Method of restoring breakdown plates' reaction pressure non-destructive measuring and equipment for application of this method

BACKGROUND OF THE INVENTION The present invention relates to a method for non-destructive measurement of the reaction pressure of reversible breakdown plates and to an apparatus for carrying out the process.

The use of reversible breakers as safety valves, which suddenly open a large flow cross-section of a pipe when a certain pressure is exceeded, is widespread. Of particular importance is the knowledge of the reaction pressure at which the plate breaks as accurately as possible. The actual method of measuring the reaction pressure, especially for mounted breakdown plates, is not yet known. The prior art method for determining the reaction pressure is to produce a number of as accurately as possible breakdown plates and to test a portion of these plates for destruction. From the reaction pressures of the destroyed breakdown plates, the rest of the series is then inferred. Either the number of platelets destroyed is very high or the tolerances of the indicated reaction pressure are too great. Moreover, the results are of a statistical nature only and cannot take account of individual differences. Thus, the prior art method is both expensive and unsatisfactory in terms of the individual breakdown plates and their properties.

The purpose of the invention is to overcome these disadvantages and to provide a method of non-destructive measurement of breakdown plates. The principle of the method according to the invention consists in measuring the resonance frequency of at least the lower harmonic oscillations of the reversing breakdown plates at different measuring pressures below the reaction pressure. The respective pressure at which the resonant frequency decreases depending on the measuring pressure this harmonic to zero and the lowest pressure at which one of the harmonics would have a zero resonant frequency, is the desired reaction pressure of the return plate.

The method according to the invention makes it possible to detect the response pressure of the breaker plate with a very low tolerance, in particular for the plates mounted at the final destination.

This allows for repeated measurements that make it possible to judge material fatigue and similar properties. In many cases, the reaction pressure can be adjusted as desired in the non-destructive measurement salt according to the invention, in particular to reduce it by changing the clamping or by targeted processing of the break-through plate.

In order to understand the method according to the invention, the relevant theory will be briefly explained in the following. In the method of the invention, the unstable bulge in the breakdown reaction is considered to be a special case of the non-damped oscillation of the rounded portion of the breakdown. The oscillation is characterized by the fact that the return force K acts against the deflection A from the rest position. The frequency f varies in a simplified correlation according to the dependence f² = const. - ---- The return force K generally comprises a component of elastic deformation of the material and an component of external load, which may be positive or negative. The positive component of the external load means that the load acts against the deflection, which is usually associated with the tensile stress. The negative component of the restoring force means that the external load promotes deflection, which is usually associated with the compressive stress. The positive benefit of the external load to the restoring force increases the frequency of free oscillations, the negative benefit reduces this frequency. In a marginal case, the negative benefit reduces the frequency to a point where there is no longer a restoring force. In this limiting case, the oscillation frequency is zero. In this case, the system should be classified as an unstable system because there is no return force; there is a buckling or buckling that results in the plate breaking.

The fact that the frequency of the self-oscillation for this limiting case of unstable plate failure is known, i.e. f-0, allows the method according to the invention, namely to make it possible to deduce from the frequency curve as a function of pressure in the noncritical load range.

It can be shown that the restoring force and thus the square of the oscillation frequency runs linearly with the external load, under all circumstances at small deformations and at stresses below the limit proportional. These conditions are met with sufficient reliability for reversible break-ins. If this is not the case in special cases, corrective measures must be taken to determine the reaction pressure.

In the application of the method according to the invention, the only difficulty is that the rounded part of the breaker plate has a plurality of waveforms which oscillate at different frequencies and whose frequencies vary differently with the internal pressure. However, there is always a linear dependence. The reaction pressure is determined by the harmonic which corresponds to the shape of the vibration at failure. It is the harmonic which at the lowest πκ of the internal pressure reaches zero frequency. In the case of an unknown breakdown plate for which the harmonic is not known in the event of failure, the frequency dependence on the internal pressure for the various oscillation shapes must be determined and extrapolated linearly to zero. In practice, however, this means only monitoring the four lowest harmonics, since higher harmonics are out of the question. The violation is often caused by the second harmonic.

In carrying out the method according to the invention, it must therefore be ensured that the measuring points of the individual harmonics are correctly assigned, since otherwise an incorrect interpolation of the result may occur. A suitable measurement procedure will be described in detail with reference to FIG.

2. It is important, in particular, that for each measuring pressure, several ping plate resonances corresponding to different harmonics are detected. As already mentioned, it is sufficient to find the four lowest resonances. When measuring at least three different pressures sufficiently distant from one another, the results are highly interpretable and naturally the accuracy of the measurements can be increased by the possible choice of the number of measuring points and the measuring pressures.

A particular significance of the method according to the invention is that it is possible to test the break-through inserts, which are permanently mounted in the. destination. In this way, it is possible to detect the influence of the method of installation on the one hand, and on the other hand the measurement can be repeated and, if necessary, measures for adjusting the reaction pressure can be taken.

According to a preferred embodiment of the invention, the reversible breaker plate is set in oscillations either by impact or by means of a noise-generating noise generator in the installed position at different measuring pressures. The oscillations are registered by a microphone or a suitable oscillator and the frequency spectrum of the oscillations is analyzed. The resonant frequencies of the various waveforms are determined.

According to the somewhat simplified method of the invention, the oscillations of the reversible breaker plate are produced by a sound generator which is driven by a frequency generator. The oscillator then registers the amplitude of the oscillation of the breakdown plate, the frequency of the frequency generator continuously changing. The resonance frequency is then determined - by maximizing the amplitude of the oscillation. This method is characterized by considerable accuracy.

