A method of constructing an FPSO moonpool structure

Abstract

The present application relates to ship equipment installation technical field, disclose a kind of FPSO moon pool structure construction method, including the manufacture of moon pool lower cylinder, including the following steps, one: lower cylinder and upper cylinder scribe positioning and jig I arrangement;Two: lower cylinder reverse state production;Three: sand blasting;Four: lower sliding ring scribe positioning and jig arrangement;Five: lower sliding ring and lower cylinder assembly;Six: turning over hoisting;Upper lifting lug is welded at the corresponding position of lower sliding ring and lower cylinder, hoisting and turning over into total assembly jig;Seven: lower sliding ring and upper cylinder assembly;Eight: assembly completion inspection.It also includes the manufacture of moon pool upper cylinder, including the following steps, one: arc plate processing;Two: cross line and jig arrangement;Three: lower cylinder normal production;Four: inspection and sand blasting;Five: cylinder pre-assembly scribe;Six: lower cylinder positioning;Seven: intermediate cylinder positioning.The present application reduces thermal stress and deformation in welding process, ensures the quality and strength of weld, and has strong construction flexibility.

Description

Technical Field

[0001] This invention relates to the field of ship equipment installation technology, specifically a method for constructing an FPSO moon pool structure. Background Technology

[0002] Floating Production Storage and Offloading (FPSO) units perform production, storage, and offloading functions. They are secured by a mooring system and move in a circular path around a single mooring point under environmental loads such as wind, waves, and currents. The entire FPSO revolves around this single point and may encounter various extreme conditions within its design life. With the increasing number of single-point suspensions and the growing size of the single-point moonpool, higher strength and precision requirements are placed on the structure of the moonpool directly connected to the hull.

[0003] As an important component of the FPSO hull, the single-point moonpool structure has the following characteristics: 1. The single-point moon pool is an important supporting structure of the mooring system, and its structural strength and balance must be guaranteed; 2. The location of a single-point moon pool needs to take into account the influence of various control and monitoring systems, and the layout needs to be carefully optimized; 3. To achieve the requirements of segmented construction and gradual assembly, the flatness of the segment interfaces must be guaranteed for a single-point moon pool.

[0004] The welding of the sliding ring to the 80mm thick circular plate area (upper and lower cylinders) in the moon pool structure requires post-weld heat treatment and CTOD testing. Especially when the upper part of the sliding ring is joined, a sealed compartment is formed. The 600℃ post-weld heat treatment temperature needs to be carefully considered due to the construction difficulty. To avoid injury to personnel, the 80mm thick force buffer area plates (upper and lower cylinders), each 2.4 meters above and below the sliding ring, need to be joined and heat-treated outside the segment before being joined to the segment, avoiding the operational risks within the sealed compartment. The lower opening of the sliding ring has a 170mm to 80mm transition slope without beveling. Beveling can only be done on the lower plate, resulting in a reverse overhead welding beveling, increasing the welding difficulty. During reverse overhead welding, the angle between the welding torch and the weld is small, making the welding position difficult, resulting in uneven welds and difficulty in guaranteeing welding quality.

[0005] To meet the requirements of a single-point moon pool in an FPSO hull, a novel construction process and method—the segmented construction method—is proposed.

[0006] CN113928504A describes a segmented construction process for an integrated shaft and rudder, which also employs a segmented construction method. However, it produces shafts and rudders that are smaller in size and more complex in shape. Therefore, the number of segments is smaller, and the segment sizes are also smaller. The method for dividing the shape and size of the segments is relatively simple, resulting in poor operational flexibility and higher production requirements for enterprises. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a construction method for FPSO moon pool structures that reduces thermal stress and deformation during the welding process, ensures the quality and strength of the weld, and provides high construction flexibility.

[0008] To address the above technical problems, this invention provides a method for constructing an FPSO moon pool structure, including the fabrication of the lower cylinder of the moon pool, comprising the following steps: Step 1: Marking and positioning the lower and upper cylinders and arranging the jig I; Step Two: Reverse fabrication of the lower cylinder; Step 3: Sandblasting; Step 4: Marking and positioning the sliding ring and arranging the tire frame; Step 5: Assemble the lower sliding ring and the lower cylinder; Step Six: Turning Over and Hoisting; After the welding of the lower sliding ring and the lower cylinder is completed and inspected, lifting lugs are welded on the corresponding positions of the lower sliding ring and the lower cylinder. The cylinder is then hoisted and turned over into the main assembly jig to prepare for the assembly of cylinder component I. Step 7: Assemble the lower sliding ring and the upper cylinder; Step 8: Complete assembly inspection.

