Acoustic imaging-based leak sound pressure level hierarchical alarm threshold setting method and system

Abstract

This invention discloses a method for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging, comprising: determining a reference sound pressure level at a predetermined distance from the leak; inversely estimating the leak diameter corresponding to each level through the quantitative relationship between the leakage rate and the leak diameter; calculating the theoretical sound pressure level of each leak diameter at different propagation distances; plotting the theoretical sound pressure level as a sound pressure level-distance trend line corresponding to each leakage level with propagation distance as the abscissa and sound pressure level as the ordinate, thereby constructing a distance-sound pressure level-leakage rate graded alarm threshold MAP; and obtaining the detection distance and sound pressure level measured by the acoustic imaging detector, comparing the measured points with the trend lines in the MAP, determining the leakage risk level based on the area where the measured points fall, and outputting an alarm signal. A system for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging is also disclosed. This invention can accurately determine the leakage safety risk level.

Description

Technical Field

[0001] This invention relates to the field of gas leak detection methods, and in particular to a method and system for setting alarm thresholds for leak sound pressure level classification based on acoustic imaging. Background Technology

[0002] When pressurized gas in a pressure vessel, pressure pipeline, or its components initially leaks through tiny gaps or holes, if the Reynolds number is greater than 4000, it will generate high-speed turbulent gas and ultrasonic waves above 20kHz, which are inaudible to the human ear. Ultrasonic imaging can detect small initial gas leaks, visualize the leak location, and provide early warning of leakage risks.

[0003] The existing national standard GB / T39173-2020, "Evaluation Method for the Effectiveness of Safety Monitoring in Intelligent Factories," Section 9.3.2, Table 9 (as shown below), classifies alarm thresholds based on sound pressure levels in different background noise areas and the effective coverage radius of ultrasonic detectors. It stipulates that the lower limit of the alarm threshold must be at least 6 dB higher than the ultrasonic background noise, and specifies alarm thresholds and detection ranges for low, medium, and high background noise environments. The appendices of GB / T50493-2019, "Design Standard for Combustible and Toxic Gas Detection Alarms in Petrochemical Industry," and SY / T6503-2022, "Safety Specification for Combustible and Toxic Gas Detection Alarm Systems in Oil and Gas Engineering," cite similar lower limits for alarm thresholds based on background noise and detection range as found in GB / T39173-2020. Neither the new industry standard "DL / T2891-2025 Guidelines for Field Testing of Acoustic Imaging of High Voltage Electrical Equipment" nor the national standard "GB / T45348-2025 Technical Specification for Real-time Positioning Sound Source Positioning Imaging System of Information Technology" mentions the basis and method for determining the risk level of abnormality or failure of the target object detected by acoustic imaging.

[0004]

[0005] However, Article 4 of the "Law of the People's Republic of China on Work Safety (2021 Revised Edition)" stipulates that "Production and business entities must abide by this Law and other relevant laws and regulations on work safety, ... establish a dual prevention mechanism for graded control of safety risks and investigation and management of hidden dangers, improve the risk prevention and mitigation mechanism, enhance the level of work safety, and ensure work safety." The "GB / T45420-2025 Technical Specification for Graded Control of Safety Production Risks of Hazardous Chemicals" clearly stipulates that enterprises that produce, store, and operate (with storage facilities) hazardous chemicals should establish acceptable risk criteria based on their own circumstances (Section 5.3.1.1); when the risk criteria adopt a risk matrix form, risks should be divided into four levels: major risk (red), relatively large risk (orange), general risk (yellow), and low risk (blue) (Section 5.3.1.2). See the table below for examples of safety risk matrices and their applications. For GDS and FDS, it is advisable to use a performance-based approach to assess the coverage of GDS and FDS detectors based on qualitative inspection and evaluation, and to verify and optimize the detector placement design. The quantitative analysis of detection coverage shall comply with the provisions of GB / T39173 (5.2.8.3).

[0006]

[0007] GB / T50493-2019, section 5.5.2, specifies the thresholds for Level 1 (low alarm) and Level 2 (high alarm) alarms for combustible and toxic gases. If the detector readings exceed these thresholds, a combustion, explosion, or poisoning accident is highly likely. Therefore, the Level 1 (low alarm) and Level 2 (high alarm) alarm thresholds specified in GB / T50493-2019, section 5.5.2, can be considered as yellow and orange alarm thresholds, respectively.

