Ocean flange bolt stress monitoring and self-fastening device and working method

Abstract

The invention relates to the technical field of ocean engineering, in particular to an ocean flange bolt stress monitoring and self-fastening device and a working method. The device comprises a fixing assembly, a monitoring assembly and a fastening assembly. The fixing assembly comprises a unit shell, and the unit shell is installed on the end face of the flange. The monitoring assembly comprises a force sensing gasket, and the force sensing gasket is installed between a nut of the bolt and the flange. The fastening assembly comprises a driving mechanism and a rotating wheel, the driving mechanism is installed on the inner wall of the unit shell, one end of the rotating wheel is installed on an output shaft of the driving mechanism, the other end of the rotating wheel is connected to a bolt in an inserted mode, the rotating wheel and the bolt are coaxially arranged, and the rotating wheel is used for fastening the bolt when the bolt is loosened. According to the invention, closed-loop control of monitoring, judgment and retightening is formed, and the long-term operation reliability in the extreme ocean environment is improved.

Description

Technical Field

[0001] This invention relates to the field of marine engineering technology, and in particular to a marine flange bolt stress monitoring and self-tightening device and its working method. Background Technology

[0002] The field of marine engineering structures involves various large-scale facilities, such as offshore oil drilling platforms, offshore wind turbines, and underwater production systems. These facilities commonly use high-strength bolts to connect critical components. Such connections need to maintain preload for extended periods in harsh marine environments to ensure the overall stability and safety of the structure.

[0003] In existing technologies, a typical bolt condition monitoring system assesses connection sealing performance by installing a sealing layer at the flange joint surface and indirectly determining flange clearance changes using vacuum monitoring. Another common approach involves directly mounting resistance strain gauges or piezoelectric sensors on the bolt surface to measure bolt strain and convert it into a preload signal. This signal is then processed by a signal conditioning circuit and transmitted to a monitoring terminal, triggering an audible and visual alarm when the preload falls below a threshold. Both systems require maintenance personnel to perform re-tightening operations on-site based on alarm information. Re-tightening tools are typically hydraulic wrenches or tensioners, carried manually or by an underwater robot.

[0004] Therefore, the existing technologies described above have the following problems: Indirect monitoring methods, such as vacuum seal testing, cannot directly reflect the specific value of the bolt preload; they can only determine the overall sealing status of the flange, resulting in insufficient monitoring accuracy and difficulty in locating specific loose bolts. Secondly, the monitoring and re-tightening processes are independent of each other. The system only has an alarm function and cannot automatically perform tightening actions after detecting preload decay. Under harsh marine weather conditions, the window from alarm to manual maintenance can be as long as several weeks, and structural safety risks persist. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a marine flange bolt stress monitoring and self-tightening device and operating method, which can realize real-time monitoring and automatic re-tightening of single bolt level preload, forming a closed-loop control of monitoring, judgment, and re-tightening, thereby improving long-term operational reliability in extreme marine environments.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A marine flange bolt stress monitoring and self-tightening device includes: a fixing component, a monitoring component, and a fastening component; the fixing component includes a unit housing, which is mounted on the end face of the flange; the monitoring component includes a force-sensing gasket, which is mounted between the bolt nut and the flange; the fastening component includes a drive mechanism and a rotating wheel, the drive mechanism is mounted on the inner wall of the unit housing, one end of the rotating wheel is mounted on the output shaft of the drive mechanism, and the other end of the rotating wheel is inserted into the bolt and arranged coaxially with the bolt, for tightening the bolt when it is loose.

[0007] Optionally, the unit housing has a semi-enclosed structure with an opening on one side that fits against the end face of the flange. The housing has a cavity inside, where the fastening assembly and monitoring assembly are located.

[0008] Optionally, the edge of the opening of the unit's outer casing is bent outward, and fixing screws are installed on the bent structure to fix the unit's outer casing onto the flange.

[0009] Optionally, a rubber sealing gasket is installed between the unit housing and the flange end face.

[0010] Optionally, the fixing assembly further includes a fixing housing, which is fixedly disposed on the inner wall of the unit housing and located on the opposite side of the bolt. The driving mechanism is a servo motor, which is installed inside the fixing housing.

[0011] Optionally, the fixed housing has a positioning hole on the side facing the bolt, and the servo motor is connected to the rotating wheel through a planetary reducer and a coupling.

[0012] Optionally, the monitoring component further includes a main piezoelectric force sensor, which is electrically connected to the force sensing pad.

