RU2583167C1 - Method of measuring gas flow in pipelines and device therefor - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment and can be used in devices for measuring gas flow in pipelines. Disclosed is a method of measuring gas flow in pipelines and device for its implementation. Disclosed method is characterised by that it comprises exciting a Lamb wave of circular structure with a circular symmetry relative to tube axis, which emits a longitudinal wave in gas, also symmetrical relative to axis; disclosed device is characterised by that piezoelectric plate and acoustic ducts have a ring structure, and acoustic ducts consist of cylindrical part end face of which is conjugated with working surface of piezoelectric plate, and conical part, providing for rotation of cylindrical ultrasonic beam and introduction into pipe wall at required angle.

EFFECT: high accuracy of measuring flow rate.

3 cl, 2 dwg

Description

The invention relates to measuring equipment and can be used in devices for measuring gas flow in pipelines.

To measure gas flow in pipelines, ultrasonic flow meters are currently widely used, the operation of which is based on measuring the propagation time of ultrasound in the direction and against the gas flow. Such flowmeters include, for example, an ultrasonic flow meter (Cl. RF No. 2106603, G01F 1/66, publ. 03/10/1998), as well as a device for measuring gas flow and a method of measuring it (Cl. RF No. 2047097, G01F 1 / 66, published on 10.27.95). Devices of this kind use a pair of ultrasonic transducers (USP) built into the pipe wall.

Another type of flow meter uses a pair of overhead SPD. This variant of devices makes it easy to install an ultrasonic protection device on pipelines without violating the integrity of the pipe and stopping the operation of the pipeline, without placing sensitive elements of the flowmeter in the gas stream, without exposing them, thus, to possible aggressive environmental influences and without interfering with the flow. However, the use of overhead ultrasonic testing is hampered by the large difference in acoustic impedances of the pipe material and gas (more than five orders of magnitude). As a result, only a negligible part of the initially emitted ultrasonic energy is emitted into the gas, and then in the receiving SPD. At the same time, the acoustic vibrations arising in the pipe wall are many times higher than the acoustic vibrations in the gas and create powerful acoustic vibrations at the receiving point at the operating frequency of the probe package, which interferes with the release of the attenuated signal transmitted through the gas. Reflections of ultrasonic vibrations from the inhomogeneities of the pipe wall (seams, flanges, bends, etc.), as well as the passage of waves (due to the presence of side lobes in the radiation pattern of the ultrasonic inspection) along spiral paths along the pipe wall, can lead to the appearance of stationary interference in the temporary the interval of occurrence of a useful signal in the receiving SPD, which disrupts the normal operation of the device.

A known method of measuring gas flow and ultrasonic gas flow meter "Controlotron's WideBeam ™, Cavity-Free ™ Ultrasonic Flowmeters Achieve Process and Natural Gas Custody Transfer Accuracy and Performance" www.iceweb.com.au/flow/ultrasonicpapers/custodytransferaccperformance.pdf, adopted as prototype, which uses overhead ultrasonic testing, exciting the Lamb wave in the pipe wall, which further excites a longitudinal ultrasonic wave in the gas. In this case, the tube is used as a waveguide of the ultrasonic Lamb wave and acts as an extension of the effective radiating surface of the sole of the ultrasonic testing device itself. A Lamb wave running along a pipe generatrix emits a longitudinal ultrasonic wave into the gas. This wave passes through the gas stream and excites in the opposite wall a similar Lamb wave, which then moves along the wall to the receiving ultrasonic protection device. Being in the gas, the wave moves along with the flow and, when it leaves the gas, reaches the pipe wall at another point on the pipe’s inner surface. Further, the “waveguide” property of the pipe transfers the signal to the receiving ultrasonic protection without additional distortions. In addition, a longitudinal wave in a gas can be reflected several times from opposing walls and only then can a Lamb wave be excited in the pipe wall, which enters the receiving ultrasonic transformer along the pipeline generatrix.

