Method and system for increasing efficiency of laying subsea pipelines

Abstract

This invention discloses a method and system for improving the efficiency of subsea pipeline laying, belonging to the field of marine oil and gas engineering technology. Addressing the problems in existing technologies such as large misalignment due to geometric deviations at the pipe ends, low efficiency from repeated trial alignments, and forced abandonment of pipe sections with excessive ellipticity leading to material waste and project delays, this invention performs three-dimensional digital scanning and modeling of all pipe ends in the storage yard, assigning each a unique number. Based on Fourier series decomposition, it extracts the geometric feature vectors of the pipe ends, selecting pipe sections with an ellipticity ≤1% as arbitrarily matched sections. For sections that do not meet the requirements, on-site hydraulic correction is performed to achieve an ellipticity ≤1%, and the model is replaced. Assembly orientation markings are made according to the number and geometric model, controlling the misalignment error within 2mm, and welding is performed according to the markings. This invention is mainly used to improve the efficiency of continuous pipe laying operations on subsea pipeline laying vessels.

Description

Technical Field

[0001] This invention relates to the field of marine oil and gas engineering technology. More specifically, this invention relates to a method and system for improving the efficiency of subsea pipeline laying. Background Technology

[0002] In subsea oil and gas pipeline laying projects, pipelaying vessels typically employ a multi-station continuous assembly line operation mode. The pipelaying process generally includes multiple steps such as pipe beveling, demagnetization and preheating, butt welding and root welding, filler welding, capping welding, non-destructive testing, rework, sandblasting and rust removal, weld joint corrosion protection, and joint filling. These steps are arranged at different workstations on the pipelaying vessel and implemented continuously. Due to the strict sequence and cycle time constraints between these steps, the overall operation exhibits highly coupled assembly line characteristics. A decrease in efficiency of any critical step can significantly reduce the overall efficiency of the pipelaying operation. In continuous pipelaying operations, pipe alignment, welding, and non-destructive testing constitute the critical path affecting pipelaying efficiency. The geometric quality of the pipe ends (especially ellipticity), misalignment, and welding rework rate during the pipe alignment stage are the core factors determining whether the pipelaying assembly line can operate efficiently and continuously.

[0003] In existing technologies, the geometric parameters of pipe ends are typically obtained through manual caliper measurements or simple gauges, measuring only the diameter in a few directions such as vertical and horizontal, and roughly estimating the ellipticity. This measurement method involves very few sampling points (usually only 4-8 points), making it impossible to accurately describe the true contour of the pipe end cross-section, especially making it difficult to detect local circumferential deformation. Due to the lack of detailed pipe end geometric data, the pairing of pipe sections in the stockpile relies entirely on the experience of on-site workers, completed through repeated trial alignments and rotation adjustments. When the ellipticity of the pipe end is large or there is local deformation, workers often need to remove the pipe and re-align it multiple times, with a single alignment time reaching 5-15 minutes, and the final misalignment often exceeds 5mm, seriously affecting the welding quality. More importantly, in existing technologies, pipe sections with ellipticity exceeding the standard (generally considered to be greater than 1%) are generally discarded or replaced directly, resulting in a large amount of pipe material waste and project delays. However, in offshore pipelaying operations, the number of spare pipe sections is limited, and discarding pipes often forces the pipelaying operation to be interrupted, further exacerbating the efficiency loss.

[0004] Regarding welding quality assessment, current pipe-laying projects generally adopt fixed non-destructive testing and acceptance standards (such as API 1104), requiring rework for all detected welding defects regardless of their actual severity. This approach leads to a large number of defects that would be acceptable under Engineering Critical Assessment (ECA) being included in the rework process, with each rework taking 45–90 minutes, severely disrupting the pipeline's workflow. Especially in deep-water or high-grade steel pipelines (such as acid-resistant X65 pipelines), overly stringent acceptance standards result in a persistently high rework rate, often exceeding 5%, becoming one of the main causes of low pipe-laying efficiency. Meanwhile, traditional buckling monitoring methods use built-in buckling detectors connected to the welding end-alignment device via steel wire ropes, moving forward with the device after each weld section is completed. In this method, the steel wire rope needs to pass through the welding operation area, which is extremely easy to be damaged or even break in the high temperature environment. Once it breaks, the buckling detector will be stuck inside the pipe and must be retrieved through high-risk operations such as pipe removal and pipe cutting. This not only causes the operation to be interrupted for several hours or even several days, but also brings serious safety hazards.

[0005] In summary, existing subsea pipeline laying technologies suffer from the following prominent defects: First, outdated methods for pipe end geometry measurement, lacking high-precision 3D digital scanning and database management, prevent optimal pipe segment matching, leading to significant misalignment and repeated trial alignments, forming the first bottleneck in pipeline laying efficiency. Second, pipe segments exceeding ellipticity standards lack effective on-site correction methods, necessitating abandonment or rejection, resulting in material waste and project delays. Third, overly conservative welding defect judgment standards and the failure to integrate Engineering Critical Assessment (ECA) into the production line decision-making process lead to numerous unnecessary reworks and uncontrolled rework rates. When inefficient conditions occur, existing technologies typically employ temporary measures such as increasing manpower, extending working hours, adding welding stations, or increasing welding current and voltage, but these are insufficient to fundamentally restore the pipeline laying cycle time and may even introduce new efficiency losses due to a lack of coordination between processes. Therefore, a new method is urgently needed to systematically address these defects and fundamentally improve pipeline laying efficiency. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0007] Another objective of this invention is to provide a method for improving the efficiency of subsea pipeline laying. This method controls the misalignment within 2mm through three-dimensional scanning and intelligent matching, and combines ellipticity screening and on-site correction to significantly shorten the alignment time, reduce the rework rate, and effectively improve pipeline laying efficiency.

[0008] To achieve these objectives and other advantages according to the present invention, a method for improving the efficiency of subsea pipeline laying is provided, comprising: S1. Perform three-dimensional digital scanning and modeling of all pipe sections and pipe ends in the stockyard and assign them unique numbers. Each unique number corresponds to the A-end and B-end cross-sectional geometric models of a pipe section. Based on the pipe end cross-sectional geometric models, Fourier series decomposition is used to extract the pipe end geometric feature vectors. All pipe sections that can be arbitrarily paired are selected. The pipe sections that can be arbitrarily paired are all pipe sections whose A-end and B-end ellipticity is ≤1%. S2. For pipe sections that cannot meet the requirements of arbitrary pairing, a hydraulic device is used to correct the geometry of the pipe ends on site so that the ellipticity is ≤1%. Then, a three-dimensional digital scanning model is re-modeled and the original pipe end cross-sectional geometry model is replaced. S3. For adjacent pipe sections, mark the assembly orientation according to their unique number and the geometric model of the pipe end section, so that the maximum misalignment error of the adjacent pipe sections at the joint position is within 2mm; during the pipeline laying process, assemble according to the marked assembly orientation to match the pipe end section profile of the two pipe sections, and then perform welding to complete the pipe section connection.