[0013] Optionally, it also includes a main control component, which includes a control module, a signal processing module and an overload protection module, embedded in a sealed cavity of the unit housing, and connected to the monitoring component and the fastening component respectively via wires.

[0014] Optionally, it also includes a power supply component and a communication and storage component. The power supply component uses a lead-acid battery as the main power source. The communication and storage component includes a communication module and a storage module, which are used to upload bolt preload data, re-tightening records, alarm status and equipment operation information to the remote monitoring platform in real time.

[0015] This invention also provides a method for operating the marine flange bolt stress monitoring and self-tightening device as described above, comprising the following steps: Real-time acquisition of bolt preload signals; The preload signal is compared with a preset threshold to determine whether the bolt preload has decayed. When the preload signal is lower than the preset threshold, the fastening assembly outputs torque to re-tighten the bolt; During the tightening operation, the axial force signal is fed back in real time; Closed-loop force control is implemented based on the axial force signal. When the axial force reaches the target value or exceeds the overload threshold, the re-tightening operation is stopped.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. The stress monitoring and self-tightening device of this invention mounts the unit casing onto the flange end face, forming a basic support structure. The force-sensing gasket in the monitoring component is directly installed between the bolt and nut and the flange to sense changes in the bolt's axial force. The drive mechanism of the fastening component outputs torque and transmits it to the bolt via a rotating wheel, achieving a re-tightening operation. The installation method of the fixed component ensures the stability of the device in a marine environment, preventing displacement due to vibration or corrosion. The force-sensing gasket, as a strain gauge sensor, outputs an electrical signal by detecting the deformation of the bolt after loading. The installation position ensures the directness of the measurement path. By directly measuring the bolt's preload, it avoids the shortcomings of indirect judgment based on the overall flange sealing performance, improving data accuracy. The coordinated work of the force-sensing gasket and the drive mechanism achieves a closed loop of monitoring and execution. When the preload decays, re-tightening is automatically triggered, reducing the need for manual intervention, avoiding delays in manual inspections, and improving the safety, durability, and intelligent operation and maintenance level of the offshore structure.

[0017] 2. It adopts a servo drive and planetary reduction structure, which ensures stable output torque and high tightening accuracy. The piezoelectric sensing and temperature compensation module work together to improve measurement accuracy and signal stability. The overall sealed structure is corrosion-resistant and prevents biofouling, adapting to extreme marine environments. It supports wireless communication and remote management, enabling intelligent maintenance and visual monitoring of marine structures.

[0018] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] 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. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0020] Figure 1 This is a cross-sectional view of the monitoring and self-tightening device provided in an embodiment of the present invention; Figure 2 This is a three-dimensional cross-sectional view of the monitoring and self-tightening device provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the operation of the monitoring and self-tightening device provided in the embodiment of the present invention; In the diagram: 1. Fixing component; 2. Fastening component; 3. Monitoring component; 4. Main control component; 5. Power supply component; 6. Communication and storage component; 11. Unit housing; 12. Fixing shell; 13. Fixing screw; 14. Positioning hole; 15. Rubber sealing gasket; 21. Servo motor; 22. Planetary reducer; 23. Coupling; 24. Rotating wheel; 31. Main piezoelectric force sensor; 32. Force sensing gasket; 51. Lead-acid battery; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Example 1 This embodiment proposes a marine flange bolt stress monitoring and self-tightening device. Users can install the device on bolts in some key locations or install the device on all bolts as needed.

[0022] like Figure 1 , Figure 2 As shown, the stress monitoring and self-tightening device includes a fixing component 1, a monitoring component 3, and a fastening component 2. The fixing component 1 includes a unit housing 11, which is mounted on the end face of a flange. The monitoring component 3 includes a force-sensing gasket 32, which is installed between the bolt nut and the flange. The fastening component 2 includes a drive mechanism and a rotating wheel 24. The drive mechanism is mounted on the inner wall of the unit housing 11. One end of the rotating wheel 24 is mounted on the output shaft of the drive mechanism, and the other end of the rotating wheel 24 is inserted into the bolt and arranged coaxially with the bolt for tightening the bolt when it becomes loose.

