Ultrasonic guided wave automatic detection system and method for large ocean engineering structure

Abstract

The invention discloses an ultrasonic guided wave automatic detection system and method for a large ocean engineering structure, and the method comprises the following steps: planning and preparing before detection; system laying and surface self-adaption are carried out; performing automatic scanning and FMC data acquisition; data processing, frequency dispersion physical model establishment and DC-TFM imaging; and carrying out image splicing, visualization and defect evaluation. A modular robot scanning platform, a guided wave phased array transducer in a specific mode and a frequency dispersion compensation full focusing (DC-TFM) algorithm are fused, wave field data are obtained through full matrix capture (FMC), frequency-dependent phase correction is carried out in a frequency domain to eliminate the frequency dispersion effect, and full-area dynamic focusing is achieved. According to the system, rapid, full-coverage and high-resolution C scanning imaging can be performed on a large structure, the small defect detection probability and the quantitative evaluation accuracy are improved, and the structural integrity and the operation safety are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and in particular relates to an automated ultrasonic guided wave testing system and method for large marine engineering structures. Background Technology

[0002] Large-scale marine engineering structures, such as subsea oil and gas pipelines, offshore platform structures, offshore wind turbine monopile or jacket foundations, and the hulls and tanks of floating production storage and offloading (FPSO) units, are critical infrastructure for national energy strategies and the marine economy. These structures operate for extended periods in extremely complex marine environments characterized by high temperatures, high pressures, high salinity, and dynamic loads, inevitably suffering from accumulated damage in various forms, including corrosion thinning, fatigue cracking, weld defect propagation, and impact damage. Failure to detect and accurately assess this damage in a timely manner can lead to catastrophic leaks and structural failures, resulting in enormous economic losses, severe environmental pollution, and personnel safety risks. Therefore, conducting regular, reliable, and comprehensive non-destructive testing on these critical structures to ensure their structural integrity is a perpetual and crucial challenge in the field of marine engineering.

[0003] However, traditional non-destructive testing methods fall short in addressing such challenges. For example, conventional methods such as handheld ultrasonic thickness gauges, magnetic particle testing, or penetrant testing, while effective in small, easily accessible areas, are extremely inefficient for subsea pipelines that can stretch for tens or hundreds of kilometers or the bottom plates of storage tanks covering thousands of square meters, failing to achieve comprehensive coverage. These methods typically require the removal of insulation or anti-corrosion layers, and for buried or underwater structures, large-scale excavation or the construction of underwater work platforms is necessary. This makes the preparation work for testing arduous, costly, and extremely risky, rendering it economically and operationally infeasible.

[0004] Therefore, the industry urgently needs a highly efficient detection technology that enables large-scale, rapid, non-contact or low-contact detection. To overcome the drawbacks of traditional methods, various advanced non-destructive testing technologies have been proposed and researched, such as guided ultrasonic wave (UGW) technology, phased array ultrasonic testing (PAUT) technology, and total focusing (TFM) imaging methods. However, when applied to the inspection of large marine structures, these technologies, if used in isolation, all reveal their inherent and insurmountable physical or technical limitations. Simply adding "guided wave" and "TFM" does not yield a feasible solution; instead, the conflicting physical principles reduce the effectiveness. Furthermore, this also leads to a disconnect between screening and quantitative analysis in current detection strategies. Existing commercial long-distance guided wave systems (LRUTs) mainly provide one-dimensional A-scan signals for preliminary defect detection and location screening, but they struggle to accurately characterize the size and shape of defects, i.e., quantitative analysis is impossible. Meanwhile, high-resolution TFM imaging technology is limited to small-scale, volume wave-based near-field detection. When LRUT discovers a suspected defect, it is often necessary to dispatch another set of high-precision testing equipment for secondary verification, which is a complicated and costly process.

[0005] Therefore, developing an integrated system that can break down the barriers between screening and quantitative analysis, and achieve both wide-area coverage and high-resolution imaging in a single test, has significant technical and economic value. Summary of the Invention

[0006] The problem this invention aims to solve is to provide an automated ultrasonic guided wave inspection system and method for large marine engineering structures. This system and method integrates automated scanning, multimodal guided wave excitation and reception, and a fully focused imaging algorithm specifically designed to compensate for dispersion effects. It enables efficient, high-resolution, and full-coverage non-destructive testing of large marine engineering structures, breaking the traditional separation between "large-scale screening" and "local precise quantification" in inspection technologies. The entire process from defect discovery to precise imaging is completed in a single automated operation, thereby fundamentally improving the reliability, efficiency, and economy of inspection.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an automated ultrasonic guided wave detection system for large marine engineering structures, comprising, An automated scanning platform is a modular robotic crawler for underwater robot deployment and retrieval. The platform integrates a high-strength permanent magnet wheel or a negative pressure adsorption module at its bottom. It adheres to the surface of a large marine engineering structure and moves precisely along a predetermined path. The platform incorporates a multi-axis encoder and an inertial measurement unit to acquire and record its precise position information on the surface of the structure under test in real time. This position information is acquired synchronously with ultrasonic data, providing a spatial reference for subsequent TFM imaging and ensuring the geometric accuracy of the imaging results. A phased array waveguide transducer is provided, comprising two coaxial and spaced ring arrays. Specific phase delay excitation is applied to the array elements of the two ring arrays. Each ring array is divided into multiple independent sectors along the circumference, and each sector contains several piezoelectric array elements. By precisely controlling the center frequency and bandwidth of the excitation signal, and combining specific array element combinations and delay rules, the phased array waveguide transducer selectively excites and receives specific waveguide modes. The data acquisition and control unit module includes a pulse generation and timing control unit, a full matrix data acquisition unit, a digitization and buffering unit, and a data communication unit. The pulse generation and timing control unit generates high-voltage, narrow-bandwidth excitation pulses for each transmitting element in the transducer array according to the instructions sent by the host computer, and controls the transmission timing with microsecond-level precision. The full matrix data acquisition unit receives and acquires echo signals from all receiving array elements in parallel and synchronously while each array element emits an ultrasonic pulse. The digitization and caching unit uses a high-speed analog-to-digital converter to digitize the received analog signal with high fidelity, and packages and stores the complete FMC data matrix and its corresponding scanning platform position information in the onboard high-speed cache. The data communication unit transmits the acquired data packets to the host computer in real time or in batches via a high-speed data interface for subsequent complex imaging processing.