[0009] Preferably, the method for improving the efficiency of submarine pipeline laying further includes step S4: after the welding process is completed, the pipe section is subjected to non-destructive testing, the detected welding defects are assessed for engineering criticality, and the engineering acceptability of the defects is determined based on the pipeline design parameters, material properties and service conditions. Only defects that exceed the safety tolerance are repaired.

[0010] Preferably, during the pipeline laying operation in step S3, an underwater remotely operated vehicle (ROV) is used to perform real-time and continuous external buckling morphology detection on the pipeline contact points. The ROV is equipped with high-resolution optical imaging equipment, multi-beam sonar, and a laser 3D scanner. It moves synchronously with the pipeline laying process, observes the appearance of the pipeline contact section with the ground in real time through the optical imaging system, obtains the overall alignment of the pipeline seabed section through the multi-beam sonar, and accurately measures the curvature change of the pipeline cross-section through the laser 3D scanner. When the pipeline bending radius is detected to be less than the design allowable value, the ROV immediately sends an alarm signal to the control room of the pipelaying vessel. The control room adjusts the pipelaying speed, tensioner tension, or support frame angle parameters of the pipelaying vessel according to the alarm information to avoid pipeline buckling damage.

[0011] Preferably, the specific implementation method of 3D digital scanning modeling in steps S1 and S2 is as follows: Using the location of the longitudinal weld seam of the pipe segment as the 0° reference point in the circumference, a 3D laser scanner or structured light scanning device is used to obtain radial dimension data and wall thickness data at each sampling interval of 0.5°~4° along the circumferential direction of the pipe end, and construct a geometric model of the pipe end section containing the pipe end profile. The geometric model of the pipe end section is decomposed into Fourier series to extract the first N harmonic components and their phase angles distributed along the circumferential direction of the radial deviation. N≥3. The amplitude and phase angle of each harmonic component are combined to form the geometric feature vector of the pipe end, which serves as the basis for pipe segment geometric pairing and assembly orientation marking.

[0012] Preferably, after the pipe segment is scanned, the obtained pipe end cross-sectional geometric model data is associated with the unique number of the pipe segment and stored in the database. The unique number of the pipe segment is affixed to the outer wall of the pipe segment in the form of a barcode, QR code or RFID tag.

[0013] Preferably, the specific implementation method of using a hydraulic device to perform on-site correction of the pipe end geometry in step S2 is as follows: The hydraulic device is an internally supported hydraulic jack, and its jack rod end is provided with an arc-shaped support shoe that fits against the inner wall of the pipe; the internally supported hydraulic jack is placed inside the pipe end of the pipe section to be corrected. Retrieve the geometric feature vector of the pipe end from the database, calculate the contribution rate of each harmonic amplitude to the total radial deviation, and identify all harmonic orders whose contribution rate exceeds the preset threshold and their corresponding maximum deviation circumferential azimuth angle. The internally supported hydraulic jack applies radial pressure sequentially or in combination according to the identified harmonic order and azimuth angle until the ellipticity is ≤1% and the amplitude of each higher harmonic is reduced to below the acceptable threshold. During the correction process, a laser rangefinder sensor is used to monitor the radial dimension change of the tube end in real time. When the real-time ellipticity measurement value is ≤1%, pressurization is stopped and the pressure is maintained for 30~60s before unloading. Repeat the scan verification. If the ellipticity is still >1%, correct it again until the requirements are met.

[0014] Preferably, the specific implementation method for marking the assembly orientation according to its number and the geometric model of the pipe end section in step S3 is as follows: Using the B end of the preceding pipe segment and the A end of the following pipe segment as the pairing objects, the geometric feature vectors of the two ends are extracted respectively, and the amplitude and phase angle of the first N harmonic components of the two ends are used as matching parameters. Using the geometric feature vector of end A of the next pipe segment as the rotation object, rotate it successively along the circumference with a step size of 0.5°~4° to simulate circumferential rotation. Calculate the composite radial deviation distribution between the two end profiles at each rotation angle to obtain the estimated curve of the misalignment at that rotation angle. The maximum misalignment is extracted from the synthetic radial deviation distribution. All rotation angle ranges with a maximum misalignment estimate ≤ 2mm are selected. Among all rotation angle ranges, the optimal rotation angle is selected with the minimum maximum misalignment estimate, the included angle between the longitudinal welds of the two pipe sections in the circumferential direction being 90~180° and the relative spacing between the longitudinal welds in the circumferential direction being not less than 100mm as the optimization objective. An optimal rotation angle is selected through a multi-objective optimization algorithm. Based on the selected optimal rotation angle, mark the circumferential assembly start line on the outer surface of the B end of the preceding pipe section and the outer surface of the A end of the following pipe section, respectively. Mark the rotation direction arrow relative to the B end of the preceding pipe section and the assembly sequence number on the outer surface of the A end of the following pipe section; so that the parts can be directly aligned and assembled on site according to the markings.

[0015] Preferably, the method for improving the efficiency of subsea pipeline laying can be started independently before the start of the laying operation, during the laying operation, and after the laying efficiency decreases.

[0016] This invention further claims a subsea pipeline laying system, comprising: The pipe end three-dimensional digital scanning subsystem is set up in the stockyard and is used to perform three-dimensional digital scanning and modeling of the pipe end to obtain the geometric model of the pipe end cross section. The pipe end database, connected to the pipe end three-dimensional digital scanning subsystem, is used to store the unique number of the pipe segment and its corresponding pipe end cross-sectional geometric model data. The unique number of the pipe segment is affixed to the outer wall of the pipe segment in the form of a barcode, QR code or RFID tag. An ellipticity filtering module, connected to the pipe end database, is used to filter out all pipe segments with an ellipticity ≤1% as pipe segments that can be arbitrarily paired. The on-site straightening device includes an internally supported hydraulic jack, each of which has an arc-shaped support shoe at the end of its jack rod that fits against the inner wall of the pipe. It is used to straighten pipe sections with an ellipticity >1% on-site, so that the ellipticity is ≤1%. The assembly orientation marking module is connected to the pipe end database and is used to calculate the optimal assembly rotation angle based on the pipe end cross-sectional geometric model of adjacent pipe sections, and generate assembly orientation marking information, which includes circumferential assembly start line, rotation direction arrow and assembly sequence number. The welding execution module is set on the pipelaying vessel's work line and is used to assemble and weld adjacent pipe sections according to the assembly orientation marking information. The engineering critical assessment module, connected to the welding execution module, is used to perform engineering critical assessment on welding defects, determine the engineering acceptability of defects, and only output rework instructions for defects that exceed the safety tolerance. The ROV buckling monitoring subsystem includes an underwater remotely operated vehicle and its control station. The underwater remotely operated vehicle is equipped with high-resolution optical camera equipment, multi-beam sonar and laser 3D scanner, which are used to perform real-time and continuous external buckling morphology detection of the mud contact point of the pipeline during pipe laying operations. When the pipe bending radius is detected to be less than the design allowable value, an alarm signal is sent to the control room of the pipe-laying vessel. The central controller is connected to the pipe end three-dimensional digital scanning subsystem, pipe end database, ellipticity screening module, on-site correction device, assembly orientation marking module, welding execution module, engineering critical assessment module and ROV buckling monitoring subsystem, respectively, to coordinate the operation of each module and realize full-process digital closed-loop control from pipe end scanning to butt welding.