[0009] By adopting the above technical solutions, breaking down the welding process into multiple steps can reduce thermal stress and deformation during welding. Step-by-step welding allows for better control of welding parameters and quality. Necessary inspections and adjustments can be made during the welding process to ensure weld quality and strength. Step-by-step construction also allows for better control of the assembly accuracy and welding quality of the sliding ring and the upper and lower cylinders. Refining the process steps allows for better quality control at each stage. Decomposing the complex process into multiple simplified steps allows for timely detection and resolution of problems, reducing the probability of errors during assembly and improving work efficiency.

[0010] Preferably, in step six, after the hoisting and turning is completed, a T-shaped beam is welded around the outside of the lower cylinder.

[0011] By adopting the above technical solutions, during the welding of the T-beam, a 2mm gap is required between the outer end face of the T-beam and the upper reinforcing structure to ensure that the moon pool cylinder and the upper reinforcing structure do not directly contact each other. When encountering severe working conditions at sea, the hull may sway or tilt. The T-beam can prevent the moon pool cylinder from directly contacting and colliding with the lower and upper reinforcing structures, thus avoiding deformation of the moon pool cylinder structure and affecting the normal operation of the internal mooring system. The T-beam can protect the integrity of the moon pool structure and improve its reliability.

[0012] A method for constructing an FPSO moon pool structure, further comprising the fabrication of the upper cylinder of the moon pool, including the following steps: Step 1: Machining the arc-shaped plate; S11: Construct a raised-type jig II based on the ground line; jig II is a template jig. S12: The arc-shaped panels are positioned with reference to the ground line. Positioning accuracy requirements: ±2mm in the length direction of the panels, ±1mm in the width direction, ≤3mm in the fit gap between the jig II and the arc-shaped panels, and ≤3mm in the end difference of the panel seams; long strips are added to the joint of the panels, with a length of ≥600mm and a spacing of ≤500mm. The convex surface welding of the arc-shaped panels and the spot welding of the vertical stiffeners are completed on the convex jig; the positioning wooden templates are used for installation during structural installation, and the wooden templates are used for support and positioning; double-sided diagonal supports are added to the joint after installation. S13: After the arc-shaped plate is spliced ​​and welded on the convex tire, it is turned over. The tire moves with the section and is turned over to complete the welding of the reverse side of the spliced ​​plate. Step 2: Mark the cross lines and arrange the jig; Draw the cross center line of the cylinder on the ground according to the position on the drawing, and arrange the jig II along the circumference; Step 3: Normal fabrication of the lower cylinder; S31: After reinforcing the processed arc plate, hoist it onto the jig II in sequence, adjust the cylinder to be level, and ensure that the level accuracy is ≤3mm. Make sure the bottom is properly shimmed with the jig II. S32: Weld horizontal clamps at the joint, the cylinder diameter accuracy requirement is ≤2mm, and the four vertical seams are welded symmetrically. Step 4: Inspection and sandblasting; After the lower cylinder is completed and inspected, and the weld tightness and NDT tests are completed, it will be moved to the sand room; the upper cylinder and the intermediate cylinder will continue to be manufactured on the original jig II; Step 5: Marking lines for pre-assembly of the cylinder; Use a total station to complete the crosshair, inspection line, inner diameter, and outer diameter inspection line, and mark the weld position on the drawing; complete the tooling jig layout with reference to the ground layout line. Step Six: Positioning the lower cylinder; During positioning, align the crosshairs of the lower cylinder with the ground sample line, check the matching degree between the lower opening of the lower cylinder and the ground sample line, measure the horizontality of the upper and lower openings of the lower cylinder, the horizontal accuracy requirement of the lower opening is ±3mm, the verticality of the lower cylinder itself is ≤3mm, and the deviation between the actual center of the lower cylinder and the center of the ground sample is ≤3mm. Step 7: Positioning the intermediate cylinder; Before positioning the intermediate cylinder, a code plate is first set at the upper opening of the lower cylinder. The code plate is set within a range of less than 170°. After the segments are in place, the initial positioning of the segments is completed using the inspection lines at the upper and lower openings and the bow and stern cross lines. After the initial positioning is completed, the horizontality of the upper opening of the intermediate cylinder, its verticality, and the deviation between the center and the center of the ground sample are measured. The positioning scheme of the upper cylinder is the same as that of the intermediate cylinder.

