Non-invasive evaluation method for low-frequency pulsed ultrasound systems and industrial multilayer structures.

Abstract

A system and method for measuring the thickness of one or more thin layers in an industrial multilayer structure. One of the layers may contain coarse-grained material. The multilayer structure may have a thickness of less than 600 mm. The method includes emitting ultrasonic pulses into the industrial multilayer structure, detecting the thickness-corresponding frequencies of the layers in the structure, and comparing them with known thickness-corresponding frequencies. The ultrasonic pulses are frequency-swept pulses or broadband frequency-swept pulses specifically programmed for the multilayer structure.

Description

Technical Field

[0001] The present invention relates to the field of the use of ultrasonic waves for industrial multilayer structures and their non-invasive evaluation.

Background Art

[0002] Multilayer linings in industrial structures may be composed of two or more material layers with different thicknesses, materials, and / or mechanical properties. In some cases, the user may only have access to one side, or the outer layer, of such a structure, and information (such as wear and condition) regarding other sides, and / or the interior of the structure, and / or one or more inner layers may be required, but the user may not have access to them. For example, some metallurgical furnaces and chemical process vessels have side walls of a multilayer structure that include a steel shell accessible from the outside of the furnace (i.e., the low-temperature side), and inner layers composed of one or more layers of refractory bricks and castings, cast copper cooling elements, and / or cast iron cooling elements. These inner layers are inaccessible (or only accessible by invasive testing) during the use of the furnace, etc. Inner layers including layers that directly contact the furnace cavity (i.e., the high-temperature side) are subject to wear and degradation due to activities inside the furnace, and if this is not discovered, it may become a problem. For example, during operation, the refractory lining of the furnace may deteriorate due to mechanical changes such as wear and thermal stress in addition to chemical degradation, and the thickness of the entire refractory lining or the cooling elements may decrease. Deterioration of the refractory lining or deterioration of the cooling elements may lead to structural failures and may cause molten materials or corrosive chemicals inside the furnace to be exposed to the outer steel shell. If such materials erode the outer shell, there is a risk of serious injury to workers working near the furnace. Even if a problem can be detected early to prevent worker injuries, if the discovery of the problem is delayed, the furnace downtime will be longer, the damage to the entire furnace will be greater, and the economic losses and environmental damage may be greater than if the problem was discovered earlier. There is a need for methods and systems for non-invasively evaluating changes in one or more layers in the structure of a multilayer furnace. <—

[0003] U.S. Patent No. 9,791,416 describes an acoustic monitoring system for smelting furnaces and similar equipment. This acoustic monitoring system can be used to identify potential damage points in thick, multi-layer furnace walls. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the thickness of thin, multilayered structures, for example, less than approximately 600 mm, cannot be measured within the desired accuracy range using known acoustic monitoring systems. [Brief explanation of the drawing]

[0005] [Figure 1] An example of a chirp pulse graph is shown. [Figure 2] An example of a tone burst pulse graph is shown. [Figure 3] An exemplary system for determining wear of the first layer of a multilayer structure according to an embodiment of this disclosure is shown. [Modes for carrying out the invention]

[0006] An ultrasonic system and method are provided for evaluating changes in the layers of industrial multilayer structures. Examples of industrial structures include process vessels or furnaces equipped with refractories, staves, cooling blocks, etc., such as metallurgical furnaces, glass furnaces, kilns, and autoclaves. The evaluation concerns changes in layer thickness, material properties, or mechanical properties. Material properties are, for example, aggregate properties such as temperature, refractive index, density, and hardness. Mechanical properties include, for example, strength, ductility, hardness, impact resistance, and fracture toughness. Thickness can be described, for example, as a unidirectional dimension of the material measured by length. A thin multilayer furnace structure may have a thickness of, for example, less than approximately 600 mm, e.g., less than approximately 500 mm, less than approximately 300 mm, less than approximately 250 mm, less than approximately 200 mm, less than approximately 150 mm, or less than approximately 100 mm, or less than approximately 50 mm. As an example, the ultrasonic system and method disclosed herein may be for evaluating changes in the layers of the lining of a metallurgical furnace. Industrial structures such as metallurgical furnaces need to be strong because they operate in harsh environments; therefore, the thickness of a single layer of the furnace structure to which the embodiments of the present invention relate is never less than 20 mm. For example, the thinnest structural component of the lining of a metallurgical furnace or chemical process vessel is the outer shell, which is usually never less than 20 mm. Other structural components or layers of a metallurgical furnace or chemical process vessel are between 20 mm and 600 mm. While 20-600 mm may be considered relatively thin for industrial structures, this thickness is still relatively thick compared to components found, for example, in consumer electronics and electronic components.

[0007] Degradation of structural elements in industrial structures, such as process vessels or metallurgical furnaces, is not limited to refractory bricks or castings. Degradation may include degradation of any layer of the structure, such as cooling blocks, staves, or deposits and appendages. For example, the cooling elements of some metallurgical furnaces are the third layer of the inner wall and can degrade due to the thermomechanical and thermochemical conditions within the furnace. The eventual wear of the cooling elements can lead to the release of cooling fluid or water into the furnace or process vessel, potentially resulting in vessel damage or failure and negative health, safety, and / or economic consequences. The present invention allows for the measurement of the thickness of refractory, cooling block, or other layers, or the detection of changes in one or more of the mechanical properties, material properties, and thickness of refractory, cooling block, or other layers, thereby enabling non-invasive evaluation of the structure of such furnaces using the collected data to help prevent partial or complete failure of the cooling block, refractory, shell, and furnace or process vessel.