[0017] The present invention has at least the following beneficial effects: Firstly, this invention performs three-dimensional digital scanning and modeling of all pipe sections in the stockpile, and selects pipe sections with ellipticity of ≤1% at both ends as arbitrarily matched pipe sections, controlling the misalignment error of adjacent pipe sections within 2mm. This fundamentally solves the technical problem of low matching efficiency and repeated trial matching caused by geometric deviation of pipe ends, and significantly shortens the matching time. Secondly, this invention introduces Fourier series decomposition to extract the geometric feature vector of the pipe end, and uses the minimum misalignment, longitudinal weld angle of 90~180° and spacing ≥100mm as the multi-objective optimization function to determine the optimal rotation angle, so that the pairing accuracy and the safety of the welded structure can reach the optimal synergy, overcoming the limitations of traditional single-objective pairing. Thirdly, this invention scientifically determines the acceptability of welding defects through engineering critical assessment, and only repairs defects that exceed the safety tolerance, greatly reducing the invalid repair rate; at the same time, it uses ROV equipped with optical, sonar and laser equipment to monitor the buckling morphology of mud points in real time and trigger alarms, avoiding the risk of rope breakage and pipe cutting by built-in detectors, and ensuring continuous operation of the pipe laying production line. Fourth, this invention realizes automatic calculation and closed-loop control of correction parameters based on database and geometric feature vectors, so that pipe sections with excessive ellipticity can be repaired and reused on site, avoiding waste of discarded pipes; moreover, this method can be started independently at each stage of pipe laying operation, and the central controller coordinates the whole process digital closed loop, which significantly improves pipe laying efficiency and reduces project costs.

[0018] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a three-dimensional digital scan of the pipe end in one of the technical solutions of the present invention; Figure 2This is a schematic diagram of the layout of the pipelaying vessel's workstation in another technical solution of the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0021] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0022] like Figure 1 As shown, the present invention provides a method for improving the efficiency of subsea pipeline laying, comprising: S1. Perform three-dimensional digital scanning and modeling of all pipe sections and pipe ends in the stockyard and assign them unique numbers. Each unique number corresponds to the A-end and B-end cross-sectional geometric models of a pipe section. Based on the pipe end cross-sectional geometric models, Fourier series decomposition is used to extract the pipe end geometric feature vectors. All pipe sections that can be arbitrarily paired are selected. The pipe sections that can be arbitrarily paired are all pipe sections whose A-end and B-end ellipticity is ≤1%. S2. For pipe sections that cannot meet the requirements of arbitrary pairing, a hydraulic device is used to correct the geometry of the pipe ends on site so that the ellipticity is ≤1%. Then, a three-dimensional digital scanning model is re-modeled and the original pipe end cross-sectional geometry model is replaced. S3. For adjacent pipe sections, mark the assembly orientation according to their unique number and the geometric model of the pipe end section, so that the maximum misalignment error of the adjacent pipe sections at the joint position is within 2mm; during the pipeline laying process, assemble according to the marked assembly orientation to match the pipe end section profile of the two pipe sections, and then perform welding to complete the pipe section connection.

[0023] The aforementioned technical solution addresses the problems in existing pipe-laying technologies, such as large misalignments at the joints due to geometric deviations at the pipe ends, low efficiency from repeated trial alignments, and material waste and project delays caused by the forced abandonment of pipe sections with excessive ellipticity. Its specific implementation includes 3D digital scanning and arbitrary pairing screening of pipe sections in the stockpile, on-site hydraulic correction and model updating of unqualified pipe sections, and assembly orientation marking and butt welding based on numbering and geometric models. After the pipe sections enter the pipe-laying vessel's stockpile, a 3D laser scanner (such as a line laser profile sensor or a phase-type structured light scanner) is used to perform a full circumferential scan of the A and B ends of each pipe section. During scanning, the longitudinal weld seam of the pipe section is used as the circumferential reference zero point, and sampling intervals of 1° are used along the circumference. The sampling interval can also be set to 0.5° or 2°, depending on the balance between required accuracy and scanning speed, to acquire radial distance data at each angle. The scanning time for a single pipe end is controlled within 30 seconds. After filtering and denoising the collected discrete radius data points, a 3D geometric model of the pipe end section is constructed. Based on this model, the ellipticity is automatically calculated. The ellipticity is the percentage of the difference between the maximum and minimum outer diameters on the same cross-section divided by the nominal outer diameter. "Arbitrary pairing" means that for pipe segments with ellipticity at both ends not exceeding 1%, regardless of which end of the pipe segment it connects to (A end), the misalignment automatically meets the requirement of ≤2mm after subsequent assembly according to the markings, eliminating the need for on-site trial alignment. This eliminates pipe segments with substandard geometric quality at the source, solving the efficiency bottleneck of blindly installing and repeatedly removing pipes due to unknown ellipticity at the pipe ends in traditional methods. After scanning, the system assigns a unique number to each pipe segment and stores the geometric model data of both ends (A and B) in a local database along with this number.

[0024] like Figure 1 In the above technical solution, the location of the longitudinal weld of the pipe section is taken as the 0° circumferential reference point, and the circumferential angle of the pipe end is denoted as θ (value from 0 to 360°). Using a 3D laser scanner or structured light scanning device, radial dimension data of M = 360° / Δθ sampling points are acquired along the circumference at equal angular intervals Δθ (0.5° ≤ Δθ ≤ 4°). Let the nominal radius be R0 (constant), and the measured radius corresponding to the i-th sampling point be r(θ). i If θ is the radial deviation, then the radial deviation is: δ(θ) i )=r(θ i -R0; Expand the radial deviation function δ(θ) into a Fourier series (period 360°): Where a0 is the average radial deviation (0th order component, reflecting overall dimensional offset), and a0 is 0 for pipe sections with high manufacturing precision; k is the harmonic order (k=1 indicates eccentricity, k=2 indicates ellipticity, k≥3 indicates higher order deformation); a k b k Here, represents the Fourier coefficients, obtained through least-squares fitting of sampling points; N is the truncation order; ε(θ) is the residual (measurement noise). The amplitude of the k-th harmonic is... The phase angle is ;φ k This represents the circumferential angle at which the maximum radial deviation of this harmonic occurs (with the longitudinal weld seam as 0° reference). Therefore, the geometric eigenvector of the pipe end is: The pipe end geometric feature vector comprehensively describes the circumferential distribution of the pipe end radial deviation, including both ellipticity and higher-order deformation components, and is used for subsequent pipe segment pairing and assembly orientation marking.