[0013] By adopting the above technical solutions, when fabricating the upper cylinder of the moon pool, the fitting gap between the jig II and the arc-shaped plate is ≤3mm. When constructing the arc-shaped plate on the jig II, the construction accuracy of the arc-shaped plate can be flexibly adjusted to match the accuracy of the jig, unifying the construction accuracy of all arc-shaped plates, improving the assembly accuracy of the cylinder, and saving material processing costs. During structural installation, positioning wooden templates are used for installation, facilitating the positioning and support of the arc-shaped plates. Adding long strips at the closure joints ensures tight adhesion between the arc-shaped plates. These long strips increase the connection area between the arc-shaped plates, improving the stability and strength of the panels and preventing loosening or deformation due to stress. The misalignment between the lower cylinder and the middle cylinder is controlled within 2mm, effectively improving the sealing performance of the cylinder, thereby enhancing the overall structural stability and strength.

[0014] Preferably, in step two, the jig II is arranged at approximately 30° intervals along the circumferential direction.

[0015] By adopting the above technical solutions, the circumferentially evenly distributed jigs in the construction of hull components can evenly distribute the load on the contact surfaces, reduce component deformation and vibration, provide uniform support, and improve construction precision. These effects can increase the durability and stability of hull components, and improve overall performance and safety.

[0016] Preferably, in step seven, the key point in the initial positioning process is to control the misalignment of the cylinder walls between the lower cylinder and the middle cylinder, with the maximum misalignment being ≤2mm; the positioning scheme for the upper cylinder is the same as that for the middle cylinder.

[0017] By adopting the above technical solutions, a small misalignment of the cylinder wall can effectively improve the sealing performance of the cylinder; a small misalignment of the cylinder wall means that the contact area between the two cylinders is increased, the connection is tighter, thereby enhancing the overall structural stability and strength.

[0018] Preferably, a lower cylinder section is set on the lower cylinder of the moon pool. Before assembly, the lower cylinder of the moon pool needs to be positioned. After positioning, the lower cylinder of the moon pool is hoisted in sections according to the general assembly sequence of lower cylinder of moon pool → section I → section II → section III → section IV → section V → section VI → section VII → section VIII. During the welding process, the welding process is strictly followed. After the general assembly is completed, multiple lifting lugs are welded on the upper surface of the platform of the lower cylinder of the moon pool according to the position required by the drawings.

[0019] By adopting the above technical solutions, the overall weight of the lower cylinder section of the moon pool is relatively large, thus requiring multiple lifting points to evenly distribute the load. This ensures a more uniform distribution of the load's weight across different lifting points, reducing the pressure on each point and the load on the lifting points and connecting components, thereby minimizing deformation and damage to materials and equipment during hoisting. Multiple lifting points also increase the number of connection points between the load and the hook, improving the load's stability. Dividing the assembly into upper and lower sections and following the principle of installing sections from bottom to top ensures a safe working environment. Each section can be completed in a clearly defined sequence, reducing the potential dangers of assembling multiple sections simultaneously and ensuring that appropriate safety measures are taken at the right time to protect workers and equipment.

[0020] Preferably, the upper cylinder of the moon pool is set with the upper cylinder of the moon pool. Before assembly, the upper cylinder of the moon pool needs to be positioned. After positioning, the upper cylinder of the moon pool is hoisted in sections according to the overall assembly sequence of upper cylinder of the moon pool → section IX → section X → section XI → section XII to ensure the overall size of the upper cylinder. The welding process is strictly followed. After the overall assembly is completed, multiple lifting lugs are welded on the upper surface of the platform of the upper cylinder of the moon pool.

[0021] By adopting the above technical solutions, the overall weight of the upper cylinder section of the moon pool is relatively large, requiring multiple lifting points to evenly distribute the load. This ensures a more uniform distribution of the load's weight across different lifting points, reducing the pressure on each point and the load on the lifting points and connecting components, thus minimizing deformation and damage to materials and equipment during lifting. Multiple lifting points also increase the number of connection points between the load and the hook, improving the load's stability. When the load is secured to multiple lifting points, the possibility of swaying or rotation is reduced, making lifting movements easier to control.

[0022] Compared with the prior art, the present invention has the following advantages: 1. This invention breaks down the welding process into multiple steps, reducing thermal stress and deformation during welding. Step-by-step welding allows for better control of welding parameters and quality. Necessary checks and adjustments can be made during the welding process to ensure weld quality and strength. Step-by-step construction allows for better control of the assembly accuracy and welding quality of the sliding ring and the upper and lower cylinders. Refining the process steps allows for better quality control at each stage. Decomposing the complex process into multiple simplified steps allows for timely detection and resolution of problems, reducing the probability of errors during assembly and improving work efficiency.

[0023] 2. The moon pool structure of this FPSO is a section of a large vessel. The moon pool structure is relatively simple, with a rectangular outer reinforcing structure and a cylindrical inner section. Therefore, the method of dividing the sections is quite diverse, depending on the size of the production site and the lifting capacity. If the site or lifting capacity is limited, the sections can be divided into smaller parts to facilitate operations; if the site is ample and the lifting capacity is excellent, larger sections can be formed to improve construction efficiency. It is suitable for enterprises with different operating sites and production capacities, offering high construction flexibility.