[0008] Changes in the thickness of one or more layers of an industrial structure that the systems and methods of this disclosure can detect may be related to the wavelength or frequency of the transmitted acoustic signal. Furnace structures, such as the walls of glass or metallurgical furnaces, rotary kilns, thin refractory linings, furnace stave coolers, multilayer pipes, concrete and masonry equipment, and other high-temperature or chemical process vessels with wall layer thicknesses of less than approximately 600 mm may be too thin to be accurately measured using conventional acoustic impact measurement techniques. This is thought to be because the acoustic waves produced when a hammer strikes the structure consist of half wavelengths longer than the thickness of the layer being evaluated within the structure. Acoustic pulses are conventionally in the frequency range of 20 Hz to 20 kHz, and therefore have wavelengths that are too long to measure individual layers, for example, within a furnace structure. In conventional acoustic impact systems and methods, when the layer thickness is less than half a wavelength of the pulse, a shadow zone appears beneath the impact source or wave source. This can hinder the measurement of the thickness of the first layer, and inaccurate results may occur because the thickness of the first layer is too small for a complete wave to propagate.

[0009] The thickness of a layer that is less than half the wavelength of the shock pulse cannot be determined because a complete wave cannot propagate through the thickness to generate usable information. In addition, shock pulsers used in prior art methods, such as hammers, can only emit acoustic ultrasound with unknown and / or uncontrollable wavelengths. In another known example, spherical shock sources have been used to generate broadband stress waves, elastic waves and / or shock waves. However, the bandwidth frequency and frequency range generated from a spherical shock source depend on the shock contact time and the diameter of the spherical shock source. Thus, prior art acoustic ultrasound emission systems using shock pulsers are insufficient for reproducible and accurate thickness measurements or measurements to evaluate changes in thickness, material and / or mechanical properties of thin industrial multilayer structures. In one aspect of the present invention, an ultrasonic emitter is controlled to generate one or more selected ultrasounds having a specific range of frequencies and wavelengths selected to generate a return signal that characterizes at least one layer in an industrial multilayer structure.

[0010] Aspects of the present invention relate to measuring the thickness, thickness variations, and / or other changes in material or mechanical properties (such as the detection of artifacts or other changes or delamination) of one or more layers in an industrial multilayer structure. An industrial multilayer structure may include at least one layer made of coarse-grained material, dissimilar material, or composite material. This is collectively referred to as evaluating one or more layers of an industrial multilayer structure. For example, this industrial multilayer structure may consist of a coarse-grained layer in a structure comprising a coarse-grained layer or a dissimilar material layer, or a coarse-grained layer in a structure comprising one or more layers made of coarse-grained material, fine-grained material, soft material, or any combination of the aforementioned materials. The coarse-grained layer whose thickness, material, or mechanical properties are evaluated or measured using the system and method of the present invention may be behind another coarse-grained layer. The coarse-grained material may contain large crystals and may contain crystals of multiple sizes and / or types. The coarse-grained material may be, for example, a heterogeneous composite material, such as concrete, wood, rock, refractory brick, cast copper, bone, or cast iron. In contrast, fine-grained, soft materials include, for example, homogeneous, non-composite materials such as aluminum rods.

[0011] One aspect of this invention provides a method for measuring the thickness of layers, changes in layer thickness, changes in mechanical properties, and / or changes in material properties of an industrial multilayer structure using ultrasound. The thickness of one or more layers of the structure measured using this method may be greater than 20 mm and less than about 600 mm individually or collectively. The method includes radiating a frequency sweep pulse or broadband pulse onto the multilayer structure. The frequency sweep pulse or broadband pulse radiates a frequency range within selected upper and lower frequency boundaries. For example, the ultrasonic frequency sweep or broadband pulse may be selected to radiate at frequencies in the range of 20 kHz to 200 kHz. Radiation at frequencies higher than 200 kHz may dissipate in the coarse-grained structure and is therefore undesirable or may not function in this invention. The radiation may come from a first side of the structure and be reflected at one or more interlayer boundaries of the structure and on the opposite side of the structure. The reflected frequencies (i.e., the frequencies of the signals returned from the multilayer structure) are not necessarily the same as the frequency range of the radiated signals. The reflection frequency of each layer depends on the layer thickness, material properties, and density, and may be higher or lower than the radiated frequency range. For example, the reflection frequency may be 3 kHz or less if the layer is very thick and has low density, and 1200 kHz or more if the layer is very thin and has high density. The frequency sweep pulse or broadband pulse may be, for example, a chirp pulse or a controlled tone burst pulse. For brevity, the frequency sweep pulse or broadband pulse will be referred to as a sweep pulse throughout this disclosure, but may be any type of frequency sweep pulse or broadband pulse within the ultrasonic range. The ultrasonic range of the transmission frequency includes frequencies above 20 kHz, and preferably includes frequencies in the low-frequency ultrasonic range, for example, between about 20 kHz and 200 kHz.

