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

Topic 6. Physical methods of control in technical diagnostics

Lecture plan

6.5. Acoustic control methods

6.6. Radio wave methods of non-destructive testing

6.7. Thermal NDT

6.7.1. Temperature controls

6.7.2. Non-contact thermometry methods

6.5. Acoustic control methods

For the acoustic method of NDT, vibrations of the ultrasonic and sonic ranges with a frequency of 50 Hz to 50 MHz are used. The intensity of fluctuations is usually small, does not exceed 1 kW/m2. Such oscillations occur in the region of elastic deformations of the medium, where stresses and deformations are proportionally related (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 change in pressure relative to the average pressure in the medium:

p = ρcv,

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

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

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

v = ∂ ∂ u , t

where t is time.

There are many acoustic methods of non-destructive testing, which are used in several versions. The classification of acoustic methods is shown in Figure 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

Passing methods emitting and receiving transducers are used, located on one or different sides of the controlled product. Apply pulsed or continuous (rarely) radiation. Then the signal that passed through the controlled object is analyzed.

Rice. 24. Passing methods:

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

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

Passing methods include:

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

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

velocimetric method, based on registration of changes in the propagation velocity of dispersion 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 usually uses dry point contact transducers. In the variant with one-sided access (Fig. 24, top), the velocity 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 bilateral 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 a longitudinal wave. Defects are indicated by a change in phase or an increase in transit time (only

in pulse variant) according to the controlled product.

AT reflection methods using pulsed radiation. This subgroup includes the following methods of flaw detection:

The echo method (Fig. 25, a) is based on the registration of echo signals from a defect. On the indicator screen, one usually observes the sent (probing) pulse I, the pulse III reflected from the opposite surface (bottom) of the product (bottom signal) and the echo signal from the defect II. The time of arrival of pulses II and III is proportional to the depth of the defect and the thickness of the product. With a combined control scheme (Fig. 25, a), the same transducer performs the functions of an emitter and a 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 mirror reflection from the bottom surface of the product and the defect, i.e. passed the path of AVSD (Fig. 25, b). A variant of this method, designed to detect vertical defects in the EF plane, is called the tandem method. To implement it, when moving transducers A and D, they are kept constant

value I A + I D \u003d 2H tgα; to obtain specular reflection from non-vertical defects, the value of I A + I D vary. 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, bottom plan view), but in different planes, but in such a way as to receive a mirror reflection from the defect. Another option, called K-method, provides for the location of the transducers on opposite sides of the product, for example, the receiver is located at point C.

Rice. 25. Reflection methods:

a - echo; b - echo - mirror; c – delta method; d - diffraction - time; e - 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 by the transducer 4 located above the defect of longitudinal waves emitted by the transducer for transverse waves 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 maxima of the echo signals of the waves diffracted at the ends of the defect. The amplitudes and time of arrival of signals from the upper and lower ends of the defect are measured.

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

AT combined methods use the principles of both passage 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 conditionally shifted to the side (Fig. 26, a). According to the execution technique (fixes the echo signal), it is referred to as reflection methods, and in terms of the physical nature of the control (the attenuation of the signal of a product that has passed twice in the defect zone is measured), it is close to the shadow method.

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

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), a through signal I, signal II, which has experienced a double reflection in the product, is recorded. In the event of a translucent defect, signals III and IV are recorded, corresponding to wave reflections from the defect and also reflected from the upper and lower surfaces of the product.

liya. A large opaque defect is detected by the disappearance or a strong decrease in the I signal, 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 oscillations of controlled objects. Natural frequencies are measured during excitation in products of both forced and free vibrations. Free vibrations are usually excited by a mechanical shock, forced vibrations - by the action of a harmonic force of a changing frequency.

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

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

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

Rice. 27. Methods of natural frequencies. Oscillation Methods:

- forced: a - integral; b - local;

- free: c - integral; d - 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 to measure thickness. In the wall of the product 3 (Fig. 27.6), with the help of transducers 2, 4, elastic waves (usually longitudinal) of continuously changing frequency are excited. Frequencies are fixed at which resonances of the converter-product system are noted. 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 applied frequencies is up to several megahertz.

AT integral method in the product 3 (Fig. 27, c), freely damped vibrations are excited by a blow of the hammer 2. These oscillations are received by microphone 4, amplified by amplifier 5 and filtered by bandpass filter 6, which passes only signals with frequencies corresponding to the selected oscillation 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.

AT local method(Fig. 27, d) vibrator 10 excited by generator 1 creates periodic impacts on the controlled product. The electrical signals from the receiving microphone 4 through the amplifier 5 are fed to the spectrum analyzer 9. The last selected spectrum of the received signal is processed by the resolver 11, the processing result appears on the indicator 8. In addition to microphones, piezoelectric receivers are used. Defects are registered by changing the spectrum of the received pulse signal. Unlike the integral method, control is performed by scanning products. The usual operating frequency range is 0.3 to 20 kHz.

