A method for fluid line leak detection and evaluation based on pressure response

Abstract

The application provides a kind of fluid (including gas and liquid) pipeline leakage detection and evaluation method based on pressure response, belongs to fluid (including gas and liquid) transmission field, mainly includes: (A) fluid pipe network system analysis modeling;(B) pressure source and system matching design;(C) pressure signal pulse width optimization;(D) system pressure response library establishment;(E) leakage detection and evaluation system verification.The application carries out mathematical modeling and calculation on fluid pipe network system, designs and optimizes the hardware and software of leakage detection system based on pressure response, and finally carries out simulation verification, solves the problems of complex structure, difficult leakage detection and long time consumption of fluid pipe network system.

Description

Technical Field

[0001] This invention belongs to the field of fluid (including gas and liquid) transmission and relates to a method for detecting and evaluating leakage in hydraulic systems based on pressure response. Background Technology

[0002] Fluid pipelines are widely used in various systems of engineering machinery, such as fuel systems, aircraft engines, and chemical pipeline systems. They are complex in structure, with numerous connecting components and supports. Components within a pipeline system are connected by pipelines to achieve their respective functions. Depending on the fluid pressure and load conditions, the degree of corrosion and aging varies among pipelines. Leaks in pipelines can alter internal flow characteristics, leading to component performance degradation and system failure. In chemical and manufacturing industries, leaked corrosive liquids can further cause safety accidents. Regarding aircraft engine pipelines, aircraft are subjected to hydraulic system pressure (28 MPa), ambient temperature (-40 to 135°C), airframe deformation, vibration, and acceleration loads throughout the entire flight profile. These complex loads subject the pipelines to strong coupling of flow, temperature, and stress fields. In aircraft manufacturing failures, pipeline failures have become the main type of failure, accounting for 71% of all failures. Therefore, to address fluid pipeline faults, condition monitoring and assessment technologies are needed. By performing condition-based maintenance, the health status of the fluid pipeline network can be monitored in real time, leaks can be quickly identified, potential faults can be located before an accident occurs, and the reliability and safety of the fluid pipeline system can be ensured. Summary of the Invention

[0003] (a) Purpose of the invention

[0004] The purpose of this invention is to address the problem of frequent and difficult-to-detect fluid (including gas and liquid) pipeline leaks by proposing a pressure-response-based method for fluid pipeline leak detection and assessment. This invention explores the inherent relationship between pipeline pressurization and leakage, and conducts research on hydraulic system pipeline leakage modeling, leakage characteristic value extraction, pressure impact response and pressure pulsation Fourier transform fusion methods, and leakage detection methods. A hydraulic system pipeline leak detection system is built and simulated for verification. The proposed pressure-response-based method for hydraulic system leakage detection and assessment provides support for the safe operation and maintenance of hydraulic systems.

[0005] (II) Technical Solution

[0006] The technical solution of this invention is: a method for detecting and evaluating leaks in fluid (including gas and liquid) pipelines based on pressure response, comprising the following steps:

[0007] (A) Fluid pipeline network system analysis and modeling;

[0008] (B) Pressure source and system matching design;

[0009] (C) Pressure signal pulse width optimization;

[0010] (D) Establishment of system stress response library;

[0011] (E) Leakage detection and assessment system calibration;

[0012] The fluid pipeline system analysis and modeling method described in step (A) is as follows:

[0013] (1) Analyze the composition of the fluid pipeline network system and count the dimensions of each pipe in the network;

[0014] (2) Establish a mathematical model of the fluid pipeline system based on geometric dimensions and calculate the pipeline volume;

[0015] (3) Derive the control equations for the fluid pipeline system;

[0016]

[0017] In the formula, ρ is the fluid density, u is the flow velocity, p is the internal pressure of the fluid, μ is the fluid shear viscosity coefficient, and λ is the fluid volume viscosity coefficient.

[0018] (4) Calculate the pressure drop within the fluid piping system;

[0019]

[0020] In the formula, λ is the friction loss coefficient, L is the pipe length, D is the equivalent pipe diameter, ρ is the fluid density, u is the flow velocity, and ξ is the local friction loss coefficient of the pipe.

[0021] The pressure source and system matching design method described in step (B) is as follows:

[0022] (1) Based on the total volume of the fluid pipeline network system, the pressure source capacity is initially determined;

[0023] (2) Based on the working pressure of the fluid pipeline network system, the pressure source pressure is initially designed;

[0024] (3) Design the pressure supply method of the pressure source (including but not limited to accumulators, liquid pump stations, etc.) based on the performance requirements of the pressure source, and calculate the time when the pressure source can provide relatively stable pressure.

