A submarine natural gas pipeline safety transportation detection device and control method

Abstract

The application relates to the technical field of leakage detection, in particular to a submarine natural gas pipeline safe conveying detection device and a control method, which comprises a submersible vehicle and a caisson assembly arranged below the submersible vehicle, a detection assembly is arranged in the caisson assembly, the detection assembly comprises an infrared camera and a tracer gas detection module; the caisson assembly is of a structure with an open lower part and a sealed upper part, high-pressure gas is sent to the upper part of the caisson assembly through a pressure increasing device in the submersible vehicle, so that a detection surface of a gas-water interface is formed in the caisson assembly; a first area and a second area composed of fluid in a detection area are arranged below the detection surface; the open lower part of the caisson assembly comprises a grid inlet, an inlet and an outlet.

Description

Technical Field

[0001] This invention relates to the field of leak detection technology, specifically to a detection device and control method for the safe transportation of subsea natural gas pipelines. Background Technology

[0002] In the field of monitoring the safe transport of subsea natural gas pipelines, timely detection and precise location of even minor leaks are crucial for preventing pipeline ruptures, environmental pollution, and resource losses. Traditional leak inspection methods primarily rely on underwater acoustic and optical systems. Remotely operated vehicles (ROVs) or autonomous underwater vehicles (AUVs) equipped with sonar or high-resolution cameras inspect the pipeline surface and surrounding water to detect leak-induced bubble plumes or pipe wall damage. However, in turbid waters near the shore, in estuaries, or where seabed sediments are easily resuspended, the large amounts of suspended sediment particles, plankton, and colloidal substances strongly scatter and absorb light, resulting in a sharp decrease in image contrast and an effective visibility distance often less than tens of centimeters. This optical barrier makes it difficult for cameras to clearly distinguish bubbles from background noise. Even if a swarm of bubbles from a leak rises to within the camera's range, it is often misjudged as seabed debris or biological disturbance due to blurred images and indistinct target edges, leading to missed detections. Conversely, the accumulation of suspended matter or the tumbling of sediments caused by ocean currents can also be misidentified as leaking bubbles, resulting in frequent false alarms and significantly reducing the reliability and automation of visual inspections.

[0003] To overcome the limitations of optical methods in turbid waters, tracer gas detection technology has been introduced into subsea pipeline leak monitoring. The basic principle is to inject a small amount of chemically stable, low-background gaseous tracer, such as sulfur hexafluoride or perfluorocarbons, into the natural gas pipeline. When a leak occurs at a point in the pipeline, the tracer gas escapes along with the natural gas, forming a plume in the seawater. By capturing and analyzing the concentration of the tracer gas using specialized sensors mounted on an underwater platform, leaks can be reliably identified without being affected by water turbidity. However, achieving efficient tracer gas capture in actual marine environments faces severe challenges: the bubble plume released from the leak point is rapidly diffused and diluted by the complex seabed flow field, and the tracer gas concentration may decrease by several orders of magnitude after rising tens of meters. Traditional open sampling inlets cannot actively converge and enrich such weak signals. At the same time, due to the flow field disturbances generated by the underwater vehicle's own movement and the presence of ocean background currents, the water body to be measured is often violently mixed with the surrounding seawater, and the residence time of the tracer gas is extremely short. The sensor is unable to obtain a stable concentration response above the detection limit, and it is easy to completely miss the leak signal due to the sampling orientation deviating from the center of the plume, resulting in low capture success rate and insufficient positioning accuracy. Summary of the Invention

[0004] To overcome the above problems, the present invention provides a safety inspection device for subsea natural gas pipelines, comprising a submersible and a caisson assembly disposed below the submersible. The caisson assembly contains a detection component, which includes an infrared camera and a tracer gas detection module. The caisson assembly has an open lower section and a sealed upper section. High-pressure gas is introduced into the caisson assembly via a pressurization device within the submersible, creating a gas-water interface detection surface within the caisson assembly. Below the detection surface are a first region and a second region composed of fluid from the detection area. The lower opening of the caisson assembly includes a mesh inlet, an inlet, and an outlet. The inlet is located at the front of the caisson assembly along the direction of travel of the submersible, and the outlet is located at the rear of the caisson assembly along the direction of travel. The mesh inlet is inclined forward towards the direction of travel of the submersible, allowing leaked fluid carrying tracer gas from the subsea natural gas pipeline to enter the second region inside the caisson assembly through the mesh inlet.

[0005] Furthermore, the detection component is fixedly installed inside the caisson assembly and located in a dry environment above the detection surface; the infrared camera of the detection component records the morphology and seepage characteristics of the detection surface, and the tracer gas detection module of the detection component performs quantitative analysis of the tracer gas concentration on the detection surface through infrared spectral absorption or electrochemical sensing.