It should be noted that in the prototype and in devices manufactured on the basis of the method, pairs of ultrasonic testing with a traditional organization are used, each of which consists of a piezo plate, sound pipe and fastening elements. Both SPDs are fixed either on one generatrix of the pipe, or on two opposite pipes located in one diametrical plane. The Lamb wave, which, due to the limited size of the radiating surface of the ultrasonic waveguide, has a certain diverging radiation pattern, propagates mainly along the generatrix, emitting an ultrasonic wave into the gas, which penetrates the part of the gas stream that is symmetrical with respect to the diametrical plane in which both the ultrasonic waves are mounted. The shape of the beam of the wave radiated into the gas is a longitudinal slit along the pipe with a decreasing width to the pipe axis and increasing after it.

Further, as in conventional flowmeters, information on the propagation time of the signal upstream and downstream, including after several reflections from the pipe wall, is used to calculate the flow rate.

The advantage of the method is a clear increase in the energy of the ultrasonic signal transmitted through the gas due to the radiation of the longitudinal wave pipe into the gas by the wall of the pipe. For radiation into the gas, not only the USP shoe area is used, which has a very limited size, but a rather long section of the pipe wall during the movement of the Lamb wave along it. Moreover, this advantage is used twice: when emitting into gas and when receiving a signal from gas.

The disadvantages of the method are:

- still low energy saturation of the signal transmitted through the gas, caused, firstly, by the large difference in acoustic impedances of the pipe material and the gas medium and, secondly, by the divergence of the Lamb wave relative to the generatrix of the pipe wall along which it propagates, due to limited dimensions applied SPD, so that only a small part of the energy radiated by the transmitting SPD gets into the receiving SPD,

- a high level of stationary interference caused, first of all, by the lateral rays of the Lamb wave, which, moving along long spiral paths, can arrive at the receiving SPD at about the same time as the useful signal transmitted through the gas, and due to significantly less attenuation when propagating through metal, have a large amplitude, mask a useful signal and make it difficult to isolate,

- limited portion of the volume of the pipeline pierced by a longitudinal ultrasonic wave in the gas, which somewhat reduces the representativeness of the measurement results; One can imagine the case when, for some reason, the main part of the gas flow carrying the bulk of the gas is displaced relative to the diametrical plane and is not captured by the probe beam, which, of course, greatly distorts the result.

Since the impedance of the gaseous medium decreases significantly with decreasing pressure, these drawbacks cause the method to be limited, which means that the minimum pressure of the gaseous medium at which measurements are still possible is at the level of 10-15 bar, i.e. measurements at lower pressures without the use of other special measures are not possible.

The objectives of the invention are:

- increasing the energy saturation of the probing ultrasonic package in order to significantly increase the amplitude of the useful signal transmitted through the gas, and not in a purely extensive way, by increasing the amplitude of the exciting voltage, but due to physical methods that allow you to rebuild the ratio of different useful and useless parts of ultrasonic energy to different stages of the passage of the signal from the transmitting to the receiving SPD,

- reduction of the level of stationary interference caused by the passage of radiation along spiral paths in the pipe wall or by reflection from various inhomogeneities in the pipe,

- an increase in the proportion of the cross section of the gas stream penetrated by the probe beam, and hence the statistical representativeness of the measurements.

The technical result consists in increasing the accuracy of flow measurement by obtaining a more powerful signal passing through the gas, while significantly reducing the effect of stationary noise on it.

The technical result is achieved by the fact that in the method of measuring the gas flow in pipelines, which consists in the excitation of longitudinal ultrasonic waves in the gas in and against the stream due to the excitation of Lamb waves in the pipe wall, isolating the signal transmitted through the gas stream, measuring the difference of the signal propagation times through the direction of the flow and against it and determining the magnitude of the gas flow, excite the Lamb wave of a circular structure with circular symmetry relative to the axis of the pipe, which, in turn, emits a longitudinal wave into gas, which then, passing through the gas, excites a similar Lamb wave with circular symmetry, which reaches the receiving SPD, which provides an increase in the power of the useful signal and, accordingly, an improvement in the operational characteristics of the flowmeter.