[0024] 3. The present invention adopts the method of flipping the slip ring for welding and then flipping it again, which avoids the working condition of reverse welding bevel, reduces the welding difficulty, and ensures the welding quality.

[0025] 4. When fabricating the upper cylinder of the moon pool using this invention, the fitting gap between the jig II and the arc-shaped plate is ≤3mm. When constructing the arc-shaped plate on the jig II, the construction accuracy of the arc-shaped plate can be flexibly adjusted to match the accuracy of the jig, ensuring uniformity in the construction accuracy of all arc-shaped plates, improving the assembly accuracy of the cylinder, and saving material processing costs. During structural installation, positioning wooden templates are used for installation, facilitating the positioning and support of the arc-shaped plates. Adding long strips at the closure joints ensures tight adhesion between the arc-shaped plates. These long strips increase the connection area between the arc-shaped plates, improving the stability and strength of the panels and preventing loosening or deformation due to stress. The misalignment between the lower cylinder 108 and the middle cylinder 107 is controlled within 2mm, effectively improving the sealing performance of the cylinder, thereby enhancing the overall structural stability and strength. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the segmentation of the moon pool according to the present invention; Figure 2 This is an assembly diagram of the upper and lower cylinders of the moon pool lower cylinder of the present invention; Figure 3 This is a diagram showing the welding sequence of the upper and lower cylinders of the moon pool lower cylinder of the present invention; Figure 4 This is a schematic diagram of the lower cylinder frame arrangement of the moon pool lower cylinder of the present invention; Figure 5 This is a schematic diagram of the tube support for the sliding ring of the present invention; Figure 6 This is a top view schematic diagram of the installation of the lifting lugs of the present invention; Figure 7 This is a schematic cross-sectional view of the lifting lug installation of the present invention; Figure 8 This is a schematic diagram of the flipping of the lower cylinder and the sliding ring of the moon pool lower cylinder of the present invention; Figure 9 This is a schematic diagram of the overall assembly frame of the present invention; Figure 10 This is a schematic diagram of the three-cylinder docking of the lower cylinder of the moon pool according to the present invention; Figure 11 This is a schematic diagram of the lower reinforcing structure assembly of the present invention; Figure 12 This is a schematic diagram of the overall assembly of the lower cylinder section of the moon pool according to the present invention; Figure 13 This is a schematic diagram of the arrangement of the lifting lugs on the lower cylinder section of the moon pool according to the present invention; Figure 14 This is a schematic diagram of the assembly of the lower cylinder of the moon pool upper cylinder of the present invention; Figure 15 This is a schematic diagram of the lower cylindrical frame arrangement of the upper cylindrical body of the moon pool according to the present invention; Figure 16 This is a schematic diagram of the tube support arrangement of the lower cylinder of the upper cylinder of the moon pool according to the present invention; Figure 17 This is a schematic diagram of the overall assembly of the upper cylindrical section of the moon pool according to the present invention; Figure 18 This is a schematic diagram of the upper reinforcing structure assembly of the present invention; Figure 19 This is a schematic diagram of the overall mounting of the upper cylindrical body of the moon pool according to the present invention;

[0027] Figure 20 This is a schematic diagram of the frame II structure of the present invention.

[0028] In the diagram, 1-Cylinder assembly I, 2-Cylinder assembly II, 100-Moon pool cylinder, 101-Lower moon pool cylinder, 102-Upper moon pool cylinder, 103-Lower cylinder, 104-Sliding lower ring, 105-Upper cylinder, 106-Upper cylinder, 107-Intermediate cylinder, 108-Lower cylinder, 200-Lower reinforcing structure, 201-Segment I, 202-Segment II, 203-Segment III, 204-Segment IV, 205-Segment V, 206-Segment VI, 207-Segment VII, 208-Segment VIII, 300-Upper reinforcing structure, 301 - Segment IX, 302- Segment X, 303- Segment XI, 304- Segment XII, 400- Connecting Component, 401- T-beam, 402- Lifting Lug, 500- Support Component, 501- Frame I, 502- Pipe Support, 503- Overall Frame, 504- Frame II, 600- Arc Plate, 601- Plate, 602- Plate, 603- Plate, 604- Plate, 605- Plate, 606- Plate, 607- Plate, 608- Plate, 700- Lower Moon Pool Cylinder Section, 800- Upper Moon Pool Cylinder Section. Detailed Implementation