[0006] Furthermore, the caisson assembly includes a first inclined plate and a second inclined plate symmetrically arranged on both sides of its longitudinal central axis, and two side plates connecting the two side edges of the first inclined plate and the second inclined plate; the first inclined plate, the second inclined plate and the two side plates together enclose and form an inverted cup-shaped structure with a lower opening and an upper sealing of the caisson assembly; the first inclined plate and the second inclined plate are both inclined outward from top to bottom, so that the internal cavity of the caisson assembly forms an flared structure with a cross-sectional area that gradually increases from top to bottom.

[0007] Furthermore, the first region is located above the second region, and the detection surface at the upper end of the first region is within the height range between the first and second inclined plates; the second region is arranged near the inlet and the grid inlet, serving as a temporary storage area for the leaked fluid after it enters the caisson assembly; the leaked fluid carrying tracer gas rises from the second region to the first region under the combined drive of buoyancy and air pressure, and finally reaches the detection surface; the detection component is fixedly installed inside the caisson assembly, above the detection surface, for performing infrared imaging and tracer gas concentration detection on the detection surface.

[0008] Furthermore, balancing chambers are symmetrically arranged on both sides of the submersible, and the caisson assembly is fixedly installed at the center of the bottom of the submersible. During operation, the horizontal attitude of the submersible is adjusted by the balancing chambers to suppress the tilt and oscillation of the detection surface inside the caisson assembly.

[0009] The control method of the submarine natural gas pipeline safety transportation detection device of the present invention, using the above-mentioned detection device, includes the following steps: Step a: Input geometric and environmental parameters based on the leakage plume model of the pipeline leak point, and set the interface disturbance model coefficients. and Maximum permissible disturbance Tracer gas concentration threshold Ocean current speed Minimum stable speed and speed adjustment step size ; Calculate the maximum permissible sailing speed The upper speed limit is limited by the ability of the grid inlet to capture leaked tracer gas, and also by the stability of the detection surface, setting the initial cruising speed. for times ; Step b: After the submersible descends to the working depth, set the speed to the initial cruising speed. And activate the attitude adjustment system of the balance chamber, and through the real-time adjustment of the balance chambers on both sides, keep the submersible in a horizontal attitude and ensure that the detection surface inside the caisson is in a horizontal and stable state. Step c, during navigation, a fixed control cycle is used. The concentration of tracer gas output by the synchronous acquisition and detection component and the interface perturbation index obtained from infrared camera image processing ; Step d, for the current disturbance index Make a judgment, if Exceeding the allowed limit This indicates that the interface is unstable due to excessive speed or external water currents. In this case, the current speed should be immediately reduced. Decrease by one step Wait for the system to stabilize and then remeasure; if the disturbance still exceeds the standard due to repeated deceleration, trigger an alarm and suspend the inspection. Step e, when the disturbance meets the standard, i.e. Under the premise of analyzing concentration data, if the tracer gas concentration Continuously reaching or exceeding the threshold Time exceeds detection confirmation delay If the leaking plume is successfully captured, the speed should be immediately reduced to the minimum permissible speed. Perform precise positioning maneuvers and record the coordinates of concentration peaks; like consistently below The time reached the undetected timing Then proceed with the search adjustment; Step f, continue in a cycle Repeat steps c to e, dynamically adjusting the speed based on the detection surface status and tracer gas signal, until the detection task for all predetermined pipeline sections is completed.

[0010] Furthermore, the geometric environment parameters include the tracer gas mass flow rate. That is, the mass of tracer gas released from the leak point per unit time; the final velocity of the rising bubbles. The final velocity of a bubble rising uniformly in water; plume entrainment coefficient. The linear proportionality constant characterizing the plume cross-sectional radius as height increases; the height of the caisson inlet above the seabed. That is, the vertical distance from the center of the grid inlet to the seabed; effective capture area. The projected area of ​​the grid inlet section in the direction of water flow; the longitudinal position of the inlet. The longitudinal coordinates of the caisson's grid inlet relative to the submersible's reference point; capture window half-width. The maximum horizontal offset between the grid inlet and the plume center is allowed.

[0011] Furthermore, the search adjustment includes increasing the lateral movement range and adjusting the speed to... The submersible is controlled to perform a reciprocating lateral scan perpendicular to the pipe direction in the current pipe section. The lateral movement amplitude is set according to the maximum possible offset distance of the plume. This scanning mode is continued until the preset scan coverage cycle is completed. If the entire reciprocating lateral scan period is... If the value remains below the threshold, it is determined that no leak has occurred in the current pipeline section.

[0012] Furthermore, the precise positioning includes using the variation law of tracer gas concentration enriched on the detection surface within the caisson assembly with spatial position, combined with infrared camera observation of the bubble plume morphology, to reverse calculate the precise location of the leak source on the pipeline, and record the coordinates of that point.

[0013] Furthermore, the submersible is controlled to perform an overhead scan in the downstream direction, at intervals... Concentration data is collected every second. The corresponding mileage is recorded simultaneously by an infrared camera, which records images of the detection surface and extracts the frequency of bubble occurrence. ,in The distance to the current location of the submersible; The submersible is controlled to perform a reverse scan and concentration gradient confirmation, and the concentration data from the two scans are averaged.