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

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. The mechanical impedance is usually estimated Z = F v , where F and v are complex

amplitudes of the perturbing force and vibrational velocity, respectively. Unlike the characteristic impedance, which is a parameter of the medium, the mechanical impedance characterizes the structure. Impedance methods use flexural and longitudinal waves.

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

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

changes are recorded by electronic equipment. In the pulse 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 - block

information bots with indicator

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

In another variant, in a controlled multilayer structure, a flat piezoelectric transducer excites longitudinal elastic waves fixed frequency. Defects are registered by changing the input electrical impedance Z E of the piezoelectric transducer. The impedance Z E is determined by the input acoustic impedance of the controlled structure, which depends on the presence and depth of defects in the connection between the elements. Changes in Z E are represented as a point on the complex plane, the position of which depends on the nature of the defect. Unlike methods that use bending waves, the transducer contacts the product through a layer of contact lubricant.

Contact impedance method, used for hardness control, is based on an estimate of the mechanical impedance of the contact zone of the diamond indenter of the rod transducer 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 oscillations of waves that occur in the controlled object itself.

The most characteristic passive method is acoustic emission method(Fig. 28.6). The phenomenon of acoustic emission consists in the fact that elastic waves are emitted by the material itself as a result of internal dynamic local rearrangement of its structure. Phenomena such as the initiation and development of cracks under the influence of an external load, allotropic transformations during heating or cooling, the movement of clusters of dislocations are the most

more characteristic sources of acoustic emission. Piezoelectric transducers contacting with the product receive elastic waves and allow to determine the place of their source (defect).

Passive acoustic methods are vibration-

diagnostic and noise diagnostic. At the first analysis of vibration parameters any a separate part or assembly using contact-type receivers. In the second case, the noise spectrum of the working mechanism is studied, usually with the help of microphone receivers.

On the basis of frequency, acoustic methods are divided into low-frequency and high-frequency. The former include oscillations in the sound and low-frequency (up to several tens of kHz) ultrasonic frequency ranges. To the second - oscillations 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 considered acoustic control methods, the echo method finds the greatest practical application. About 90% of objects. Using various types of waves, it solves the 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 one-sided access. If the thickness of the product is unknown, then the speed is measured from the bottom signal, the attenuation of ultrasound is estimated, 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 a higher sensitivity to such defects, but it 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 angle-beam transducer. However, in this case, the specularly reflected wave goes to the side and only a weak scattered signal reaches the transducer. The echo-mirror method is used to detect vertical cracks and lack of penetration in the control of welded joints.

Delta and diffraction time methods are also used for semi-

additional information about defects in the 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, in the study of the physical and mechanical properties of materials with high attenuation and scattering of acoustic waves, for example, when controlling the strength of concrete by ultrasonic speed.

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

The integral method of free vibrations is used to check the tires of wagon wheels or glassware "by the purity of the ringing" with a subjective assessment of the results by ear. The method with the use of 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.

Reverb, impedance, velosymmetric, acoustic

topographic methods and the local method of free vibrations are mainly used to control multilayer structures. reverb The method mainly detects violations of the connections of metal layers (skins) with metal or non-metallic power elements or fillers. The impedance method reveals connection defects in multilayer structures made of composite polymer materials and metals used in various combinations. Velosymmetric the method and the local method of free oscillations control mainly 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 serve to diagnose working mechanisms. The acoustic emission method is used as a means of studying materials, structures, product control and diagnostics during operation. Its important advantages over other testing methods are that it reacts only to developing, really dangerous defects, as well as the ability to check large areas or even the entire product without scanning it with a transducer. Its main disadvantage as a means of control is the difficulty of isolating signals from developing defects against the background of interference.

6.6. Radiation methods of non-destructive testing

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

source of ionizing radiation;

controlled object;

a detector that registers flaw detection information.

Rice. 29. Transmission scheme:

1 – source; 2 - product; 3 - detector

When passing through the 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 the radiation. In the presence of internal defects of size ∆δ in the substance, the intensity and energy of the radiation beam change.

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

graphic, radioscopic and radiometric.

Radiation monitoring methods

Radiographic:			Radioscopic:				Radiometric:
Image fixation			Image observation				Registration of electronic
on film			on the screen.				tric signals.
(on the paper).

Rice. 30. Methods of radiation control

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 memory device with subsequent conversion into a light image. In practice, this method is the most widely used due to its simplicity and documentary confirmation of the results obtained. Depending on the detectors used, film radiography and xeroradiography (electroradiography) are distinguished. In the first case, a photosensitive film serves as a latent image detector and a static visible image recorder, in the second case, a semiconductor wafer, and ordinary paper is used as a recorder.

Depending on the radiation used, several types of industrial radiography are distinguished: X-ray, gamma, accelerator and neutron radiography. Each of these methods has its own area of ​​use. These methods can be used to scan steel products with a thickness of 1 to 700 mm.

Radiation introscopy- method of radiation non-destructive testing, based on the transformation of 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 in the control process.

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

Radiometric flaw detection- a method for obtaining information about the internal

the early state of a controlled product, translucent with ionizing radiation, in the form of electrical signals (of various sizes, durations or quantities).