[0023] The housing 11 of the fixed assembly 1 is mounted on the flange end face, providing a stable mounting base for components such as the monitoring assembly 3 and the fastening assembly 2, ensuring that each component maintains relative positional stability under vibration conditions in the marine environment. The force-sensing gasket 32 ​​of the monitoring assembly 3 is directly installed between the bolt nut and the flange, directly acquiring the preload change of a single bolt, avoiding the problem of insufficient single-bolt monitoring accuracy caused by indirectly inferring the connection status through flange gaps. The coaxial design of the rotating wheel 24 ensures that the torque output by the drive mechanism is accurately transmitted to the bolt, guaranteeing the reliability of the re-tightening action.

[0024] This structure integrates monitoring and fastening functions into the same device, solving the problem of separation between monitoring and re-tightening in existing technologies where monitoring devices can only alarm and fastening devices require manual operation. At the same time, the direct monitoring method at the single bolt level can accurately locate loose bolts and avoid the defect that the overall monitoring cannot distinguish the state of individual bolts. It is suitable for monitoring and maintenance of bolts that are distributed in large marine structures such as marine jackets and offshore wind turbine towers.

[0025] The unit housing 11 has a semi-enclosed structure with an opening on one side. The opening fits against the end face of the flange. The housing has a cavity, and the fastening assembly 2 and monitoring assembly 3 are located in the cavity.

[0026] The semi-enclosed shape can be adapted to the connection structure of flanges and bolts. The opening close to the flange end face can reduce the space occupied by the device. At the same time, the fastening component 2 and the monitoring component 3 are housed in the chamber, so that each component forms a relatively closed installation environment, avoiding direct contact between seawater and salt spray in the marine environment and the internal mechanical and sensing components, thus reducing the risk of corrosion.

[0027] The edge of the opening of the unit housing 11 is bent outward, and fixing screws 13 are installed on the bent structure to fix the unit housing 11 to the flange. A rubber sealing gasket 15 is installed between the unit housing 11 and the flange end face.

[0028] The outer bent edge can increase the contact area between the unit housing 11 and the flange, so that the tightening force of the fixing screw 13 can be transmitted more evenly to the flange end face, avoiding stress concentration caused by single-point fixing and reducing the loosening of the housing caused by wind and wave vibration in the marine environment.

[0029] The unit's outer casing 11 is a hollow, sealed chamber with an anti-biofouling coating on its outer surface and a multi-layered sealing structure inside to house and protect electronic, electrical, and mechanical components. Fluororubber gaskets 15 are fitted at the connection points of the unit casing 11 and the motor shaft through-hole, while perfluoroelastomer gaskets are used at the interface of the monitoring component 3. This sealing design achieves an overall protection rating of IP68, effectively preventing seawater immersion, salt spray corrosion, and biofouling, ensuring long-term stable operation. An exhaust valve and a waterproof and breathable membrane structure are located at the bottom of the unit casing 11 to balance internal pressure changes, achieving waterproof sealing while preventing internal condensation caused by temperature differences, thus extending the lifespan of electronic components.

[0030] The fixing component 1 also includes a fixing shell 12, which is fixedly disposed on the inner wall of the unit housing 11 and located on the opposite side of the bolt. The driving mechanism is a servo motor 21, which is installed inside the fixing shell 12.

[0031] The fixed housing 12 provides an independent and stable mounting space for the servo motor 21, preventing the servo motor 21 from being displaced due to vibration of the housing if it is directly mounted on the inner wall of the housing 11. The mounting position allows the output shaft of the servo motor 21 to be directly aligned with the bolt through subsequent transmission components, shortening the torque transmission path, reducing force loss, and ensuring that the power output by the servo motor 21 can be efficiently transmitted to the rotating wheel 24.

[0032] The fixed housing 12 has a positioning hole 14 on the side facing the bolt, and the servo motor 21 is connected to the rotating wheel 24 through a planetary reducer 22 and a coupling 23.

[0033] Servo motor 21 provides torque, planetary reducer 22 reduces and increases the torque, and the torque is output through rotating wheel 24. The transmission ratio of the reduction mechanism is 1:15 to 1:30, which is used to convert the high-speed, low-torque output of servo motor 21 into a low-speed, high-torque output to meet the tightening requirements of large-size bolts. Through the combination of servo motor 21 and planetary reducer 22, high-precision, controllable torque output is achieved, giving the bolt retightening process good repeatability and response stability. By setting the positioning hole 14 structure, the output shaft of servo motor 21 and the axis of rotating wheel 24 are kept coaxially positioned, ensuring a stable and reliable force transmission path and improving retightening accuracy.