[0014] The beneficial effects of this invention, compared with the prior art, are that the gas-water interface detection surface formed by pressurization inside the caisson assembly allows the infrared camera and tracer gas detection module to operate in a dry environment, eliminating interference from factors such as seabed sediment suspension, biological attachment, or optical refraction on the detection results. Traditional underwater direct optical observation is easily affected by suspended particle scattering and biofilm coverage, resulting in false alarms. In this invention, the tracer gas bubbles must cross the water body to reach the detection surface and be released into the gas phase space. The infrared camera images the bubble morphology and seepage characteristics of the detection surface, and the tracer gas detection module simultaneously measures the concentration of the enriched gas. Quantitative analysis shows that the two constitute a dual-mode composite verification system, where a single interference source cannot simultaneously trigger both types of signals, thus effectively filtering out false alarms introduced by the complex seabed environment. Secondly, the flared structure formed by the symmetrical inclination of the first and second inclined plates gives the gas-water interface of the caisson cavity self-stabilizing capability. The flared structure causes the internal cross-sectional area to gradually increase from top to bottom. When the gas-water interface is disturbed and shifts, the geometric feature of being narrower at the top and wider at the bottom produces an asymmetric recovery effect: when the interface moves upward, the upper contraction section makes the gas compression response more sensitive, generating a stronger reverse driving force to prevent the interface from further upward movement; when the interface moves downward, the lower expansion section... The hydrostatic pressure changes gradually level off, mitigating the interface's downward tendency. This dynamic buffering mechanism effectively suppresses interface oscillations without additional active control, while simultaneously ensuring the interface maintains a nearly flat, mirror-like surface in the horizontal direction. This provides an ideal focusing target for the infrared camera, eliminating optical refraction distortion or focus drift caused by interface irregularities. The partitioned design of the first and second zones inside the caisson, combined with the directional arrangement of the front inlet and rear outlet, establishes an orderly fluid transport path within the cavity. Leaking fluid carrying tracer gas is efficiently captured by the forward-facing inclined grid inlet and first enters the second zone for temporary storage. This area, located near the inlet, serves to buffer fluid velocity and balance concentration gradients. It allows the leaking fluid to rise smoothly to the first area under the combined influence of buoyancy and air pressure, eventually reaching the detection surface. Simultaneously, as the submersible moves, a pressure difference is created at the bottom of the caisson, driving the fluid in the detection area from the front inlet to the rear outlet. This prevents large-scale influx of external water from interfering with the detection surface and ensures the directional migration and continuous renewal of the leaking fluid within the cavity. The continuous discharge from the outlet maintains a dynamic balance of internal pressure, preventing gas escape or interface instability, thus achieving highly sensitive capture and highly stable detection. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the submarine natural gas pipeline safety transportation detection device of the present invention; Figure 2 This is a bottom view of the detection device of the present invention; Figure 3 This is a view of the detection device of the present invention from another direction; Figure 4 This is a schematic diagram of the caisson assembly of the present invention; Figure 5 This is a schematic diagram of an image detected by the infrared camera of the present invention, wherein (a) is a comparison diagram of a undisturbed, calm detection surface, and (b) is a detection surface disturbed by leaked gas containing tracer gas. Figure 6 This is a flowchart of the control method for the detection device of the present invention; In the diagram: 1. Submersible; 2. Caisson assembly; 21. First inclined plate; 22. Second inclined plate; 23. Side plate; 24. Outlet; 25. Grid inlet; 26. Inlet; 3. Balance chamber; 4. Detection assembly. Detection surface 20, first area 201, second area 202; Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] The present invention will now be described in detail with reference to the accompanying drawings. The subsea natural gas pipeline safety transmission detection device of the present invention includes a submersible 1 and a caisson assembly 2 disposed below the submersible 1. A detection component 4 is disposed within the caisson assembly 2, and the detection component 4 includes an infrared camera and a tracer gas detection module. The caisson assembly 2 has an open lower section and a sealed upper section. High-pressure gas is introduced into the caisson assembly 2 through a pressurization device within the submersible 1, forming a gas-water interface detection surface 20 within the caisson assembly 2. Below the detection surface 20 is a detection area. The caisson assembly 2 is configured with a first region 201 and a second region 202, which are formed by fluids. The lower opening of the caisson assembly 2 includes a grid inlet 25, an inlet 26, and an outlet 24. The inlet 26 is located at the front of the caisson assembly 2 along the direction of travel of the submersible 1, and the outlet 24 is located at the rear of the caisson assembly 2 along the direction of travel. The grid inlet 25 is inclined forward toward the direction of travel of the submersible 1, so that the leaking fluid carrying the tracer gas of the subsea natural gas pipeline enters the second region 202 inside the caisson assembly 2 through the grid inlet 25.