[0008] Referring to the classification of PSE process safety incidents Tier 1 / 2 / 3 / 4 in the US API 754-2021 Process Safety Performance Indicators for the Refining and Petrochemical Industries, Section 6.3.2 of the group standard T / CCSAS022-2022 Guidelines for Leakage Management of Hazardous Chemical Enterprises stipulates that enterprises should classify and manage leaks. The classification of leak severity is shown in Appendix C, including serious leaks (as shown in Table C.1 below), moderate leaks (as shown in Table C.2 below), and minor leaks (as shown in Table C.3 below).

[0009]

[0010]

[0011]

[0012] When existing acoustic imaging instruments or detectors are used for leak monitoring and detection, there is no basis or standard to judge the leakage risk level of abnormal sound source imaging points, which does not meet the "dual prevention requirements of safety risk classification and control and hidden danger investigation". As a result, acoustic imaging technology can only be used as an auxiliary means for leak monitoring and detection so far.

[0013] This invention proposes a MAP method for setting graded alarm thresholds for acoustic imaging leak detection based on the sound pressure level, leakage rate, and propagation attenuation law of leaking ultrasonic waves in compressed gas through small holes or gaps. The MAP method quickly assesses the leakage risk level based on different leakage rates and sound pressure levels at different distances, solving the problem that existing acoustic imaging leak detection technologies lack accurate and reliable grading alarm criteria and can only be used as an auxiliary means of leak detection, failing to meet the "dual prevention requirements of safety risk grading control and hidden danger investigation". Summary of the Invention

[0014] One of the technical problems to be solved by the present invention is to provide a method for setting a leakage sound pressure level classification alarm threshold based on acoustic imaging to address the shortcomings of the prior art. This method aims to solve the problem that the presence or absence of leakage can only be assessed by sound pressure level, but the leakage risk level cannot be scientifically assessed based on the distance to the leak point and the source strength or the amount of leakage from the leakage release source.

[0015] The second technical problem to be solved by the present invention is to provide a leakage sound pressure level classification alarm threshold setting system based on acoustic imaging.

[0016] As a first aspect of the present invention, a method for setting a leakage sound pressure level classification alarm threshold based on acoustic imaging includes:

[0017] A method for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging, characterized in that it includes:

[0018] Determine the reference sound pressure level at a predetermined distance from the leak based on the stagnation pressure of the leak source, the diameter of the leak hole, and the type of leaked gas.

[0019] Based on the preset leakage rate threshold corresponding to the leakage risk level, the leakage diameter corresponding to each level is inversely calculated through the quantitative relationship between the leakage rate and the leakage hole diameter.

[0020] Based on the hole diameters corresponding to each level, and combined with the sound wave propagation attenuation model in air, the theoretical sound pressure level of each hole diameter at different propagation distances is calculated.

[0021] Using propagation distance as the x-axis and sound pressure level as the y-axis, the theoretical sound pressure level is plotted as a sound pressure level-distance trend line corresponding to each leakage level, thereby constructing a distance-sound pressure level-leakage rate graded alarm threshold MAP; and

[0022] The detection distance and sound pressure level of the acoustic imaging detector are obtained. The measured point is compared with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP. The leakage risk level is determined according to the area where the measured point falls and an alarm signal is output.

[0023] In a preferred embodiment of the present invention, the leakage risk level includes three levels: slight leakage, moderate leakage, and severe leakage, or four levels: micro leakage, slight leakage, moderate leakage, and severe leakage. The sound pressure level-distance trend line corresponding to each level is drawn in the distance-sound pressure level-leakage rate graded alarm threshold MAP graph, and the area between adjacent trend lines constitutes the alarm judgment interval for the corresponding level.

[0024] In a preferred embodiment of the present invention, the maximum scale of the vertical axis of the distance-sound pressure level-leakage rate graded alarm threshold MAP is set to the upper limit of the sound pressure level detection of the acoustic imaging detector, so as to avoid sensor saturation or damage.