[0025] The pressure signal pulse width optimization method described in step (C) is as follows:

[0026] (1) Set the pressure signal amplitude according to the working pressure of the pressure source;

[0027] (2) Analyze the influence of pressure pulse width on the system's pressure build-up characteristics;

[0028] (3) Set the upper limit of the pressure pulse width according to the relatively stable pressure supply time of the pressure source;

[0029] (4) Analyze the pressure build-up curve of the system under this pressure amplitude, calculate the lower limit of the pressure pulse width, and make the peak pressure after the system builds up close to the pressure source pressure.

[0030] (5) The pressure pulse width range and pressure amplitude of the hydraulic system are optimized to match the detection accuracy of the pressure sensor and meet the accuracy of pressure drop detection.

[0031] The method for establishing the system stress response library described in step (D) is as follows:

[0032] (1) Analyze the pressure build-up characteristics of the system under the initial leak-free operating condition;

[0033] (2) Establish a pressure response database for different leakage conditions within the system;

[0034] (3) Optimize the pressure pulse width for the system and update the pressure response library.

[0035] The verification method for the leak detection and assessment system described in step (E) is as follows:

[0036] According to the design scheme, select and assemble the system hardware, design the leak detection and assessment algorithm, develop the touch screen human-machine interface, and package the leak detection and assessment system. Conduct experiments / simulations on the system to verify whether the leak detection and assessment effect meets the design requirements. If it does not meet the design requirements, reselect the pressure source pressure, optimize the pressure pulse width signal, and repeat steps (B), (C), and (D).

[0037] (III) Beneficial Effects of the Invention

[0038] The beneficial effects of this invention are as follows: This invention provides a pressure-response-based method for leak detection and evaluation of fluid (including gas and liquid) pipelines. Starting with leak detection in fluid pipeline systems, it matches the pressure source according to the flow characteristics of the fluid pipeline system, optimizes the pressure signal pulse width, and finally verifies the reliability of the system through simulation. This solves the shortcomings of current methods for leak detection in fluid pipeline systems, such as difficulty and long detection times. This invention effectively shortens the leak detection time of fluid pipeline systems, and the system pressure source supply method is flexible, making it applicable to a wide range of scenarios. Attached Figure Description

[0039] Figure 1 This is a flowchart of the pressure response-based leak detection method of the present invention.

[0040] Figure 2 This is a schematic diagram of the pressure-response-based hydraulic system of the present invention.

[0041] Figure 3This is an installation diagram of the hardware equipment for the airborne leak detection system in an embodiment of the present invention.

[0042] Figure 4 This is a pressure response library for an airborne leak detection system in an embodiment of the present invention.

[0043] Figure 5 This is a schematic diagram of leakage detection (pressure build-up curve) in an embodiment of the present invention. Detailed Implementation

[0044] The invention will now be explained in detail with reference to simulation examples.

[0045] This embodiment takes a fluid pipeline system as the research object. The system uses an accumulator as a pressure source, which is a special case of pressure source selection. The system includes a drive motor, a pump station, an overflow valve, and a pressure relief valve, the purpose of which is to maintain a relatively stable pressure in the accumulator. Figure 1 The flowchart of the pressure response-based leak detection method of the present invention is shown below, and the specific implementation steps are as follows:

[0046] (A) Fluid pipeline network system analysis and modeling;

[0047] Based on the actual pipe dimensions measured by the prototype of the fluid pipeline system, the internal pipe routing of the fluid pipeline network was analyzed. The flow characteristics of the fluid in the pipe were described according to the fluid continuity equation and the Navier-Stokes equation for compressible fluids. Subsequently, a mathematical model of the fluid pipeline system was established, and the parameters of each pipeline were set. In this embodiment, three pipelines in the system were selected as the detection objects. The pressure loss caused by fluid viscosity in the pipeline was calculated to be 0.153 kPa, which has little impact on the pressure drop caused by leakage. Therefore, the ordinary pipeline model was used to ignore the pipeline flow resistance in the subsequent steps.