[0017] The caisson assembly 2 adopts an inverted cup-shaped design with an open bottom and a sealed top. Under the pressure of the pressurization device on the submersible 1, high-pressure gas is continuously injected into its internal hollow cavity, driving the original water inside downwards. This creates a stable and clear gas-water interface detection surface 20 at the bottom of the caisson assembly 2. This detection surface 20 serves as the boundary between the gas and liquid phases. The lower opening of the caisson assembly 2 consists of a mesh inlet 25, an inlet 26, and an outlet 24. The inlet 26 is located at the front of the caisson assembly 2 along the direction of travel of the submersible 1, and the outlet 24 corresponds to... Located at the rear, this design creates a pressure difference at the bottom of the caisson assembly 2 as the submersible 1 moves, guiding the fluid in the detection area to flow orderly from front to back through the interior of the caisson assembly 2 along the direction of travel. This prevents large-scale influx of external water from interfering with the detection surface 20 and ensures the directional migration of the leaking fluid within the cavity. The grid inlet 25, serving as the main absorption channel for the leaking fluid, has a forward-sloping design that maximizes its frontal area. This allows it to actively intercept leaking fluid that may be carrying tracer gas along the submersible 1's path and utilize the tilt angle... The generated Venturi effect accelerates fluid introduction, ensuring that the leaking fluid efficiently enters the second region 202 inside the caisson assembly 2. The second region 202 is close to the inlet 26 and the grid inlet 25, serving as a temporary storage area for the leaking fluid after entering the caisson assembly 2. It buffers the fluid velocity and balances the concentration gradient, allowing the incoming leaking fluid to rise smoothly to the first region 201 under the combined action of buoyancy and air pressure, and finally reach the detection surface 20. The detection component 4 is fixedly installed in the dry environment inside the caisson assembly 2 above the detection surface 20. Its integrated infrared camera and tracer gas detection module constitute a dual-mode composite detection unit. The infrared camera is responsible for recording the bubble morphology and seepage characteristics of the detection surface 20 in real time. The tracer gas detection module uses the infrared spectral absorption principle or electrochemical sensing technology to quantitatively analyze the concentration of tracer gas enriched in the detection surface 20. The two are cross-checked to eliminate false alarms caused by factors such as seabed sediment, biological attachment, or optical refraction. The outlet 24 can maintain the directional flow of fluid and ensure the dynamic balance of pressure inside the caisson assembly 2, avoiding instability of the detection surface 20 or gas escape due to pressure accumulation.

[0018] The detection component 4 is fixedly installed inside the caisson component 2 and located in a dry environment above the detection surface 20; the infrared camera of the detection component 4 records the morphology and seepage characteristics of the detection surface 20; the tracer gas detection module of the detection component 4 performs quantitative analysis of the tracer gas concentration of the detection surface 20 through infrared spectral absorption or electrochemical sensing.

[0019] The caisson assembly 2 includes a first inclined plate 21 and a second inclined plate 22 symmetrically arranged on both sides of its longitudinal central axis, and two side plates 23 connecting the two side edges of the first inclined plate 21 and the second inclined plate 22; the first inclined plate 21, the second inclined plate 22 and the two side plates 23 together form an inverted cup-shaped structure with an open bottom and a sealed top of the caisson assembly 2; the first inclined plate 21 and the second inclined plate 22 are both inclined outward from top to bottom, so that the internal cavity of the caisson assembly 2 forms an flared structure with a cross-sectional area that gradually increases from top to bottom.

[0020] The caisson assembly 2 adopts a flared structure formed by the symmetrical inclination of the first inclined plate 21 and the second inclined plate 22. That is, the cross-sectional area of ​​the internal cavity gradually increases from top to bottom. When the pressurization device in the submersible 1 continuously supplies high-pressure gas to the sealed top of the caisson assembly 2, the gas displaces the original water in the cavity from top to bottom, forming a clear detection surface 20 between the gas and liquid phases. The flared design gives the lower part of the cavity a larger flow cross-sectional area, while the upper part has a smaller cross-sectional area. This geometric feature provides a natural buffer zone for the gas-water interface. When the seabed current disturbance or the pitch attitude of the submersible 1 changes slightly, the gas can pass through the water. When the interface position shifts upward (i.e., the air pressure is higher), the volume change rate corresponding to the unit height change increases due to the contraction of the upper cross-sectional area. The gas compression or expansion response is more sensitive, thereby generating a stronger counter-driving force to prevent the interface from rising further to the top of the caisson and to avoid the escape of bubbles or submersion of the detection component 4. Conversely, if the interface position shifts downward (i.e., the air pressure is lower), the expanded cross-sectional area at the bottom makes the volume increase of the water displaced when the interface moves downward larger, and the hydrostatic pressure change is more gradual. This can effectively slow down the downward trend of the interface and prevent a large amount of external water from rushing in and diluting the concentration of the tracer gas.