[0012] The sweep pulse can be selected / programmed based on the thickness, mechanical properties, and / or material properties of the layers in a multilayer structure, for example, based on the P-wave or longitudinal wave velocity in at least one layer, or based on a combination of wave velocities for all layers in the multilayer structure. Selecting the sweep pulse configuration involves controlling the ultrasonic transmitter to generate ultrasound with the desired sweep pulse characteristics. As an example, the sweep pulse is selected such that half wavelengths are smaller than the thickness of the thinnest layer in the industrial structure under evaluation. The sweep pulse can be provided such that the upper limit of the pulse bandwidth (i.e., the pulse frequency range), i.e., the lowest frequency, corresponds to the total thickness of the multilayer structure, and the lower limit, i.e., the highest frequency, corresponds to the thickness of the smallest layer in the multilayer structure. In some cases, the smallest layer may be the layer being measured, or the layer being measured may be another layer in the structure. The sweep pulse duration, i.e., the length of time required for the pulse to emit the entire range of selected frequencies, can also be programmed to produce a desired excitation frequency (i.e., a selected frequency range formed by, for example, the vibration of the pulse transmitter emitting the pulse). For example, the desired excitation frequency can be between 20 kHz and 150 kHz, or other desired ranges based on the structure, material, and layer thickness. For instance, the frequency of a high-density or low-porosity layer may be higher because the wave can travel faster through the material, while the frequency of a low-density or high-porosity layer of the same thickness may be lower.

[0013] In one embodiment, the frequency of a single layer is calculated with a P-wave velocity of 3000 m / s and a thickness of 150 mm, and the thickness-corresponding frequency is 10000 Hz or 10 kHz. To select the chirp frequency, pulses from 20 kHz to 200 kHz have a higher frequency than the pre-calculated layer thickness-corresponding frequency (half-wavelength smaller than the thickness). In the case of three layers, for example, the first layer T1 has a thickness of 150 mm, the second layer T2 has a thickness of 200 mm, and the third layer T3 has a thickness of 180 mm, with wave velocities of 3000 m / s, 4500 m / s, and 6000 m / s. The thickness-corresponding frequency of the first layer T1 is 10 kHz, the thickness-corresponding frequency of the second layer T2 is 11.25 kHz, and the thickness-corresponding frequency of the third layer T3 is 16.6 kHz. In one example, the thickness-corresponding frequency can be less than 20 kHz, and the cumulative thickness-corresponding frequency of the three layers can be less than 10 kHz. By emitting such high frequencies, it may be possible to achieve a higher resolution response for thin layers less than 150 mm thick.

[0014] The duration of the sweep pulse can be programmed based on the thickness, material, and / or mechanical properties of one or more layers. In one example, the sweep pulse duration is 5 milliseconds. In other examples, the sweep pulse duration may be longer or shorter than 5 milliseconds, up to a maximum of 10 milliseconds. During the sweep pulse duration, the pulse frequency increases from a lower limit to an upper limit. Figure 1 shows an example of a chirp pulse where the frequency increases over a set duration from 20 kHz to 200 kHz. The emitted (transmitted) chirp pulse (pulse bandwidth) contains frequencies higher than the returning thickness-corresponding frequencies that the receiving sensor captures. This ensures that the wavelength is smaller than the thickness of each layer, thereby improving measurement accuracy.

[0015] Sweep pulses can be generated by a piezoelectric ultrasonic transducer, a magnetic solenoid, or a solenoid oscillator. For example, a piezoelectric crystal can be used. Alternatively, a solenoid transducer can be used. The vibration of the sweep pulse generator can be selected to correspond to the desired excitation frequency. The generated sweep pulses exhibit a low-to-high (or high-to-low) frequency sweep within an ultrasonic range where the bandwidth includes the thickness-corresponding frequencies of all layers in a multilayer structure. Generating sweep pulses allows us to determine pulse parameters such as frequency and power. The sweep pulses include thickness-corresponding frequencies for each layer and thickness-corresponding frequencies for the entire structure. The thickness-corresponding frequency for the entire structure is the sum of the thickness-corresponding frequencies of all layers within the structure. For example, the emitted sweep pulses include frequencies higher than the thickness-corresponding frequencies reflected and received by the receiver. In this way, the wavelength becomes smaller than the thickness of each layer, improving the accuracy of the measurement. The sweep pulse can also generate oscillations or pulses that result in frequency bandwidths lower or higher than the radiated 20-200 kHz frequency bandwidth, allowing the receiver to detect much lower or higher frequency thickness-corresponding frequencies reflected from the boundaries of each layer in the multilayer structure. If the half-wavelength of the radiated sweep pulse is longer than the thickness of the layer, the layer boundary cannot "detect" this signal, and the layer does not provide a return signal. Therefore, the radiated wavelength must be smaller than the thickness of the layer, and the detected thickness-corresponding frequency of the layer will be lower than the radiated frequency. For example, the detected thickness-corresponding frequency can be higher by detecting second, third, etc. modes / harmonics of this thickness-corresponding frequency, which can be less than 20 kHz, for example, and where the mode (m) is a multiple of the thickness-corresponding frequency (f) (i.e., m1=f, m2=2f, m3=3f). For example, if the thickness-corresponding frequency is m1=10 kHz, the presence of m2=20 kHz, m3=30 kHz, etc., may also be detected.