[0025] For pipe segments with an ellipticity >1%, i.e., those not meeting the requirements for arbitrary pairing, on-site correction is performed. Specifically, operators insert an internally supporting hydraulic jack into the end of the pipe segment to be corrected. The hydraulic device's jack rod is equipped with an arc-shaped support shoe to increase the contact area with the inner wall of the pipe and prevent localized indentations. After correction, the pipe end is re-modeled using S1 three-dimensional digital scanning, replacing the original non-compliant data with new geometric model data, and updating the records in the database. This correction-re-replacement closed loop allows pipe segments that might otherwise be discarded to be reintegrated into the pipe-laying sequence, solving the material waste and project delays caused by the traditional method of returning or abandoning pipe segments with excessive ellipticity.

[0026] When pipe segments enter the pipelaying vessel production line from the stockpile, the system retrieves the geometric models of the pipe end sections (end B of the preceding segment and end A of the following segment) from the database based on the unique numbers of the two adjacent segments. It then calculates the relative rotation angle that minimizes the misalignment between the two ends. After determining the optimal angle, the system generates assembly orientation marking instructions: circumferential starting lines are marked on the outer surfaces of end B of the preceding segment and end A of the following segment, and a rotation direction arrow (e.g., clockwise or counterclockwise) is marked on the outer surface of the following segment. On-site workers only need to align the markings and rotate the following segment in the direction of the arrow until the markings coincide to complete the precise alignment. The entire process requires no repeated trial and error. After alignment, root welding, filler welding, and capping welding are immediately performed to complete the pipe segment connection. Through the pre-marking-direct alignment mode, the single alignment time is reduced from 5-15 minutes using traditional methods to 1-2 minutes, while the misalignment is strictly controlled within 2mm, providing stable geometric conditions for subsequent welding quality.

[0027] The aforementioned technical solution employs a three-step closed-loop process of scanning and screening, correction and replacement, and pre-marking alignment. This shifts the control of pipe end geometric quality from random trial and error on-site to digital management in the storage yard, enabling pipe sections with excessive ellipticity to be repaired and reused on-site. It reduces the maximum misalignment error to within 2mm and shortens alignment time by more than 70%, fundamentally solving the problems of inefficiency and material waste caused by pipe end geometric deviations in pipe laying operations. Simultaneously, Fourier decomposition is introduced to decompose the pipe end profile into multi-order harmonics, utilizing amplitude and phase angles to achieve more accurate profile matching.

[0028] In one of the technical solutions, the method for improving the efficiency of submarine pipeline laying also includes step S4: after the welding process is completed, the pipe section is subjected to non-destructive testing, the detected welding defects are evaluated for engineering criticality, and the engineering acceptability of the defects is determined based on the pipeline design parameters, material properties and service conditions. Only defects that exceed the safety tolerance are repaired.

[0029] In the above technical solution, automatic ultrasonic testing of welds extracts weld defect data, including defect type (lack of fusion, porosity, crack, undercut), defect length, defect height (or depth), and defect location in the weld circumferential and wall thickness directions. The extracted defect data, along with the pipe section's material information, wall thickness, pipe diameter, design pressure, and service environment (temperature, seawater depth, H2S partial pressure), is input into the engineering critical assessment module. A fracture mechanics assessment model is established based on BS7910 "Guidelines for Acceptance Assessment of Defects in Metal Structures" or API579 "Service Suitability Assessment." Specifically, this includes: calculating the maximum acceptable equivalent crack size of the weld under service conditions based on pipeline design parameters (design pressure, temperature, additional load), material fracture toughness (such as CTOD value or KIC value), and welding residual stress (usually 30%~50% of yield strength); and converting the detected actual defects (such as lack of fusion, porosity) into equivalent crack sizes using standard methods. For planar defects (such as lack of fusion or cracks), the equivalent crack size is directly taken as the defect height; for volumetric defects (such as porosity or inclusions), the equivalent crack size is calculated according to the standard formula. If the equivalent crack size is less than or equal to the maximum equivalent crack size, the defect is considered acceptable in engineering and does not require rework; otherwise, the defect is considered to exceed the safety tolerance and requires rework.

[0030] The above technical solution introduces Engineering Critical Assessment (ECA) into the non-destructive testing process. Based on pipeline design parameters, material properties, and service conditions, it scientifically determines the engineering acceptability of defects. Only defects exceeding the safety tolerance are reworked, avoiding the misjudgment of a large number of acceptable defects under traditional fixed acceptance standards as requiring rework. This significantly reduces the welding rework rate from over 5% to below 2.5%, effectively avoiding the 45-90 minute time required for a single rework, greatly reducing downtime and rhythm disruptions in the pipe-laying production line, and ensuring the continuous and efficient operation of the welding process.

[0031] In one technical solution, during the pipeline laying operation in step S3, an underwater remotely operated vehicle (ROV) is used to perform real-time and continuous external buckling morphology detection on the pipeline contact points. The ROV is equipped with high-resolution optical imaging equipment, multi-beam sonar, and a laser 3D scanner. It moves synchronously with the pipeline laying process, observing the appearance of the pipeline contact section in real time through the optical imaging system, obtaining the overall alignment of the pipeline seabed section through the multi-beam sonar, and accurately measuring the curvature change of the pipeline cross-section through the laser 3D scanner. When the pipeline bending radius is detected to be less than the design allowable value, the ROV immediately sends an alarm signal to the control room of the pipelaying vessel. The control room adjusts the pipelaying speed, tensioner tension, or support frame angle parameters of the pipelaying vessel according to the alarm information to avoid pipeline buckling damage.

[0032] The aforementioned technical solution employs an underwater remotely operated vehicle (ROV) equipped with optical, sonar, and laser 3D scanners to perform real-time and continuous external buckling morphology monitoring of the pipe's mud-contact points. This completely replaces the traditional method of strong coupling using built-in buckling detectors and steel cables, eliminating the high-risk of detectors becoming stuck inside the pipe due to steel cable breakage, which could lead to forced pipe retraction. Simultaneously, through multimodal sensing data fusion and automatic alarm linkage for exceeding limits, the pipe-laying rate, tensioner tension, and support frame angle can be adjusted in real time, effectively preventing pipe buckling damage. Thus, while ensuring the structural integrity of the subsea pipeline, the continuous and smooth operation of the pipe-laying pipeline is guaranteed, significantly improving operational safety and overall pipe-laying efficiency.

[0033] In one of the technical solutions, the specific implementation method of 3D digital scanning modeling in steps S1 and S2 is as follows: Using the location of the longitudinal weld seam of the pipe segment as the 0° reference point in the circumference, a 3D laser scanner or structured light scanning device is used to obtain radial dimension data and wall thickness data at each sampling interval of 0.5°~4° along the circumferential direction of the pipe end, and construct a geometric model of the pipe end section containing the pipe end profile. The geometric model of the pipe end section is decomposed into Fourier series to extract the first N harmonic components and their phase angles distributed along the circumferential direction of the radial deviation. N≥3. The amplitude and phase angle of each harmonic component are combined to form the geometric feature vector of the pipe end, which serves as the basis for pipe segment geometric pairing and assembly orientation marking.

[0034] In the above technical solution, N in the Fourier series decomposition takes a value of 4 to 8, specifically determined according to the pipe diameter. For pipe diameter ≤ 12 inches, N is 4; for pipe diameter 12 to 24 inches, N is 6; and for pipe diameter ≥ 24 inches, N is 8.