[0029] like Figure 1 As shown, the FPSO moon pool structure of the present invention includes a moon pool cylinder 100, a lower reinforcing structure 200, an upper reinforcing structure 300, and a connecting assembly 400. The moon pool cylinder 100 includes a lower moon pool cylinder 101 and an upper moon pool cylinder 102. The connecting assembly 400 includes a T-beam 401. The moon pool cylinder 100 is located in the middle of the moon pool structure. The T-beam 401 is welded to the outer ring of the moon pool cylinder 100. A 2mm gap is left between the end face of the T-beam 401 and the lower reinforcing structure 200 and the upper reinforcing structure 300 to ensure that the moon pool cylinder 100 and the lower reinforcing structure 200 and the upper reinforcing structure 300 do not directly contact each other, thereby avoiding deformation of the moon pool cylinder 100 under external forces and improving the stability and reliability of the overall moon pool structure. When encountering adverse working conditions at sea, the hull may sway and tilt. The T-beam 401 prevents direct contact and collision between the moon pool cylinder 100 and the upper reinforcing structure 300 and lower reinforcing structure 200, thus avoiding deformation of the moon pool cylinder structure and affecting the normal operation of the internal mooring system. The T-beam 401 protects the integrity of the moon pool structure and improves its reliability. The lower reinforcing structure 200 is located below the upper reinforcing structure 300, and both the lower reinforcing structure 200 and the upper reinforcing structure 300 are arranged on the outside of the moon pool cylinder 100.

[0030] like Figures 2-10As shown, the lower cylinder 101 of the moon pool of the present invention includes a cylinder assembly I1 and a connecting assembly 400. A lower cylinder section 700 is installed on the lower cylinder 101. The cylinder assembly I1 includes a lower cylinder 103, a sliding ring 104, and an upper cylinder 105. The lower cylinder 103, sliding ring 104, and upper cylinder 105 are constructed using the same method, all being assembled from four arc-shaped plates 600. The connecting assembly includes a T-beam 401 and a lifting lug 402; a support assembly 500 is used during construction for auxiliary support. The support assembly 500 includes a jig I 501, a pipe brace 502, and a general assembly jig 503; the arc-shaped plates include plates 601, 602, 603, and 604. During construction, the lower cylinder 103 and upper cylinder 105 are manufactured first, followed by the sliding ring 104; simultaneous manufacturing of the upper and lower cylinders effectively ensures the assembly accuracy of the cylinder weld joints. Both the lower cylinder 103 and the upper cylinder 104 are composed of four 600mm arc-shaped plates welded together. The lower cylinder 103 has a height of 2410mm, and the upper cylinder 105 has a height of 2450mm. The cylinders are joined using FCAW vertical welding. Since the upper and lower openings of the sliding ring 104 have no bevels, the butt joint bevels are all made on the upper and lower cylinders, and the welding bevels are X-shaped. This avoids the reverse overhead welding situation during welding, reduces the construction difficulty, and improves the welding quality. The lower cylinder 101 of the moon pool is first assembled using the sliding ring 104 as a template. The sliding ring 104 and the lower cylinder 103 are assembled first, and then the sliding ring 104 is mounted on the template in reverse, and then the sliding ring 104 is assembled onto the cylinder 105. Its construction and assembly method includes the following steps: Step 1: Marking and positioning the lower cylinder 103 and upper cylinder 105 and arranging the jig I501; S11: On the hoisting site under the 1t crane, use a total station to complete the marking of the crosshair, the ∅11720mm inner diameter inspection line, the ∅11920mm inner diameter, and the vertical weld projection position, with a marking accuracy of 1mm.