[0021] The flared structure also improves the flatness of the detection surface 20. Under the geometric constraint of being narrow at the top and wide at the bottom, the surface tension and gas pressure of the gas-water interface are more evenly distributed radially, and the curvature of the interface in the horizontal direction is reduced, presenting an approximately flat mirror state. This provides an ideal imaging target surface for the infrared camera, eliminating optical refraction distortion or focus drift caused by unevenness of the interface, thereby ensuring that the tracer gas detection module can focus stably and acquire clear image data.

[0022] The first region 201 is located above the second region 202, and the detection surface 20 at the upper end of the first region 201 is within the height range between the first inclined plate 21 and the second inclined plate 22; the second region 202 is arranged near the inlet 26 and the grid inlet 25, serving as a temporary storage area for the leaked fluid after it enters the caisson assembly 2; the leaked fluid carrying the tracer gas rises from the second region 202 to the first region 201 under the combined drive of buoyancy and air pressure, and finally reaches the detection surface 20; the detection component 4 is fixedly installed inside the caisson assembly 2, above the detection surface 20, for performing infrared imaging and tracer gas concentration detection on the detection surface 20.

[0023] The submersible 1 is symmetrically provided with balance chambers 3 on both sides, and the caisson assembly 2 is fixedly installed at the center of the bottom of the submersible 1. During operation, the horizontal attitude of the submersible 1 is adjusted by the balance chambers 3 to suppress the tilt and oscillation of the detection surface 20 inside the caisson assembly 2.

[0024] The symmetrically arranged balancing chambers 3 on both sides of the submersible 1 play a role in leveling and stabilizing the attitude during underwater navigation. The balancing chambers 3 output a reverse regulating torque by adjusting the water volume or air pressure in the chamber in real time to counteract the deflection trend caused by the impact of the ocean current and the inertia of the submersible 1 itself. This ensures that the submersible 1 maintains a near-horizontal attitude, and the detection surface 20 in the flared cavity is confined to a near-horizontal ideal position. This effectively avoids abnormal accumulation or dissipation of tracer gas on one side of the cavity due to interface tilt. At the same time, it greatly suppresses the up-and-down oscillation and surface ripples of the detection surface 20 caused by the pitch and sway of the submersible 1. This provides the infrared camera with a stable, flat and focused imaging target surface, thereby ensuring the continuity and reliability of the tracer gas concentration detection data.

[0025] Based on the safety transmission detection device for subsea natural gas pipelines, a closed-loop control method is established with navigation speed as the control variable and the quality of the detection surface signal as feedback, including the following steps: Step a: Input geometric and environmental parameters based on the leakage plume model of the pipeline leak point, and set the interface disturbance model coefficients. and Maximum permissible disturbance Tracer gas concentration threshold Ocean current speed Minimum stable speed and speed adjustment step size ; Calculate the maximum permissible sailing speed The upper speed limit is limited by the ability of the grid inlet 25 to capture leaked tracer gas, and also by the stability of the detection surface 20, which sets the initial cruising speed. for times ; Step b: After submersible 1 descends to the working depth, set the speed to the initial cruising speed. And activate the attitude adjustment system of the balance chamber 3, and through the real-time adjustment of the balance chambers 3 on both sides, keep the submersible 1 in a horizontal attitude and ensure that the detection surface 20 inside the caisson is in a horizontal and stable state. Step c, during navigation, a fixed control cycle is used. The tracer gas concentration output by the synchronous acquisition and detection component 4 and the interface perturbation index obtained from infrared camera image processing ; Step d, for the current disturbance index Make a judgment, if Exceeding the allowed limit This indicates that the interface is unstable due to excessive speed or external water currents. In this case, the current speed should be immediately reduced. Decrease by one step Wait for the system to stabilize and then remeasure; if the disturbance still exceeds the standard due to repeated deceleration, trigger an alarm and suspend the inspection. Step e, when the disturbance meets the standard, i.e. Under the premise of analyzing concentration data, if the tracer gas concentration Continuously reaching or exceeding the threshold Time exceeds detection confirmation delay If the leaking plume is successfully captured, the speed should be immediately reduced to the minimum permissible speed. Perform precise positioning maneuvers and record the coordinates of concentration peaks; like consistently below The time reached the undetected timing Then proceed with the search adjustment; Step e, continue in a cycle Repeat steps c to e, dynamically adjusting the speed based on the detection surface status and tracer gas signal, until the detection task for all predetermined pipeline sections is completed.

[0026] The leak point continuously releases tracer gas, with a mass flow rate of... (kg / s), set the average final velocity of the bubble rise to be (m / s); Detecting the current horizontal current of seawater The submersible's speed is The relative water flow velocity is .

[0027] The plume trajectory is approximated by a linear trajectory: ,in The height above the seabed. This represents the downstream horizontal distance. The plume cross-sectional radius adopts the entrainment assumption: If the tracer mass is conserved, then it is highly likely to be conserved. Average concentration at the cross section: .