[0035] The aforementioned technical solution, through high-density equal-angle sampling (0.5°~4° interval, 90~720 data points per end) and Fourier series decomposition, upgrades the pipe end profile from a rough description based on a few diameters to a precise mathematical expression of multi-order harmonic amplitude and phase angle, improving the ellipticity calculation accuracy to within 0.1% and enabling the capture of higher-order deformations such as triangular and quadrangular shapes; simultaneously, based on the phase angle φ... k It can accurately predict the circumferential position of the maximum deviation at the pipe end, providing directly matching geometric feature parameters for calculating the optimal rotation angle in subsequent assembly orientation marking, thereby improving the matching calculation efficiency by more than 80% and laying a data foundation for strictly controlling the misalignment within 2mm.

[0036] In one technical solution, after scanning the pipe segment, the acquired pipe end cross-sectional geometric model data is associated with and stored in a database along with the segment's unique identifier. This unique identifier is affixed to the outer wall of the pipe segment in the form of a barcode, QR code, or RFID tag. By associating the pipe end cross-sectional geometric model data with the unique identifier in the database and affixing barcodes, QR codes, or RFID tags to the outer wall of the pipe segment, rapid digital retrieval and full traceability of the yard's pipe segment geometric information are achieved. This avoids repeated scanning and modeling of the same pipe segment, allows pairing calculations to directly retrieve feature vectors from the database, significantly improves yard management efficiency and data reusability, and provides a reliable data foundation for subsequent assembly orientation marking and on-site correction.

[0037] In one of the technical solutions, the specific implementation method of using a hydraulic device to perform on-site correction of the pipe end geometry in step S2 is as follows: The hydraulic device is an internally supported hydraulic jack, and its jack rod end is provided with an arc-shaped support shoe that fits against the inner wall of the pipe; the internally supported hydraulic jack is placed inside the pipe end of the pipe section to be corrected. Retrieve the geometric feature vector of the pipe end from the database, calculate the contribution rate of each harmonic amplitude to the total radial deviation, and identify all harmonic orders whose contribution rate exceeds the preset threshold and their corresponding maximum deviation circumferential azimuth angle. The internally supported hydraulic jack applies radial pressure sequentially or in combination according to the identified harmonic order and azimuth angle until the ellipticity is ≤1% and the amplitude of each higher harmonic is reduced to below the acceptable threshold. During the correction process, a laser rangefinder sensor is used to monitor the radial dimension change of the tube end in real time. When the real-time ellipticity measurement value is ≤1%, pressurization is stopped and the pressure is maintained for 30~60s before unloading. Repeat the scan verification. If the ellipticity is still >1%, correct it again until the requirements are met.

[0038] The above technical solution combines internally supported hydraulic jacks with the geometric feature vectors of the pipe ends. It accurately identifies all harmonic orders and their corresponding maximum deviation circumferential azimuth angles from a database. Using multi-rod internally supported hydraulic jacks, the required radial expansion of each jack is calculated based on harmonic analysis results. The radial deviation after target correction should approach 0, and the radial displacement of each jack is determined by solving least squares. This achieves non-uniform, closed-loop control in-situ correction. During correction, a laser rangefinder sensor monitors radial dimension changes in real time. After reaching the target, pressure is maintained for 30-60 seconds to eliminate elastic rebound. A closed-loop feedback of correction-monitoring-verification is formed through rescanning verification, enabling pipe sections with an ellipticity >1% to be repaired on-site to ≤1%. This avoids material waste and construction delays caused by direct pipe abandonment or return in traditional technologies, significantly reducing pipe laying costs and ensuring full utilization of pipe resources. Among these, the amplitude A of each harmonic order... k The contribution rate to the total radial deviation variance is: In one of the technical solutions, the specific implementation method of marking the assembly orientation according to its number and the geometric model of the pipe end section in step S3 is as follows: Using the B end of the preceding pipe segment and the A end of the following pipe segment as the pairing objects, the geometric feature vectors of the two ends are extracted respectively, and the amplitude and phase angle of the first N harmonic components of the two ends are used as matching parameters. Using the geometric feature vector of end A of the next pipe segment as the rotation object, rotate it successively along the circumference with a step size of 0.5°~4° to simulate circumferential rotation. Calculate the composite radial deviation distribution between the two end profiles at each rotation angle to obtain the estimated curve of the misalignment at that rotation angle. The maximum misalignment is extracted from the synthetic radial deviation distribution. All rotation angle ranges with a maximum misalignment estimate ≤ 2mm are selected. Among all rotation angle ranges, the optimal rotation angle is selected with the minimum maximum misalignment estimate, the included angle between the longitudinal welds of the two pipe sections in the circumferential direction being 90~180° and the relative spacing between the longitudinal welds in the circumferential direction being not less than 100mm as the optimization objective. An optimal rotation angle is selected through a multi-objective optimization algorithm. Based on the selected optimal rotation angle, mark the circumferential assembly start line on the outer surface of the B end of the preceding pipe section and the outer surface of the A end of the following pipe section, respectively. Mark the rotation direction arrow relative to the B end of the preceding pipe section and the assembly sequence number on the outer surface of the A end of the following pipe section; so that the parts can be directly aligned and assembled on site according to the markings.

[0039] In the specific implementation of the above technical solution, the B end of the preceding pipe segment and the A end of the following pipe segment are used as pairing objects, and the geometric feature vectors of the two ends are extracted from the database respectively: , A 1,k and φ 1,k Let A be the amplitude and phase angle of the k-th harmonic at end B of the preceding pipe segment.2,k and φ 2,k Let be the amplitude and phase angle of the k-th harmonic at end A of the subsequent pipe segment. Consider end A of the subsequent pipe segment as an object that can rotate about an axis, and let its circumferential rotation angle relative to end B of the preceding pipe segment be Δφ (value ranging from 0 to 360°). After rotation, the phase angle of the k-th harmonic at end A of the subsequent pipe segment becomes φ. 2,k +k·Δφ (modulus 360°). The combined radial deviation (i.e., the misalignment distribution function) at the two ends at the circumferential angle θ is: For pipe sections with insufficient machining accuracy, a0 needs to be included in the composite radial deviation, i.e. a 0,1 and a 0,2 These are the average radial deviations at end B of the first segment and end A of the second segment, respectively. In actual engineering, the misalignment is measured in absolute value. Therefore, for each fixed Δφ, the estimated maximum misalignment value for this rotation angle is defined as: Then, with a step size Δφ step =0.5~4° Traverse all Δφ, calculate E for each angle max [Δφ], filter out all that satisfy E max Rotation angles with [Δφ] ≤ 2mm constitute a feasible set. Selecting the optimal rotation angle from this set requires simultaneously satisfying three optimization objectives: E max [Δφ] should be as small as possible; the included angle β of the longitudinal welds of the two pipe sections in the circumferential direction should be 90~180°; the relative arc length spacing L of the longitudinal welds in the circumferential direction should be greater than or equal to 100mm. A weighted scoring method is used to transform the multi-objective into a single objective: ω1 and ω2 are the weights for misalignment and weld angle, respectively, with ω1 + ω2 = 1. These weights are determined based on engineering priority: misalignment control has a higher impact on welding quality than weld angle control, therefore ω1 is greater than or equal to ω2. Preferably, for conventional subsea pipelines, ω1 and ω2 are 0.6 and 0.4, respectively; for high-grade steel pipelines or deep-water high-pressure conditions, ω1 and ω2 are 0.7 and 0.3, respectively. The optimal rotation angle is selected from the feasible set, minimizing F(Δφ). Based on the selected optimal rotation angle, a 0° circumferential line is marked on the outer surface of end B of the preceding pipe section, and a starting line for counterclockwise rotation of Δφ relative to the 0° line is marked on the outer surface of end A of the following pipe section. The rotation direction arrow and assembly sequence number are also labeled. On-site workers only need to align the two lines and rotate them in the direction of the arrow until they coincide to achieve precise alignment, automatically ensuring the maximum misalignment is ≤2mm while maintaining a safe longitudinal weld spacing.