[0008] Furthermore, the present invention also provides an automated ultrasonic guided wave detection method for large marine engineering structures, utilizing the aforementioned automated ultrasonic guided wave detection system for large marine engineering structures, comprising the following steps: S1: Planning and preparation before testing; S2: Deployment and surface adaptation of an automated ultrasonic guided wave detection system for large marine engineering structures; S3: Automated scanning and FMC data acquisition; S4: Data processing, dispersive physical model establishment and DC-TFM imaging; S5: Image stitching, visualization, and defect assessment.

[0009] Furthermore, S1 includes the following steps: S11: Based on the design data of the surface of the structure to be tested, simulation calculations are performed using the matching guided wave dispersion analysis software; S12: By analyzing the dispersion curves, displacement distributions, and sensitivity to defects of different guided wave modes on the surface of the structure under test, the optimal detection mode and its corresponding center frequency and bandwidth are selected. S13: Based on the CAD model or as-built drawings of the surface of the structure to be tested, plan the scanning path of the automated scanning platform, wherein the scanning path completely covers the target circumferential weld and the heat-affected zone on both sides.

[0010] Furthermore, S2 includes the following steps: S21: The ultrasonic guided wave automated detection system for large marine engineering structures is installed in the work tool basket of the automated scanning platform and deployed by the mother ship to the surface of the structure to be tested; S22: The automated scanning platform grasps the detection system and places it on the surface of the structure to be tested; S23: Activate the magnetic adsorption system of the automated scanning platform to firmly attach it to the surface of the structure to be tested; S24: The ultrasonic guided wave automated testing system for large marine engineering structures performs an adaptive calibration procedure. The pressure sensor built into the phased array guided wave transducer measures the contact pressure with the surface of the structure under test and fine-tunes the attitude to ensure that all array elements obtain the best acoustic coupling effect.

[0011] Furthermore, S3 includes the following steps: S31: The operator starts the automated scanning program at the water surface control console, and the automated scanning platform will start moving strictly according to the preset path; S32: At each discrete location point on the scanning path, the data acquisition and control unit module will trigger a complete FMC acquisition process; S33: The ultrasonic guided wave automated detection system for large marine engineering structures supports the function of resuming scanning after interruption. If the detection is interrupted for any reason, it will continue from the interruption point after the recovery, thus ensuring the integrity of the data.

[0012] Furthermore, in step S32, for a phased array transducer containing N independent array elements, there are N excitations. During the m-th excitation, array element m emits the signal, and all N array elements receive the signal synchronously, thereby obtaining a full matrix time-domain A-scan dataset. Its size is N×N. in: , represents the A-scan signal transmitted by the m-th array element and received by the n-th array element; m, n=1,…,N are the array element numbers (dimensionless); t is time (unit: s); The dimensions are consistent with the output of the receiving channel (commonly voltage V, or dimensionless after normalization).

[0013] Furthermore, S4 includes the following steps: S41: The massive amount of raw data frames collected are uploaded to the main control computer of the mother ship in real time or in batches via fiber optic umbilical cable. S42: The dedicated software on the main control computer calls the DC-TFM algorithm module to process each data frame and generate a high-resolution C-scan image corresponding to the scan position.