This method provides the greatest opportunities for automation of the control process and the implementation of automatic feedback control and the technological process of manufacturing the product. The advantage of the method is the possibility of continuous high-performance product quality control, due to the high speed of the equipment. In terms of sensitivity, this method is not inferior to radiography.

6.7. Thermal NDT

Thermal methods of non-destructive testing (NDT) use thermal energy propagating in the test object as a test energy. The temperature field of the object surface 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. In this case, a defect is understood as the presence of hidden shells, cavities, cracks, lack of penetration, foreign inclusions, etc., all kinds of deviations of the physical properties of the object from the norm, the presence of places of local overheating (cooling), etc.

Distinguish between passive and active TNCs. With passive TNC, the analysis of thermal fields of products is carried out in the course of their natural functioning. Active TNC involves heating the object with an external energy source.

Non-contact methods of thermal control 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, which is mainly determined by its material and the microstructural characteristics of the radiating surface. For example, rough surfaces radiate more strongly than mirrored ones.

Welcome!
Ball joints are a very serious element of the front suspension, this is especially true for classic VAZ cars. There are twice as many ball joints than in front-wheel drive cars (4 pieces), due to which the car becomes more dangerous. After all, if you do not keep track and drive a car on which the ball joints are out of order, then the wheel can simply fall on its side. If you drive at this time, the car will immediately lose control and it will be very, very difficult to stop it. We want to show you a vivid example in the video below, where the ball joint fails, and the right wheel of the car simply collapses on its side.

Note!
To carry out the diagnosis of ball bearings, you will need a mount, either a mounting blade or a crowbar; in addition, a very thin stick will need either a metal one or just a twig, but, which is very important, the stick should be even, without bends and the like. (It is best to use a metal stick 5.6 cm long). And besides all this, you will need another ruler and a small knife. Or instead of a stick, ruler and knife, take a good caliper, which will replace all these tools!

It all depends on the area where the car is operated. If you operate it in very large cities (such as Moscow), in the very center of the city, mostly on ideal roads, or in St. Petersburg, where the roads are clearly not inferior, then you don’t even bother with suspension diagnostics. Just once a year or every 100,000 km, look there, check everything and drive on. But, basically, cars of the Zhiguli brand are operated in small towns, villages and similar places where the roads, as they say, leave much to be desired. In this case, the diagnosis of the entire suspension as a whole, as well as the diagnosis of ball bearings, should be carried out as often as possible, approximately once every 20,000 km. Or after a good run into a deep hole at speed. Thus, you will always be confident in your car and will not be afraid to operate it, because after a thorough check you will know with high accuracy that the suspension is fully functional.

Note!
Few people adhere to this, because every 20,000 km to look into the suspension of a car is quite expensive for people who drive almost every day, and these 20,000 km will roll in a very short period. In this case, the ball bearings can be diagnosed immediately after the appearance of a dull knock in the front of the car or when hitting a pit. Usually such a sound appears when one of the bearings fails, but until you hear this sound, you will not understand whether the ball joints are working correctly or not. Perhaps these knocks can even be imagined. Therefore, so that this does not happen and you just do not climb into the suspension of the car, take a close look at the video below, which shows a car with a faulty and noisy ball joint.

How to diagnose ball joints on a VAZ 2101-VAZ 2107?

Note!
Ball joints are diagnosed in several ways, the most correct of which is the last (third) method. If you act according to it, then you will immediately understand whether the support needs to be replaced or not yet. But there is a big minus in this method, because in order to implement it, you will need to remove the ball joints from the car, and this takes time. Therefore, in this way, few people check ball bearings for serviceability. On the other hand, if you correctly perform the other two methods of verification, they will also give their result. And if the ball bearings are very badly damaged, then by checking them in such ways, it will also be possible to understand that they are faulty and must be replaced.

Method one (hanging the car and loading the front suspension):

1. First loosen all the nuts securing the wheel to the car, then raise the car with a jack. As soon as it hangs in the air, completely unscrew the nuts and remove the desired wheel from the car (read the article ""). After the operation, place the planks under the lower suspension arm (indicated by the red arrow) and lower the car on them. After that, you will have to get it so that the car lies completely on the suspension, or to be more precise, on the spring. The part on which the wheel is put on (indicated by the blue arrow) will have to hang in the air. That's all, start checking.

1. To check the ball joints on the car, by hanging the car, do the following. To get started, pick up a mount (as an option, a crowbar or mounting blade), then insert it as shown in the photos below. The large photo shows how to fix the mounting blade when checking the upper ball joint, the small photo shows how to fix it when checking the lower ball joint. In a small photo, little is visible and it is difficult to understand where the mounting blade should be inserted. But when you work with the car live, you will immediately understand everything and, using the spatula as a lever, move it down, then up, then down, then up, etc. During the implementation of this procedure, do not damage the anther, be careful. In the event that the support is badly damaged, then the suspension will walk a lot and already move from a small effort. In this case, the ball joints must be replaced.

Note!
It is best to check only the upper ball joints in this way, because the lower ball joints are checked a little differently. See Method 2 below for more details on how to do this!

