular bearing defect carries useful information, but this information is of little practical use. Maintenance personnel are more interested in the question of the possibility of further practical operation of equipment with a defective bearing and the restrictions that the detected defect imposes on the possibility of using the equipment. A very important question for practice is the timing of the next repair. All these questions relate to the area related to the equipment maintenance system.

The issue of predicting the residual life of a rolling bearing is in many ways similar to predicting the total residual life of equipment, but it also has its own individual characteristics. Without going into details, we will consider the main problems that arise when calculating the residual life of bearings.

• Each bearing has its own unique physical characteristics, resulting in specific internal processes. Therefore, each bearing must be described by its own mathematical model.
• Each bearing must be described by two different models - one must describe the general wear processes of a bearing without defects, and the other must describe the development processes of internal defects.
• The time for the complete development of defects located on different elements of the bearing, for example, on the outer ring or on the cage, is different. For defects of each bearing element there must be its own mathematical model.

Even from this simple enumeration of the features of the mathematical description of the physical processes in a rolling bearing, it is clear how difficult the task of predicting the residual life of a bearing based on the results of vibration diagnostics is.

Initially, the condition of the bearing is “monitored” using a fairly stable normal wear pattern, when there are no internal defects. This continues until any defect is detected in the bearing. Here we have to abandon the normal model and move on to models of the development of defects. A very important task solved during the transition from a normal model to state monitoring using a defect development model is the most accurate possible determination of the time of defect initiation. The more accurately it is determined, the more reliable will be further predictions regarding the residual life of the bearing.

The maximum rate of development of different defects is different, therefore the development of all possible defects should be monitored, even when one of them has just arisen and the other is already quite developed. You can never say in advance which of the defects will develop to an unacceptable level first and cause the rolling bearing to be replaced during repair.

The frequency of diagnostic vibration measurements depends on the maximum rate of development of a bearing defect in a given equipment. In practical cases, measurements can be carried out over time intervals ranging from several hours to one year. With normal operation of standard equipment and taking measurements after about six months, it is possible to identify most defects at a fairly early stage and prevent accidents.

After identifying the first signs of an incipient defect, the time interval between two measurements must be reduced. Depending on the location of the defect, the time interval between measurements varies greatly. It is minimal for rolling element defects, which can develop very quickly.

The bearing must be replaced or monitored daily if it has two severe defects.

To ensure the necessary accuracy in calculating the residual life and the date of repair in the calculations, it is necessary to use mathematical models with an order of at least three to four. If we remember that one bearing is described by no less than a dozen mathematical models, then the mathematical costs necessary to correctly predict the operating parameters of a rolling bearing become imaginable. And there may be several thousand such bearings in operation at the same time at an enterprise.

The procedure for monitoring the condition of many bearings at an enterprise becomes possible only with the use of computers in which bearing databases and modern expert diagnostic systems are created and operated.

Devices of our production for diagnostics of rolling bearings

• DPK-Vibro – compact vibrometer, device for rapid diagnostics of rolling bearings
• Vibro Vision-2 – vibration signal analyzer with advanced diagnostic functions for rolling bearings

About diagnostics of reinforced concrete supports

Recently, the Department of Electrification and Power Supply (CE) of the Ministry of Railways of the Russian Federation, together with VNIIZh-Tom, developed technical instructions K-3-94, supplementing the Instructions for the maintenance and repair of reinforced concrete supporting structures of the contact network K-146-88. It is intended for power supply distances using various methods and means of diagnosing reinforced concrete supports of the contact network.

The new document clarifies the purpose of diagnostics. It is carried out to determine the actual load-bearing capacity of structures, identify supports with insufficient strength and prevent them from falling

The decrease in the bearing capacity of supports is explained mainly by two reasons: aging of concrete in the above-ground part, electrocorrosion of reinforcement in the underground part of the structure. Aging develops in all supports, regardless of the type of traction current, as a result of natural, climatic and operational influences. It is accompanied by a decrease in its strength characteristics.

This process occurs most intensively in supports with low quality manufacturing of the racks in harsh climatic conditions. An aggressive environment accelerates the aging of concrete. With good quality manufacturing of support racks and in moderate climatic conditions, the process develops quite slowly.

In the underground part of the supports, in the absence of soil aggressiveness and insignificant influence of climatic factors, concrete aging is practically not observed. On the contrary, its strength even increases over time. In aggressive soils, the loss of concrete’s strength properties is determined by the type and content of aggressive substances.

Electrocorrosion of reinforcement in the underground part of the supports occurs when leakage currents flow from the rails through the reinforcement with low ohmic resistance of the supports and faulty protective devices. The greatest danger of electrocorrosion of reinforcement is observed in the anodic and alternating zones, when the flowing current density exceeds 0.6 or the support resistance is less than 25 Ohms for each volt of rail-to-ground potential.

In areas with supports connected by group grounding, supports whose ohmic resistance is less than 100 Ohms are in all cases dangerous. This is explained by the possibility of their destruction by flowing eyes.

Depending on the location of the inspection of the supports and the reasons causing a decrease in their load-bearing capacity, a distinction is made between the diagnosis of the above-ground part and the underground part of the supports. Checking the above-ground part allows you to evaluate the bearing capacity of the supports, which changes due to the aging of concrete and a decrease in its strength characteristics. Diagnostics of the underground part is carried out to assess the condition and load-bearing capacity of supports in case of electrical corrosion damage to reinforcement, as well as in cases of concrete destruction by aggressive soils.

The type of trolling depends on the type of traction current. Thus, in areas of alternating current, where there is no electrocorrosion danger for the reinforcement, the above-ground part of the supports should mainly be diagnosed. In the underground part, diagnostics are carried out in cases where signs of damage to supports in the above-ground part are detected.

If there are no such signs, then the underground part is checked selectively on 1 - 2 supports out of every 100 supports once every 6 years. In DC sections, both types of diagnostics are mandatory.

In turn, diagnostics of the above-ground part of the supports can be selective or continuous. Selective allows you to establish the load-bearing capacity of supports that, upon visual inspection, have revealed any damage: cracks, potholes, weathering of the surface layer, its peeling, etc., as well as deflections in the console area.

When carrying out selective diagnostics, it is recommended to also check the condition of anchor supports and supports in small radius curves, regardless of the presence of damage on them. The first spot check must be carried out no later than 3 years after the site is put into operation. Subsequently, control is carried out at least once every 3 years in direct current sections and once every 6 years in alternating current sections.

Complete diagnostics are necessary to determine the actual load-bearing capacity of all supports. Under normal operating conditions, when there is no excessive aggressiveness of the environment and no signs of accelerated aging of the supports, the first complete diagnostics are carried out 20 years after the commissioning of the site.

If the same operating conditions are maintained, the second complete diagnosis is carried out 10 years after the first. Subsequent examinations are prescribed individually for each site, depending on the condition of the supports and taking into account the data from previous diagnostics.