[0048] (B) Pressure source and system matching design;

[0049] Preliminary calculations were performed on the basic parameters of the accumulator, and it was matched with the system. Based on the inner diameter and length of each pipe in the hydraulic system, the total volume of the hydraulic system network was calculated, and the accumulator capacity was designed to be 2L. Based on the rated operating conditions of the fluid network, the rated pressure of the accumulator was designed to be 28MPa. This embodiment uses a hydraulic pump station to provide a stable pressure source for the accumulator. The equipment installation is as follows... Figure 3 As shown, mathematical models of the accumulator, pump, motor, pressure relief valve, and overflow valve are established based on mathematical formulas.

[0050] (C) Pressure signal pulse width optimization;

[0051] The pressure build-up characteristics of the fluid pipeline system were analyzed to optimize the pressure signal pulse width range. A lower limit for the pressure signal pulse width was initially set, and the pressure build-up curve of the model was simulated and analyzed. Calculations showed that when the pulse width length was greater than 0.15s, the peak value of the pressure build-up curve was close to the rated pressure of the accumulator, facilitating leak identification and detection. An upper limit for the pressure signal pulse width was initially set. Based on the 0.1% detection accuracy constraint of the pressure sensor, calculations showed that when the pulse width length was less than 0.3s, the pressure sensor could detect a leak 3 minutes after the start of pressure build-up, meeting the design requirements. Therefore, this embodiment can effectively detect leaks within a pressure pulse width range of 0.15s-0.3s.

[0052] (D) Establishment of system stress response library;

[0053] The initial pressure drop of the fluid pipeline system without any additional leaks was analyzed and used as a benchmark. The simulation calculation showed that the pressure drop after 180 seconds of pressure build-up was only 52 Pa, which is negligible. Therefore, this embodiment assumes that the system enters a stable pressure state after pressure build-up, with no pressure drop.

[0054] This embodiment simulates pipe leaks by adding orifice gaps. Different orifice diameters are added, and their pressure build-up curves and total leakage are calculated. Pressure values ​​at 60s, 180s, and 300s are recorded to establish a pressure response database. Figure 4 As shown.

[0055] (E) Leakage detection and assessment system calibration;

[0056] Based on the system pressure response library, a leak detection algorithm is designed, and a leak detection and assessment system is encapsulated. The system is then used to determine if the model can detect and assess pipeline leaks. If the design requirements are not met, the pressure amplitude is reselected, and the pressure pulse width is optimized for the system's flow characteristics. Steps (B), (C), and (D) are repeated. Under the optimized parameters (pressure amplitude 28 MPa, pressure pulse width 0.2 s), leaks can be effectively identified. Figure 5 As shown, the initial system pressure build-up curve shows no pressure drop after pressure build-up is completed; when a leak is added to the system, the pressure gradually decreases over time after pressure build-up, which is the pressure drop caused by internal leakage. This method can quickly and accurately detect whether there is a leak inside the system.

Claims

1. A method for monitoring and assessing fluid pipeline leakage based on pressure response, characterized in that, Includes the following steps: (A) Fluid pipeline network system analysis and modeling; (B) Pressure source and system matching design; The purpose of a pressure source is to provide a relatively stable pressure for the leak monitoring and assessment system. Its implementation methods include, but are not limited to, using accumulators and constant-pressure pumps. Specific methods are as follows: (1) Based on the state equation of the fluid pipeline system, analyze the capacity of each pipeline in the fluid pipeline system and initially set the volume of the pressure source element of the monitoring system; (2) Based on the inner diameter and length of each pipe in the pipeline network system, calculate the local loss caused by the change of cross section in the fluid flow in the pipeline network; combined with the working temperature of the pipeline network system under test and the viscosity-temperature characteristics of the working fluid, calculate the pressure loss caused by the flow resistance in the pipeline network. (3) The rated pressure of the pressure source is initially set based on the working pressure and pressure limit of the fluid pipeline system; (4) Based on the compressibility of the fluid inside the pipeline system and the initial pressure source pressure, calculate the pressure loss caused by the fluid being pressurized, and further optimize the rated pressure of the pressure source; (C) Pressure signal pulse width optimization; When a leak occurs within the system, the pressure build-up process slows down, and the pressure response curve changes. A suitable pulse width is needed to identify and extract the characteristics of the pipeline leak. The specific method is as follows: (1) Based on the analysis of the fluid pipeline network system and the basic parameters of the pressure source, calculate the time during which the pressure source can supply pressure relatively stably, and select the pulse width interval within this time. (2) The upper limit of the pressure pulse width is initially designed. If the pressure pulse width is too long, the stable pressure provided by the pressure source will continue to replenish the pressure loss caused by the leakage. It is difficult to detect the pressure drop inside the pipeline and it is impossible to determine whether the leakage exists. (3) The lower limit of the pressure pulse width is initially designed. If the pressure pulse width is too short, the pressure peak inside the pipeline is small, and the pressure drop caused by leakage is also small. Due to the limitation of sensor accuracy, it is difficult to detect leakage. The ideal lower limit of the pressure pulse width is that after the system pressure is built up, the pressure amplitude inside the pipeline is close to the pressure provided by the pressure source. (4) Based on the flow characteristics of the fluid pipeline system and the selection of sensors, the pressure pulse width is optimized, and a pulse width range that can effectively monitor system leakage is proposed. (D) Establishment of system stress response library; (E) Leakage monitoring and assessment system verification.