[0031] S12: Complete the arrangement of tooling and jig Ⅰ501 according to the marked ground line. Arrange one jig 501 every 30° along the circumference, for a total of 12 (more jigs can be added on site according to actual conditions), and fix the jig 501 to the ground reinforcement; S13: Use a total station to check the level of the upper surface of the fixture; the levelness standard is ±1mm. Step 2: Fabrication of the lower cylinder 103 in reverse state; S21: Before hoisting the 600mm arc plate, the inspection line should be marked, the light target points should be attached, and the upper and lower adjustment plates should be preset. S22: Hoist the arc plate 600 onto the jig I501 in sequence, and use tooling and wind ropes to pull it for later posture adjustment. Adjust the alignment of the arc plate 600 with the ground line by using the lower wedge. Use a hammer to hang a line to check and adjust the verticality of the arc plate 600 assembly, and ensure that the verticality deviation is within 1mm. S23: After positioning, fix the anti-tipping fixture and tighten the wire rope; S24: Install positioning plates 601, 602, 603, and 604 in sequence, set up anti-tipping fixtures and wind ropes, and control the splicing accuracy of the left and right arc plates to be ≤3mm. Complete the splicing of the entire cylinder by adjusting the alignment of the ground line and the flatness of the upper and lower ends. S25: After the 600mm arc plate is assembled, the 1 / 2 and 3 / 4 welds are welded symmetrically simultaneously. When welding the four welds, one welder completes the 1 / 3 thickness weld on the outer side of the cylinder, and performs carbon gouging on the inner side of the cylinder. During the root cleaning process, the root pass must be thoroughly cleaned, and the bevel area must be ground clean using a grinding wheel or similar method. After completing the 1 / 2 thickness weld on the inner side of the cylinder, the inner and outer sides are welded alternately or simultaneously symmetrically until completion to reduce welding deformation. When welding each weld, leave approximately 200-300mm between the upper and lower bevels for later welding. S26: After the cylinder is assembled, measure the overall accuracy of the cylinder to ensure that the upper and lower end faces are 2mm coplanar and the deviation between the actual center point of the cylinder and the center point of the ground line is ±1mm. The closure joint uses an arc template to accommodate the mounting plate. The mounting plate is set on the outside of the cylinder and the spacing between the mounting plates is ≤500mm. The manufacturing processes of the sliding ring 104, the upper cylinder 105, and the lower cylinder 103 are the same.

[0032] Step 3: Sandblasting; After the lower cylinder 103 and the upper cylinder 105 are completed, they are reinforced with pipe supports 502 to enter the sand chamber, while the lower sliding ring 104 does not enter the sand chamber. Step 4: Marking and positioning the lower sliding ring 104 and arranging the tire frame; Find another location near the assembly point of the lower cylinder 103 and draw the crosshair of the sliding ring 104. Re-lay the jig I501, placing one jig I501 every 30 mm along the circumference, for a total of 12 (add jigs as needed on site). Fix the jig I501 to the ground reinforcement. After the jig I501 is laid out, check the levelness of the jig I501 to ensure that the tread is level and the levelness of the jig is ≤1 mm. Step 5: Assemble the lower sliding ring 104 with the lower cylinder 103; S51: After the acceptance of the jig frame I501, first hoist the sliding ring 104 to the top of the jig frame I501, and make sure the upper opening of the sliding ring 104 is properly supported by the jig frame I501; then measure the overall accuracy of the sliding ring 104 to ensure that the upper and lower end faces are 2mm coplanar and the deviation between the actual center point of the cylinder and the center point of the ground line is ±1mm. S52: After the lower sliding ring 104 is adjusted into place, the lower cylinder 103, which has been sandblasted, is hoisted onto the lower opening of the lower sliding ring 104, with the lower opening facing upwards, thus completing the assembly. S53: Joint welding; preheating to the required welding temperature, using FCAW horizontal welding, with a K-type bevel, and the butt joint is welded simultaneously by at least 4 welders using a segmented back-welding method. Divide the circumferential weld into sections as follows: Figure 3 The cylinder is divided into eight equal parts, and welded symmetrically by an even number of welders in the order of 1 / 1', 2 / 2', 3 / 3', and 4 / 4'. First, complete approximately 1 / 3 of the thickness of the inner circumferential weld, then perform carbon gouging on the outer side. During the gouging process, the root pass must be thoroughly cleaned, and the bevel should be ground clean using a grinding wheel or similar method. After completing approximately 1 / 2 of the thickness of the outer weld on the cylinder, alternate welding on the inner and outer sides or simultaneous symmetrical welding until completion, thereby reducing welding deformation and stress concentration. After welding, inspect the roundness; the diameter deviation should be controlled within ±4mm, and the concentricity ≤2mm. If these tolerances are exceeded, correction is required. Step Six: Turning Over and Hoisting; S61: Before the lower sliding ring 104 and the lower cylinder 103 are turned over and hoisted, the accuracy of the main assembly jig 503 must be checked. The main assembly jig 503 consists of 12 sets of 2815mm high stabilizing frames. The jig diameter of ∅11580mm is marked on the cross-shaped ground line, with an accuracy requirement of ±2mm. The levelness of the main assembly jig 503 is 1mm. The main assembly jig 503 must be fixed to the ground reinforcement, and the stabilizing frames must be rigidly fixed together.

[0033] S62: After the welding of the lower sliding ring 104 and the lower cylinder 103 is completed and inspected, the lifting lugs 402 are welded on the corresponding positions of the lower sliding ring 104 and the lower cylinder 103. The cylinder is then hoisted and turned over into the PMF101C assembly jig 503 to prepare for the assembly of cylinder component I1.

[0034] S63: After hoisting and turning over, weld a ring of T-beams 401 around the outside of the lower cylinder 103.