In areas with difficult operating conditions and an extremely aggressive environment (in the area of ​​industrial enterprises on the coasts of seas and lakes), complete diagnostics of supports must be carried out more often, setting these terms based on the conditions for ensuring the safety of train traffic.

The above-ground part of the supports is examined using non-destructive testing. To do this, it is necessary to use the IZS-10N concrete protective layer thickness meter and the UK-14PM ultrasonic device, which determines the strength of concrete. Before use, devices must be checked in accordance with the operating instructions and be in working condition.

Let's consider the verification sequence. First, according to the book of supports (form EU-87), the type of structure (reinforced reinforced concrete concrete concrete, reinforced concrete concrete, metal, etc.), its standard load-bearing capacity (3.5; 4.5; 60; 8" 10 m), purpose (cantilever , transitional, anchor, locking, rigid crossbars) and service life (year of installation) They also use as-built documentation, design certificates, markings preserved on the racks, and the results of external inspection.

To establish the type of reinforced concrete support pillars in the absence of markings and as-built documentation, it is also recommended to use the IZS-10N device. To do this, the diameter indicator on its front panel is set to the number “41”, and the converter is moved around the circumference of the support post.

If the instrument readings change from 3 - 4 to 10 -15 mm, then this is a reinforced concrete rack. If the instrument arrow constantly shows 15 - 18 mm, then this is a reinforced concrete rack. The updated data is entered into the support book or into a PC in accordance with the “Supports” program of the Scientific and Technical Center “Eridan 1”.

Taking into account the data from previous surveys carried out in accordance with the requirements of the Guidelines for the maintenance and repair of reinforced concrete support structures of the contact network (K-146-88), supports with damage and defects are selected, as well as anchor supports and supports in small radius curves.

At each of them, using an ultrasonic device UK-14PM, the propagation time of ultrasound in concrete is measured and indirect indicators necessary to assess the bearing capacity of supports are determined. Changes and assessment of the bearing capacity of supports are carried out in accordance with the “Recommendations for assessing the bearing capacity of centrifuged reinforced concrete pillars of overhead contact network supports using the ultrasonic method.”

During continuous diagnostics, the ultrasound propagation time and load-bearing capacity are determined for all supports, primarily for the oldest structures. The results are analyzed and the supports are divided into groups depending on their residual load-bearing capacity.

The first group includes all supports whose measured load-bearing capacity is not lower than the minimum value established by the regulatory and technical documentation (not less than , where is the standard power of the rack, 1.6 is the minimum safety factor). Such supports continue to be used without restrictions; the next inspection period is scheduled in accordance with the established frequency.

The second group includes all supports whose load-bearing capacity was below the level established by the normative and technical documentation (less than ), where but exceeds the value of the standard bending moment (more For such structures, their actual load-bearing capacity is determined according to the table specified in the recommendations, and the actual bending moment from external load at the level of the conventional image of the foundation (at 0.5 m below the rail head).

If the actual bearing capacity of the supports exceeds the values ​​(the actual bending moment at the level of the conventional foundation cut from the total external load), then such supports continue to be used. However, they must be examined every 3 years. In cases where the actual load-bearing capacity turns out to be less, but more, the supports are installed on guys and replaced within 2-3 years (first of all, with the lowest load-bearing capacity).

The third group includes supports for which, according to measurements of indirect indicators, the load-bearing capacity is below the minimum permissible value required to bear external loads. Such structures are considered to have exhausted their service life and are replaced. Before replacement, the supports are placed on guy wires and, if possible, partially unloaded.

Diagnostics of the underground part of supports in DC sections is carried out to determine the condition of the reinforcement. OCA includes the following stages: assessment of the electrical corrosion hazard for support reinforcement; determination of the actual state of the reinforcement of supports located in zones hazardous in terms of corrosion.

In this case, the following order should be followed. At all stages and sections, the rail-ground potentials are measured and the approximate boundaries of the anodic, cathode and alternating sections are determined. Potential diagrams are constructed in accordance with the Guidelines for the maintenance and repair of reinforced concrete support structures of the contact network. The measurement data is presented in the form of potential plot diagrams.

Within each potential zone, the resistance to current spreading of each support is measured. First of all, they are necessary in the anodic and alternating zones. For individual groundings, measurements are carried out using an ammeter-voltmeter method using M231 devices or using a resistance meter MC07 (08).

For group groundings, measurements are carried out in two stages. At the first, the input impedance of the group is fixed. If it is more than 100 Ohms, then the resistance of each support is not controlled. If the input resistance is less than 100 Ohms, then they look for low-impedance supports in the group.

At the second stage, their search is carried out. To do this, they either measure the resistance of each support, disconnecting it from the group grounding, or the potential gradient near the support using an additional current source connected between the cable rail and ADO or Diakor devices. Methodology for searching for low-resistance supports using the mentioned devices is contained in the instructions supplied with them.

Based on potential conditions and measurements of support resistances or group input resistances: groundings, the electrocorrosion hazard for the fittings is assessed. Supports in which the leakage current density exceeds 0.6, or the leakage current exceeds 40 mA, or the potential gradient near them is more than 0.1, or their resistance is less than I00 Ohm are considered dangerous in terms of electrocorrosion and their underground part must be inspected.

In particularly difficult operating conditions, the method of constructing electrocorrosion diagrams is used to assess the limits of electrocorrosion hazard and establish the intensity of electrocorrosion diagrams. It is based on the use of integrating sensors.

The integrating electrocorrosion sensor is a concrete prism with a cross-section of 20x20 mm and a length of 150 mm. Inside it there is a metal electrode protruding 20 mm above one end face and having the same protective layer on the other. The electrodes are made from wire of the same diameter and class as that used for supports. Before installation in sensors, they are carefully weighed to the nearest 0.01 g and marked.

The prepared electrodes are installed in molds and filled with cementitious mortar or concrete, the composition of which is similar to that used in the manufacture of supports. If there is no data on the composition of the concrete of the supports, a mortar or concrete mixture with a cement consumption of at least 450 is used. After concreting, the sensors are kept in the molds for at least 7 days and then freed from the formwork.

The prepared sensors are supplied with an insulated conductor 2.5 - 3 m long. The place where it is connected to the electrode is carefully insulated with bitumen mastic or adhesive tape. After equipment, the sensor is buried in the ground in the alignment at a distance of 2 - 3 m and connected to the protective device on the rail side. The depth of the sensor is assumed to be approximately 0.5 m.

For individual grounding of supports, one sensor is installed per kilometer of track; for group grounding, one sensor is installed per group of supports. In the latter case, it is located at the location of the protective block. Integrating sensors attached to the rail are exposed to leakage currents for 3-6 months, then they are removed from the ground.

The sensors are broken and the electrodes are removed. They are cleaned of rust and insulation and weighed again with an accuracy of 0.01 g. Based on the results of the initial weighing and weighing after electrical corrosion exposure, metal losses are determined and the specific metal removal in is calculated. for each sensor.