[0025] In a preferred embodiment of the present invention, the specific method for comparing the measured point with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP chart, and determining the leakage risk level based on the area where the measured point falls, is as follows:

[0026] If the measured point is located below the trend line corresponding to a certain leakage level and above the adjacent lower-level trend line, it is determined to be that leakage level.

[0027] If the measured point is located above the highest level trend line, it is determined to be the highest leakage level;

[0028] If the measured point is below the lowest level trend line, it is determined that there is no leakage or the value is below the alarm threshold.

[0029] As a second aspect of the present invention, a leakage sound pressure level classification alarm threshold setting system based on acoustic imaging includes:

[0030] An acoustic imaging detector is used to collect ultrasonic signals from the leak point and output the measured sound pressure level and detection distance.

[0031] Storage unit, the storage unit being used to store a pre-built distance-sound pressure level-leakage rate graded alarm threshold MAP;

[0032] The processing unit is used to compare the measured distance and sound pressure level with the distance-sound pressure level-leakage rate classification alarm threshold MAP to determine the leakage risk level; and

[0033] An alarm unit is used to output an alarm signal corresponding to the leakage risk level.

[0034] The distance-sound pressure level-leakage rate graded alarm threshold MAP is pre-constructed using the aforementioned acoustic imaging-based leakage sound pressure level graded alarm threshold setting method.

[0035] Due to the adoption of the above technical solution, the beneficial effects of this invention are as follows: Based on the propagation attenuation law of leakage ultrasonic waves and the "leakage rate-sound pressure level relationship curve at 1 meter", this invention draws a distance-sound pressure level-leakage rate MAP diagram according to the API754 TIER1 / 2 / 3 PSE events (which can be regarded as corresponding to severe leakage, moderate leakage and mild leakage respectively). Based on the leakage ultrasonic wave sound pressure level graded alarm threshold MAP diagram, the leakage safety risk level can be quickly and accurately determined. This solves the problem that existing methods only assess whether there is a leak based on sound pressure level, but cannot scientifically assess the leakage risk level based on the distance of the leak point and the source strength or the size of the leakage release source. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of the method for setting the leakage sound pressure level classification alarm threshold based on acoustic imaging according to the present invention.

[0038] Figure 2 This is a schematic diagram of the distance-sound pressure level-leakage rate graded alarm threshold MAP of the present invention.

[0039] Figure 3 This is a schematic diagram of the structure of the leakage sound pressure level classification alarm threshold setting system based on acoustic imaging of the present invention. Detailed Implementation

[0040] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0041] See Figure 1 The figure shows a method for setting the alarm threshold for leakage sound pressure level classification based on acoustic imaging, which includes the following steps:

[0042] Step S10: Determine the reference sound pressure level at a predetermined distance from the leak hole based on the stagnation pressure of the leak source, the diameter of the leak hole, and the type of leaked gas.

[0043] Step S20: Based on the preset leakage rate threshold corresponding to the leakage risk level, the leakage diameter corresponding to each level is calculated by back-calculating the quantitative relationship between the leakage rate and the leakage hole diameter.

[0044] Step S30: Based on the corresponding hole diameter for each level, and combined with the sound wave propagation attenuation model in air, calculate the theoretical sound pressure level of each hole diameter at different propagation distances.

[0045] Step S40: Using the propagation distance as the abscissa and the sound pressure level as the ordinate, plot the theoretical sound pressure level as a sound pressure level-distance trend line corresponding to each leakage level, thereby constructing a distance-sound pressure level-leakage rate graded alarm threshold MAP chart.

[0046] Step S50: Obtain the actual detection distance and sound pressure level of the acoustic imaging detector, compare the actual measurement point with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP, determine the leakage risk level based on the area where the actual measurement point falls, and output an alarm signal.

[0047] In step S10, the leakage stagnation pressure P and the leak diameter D determine the sound pressure level of the turbulent sound. The reference sound pressure level is determined using the following formula:

[0048] (1)

[0049] Where L1 represents the sound pressure level (in dB) at a distance of 1 m from the leak in a direction perpendicular to the injection, D represents the diameter of the leak (in mm), D0 represents a circular leak with a diameter of 1 mm, M0 represents the molar mass of air, M represents the molar mass of the leaking gas, P0 represents the absolute pressure of the ambient atmosphere (Pa), P represents the stagnant pressure at the leak (Pa), and C0, C1, C2, and C3 represent constants related to the injection medium and can be determined experimentally.