[0034] The monitoring component 3 also includes a main piezoelectric force sensor 31, which is electrically connected to the force sensing pad 32 to form an axial force transmission structure for real-time acquisition of bolt preload change signals. This device adds a force sensor under the bolt, primarily for measuring the bolt preload. This preload reflects the bolt's tightness, and by determining whether the preload reaches the design threshold, it can be determined whether the bolt needs to be re-tightened.

[0035] Monitoring component 3 incorporates a signal conditioning and temperature compensation module. The raw signal is amplified, demodulated, and subjected to a second-order low-pass filter before being output as a standard voltage signal. It also features a PT100 temperature compensation chip to correct measurement deviations caused by temperature and humidity changes, ensuring stable signal transmission and reliable measurement accuracy even in extreme environments. After multi-stage amplification and filtering, the signal effectively suppresses noise from wave vibrations, electromagnetic interference, and temperature drift. The temperature compensation module corrects for piezoelectric response deviations caused by environmental temperature differences in real time, ensuring that the force signal output remains highly consistent with the actual preload.

[0036] A redundant signal channel is provided between the main control component 4 and the monitoring component 3. The main signal line and the backup line are arranged inside the unit's fixed shell 12. Through the dual-channel synchronous acquisition and verification mechanism, the reliability and fault tolerance of data transmission are improved, and monitoring failure is avoided due to single point of failure.

[0037] The device also includes a main control component 4, which comprises a control module, a signal processing module, and an overload protection module. It is embedded in the sealed cavity of the unit's fixed housing 12 and connected to the monitoring component 3 and the servo motor 21 via wires. The control module stores bolt preload thresholds and determines looseness in real time. When the preload is detected to be below the set lower limit, it automatically outputs a re-tightening signal. When the preload is detected to exceed 120% of the set upper limit, the overload protection module immediately issues a stop command and triggers an audible and visual alarm. This control strategy prevents bolt or flange structure damage due to stress, achieving dynamic safety protection.

[0038] The device also includes a power supply component 5 and a communication and storage component 6. The power supply component 5 uses a maintenance-free sealed lead-acid battery 51 as the main power source. The overall structure is compact, and the casing is treated with an anti-salt spray coating, providing excellent corrosion resistance and making it directly adaptable to the independent power supply requirements of marine environments. With this power supply solution, the system can achieve long-term independent operation without external cables or auxiliary power supply devices, reducing the difficulty and safety risks of offshore maintenance.

[0039] The communication and storage component 6 includes a communication module and a storage module. The communication module supports 4G / 5G and BeiDou dual-mode communication, and is used to upload bolt preload data, re-tightening records, alarm status, and equipment operation information to the remote monitoring platform in real time. Through this module, data visualization management and remote intelligent operation and maintenance can be realized, improving the system's intelligence level.

[0040] The communication module also connects bidirectionally to the remote monitoring platform. In addition to real-time data upload, it can also remotely adjust the preload threshold, servo response speed and alarm strategy via command downlink, enabling online updates and remote control of system parameters.

[0041] Example 2 This embodiment provides a working method for the marine flange bolt stress monitoring and self-tightening device as described above, including the following steps: Step 1: Fix the device at the flange bolt connection position, ensuring that the monitoring component is concentric and stably fitted with the bolt axis; Step 2: The monitoring component collects bolt preload signals in real time and transmits them to the main control component; Step 3: The main control component filters, compensates for temperature, and calibrates the acquired signals to generate actual preload data; Step 4: The control module compares the actual preload with the preset threshold to determine whether the bolt has become loose; Step 5: When the preload is detected to be lower than the set threshold, the control module issues a re-tightening command, driving the servo motor to output torque through the planetary reduction mechanism for re-tightening; Step 6: During the re-tightening process, the control module implements closed-loop force control based on real-time force feedback from the sensor. When the axial force reaches the target value or exceeds the limit, the servo action is stopped immediately, and the re-tightening operation is completed.

[0042] Through the above working method, a closed-loop control of bolt connection detection, judgment, re-tightening, and protection is realized, which has a fully autonomous condition monitoring and maintenance capability and can operate stably for a long time under unattended conditions.

[0043] Using the M64 high-strength bolts (preload design threshold 280kN) connecting the offshore jacket to the upper module flange as the monitoring and re-tightening target, the operational procedures and component coordination logic of the device are described in detail, such as... Figure 3 As shown, it includes the following steps: Step 1: Secure the device to the flange bolt connection position to ensure that the monitoring components fit tightly with the bolts and operate stably; When fixing the device to the flange bolt connection position, first rinse the surface of the bolts with high-pressure fresh water to remove salt scale and marine organism residue, and then wipe the nut and flange contact surface with anhydrous ethanol.