Then the location of the sensors is plotted horizontally on the graph to scale and vertical segments are laid out in them, depicting the specific metal removal. The ends of the segments are connected by lines. The resulting graph is an electrocorrosion diagram. It allows you to identify areas with the greatest electrical corrosion hazard, take measures to protect supports and limit the diagnosis of supports only to these areas.

The actual state of the reinforcement of supports prone to electrical corrosion is determined using ADO or Diakor UK 14PM instruments. Using the ADO device, the value of the total transition potential after positive and negative polarization by an external current source is estimated, the “Diakor” device is the time the polarization potential reaches the control value.

If the total transition potential of the reinforcement turns out to be more than 0.75 V or the time to reach a polarization potential of 0.6 V is less than 5 minutes, then it is considered that the reinforcement is not corroded and is in good condition. When the total transition potential or the time it takes for the potential to reach the control value is less than the marked values, the underground part of the supports must be inspected.

To do this, it is chipped off. If concrete peeling cracks and rust are detected, then a conclusion is drawn about corrosion damage to the reinforcement. The support with such damage is replaced. If there are no visible damages on the surface of the support, the underground part is examined with a UK-14PM device for the presence of hidden cracks.

When there are no sharp deviations in instrument readings at different measurement locations, it is said that there is no internal damage or corrosion of the fittings. In which case, check the protective
device, and the support continues to be used. If there are signs of hidden cracks, then the support is installed on guy wires and subsequently replaced. There are situations when there are no ADO or Diakor devices. Then the condition of the underground part of the supports can be checked with the UK-14PM device. In this case, all supports assessed as dangerous in terms of electrical corrosion are dug up.

An inspection of the underground part of the supports is carried out each time after their long-term (3-4 months) operation with faulty protective devices. If the protective devices are in working order, the condition of supports with an electrocorrosion hazard should be checked at least once every 3 years.

When assessing the condition of the underground part of the supports, it is necessary to analyze the quantities! resistance of the same supports in different years. Its decrease over time may indicate failure of the insulating bushings. Particular concern is caused by cases when the resistance of supports increases sharply from a low to a high value.

This is possible for several reasons: as a result of corrosion, the fittings are completely destroyed and the electrical circuit through it has disappeared; after an accidental rupture of the contact between the reinforcement and the embedded bolt and the formation of a gap between them, due to the formation of corrosion products on the reinforcement without destruction of the protective layer of concrete. Such supports are especially carefully examined and after that a decision is made on their further operation

When the concrete is damaged by an aggressive environment, the underground part of the supports is checked after they have rebounded by 0.7 -1 m. The testing method is no different from the diagnosis of supports in the above-ground part. When selectively diagnosing the underground part of supports in AC sections, structures located in the most unfavorable conditions. The ik is dug up and kept in this state for 4-5 days. Then the necessary measurements are carried out using the same method as measurements in the above-ground part. The load-bearing capacity of structures is also assessed.

In DC areas, inspection of the above-ground and underground parts of supports can be combined or carried out separately. The specific sequence of work is determined by the condition of the supports. For metal supports, the above-ground part is diagnosed in accordance with the Instructions for assessing the load-bearing capacity and maintenance of metal support structures of overhead contact networks and floodlight masts, and the foundation part in accordance with the Instructions for the maintenance and repair of reinforced concrete support structures of overhead contact networks (K-146-88).

Based on the diagnostic results, the condition of the pole park is assessed. The analysis includes general data on the number of supports on a distance (road), including reinforced concrete and metal ones, and a detailed description of the fleet of reinforced concrete supports by type and service life.

IN AND. PODOLSKY,
head of laboratory
contact network supports of VNIIZhT
B.F. KOZHANOV,
Chief Technologist of the Central Electrical Station of the Ministry of Railways

DIAGNOSTICS OF SUPPORTS AND FOUNDATIONS OF OHL
MODERN ASSESSMENT METHODS

Electric grid construction in Russia was actively carried out from the 60s to the mid-80s of the last century. Currently, the standard service life of these facilities is ending. The lack of necessary and sufficient investments for the reconstruction of electric power facilities over the past 10-15 years has led to the accumulation of large volumes of “deferred demand”. As a result, there is an extremely serious problem: on the one hand, there is a huge number of objects that require immediate reconstruction based on standard service life; and on the other hand, the lack of financial capabilities to implement it.
From the above, an unambiguous conclusion follows: it is necessary to abandon “total reconstruction” in favor of “targeted restoration repairs” and “targeted replacement” of electrical network equipment and structures. The initial stage of this work is the diagnosis of overhead line structures. Along with traditional methods, modern diagnostic methods, which our Novosibirsk authors talk about, are increasingly beginning to be used.

Yuri Gunger, Ph.D., General Director
Victor Chernev, Head of Electrical Equipment Diagnostics Department
Group of companies "ELSI", Novosibirsk

The purpose of diagnostics is to rank equipment and structures according to their residual operational characteristics, divided into 3 groups.
The first of them is a life extension group, which includes objects with normal residual operational characteristics, despite the end of their standard service life.
The second group – “targeted restoration repair” – includes objects whose residual operational characteristics can be restored as a result of routine or major repairs.
The third group - “targeted replacement” - consists of objects whose residual operational characteristics are below normalized values ​​and cannot be restored as a result of repairs.
In recent years, various methods for diagnosing electrical devices, as the most expensive and critical elements of the electrical network, have become widespread. Methods for diagnosing the electrical part of overhead lines (OHL) and substations (SS) - wires, contact connections and insulation - have also been developed and are being introduced into operational practice. Against this background, the only widespread method for diagnosing the mechanical part of overhead lines and substations - supports, racks for equipment and foundations - remains external inspections, regulated by the operating rules of electrical installations. Unfortunately, external examinations cannot be considered as any serious diagnostic method, since such structures, along with visible defects, may also have hidden ones. At the same time, given the massive nature of these elements in any electrical network, the likelihood of accidents due to damage to the mechanical part of individual structures is quite high.

General test methods for concrete supports of overhead lines

In our opinion, the problem of diagnosing the mechanical part of overhead lines and substations that are in long-term operation should be given more serious attention. Experience shows that all reinforced concrete structures with a service life of more than 20 years should be subject to diagnostics. Currently in Russia there are several tens of thousands of reinforced concrete substation racks in use and several hundred thousand overhead line supports with reinforced concrete foundations or centrifuged racks with a service life of about 40 years.
It should be noted that the destructive processes that reduce the load-bearing capacity of reinforced concrete foundations and overhead line support posts in operation are multi-parametric: these are the influence of soil and climatic environmental factors, the influence of vibrations from wind loads, and other specific, including electrophysical, operating conditions of the electrical network. Currently, the following methods for testing concrete for strength are quite well developed:
Method of standard samples. Cubic samples are tested 28 days after manufacture, for which they are installed in a press and loaded until the sample is destroyed.
The use of cores drilled from the structure, which are tested similarly to standard samples under pressure.
A group of non-destructive testing (NDT) methods based on measuring the surface hardness of concrete.
The first method is not applicable in operation. The use of the second method is problematic because it worsens the strength characteristics of structures due to drilling samples from the body of the structure, and also because of the complex technical feasibility of such an operation in the field.