Method two (checking the lower ball joints with a caliper):

Let's start with the fact that not all motorists have calipers. If you are in this number, then take a knife, thin wire and rulers and also proceed to check. First, you will need to use a “7 mm” wrench (or ring wrench) and completely unscrew the lower plug of the ball joint (indicated by the red arrow) with their help. Then put a caliper into the hole (some calipers have a special thin part) and measure the distance it will go. If you can’t put the caliper in (it rests on the ground, for example, but there is no jack) or if it doesn’t exist, then take a thin wire, put it into the hole until it stops, make an incision with a knife flush with the end of the ball joint and take it out. Then measure the distance from the end of the wire to this notch with a ruler. If this distance is greater than 11.8 mm, then the ball joint must be replaced.

Method three (removal of ball bearings and their visual inspection):

This is the longest way, but on the other hand, you will know for sure whether the ball joints are in good condition or if there is already play in them and they are all broken. In order to implement this method, remove the ball joints you need from the car (How to do this, read the article ""), and then carefully inspect the anther of the ball joints. It should not have cracks, breaks and similar defects. Then remove the boot completely; make sure that there is grease in the ball joint and that there is no water, dirt, etc. in the ball joint. Next, grab the tip of the ball finger with your hand (see photo below) and shake it from side to side. The finger will have to move from the effort of the hand, but hard. If the finger dangles and moves easily, or if you cannot even move it from its place, then such a ball joint is considered faulty and must be replaced.

This information can be an example for the preparation of reports on the survey of supports.

Explanatory note

to the report on the results of the inspection of the condition of reinforced concrete supports

Basis for work

The work is carried out under Contract No. 07/11 for the performance of work on the repair, maintenance and diagnostic examination of electric grid facilities

General provisions.

Composition of diagnostic work:

Checking the condition of reinforced concrete supports by non-destructive ultrasonic express method

Checking the position of the supports

List of lines and number of reinforced concrete supports to be diagnosed:

VL 220 kV D-1 Ulyanovsk - Zagorodnaya 169 supports

VL 220 kV D-9 Luzino - Nazyvaevskaya 466 supports

VL 220 kV D-13 Tavricheskaya - Moskovka 130 supports

VL 220 kV D-14 Tavricheskaya - Moskovka 130 supports

VL 220 kV L-225 Irtyshskaya - Valikhanovo 66 supports

A total of 961 reinforced concrete supports were subject to inspection.

The results of the survey of overhead lines.

In total, 1036 intermediate reinforced concrete supports were actually examined

VL 220 kV D-1 Ulyanovsk - Zagorodnaya 165 supports

VL 220 kV D-9 Luzino - Nazyvaevskaya 504 supports

VL 220 kV D-13 Tavricheskaya - Moskovka 130 supports

VL 220 kV D-14 Tavricheskaya - Moskovka 130 supports

VL 220 kV L-224 Irtyshskaya - Mynkul 53 supports

VL 220 kV L-225 Irtyshskaya - Valikhanovo 52 supports

Condition of spin racks

VL 220 kV D-1 Ulyanovsk - Zagorodnaya (165 units)

54 centrifuged drains (32.7%) are in normal condition

In the working 102 pcs. (61.8%)

In degraded 9 pcs. (5.4%)

VL 220 kV D-9 Luzino - Nazyvaevskaya (506 units)

260 centrifuge racks are in normal condition (51.4%)

In the working 170 pcs. (33.6%)

In degraded 42 pcs. (8.3%)

In pre-emergency 34 pcs. (6.7%)

VL 220 kV D-13 Tavricheskaya - Moskovka (130 pieces)

75 centrifuge racks (57.7%) are in good condition

In the working 48 pcs. (36.9%)

In degraded 5 pcs. (3.8%)

In pre-emergency 2 pcs. (1.54%)

VL 220 kV D-14 Tavricheskaya - Moskovka (130 pieces)

79 centrifuge racks are in normal condition (60.7%)

In the working 39 pcs. (30.0%)

In degraded 11 pcs. (8.46%)

In pre-emergency 1 pc. (0.76%)

VL 220 kV L-224 Irtyshskaya - Mynkul (53 units)

37 centrifuged racks (69.8%) are in good condition

In the working 11 pcs. (20.8%)

In degraded 2 pcs. (3.8%)

In pre-emergency 3 pcs. (5.7%)

VL 220 kV L-225 Irtyshskaya - Valikhanovo (52 units)

31 centrifuge racks (59.6%) are in good condition

In the working 18 pcs. (34.6%)

In degraded 1 pc. (1.9%)

In pre-emergency 2 pcs. (3.8%)

Conclusion

The examined reinforced concrete supports of the 220 kV overhead line of the Omsk enterprise of the MES of Siberia are in working order, with some operational deviations in the values ​​of the controlled parameters of individual elements from the normal state.

The main visible defects of the reinforced concrete conical and cylindrical struts SK-5, SK-7 and SN-220, from which the reinforced concrete poles of the majority of the surveyed overhead lines were made, were identified during their examination:

Local exposure of reinforcement and slight longitudinal cracking of concrete (working condition)

Slopes of centrifuge racks over acceptable limits (deteriorated condition)

The presence of transverse cracks in concrete above the allowable size (pre-emergency condition).