[0014] Furthermore, S42 includes the following steps: S421: Path calculation, for each target pixel in the ROI. and each transmit-receive pair in the FMC dataset The position of the sound wave from the transmitting element m is calculated. After pixels Arrive at the position of receiving array element n The total propagation distance is given by the following formula: ; S422: Frequency domain dispersion compensation, for each A-scan signal in the FMC dataset. The spectrum is obtained by converting it to the frequency domain using a fast Fourier transform. ; A frequency-dependent phase correction factor is applied to the spectrum. This correction factor aims to compensate for the phase distortion accumulated by the signal due to dispersion over the propagation distance. The mathematical expression for this correction factor is: in, The complex spectrum after dispersion compensation; The original complex spectrum is the time-domain A-scan signal transmitted by the m-th array element and received by the n-th array element. Obtained by Fast Fourier Transform; Angular frequency, in rad / s; The imaginary unit; Let be the wavenumber of the selected mode, and be the phase constant in rad / m, satisfying the following relationship: in, This is the phase velocity of the mode, in m / s; To be related to imaging pixels The relevant propagation path length, in meters (m), is preferably defined as the sum of the paths from the transmitting element to the pixel and from the pixel to the receiving element, as shown in the following formula: Index Term It is a dimensionless phase quantity, thus ensuring the autonomy of the dimensions of the correction factor; if the propagation model adopts The phase convention is then multiplied by Phase compensation can be achieved; if the opposite convention is used, the exponent sign will be adjusted accordingly. S423: Time-domain signal reconstruction, converting the phase-corrected spectrum... By converting back to the time domain using inverse fast Fourier transform, the reconstructed A-scan signal without dispersion distortion is obtained. S424: Coherent superposition imaging, all compensated signals Its energy has already been stored at a certain reference time. Alignment, pixels final intensity value The following is obtained by coherently superimposing the amplitudes of the compensated signals of all transmit-receive pairs at the reference time point: in, For pixels The imaging intensity; Let be the imaging plane coordinates, in meters; N be the number of array elements, dimensionless; m,n=1,…,N be the transmitter / receiver element numbers, dimensionless; let For the m-th transmit and n-th receive channels at pixel point The complex time-domain signal after propagation delay alignment has the same unit as the original A-scan signal, usually V, or dimensionless after normalization; For alignment with reference time, the unit is seconds; S425: By repeating the above steps for all pixels in the ROI, a complete high-resolution, fully focused C-scan image is generated.

[0015] Furthermore, the dispersion curve of the selected waveguide mode is obtained in the following way: For a Lamb wave propagating in a plate-like or tubular structure with a thickness of 2h, its dispersion characteristics are determined by the classical Rayleigh-Lamb frequency equation, which has two forms, corresponding to symmetric and antisymmetric modes, respectively: Symmetric modes: Anti-symmetric modes: Where h is half the material thickness in meters (m); k is the in-plane wavenumber along the propagation direction in 1 / m; ω is the angular frequency in rad / s; and p and q are the intermediate wavenumbers associated with longitudinal and transverse vibrations, respectively. , The units are all 1 / m; and These are the longitudinal and transverse wave velocities of the material, respectively, in m / s. For a given material and structural thickness, the dispersion curve k(ω) of a specific guided wave mode is obtained by numerically solving the above equations.

[0016] Furthermore, in S424, a waveform similarity factor is introduced to obtain the time-domain signal after all compensations. Then, the pairwise correlations of these pixels within a time window near the focal point are calculated, and the sum of the correlations is multiplied by the amplitude superposition result as a weighting factor to obtain the final pixel intensity.

[0017] The advantages and positive effects of this invention are: 1. This invention combines the long-distance propagation characteristics of guided wave technology with an automated scanning platform to achieve rapid and continuous scanning of large areas. A single deployment can inspect pipe sections tens of meters long or plate structures several square meters in size. Compared to traditional point-by-point manual inspection methods, its inspection efficiency is increased by orders of magnitude, greatly shortening the inspection cycle and reducing the time spent on expensive ship time and underwater operations, thereby significantly reducing the overall inspection cost. The inspection efficiency and coverage have achieved a revolutionary improvement.

[0018] 2. The core innovation of this invention—the DC-TFM algorithm—successfully introduces the powerful capabilities of full-focusing imaging into the field of guided wave detection for the first time. By compensating for dispersion effects through a precise physical model, this algorithm fundamentally overcomes the physical obstacles that cause imaging failures in traditional methods. The result is the generation of high-resolution, high signal-to-noise ratio C-scan images, capable not only of detecting defects but also of accurately and quantitatively characterizing their size, shape, and orientation. This represents a qualitative leap from "discovery" to "evaluation," something completely unmatched by traditional long-distance guided wave technology, achieving unprecedented high-resolution imaging in guided wave detection.

[0019] 3. The coherent superposition principle of the TFM algorithm, after dispersion compensation correction according to this invention, can effectively amplify the real defect echo that matches the theoretical propagation path, while suppressing randomly distributed background noise and incoherent structural reflection clutter, thereby fundamentally improving the signal-to-noise ratio. Further weighting with waveform similarity factors can further enhance the ability to identify weak defect signals and suppress false defects, making the detection results more reliable and trustworthy, and significantly improving signal quality and detection reliability.

[0020] 4. The system employs a flexible robotic crawler, combined with magnetic or vacuum adsorption technology, which can easily adapt to complex curved surfaces such as pipes, spherical storage tanks, and towers, without requiring special treatment of the surface being tested. Only a thin layer of coupling agent is needed between the transducer and the structure under test, or non-contact can be achieved under specific designs (such as EMAT), enabling the detection of in-service structures with coatings or minor deposits. This significantly reduces pre-test cleaning work and its high adaptability to complex geometries and in-service conditions makes it ideal for complex field conditions.

[0021] 5. Each image generated by this system carries a precise location code, thus establishing a permanent, high-fidelity "health snapshot" of the tested structure and creating a traceable and comparable digital inspection record. This digital inspection record not only provides a basis for current maintenance decisions, but more importantly, it provides quantifiable and comparable baseline data for future condition monitoring, serving as a crucial foundation for realizing data-driven structural integrity management and predictive maintenance strategies. Attached Figure Description

[0022] Figure 1 This is a system principle framework diagram of an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the overall process of an embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0025] The embodiments of the present invention will be further described below with reference to the accompanying drawings: like Figure 1 As shown, the ultrasonic guided wave automated detection system for large marine engineering structures includes an automated scanning platform, a phased array guided wave transducer, and a data acquisition and control unit module, with each module working together in coordination.