Non-destructive testing methods NDT methods are more acceptable, such as: 1. Plastic deformation method, based on measuring the size of the imprint that remains on the concrete surface after a steel ball (Kashkarov hammer) collides with it. 2. Elastic rebound method, which consists in measuring the magnitude of the rebound of the striker from the concrete surface (Schmidt sclerometer). 3. Shock pulse method, which records the impact energy that occurs at the moment the striker hits the concrete surface. 4. Tear-off method with chipping of a structure rib, which consists in recording the force required to chip off a section of concrete on the edge of a structure, or local destruction of concrete when the anchor device is pulled out of it. 5. Method for tearing off steel discs. 6. Ultrasound method, measuring the speed of passage of ultrasonic (US) waves. The first five methods make it possible to determine the strength characteristics of only the surface layer of concrete of a reinforced concrete structure, moreover, at one point, and this is their significant drawback. The ultrasonic testing method is considered the most adequate, since, unlike other methods, it allows one to measure integral strength parameters. According to the testing technique, this method is divided into through ultrasonic sounding, when the sensors are located on different sides of the test sample, and surface ultrasonic sounding, when the sensors are located on one side. The method of through ultrasonic sounding allows, unlike all other NDT methods, to control the strength of not only the near-surface layers of concrete, but also the entire volume of concrete in the structure. It should be added that modern devices (UK1401, Pulsar, Beton-32, UK-14P) make it possible to measure the strength characteristics of concrete with acceptable accuracy (8–10%). The main advantage of NDT tools based on the use of ultrasonic methods for assessing the strength of concrete is the existence of a stable dependence of the parameters of the propagation of ultrasonic vibrations in concrete on the state of its structure, the presence and accumulation of certain defects and damage in it. The occurrence of any defects in the structure of concrete that reduce its strength correspondingly changes the speed and time of propagation of ultrasound in concrete. Analysis of extensive statistical material accumulated during laboratory and field surveys revealed patterns between ultrasonic and strength characteristics. They are used to obtain comprehensive assessments of the technical condition of structures, and most importantly, to conclude about their performance in the time interval of interest. Comparing ultrasonic testing methods with such traditional methods of monitoring (TMK) of the technical condition of reinforced concrete structures, such as a Kashkarov or Fizdel hammer, a Brinell microscope or a Poldi magnifying glass, we note the main drawback of the latter: TMCs do not provide identification of defects in concrete at an early stage of their appearance and do not allow obtain quantitative estimates of the development of these defects over time due to the large error of the obtained result. The relative simplicity and low cost of these TMK instruments and accessories are their attractive advantage and explain the reason for their use.

Photo 1. Defective reinforced concrete foundation of 500 kV overhead line Photo 2. Condition of the previously repaired foundation Photo 3. Defective reinforced concrete rack of 110 kV overhead line

A comparison of the results of measuring the strength of concrete obtained on real reinforced concrete structures of different defects using ultrasonic testers and TMK shows that their similarity is observed only for structures that do not have significant visible damage. For example, when assessing the strength of concrete in a structure that has a crack, the traditional method may give an acceptable estimate of the strength, whereas when using an ultrasonic instrument, the measurement will indicate the presence of a defect.

Not only strength

The strength characteristics of concrete are very important, but not the only parameters characterizing the reliability and performance of a reinforced concrete structure. The appearance of cracks in concrete for one reason or another can cause corrosion of the reinforcement and a weakening of the load-bearing capacity of the structure from the inside. The assessment of the corrosion state of the reinforcement is carried out using electrochemical methods by polarizing it from an external current source. The resistances of anodic and cathodic polarization of reinforcement in undamaged and damaged concrete have significant differences, which provide information about the corrosion state of the reinforcement.
But a generalized assessment of the state of the entire reinforced concrete structure (foundation or support column) can be obtained using only vibration diagnostic methods based on the analysis of the attenuation decrements of low- and high-frequency mechanical vibrations artificially excited in the reinforced concrete structure. There is a certain relationship between these parameters and the state of concrete, reinforcement and their adhesion to each other. With the appearance of cracks in concrete or corrosion of reinforcement, their interaction is disrupted, which leads to a decrease in the load-bearing capacity of the structure.

Ultrasound plus vibration

The most effective modern means of monitoring the technical and corrosion state of reinforced concrete structures of substation and overhead lines is a set of tests using ultrasonic and vibration methods for assessing mechanical properties, as well as electrochemical methods for determining the corrosion state of reinforcement and metal structures of overhead lines.
For reinforced concrete structures that do not have visible defects, comprehensive and traditional inspections have approximately the same results and time costs. In the case where there is a hidden defect, the traditional method cannot determine it, even if the structure is excavated from the ground.
Despite the fact that complex diagnostics is more detailed, when working with a structure in normal condition, it takes relatively little time (~7 minutes). When diagnosing a defective or even emergency structure, the time spent doubles due to the increased volume of vibration control (~14 minutes). The traditional method of examining a structure in normal condition using a sclerometer allows it to be completed in one minute. However, in the case of examining a defective foundation or support column, they require excavation (to a depth of 0.5 to 1.5 meters), which increases the time costs by three to five times (compared to complex diagnostics).

Inspection of foundations and supports of overhead lines

The ELSI group of companies, together with NPP Elektrokorr, carried out comprehensive inspections of the foundations of a 500 kV overhead line in Irkutskenergo and the reinforced concrete supports of a 110 kV overhead line in Novosibirskenergo. At Irkutskenergo, based on survey results, the distribution of foundations into groups is as follows:

• in the foundation life extension group – 38%;
• the “addressed restoration repair” group contains 62%, of which 19% are defective foundations requiring urgent repairs during 2006, 43% are foundations that can be repaired in subsequent years;
• No emergency foundations were found, so in the group of “targeted replacement” of foundations – 0%.

At Novosibirskenergo, centrifuged racks of 110 kV overhead lines, which were visually in the worst condition, were subjected to a random inspection. However, according to the survey results, the distribution of racks into groups looks like this:

• the life extension group contains 84% ​​of racks;
• the group of “targeted restoration repairs” is 8%;
• “targeted replacement” group – 8%.

Main defects

The causes of defects in reinforced concrete foundations and metal supports are:

• active leaching of cement stone under the influence of acidic rusty water formed from rainwater in combination with corrosion products of steel support posts;
• shedding and peeling of concrete and filler, leading to exposure of the reinforcement, which subsequently leads to corrosion of the reinforcement and loss of foundation strength;
• vulnerability of the “head” of the foundation from the action of “freezing-thawing” processes of moisture.