[0016] By using frequency-swept pulses from an ultrasonic transmitter, high controllability can be obtained over the frequency of the emitted pulses, thus allowing for more precise determination of the frequency pulse parameters and, for example, more accurate measurement of the pulse's reflection compared to pulses created by an impact hammer. Accurate measurement may be achieved, for example, by ensuring the emission of an array of frequencies with wavelengths small enough to be detected in thin layers of industrial structures. However, since higher frequencies tend to result in faster energy attenuation or loss, it is necessary to select frequencies that are not only small enough to be detected in thin layers but also not too small to penetrate the material of the layer. Furthermore, the emitter must generate acoustic waves with sufficiently large amplitudes so as not to dissipate in industrial structural materials such as coarse-grained materials. Using an ultrasonic emitter allows for the generation of a wide frequency band, thereby ensuring that frequencies that meet this criterion are included for all layer thicknesses.

[0017] An example of a tone burst pulse waveform is shown in Figure 2. A tone burst pulse is a powerful, single-punch ultrasonic pulse that includes a frequency bandwidth, but because the frequency bandwidth does not necessarily correspond to the thickness-corresponding frequency of a multilayer structure, it may not achieve the same level of precision as a sweep pulse such as a chirp pulse.

[0018] After a pulse is radiated into a multilayer structure using an ultrasonic transmitter, the pulse propagates through the structure, and each layer radiates an acoustic wave with a thickness-dependent frequency, which is returned to the ultrasonic broadband receiver. The ultrasonic broadband receiver can detect the reflection of the radiated pulse corresponding to the thickness-dependent frequency of each layer in the multilayer structure. The ultrasonic broadband receiver may have a different frequency range than the ultrasonic broadband transmitter. The ultrasonic broadband receiver may have a wider bandwidth than the broadband transmitter so that it can detect lower or higher frequencies generated by the pulse as a result of the vibration of the layers. For example, the transmitter radiates frequencies in the range of 20 kHz to 200 kHz, but the receiver receives a different or wider range of frequencies, such as return frequencies or reflected frequencies from 3 kHz to 1200 kHz. Different layer thicknesses generate their own unique reflected or return frequencies. The return or reflected frequencies received by the receiver are related to the thickness of each layer, with thicker layers having lower frequencies. The frequency returned from the layer as a result of stimulation at the frequency of the transmitted ultrasound is referred to herein as the layer's "thickness-dependent frequency" or "actual thickness-dependent frequency."

[0019] In the example shown in Figure 3, a data acquisition system connected to the transmitter (Tx) and receiver (Rx) can be used. The data acquisition system may include one or more of the following: a digitizer, amplifier, pulser, memory device, and analyzer. The data acquisition system can be used, for example, to determine an increase (or decrease) in the thickness-response frequency of a multilayer structure by comparing the thickness-response frequencies received by a wideband receiver over time. For example, an increase in frequency indicates that the thickness of the layer has decreased, for example, due to erosion or wear of the layer. A decrease in frequency indicates that the thickness of the layer has increased (less commonly), but this may be due to expansion of the layer for some reason. Ultrasonic resonance within a single or multilayer structure generates the thickness-response frequency of a single or multilayer structure. This thickness-response frequency of a single or multilayer structure is the ultrasonic bandwidth or acoustic bandwidth and depends on the thickness, material properties, and stress wave velocity within the single or multilayer structure.

[0020] In one embodiment, the method disclosed herein may be used to determine the wear state or change of at least one layer of a multilayer structure based on whether the measured thickness-corresponding frequency is higher or lower than the theoretical thickness-corresponding frequency of the structure or layer. The theoretical thickness-corresponding frequency is the single-layer thickness-corresponding frequency of a structure or layer that is expected to be returned to a given layer, such as before wear or change occurs, when the structure or layer is in like-new condition. The theoretical thickness-corresponding frequency of a layer is the expected single-layer thickness-corresponding frequency, not a range of potential frequencies. The theoretical thickness-corresponding frequency can be determined based on the known thickness of the structure or layer and / or material type before wear or change, or by obtaining the actual thickness-corresponding frequency according to the embodiments disclosed herein, or by determining the thickness calculated based on the known longitudinal wave velocity of pulses radiated within the structure. The theoretical thickness-corresponding frequency can be used as a marker or baseline to help determine whether the thickness-corresponding frequency of the structure, in particular any layer, has changed, i.e., whether it indicates a change in the layer itself. For example, the thickness of the layer furthest from the pulse-emitting transducer may be desired. To determine the thickness of this last layer, the frequency of the entire multilayer structure is subtracted from the frequencies of the layers that passed before the last layer. The thickness of the final layer can be calculated as the difference.