[0026] The Automated Scanning Platform, in this embodiment, employs a modular robotic crawler that can be deployed and retrieved by an underwater robot (ROV) as its mobile platform. This automated scanning platform possesses strong environmental adaptability; its bottom integrates high-strength permanent magnet wheels or negative pressure adsorption modules, enabling it to stably adhere to steel structure surfaces of varying curvatures (such as pipes, tank walls, and towers) and move precisely along a predetermined path. The platform incorporates a high-precision multi-axis encoder and an inertial measurement unit (IMU), capable of acquiring and recording the crawler's precise position information (i.e., three-dimensional coordinates) on the surface of the structure under test in real time. and attitude angle This location information is acquired synchronously with the ultrasound data, providing the necessary spatial reference for subsequent TFM imaging and ensuring the geometric accuracy of the imaging results.

[0027] The core sensing component of this invention is a phased array guided wave transducer module specifically optimized for guided wave detection. To optimize waveform control and signal quality, this embodiment proposes a segmented dual-ring piezoelectric transducer array.

[0028] Specifically, the dual-ring structure consists of two coaxial ring arrays spaced a certain distance apart. By applying specific phase delay excitation to the array elements of the two rings, unidirectional propagation control of the guided wave can be achieved. That is, the guided wave energy propagating in one direction along the pipe or plate can be enhanced while suppressing propagation in the opposite direction. This greatly simplifies the determination of the source of the echo signal, eliminates irrelevant reflection interference from the rear, and thus improves the signal-to-noise ratio and the clarity of interpretation.

[0029] Segmented design: Each ring array is divided into multiple independent sectors (e.g., 8 or 16 sectors) along the circumference, and each sector contains several piezoelectric elements. This design not only allows for uniform excitation and reception of guided waves across the entire circumference, but also enables circumferential focusing of the sound beam by applying phase control to different sectors, thereby allowing for more precise localization of the circumferential location and extent of defects.

[0030] Mode selection capability: By precisely controlling the center frequency and bandwidth of the excitation signal, and combining specific array element combinations and delay rules, this transducer module can selectively excite and receive specific guided wave modes. For example, at a lower frequency-thickness product, it can excite the almost dispersion-free torsional mode T(0,1) or SH0 mode for long-distance screening; or select the bending A0 mode or stretching S0 mode, which are sensitive to specific types of defects (such as surface cracks), for fine imaging.

[0031] The Data Acquisition and Control Unit (DAU) module is a high-performance, multi-channel (e.g., 64 or 128 channels) embedded data acquisition and control unit. This unit is the nerve center connecting sensing and processing, and its core function is to execute full matrix capture (FMC) data acquisition sequences at high speed.

[0032] Specifically, the data acquisition and control unit module includes a pulse generation and timing control unit, a full matrix data acquisition unit, a digitization and buffering unit, and a data communication unit, with the following specific responsibilities: Pulse generation and timing control: Based on the instructions sent by the host computer, a high-voltage, narrow-bandwidth excitation pulse is generated for each transmitting element in the transducer array, and the transmission timing is controlled with microsecond-level precision.

[0033] Full matrix data acquisition: While each array element emits an ultrasonic pulse, the echo signals (A-scan) on all receiving array elements (including itself) are received and acquired in parallel and synchronously.

[0034] Digitization and caching: The received analog signal is digitized with high fidelity using a high-speed analog-to-digital converter (ADC), and the complete FMC data matrix (an N×N set of A scan signals, where N is the total number of array elements) and its corresponding scan platform position information are packaged and stored in the onboard high-speed cache.

[0035] Data communication: The acquired data packets are transmitted to the host computer in real time or in batches via a high-speed data interface (such as fiber optic Ethernet) for subsequent complex imaging processing.

[0036] like Figure 2 As shown, the present invention also provides an automated ultrasonic guided wave detection method for large marine engineering structures, utilizing the aforementioned automated ultrasonic guided wave detection system for large marine engineering structures, comprising the following steps: S1: Pre-test planning and preparation. Specifically, S1 includes the following steps: S11: Based on the design data of the structure under test, simulation calculations are performed using the matching guided wave dispersion analysis software.

[0037] S12: By analyzing the dispersion curves, displacement distribution, and sensitivity to defects of different guided wave modes in the structure under test, the optimal detection mode and its corresponding center frequency and bandwidth are selected.

[0038] S13: Based on the CAD model or as-built drawings of the structure to be tested, plan the scanning path of the automated scanning platform, and ensure that the scanning path completely covers the target circumferential weld and the heat-affected zone on both sides.

[0039] S2: Deployment and surface adaptation of an automated ultrasonic guided wave inspection system for large marine engineering structures. Specifically, S2 includes the following steps: S21: The ultrasonic guided wave automated inspection system for large marine engineering structures is installed in the work tool basket of the automated scanning platform and deployed by the mother ship to the vicinity of the target pipe section on the seabed.

[0040] S22: An automated scanning platform captures and inspects the system and places it precisely on the surface of the pipe.

[0041] S23: Activate the magnetic adsorption system of the automated scanning platform to firmly attach it to the surface of the structure to be tested.