[0050] As shown in the above formula, at a distance of 1 meter from the leak, the sound pressure level of the ultrasonic waves generated by a leak in a pressure vessel or pipeline varies with the size of the leak and the gas pressure at the leak point. The ultrasonic wave generated by the leak has a relatively wide frequency band, generally between 20kHz and 100kHz. The energy of the ultrasonic wave is different at different frequencies; in fact, its spectral peak also varies with the size of the leak and the pressure of the medium.

[0051] For far-field plane waves propagating in the same direction, since diffusion attenuation does not need to be considered, the sound pressure L x The variation with distance x can be described by formulas (2) and (3), that is, the propagation attenuation model of sound waves in air is:

[0052] (2)

[0053] (3)

[0054] In the formula: L0 represents a constant, x represents the propagation distance (unit: m), α represents the absorption attenuation coefficient (unit: dB / m), f represents the ultrasonic frequency (unit: Hz), μ represents the dynamic viscosity of air (unit: uPa·s), and ρ represents the air density (unit: kg / m³). 3 ), c represents the speed of sound (unit: m / s).

[0055] Based on equations (1), (2), and (3), the sound pressure value L at a distance x meters from the leak point is... x The sound attenuation coefficient α is closely related to the detection distance, sound frequency, stagnation pressure, sound velocity, and molar mass of the leaking medium. The ambient air temperature T (°C) and humidity RH (%) directly affect the sound velocity c and air density ρ, thus affecting the attenuation coefficient α. The higher the ambient air temperature and humidity, the faster the sound attenuation.

[0056] In step S20, for an ideal gas under standard conditions, when the pressure of the medium inside the container or pipe p ≥ 0.3 MPa, the gas leaking from the gaps or leaks in the container or pipe is critical flow or sonic flow. That is, the quantitative relationship between the leakage rate and the leak diameter is expressed by the critical flow leakage rate formula:

[0057] (4)

[0058] Where Q0 represents the leakage rate (unit: kg / s), C d The value represents the gas leak pore shape factor (1.00 for circular pores, 0.95 for triangular pores, and 0.90 for rectangular pores), and A represents the pore area (unit: m²). 2 ), p represents the pressure of the medium inside the container or pipeline (unit: Pa), M gas R represents the molar mass of the gas under standard conditions (unit: kg / mol), R represents the gas constant (unit: J / mol·K), T represents the gas temperature (unit: K), and k represents the adiabatic index of the gas (i.e., the specific heat capacity at constant pressure C). p Compared with the specific heat capacity at constant volume C v The ratio of C p / C v ).

[0059] For initial leaks from small holes or gaps in pressure vessels or pipelines of refining and chemical plants, the pressure changes very slowly due to a continuous gas supply. Therefore, the pressure p of the medium inside the vessel or pipeline can be considered constant during the initial leakage stage. For critical flow leaks of gas under specific operating conditions, the leakage rate is proportional to the shape, area, and gas pressure of the leak.

[0060] If the gas type or composition, detection distance, pressure inside the container or pipeline, and ambient air pressure, temperature, and humidity are known, the sound pressure value L at a distance of x meters from the actual leak can be measured on-site. x Then, the leakage rate, i.e. the source strength Q0 at the leakage release source, can be estimated according to the above formulas (1), (2), (3) and (4).

[0061] Leakage risk levels include at least three levels: minor leakage, moderate leakage, and severe leakage. The distance-sound pressure level-leakage rate graded alarm threshold MAP chart is used to draw the sound pressure level-distance trend line corresponding to each level. The area between adjacent trend lines constitutes the alarm judgment interval for the corresponding level.

[0062] The maximum scale of the vertical axis of the distance-sound pressure level-leakage rate graded alarm threshold MAP is set to the upper limit of the sound pressure level detection of the acoustic imaging detector to avoid sensor saturation or damage.