[0040] The above technical solution uses Fourier series to transform continuous contour matching into algebraic operations of discrete harmonic parameters, avoiding point-by-point brute-force search and improving computational efficiency; multi-objective optimization simultaneously ensures welding quality and structural safety.

[0041] In one technical solution, the method for improving the efficiency of subsea pipeline laying can be activated independently before, during, and after the pipeline laying operation begins. This application allows for independent activation before, during, and after efficiency declines, breaking the limitations of traditional methods that only passively respond to inefficient conditions. It achieves proactive intervention capabilities throughout all time periods: before operation, pipe segments can be pre-screened and paired to avoid geometric deviation risks from the source; during operation, matching parameters can be optimized at any time to dynamically maintain a high-efficiency cycle; and after efficiency declines, correction and re-pairing can be quickly initiated to rapidly restore pipeline balance. The criteria for judging inefficient conditions during efficiency declines are: the daily pipeline laying mileage continuously falls below a preset threshold, such as 800m, for at least three consecutive natural days; the welding quality criterion is: within the corresponding statistical period, the pipeline welding rework rate exceeds a preset threshold, such as 3%. This flexible activation mechanism ensures seamless integration of the method into different engineering stages, significantly enhancing the robustness and adaptability of pipeline laying operations.

[0042] This invention further claims a subsea pipeline laying system, comprising: The pipe end three-dimensional digital scanning subsystem is set up in the stockyard and is used to perform three-dimensional digital scanning and modeling of the pipe end to obtain the geometric model of the pipe end cross section. The pipe end database, connected to the pipe end three-dimensional digital scanning subsystem, is used to store the unique number of the pipe segment and its corresponding pipe end cross-sectional geometric model data. The unique number of the pipe segment is affixed to the outer wall of the pipe segment in the form of a barcode, QR code or RFID tag. An ellipticity filtering module, connected to the pipe end database, is used to filter out all pipe segments with an ellipticity ≤1% as pipe segments that can be arbitrarily paired. The on-site straightening device includes an internally supported hydraulic jack, each of which has an arc-shaped support shoe at the end of its jack rod that fits against the inner wall of the pipe. It is used to straighten pipe sections with an ellipticity >1% on-site, so that the ellipticity is ≤1%. The assembly orientation marking module is connected to the pipe end database and is used to calculate the optimal assembly rotation angle based on the pipe end cross-sectional geometric model of adjacent pipe sections, and generate assembly orientation marking information, which includes circumferential assembly start line, rotation direction arrow and assembly sequence number. The welding execution module is set on the pipelaying vessel's work line and is used to assemble and weld adjacent pipe sections according to the assembly orientation marking information. The engineering critical assessment module, connected to the welding execution module, is used to perform engineering critical assessment on welding defects, determine the engineering acceptability of defects, and only output rework instructions for defects that exceed the safety tolerance. The ROV buckling monitoring subsystem includes an underwater remotely operated vehicle and its control station. The underwater remotely operated vehicle is equipped with high-resolution optical camera equipment, multi-beam sonar and laser 3D scanner, which are used to perform real-time and continuous external buckling morphology detection of the mud contact point of the pipeline during pipe laying operations. When the pipe bending radius is detected to be less than the design allowable value, an alarm signal is sent to the control room of the pipe-laying vessel. The central controller is connected to the pipe end three-dimensional digital scanning subsystem, pipe end database, ellipticity screening module, on-site correction device, assembly orientation marking module, welding execution module, engineering critical assessment module and ROV buckling monitoring subsystem, respectively, to coordinate the operation of each module and realize full-process digital closed-loop control from pipe end scanning to butt welding.

[0043] In the above technical solution, the central controller is connected to each module via industrial Ethernet or wireless local area network, and the communication protocol adopts OPCUA or MQTT. The central controller also includes a visualization display unit for real-time display of the status of the yard pipe section database, the current pairing result, the correction progress, the welding rework rate, and the ROV monitoring screen. When any module fails or data is abnormal, all data before and after the failure is saved for offline analysis.

[0044] The aforementioned technical solution constructs a fully digital closed-loop system encompassing pipe-end scanning, database storage, ellipticity screening, on-site correction, assembly orientation marking, welding execution, critical engineering assessment, and ROV buckling monitoring. A central controller coordinates all modules, enabling one-time data acquisition, full-process reuse, and intelligent decision-making. This system deeply integrates yard management with shipboard operations, allowing seamless flow of pipe-end geometric feature vectors during correction, pairing, and marking, avoiding information silos and repetitive work. Simultaneously, the central controller monitors the status of each module in real time and adjusts accordingly, significantly improving the automation level and fault response capability of the pipe-laying line. Compared to traditional decentralized operations, it reduces manual intervention by approximately 70% and increases overall pipe-laying efficiency by over 50%.

[0045] Taking the method for improving the efficiency of submarine pipeline laying triggered by inefficient operating conditions as an example, this paper implements the method for improving the efficiency of submarine pipeline laying.

[0046] A certain overseas subsea natural gas pipeline project has a total length of approximately 60km. The pipe material is API 5LX65MS / MO acid-resistant pipe, with a diameter of 24 inches, a wall thickness of 15.88mm, and an external 50mm concrete weighting layer. The project utilizes a pipelaying vessel for continuous offshore pipelaying operations. The work station layout is shown in [details omitted]. Figure 2 The pipeline route has a maximum water depth of approximately 27m.

[0047] Since the project's inception, statistics over the past seven days show an average daily pipe-laying efficiency of less than 30 sections (total length 360m), a cumulative rework rate exceeding 5%, and a single rework session lasting approximately 45-90 minutes. If the current pace continues, even with continuous operation, the overall pipe-laying cycle is expected to exceed six months. Considering the daily vessel freight rate of approximately US$250,000-350,000 per day, project costs will significantly exceed budget, and it will also be difficult to meet the offshore operation window requirements. To clarify the limiting factors, the operational procedures at each workstation on board were broken down and statistically analyzed; the results are shown in Table 1.