However, in a number of cases, instrumental control did not confirm the pre-accident danger of transverse cracks at the supports of the supports. In this regard, those supports that still have a sufficient design resource for the bearing capacity of concrete and reinforcement, and which are referred to the pre-accident state only by the presence of transverse cracks in the dangerous section of the racks, less costly measures were chosen as repair and preventive maintenance. Recommended measures for some of these supports instead of steel replacement: additional the control conditions 1 time in 3 years, protection from VOS (environmental influences), installation of temporary metal bandages. To check the correctness of the rejection of centrifuged racks of reinforced concrete supports based on the data of instrumental control of their condition, it is desirable to conduct mechanical tests of the ultimate bearing capacity of the racks in operation. Such tests have already been carried out by us earlier (Appendix 1) and showed the degree of danger of certain defects for the bearing capacity of the racks.

According to the Operating Instructions for overhead lines, supports that are in working condition require cosmetic repairs, and supports that have a slope above the permissible limit (more than 3.0 degrees) must be straightened immediately. However, in some cases, the straightening of reinforced concrete supports is undesirable because of its more harm than good. We are talking about the initially non-vertical installation of a reinforced concrete support in a prepared pit. This happens when the relief of the overhead line route does not make it possible to obtain a strict verticality of the excavation for the installation of a reinforced concrete support, or when the crossbars are incorrectly installed (Fig. 1). In any case, if the verticality of the support is not ensured during the construction of the overhead line, and during its operation there has not been a significant change in the value of the initial slope of the support, then bringing such a support to a vertical position, for example, by the ORGRES method, may lead to premature occurrence of transverse cracks at the support and weakening of the support concrete in the zone of maximum bending moment (Fig. 2). It is more correct in such cases either to organize observation of inclined supports in order to determine the trends and rates of their inclination, or to reinstall the supports in a new pit.

Rice. 1. Inclination of support No. 193 along the 220 kV overhead line D-9 "Luzino - Nazyvaevskaya"

It is known that random (or permanent) eccentricities from an external load on a support are perceived by the reinforcement of a reinforced concrete rack, and the concrete itself mainly carries a compressive load. Therefore, as long as the reinforcement of a reinforced concrete post is capable of providing a prestressing of concrete at a level significantly exceeding the breaking force that occurs in concrete due to the inclination of the post, the support is able to perform its working functions without straightening.

It is also known that corrosion of reinforcement under a layer of undamaged concrete is impossible due to the passivation of its surface under the action of an alkaline pore solution of concrete (the pH value of the concrete solution is about 10-12).

Therefore, in order to maintain the long-term operation of a reinforced concrete support that has a slope and deep cracks, sometimes it becomes more important to redecorate the damaged concrete while protecting it from environmental influences. For example, impregnation of its surface and existing cracks with highly adhesive protective materials (such as Siberia-ultra) and closing the upper opening of the rack from atmospheric moisture getting inside it.

For example, we surveyed in 2010 274 ​​pcs. reinforced concrete supports of the 220 kV Tyumen-Tavda overhead line (MES of Western Siberia), built in 1964 using cylindrical centrifuged racks CH-220, galvanized traverses and galvanized metal covers covering the upper opening of the rack, almost completely retained their bearing capacity ( fig 3). Although among them there were inclined racks (Fig. 4).

Rice. Fig. 2. Transverse cracks that have arisen in the concrete of the inclined centrifuged column of support No. 875 VL 225 due to its straightening.

Rice. 3. The top of support No. 45 of the 220 kV Tyumen-Tavda overhead line has been covered with a galvanized metal cover since the construction of the overhead line

Rice. 4. The slope of support No. 44 of the 220 kV Tyumen-Tavda overhead line is visible.

findings

1. In each specific case of detecting a slope of a reinforced concrete support that exceeds the allowable limit, it is initially necessary to organize monitoring of it in order to determine trends and rates of slope, as well as the development of existing defects. In the event of dangerous trends or threats, it is necessary either to reinstall the support in a new pit or replace it. A similar approach can be applied to struts that have not yet developed (non-hazardous) transverse cracks.

2. The pre-emergency state of some props (less than 4.5% of those examined) is caused by the presence of transverse cracks, the appearance of which is associated both with the alignment of the supports and with supercritical external influences. In total, there are 42 such racks that need to be replaced before 2016. This includes the replacement of support posts No. 9 on each 220 kV overhead line D-13 and D-14 and support posts No. 74, 85, 120, 181 and 183 on 220 kV overhead lines D-1.

During the year, it is necessary to reinstall or replace support No. 152 on a 220 kV D-9 overhead line with a slope of more than 7 degrees, and install metal bandages on supports No. 172 and 350 of this overhead line in the zone of their intense cracking.

Overhead line diagnostics

Overhead power line (VL) - a device for the transmission and distribution of electrical energy through wires located in the open air and attached to supports or brackets and racks on engineering structures using insulators and fittings. Branches to inputs to buildings belong to VL.