[0042] S24: An automated ultrasonic guided wave testing system for large marine engineering structures performs an adaptive calibration procedure. The pressure sensor built into the phased array guided wave transducer measures the contact pressure with the surface of the structure under test and fine-tunes the attitude to ensure that all array elements achieve the best acoustic coupling effect.

[0043] S3: Automated scanning and FMC data acquisition. Specifically, S3 includes the following steps: S31: The operator starts the automated scanning program at the surface control console, and the automated scanning platform will start moving strictly according to the preset path.

[0044] S32: At each discrete location point on the scan path, the aforementioned system hardware executes the FMC acquisition sequence. The data acquisition and control unit module triggers a complete FMC acquisition process. For a phased array transducer containing N independent elements, there are N excitations. During the m-th excitation, element m emits, and all N elements receive synchronously, thus obtaining the full matrix time-domain A-scan dataset. Its size is N×N. in , represents the A-scan signal transmitted by the m-th array element and received by the n-th array element. m, n=1,…,N are the array element numbers (dimensionless); t is the time (unit: s); The dimensions are consistent with the output of the receiving channel (commonly voltage V, or dimensionless after normalization).

[0045] This FMC dataset contains all the wavefield information of the measured area from various angles, and is the basis for subsequent imaging.

[0046] S33: The system supports the function of resuming scanning from the point of interruption. If the detection is interrupted for any reason, it can continue from the point of interruption after recovery, thus ensuring the integrity of the data.

[0047] S4: Data Processing and DC-TFM Imaging. S4 includes the following steps: S41: The massive amount of raw data frames collected are uploaded to the main control computer of the mother ship in real time or in batches via fiber optic umbilical cable.

[0048] S42: The dedicated software on the main control computer calls the DC-TFM algorithm module to process each data frame and generate a high-resolution C-scan image corresponding to the scan position.

[0049] Specifically, the DC-TFM imaging algorithm calculates any pixel point in the region of interest (ROI). final imaging amplitude This includes the following steps: S421: Path calculation, for each target pixel in the ROI. and each transmit-receive pair in the FMC dataset The position of the sound wave from the transmitting element m is calculated. After pixels Arrive at the position of receiving array element n The total propagation distance is given by the following formula: ; S422: Frequency domain dispersion compensation. The standard TFM algorithm uses a constant speed of sound, c, to calculate the time of flight. This is the root cause of its failure in waveguide applications. The method of this invention performs precise compensation in the frequency domain. For each A-scan signal in the FMC dataset... The spectrum is obtained by converting it to the frequency domain using a fast Fourier transform. ; A frequency-dependent phase correction factor is applied to the spectrum to compensate for the phase distortion that accumulates due to dispersion over the propagation distance. The mathematical expression for this correction factor is: in, The complex spectrum after dispersion compensation; The original complex spectrum is the time-domain A-scan signal transmitted by the m-th array element and received by the n-th array element. Obtained by Fast Fourier Transform; Angular frequency, in rad / s; The imaginary unit; Let be the wavenumber of the selected mode, and be the phase constant in rad / m, satisfying the following relationship: in, This represents the phase velocity of the mode, in m / s. To be related to imaging pixels The relevant propagation path length, in meters (m), is preferably defined as the sum of the paths from the transmitting element to the pixel and from the pixel to the receiving element. The index term It is a dimensionless phase quantity, thus ensuring the dimensionlessness of the correction factor. If the propagation model adopts... The phase convention is then multiplied by Phase compensation can be achieved; if the opposite convention is used, the exponent sign will be adjusted accordingly.

[0050] The physical meaning of this operation is to "retrograde" the phase of all frequency components back to the in-phase state they should have at the focal point, thereby "compressing" the wave packet that has been broadened in the time domain.

[0051] Specifically, the dispersion curve of the selected guided wave mode is obtained through the following dispersion physical model. To accurately compensate for dispersion, a mathematical-physical model describing the propagation behavior of guided waves must first be established. For a Lamb wave propagating in a plate or tubular structure with a thickness of 2h, its dispersion characteristics are determined by the classical Rayleigh-Lamb frequency equation. This equation exists in two forms, corresponding to symmetric and antisymmetric modes, respectively: Symmetric modes: Anti-symmetric modes: Where h is half the material thickness in meters (m); k is the in-plane wavenumber along the propagation direction in 1 / m; ω is the angular frequency in rad / s; and p and q are the intermediate wavenumbers associated with longitudinal and transverse vibrations, respectively. , The units are all 1 / m; and These represent the longitudinal and transverse wave speeds of the material, respectively, in m / s. For a given material and structural thickness, the transcendental equations are numerically solved to obtain the dispersion curve k(ω) for a specific guided wave mode. This curve is the key input for dispersion compensation, accurately describing the phase changes of different frequency components during propagation. Similar dispersion equations exist for solving SH waves.

[0052] S423: Time-domain signal reconstruction, converting the phase-corrected spectrum... By converting back to the time domain using Inverse Fast Fourier Transform (IFFT), the reconstructed A-scan signal without dispersion distortion is obtained.