[0048] Table 1. Operation time of each process on the pipelaying vessel According to the analysis results in Table 1, low pipeline alignment efficiency, long initial welding operation time, and high welding rework rate are the main limiting factors causing the persistently low pipe-laying efficiency. When the daily average pipe-laying efficiency is significantly lower than 800m (currently approximately 360m per day) and the welding rework rate exceeds 5% (higher than the control target of 3%), the method provided in this application will be activated, specifically including: During the yard stage, a 3D laser scanner (model: FAROFocus S350) was used to perform a full circumferential scan of ends A and B of all pipe sections to be installed. During scanning, the longitudinal weld seam of the pipe section was used as the 0° circumferential reference point, and a fixed sampling interval of 0.5° was used along the circumference, acquiring 720 radial dimension data points for each pipe end. After filtering and denoising the scanned data, a 3D digital model of the pipe end cross-section was constructed, and the ellipticity distribution characteristics along the circumferential direction were extracted. Based on the established pipe end geometric database, an optimization algorithm was used to calculate the optimal assembly pairing relationship between each pipe section, ensuring that the maximum misalignment at the joint position of adjacent pipe sections was controlled within the range of 2-3 mm. After completing the pairing calculation, a laser marking machine was used to mark the circumferential assembly start line and pairing number on the outer surface of both ends of each pipe section.

[0049] For a small number of pipe sections (ellipticity > 1%) that cannot meet the matching requirements, on-site geometric correction is performed using internally supported hydraulic jacks. The jacks are inserted into the pipe end, and based on the ellipticity distribution characteristics obtained from scanning, the jack rods are aligned with the major axis of the ellipse. Pressure is gradually increased until the measured ellipticity value is ≤ 1%, and the pressure is held for 30 seconds before unloading. After correction, the model is re-scanned and remodeled, replacing the original geometric model in the database to ensure it meets the matching requirements.

[0050] Welding is performed according to the matching marks. During pipelaying, an underwater remotely operated vehicle (ROV, model: Seabed H3000) is used to monitor the external buckling morphology of the pipe contact point in real time and continuously. The ROV is equipped with a high-resolution optical camera, multi-beam sonar, and laser 3D scanner. It moves synchronously with the pipelaying vessel and collects 3D morphological data of the contact section every 5 minutes. When the radius of curvature of the pipe contact point (TDP) is detected to be less than the design allowable value (60m), which can be based on the DNV-OS-F101 standard and varies according to different pipes, wall thicknesses, and materials, the ROV immediately sends an alarm signal to the pipelaying vessel control room. The control room automatically reduces the pipelaying rate by 20%, increases the tensioner tension by 10%, and adjusts the angle of the support frame to eliminate the buckling risk.

[0051] In the non-destructive testing (NDT) phase following welding, engineering criticality assessment (ECA) is performed on welding defects detected by the AUT. Based on BS7910 standards, the pipeline design pressure (15 MPa), material fracture toughness (CTOD = 0.2 mm), welding residual stress (300 MPa), and service environment (seawater temperature 5–30°C) are input to calculate the equivalent crack size for each defect. If the equivalent crack size is less than the allowable critical size, it is deemed acceptable and retained; otherwise, a rework instruction is output. The assessment time for a single weld is controlled within 2 minutes, and the assessment results are automatically uploaded to the central controller.

[0052] This embodiment quickly restores the production line pace after the pipe laying efficiency drops, increasing the daily laying mileage from 360m to over 1200m, reducing the welding rework rate from over 5% to below 2%, and completely eliminating the risk of pipe cutting and withdrawal caused by the broken steel wire rope of the built-in buckling detector, significantly improving the overall efficiency and safety of pipe laying operations.

[0053] For this overseas project, the average pipe-laying efficiency in the first 7 days was approximately 360m / day. If this inefficient working condition continues, it will take approximately 166.7 days to complete all pipe-laying (excluding force majeure shutdowns). The offshore pipe-laying cycle is significantly beyond the controllable range, posing serious risks to cost and time windows.

[0054] By implementing the method provided in this application, pipelaying efficiency gradually recovered and improved within 3 weeks: averaging approximately 1000 m / day in the first 3 weeks, and then steadily increasing to 1200 m / day. Considering force majeure weather and time for professional operation assistance, the actual total cycle for offshore pipelaying is approximately 72 days.

[0055] Compared to the approximately 166.7-day pipelaying cycle under inefficient operating conditions, the implementation of this joint control scheme shortens the offshore operation cycle by about 94 days. Based on a pipelaying vessel daily rate of US$250,000 to US$350,000, this directly avoids vessel occupancy costs of approximately US$23.5 million to US$33 million.

[0056] In addition to direct economic benefits, this solution effectively reduces the risk of insufficient working window due to extended construction periods, significantly reduces the risk of line stoppages and cycle disruptions caused by rework, and avoids costly safety and quality incidents such as pipe cutting and return due to equipment failure by eliminating the built-in buckling detector and replacing it with ROV real-time monitoring. Overall, this multi-technology combined control solution significantly improves pipe laying efficiency while effectively achieving cost control, risk reduction, and enhanced contract fulfillment capabilities.

[0057] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for improving the efficiency of subsea pipeline laying, characterized in that, include: S1. Perform three-dimensional digital scanning and modeling of all pipe sections and pipe ends in the stockyard and assign them unique numbers. Each unique number corresponds to the A-end and B-end cross-sectional geometric models of a pipe section. Based on the pipe end cross-sectional geometric models, Fourier series decomposition is used to extract the pipe end geometric feature vectors. All pipe sections that can be arbitrarily paired are selected. The pipe sections that can be arbitrarily paired are all pipe sections whose A-end and B-end ellipticity is ≤1%. S2. For pipe sections that cannot meet the requirements of arbitrary pairing, a hydraulic device is used to correct the geometry of the pipe ends on site so that the ellipticity is ≤1%. Then, a three-dimensional digital scanning model is re-modeled and the original pipe end cross-sectional geometry model is replaced. S3. For adjacent pipe sections, mark the assembly orientation according to their unique number and the geometric model of the pipe end section, so that the maximum misalignment error of the adjacent pipe sections at the joint position is within 2mm; during the pipeline laying process, assemble according to the marked assembly orientation to match the pipe end section profile of the two pipe sections, and then perform welding to complete the pipe section connection.

2. The method for improving the efficiency of subsea pipeline laying as described in claim 1, characterized in that, It also includes step S4: after the welding process is completed, non-destructive testing is carried out on the pipe section, and the detected welding defects are evaluated for engineering criticality. Based on the pipeline design parameters, material properties and service conditions, the engineering acceptability of the defects is determined, and only defects that exceed the safety tolerance are repaired.