[0044] The 316L stainless steel unit casing was inspected and found to be free of deformation and damage to the anti-biological coating. Fluororubber gaskets were embedded at the interface between the unit casing and the fixed shell, and perfluoroelastomer gaskets were installed between the unit casing and the flange to achieve IP68 protection.

[0045] Secure the unit housing with the arc groove to the flange face using M12 socket head cap screws. Insert the fixed housing into the limiting groove. After adjusting the servo motor shaft and the bolt to be coaxial using a laser alignment instrument, lock it in place with M8 set screws.

[0046] Insert the force sensing gasket between the nut and the flange. The main piezoelectric force sensor is threaded onto the fixed shell and fits the gasket. Start the tilt sensor to confirm that the device is tilted ≤3°, and ensure that the monitoring component is coaxially fitted with the bolt.

[0047] Step 2: The monitoring component collects the bolt axial force signal in real time and transmits it to the main control component; When the monitoring component collects the axial force of the bolt, the power supply component supplies power, the main piezoelectric force sensor performs a self-test calibration of the zero point, and the metal foil strain gauge of the force sensing pad is connected to the integrated signal conditioning module via a Wheatstone bridge to amplify the weak signal.

[0048] When the bolt is subjected to axial force, the gasket deforms, causing the strain gauge to convert into a voltage signal. The piezoelectric crystal in the main piezoelectric force sensor generates charge, which is also converted into a voltage signal. The two signals are collected synchronously and transmitted to the main control component via shielded twisted pair cable. At the same time, the PT100 temperature sensor transmits temperature data, and the signal diagnostic unit monitors the deviation. If the deviation exceeds the limit, an audible and visual alarm is triggered.

[0049] Step 3: The main control component filters, compensates for temperature, and calibrates the acquired signals to generate actual preload data; When the main control component processes the acquired signal, the signal processing module first performs a second-order low-pass filter on the signal to filter out wave vibration, electromagnetic interference and mechanical noise, and then performs a 10-point moving average filter to make the signal fluctuation ≤0.5kN. The signal is then fused according to the weights of 0.7 for the main sensor and 0.3 for the auxiliary pad.

[0050] By combining the real-time temperature data of PT100 with the pre-stored "temperature-force signal deviation curve", the temperature deviation is corrected; the factory calibration coefficient is called to correct the initial preload data and generate the actual preload data.

[0051] The data storage module associates and stores data on collection time, temperature, and sensor status, and simultaneously uploads it to the remote monitoring platform via a 4G / 5G+BeiDou dual-mode communication module.

[0052] Step 4: The control module receives the actual preload data and compares it with the preset preload threshold to determine whether the bolt has experienced preload decay or loosening. The control module reads the preload threshold from the storage unit, including the normal range, warning value, re-tightening trigger value and overload value, and compares the actual preload with the threshold at regular intervals.

[0053] When the actual preload is within the normal range, the green LED stays on and sends a "normal status" signal; when it is between the warning value and the re-tightening trigger value, the yellow LED flashes and sends a warning and loosening trend data; when it is below the re-tightening trigger value, the red LED stays on, sends an emergency re-tightening request, and sends a "high power output" command to the power supply component; when the overload value is exceeded, the overload protection module cuts off the servo power supply, and the buzzer sounds a continuous alarm.

[0054] Step 5: When the preload is lower than the set threshold, the control module sends a command to the servo motor; The servo motor output shaft converts high-speed, low-torque into low-speed, high-torque through a coupling and a planetary reducer to meet bolt tightening requirements.

[0055] Step 6: During the re-tightening process, the main piezoelectric force sensor feeds back the axial force signal to the control module every 50ms to achieve closed-loop force control; When the axial force reaches the target value, the control module immediately outputs a stop command to cut off the power supply to the servo motor; if it exceeds the 336kN overload threshold, the overload protection module will stop the machine synchronously to avoid damage to the bolts or flanges.

[0056] After shutdown, the control module records the re-tightening time, torque, and final preload data, stores and uploads them to the remote platform, and confirms for the second time that the device has no displacement through the tilt sensor, thus completing the re-tightening operation.

[0057] Furthermore, in marine environments, bolts are prone to corrosion and thread jamming, which can cause the torque output and preload to increase asynchronously. Forcibly tightening them may cause thread damage and flange deformation, and it cannot be adapted to bolts with different attenuation rates.