On the surveyed 500 kV overhead lines, it was found that 68% of all foundations had already been repaired by “monolishing” the upper part of the foundation with concrete to a depth of 200 to 600 mm from the top of the foundation, while the vast majority of foundations were repaired to a depth of 200 mm. As a result of studying the degradation of concrete foundations, the optimal depth of repair of foundations was clarified, which was 500–700 mm from the ground surface. Thus, repairs to a depth of 200 mm do not make sense and are, in fact, an unproductive expenditure of allocated repair resources, since three quarters of the number of foundations that were previously repaired are again classified as defective. This fact indicates the need to search for new repair compositions and technologies that provide the required strength, greater frost resistance, less water absorption and more reliable adhesion to old concrete.
Photo 1 shows the technical condition of the defective reinforced concrete foundation of a 500 kV overhead line, and photo 2 shows the previously repaired defective foundation.
The causes of defects in centrifuged reinforced concrete pillars are:

• loosely pressed edges of the formwork allowed during the manufacture of centrifuged racks, which resulted in rapid destruction of the seams of the half-forms in operation. This defect often leads to the formation of large through holes, exposed reinforcement and the formation of significant cracks along the seams of the half-forms (photo 3);
• damage, chips received during transportation and installation of supports;
• influence of soil and climatic factors on the support pillars (formation of small and large cracks on the support pillar). These defects during operation also contributed to a decrease in the load-bearing capacity of structures, which is confirmed by vibration diagnostic data.

conclusions

1. Instead of “total reconstruction,” it is necessary to introduce local “targeted restoration repairs” and “targeted replacement” of defective elements and structures into the practice of planning the repair of electrical network equipment. This approach will allow, within the framework of limited financial and technological resources, to ensure an economically feasible level of reliability of power supply to consumers.
2. The economic effect of the proposed method is obtained by excluding from the volumes those supports and foundations, the repair of which can reasonably be postponed to a later date.
3. The main condition for effectively solving the problem of minimizing repair costs is reliable assessments of the operational condition of all elements and nodes of power transmission lines, obtained with the required accuracy as a result of the use of modern diagnostic tools.
4. Traditional methods for assessing the technical condition of reinforced concrete electrical grid structures, currently used, do not provide identification of defects in concrete at an early stage of their occurrence and do not allow obtaining quantitative estimates of the development of these defects over time due to the large error of the result obtained.
5. The most comprehensive information about the residual operational life of reinforced concrete and metal racks of supports and foundations of overhead power lines is provided by estimates obtained using ultrasonic, vibration and electrochemical diagnostics of the condition.

Literature

1. Rules for the technical operation of power plants and networks of the Russian Federation / Ministry of Fuel and Energy of the Russian Federation, RAO "UES of Russia", RD 34.20.501 - 95. - 15th ed., revised. and additional – M.: SPO ORGRES, 1996. – 160 p.
2. Shtengel V.G. On methods and means of non-destructive testing for inspection of operating reinforced concrete structures // In the world of NK. – 2002. – No. 2(16). – P.12–15.
3. Botin G.P., Poponin S.A., Tarasov A.G. Ultrasonic monitoring of the condition of reinforced concrete pillars of supports and foundations of overhead power transmission lines / Materials of the First International Scientific and Practical Conference “Power Transmission Lines - 2004: Operating Experience and Scientific and Technical Progress”. – Novosibirsk, September 20–24, 2004.
4. Gunger Yu.R., Tarasov A.G., Chernev V.T. Ultrasonic and vibration monitoring of the condition of reinforced concrete pillars of supports and foundations of overhead power lines // Electroinfo. – 2005. – No. 11. – P. 40–43.
5. Rosenthal N.K. Electrochemical method for studying the corrosion of steel in concrete by polarization resistance // Electricity supply of railways / ZI: Central Research Institute Tei MPS. – 1993. – No. 2. – P. 14–19.
6. Gukov A.I., Chadin A.B. Support diagnostic equipment. Vibration and electrochemical methods // Electric and diesel traction. – 1981. – No. 4. – P. 38–40.

SECTION 1. MATHEMATICAL MODELS AND METHODS IN THE THEORY OF TECHNICAL DIAGNOSTICS

Topic 6. Physical control methods in technical diagnostics

Lecture outline

6.5. Acoustic control methods

6.6. Radio wave methods of non-destructive testing

6.7. Thermal non-destructive testing

6.7.1. Temperature controls

6.7.2. Non-contact thermometry methods

6.5. Acoustic control methods

For the acoustic NDT method, vibrations in the ultrasonic and sound ranges with a frequency from 50 Hz to 50 MHz are used. The intensity of fluctuations is usually low, not exceeding 1 kW/m2. Such oscillations occur in the region of elastic deformations of the medium, where stress and deformation are related by a proportional relationship (the region of linear acoustics).

The amplitude of acoustic waves in liquids and gases is characterized by one of the following parameters:

acoustic pressure (Pa) or pressure change relative to the average pressure in the medium:

p = ρ c v,

where c is the speed of propagation of acoustic waves; ρ is the density of the medium;

displacement in (m) of particles of the medium from the equilibrium position in the process of oscillatory motion;

speed (m/s) of oscillatory motion of particles of the medium

v = ∂ ∂ u, t

where t is time.

There are many known acoustic methods of non-destructive testing, which are used in several versions. The classification of acoustic methods is shown in Fig. 23. They are divided into two large groups - active and passive methods.

Active methods are based on the emission and reception of elastic waves, passive methods are based only on the reception of waves, the source of which is the controlled object itself.

Active methods are divided into transmission, reflection, combined (using both transmission and reflection), impedance and natural frequency methods.

Fig.23. Classification of acoustic types of non-destructive testing

Passage methods use emitting and receiving converters located on one or different sides of the controlled product. Pulsed or continuous (less often) radiation is used. Then the signal passing through the controlled object is analyzed.

Rice. 24. Passing methods:

a- shadow; b – temporary shadow; c – velocimetric; 1 – generator; 2 emitter; 3 – object of control, 4 – receiver; 5 – amplifier,

6 – amplitude meter; 7 – travel time meter; 8 – phase meter

Passage methods include:

amplitude shadow method, based on recording a decrease in the amplitude of the wave passing through the controlled object due to the presence of a defect in it (Fig. 24, a);

temporary shadow method, based on recording the delay of the pulse caused by an increase in its path in the product when going around a defect (Fig. 24, b). The wave type does not change;

velocimetric method, based on recording changes in the speed of propagation of dispersive modes of elastic waves in the defect zone and used for one-sided and two-sided access to the controlled object (Fig. 24, c). This method typically uses dry point contact transducers. In the version with one-way access (Fig. 24, c above), the speed of the zero-order antisymmetric wave (a0) excited by the emitter in the layer separated by the defect is less than in the defect-free zone. With double-sided access (Fig. 24, c below), in the defect-free zone, energy is transmitted by a longitudinal wave L, in the defect zone - by waves a0, which travel a longer distance and propagate at lower speeds than the longitudinal wave. Defects are noted by a change in phase or an increase in transit time (only

V pulse version) for the controlled product.