According to another feature of the invention, the sound can be transmitted to the break-through plate through the apparatus structure. This has the advantage that the sound generator does not have to be bound to the fluid, which could in certain circumstances lead to difficulties when the wafers are mounted.

However, it may also be advantageous to transmit sound to the break-through plate through the fluid, especially when the design of the apparatus is unsuitable for sound transmission. In this case, the sound generator is bound to the fluid, and the sound is then transmitted to the return plate.

In order to minimize the influence of the measuring devices on the breakthrough of the break-through plate, the oscillation can be measured without contact according to the invention. Inductive or capacitive measuring methods are suitable, for example. Since reversible breaker plates are very sensitive and external influences are to be avoided when measuring, this method is preferable to mounting measuring devices.

According to the invention, the resonant frequencies can be identified without great demands on the measuring device. For this purpose, the oscilloscope beam is excited in one coordinate axis by the output of the frequency generator and in the other coordinate axis by the oscillation amplitude of the breakdown plate. When the frequencies of the sound generator change continuously, Lissajous patterns are formed on the oscilloscope screen, allowing the harmonic oscillations and resonant frequencies to be identified directly. The resonance frequencies detected at a particular measurement pressure can then be plotted, as explained in connection with FIG. 2, to facilitate graphical retrieval of the reaction pressure. Apparatus For carrying out the method according to the invention, the reversible breaker plate is clamped in the structure by means of a holder, inside the structure there is a fluid whose pressure is changeable, with a sound generator and a pressure gauge for measuring the pressure of liquid, is connected to a frequency generator for exciting the oscillations of the reversible breaker plate, which is associated with an oscillator meter, which is connected to the input of the amplifier to which it is assigned, respectively, which is associated with a device for determining the resonant frequency of the oscillations of the reversible breakdown plate.

The sound generator may be mounted on the structure, or may optionally be coupled acoustically to the fluid. Both options are suitable, depending on the circumstances, in order to be able to set the breaker plate in motion. According to the invention, a proximity sensor can be used as a vibration meter; in case the outside of the breaker plate is not accessible, the oscillator can be mounted on a structure close to the breaker plate. In many cases, the breaker plate separates only two pipe sections so that a sensor cannot be placed near the rounded portion of the breaker plate. In this case, the oscillation is measured through the structure, and the oscillation through the fluid is expediently generated.

The sound generator, sound transducer and auxiliary devices can be combined into a portable unit, the sound generator and vibration meter being designed to be mounted on different constructions. By means of such a device, the reaction pressure of the breakdown plates mounted in any structure can be determined. Only a sound generator and sound sensor are mounted at a suitable location, and the breakdown plate is then tested as described.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in conjunction with the drawing, in which Fig. 1 schematically illustrates a device for non-destructive determination of the reaction pressure of the return breakdown plates - and Fig. 2 a diagram which results from recording of measured values ​​and graphical extrapolation.

FIG. 1 shows a structure 1 which, in the simplest case, can form a pipe of suitable diameter. Inside this structure, the fluid 2 is provided. By means of the holder 3, a reversible breaker plate 4 is mounted in the structure 1. At a suitable location of the structure 1, a sound generator 5 is mounted which is acoustically coupled to the liquid 2 or transmits sound to the breaker plate 4 through the structure 1. . The frequency generator 6 serves to excite the sound generator 5, and a vibration meter 7, preferably consisting of a proximity sensor, is mounted near the break-through plate 4. For example, the sensor may be inductive or capacitive. The amplifier 8 amplifies the received signals -and directs them to the inputs y of the oscilloscope 9. When simultaneously outputting the output signal of the frequency generator 6 to the input of the oscilloscope 9, Lissajous patterns are generated on the screen of the S-axis. Since the measurement is to be carried out at different pressures of the fluid 2, the device is provided with a pressure gauge 10 and a device 11, for example a pump for adjusting the desired pressure. Apparatus in which the breakdown pads are used typically has the ability to adjust and read the pressure, so you only need to connect a sound generator and oscillation sensor to it. As a result, it is possible to investigate the behavior of the piercing plates mounted at the destination.

Giant. 2 shows a diagram that results from a graphical evaluation of measurements performed by the method of the invention. The pressure axis P1 is plotted on the x-axis and the frequency square f2 is plotted on the y-axis. In this way, the desired functional dependence is created as a straight line. The lines a, b, c represent the frequency response as a function of the system pressure for the three lowest harmonics. It can be seen that these lines can intersect in the measuring range so that correct assignment of the measuring points is not quite easy under certain circumstances. In principle, three measuring points at different pressures would have to be sufficient for a high measurement accuracy, but difficulties may arise when one of the measuring points lies close to the intersection. It is therefore proposed, as indicated in FIG. 2, to record at least three measurement groups I, II, III in order to obtain an accurate interpretation of the measurement points and to assign them to the respective harmonics. In this way, a sufficient number of measuring points are generated to accurately determine each line, and these lines can then be interpolated with sufficient accuracy to the reaction pressure region.

The line that intersects the axis. x at the lowest PA pressure, corresponds to the harmonic in case of plate failure. The x 'intersection indicates the exact reaction pressure. In this diagram, the lines for the higher harmonics would all lie higher, so they do not play a role in monitoring the reaction pressure.

For the sake of simplicity and clarity, the method of graphical evaluation has been described above. It goes without saying that it is always possible to carry out evaluations even numerically, possibly using a computer. In this case, the straight lines would be calculated from the measured points by one. from known compensation procedures and the x-axis intersection would be calculated.

In principle, the described process gives the possibility to measure the reaction pressure with almost any small tolerance for each individual breakthrough in a non-destructive manner. As the number of measuring points increases and the measuring range can be extended. the accuracy of measurements in all circumstances should be much greater than is still possible using statistical methods and destructive testing.