[0035] Step 7: Assemble the lower sliding ring 104 with the upper cylinder 105; S71: After the jig I 501 passes the acceptance test, the lower sliding ring 104 and the lower cylinder 103 are flipped over and hoisted into the main jig 503. After adjusting the concentricity and level, the upper cylinder 105 is pulled into the upper part of the lower sliding ring 104. During the assembly of the upper cylinder 105, anti-tipping fixtures and wind ropes are also required.

[0036] S72: Weld the lifting lug 402 and the T-beam 401. The welding method is the same as that used for welding the sliding ring 104 and the lower cylinder 103. The T-beam 401 needs to be welded to the upper cylinder 105, but not to the sliding ring 104. By using a method of flipping the slip ring for welding and then flipping it again, the reverse welding bevel condition is avoided, the welding difficulty is reduced, and the welding quality is guaranteed.

[0037] Step 8: Final assembly inspection; After the three hulls are joined together, all main welds will undergo 100% UT + 100% MT, with the RT quantity to be agreed upon by the Quality Department, the shipowner, and the ship inspection department. All watertight welds will be vacuum-tested for tightness. After the lower hull 103 of the moon pool is leveled and installed, it will enter the final assembly stage of the section belonging to PMF101C.

[0038] The assembly of the lower cylinder 103 and upper cylinder 105, and the docking of the lower sliding ring 104 with the lower and upper cylinders 103 and 105, are all based on marking and positioning. Marking and positioning are performed before the fabrication and assembly of the lower and upper cylinders 103 and 105 to ensure construction accuracy and quality. The sandblasting process after the lower and upper cylinders 103 and 105 are fabricated further consolidates the construction accuracy and enhances the strength of the cylinders. Decomposing the welding process into multiple steps reduces thermal stress and deformation during welding. Step-by-step welding allows for better control of welding parameters and quality. Necessary inspections and adjustments can be made during welding to ensure weld quality and strength. Step-by-step construction allows for better control of the assembly accuracy and welding quality of the lower sliding ring with the upper and lower cylinders; refining the process steps allows for better control of the quality of each stage. Decomposing complex processes into multiple simplified steps allows for timely detection and resolution of problems, reducing the probability of errors during assembly and improving work efficiency.

[0039] like Figures 11-13 As shown, the assembly process of the moon pool lower cylinder section 700 of the present invention includes the assembly of the moon pool lower cylinder 101, the lower reinforcing structure 200, and the connecting assembly 400. The lower reinforcing structure 200 consists of segments I 201, II 202, III 203, IV 204, V 205, VI 206, VII 207, and VIII 208; the connecting assembly includes lifting lugs 402. The assembly sequence is: moon pool lower cylinder 101 → segment I 201 → segment II 202 → segment III 203 → segment IV 204 → segment V 205 → segment VI 206 → segment VII 207 → segment VIII 208. Before assembly, the moon pool lower cylinder 101 needs to be positioned. After positioning, the remaining segments are hoisted according to the assembly sequence to ensure the overall dimensions of the section. Welding was carried out strictly in accordance with the welding process. After the assembly was completed, 16 lifting lugs 402 were welded to the upper surface of the 700 section of the lower cylinder of the moon pool according to the positions required by the drawings. Then, the gantry crane was used to lift the 700 section of the lower cylinder of the moon pool into place.

[0040] The upper surface, formed by the combination of segments V205, VI206, VII207, and VIII208, constitutes a rectangular platform. This rectangular platform is the upper surface of the lower cylinder section 700 of the moon pool. Four lifting lugs 402 are welded in a rectangular distribution at each corner of the upper surface of the lower cylinder section 700, with each corner lug 402 symmetrically distributed, totaling 16 lifting lugs. The number of lifting lugs can be adjusted according to the dimensions of the moon pool structure; if the structure is smaller, the number of lifting lugs 402 can be reduced accordingly. The lower cylinder section 700 is relatively heavy, requiring multiple lifting points to evenly distribute the load, ensuring a more uniform distribution of the weight across different lifting points. This reduces the pressure on each lifting point, decreases the load on the lifting points and connecting components, and reduces deformation and damage to materials and equipment during lifting. Multiple lifting points also increase the number of connection points between the load and the hook, improving the stability of the load. When the load is secured to multiple lifting points, the possibility of swaying or rotation can be reduced, making it easier to control the lifting movement and improving the safety of the lifting operation. After the lower cylinder section 700 of the moon pool is lifted into place, the lifting lug 402 is removed.