[0021] A pulse transmitter or transducer according to the embodiments described herein can be controlled to generate a “chirp” within a very short time, such as 5 milliseconds, to create a frequency sweep or tone burst pulse. In such cases, the duration of pulsing and reception must remain within 10-20 milliseconds, so the receiver must be broadband enough to capture the acoustic signal reflected from the inner layers of the multilayer structure within 5 milliseconds. In one embodiment, the layers of the multilayer structure are defined by boundaries of different materials. In industrial multilayer structures containing coarse-grained materials, high signal intensity is required to penetrate the layers. Signal intensity refers to the amplitude of the signal wave. Signal intensity can be described in terms of the voltage supplied to the ultrasonic emitter to generate the ultrasonic signal. For example, to achieve high signal intensity (above the normal ultrasonic signal intensity range), more than 500 volts, or more than 1000 volts, or more than 2000 volts can be supplied to the ultrasonic emitter. In addition to selecting a desired frequency range, the radiated signal is selected to have sufficient energy (intensity) to penetrate to the furthest layers of the multilayer structure and be reflected back. The lower the signal energy, the smaller the amplitude of the signal wave. If the signal energy is too low, it may attenuate completely, causing the wave to disappear within the multilayer structure. In particular, very thin structures, such as those in the micrometer range or less than 10 mm, do not need to balance the signal energy output with the frequency. This is because very low-energy signals can propagate and reflect through very thin, micrometer-thick structures without attenuation. The reflected energy of a signal can also be used to characterize the material of the layers in a multilayer structure. For example, if the radiated signal intensity is returned relatively high, it may indicate good material that has not worn down. If the signal intensity is high and the returned signal is relatively low, it may indicate poor material where the signal has attenuated during propagation and reflection.

[0022] For example, in the case of a metallurgical furnace such as a blast furnace, the multilayer structure can include a cast iron shell, castable grout, and cast iron or cast copper staves, all of which contain coarse-grained materials. Other coarse-grained materials include concrete, wood, rock, refractory bricks, and bone. In an example where the furnace wall thickness is 250 mm, and the shell is approximately 50 mm, the castable grout is approximately 50 mm, and the stave cooler is approximately 150 mm, the pulse intensity must be sufficiently strong to measure the thickness of the last layer (staves), and this intensity must be maintained uniformly throughout the entire 250 mm thickness; otherwise, it will affect the resulting frequency amplitude.

[0023] In one aspect of this disclosure, an ultrasonic system for determining wear of the last or innermost layer of an industrial multilayer structure is disclosed. The system may comprise a pulser (pulse transmitter) located on the first or outermost layer, or outside the structure, furthest from the last layer. There may be one or more other layers between the first and last layers of the multilayer structure. At least one of the layers, and optionally two or more, contains coarse-grained material. The coarse-grained material may be a composite material. The pulser may be a piezoelectric crystal or other piezoelectric ultrasonic pulser, or a magnetic solenoid or other programmable vibrating solenoid. The pulser radiates ultrasonic pulses with a selected bandwidth, such as frequency sweep pulses, broadband pulses, chirp pulses, or tone bursts, through the multilayer structure, and the ultrasonic pulses are specific to the thickness-corresponding frequency, mechanical properties, and material properties of each layer's structure. An ultrasonic broadband receiver is also located on the first layer or outside the multilayer structure and receives thickness-corresponding frequency information of the multilayer structure from the reflected ultrasonic pulses. The analyzer compares the received thickness-corresponding frequency of each layer (or selected layer) with the known, calculated, theoretical, or historical thickness-corresponding frequency of each layer (or selected layer) before exposure to the abrasive environment.

[0024] In one example, the distance between the broadband transducer and the broadband receiver is close enough so that the device can function as a point transmission and reception system. The distance between the transmitter and the receiver on the same plane is preferably less than 70 mm, such as less than 60 mm, or less than 50 mm, or less than 40 mm, or less than 30 mm, or less than 20 mm. The frequency bandwidth between the transmitter and the receiver may be the same, or the bandwidth of the receiver may be wider. If the frequency bandwidth is wide, the transmitter may be able to capture lower or higher thickness-corresponding frequencies in the acoustic range that is the result of vibration.

[0025] In one embodiment, the system and method for measuring the thickness of layers described herein can be used to measure the thickness of the walls of a stave cooler encased in the refractory of the furnace from the outside of the furnace. The furnace can be operated so that the inner walls become hot. The thickness of the stave cooler walls is typically about 150 mm. An ultrasonic transducer or magnetic solenoid can be programmed to radiate a frequency sweep into the furnace shell. The frequency sweep can be selected to include thickness-corresponding frequencies for each layer moving from the blast furnace shell toward the inside of the furnace. For example, the frequency sweep can include thickness-corresponding frequencies for the shell, the stave cooler walls, and the refractory brick layer and ramming (paste) between the shell and the stave cooler walls. Periodic measurements of thickness based on the sum of the thickness-corresponding frequencies can be used to determine whether there has been erosion of the stave walls. For example, when iron and coke are added to a blast furnace, these pellets tend to erode the inner walls of the furnace, and once the walls are eroded, the stave cooler becomes exposed to high-temperature metal and abrasive forces. Periodic thickness measurements, as disclosed herein, can be used to compare the overall thickness-corresponding frequencies collected over time to determine if any changes have occurred. Since each overall thickness-corresponding frequency includes the sum of the thickness-corresponding frequencies of each individual layer, an engineer can determine which layer's thickness-corresponding frequency has changed. As the frequency increases with decreasing layer thickness, if the walls of the stave cooler are eroded and thinned, the thickness-corresponding frequency of that layer will increase proportionally. The received signal is collected by a broadband transducer, a vertical displacement transducer, and an accelerometer. The bandwidth of the receiving transducer may be the same as or wider than that of the transmitting transducer. The bandwidth of the receiving transducer may be, for example, in the range corresponding to the thickness-corresponding frequencies of single-layer and multi-layer structures, and thus to the theoretical total thickness of the structure. The frequency bandwidth of the receiving transducer may be in the acoustic-ultrasonic range.