[0028] The effective capture cross-sectional projected area of ​​the grid inlet 25 is: Its dimensions are determined by the geometry and inclination angle of the inlet, and the center of the grid inlet 25 is at a height of [missing information - likely a value or value]. The plume reached an altitude The required downstream distance is: The entrance is located longitudinally on the submersible. Define the capture window half-width Only when At this point, the plume cross-section overlaps with the inlet, and the mass flow rate of the tracer gas entering the caisson can be expressed as: In practical applications, At this time, the capture flow is approximately constant; only when the window is misaligned does the flow drop sharply to zero. Therefore, the speed is mainly limited by the geometric capture conditions. The speed constraint is the upper limit of the speed that can be obtained from the capture window: At the same time, a certain positive pressure difference and Venturi effect must be maintained, and a minimum inflow velocity must exist. Below this speed, a stable air-water interface and flow cannot be established. Therefore, the cruising speed needs to be below a certain level. Only within the specified range can an effective tracer gas sample be obtained.

[0029] The geometric environment parameters include tracer gas mass flow rate. That is, the mass of tracer gas released from the leak point per unit time; the final velocity of the rising bubbles. The final velocity of a bubble rising uniformly in water; plume entrainment coefficient. The linear proportionality constant characterizing the plume cross-sectional radius as height increases; the height of the caisson inlet above the seabed. Vertical distance from the center of the grid inlet to the seabed; effective capture area The projected area of ​​the grid inlet 25 section in the direction of water flow; the longitudinal position of the inlet. The longitudinal coordinates of the caisson's grid inlet 25 relative to the submersible's reference point; half-width of the capture window. The maximum horizontal offset between the grid inlet 25 and the plume center is allowed.

[0030] The smoothness of the air-water interface directly affects the reliability of infrared imaging and gas detection. As speed increases, external water inflow and increased pressure fluctuations inside the caisson lead to interface oscillations and bubble tearing. An interface disturbance index is defined. (Interface wave height root mean square), described by the velocity correlation function: ,coefficient Calibrated by hydrodynamic experiments or CFD. The minimum standard for the detection component is: tracer gas concentration: Interface disturbance: The upper limit of speed can be obtained from the perturbation constraints. .

[0031] The overall speed control logic is as follows: Permissible speed range: The optimal cruising speed, within the permissible range, prioritizes higher speeds to improve inspection efficiency, but a stability margin must be reserved; generally, a certain speed is chosen. Real-time feedback correction is performed, and the tracer gas concentration is monitored in real time through the detection component. and interface disturbance Adjust the speed dynamically. If no detection is detected and the disturbance is low, it may be that the plume area has not been reached or there is no leak in the current pipeline section. The speed should be reduced and the lateral scan range should be increased. If the detected concentration increases, the speed should be reduced immediately for precise positioning.

[0032] The search adjustments include increasing the lateral movement range and adjusting the speed to... The submersible 1 is controlled to perform a reciprocating lateral scan perpendicular to the pipe direction in the current pipe section. The lateral movement amplitude is set according to the maximum possible offset distance of the plume. This scanning mode is continued until the preset scanning coverage cycle is completed. If the entire reciprocating lateral scan period is... If the value remains below the threshold, it is determined that no leak has occurred in the current pipeline section.

[0033] The precise positioning involves using the variation of tracer gas concentration enriched on the detection surface inside the caisson assembly with spatial position, combined with infrared camera observation of the bubble plume morphology, to reverse-calculate the precise location of the leak source on the pipeline, and record the coordinates of that point.

[0034] Real-time tracking of gas concentration continuous Instant satisfaction When the system determines that it has entered the fine-locate state, it sets the flag fine_locate = true.

[0035] To clearly describe the fine positioning process, the following parameter is introduced: the mileage coordinates along the pipeline axis are denoted as (Unit: m), the origin can be taken as the starting point of the inspection or the pipeline marker; the lateral offset distance perpendicular to the pipeline direction is denoted as... (Unit: m). The maximum tracer gas concentration recorded during the fine scanning process is denoted as... (unit and) (Consistent), the estimated location of the leak point along the pipeline direction calculated using the concentration distribution characteristics is denoted as... (Unit: m). The single-pass scan length for fine positioning is set to... (Unit: m), usually taken as the lateral expansion scale of the plume. The speed is 3 to 5 times that of the ship to ensure sufficient coverage of possible concentration peaks. The spatial interval of the concentration sampling points is determined by the ship's speed. With sampling period Decision, that is ,in To accurately determine the speed, the value is taken. To achieve the lowest perturbation and the highest spatial resolution. The data refresh period (in seconds) for the tracer gas detection module. The system response time constant is denoted as... (Unit: s), representing the time delay from gas transport from the inlet to the detection module and reaching a stable reading, which needs to be obtained through offline calibration. The final confirmed three-dimensional coordinates (longitude, latitude, depth) of the leak point are denoted as... .

[0036] First, lock the initial state and record the coordinates, then immediately and smoothly reduce the speed. Simultaneously, the submersible's attitude is adjusted to absolute horizontal using the balancing chamber, eliminating any tilt on the detection surface. The current geographical location of the submersible is recorded. and the corresponding pipeline mileage This serves as the starting reference point for fine-tuning. Set variables. , .

