RU2251687C1 - Method of acoustical testing of pump rods - Google Patents

Abstract

FIELD: testing engineering.

SUBSTANCE: method comprises setting the rod on three supports. The center of symmetry of the rod is set on one of the supports. The two other supports are positioned at the same distance from the first support. The first support receives the receiver of acoustical signals. The two other supports receive strikers. The acoustical signal generating by each striker is analyzed in the receiver. The analysis is divided into time intervals which allow the analysis of the condition of each part of the rod, including its heads.

EFFECT: enhanced reliability of testing.

7 dwg

Description

The invention relates to acoustic non-destructive testing methods and can be used to diagnose the quality of sucker rods according to their vibration parameters.

A known method of magnetic induction flaw detection of the body of the sucker rods [1] and a modern device for its implementation [2]. The device, in particular, contains a flaw detector and a mechanism for moving it along the rod.

The rod is magnetized and the flaw detector reads the magnetic induction of the rod body when moving along it. If there is a defect in the rod, the magnitude of the magnetic induction changes. This method is widely used at present.

The disadvantages of this method are:

1. The inability to determine defects in the rod heads.

2. Insufficient accuracy of defect determination in the body of the rod ([1], p.15).

A known method for detecting cracks in products having a plane of symmetry [3]. Free vibrations of a product fixed at a point of symmetry are excited, and decrements of vibration damping at two symmetric points are measured. If there are no defects, then the damping decrements will be the same. In the presence of a defect, the attenuation decrement in the defective part will be greater.

This method, apparently, is applicable to sucker rods. However, due to the large length of the rod (8 m) and its strong deflection (up to 1 m), it is difficult to do.

A known method of non-destructive quality control of a product [4], including installing a controlled product on supports, exciting vibrations in it, determining the frequency and decrement of these vibrations, comparing the obtained values with the values of the same parameters obtained on the reference product.

This method is by technical essence closest to the proposed one and therefore we have chosen for the prototype.

The disadvantage of the method described in the prototype is that it only determines whether there is a defect in the product, but does not allow to judge, at least approximately, on the location of the defect.

To overcome this drawback, we propose a method of acoustic control of sucker rods, including installing a controlled rod on supports, excitation of natural elastic vibrations and comparing the results of analysis with reference data, characterized in that the excitation of acoustic vibrations is carried out sequentially at two points located at equal distances from the center the symmetry of the rod, the removal of oscillations is carried out in a plane passing through the center of symmetry of the rod, and acoustic signals are divided into several Yemen intervals (containing information about the status of different parts of the bar), each of which is performed spectral analysis, which gives an indication of the state as the different parts of the rod body and her head.

Figure 1 shows the measurement scheme, figure 2 and 3 - frequency spectra of natural vibrations from sections A and D of the pump rods SHN-25 without defects and with a defect, figure 4, 5 is a view of the original acoustic signals from rods SHN -19, Fig.6, 7 - frequency spectrum of vibrations from sections A and D of the rods SHN-19 without defects and with a defect.

The proposed method is as follows.

The rod 1 is mounted on three supports 2, 3, 4. An acoustic vibration detector is mounted in the central support 3, and piezoelectric drums are mounted in the supports 2 and 4. Supports 2 and 4 are located at equal distances from the support 3. The center of symmetry of the rod should be located above the support 3.

Include one of the drummers, for example 2, and strike the first blow. Fluctuations from the point of impact extend in both directions. At the same time, oscillations from different sections of the rod containing spectral information about their state come sequentially to the vibration receiver. The first to the oscillation receiver 3 is the signal propagating to the right of the drummer and the past section B. The second to the receiver is the signal propagating to the left of the drummer 2, past the section A and reflected from the left end of the rod. The signal arriving last to the right and reflected from the right end of the bar comes last. Their location on the recording curve of the oscillations of the bar is easy to note, knowing the length of sections A, B, C, D, determining the propagation speed of the signal V = lv / tv, where lv is the length of section B, tv is the travel time of section B by the signal arriving at receiver 3 first (delay time to start recording vibrations by receiver 3 after firing of trigger 2).

The second drummer 4 is turned on and a second strike is applied, after recording the oscillations after which spectral information on the state of the parts of the rod C, D and A + B is likewise obtained, which confirm and supplement the results obtained by spectral analysis of the oscillations after the first impact.