[0026] The signal may be collected in the time domain, but signal analysis is generally performed in the frequency domain. The analysis can also be performed in the time domain, or in combination with the time domain and the frequency domain. The received frequency is analyzed and the pick frequency is selected. There is a pick frequency that matches the theoretically calculated thickness-corresponding frequency or a pick frequency that is very similar. The further thickness-corresponding frequency or the inner layer thickness-corresponding frequency is the desired result frequency for determining the thickness of the final layer. Correction factors for shape, temperature, and vibration can be used to more accurately determine the position within or between layers of the multilayer structure, the layer thickness, the overall thickness, the crack, delamination, joint position, chemical change, and / or material change.

[0027] In embodiments, the systems and methods disclosed herein can be used to evaluate layers to determine the location of delamination, cracks, joints, or defects between any layers in a multilayer structure, or within any one or more layers in a multilayer structure. The systems and methods can also be used to detect changes in the location, size, propagation, and state of cracks within or between layers in a multilayer structure. For example, the systems and methods can be used to detect the location of infiltrated molten metal within a single layer or between layers in a multilayer structure. The systems and methods can be used to determine the location and location of chemical changes in a material, or to detect and distinguish between unchanged, altered, or metal-impregnated refractories within or between layers in a multilayer structure. The system can also detect buildup or skull formation on the hot surface of a metallurgical furnace. In any case, artifacts, anomalies, or changes in a multilayer structure generate reflections of sweep pulses, similar to the reflections that occur at layer boundaries as described earlier in this disclosure. Thickness-corresponding frequencies correspond to the thickness or distance at the location of the artifact, anomaly, or change. For example, a crack is a discontinuity surface that causes wave reflections. Reflection measures the distance from the sound source to the crack. Similarly, metal penetration and delamination also cause reflections, which can be measured. If there are changes in material properties due to chemical attack or other factors, the response thickness corresponding frequency will also change. As an example, further material changes in the layers can be detected by comparing the input signal intensity and output signal intensity of a sweep pulse.

[0028] In further embodiments, systems and methods are provided for estimating the thickness and wear state of refractory material in a metallurgical furnace. Ultrasound can be generated such that waves propagate through the refractory material. An ultrasonic sensor is used to sense at least one reflected wave onto the refractory material. A database of theoretical thickness-corresponding frequency-domain data, e.g., simulated spectra, can be used to represent simulated waves reflected in a simulated refractory material of known state and thickness. Each simulated spectrum can be correlated with both known state and thickness data of the simulated refractory material. Processing means may be used to record the reflected waves as time-domain signals and convert them to frequency-domain data to generate, for example, experimental spectra. Processing means may also be used to compare experimental spectra of thickness-corresponding frequencies for multiple layers with multiple simulated spectra from the database. The processing means can further be used to sequentially determine the location of resonant frequency peaks in the frequency-domain data and / or to filter simulated spectra from the database that have resonant frequency peaks and to select a reduced corresponding group of simulated spectra containing this resonant frequency peak. Resonant frequency peaks can be generated by the reflection of elastic waves, shock waves, or stress waves between the boundaries of two structural elements. The boundaries of structural elements can be defined and caused by the thickness, delamination, or cracks of a single-layer or multi-layer structure. Resonant frequency peaks are sometimes referred to as thickness-dependent frequencies. Elastic wave sensors or stress wave sensors may be, for example, accelerometers or directional transducers configured to measure the mechanical reaction of a refractory material caused by the reflection of generated elastic or stress waves. Multiple reflected waves can be sensed and recorded as time-domain signals, which can then be converted to frequency-domain signals.

[0029] In another embodiment, a method is provided for estimating both the thickness and wear state of refractory or cooling element material in a metallurgical furnace. This method may include generating elastic or stress waves propagating through the refractory material, sensing the waves reflected by the refractory material, recording the reflected elastic or stress waves as time-domain signals, and converting the time-domain signals into frequency-domain data, for example, an experimental spectrum, by comparing the experimental spectrum with at least several simulated spectra from a database, each simulated spectrum being correlated with both known state and thickness data of the refractory material in question. The method may further include comparing the experimental spectrum with several simulated spectra to determine the location of a resonant frequency peak in the experimental spectrum, filtering the simulated spectra from the database where the resonant frequency peak was detected, and selecting a reduced corresponding group of simulated spectra consisting of this resonant frequency peak. This allows for the determination of a unique simulated spectrum from the reduced corresponding group that is closest in height to the resonant frequency peak in the experimental spectrum.

[0030] The thickness and / or state of the refractory material can be estimated by estimating the total thickness of the refractory material and the location and thickness of at least one layer where the refractory material is weakened by anomalies, which is named the brittle layer. Furthermore, determining the location of the resonant frequency peak in the experimental frequency spectrum can be achieved by arithmetic meanning the experimental spectrum and selecting a first set of representative peaks, geometrically meanning the experimental spectrum and selecting a second set of representative peaks, and selecting a final set of peaks selected in both the first and second sets, which is the resonant frequency peak at the thickness-corresponding frequency. As an example, peaks in the first set may be selected if their width is greater than a threshold between 10 Hz and 20 Hz.