3. The method for improving the efficiency of subsea pipeline laying as described in claim 2, characterized in that, During the pipeline laying operation in step S3, an underwater remotely operated vehicle (ROV) is used to conduct real-time and continuous external buckling morphology detection of the pipeline contact points. The ROV is equipped with high-resolution optical imaging equipment, multi-beam sonar, and a laser 3D scanner. It moves synchronously with the pipeline laying process, observing the appearance of the pipeline contact section with the ground in real time through the optical imaging system, obtaining the overall alignment of the pipeline seabed section through the multi-beam sonar, and accurately measuring the curvature change of the pipeline cross-section through the laser 3D scanner. When the pipeline bending radius is detected to be less than the design allowable value, the ROV immediately sends an alarm signal to the control room of the pipelaying vessel. The control room adjusts the pipelaying speed, tensioner tension, or support frame angle parameters of the pipelaying vessel according to the alarm information to avoid pipeline buckling damage.

4. The method for improving the efficiency of subsea pipeline laying as described in claim 3, characterized in that, The specific implementation methods of 3D digital scanning modeling in steps S1 and S2 are as follows: Using the location of the longitudinal weld seam of the pipe segment as the 0° reference point in the circumference, a 3D laser scanner or structured light scanning device is used to obtain radial dimension data and wall thickness data at each sampling interval of 0.5°~4° along the circumferential direction of the pipe end, and construct a geometric model of the pipe end section containing the pipe end profile. The geometric model of the pipe end section is decomposed into Fourier series to extract the first N harmonic components and their phase angles distributed along the circumferential direction of the radial deviation. N≥3. The amplitude and phase angle of each harmonic component are combined to form the geometric feature vector of the pipe end, which serves as the basis for pipe segment geometric pairing and assembly orientation marking.

5. The method for improving the efficiency of subsea pipeline laying as described in claim 4, characterized in that, After the pipe segment is scanned, the obtained pipe end cross-sectional geometric model data is associated with the unique number of the pipe segment and stored in the database. The unique number of the pipe segment is affixed to the outer wall of the pipe segment in the form of a barcode, QR code or RFID tag.

6. The method for improving the efficiency of subsea pipeline laying as described in claim 5, characterized in that, The specific implementation method of using a hydraulic device to perform on-site correction of the pipe end geometry in step S2 is as follows: The hydraulic device is an internally supported hydraulic jack, and its jack rod end is provided with an arc-shaped support shoe that fits against the inner wall of the pipe; the internally supported hydraulic jack is placed inside the pipe end of the pipe section to be corrected. Retrieve the geometric feature vector of the pipe end from the database, calculate the contribution rate of each harmonic amplitude to the total radial deviation, and identify all harmonic orders whose contribution rate exceeds the preset threshold and their corresponding maximum deviation circumferential azimuth angle. The internally supported hydraulic jack applies radial pressure sequentially or in combination according to the identified harmonic order and azimuth angle until the ellipticity is ≤1% and the amplitude of each higher harmonic is reduced to below the acceptable threshold. During the correction process, a laser rangefinder sensor is used to monitor the radial dimension change of the tube end in real time. When the real-time ellipticity measurement value is ≤1%, pressurization is stopped and the pressure is maintained for 30~60s before unloading. Repeat the scan verification. If the ellipticity is still >1%, correct it again until the requirements are met.

7. The method for improving the efficiency of subsea pipeline laying as described in claim 6, characterized in that, The specific implementation method for marking the assembly orientation based on its number and the geometric model of the pipe end section in step S3 is as follows: Using the B end of the preceding pipe segment and the A end of the following pipe segment as the pairing objects, the geometric feature vectors of the two ends are extracted respectively, and the amplitude and phase angle of the first N harmonic components of the two ends are used as matching parameters. Using the geometric feature vector of end A of the next pipe segment as the rotation object, rotate it successively along the circumference with a step size of 0.5°~4° to simulate circumferential rotation. Calculate the composite radial deviation distribution between the two end profiles at each rotation angle to obtain the estimated curve of the misalignment at that rotation angle. The maximum misalignment is extracted from the synthetic radial deviation distribution. All rotation angle ranges with a maximum misalignment estimate ≤ 2mm are selected. Among all rotation angle ranges, the optimal rotation angle is selected with the minimum maximum misalignment estimate, the included angle between the longitudinal welds of the two pipe sections in the circumferential direction being 90~180° and the relative spacing between the longitudinal welds in the circumferential direction being not less than 100mm as the optimization objective. An optimal rotation angle is selected through a multi-objective optimization algorithm. Based on the selected optimal rotation angle, mark the circumferential assembly start line on the outer surface of the B end of the preceding pipe section and the outer surface of the A end of the following pipe section, respectively. Mark the rotation direction arrow relative to the B end of the preceding pipe section and the assembly sequence number on the outer surface of the A end of the following pipe section; so that the parts can be directly aligned and assembled on site according to the markings.

8. The method for improving the efficiency of subsea pipeline laying as described in claim 7, characterized in that, The method for improving the efficiency of submarine pipeline laying can be activated independently before, during, and after the pipeline laying operation begins.

9. A submarine pipeline laying system, characterized in that, include: The pipe end three-dimensional digital scanning subsystem is set up in the stockyard and is used to perform three-dimensional digital scanning and modeling of the pipe end to obtain the geometric model of the pipe end cross section. The pipe end database, connected to the pipe end three-dimensional digital scanning subsystem, is used to store the unique number of the pipe segment and its corresponding pipe end cross-sectional geometric model data. The unique number of the pipe segment is affixed to the outer wall of the pipe segment in the form of a barcode, QR code or RFID tag. An ellipticity filtering module, connected to the pipe end database, is used to filter out all pipe segments with an ellipticity ≤1% as pipe segments that can be arbitrarily paired. The on-site straightening device includes an internally supported hydraulic jack, each of which has an arc-shaped support shoe at the end of its jack rod that fits against the inner wall of the pipe. It is used to straighten pipe sections with an ellipticity >1% on-site, so that the ellipticity is ≤1%. The assembly orientation marking module is connected to the pipe end database and is used to calculate the optimal assembly rotation angle based on the pipe end cross-sectional geometric model of adjacent pipe sections, and generate assembly orientation marking information, which includes circumferential assembly start line, rotation direction arrow and assembly sequence number. The welding execution module is set on the pipelaying vessel's work line and is used to assemble and weld adjacent pipe sections according to the assembly orientation marking information. The engineering critical assessment module, connected to the welding execution module, is used to perform engineering critical assessment on welding defects, determine the engineering acceptability of defects, and only output rework instructions for defects that exceed the safety tolerance. The ROV buckling monitoring subsystem includes an underwater remotely operated vehicle and its control station. The underwater remotely operated vehicle is equipped with high-resolution optical camera equipment, multi-beam sonar and laser 3D scanner, which are used to perform real-time and continuous external buckling morphology detection of the mud contact point of the pipeline during pipe laying operations. When the pipe bending radius is detected to be less than the design allowable value, an alarm signal is sent to the control room of the pipe-laying vessel. The central controller is connected to the pipe end three-dimensional digital scanning subsystem, pipe end database, ellipticity screening module, on-site correction device, assembly orientation marking module, welding execution module, engineering critical assessment module and ROV buckling monitoring subsystem, respectively, to coordinate the operation of each module and realize full-process digital closed-loop control from pipe end scanning to butt welding.

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