To obtain information about the condition of the heads, the length of sections A and B must be taken close enough to the length of the heads.

The present invention allows to determine the condition of both the body of the rod and its heads, increases the reliability of flaw detection and the speed of inspection of the pump rod.

Example 1

The proposed acoustic control method was tested on two rods SHN-25 of the Ochersky Engineering Plant with a length of 8 m from steel 15Kh2GMF made in accordance with GOST 13877-96. One rod was defect-free, and the second one had a crack near one of the heads.

The rods were placed on three supports in accordance with the scheme in figure 1. The lengths of sections A, D and B, C were 0.3 m and 3.7 m, respectively. The length of the heads of the examined rods is 0.12 m. The vibrations after impacts were recorded using the Metacon-express acoustic control device certified in the certification system in the electric power industry (registration number SP 0034300704), entered into the Register of measuring instruments approved for use on railroad transport in the section "Measuring instruments used in the electrification and power supply facilities" under the number MT-024.2001. The mechanical vibrations in it are converted into electrical ones with a sampling frequency of 100 kHz (the time interval between adjacent points is 0.01 ms).

Figure 2 and 3 shows the acoustic spectra obtained by the Fourier analysis of those time segments of the recorded signals that relate to sections of the rods A (under the action of the hammer 2) and D (under the action of the hammer 4). The frequencies in kHz are plotted along the abscissa, and the relative amplitudes of the spectrum components are plotted along the ordinates. In a defect-free rod (Fig. 2), the spectra from these sections are the same, while in a rod with a defect (Fig. 3), the vibration spectra from sections A and D do not coincide. Additional high frequencies appear in the spectrum of vibrations from section D, while the spectrum of vibrations from section A of this rod is similar to the spectra of a defect-free rod. Changing the shape of the spectrum compared to a defect-free sample allows you to register the area on which the defect is located. In our case, this section D, i.e. the crack is located in the head or in the immediate vicinity of it.

Example 2

Two rods SHN-19 of the Ochersky machine-building plant with a diameter of 19 mm and a length of 8 m made of steel grade "N" were tested. One of them did not contain defects, and in the second there was a crack near the head. The test conditions were the same as in example 1. FIGS. 4 and 5 show a view of the original acoustic signals received from a defect-free rod (FIG. 4) and containing a defect (FIG. 5). The number (1) denotes the signal received when the oscillator was excited by the drummer 2, the number (2) - when the oscillator was excited by the drummer 4. The time in ms is plotted on the abscissa, and the signal amplitude in mv on the ordinate. On these signals, time intervals corresponding to sections B, A (in FIG. 4) and C, D (in FIG. 5) are highlighted. A view of the spectra of the signals from sections A and D is shown in Fig.6. It can be seen that the spectra are similar. Figure 7 shows a view of the spectra of signals from sections A and D obtained on a defective rod. In the spectrum of vibrations from section D, there is an additional higher frequency, which makes it possible to register the section on which the defect is located (section D).

Thus, the above examples show the possibility of rejecting defective rods according to their acoustic characteristics with registration of the area where the defect is located.

LITERATURE

1. Okrushko E.N., Urakseev M.A. Flaw detection of sucker rods. M., Nedra, 1983

2. Installation for non-destructive testing of deep-sucker rods. Russian Patent No. 2106624, publ. 06/06/96

3. V.I. Kirsa, A.S. Kireev, V.P. Lysenko. A method for detecting cracks in an article. A.S. No. 1228008, publ. 04/30/86

4. Slyusarev G.V. The method of non-destructive quality control of the finished reinforced concrete product. Russian Patent No. 2160893, publ. 03/29/99

Claims (1)

The method of acoustic control of sucker rods, including the installation of sucker rods on three supports with an oscillation receiver and two shockers, excitation of natural elastic vibrations, vibration analysis and comparison of the analysis results with passport data, characterized in that the acoustic vibrations are taken at the center of symmetry of the rod, sequential excitation of vibrations is carried out at two points located at equal distances from the center of symmetry of the rod, and the acoustic signals obtained in this case are divided into several lko time slots, each of which is analyzed separately, allowing you to determine the status of various parts of the bar, including its head.

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