A device for measuring gas flow in a pipeline consists of a pair of overhead ultrasonic testing devices for exciting in a pipeline and receiving Lamb waves from the pipeline. The piezoelectric plates and sound ducts of the ultrasonic testing device have a ring design. Sound ducts consist of a cylindrical part, the end surface of which is interfaced with the working plane of the piezoelectric plate, and a conical part, which ensures rotation of the cylindrical ultrasonic beam and its entry into the pipe wall at the required angle.

Each transducer can consist of two assemblies symmetrical with respect to the diametrical plane, with each assembly consisting of a piezoelectric plate in the form of a half ring and an associated sound duct in the form of a half ring, tightened by clamps and forming ring structures.

The proposed method and device have the following advantages:

- firstly, the pipe surface is used to the maximum extent available for transmitting ultrasonic energy to and from the pipe wall, which, in principle, allows to increase the power of the emitted and received signal,

- secondly, the directivity diagram of each of the pair of circular ultrasonic scanning devices with circular symmetry with respect to the axis, when deployed on a plane, corresponds to an emitter and a receiver with an "unlimited" transverse dimension that has no side lobes, which excludes the emission and reception of spiral waves, and, accordingly, the signal loss due to the divergence of the ultrasonic beam in comparison with traditional ultrasonic scanning, used in the prototype,

- thirdly, due to a significant increase in the energy saturation of the signal (about 700-900 times) and a significant suppression of spiral noise, it becomes possible to register useful signals after several reflections (for example, after 32 reflections); in this case, the recorded useful signal carries information on a longer “shot through” gas volume, which, on the one hand, increases the statistical value of one measurement cycle and, on the other hand, increases the signal residence time in the gas, and, accordingly, the longer total time the passage of the signal from the transmitting SPD to the receiving allows you to measure it with a smaller relative error,

- fourthly, the probing ultrasonic signal penetrates the entire cross section of the pipe, thus increasing the statistical representativeness of the measurements.

Thus, in comparison with the prototype, the proposed method for isolating a signal transmitted through a gas stream uses, on the one hand, a significantly more powerful signal passing through a gas, and on the other hand, the influence of stationary noise caused by spiral paths is significantly attenuated Lamb wave propagation.

Measurement of the transit time of the ultrasonic packet in the direction of the flow and against it and, accordingly, the sending of probe pulses can be carried out simultaneously or in turn by both ultrasound couples. If the alternate sensing mode is selected, then first one SPD becomes the transmitting one, and the second one the receiving one, and then they change roles. In the case of simultaneous sounding, both SPDs emit a packet at the same time, and then switch to the reception mode. Since in both cases the functioning in both directions of sounding is symmetrical, then in the text work in only one direction is considered.

In FIG. 1 shows a device for measuring gas flow in a pipeline; FIG. 2 is a variant of the device in which the converter may consist of two assemblies, where

1 - pipeline with gas,

2 - annular piezoelectric plate,

3 - sound duct,

4 - reflective conical surface of the sound duct,

5 - sound pipe in the form of a half ring,

6 - a piezoelectric plate in the form of a half ring,

7 - a tightening collar.

The device operates as follows (see Fig. 1).

The high-frequency package of ultrasonic vibrations generated in piezoelectric plate 2 (the right piezoelectric plate is transmitting in Fig. 1) due to the supply of an electric vibrations packet from the output stages of the electronic part of the flowmeter (not shown in Fig. 1) to it, propagates inside and along the cylindrical part of the sound pipe 3 (in parallel the axis of the pipeline) to the conical reflecting surface 4, reflected from which, it propagates further in the form of a cone-shaped beam suitable to the surface of the pipe 1 at an angle α necessary for excitation occur during the pipe wall 1 a predetermined Lamb wave. In this case, the ultrasonic beam in each section of the sound duct is symmetric about the axis, i.e. uniform along any circle centered on the axis crossing the pipe 1 and the sound pipe 3 in the plane normal to the pipe axis 1. The Lamb wave excited in the pipe wall 1 also has the same property, i.e. it is symmetrical about the axis of the pipe, and the amplitude and phase along any circle centered on the axis crossing the pipe 1 and the sound pipe 3 in a plane normal to the axis have a constant value. Thus, due to the structural symmetry of the ring ultrasonic ultrasound, the ultrasonic rays of the Lamb wave do not diverge, but move parallel to each other along the generatrix of the pipe wall 1. In this case, almost all the ultrasonic energy radiated into the pipe wall 1, with the exception of losses due to natural attenuation in the material, reaches receiving ring SPD, not decreasing due to beam divergence, as is the case in SPD of the prototype.