Insulator diagnostics. An important place in ensuring the reliable operation of power supply devices is occupied by modern and high-quality diagnostics of network insulation. To date, there are no sufficiently reliable methods for remote detection of defective insulators and technical means that allow these methods to be implemented. Porcelain disk insulators are tested with a voltage of 50 kV industrial frequency for 1 min, then with a megohmmeter for a voltage of 2.5 kV their resistance is measured, which should be at least 300 MOhm. Diagnostics of insulators in operation is carried out by remote control devices or measuring rods (Figures 2.6 - 2.8). Let us consider what physical effects arise as a result of applying a high voltage to an insulator. From the theory it is known that if an electric field of sufficient strength is applied to two electrodes separated by an insulator, then an electrically conductive layer is formed on the surface or in the body of the insulator, in which an electric discharge arises and develops - a streamer. The emergence and development of the discharge is accompanied by the generation of oscillations in a wide frequency range (in the infrared, i.e. thermal, sound, ultrasonic frequency ranges, in the visible spectrum and in a wide range of radio frequencies). Hence, it is obvious that the receiving part of the diagnostic device should detect one or another of the listed consequences of the formation and development of the streamer. Polymer insulators fail in different ways than porcelain or glass insulators, and it is difficult to determine the condition of such insulators in the absence of any observable physical defects such as cracks or blackening.

On VL 110 kV only suspension insulators are used; on VL 35 kV and below, both suspension and pin insulators can be used. When an insulator breaks down in a garland, its dielectric "skirt" collapses and falls to the ground if the skirt is made of glass, and when a porcelain insulator breaks down, the skirt remains intact. Therefore, faulty glass insulators are visible to the naked eye, while the diagnosis of broken porcelain insulators is possible only with the help of special devices, for example, the Filin ultraviolet diagnostic device.

Overhead lines (VL) of power transmission with a voltage of 35 kV and above are the main ones in power transmission systems. And therefore, defects and malfunctions occurring on them require immediate localization and elimination. An analysis of accidents overhead lines shows that numerous failures of overhead lines occur annually as a result of changes in the properties of the material of wires and their contact connections (CS): destruction of wires due to corrosion and vibration effects, abrasion, wear, fatigue, oxidation, etc. In addition, every year the number of damage to porcelain, glass and polymer insulators is growing. There are many methods and systems for diagnosing the above elements, however, they are usually laborious, have increased danger and, in addition, require disconnecting the equipment from voltage. The method of surveying overhead lines by helicopter patrols is characterized by high productivity. Per day of work (5 - 6 h) are examined up to 200 km lines. During helicopter patrols, the following types of work are carried out:

Thermal imaging diagnostics of overhead lines, insulators, contact joints and fittings in order to identify elements subjected to thermal heating due to emerging defects (Figure 5.8);

Ultraviolet diagnostics of overhead lines, insulators, contact connections in order to detect corona discharges on them (Figure 5.10);

Visual control of supports, insulators, contact connections (Figure 5.9, a high-resolution video camera is used).

The use of thermal imagers makes it possible to greatly simplify the process of monitoring the state of arresters installed on overhead lines 35, 110 kV. Based on the thermogram, it is possible to determine not only the phase of the arrester with an increased conduction current, but also a specific defective element that affected the growth of this current. Timely replacement and repair of defective elements allows you to continue the further operation of the arresters.

The use of aviation inspections, as inspection technologies develop, is also increasing in foreign countries. For example, TVA is working on the use of high-resolution infrared cameras on a stabilized suspension and DayCor cameras for detecting corona on elements of overhead lines during the daytime, radar for

detecting rotting wooden supports, etc. The formation of a corona on the elements of overhead lines indicates short circuits, cracks or contamination of ceramic insulators or breaks in wire strands. Corona produces a weak ultraviolet radiation that cannot be seen during the daytime. DayCor camera thanks to a filter that allows only ultraviolet radiation in the wavelength range 240 - 280 nm, allows you to detect the corona in the daytime.

For operational diagnostics of the state of support-rod insulators and ceramics of high-voltage bushings, a small-sized portable vibrodiagnostic device "Ajax-M" is used. To obtain diagnostic information, an impact is applied to the shoe of the support insulator, after which resonant oscillations are excited in it. The parameters of these oscillations are related to the technical condition of the insulator. The appearance of defects of any type leads to a decrease in the frequency of resonant oscillations and an increase in their decay rate. To eliminate the influence of resonant vibrations of structures associated with the insulator, vibrations are recorded after two impacts - on the upper and lower shoes of the insulator. Based on a comparison of the spectra of resonant vibrations upon impact on the upper and lower parts of the insulator, an assessment of the technical condition and a search for defects is carried out.

With the help of the Ajax-M device, it is possible to diagnose the condition of the support insulation and search for the following types of defects: the presence of cracks in the ceramics of the insulator or the places where the ceramics are embedded in the support shoes; the presence of porosity in the ceramics of the insulator; determination of the coefficient of technical condition of the insulator. Based on the results of the diagnostics, the categories of the insulator state are determined - “requires replacement”, “requires additional control” or “can be operated”. The registered parameters of the insulator state can be written to the long-term memory of the device and, later, to the computer memory for storage and processing. With the help of an additional program, it is possible to evaluate the change in the parameters of the insulator from measurement to measurement. With the help of the device, diagnostics of the state of insulators of almost any type and brand can be carried out.