[0037] Perform a forward scan (overhead scan) in the downstream direction while maintaining speed. Along the direction of the pipeline (which may be the same as or opposite to the direction of the leak plume transport, depending on the ocean currents). (Depending on the direction) Slowly move forward, the distance traveled is fixed. Each interval Concentration data is collected every second. and corresponding mileage Simultaneously, an infrared camera records images of the detection surface and extracts the frequency of bubble occurrence. For the collected sequences A moving average filter is applied to eliminate instantaneous fluctuations caused by turbulence. The filtered concentration is denoted as... .

[0038] Then, a reverse scan and concentration gradient confirmation were performed. After completing the forward scan, the submersible rotated 180° in place and proceeded along the same path. Reverse driving, same coverage length The concentration sequence was recorded again. The concentration data from the two scans were averaged to obtain a two-way average concentration profile. To eliminate system response delay This results in a shift in the peak position. Shift compensation can be achieved using the formula... Implementation, in which Obtained from offline calibration. In the profile. Find the global maximum point And assign the corresponding maximum concentration to .

[0039] Perform lateral offset verification and infrared verification to control the submersible to Centered on the pipe, perform a small-amplitude lateral scan, that is, perpendicular to the pipe direction, with a lateral movement range of [value missing]. This ensures that the leak point is indeed located directly above the pipe and not at the edge of the lateral plume. If the concentration remains highest in the middle position during the lateral scan, it confirms no lateral deviation; otherwise, correct the lateral position and repeat the downstream over-the-top scan and reverse back scan to confirm the concentration gradient.

[0040] Activate the high frame rate mode of the infrared camera and capture an image of the bubble plume at the detection surface. If in A regularly rising cluster of bubbles was observed, and the bubble frequency was... Exceeding the preset threshold If visual judgment indicates the presence of leakage, the reliability of location determination is improved.

[0041] Finally, coordinate calculation and data uploading are performed. Combined with fused data from the submersible's inertial navigation system (INS) and Doppler log (DVL), the pipeline mileage is determined. Inversely calculated into geographic coordinates and depth Record complete information about the leak point: precise coordinates. Maximum concentration Bubble frequency The system records timestamps and uploads the data to the mother ship or shore-based control center via underwater acoustic communication or a satellite link after surfacing. It then exits fine positioning mode (fine_locate = false), resets scan-related flags, and resumes cruising speed. Continue the inspection along the pipeline.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A safety inspection device for subsea natural gas pipelines, comprising a submersible (1) and a caisson assembly (2) disposed below the submersible (1), characterized in that: The caisson assembly (2) is provided with a detection assembly (4), which includes an infrared camera and a tracer gas detection module; The caisson assembly (2) has an open bottom and a sealed top structure. High-pressure gas is sent to the top of the caisson assembly (2) through the pressurization device inside the submersible (1), so that a gas-water interface detection surface (20) is formed inside the caisson assembly (2). Below the detection surface (20) are a first region (201) and a second region (202) composed of fluid from the detection area; The lower opening of the caisson assembly (2) includes a mesh inlet (25), an inlet (26), and an outlet (24). The inlet (26) is located at the front of the caisson assembly (2) along the direction of travel of the submersible (1), and the outlet (24) is located at the rear of the caisson assembly (2) along the direction of travel. The grid inlet (25) is tilted forward toward the direction of travel of the submersible (1) so that the leaked fluid carrying the tracer gas of the subsea natural gas pipeline enters the second region (202) inside the caisson assembly (2) through the grid inlet (25).

2. The subsea natural gas pipeline safety transportation detection device according to claim 1, characterized in that: The detection component (4) is fixedly installed inside the caisson component (2) and located in a dry environment above the detection surface (20); The infrared camera of the detection component (4) records the morphology and seepage characteristics of the detection surface (20) in images, and the tracer gas detection module of the detection component (4) performs quantitative analysis of the tracer gas concentration of the detection surface (20) through infrared spectral absorption or electrochemical sensing.

3. The subsea natural gas pipeline safety transportation detection device according to claim 2, characterized in that: The caisson assembly (2) includes a first inclined plate (21) and a second inclined plate (22) symmetrically arranged on both sides of its longitudinal central axis, and two side plates (23) connected between the two side edges of the first inclined plate (21) and the second inclined plate (22). The first inclined plate (21), the second inclined plate (22), and the two side plates (23) together form an inverted cup-shaped structure with a lower opening and an upper sealing of the caisson assembly (2); The first inclined plate (21) and the second inclined plate (22) are both inclined outward from top to bottom, so that the internal cavity of the caisson assembly (2) forms an flared structure with the cross-sectional area gradually increasing from top to bottom.