2. The method for monitoring and assessing fluid pipeline leakage based on pressure response according to claim 1, characterized in that: The fluid pipeline system analysis and modeling method described in step (A) is as follows: (1) Analyze the hardware composition of the fluid pipeline network system and establish mathematical models of the actuators, control elements and pipelines inside the system; (2) Calculate the flow rate and flow resistance of the pipeline network based on the pipeline length and inner diameter parameters; When detecting leaks in a fluid pipeline system, the system load is all stopped and the flow inside the pipeline is very small. Therefore, if the pressure inside the closed pipeline decreases, it is due to internal leakage or pressure drop caused by fluid compressibility. (3) Based on the fluid continuity equation and momentum equation, describe the fluid characteristics in the pipeline, establish the system state equation, and explore the flow characteristics in the pipeline network system; (4) Considering the pressure drop caused by the compressibility of the fluid, when the fluid is compressed, the intermolecular distance decreases, which leads to a decrease in volume; Calculate the bulk modulus E of common liquids p At 1.4×10 9 ~4.3×10 9 N / m 2 When the fluid volume elastic modulus is large, the volume change caused by pressure is small, indicating that the fluid is less compressible. Therefore, pressure loss due to the compressibility of the fluid is not considered in the liquid pipeline system and it is regarded as an incompressible fluid. When calculating the bulk modulus of common gases, the bulk modulus of common gases is relatively small, and the pressure drop caused by pressure cannot be ignored. Therefore, the leakage monitoring of gas pipelines needs to be designed in combination with the compressibility of the gas.

3. The method for monitoring and assessing fluid pipeline leakage based on pressure response according to claim 1, characterized in that: The specific method for modeling the system stress response library in step (D) is as follows: (1) Based on the analysis of the fluid pipeline system, establish a mathematical model of the fluid pipeline system with and without leakage based on the mass and energy balance equation; (2) Based on the pressure signal pulse width range, the system pressure pulse width is initially set. The pressure source provides the signal and records the pressure in the pipeline system at each time point, and the pressure response curve is plotted. (3) Analyze the pressure response curve when there is no leakage in the pipeline system. Since the sealing problems of control components and actuators in the system may cause a small pressure drop, use this pressure response curve as the benchmark group. (4) Summarize and analyze the characteristics of the pressure build-up curve when the system has leakage, extract the pressure values ​​of the system at different times from the start of pressure build-up, and derive and calculate the cumulative leakage of the system at different times based on the system state equation; (5) If the pressure drop caused by leakage does not match the detection accuracy of the pressure sensor, select a larger pressure pulse width according to the pressure signal pulse width range, and repeat steps (2), (3), and (4) to establish a pressure response database for the fluid pipeline system.

4. The method for monitoring and assessing fluid pipeline leakage based on pressure response according to claim 3, characterized in that: The specific method for designing the pressure response algorithm in step (E) is as follows: (1) Based on the pressure source matching design, select and build the hardware for the leakage monitoring system, and install and connect it with the pipeline network system of the fluid to be tested; (2) Based on the pressure pulse width signal optimization, select appropriate pressure amplitude and pressure signal pulse width according to the fluid pipeline network configuration and system load conditions; (3) Extract leakage characteristics based on the required system pressure response library and establish a system pressure response-based database; (4) Combine sensor detection accuracy and system response time to optimize leak identification and monitoring algorithms, develop touch screen human-machine interface, and encapsulate leak monitoring and assessment software; (5) Test the hydraulic system under test to verify whether the system can accurately monitor and evaluate the leakage. If the performance indicators are not met, recalculate the pressure source and pressure signal pulse width for the system and repeat steps (B), (C), (D), and (E).

Images