IN reflection methods pulsed radiation is used. This subgroup includes the following flaw detection methods:

The echo method (Fig. 25, a) is based on recording echo signals from a defect. On the indicator screen, the sent (probing) pulse I, pulse III reflected from the opposite surface (bottom) of the product (bottom signal) and the echo signal from defect II are usually observed. The arrival time of pulses II and III is proportional to the depth of the defect and the thickness of the product. With a combined control circuit (Fig. 25, a), the same converter performs the functions of emitter and receiver. If these functions are performed by different converters, then the circuit is called separate.

The echo-mirror method is based on the analysis of signals that have experienced specular reflection from the bottom surface of the product and the defect, i.e. passed the path ABCD (Fig. 25, b). A variant of this method, designed to detect vertical defects in the EF plane, is called the tandem method. To implement this, when moving transducers A and D, they are kept constant

value I A + I D = 2Н tgα ; to obtain specular reflection from non-vertical defects, the value of I A + I D varies. One of the variants of the method, called "oblique tandem", provides for the location of the emitter and receiver not in the same plane (Fig. 25, b, plan view below), but in different planes, but in such a way as to receive a specular reflection from the defect. Another option, called K-method, involves placing the transducers on different sides of the product, for example, placing the receiver at point C.

Rice. 25. Reflection methods:

a – echo; b – echo - mirror; c – delta method; d – diffraction – time; d – reverberation;

1 – generator; 2 – emitter; 3 – object of control; 4 – receiver; 5 – amplifier; 6 – synchronizer; 7 – indicator

The delta method (Fig. 25, c) is based on the reception of longitudinal waves by a transducer 4 located above the defect, emitted by a transverse wave transducer 2, and scattered on the defect.

Diffraction-time method (Fig. 25,d), in which emitters 2 and 2’,

receivers 4 and 4' emit and receive either longitudinal or transverse waves, and can emit and receive different types of waves. The transducers are positioned so as to receive the maximum echo signals of waves diffracted at the ends of the defect. The amplitudes and arrival times of signals from the upper and lower ends of the defect are measured.

Reverberation method(Fig. 25, e) uses the influence of the defect on the decay time of repeatedly reflected ultrasonic pulses in the controlled object. For example, when testing a glued structure with an outer metal layer and an inner polymer layer, a bond defect prevents energy transfer to the inner layer, which increases the decay time of multiple echoes in the outer layer. Pulse reflections in the polymer layer are usually absent due to the high attenuation of ultrasound in the polymer.

IN combined methods use the principles of both passing and

And reflections of acoustic waves.

Mirror-shadow The method is based on measuring the amplitude of the bottom signal. In this case, the reflected beam is conventionally shifted to the side (Fig. 26, a). According to the technique of implementation (records the echo signal), it is classified as a reflection method, and according to the physical nature of the control (measures the attenuation of the signal of a product that has passed twice in the defect area), it is close to the shadow method.

The echo-shadow method is based on the analysis of both transmitted and reflected waves (Fig. 26, b).

Rice. 26. Combined methods using transmission and reflection:

a – mirror-shadow; b – echo-shadow; c – echo-through: 2 – emitter; 4 – receiver; 3 – object of control

In the echo-through method (Fig. 26, c), through signal I and signal II, which has experienced double reflection in the product, are recorded. If a translucent defect appears, signals III and IV are recorded, corresponding to the reflections of waves from the defect and also experienced reflection from the upper and lower surfaces of the product.

Leah A large opaque defect is detected by the disappearance or strong decrease in signal I, i.e. shadow method, as well as signal II. Translucent or small defects are detected by the appearance of signals III and IV, which are the main information signals.

Natural frequency methods are based on the measurement of these frequencies (or spectra) of vibrations of controlled objects. Natural frequencies are measured when both forced and free vibrations are excited in products. Free vibrations are usually excited by mechanical shock, while forced vibrations are excited by the influence of a harmonic force of varying frequency.

There are integral and local methods. Integral methods analyze the natural frequencies of a product oscillating as a whole. In local methods, vibrations of its individual sections.

In the natural frequency method, forced oscillations are used. IN

integral method generator 1 (Fig. 27, a) of adjustable frequency is connected to emitter 2, which excites elastic vibrations (usually longitudinal or bending) in the controlled product 3. Receiver 4 converts the received vibrations into an electrical signal, which is amplified by amplifier 5 and sent to resonance indicator 6. By adjusting the frequency of generator 1, the natural frequencies of product 3 are measured. The range of applied frequencies is up to 500 kHz.

Rice. 27. Natural frequency methods. Oscillation methods:

- forced: a – integral; b – local;

- free: in – integral; g – local;

1 – generator of continuous oscillations of varying frequency; 2 – emitter; 3 – object of control; 4 – receiver; 5 – amplifier; 6 – resonance indicator; 7 – frequency modulator; 8 – indicator; 9 – spectrum analyzer; 10 – impact vibrator; 11 – information processing unit

The local method using forced oscillations is known as ultrasonic resonance method. It is mainly used for measuring thickness. In the wall of the product 3 (Fig. 27.6), with the help of converters 2, 4, elastic waves (usually longitudinal) of continuously varying frequency are excited. The frequencies at which resonances of the converter-product system are observed are recorded. The resonant frequencies determine the wall thickness of the product and the presence of defects in it. Defects parallel to the surface change the measured thickness, and those located at an angle to the surface lead to the disappearance of resonances. The range of frequencies used is up to several megahertz.

IN integral method in product 3 (Fig. 27, c), freely damped vibrations are excited by the blow of hammer 2. These vibrations are received by microphone 4, amplified by amplifier 5 and filtered by bandpass filter 6, which transmits only signals with frequencies corresponding to the selected vibration mode. The frequency is measured with a frequency meter 7. A sign of a defect is a change (usually a decrease) in frequency. As a rule, the main natural frequencies are used, not exceeding 15 kHz.

IN local method(Fig. 27, d) vibrator 10, excited by generator 1, creates periodic impacts on the controlled product. Electrical signals from the receiving microphone 4 through the amplifier 5 are sent to the spectrum analyzer 9. The spectrum of the received signal, isolated by the latter, is processed by the decision device 11, the result of the processing appears on the indicator 8. In addition to microphones, piezoreceivers are used. Defects are detected by changes in the spectrum of the received pulse signal. Unlike the integral method, control is performed by scanning products. Typical operating frequency range is from 0.3 to 20 kHz.

Acoustic-topographic the method has features of integral and local methods. It is based on excitation of intense bending vibrations of a continuously changing frequency in a product and recording the distribution of vibration amplitudes using powder applied to the surface. Elastic vibrations are excited by a transducer pressed against a dry product. The converter is powered by a powerful (about 0.4 kW) generator of continuously varying frequency. If the natural frequency of the zone separated by a defect (delamination, failure of connection) falls within the range of excited frequencies, the vibrations of this zone are amplified, the powder covering it is shifted and concentrated along the boundaries of the defects, making them visible. Frequency range used

From 40 to 150 kHz.