For condition assessment valve arresters

resistance measurement;

measurement of conduction current at rectified voltage;

breakdown voltage measurement;

thermal imaging control.

For condition assessment surge arresters the following tests are used:

resistance measurement;

conduction current measurement;

thermal imaging control.

Wire diagnostics. To identify possible problem areas on power lines due to vibration, a device is used to monitor and analyze the vibration of wires of power lines. The device allows you to evaluate on site in real weather conditions the vibration characteristics of power lines with different designs, wire tensions and technical support, to determine the nominal service life of wires subjected to vibration. The instrument is a vibration instrument used in the field to monitor and analyze the vibration of overhead power line wires due to wind. It measures the frequencies and amplitudes of all vibration cycles, stores the data in a high-definition matrix, and processes the results to provide an average lifetime estimate.

investigated wires. Measurement and evaluation methods are based on the international IEEE standard and the CIGRE procedure. The device can be installed directly on the wire near any type of terminals. The instrument consists of a calibrated beam sensor bracket clipped onto a wire clamp that supports a short cylindrical body. The sensing element in contact with the wire transmits the movement to the sensor. Inside the case are a microprocessor, an electronic circuit, a power supply, a display and a temperature sensor. Using the bend amplitude ( Yb) as a measurement parameter for evaluating the vibration severity of a wire is a well-recognized practice. Differential offset measurement at 89 mm from the last point of contact between the wire and the metal suspension clamp is the starting point for the IEEE standardization of wire vibration measurements. The sensor is a cantilever beam that senses the bending of the wire near the suspension or hardware clamps. For each cycle of vibration, the strain gauges generate an output signal proportional to the bending amplitude of the wire. Vibration frequency and amplitude data are stored in the amplitude/frequency matrix according to the number of events. At the end of each monitoring period, the built-in microprocessor calculates the nominal wire life index. This value is stored in memory, after which the microprocessor returns to the waiting mode for the next start. The microprocessor can be directly accessed from any I/O terminal or computer via the RS-232 communication line.

Defectoscopy of wires and lightning protection cables of overhead power lines. The reliability of overhead lines depends on the strength of steel ropes used as current-carrying, load-bearing elements in combined wires, lightning protection cables, guy wires. The control of the technical condition of the overhead line and its elements is based on a comparison of the identified defects with the requirements of the standards and tolerances given in the design materials of the examined overhead line, in state standards, PUE, SNiP, TU and other regulatory documents. The condition of wires and cables is usually assessed by visual inspection. However, this method does not allow you to detect breaks inside the wires. For a reliable assessment of the condition of wires and cables of overhead lines, it is necessary to use a non-destructive instrumental method using a flaw detector, which allows you to determine both the loss of their cross section and internal wire breaks.

Thermal method for diagnosing VL. It is possible to detect a heat leak and prevent an accident associated with overheating on overhead lines at the earliest stages of its occurrence. Thermal imagers or pyrometers are used for this purpose.

Assessment of the thermal state of current-carrying parts and insulation of overhead lines, depending on the conditions of their operation and design, is carried out:

According to normalized heating temperatures (temperature exceedances);

Excessive temperature;

Dynamics of temperature change over time;

With a change in load;

By comparing measured temperature values ​​within a phase, between phases, with known good areas.

The limit values ​​of the heating temperature and its excess are given in the regulatory directives RD 153-34.0-20363-99 "Basic provisions of the methodology for infrared diagnostics of electrical equipment and overhead lines", as well as in the "Instructions for infrared diagnostics of overhead power lines".

For contacts and contact connections, calculations are carried out at load currents (0.6 - 1.0) I nom after the corresponding recalculation. The conversion of the excess of the measured temperature value to the normalized one is carried out based on the ratio:

, (2.5)

where ∆ T nom - temperature rise at I nom;

Δ T slave - temperature rise at I slave;

For contacts at load currents (0.3 - 0.6) I The nominal assessment of their state is carried out according to the excess temperature. The temperature value converted to 0.5 is used as a standard I nom. For conversion, the ratio is used:

, (2.6)

where: Δ T 0.5 - excess temperature at load current 0.5 I nom.

Thermal imaging control of equipment and current-carrying parts at load currents below 0.3 I nom is not effective for detecting defects at an early stage of their development. Defects detected under the specified loads should be attributed to defects in the emergency degree of failure. And a small part of the defects should be attributed to defects with a developing degree of failure. It should be noted that there is no assessment of the degree of failure of defects on indirectly overheated equipment surfaces. Indirect overheating can be caused by latent defects, such as cracks, inside the disconnector insulators, the temperature of which is measured from the outside, and often the defective parts inside the object are very hot and badly burnt. Equipment with indirect overheating should be referred to the second or third degree of overheating. The assessment of the state of joints, welded and made by compression, should be carried out according to the excess temperature.