[0031] The simulated spectra from the database can be filtered by the detected resonant frequency peaks using at least a numerical dispersion curve model to determine the wave propagation mode, filter by the detected resonant frequency peaks, and select a reduced corresponding group of simulated spectra. Furthermore, intrinsic simulated spectra can be determined from the reduced corresponding group using at least a numerical transient model. The spectra of the reduced corresponding group can be selected and compared to the experimental spectra by performing at least one of the following steps: (1) evaluating the direct difference between the simulated and experimental spectra for the layer; (2) comparing the overall shapes of the simulated and experimental spectra for the layer; (3) determining the difference in the maximum height peak positions of the simulated and experimental spectra for the layer; and / or (4) determining the cross-correlation between the simulated and experimental spectra for the layer.

[0032] In another embodiment, a method is provided for detecting crack propagation in the wall of a metallurgical furnace using a detection unit. This method may include: transmitting a stress signal to the wall, for example, at one or more locations on the wall of the metallurgical furnace, using an ultrasonic signal generating unit of the detection unit; receiving the reflected stress signal from each of the one or more locations based on the corresponding stress signal; extracting one or more dominant frequency parameters from the corresponding reflected stress signal from each of the one or more locations; and analyzing the phase from each of the one or more dominant frequency parameters for the corresponding locations of the one or more locations. The step of analyzing the phase may include, for example, determining one or more coefficients for each of the one or more dominant frequency parameters based on the reflected stress signal and a reference signal; identifying a dominant phase for each of the one or more dominant frequency parameters based on the corresponding one or more coefficients; selecting a frequency related to the thickness parameter from one or more dominant frequency parameters at the corresponding locations on the wall based on the dominant phase; and detecting crack propagation in the wall of the metallurgical furnace based on the frequency related to the thickness parameter at each of the one or more locations.

[0033] This method may further include, for example, calculating a thickness value based on a frequency associated with a thickness parameter, and determining the propagation of a crack in a wall by comparing the thickness value at one of one or more locations with the corresponding thickness value at another of one or more locations. The thickness values ​​may correspond to the thickness of each of multiple layers of the wall at one or more locations.

[0034] The method may further include modulating the reflected stress signal with a reference signal and / or calculating one or more coefficients by incrementing one or more predefined phase values ​​of the reference signal, in order to determine one or more coefficients for each of one or more dominant frequency parameters, where one or more predefined phase values ​​are in the range of about 0 to about 360 degrees. Furthermore, the method may further include generating a coefficient plot based on one or more coefficients and one or more predefined phase values, in order to identify the dominant phase for each of the one or more dominant frequency parameters, where one or more peak values ​​of the coefficient plot may be detected to identify the dominant phase. The reflected stress signal defined in the method may be a time-domain parameter, and the method may include converting the reflected stress signal of a time-domain parameter to a frequency-domain parameter.

[0035] In a further exemplary embodiment, a detection unit is provided for detecting the propagation of cracks in the wall of a metallurgical furnace. The detection unit may comprise, for example, a signal generating unit for transmitting ultrasonic stress signals propagating within the wall at one or more locations on the wall of the metallurgical furnace, a processor, and a memory communicatively coupled to the processor and storing processor-executable instructions. Instructions may be used to cause the processor to receive reflected stress signals for each of one or more locations based on corresponding stress signals, to extract one or more dominant frequency parameters from the corresponding reflected stress signals for each of one or more locations, and to analyze the phase of each of the one or more dominant frequency parameters for the corresponding locations from one or more locations. The analysis may include, for example, determining one or more coefficients for each of the one or more dominant frequency parameters based on the reflected stress signals and a reference signal, identifying a dominant phase for each of the one or more dominant frequency parameters based on the corresponding coefficients, and selecting frequencies related to the thickness parameter from the one or more dominant frequency parameters for the corresponding locations among one or more locations on the wall based on the dominant phase. The instruction can further cause the processor to detect crack propagation in the wall of a metallurgical furnace based on frequencies associated with a thickness parameter at each of one or more locations. The detection unit may include at least one sensor unit for receiving reflected stress signals from the wall, which may calculate a thickness value based on the frequency associated with the thickness parameter, and the thickness value may correspond to the thickness of each of several layers of the wall at one or more locations, and may be used to determine crack propagation in the wall by comparing the thickness value at one of the one or more locations with the corresponding thickness value at another of the one or more locations.

Claims

1. A method for evaluating industrial multilayer structures, A step to identify the frequency corresponding to a single theoretical thickness of a layer within a multilayer structure, Steps include: radiating an ultrasonic frequency sweep pulse or an ultrasonic broadband pulse into an industrial multilayer structure, wherein the pulse has a known frequency based on the single theoretical thickness-corresponding frequency; A step of using a broadband acoustic ultrasonic receiver to detect the frequency corresponding to the actual thickness of the layer within the multilayer structure, which is returned from the multilayer structure in response to the frequency sweep pulse, A step of comparing the actual thickness-corresponding frequency with the theoretical thickness-corresponding frequency and identifying the changes in the layers of the industrial multilayer structure, A method that includes this.

2. The method according to claim 1, wherein the frequency sweep pulse is in the low-frequency ultrasonic range.

3. The method according to claim 1 or 2, wherein the industrial multilayer structure includes a layer made of coarse-grained material.