[0063] The process for drawing a distance-sound pressure level-leakage rate graded alarm threshold MAP is as follows:

[0064] (1) Determine the molar mass M, pressure p, and adiabatic coefficient k of the gas medium being measured;

[0065] (2) Determine the leakage category and the threshold / source strength (kg / s) of the gas medium being tested according to Tables C.1, C.2 and C.3, or refer to API 754 Tier 1, Tier 2, Tier 3 and Tier 4 process safety events to determine the leakage category and the threshold / source strength (kg / s) of the gas medium being tested;

[0066] (3) Calculate the leak diameter D based on the gas leak category and the severe / moderate / minor leak threshold / source strength (kg / s) and formula (4);

[0067] (4) Calculate the sound pressure level L1 at 1 meter from the circular leak hole according to the above formula (1);

[0068] (5) Calculate or test the leakage ultrasonic pressure level at different distances from the leak hole under the test conditions according to the above formulas (2) and (3);

[0069] (6) Draw a MAP diagram of the alarm thresholds for distance (x / m), sound pressure level (y / dB), and leakage rate (kg / s).

[0070] Based on the above drawing process, the following is a specific example of drawing a distance-sound pressure level-leakage rate graded alarm threshold MAP:

[0071] 1. Assume or know that hydrogen gas with p = 7 MPa is continuously leaking from a pressure vessel or pipeline; the adiabatic index of hydrogen gas is k = 1.416, and the molar mass is M = 2 g / mol.

[0072] 2. Hydrogen is a flammable gas, and the leakage category is 5; the leakage threshold / source strength for severe, moderate, and minor outdoor hydrogen leaks are respectively: R = 1.39 × 10⁻⁶. -1 kg / s, O = 1.39×10 -2 kg / s, Y = 1.67×10 -3 kg / s.

[0073] 3. Based on equation (4), the source strength R is calculated as 1.39 × 10⁻⁶. -1 kg / s, O = 1.39×10 -2 kg / s, Y = 1.67×10 -3 The diameters of the circular leak corresponding to kg / s are 6.95 mm, 2.2 mm, and 0.763 mm, respectively.

[0074] 4.7 MPa of hydrogen gas leaked into the ambient air through circular holes of 6.95 mm, 2.2 mm, and 0.763 mm. According to formula (1), the sound pressure levels at 1 meter were 141.8 dB, 131.8 dB, and 122.6 dB, respectively.

[0075] 5. Numerical calculations or experiments are used to determine the ultrasonic pressure level of leakage at different distances from the leak under test conditions (see the table below).

[0076] Simulated calculation values ​​of ultrasonic pressure levels at different distances from the leak.

[0077]

[0078] 6. Plot a MAP (map of alarm thresholds) based on distance (x / m), sound pressure level (y / dB), and leakage rate (kg / s), as shown below. Figure 2 As shown.

[0079] Since the upper limit of the sound pressure level detection of acoustic imaging detectors is generally 120dB (exceeding 120dB may damage the sensor or cause the detector to overheat), the maximum scale of the vertical axis y is taken as 120dB.

[0080] In step S50, the measured point is compared with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP chart. The specific method for determining the leakage risk level based on the area where the measured point falls is as follows:

[0081] If the measured point is located below the trend line corresponding to a certain leakage level and above the adjacent lower-level trend line, it is determined to be that leakage level.

[0082] If the measured point is located above the highest level trend line, it is determined to be the highest leakage level;

[0083] If the measured point is below the lowest level trend line, it is determined that there is no leakage or the value is below the alarm threshold.

[0084] See Figure 2 During on-site testing or online monitoring, if the distance x between the acoustic imager or detector and the leak point is known... a and measured sound pressure level y a Then we can determine the value based on point (x) a , y a )exist Figure 2 The location of the leak can be quickly determined to assess the risk level. For example, if the detector is 20 meters away from the stable imaging point or the leak point, and the maximum sound pressure level measured by the detector is 100 dB, the point (20, 100) in the rectangular coordinate system is located at a leakage rate of 1.67 × 10⁻⁶. -3 kg / s and 1.39×10 -2 The area between the sound pressure level trend line corresponding to kg / s is classified as a yellow leakage risk level.