4. The subsea natural gas pipeline safety transportation detection device according to claim 3, characterized in that: The first region (201) is located above the second region (202), and the detection surface (20) at the upper end of the first region (201) is within the height range between the first inclined plate (21) and the second inclined plate (22); The second area (202) is located near the inlet (26) and the grid inlet (25) as a temporary storage area for leaked fluid after it enters the caisson assembly (2); The leaking fluid carrying the tracer gas rises from the second region (202) to the first region (201) under the combined drive of buoyancy and air pressure, and finally reaches the detection surface (20). The detection component (4) is fixedly installed inside the caisson component (2) and above the detection surface (20) for performing infrared imaging and tracer gas concentration detection on the detection surface (20).

5. The subsea natural gas pipeline safety transmission detection device according to any one of claims 1-4, characterized in that: The submersible (1) is symmetrically provided with balance chambers (3) on both sides, and the caisson assembly (2) is fixedly installed at the center of the bottom of the submersible (1). During the operation, the horizontal attitude of the submersible (1) is adjusted by the balance chamber (3) to suppress the tilt and oscillation of the detection surface (20) inside the caisson assembly (2).

6. A control method for a subsea natural gas pipeline safety transmission detection device, employing the detection device described in any one of claims 1-5, characterized in that, Includes the following steps: Step a: Input geometric and environmental parameters based on the leakage plume model of the pipeline leak point, and set the interface disturbance model coefficients. and Maximum permissible disturbance Tracer gas concentration threshold Ocean current speed Minimum stable speed and speed adjustment step size ; Calculate the maximum permissible sailing speed The upper speed limit is limited by the ability of the grid inlet (25) to capture leaked tracer gas, and is also limited by the stability of the detection surface (20), setting the initial cruising speed. for times ; Step b, after the submersible (1) descends to the working depth, the speed is set to the initial cruising speed. And activate the attitude adjustment system of the balance chamber (3), and through the real-time adjustment of the balance chambers (3) on both sides, keep the submersible (1) in a horizontal attitude, and ensure that the detection surface (20) inside the caisson is in a horizontal and stable state. Step c, during navigation, with a fixed control cycle The tracer gas concentration output by the synchronous acquisition and detection component (4) and the interface perturbation index obtained from infrared camera image processing ; Step d, for the current disturbance index Make a judgment, if Exceeding the allowed limit This indicates that the interface is unstable due to excessive speed or external water currents. In this case, the current speed should be immediately reduced. Decrease by one step Wait for the system to stabilize and then remeasure; if the disturbance still exceeds the standard due to repeated deceleration, trigger an alarm and suspend the inspection. Step e, when the disturbance meets the standard, i.e. Under the premise of analyzing concentration data, if the tracer gas concentration Continuously reaching or exceeding the threshold Time exceeds detection confirmation delay If the leaking plume is successfully captured, the speed should be immediately reduced to the minimum permissible speed. Perform precise positioning maneuvers and record the coordinates of concentration peaks; like consistently below The time reached the undetected timing Then proceed with the search adjustment; Step f, continue in a cycle Repeat steps c to e, dynamically adjusting the speed based on the detection surface status and tracer gas signal, until the detection task for all predetermined pipeline sections is completed.

7. The control method for the detection device according to claim 6, characterized in that: Geometric environmental parameters include tracer gas mass flow rate That is, the mass of tracer gas released from the leak point per unit time; Final velocity of rising bubbles The final velocity of an air bubble as it rises at a constant speed in water; plume entrainment coefficient , which characterizes the linear proportionality constant of the plume cross-sectional radius as height increases; Caisson entrance height above sea level That is, the vertical distance from the center of the grid entrance (25) to the seabed; Effective capture area The projected area of ​​the grid inlet (25) section in the direction of water flow; Entrance longitudinal position The longitudinal coordinate of the caisson's grid inlet (25) relative to the submersible reference point; Capture window half width The maximum horizontal offset between the grid inlet (25) and the plume center is allowed.

8. The control method for the detection device according to claim 6, characterized in that: The search adjustments include increasing the lateral movement range and adjusting the speed to... The submersible (1) performs a reciprocating lateral scan perpendicular to the pipe direction in the current pipe section, and the lateral movement amplitude is set according to the maximum possible offset distance of the plume. Continue in this scanning mode until the preset scan coverage cycle is completed. During the entire reciprocating lateral scan... If the value remains below the threshold, it is determined that no leak has occurred in the current pipeline section.

9. The control method for the detection device according to any one of claims 6-8, characterized in that: The precise positioning includes using the variation law of tracer gas concentration enriched on the detection surface (20) inside the caisson assembly (2) with spatial position, combined with infrared camera observation of bubble plume morphology, to reverse calculate the precise location of the leak source on the pipeline, and record the coordinates of that point.

10. The control method for the detection device according to claim 9, characterized in that: The submersible (1) is controlled to perform an overhead scan in the downstream direction at intervals. Concentration data is collected every second. The corresponding mileage is recorded simultaneously by an infrared camera, which records images of the detection surface and extracts the frequency of bubble occurrence. ,in The distance to the current location of the submersible (1); The submersible (1) is controlled to perform a reverse scan and concentration gradient confirmation, and the concentration data from the two scans are averaged.

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