Checking all types of wires of overhead power lines by thermal imaging method is carried out:

Newly commissioned overhead lines - in the first year of their commissioning at a current load of at least 80%;

Overhead lines operating with maximum current loads, or supplying critical consumers, or operating in conditions of increased atmospheric pollution, large wind and ice loads - annually;

Overhead lines that have been in operation for 25 years or more, with the rejection of 5% of contact connections - at least 1 time in 3 years;

The rest of the VL - at least 1 time in 6 years.

Ultrasonic diagnostics of overhead lines. Assessment of the state of reinforced concrete supports with an ultrasonic surface sounding device. Constant monitoring of the condition of the overhead line supports not only prevents accidents, but also significantly increases the profitability of the operation of electrical networks, repairing only those supports that really need to be repaired or replaced. A significant proportion of overhead lines in our country and abroad is made of reinforced concrete. A common type of reinforced concrete support is a column in the form of a thick-walled pipe, made by centrifugation. Under the influence of climatic factors, vibration and workload, the concrete of the rack changes its structure, cracks, receives various damages, and as a result, the rack gradually loses its bearing capacity. Therefore, to determine the need to replace the rack, regular inspections of all racks of electrical networks are required. Such surveys also prevent unnecessary rejection of supports.

The possibility of an objective assessment of the bearing capacity of centrifuged reinforced concrete pillars is based on the fact that with a change in the structure of concrete and the appearance of defects in it, the strength of concrete deteriorates, which manifests itself in a decrease in the propagation velocity of ultrasonic vibrations. 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 speed of ultrasound in the transverse direction decreases faster with time, which, apparently, can be explained by an increase in the concentration of microcracks with a predominantly longitudinal orientation . By changing the values ​​of the velocities of propagation of ultrasound along and across the rack during its operation, as well as their ratio, one can judge the degree of loss in the bearing capacity of the rack and make a decision about its replacement.

The loss of the bearing capacity of the support of the contact network of the electrified railway can lead to a very serious accident with the death of people. More than half of the poles of the contact network of railways 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 workload, the concrete of the rack changes its structure, cracks, receives various damages, and as a result, the rack gradually loses its bearing capacity. Therefore, to determine the need to replace the rack, regular inspections of all racks of a certain section of the road are required. Such inspections also prevent unnecessary rejection of supports.

The possibility of an objective assessment of the bearing capacity of centrifuged reinforced concrete pillars is based on a decrease in the propagation velocity 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, the changes in the properties of concrete in the directions along and across the rack are not the same: the speed of ultrasound in the transverse direction decreases faster with time, which, apparently, can be explained by an increase in the concentration of microcracks with a predominantly longitudinal orientation. By changing the values ​​of the propagation velocities of ultrasound along and across the rack during its operation, as well as by their ratio, one can judge the degree of loss in the bearing capacity of the rack and make a decision about its replacement.

In the practice of operating railways in Russia in the past few years, a fairly simple method has been used to assess the bearing capacity of centrifuged reinforced concrete poles of contact network supports, based on measurements of the propagation velocity of longitudinal ultrasonic waves in the body of the pole 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 piers and its relation to the speed of ultrasound. The UK1401 ultrasonic tester is used as the main measuring tool in the control of supports, designed to measure the time and velocity of propagation of longitudinal waves in solid materials with surface sounding at 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 a dry acoustic contact built into its body.

Support Ultrasonic Inspection is carried out with surface sounding of the rack material in two mutually perpendicular directions (across and along the axis of the rack) in one or more of its places, depending on the type and degree of damage to it. The method of surface sounding allows you to control in any place of the racks. During the control, three measurements of the propagation time of ultrasound between the transducers of the tester in each direction are performed and the average values ​​of these measurements are determined. The use of time readings instead of speed is methodically more convenient. Based on the obtained average value of the propagation time of ultrasound in the transverse direction (“P1 index”) and its relation to the propagation time of ultrasound in the longitudinal direction (“P2 index”), the actual bearing capacity of the support is estimated. Based on the accumulated experience in assessing the state of the supports of various types of supports, the limit values ​​\u200b\u200bof indicators P1 and P2 are established, upon reaching which the supports must be replaced.

On fig. Figure 2 shows the positions of the UK1401 device during the control of the support leg. The installation points of the transducers of the tester when sounding across the rack are chosen so that the 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 the waves between the transducers. With longitudinal sounding of the rack 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 measuring device of the protective layer of concrete is used. Measurements are taken, as a rule, in places where the rack is most loaded, for example, from the side of the track.

The control process itself, if you do not take into account the inspection of the rack and the choice of measurement sites, takes several minutes. In the selected place, the device in a horizontal position is pressed against the rack 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 reattached to the rack. Then three results are obtained with the vertical arrangement of the device, and they are also entered in the table. Indicators P1 and P2 are calculated and the state of the rack is assessed.

Currently, the production of a modernized version of the UK1401 ultrasonic tester (defectoscope) is being prepared, which will automatically calculate the average values ​​of the propagation time of ultrasound over several measurements, 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.