[0058] Based on this, in another implementation, the preload decay rate is calculated using the main control component, and the decay slope is derived from nearly five sets of sampled data; then, a graded re-tightening strategy is adopted: Slow decay, for example, decay rate ≤ 2kN / h, then the target torque is output in one go to complete the re-tightening; For moderate attenuation, such as 2kN / h < attenuation rate ≤ 5kN / h, the tightening is done in two stages. The first stage outputs 70% of the target torque, rests for 30 seconds to release the thread stress, and then outputs the remaining 30% of the torque. For rapid attenuation, such as attenuation rate > 5kN / h, the preload is tightened in three stages, with each stage outputting 1 / 3 of the target torque and each stage spaced 30 seconds apart. At the same time, the torque-preload conversion efficiency is monitored in real time.

[0059] If, during a certain stage of re-tightening, the torque output increases by 10% but the preload does not increase, it is determined to be jammed. Re-tightening is immediately paused, and a bolt jamming alarm is uploaded to prevent forced operation.

[0060] By employing a graded re-tightening strategy, bolt damage caused by thread jamming and corrosion is reduced, extending bolt service life. Stress is released through step-by-step re-tightening, improving the long-term stability of preload, and timely identification of jamming faults can prevent ineffective torque output, thereby reducing power consumption and mechanical wear.

[0061] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A marine flange bolt stress monitoring and self-tightening device, characterized in that, Includes: fixing components, monitoring components, and fastening components; The mounting assembly includes a unit housing, which is mounted on the end face of a flange; The monitoring component includes a force-sensing pad, which is installed between the bolt nut and the flange; The fastening assembly includes a drive mechanism and a rotating wheel. The drive mechanism is mounted on the inner wall of the unit housing. One end of the rotating wheel is mounted on the output shaft of the drive mechanism, and the other end of the rotating wheel is inserted into a bolt and arranged coaxially with the bolt, for fastening the bolt when it becomes loose.

2. The marine flange bolt stress monitoring and self-tightening device as described in claim 1, characterized in that, The unit's outer casing has a semi-enclosed structure with an opening on one side that fits against the end face of the flange. The casing contains a cavity, and the fastening assembly and monitoring assembly are located within the cavity.

3. The marine flange bolt stress monitoring and self-tightening device as described in claim 2, characterized in that, The edge of the opening of the unit's outer casing is bent outward, and fixing screws are installed on the bent structure to fix the unit's outer casing onto the flange.

4. The marine flange bolt stress monitoring and self-tightening device as described in claim 2, characterized in that, A rubber sealing gasket is installed between the unit's outer casing and the flange end face.

5. The marine flange bolt stress monitoring and self-tightening device as described in claim 1, characterized in that, The fixing assembly also includes a fixing shell, which is fixedly mounted on the inner wall of the unit housing and located on the opposite side of the bolt. The driving mechanism is a servo motor, which is installed inside the fixing shell.

6. The marine flange bolt stress monitoring and self-tightening device as described in claim 5, characterized in that, The fixed housing has a positioning hole on the side facing the bolt, and the servo motor is connected to the rotating wheel through a planetary reducer and a coupling.

7. The marine flange bolt stress monitoring and self-tightening device as described in claim 1, characterized in that, The monitoring component also includes a main piezoelectric force sensor, which is electrically connected to the force sensing pad.

8. The marine flange bolt stress monitoring and self-tightening device as described in claim 1, characterized in that, It also includes a main control component, which includes a control module, a signal processing module and an overload protection module, and is embedded in a sealed cavity of the unit's outer casing, and is connected to the monitoring component and the fastening component respectively through wires.

9. The marine flange bolt stress monitoring and self-tightening device as described in claim 1, characterized in that, It also includes power supply components and communication and storage components. The power supply components use lead-acid batteries as the main power source. The communication and storage components include a communication module and a storage module, which are used to upload bolt preload data, re-tightening records, alarm status and equipment operation information to the remote monitoring platform in real time.

10. A method for operating the marine flange bolt stress monitoring and self-tightening device as described in any one of claims 1-9, characterized in that, Includes the following steps: Real-time acquisition of bolt preload signals; The preload signal is compared with a preset threshold to determine whether the bolt preload has decayed. When the preload signal is lower than the preset threshold, the fastening assembly outputs torque to re-tighten the bolt; During the tightening operation, the axial force signal is fed back in real time; Closed-loop force control is implemented based on the axial force signal. When the axial force reaches the target value or exceeds the overload threshold, the re-tightening operation is stopped.

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