[0085] See Figure 3 The figure shows a leakage sound pressure level classification alarm threshold setting system based on acoustic imaging, including an acoustic imaging detector 100, a storage unit 200, a processing unit 300, and an alarm unit 400.

[0086] The acoustic imaging detector 100 is used to acquire ultrasonic signals from the leak point and output the measured sound pressure level and detection distance. The storage unit 200 is used to store a pre-constructed distance-sound pressure level-leakage rate graded alarm threshold MAP. This MAP is pre-constructed using the aforementioned acoustic imaging-based leak sound pressure level graded alarm threshold setting method. The processing unit 300 compares the measured distance and sound pressure level with the distance-sound pressure level-leakage rate graded alarm threshold MAP to determine the leak risk level. The alarm unit 400 outputs an alarm signal corresponding to the leak risk level.

[0087] Each unit or module in the system of the present invention can be implemented entirely or partially through software, hardware, or a combination thereof. The aforementioned units or modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to the aforementioned modules.

[0088] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging, characterized in that, include: Determine the reference sound pressure level at a predetermined distance from the leak based on the stagnation pressure of the leak source, the diameter of the leak hole, and the type of leaked gas. Based on the preset leakage rate threshold corresponding to the leakage risk level, the leakage diameter corresponding to each level is inversely calculated through the quantitative relationship between the leakage rate and the leakage hole diameter. Based on the hole diameters corresponding to each level, and combined with the sound wave propagation attenuation model in air, the theoretical sound pressure level of each hole diameter at different propagation distances is calculated. Using propagation distance as the x-axis and sound pressure level as the y-axis, the theoretical sound pressure level is plotted as a sound pressure level-distance trend line corresponding to each leakage level, thereby constructing a distance-sound pressure level-leakage rate graded alarm threshold MAP; and The detection distance and sound pressure level of the acoustic imaging detector are obtained. The measured point is compared with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP. The leakage risk level is determined according to the area where the measured point falls and an alarm signal is output.

2. The method for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging as described in claim 1, characterized in that, The leakage risk level includes three levels: slight leakage, moderate leakage, and severe leakage, or four levels: micro leakage, slight leakage, moderate leakage, and severe leakage. The distance-sound pressure level-leakage rate graded alarm threshold MAP graph plots the sound pressure level-distance trend lines corresponding to each level, and the area between adjacent trend lines constitutes the alarm judgment interval for the corresponding level.

3. The method for setting the leakage sound pressure level classification alarm threshold based on acoustic imaging as described in claim 2, characterized in that, The maximum scale of the vertical axis of the distance-sound pressure level-leakage rate graded alarm threshold MAP is set to the upper limit of the sound pressure level detection of the acoustic imaging detector to avoid sensor saturation or damage.

4. The method for setting a graded alarm threshold for leakage sound pressure level based on acoustic imaging as described in any one of claims 1 to 3, characterized in that, The specific method for comparing the measured point with the trend line in the distance-sound pressure level-leakage rate graded alarm threshold MAP chart, and determining the leakage risk level based on the area where the measured point falls, is as follows: If the measured point is located below the trend line corresponding to a certain leakage level and above the adjacent lower-level trend line, it is determined to be that leakage level. If the measured point is located above the highest level trend line, it is determined to be the highest leakage level; If the measured point is below the lowest level trend line, it is determined that there is no leakage or the value is below the alarm threshold.

5. A leakage sound pressure level classification alarm threshold setting system based on acoustic imaging, characterized in that, include: An acoustic imaging detector is used to collect ultrasonic signals from the leak point and output the measured sound pressure level and detection distance. Storage unit, the storage unit being used to store a pre-built distance-sound pressure level-leakage rate graded alarm threshold MAP; The processing unit is used to compare the measured distance and sound pressure level with the distance-sound pressure level-leakage rate graded alarm threshold MAP to determine the leakage risk level; as well as An alarm unit is used to output an alarm signal corresponding to the leakage risk level. The distance-sound pressure level-leakage rate graded alarm threshold MAP is pre-constructed by the leakage sound pressure level graded alarm threshold setting method based on acoustic imaging as described in any one of claims 1 to 4.

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