Impedance methods use the dependence of the impedances of products during their elastic vibrations on the parameters of these products and the presence of defects in them. Mechanical impedance is usually estimated Z = F v, where F and v are complex

amplitudes of the disturbing force and oscillatory speed, respectively. Unlike characteristic impedance, which is a parameter of the medium, mechanical impedance characterizes the structure. Impedance methods use bending and longitudinal waves.

When using bending waves, a rod-type transducer (Fig. 28, a) contains 2 radiating and receiving 4 piezoelements connected to the generator 1. Through a dry point contact, the transducer excites 3 harmonic bending vibrations in the product. In the defect zone, the module Z of mechanical

impedance Z = Z e j ϕ decreases and its argument φ changes. These

changes are recorded by electronic equipment. In the pulsed version of this method, pulses of freely damped oscillations are excited in the converter-product system. A sign of a defect is a decrease in the amplitude and carrier frequency of these oscillations.

Rice. 28. Control methods: a- impedance; b – acoustic emission; 1 – generator; 2 – emitter; 3 – object of control; 4 – receiver; 5 – amplifier; 6 – processing block

information boxes with indicator

In addition to the combined converter, separate-combined converters are used, which have separate emitting and receiving vibrators in a common housing. These converters operate in pulse mode. When working with combined converters, frequencies up to 8 kHz are used. For separate-combined ones, pulses with carrier frequencies of 15-35 kHz are used.

In another embodiment, in a controlled multilayer structure, a flat piezoelectric transducer is used to excite longitudinal elastic waves fixed frequency. Defects are recorded by changes in the input electrical impedance Z E of the piezoelectric transducer. Impedance Z E is determined by the input acoustic impedance of the controlled structure, depending on the presence and depth of defects in the connection between the elements. Changes Z E are represented as a point on the complex plane, the position of which depends on the nature of the defect. Unlike methods using bending waves, the transducer contacts the workpiece through a layer of contact lubricant.

Contact impedance method, used for hardness control, is based on an assessment of the mechanical impedance of the contact zone of the diamond indenter of the transducer rod, pressed against the test object with a constant force. A decrease in hardness increases the area of ​​the contact zone, causing an increase in its elastic mechanical impedance, which is noted by an increase in the natural frequency of the longitudinal oscillating transducer, which is uniquely related to the measured hardness.

Passive acoustic methods are based on the analysis of elastic vibrations of waves arising in the controlled object itself.

The most typical passive method is acoustic emission method(Fig. 28.6). The phenomenon of acoustic emission is that elastic waves are emitted by the material itself as a result of internal dynamic local restructuring of its structure. Phenomena such as the appearance and development of cracks under the influence of external loads, allotropic transformations during heating or cooling, and the movement of dislocation clusters are the most

more typical sources of acoustic emission. Piezoelectric transducers in contact with the product receive elastic waves and make it possible to determine the location of their source (defect).

Passive acoustic methods are vibration-

diagnostic and noise diagnostic. The first one analyzes the vibration parameters any individual part or assembly using contact-type receivers. In the second, the noise spectrum of the operating mechanism is studied, usually using microphone receivers.

Based on frequency, acoustic methods are divided into low-frequency and high-frequency. The first include vibrations in the audio and low-frequency (up to several tens of kHz) ultrasonic frequency ranges. The second includes vibrations in the high-frequency ultrasonic frequency range: usually from several 100 kHz to 20 MHz. High frequency methods are usually called ultrasonic.

Areas of application of methods. Of the acoustic control methods considered, the echo method finds the greatest practical application. About 90% of objects. Using various types of waves, it is used to solve problems of flaw detection of forgings, castings, welded joints, and many non-metallic materials. The echo method is also used to measure the dimensions of products. The time of arrival of the bottom signal is measured and, knowing the speed of ultrasound in the material, the thickness of the product is determined with unilateral access. If the thickness of the product is unknown, then the speed is measured using the bottom signal, the attenuation of ultrasound is assessed, and the physical and mechanical properties of the materials are determined from them.

The echo-mirror method is used to detect defects oriented perpendicular to the input surface. At the same time, it provides higher sensitivity to such defects, but requires that there be a sufficiently large area of ​​​​a flat surface in the area where the defects are located. In rails, for example, this requirement is not met, so only the mirror-shadow method can be used there. The defect can be detected by a combined inclined transducer. However, in this case, the specularly reflected wave goes to the side and only a weak scattered signal reaches the converter. The echo-mirror method is used to detect vertical cracks and lack of penetration when inspecting welded joints.

Delta and diffraction-time methods are also used for semi-

obtaining additional information about defects during inspection of welded joints.

The shadow method is used to control products with a high level of structural reverberation, i.e. noise associated with the reflection of ultrasound from inhomogeneities, large grains, flaw detection of multilayer structures and products made of laminated plastics, when studying the physical and mechanical properties of materials with high attenuation and scattering of acoustic waves, for example, when monitoring the strength of concrete by ultrasound speed.

The local forced vibration method is used to measure small cracks with one-sided access.

The integral method of free vibrations is used to test carriage wheel tires or glassware “by ringing purity” with a subjective assessment of the results by ear. The method using electronic equipment and an objective quantitative assessment of the results is used to control the physical and mechanical properties of abrasive wheels, ceramics and other objects.

Reverberation, impedance, velosymmetric, acoustic

topographic methods and the local free vibration method are used mainly for testing multilayer structures. Reverberation The method mainly detects defects in the connections of metal layers (skin) with metal or non-metallic load-bearing elements or fillers. The impedance method detects defects in connections in multilayer structures made of composite polymer materials and metals used in various combinations. Velosymmetric The method and local method of free vibrations are used mainly to control products made of polymer composite materials. Acoustic-topographic The method is used to detect defects mainly in metal multilayer structures (honeycomb panels, bimetals, etc.).

Vibration diagnostic and noise diagnostic methods are used to diagnose working mechanisms. The acoustic emission method is used as a means of studying materials, structures, monitoring products and diagnostics during operation. Its important advantages over other inspection methods are that it reacts only to developing, truly dangerous defects, as well as the ability to test large areas or even the entire product without scanning it with a converter. Its main drawback as a means of monitoring is the difficulty of isolating signals from developing defects against a background of noise.

6.6. Radiation methods of non-destructive testing

Radiation monitoring uses at least three main elements (Fig. 29):

source of ionizing radiation;

controlled object;

detector that records flaw detection information.

Rice. 29. Transmission scheme:

1 – source; 2 – product; 3 - detector

When passing through a product, ionizing radiation is attenuated - absorbed and scattered. The degree of attenuation depends on the thickness δ and density ρ of the controlled object, as well as on the intensity M 0 and energy E 0 of radiation. If there are internal defects of size ∆δ in a substance, the intensity and energy of the radiation beam change.

Radiation monitoring methods (Fig. 30) differ in the methods of detecting flaw detection information and are accordingly divided into radio-

graphic, radioscopic and radiometric.