4. The method according to any one of claims 1 to 3, wherein the frequency sweep pulse or the broadband pulse has an ultrasonic signal intensity capable of causing reflections at a thickness-corresponding frequency within the layer containing the coarse-grained material.

5. The method according to any one of claims 1 to 4, wherein the frequency sweep pulse or the broadband pulse has an ultrasonic signal intensity capable of causing a reflection at a thickness-corresponding frequency in a front layer having a thickness of at least 20 mm.

6. The method according to any one of claims 1 to 5, wherein the frequency sweep pulse or the broadband pulse has an ultrasonic signal intensity of at least 500 volts, or at least 1000 volts, or at least 2000 volts.

7. The method according to any one of claims 1 to 6, wherein the frequency sweep pulse has a half-wavelength smaller than the thickness of the thinnest layer of the multilayer structure.

8. The method according to any one of claims 1 to 7, wherein the total thickness of the multilayer structure is 20 mm or more and 600 mm or less.

9. The method according to any one of claims 1 to 8, further comprising the step of emitting a frequency sweep pulse having a known frequency based on the single theoretical thickness-corresponding frequency of each layer in the industrial multilayer structure.

10. The method according to any one of claims 1 to 9, further comprising the step of emitting pulses having a known frequency based on the properties of one or more layers of the industrial multilayer structure.

11. The method according to any one of claims 1 to 10, wherein the duration of the frequency sweep pulse is determined based on the thickness and material properties of the industrial multilayer structure.

12. The method according to any one of claims 1 to 11, wherein the frequency sweep pulse is emitted from a piezoelectric ultrasonic transducer or a magnetic solenoid.

13. The method according to any one of claims 1 to 12, wherein the industrial multilayer structure is a lining or wall for a metallurgical furnace, glass furnace, chemical process vessel, other high-temperature vessel, pipe, or rotary kiln.

14. The method according to any one of claims 1 to 13, further comprising the step of determining at least one wear state of the layer based on the fact that the actual thickness-corresponding frequency is higher than the theoretical thickness-corresponding frequency.

15. The method according to any one of claims 1 to 14, wherein the at least one layer of the multilayer structure is the layer furthest from the location from which the frequency sweep pulse is radiated into the structure.

16. The method according to any one of claims 1 to 15, wherein the frequency sweep pulse is in the range between approximately 20 kHz and approximately 200 kHz.

17. The method according to any one of claims 1 to 16, wherein the change to be evaluated is a change in the thickness, material, and / or mechanical properties of the multilayer structure.

18. The method according to any one of claims 1 to 17, wherein the change in the layer is an artifact, a crack, delamination, a joint, or a chemical change.

19. An ultrasonic system for evaluating layers in industrial multilayer structures, An ultrasonic pulser is positioned in the outermost layer of an industrial multilayer structure, wherein the outermost layer is the layer furthest from the innermost layer, and the ultrasonic pulser emits ultrasonic frequency sweep pulses or ultrasonic broadband pulses into the industrial multilayer structure, wherein the pulses have known frequencies based on a single theoretical thickness-corresponding frequency of the layer. A broadband acoustic ultrasonic receiver for receiving a frequency corresponding to the actual thickness from the industrial multilayer structure in response to the frequency sweep pulse or the broadband pulse, An analyzer for identifying changes in the layer by comparing the actual thickness-corresponding frequency with the theoretical thickness-corresponding frequency of the layer in the industrial multilayer structure, An ultrasonic system equipped with [unspecified features].

20. The system according to claim 19, wherein the pulser is configured to emit frequency sweep pulses or broadband frequency pulses within the multilayer structure.

21. The system according to claim 19 or 20, wherein the frequency sweep pulse is a broadband pulse or a chirp pulse.

22. The system according to any one of claims 19 to 21, wherein the thickness-corresponding frequency is received in the time domain by the broadband acoustic ultrasonic receiver, and the analyzer performs analysis in the time domain and / or frequency domain.

23. The system according to any one of claims 19 to 22, wherein the industrial multilayer structure is a lining or wall of a metallurgical furnace, glass furnace, chemical process vessel, other high-temperature vessel, pipe, or rotary kiln.

24. The system according to any one of claims 19 to 23, wherein the industrial multilayer structure is a coarse-grained composite material comprising at least one layer of coarse-grained material, or a combination of coarse-grained material and fine-grained material.

25. The system according to any one of claims 19 to 24, wherein the total thickness of the multilayer structure is 20 mm or more and 600 mm or less.

26. The system according to any one of claims 19 to 25, wherein the frequency sweep pulse or the broadband pulse has an ultrasonic signal intensity capable of causing reflections at a thickness-corresponding frequency in the layer containing the coarse-grained material.

27. The system according to any one of claims 19 to 26, wherein the pulser is configured to provide an ultrasonic signal of an intensity capable of causing reflections at thickness-dependent frequencies in a layer with a thickness of at least 20 mm.

28. The system according to any one of claims 19 to 27, wherein the pulser is configured to provide an ultrasonic signal having an intensity of at least 500 volts, or at least 1000 volts, or at least 2000 volts.

29. The system according to any one of claims 19 to 28, wherein the change in the layer is an artifact, a crack, delamination, a joint, or a chemical change.

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