The Lamb wave excited in the wall of pipe 1 with circular symmetry about the axis, moving along the generators of pipe 1, in turn, excites a longitudinal ultrasonic wave in the gas, which moves at an angle β to the axis of the pipe 1, and whose front also represents a conical surface, with uniform density of ultrasonic energy along any circle (centered on the axis) on the surface of this cone. Having reached the opposite wall of the pipe 1, a longitudinal wave of gas excites in it a similar Lamb wave, which along the wall of the pipe 1 reaches the sound duct 3 and the piezoelectric plate 2 of the receiving ultrasonic protection device (on the left in Fig. 1). Those. and the useful signal that passed through the gas has symmetry about the axis and also has an increased energy level compared to the prototype with a pair of traditional SPDs. The movement of ultrasonic energy in the form of a Lamb wave in a pipe wall or in the form of a longitudinal wave in a sound duct and in a gas is shown in the figure by arrows.

At the same time, due to the symmetry of the SPD relative to the axis of the pipeline, another useful property of the ring SPD is a sharp decrease in the level of ultrasonic energy radiation along spiral paths and, as a result, a lower level of stationary interference. Essentially, the possibility of their absolute suppression is limited only by the non-uniformity of the electromechanical properties of the piezoelectric plates and the imperfect performance of the elements of the sound duct.

The time stamps thus obtained are then used in the traditional way to calculate the gas flow rate and its volumetric flow rate.

In the process of application of VUZP, a situation may arise when, under operating conditions, the possibility of installing ring-type ultrasonic couplers by pulling through the ends of the pipeline is excluded. In this case, the construction shown in FIG. 2, which is a pair of identical circular SPDs, each of which consists of two identical assemblies obtained by cutting the original structure in FIG. 1 along the diametrical plane. Each assembly consists of a piezoelectric plate 6 in the form of a half ring and a sound duct 5 in the form of a half ring conjugated to it. After overlapping both assemblies of each ultrasonic couple on the surface of the pipe, they are pulled together by a clamp 7 and form a complete ring structure that has all of the above advantages.

Claims (3)

1. The method of measuring gas flow in pipelines, which consists in the excitation of longitudinal ultrasonic waves in the gas upstream and against it due to the excitation of the Lamb waves in the pipe wall, isolating the signal transmitted through the gas flow, measuring the difference in the propagation time of the signal in the direction of flow and against it and determining a gas flow rate, characterized in that they excite a Lamb wave of circular structure with circular symmetry about the axis of the pipe, which, in turn, emits a longitudinal wave in the gas, is also symmetrical relative to the axis. 2. A device for measuring gas flow in a pipeline, consisting of a pair of overhead ultrasonic transducers for excitation of a Lamb wave in a pipeline, characterized in that the piezoelectric plates and sound ducts have an annular structure, and the sound ducts consist of a cylindrical part, the end surface of which is interfaced with the working plane of the piezoelectric plate, and the conical part, providing the rotation of the cylindrical ultrasonic beam and entering it into the pipe wall at the required angle. 3. The device according to claim 2, characterized in that each transducer consists of two assemblies symmetrical with respect to the diametrical plane, each assembly consisting of a piezo-plate in the form of a half ring and an associated sound guide in the form of a half ring, tightened with clamps and forming ring structures.

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