[0053] S424: Coherent superposition imaging, all compensated signals Its energy has already been stored at a certain reference time. Alignment, pixels final intensity value The following is obtained by coherently superimposing the amplitudes of the compensated signals of all transmit-receive pairs at the reference time point: To further improve the signal-to-noise ratio and suppress artifacts in the image, a waveform similarity factor is introduced, which is applied to the time-domain signal after all compensations are obtained. Then, the pairwise correlations (such as the Pearson correlation coefficient) within the time window near the focal point are calculated, and the sum of the correlations is used as a weighting factor, which is multiplied by the amplitude superposition result to obtain the final pixel intensity. This method utilizes the prior knowledge that "signals reflected by real defects should have highly similar waveforms under different transmission and reception paths," which can effectively filter out random noise and clutter that do not conform to the theoretical model.

[0054] S425: By repeating the above steps for all pixels in the ROI, a complete high-resolution, fully focused C-scan image is generated.

[0055] S5: Image stitching, visualization and defect assessment. It precisely stitches together the local C-scan images generated at all scan locations according to their corresponding coordinate information, and finally forms a seamless, high-resolution two-dimensional or three-dimensional (if multi-layer scanning) defect image covering the entire detection area.

[0056] The following example, "Corrosion and crack detection of circumferential welds in a section of a subsea pipeline," will be used to illustrate the invention in detail: S1: Planning and preparation before testing.

[0057] Before performing the inspection task, simulation calculations are first performed using the matching guided wave dispersion analysis software based on the design data of the subsea pipeline to be inspected (such as material grade, nominal diameter, wall thickness, etc.). By analyzing the dispersion curves, displacement distribution, and sensitivity to defects of different guided wave modes in the pipeline structure, the optimal inspection mode (e.g., T(0,1) torsional wave sensitive to volumetric corrosion or S0 Lamb wave sensitive to surface cracks) and its corresponding center frequency and bandwidth are selected. Subsequently, based on the pipeline's CAD model or as-built drawings, the scanning path of the automated scanning platform is planned, which should completely cover the target circumferential weld and the heat-affected zones on both sides.

[0058] S2: System deployment and surface adaptation.

[0059] The integrated detection system (including a scanning platform, transducers, and data acquisition units) is installed in the ROV's work tool basket and deployed by the mother ship to the vicinity of the target pipe section on the seabed. The ROV's robotic arm grasps the detection system and precisely places it on the pipe surface. The platform's magnetic adsorption system is activated, firmly attaching it to the pipe wall. The system then performs an adaptive calibration procedure: the pressure sensors built into the transducer modules measure the contact pressure with the pipe wall and fine-tune the orientation to ensure optimal acoustic coupling for all elements, which is crucial for guaranteeing the quality of signal transmission and reception.

[0060] S3: Automated scanning and FMC data acquisition.

[0061] After confirming the system is functioning correctly, the operator initiates the automated scanning program from the surface control console. The scanning platform will move strictly according to a preset path, performing a linear scan along the pipe axis while simultaneously conducting a circumferential rotational scan at specific locations to achieve comprehensive coverage of the circumferential weld area. At each discrete point along the scanning path, the data acquisition and control unit triggers a complete FMC acquisition process: N array elements transmit sequentially, all array elements receive synchronously, and the acquired N×N A-scan signals, along with the precise coordinates of that point, are processed. The data is packaged into a single data frame. The system supports breakpoint resume scanning; if an interruption is detected, execution can resume from the point of interruption after recovery, ensuring data integrity.

[0062] S4: Data processing and DC-TFM imaging.

[0063] The massive amounts of raw data frames acquired are uploaded to the main control computer of the surface mother ship in real time or in batches via fiber optic umbilical cables. Dedicated software on the main control computer calls the core DC-TFM algorithm module of this invention to process each data frame. First, based on the waveguide mode k(ω) selected in the planning phase, the software performs frequency domain dispersion compensation and time domain reconstruction on the signal of each pixel and each transmit / receive path. Finally, it performs coherent superposition to generate a small high-resolution C-scan image corresponding to that scan position.

[0064] S5: Image stitching, visualization, and defect assessment.

[0065] The system precisely stitches together the local C-scan images generated from all scan locations based on their corresponding coordinate information, ultimately forming a seamless, high-resolution 2D or 3D (if multi-layer scanning) defect image covering the entire inspection area. This image visually displays the internal condition of the weld and surrounding area, with defects such as corrosion pits, cracks, and incomplete penetration clearly presented as high-brightness feature points or areas. Inspection engineers can use image analysis tools to accurately locate, measure, and assess the morphology of these high-brightness indicators, providing reliable data support for subsequent structural integrity evaluation and maintenance decisions. Upon user request, the system can output the processed image data to third-party visualization or analysis platforms without requiring specific imaging software.

[0066] The advantages and positive effects of this invention are: 1. This invention combines the long-distance propagation characteristics of guided wave technology with an automated scanning platform to achieve rapid and continuous scanning of large areas. A single deployment can inspect pipe sections tens of meters long or plate structures several square meters in size. Compared to traditional point-by-point manual inspection methods, its inspection efficiency is increased by orders of magnitude, greatly shortening the inspection cycle and reducing the time spent on expensive ship time and underwater operations, thereby significantly reducing the overall inspection cost. The inspection efficiency and coverage have achieved a revolutionary improvement.