Radiation monitoring methods

Radiographic:			Radioscopic:				Radiometric:
Fixing the image			Image observation				Electronic registration
on film			marriage on the screen.				tric signals.
(on paper).

Rice. 30. Radiation monitoring methods

Radiographic Radiation non-destructive testing methods are based on converting a radiation image of a controlled object into a radiographic image or recording this image on a storage device with subsequent conversion into a light image. In practice, this method is the most widely used due to its simplicity and documentary evidence of the results obtained. Depending on the detectors used, a distinction is made between film radiography and xeroradiography (electroradiography). In the first case, a photosensitive film serves as a latent image detector and a static visible image recorder; in the second, a semiconductor wafer is used, and ordinary paper is used as a recorder.

Depending on the radiation used, several types of industrial radiography are distinguished: radiography, gammagraphy, accelerator and neutron radiography. Each of the listed methods has its own scope of use. These methods can be used to illuminate steel products with a thickness of 1 to 700 mm.

Radiation introscopy- a method of radiation non-destructive testing, based on converting the radiation image of the controlled object into a light image on the output screen of the radiation-optical converter, and the analysis of the resulting image is carried out during the control process.

The sensitivity of this method is somewhat less than radiography, but its advantages are the increased reliability of the results obtained due to the possibility of stereoscopic vision of defects and viewing products from different angles, “express” and continuity of control.

Radiometric flaw detection- method of obtaining information about internal

the early state of the controlled product, illuminated by ionizing radiation, in the form of electrical signals (of varying magnitude, duration or quantity).

This method provides the greatest possibilities for automating the control process and implementing automatic feedback of control and the technological process of product manufacturing. The advantage of the method is the possibility of carrying out continuous high-performance quality control of the product, due to the high speed of the equipment. This method is not inferior in sensitivity to radiography.

6.7. Thermal non-destructive testing

In thermal methods of non-destructive testing (TDT), thermal energy propagating in the test object is used as test energy. The temperature field of the surface of an object is a source of information about the features of the heat transfer process, which, in turn, depend on the presence of internal or external defects. A defect is understood as the presence of hidden cavities, cavities, cracks, lack of penetration, foreign inclusions, etc., all possible deviations of the physical properties of an object from the norm, the presence of places of local overheating (cooling), etc.

There are passive and active TNCs. With passive TNC, the thermal fields of products are analyzed during their natural functioning. Active TNC involves heating an object with an external energy source.

Non-contact thermal control methods are based on the use of infrared radiation emitted by all heated bodies. Infrared radiation occupies a wide range of wavelengths from 0.76 to 1000 microns. The spectrum, power and spatial characteristics of this radiation depend on the temperature of the body and its emissivity, determined mainly by its material and the microstructural characteristics of the emitting surface. For example, rough surfaces emit more radiation than mirrored ones.

Loss of the bearing capacity of the contact network support of an electrified railway can lead to a very serious accident with loss of life. More than half of the railway contact network supports in our country and abroad are made of reinforced concrete. The basis of such a support is a stand in the form of a thick-walled pipe with an outer diameter of 300 - 400 mm, made by centrifugation. Under the influence of climatic factors, vibration and work load, the concrete of the rack changes its structure, cracks, receives various damages, and as a result, the rack gradually loses its load-bearing capacity. Therefore, to determine the need to replace a strut, regular inspections of all struts on a certain section of the road are required. Such inspections also prevent unnecessary rejection of supports.

The possibility of objectively assessing the bearing capacity of centrifuged reinforced concrete pillars is based on reducing the speed of propagation of ultrasonic vibrations in concrete when defects appear in it. Moreover, due to the design features of the racks and the nature of the loads on them, changes in the properties of concrete in the directions along and across the rack are not the same: the ultrasound speed in the transverse direction decreases faster over time, which, apparently, can be explained by an increase in the concentration of microcracks with a predominantly longitudinal orientation. By changing the speed of ultrasound propagation along and across the rack during its operation, as well as by their ratio, one can judge the degree of loss of the bearing capacity of the rack and make a decision about its replacement.

In the practice of operating railways in Russia over the past few years, a fairly simple method has been used to assess the load-bearing capacity of centrifuged reinforced concrete pillars of overhead contact network supports, based on measurements of the speed of propagation of longitudinal ultrasonic waves in the body of the pillar in the longitudinal and transverse directions. This technique was developed at VNIIZhT as a result of many years of research into the strength of concrete in support columns and its relationship with ultrasound speed. The UK1401 ultrasonic tester is used as the main measuring tool for monitoring supports, designed to measure the time and speed of propagation of longitudinal waves in solid materials during surface sounding on a constant base of 150 mm. The tester (photo 1) is a small-sized (held in the hand) electronic unit with a digital indicator of measurement results and two ultrasonic transducers with dry acoustic contact built into its body.

Ultrasonic inspection of supports is carried out by superficially sounding the material of the rack in two mutually perpendicular directions (across and along the axis of the rack) in one or more places, depending on the type and degree of its damage. The surface sounding method allows monitoring at any place in the racks. During testing, three measurements of the ultrasound propagation time between the tester transducers in each direction are performed and the average values ​​of these measurements are determined. Using time counts instead of speed is methodologically more convenient. Based on the obtained average value of the ultrasound propagation time in the transverse direction (“P1 indicator”) and its relation to the ultrasound propagation time in the longitudinal direction (“P2 indicator”), the actual load-bearing capacity of the support is estimated. Based on the accumulated experience in assessing the condition of support posts of various types, limit values ​​of indicators P1 and P2 have been established, upon reaching which the supports must be replaced.

In Fig. Figure 2 shows the positions of the UK1401 device when monitoring the support post. The installation points of the tester transducers when sounding across the stand are selected so that longitudinal cracks, if any, pass no closer than 30 mm to any of the transducers, and there is not a single crack in the path of waves between the transducers. When sounding the rack longitudinally in the same place, the device is located between the bundles of longitudinal reinforcement in order to minimize its influence on the measurement result. To determine the position of the reinforcement, an electromagnetic concrete cover layer meter is used. Measurements are carried out, as a rule, in places where the rack is most loaded, for example, on the track side.

The control process itself, if you do not take into account the inspection of the rack and the selection of measurement locations, takes several minutes. At the selected location, the device is pressed in a horizontal position against the stand for 10-15 s, after which the measurement result is read from the indicator and recorded in the table. These steps are repeated twice, and the device is re-attached to the stand. Then three results are obtained with the instrument in a vertical position, and they are also entered into the table. Indicators P1 and P2 are calculated and the condition of the rack is assessed.

Currently, preparations are underway for the production of an upgraded version of the ultrasonic tester (flaw detector) UK1401, which will automatically calculate the average values ​​of the ultrasound propagation time over several dimensions, indicators P1 and P2, and compare them with the corresponding limit values ​​to obtain a conclusion about the suitability of the support for further operation.