[0067] 2. The core innovation of this invention—the DC-TFM algorithm—successfully introduces the powerful capabilities of full-focusing imaging into the field of guided wave detection for the first time. By compensating for dispersion effects through a precise physical model, this algorithm fundamentally overcomes the physical obstacles that cause imaging failures in traditional methods. The result is the generation of high-resolution, high signal-to-noise ratio C-scan images, capable not only of detecting defects but also of accurately and quantitatively characterizing their size, shape, and orientation. This represents a qualitative leap from "discovery" to "evaluation," something completely unmatched by traditional long-distance guided wave technology, achieving unprecedented high-resolution imaging in guided wave detection.

[0068] 3. The coherent superposition principle of the TFM algorithm, after dispersion compensation correction according to this invention, can effectively amplify the real defect echo that matches the theoretical propagation path, while suppressing randomly distributed background noise and incoherent structural reflection clutter, thereby fundamentally improving the signal-to-noise ratio. Further weighting with waveform similarity factors can further enhance the ability to identify weak defect signals and suppress false defects, making the detection results more reliable and trustworthy, and significantly improving signal quality and detection reliability.

[0069] 4. The system employs a flexible robotic crawler, combined with magnetic or vacuum adsorption technology, which can easily adapt to complex curved surfaces such as pipes, spherical storage tanks, and towers, without requiring special treatment of the surface being tested. Only a thin layer of coupling agent is needed between the transducer and the structure under test, or non-contact can be achieved under specific designs (such as EMAT), enabling the detection of in-service structures with coatings or minor deposits. This significantly reduces pre-test cleaning work and its high adaptability to complex geometries and in-service conditions makes it ideal for complex field conditions.

[0070] 5. Each image generated by this system carries a precise location code, thus establishing a permanent, high-fidelity "health snapshot" of the tested structure and creating a traceable and comparable digital inspection record. This digital inspection record not only provides a basis for current maintenance decisions, but more importantly, it provides quantifiable and comparable baseline data for future condition monitoring, serving as a crucial foundation for realizing data-driven structural integrity management and predictive maintenance strategies.

[0071] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. An automated ultrasonic guided wave testing system for large marine engineering structures, characterized in that: include, An automated scanning platform is a modular robotic crawler for underwater robot deployment and retrieval. The platform integrates a high-strength permanent magnet wheel or a negative pressure adsorption module at its bottom. It adheres to the surface of a large marine engineering structure and moves precisely along a predetermined path. The platform incorporates a multi-axis encoder and an inertial measurement unit to acquire and record its precise position information on the surface of the structure under test in real time. This position information is acquired synchronously with ultrasonic data, providing a spatial reference for subsequent TFM imaging and ensuring the geometric accuracy of the imaging results. A phased array waveguide transducer is provided, comprising two coaxial and spaced ring arrays. Specific phase delay excitation is applied to the array elements of the two ring arrays. Each ring array is divided into multiple independent sectors along the circumference, and each sector contains several piezoelectric array elements. By precisely controlling the center frequency and bandwidth of the excitation signal, and combining specific array element combinations and delay rules, the phased array waveguide transducer selectively excites and receives specific waveguide modes. The data acquisition and control unit module includes a pulse generation and timing control unit, a full matrix data acquisition unit, a digitization and buffering unit, and a data communication unit. The pulse generation and timing control unit generates high-voltage, narrow-bandwidth excitation pulses for each transmitting element in the transducer array according to the instructions sent by the host computer, and controls the transmission timing with microsecond-level precision. The full matrix data acquisition unit receives and acquires echo signals from all receiving array elements in parallel and synchronously while each array element emits an ultrasonic pulse. The digitization and caching unit uses a high-speed analog-to-digital converter to digitize the received analog signal with high fidelity, and packages and stores the complete FMC data matrix and its corresponding scanning platform position information in the onboard high-speed cache. The data communication unit transmits the acquired data packets to the host computer in real time or in batches via a high-speed data interface for subsequent complex imaging processing.

2. An automated ultrasonic guided wave detection method for large marine engineering structures, characterized in that: Using the automated ultrasonic guided wave detection system for large marine engineering structures as described in claim 1, Includes the following steps, S1: Planning and preparation before testing; S2: Deployment and surface adaptation of an automated ultrasonic guided wave detection system for large marine engineering structures; S3: Automated scanning and FMC data acquisition; S4: Data processing, dispersive physical model establishment and DC-TFM imaging; S5: Image stitching, visualization, and defect assessment.

3. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 2, characterized in that: S1 includes the following steps: S11: Based on the design data of the surface of the structure to be tested, simulation calculations are performed using the matching guided wave dispersion analysis software; S12: By analyzing the dispersion curves, displacement distributions, and sensitivity to defects of different guided wave modes on the surface of the structure under test, the optimal detection mode and its corresponding center frequency and bandwidth are selected. S13: Based on the CAD model or as-built drawings of the surface of the structure to be tested, plan the scanning path of the automated scanning platform, wherein the scanning path completely covers the target circumferential weld and the heat-affected zone on both sides.

4. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 3, characterized in that: S2 includes the following steps: S21: The ultrasonic guided wave automated detection system for large marine engineering structures is installed in the work tool basket of the automated scanning platform and deployed by the mother ship to the surface of the structure to be tested; S22: The automated scanning platform grasps the detection system and places it on the surface of the structure to be tested; S23: Activate the magnetic adsorption system of the automated scanning platform to firmly attach it to the surface of the structure to be tested; S24: The ultrasonic guided wave automated testing system for large marine engineering structures performs an adaptive calibration procedure. The pressure sensor built into the phased array guided wave transducer measures the contact pressure with the surface of the structure under test and fine-tunes the attitude to ensure that all array elements obtain the best acoustic coupling effect.

5. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 3 or 4, characterized in that: S3 includes the following steps: S31: The operator starts the automated scanning program at the water surface control console, and the automated scanning platform will start moving strictly according to the preset path; S32: At each discrete location point on the scanning path, the data acquisition and control unit module will trigger a complete FMC acquisition process; S33: The ultrasonic guided wave automated detection system for large marine engineering structures supports the function of resuming scanning from the point of interruption. If the detection is interrupted for any reason, it will continue to be executed from the point of interruption after the detection is resumed, thus ensuring the integrity of the data.

6. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 5, characterized in that: In step S32, for a phased array transducer containing N independent array elements, there are N excitations. During the m-th excitation, array element m emits the signal, and all N array elements receive the signal synchronously, thereby obtaining a full matrix time-domain A-scan dataset. Its size is N×N. in, , represents the A-scan signal transmitted by the m-th array element and received by the n-th array element; m, n=1,…,N are the array element numbers (dimensionless); t is the time (unit: s); The dimensions are consistent with the output of the receiving channel (commonly voltage V, or dimensionless after normalization).

7. The automated ultrasonic guided wave detection method for large marine engineering structures according to any one of claims 2 to 4, characterized in that: S4 includes the following steps: S41: The massive amount of raw data frames collected are uploaded to the main control computer of the mother ship in real time or in batches via fiber optic umbilical cable. S42: The dedicated software on the main control computer calls the DC-TFM algorithm module to process each data frame and generate a high-resolution C-scan image corresponding to the scan position.

8. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 7, characterized in that: S42 includes the following steps: S421: Path calculation, for each target pixel in the ROI. and each transmit-receive pair in the FMC dataset The position of the sound wave from the transmitting element m is calculated. After pixels Arrive at the position of receiving array element n The total propagation distance is given by the following formula: ; S422: Frequency domain dispersion compensation, for each A-scan signal in the FMC dataset. The spectrum is obtained by converting it to the frequency domain using a fast Fourier transform. ; A frequency-dependent phase correction factor is applied to the spectrum. This correction factor aims to compensate for the phase distortion accumulated by the signal due to dispersion over the propagation distance. The mathematical expression for this correction factor is: in, The complex spectrum after dispersion compensation; The original complex spectrum is the time-domain A-scan signal transmitted by the m-th array element and received by the n-th array element. Obtained by Fast Fourier Transform; Angular frequency, in rad / s; The imaginary unit; Let be the wavenumber of the selected mode, and be the phase constant in rad / m, satisfying the following relationship: in, This is the phase velocity of the mode, in m / s; To be related to imaging pixels The relevant propagation path length, in meters (m), is preferably defined as the sum of the paths from the transmitting element to the pixel and from the pixel to the receiving element, as shown in the following formula: Index Term It is a dimensionless phase quantity, thus ensuring the autonomy of the dimensions of the correction factor; if the propagation model adopts The phase convention is then multiplied by Phase compensation can be achieved; if the opposite convention is used, the exponent sign will be adjusted accordingly. S423: Time-domain signal reconstruction, converting the phase-corrected spectrum... By converting back to the time domain using inverse fast Fourier transform, the reconstructed A-scan signal without dispersion distortion is obtained. S424: Coherent superposition imaging, all compensated signals Its energy has already been stored at a certain reference time. Alignment, pixels final intensity value The following is obtained by coherently superimposing the amplitudes of the compensated signals of all transmit-receive pairs at the reference time point: in, For pixels The imaging intensity; Let be the imaging plane coordinates, in meters; N be the number of array elements, dimensionless; m,n=1,…,N be the transmitter / receiver element numbers, dimensionless; let For the m-th transmit and n-th receive channels at pixel point The complex time-domain signal after propagation delay alignment has the same unit as the original A-scan signal, usually V, or dimensionless after normalization; For alignment with reference time, the unit is seconds; S425: By repeating the above steps for all pixels in the ROI, a complete high-resolution, fully focused C-scan image is generated.

9. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 8, characterized in that: The dispersion curve of the selected waveguide mode is obtained in the following way. For a Lamb wave propagating in a plate-like or tubular structure with a thickness of 2h, its dispersion characteristics are determined by the classical Rayleigh-Lamb frequency equation, which has two forms, corresponding to symmetric and antisymmetric modes, respectively: Symmetric modes: Anti-symmetric modes: Where h is half the material thickness in meters (m); k is the in-plane wavenumber along the propagation direction in 1 / m; ω is the angular frequency in rad / s; and p and q are the intermediate wavenumbers associated with longitudinal and transverse vibrations, respectively. , The units are all 1 / m; and These are the longitudinal and transverse wave velocities of the material, respectively, in m / s. For a given material and structural thickness, the dispersion curve k(ω) of a specific guided wave mode is obtained by numerically solving the above equations.

10. The automated ultrasonic guided wave detection method for large marine engineering structures according to claim 8, characterized in that: In step S424, a waveform similarity factor is introduced to obtain the time-domain signal after all compensations. Then, the pairwise correlations of these pixels within a time window near the focal point are calculated, and the sum of the correlations is multiplied by the amplitude superposition result as a weighting factor to obtain the final pixel intensity.

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