[0041] The 700-unit assembly of the lower cylinder of the moon pool adopts the following sequence: Lower Cylinder 101 → Segment I 201 → Segment II 202 → Segment III 203 → Segment IV 204 → Segment V 205 → Segment VI 206 → Segment VII 207 → Segment VIII 208. The assembly is divided into upper and lower parts, following the principle of bottom-to-top. Sequential segment installation ensures a safe working environment. Each segment is completed within a defined sequence, ensuring correct installation and connection. This reduces the risk of incorrect combinations and connections, ensures proper matching and alignment between segments, and minimizes the potential hazards of assembling multiple segments simultaneously. It ensures that appropriate safety measures are taken at the right time to protect workers and equipment. Furthermore, precise segment installation helps maintain the strength and stability of the structure and reduces the need for subsequent maintenance and repair. Sequential segment installation also simplifies quality control and inspection. Each segment can be independently recorded and evaluated to ensure that assembly quality and standards are met. Any errors or quality issues can be detected and corrected at an early stage, preventing subsequent segments from being affected and thus improving work efficiency.

[0042] like Figures 14-17As shown, the moon pool upper cylinder 102 of the present invention includes a cylinder assembly II2 and a connecting assembly 400. A moon pool upper cylinder section 800 is installed on the moon pool upper cylinder 102. The connecting assembly 400 includes a T-beam 401 and a lifting lug 402; the cylinder assembly II2 includes an upper cylinder 106, a middle cylinder 107, and a lower cylinder 108. The three cylinders are constructed using the same method, each consisting of four arc-shaped plates 600 spliced ​​together. A support assembly 500 is used during construction for auxiliary support. The support assembly 500 includes a jig II 504, and the arc-shaped plates 600 include plates 605, 606, 607, and 608. Each cylinder is composed of four arc-shaped plates spliced ​​together, and reinforcing ribs are welded to the outer side of the cylinder; during assembly, the outer reinforcing ribs of the lower cylinder 108 and the middle cylinder 107 must be aligned and installed. To avoid cross welds, the plates are in an interlocking state. First, construct the lower cylinder 108, then the middle cylinder 107 and the upper cylinder 106 in sequence. After construction, assemble the cylinders, with the lower cylinder 108 at the bottom, the middle cylinder 107 in the middle, and the upper cylinder 106 at the top. The construction and assembly method includes the following steps: Step 1: Machining the 600mm curved plate; S11: Construct a raised-type jig II504 based on the ground line. Jig II504 is a template jig, made of FB400x20 and L100x100x10 angle steel. The fitting gap between jig II504 and the 600mm curved plate is ≤3mm. The center line and 150mm inspection lines at the top and bottom edges of the curved plate should be marked before assembly.

[0043] Here, the frame II 504 is a component consisting of a support assembly perpendicular to the ground and a template frame, such as... Figure 20 Unlike the previous jig I501, this one is used to construct curved plates. Leaving a certain fitting gap allows for flexible adjustment of the construction precision of the curved plates to match the precision of the jig template when constructing curved plates on the II504 jig template. This ensures uniform construction precision across all curved plates, improves the assembly precision of the cylinder, and saves on material processing costs.

[0044] S12: The curved panels are positioned according to the ground line. Positioning accuracy requirements: ±2mm in the length direction of the panels, ±1mm in the width direction, ≤3mm gap between the jig II 504 and the curved panel 600, and ≤3mm difference between panel seams. A long strip is added to the joint of the panels, with a length ≥600mm and a spacing ≤500mm. The convex surface welding of the curved panels and the spot welding of the vertical stiffeners are completed on the raised jig. During structural installation, positioning wooden templates are used for installation and positioning. After installation, double-sided diagonal supports are added to the joint. The long strip at the joint ensures tight adhesion between the curved panels. The long strip increases the connection area between the curved panels, improving the stability and strength of the panels and preventing loosening or deformation under stress. The positioning wooden template, long strip, and joint supports are all built into the component.

[0045] S13: Welding process must be strictly followed. Finished accuracy standards for the arc-shaped plates: structural installation accuracy ±6mm, cylinder body inspection and marking ±1mm. The 600mm arc-shaped plates are joined and welded on a raised platform, then flipped over. The platform moves with the section as the plates are flipped over to complete the welding on the reverse side of the joint.

[0046] When manufacturing the upper cylinder 106, after the flipping is completed, a ring of T-beams 401 is welded to the outer side of the arc-shaped plates of the upper cylinder 106. During welding, lines are first drawn on the outer side of the arc-shaped plates of the upper cylinder 106 to mark the welding positions of the T-beams 401. The drawn lines on the four arc-shaped plates must be consistent. One section of the T-beam 401 is placed on the arc-shaped plate and fixed in place using suitable clamps or welding supports. Ensure an appropriate gap exists between the beam and the contact surface of the arc-shaped plate for subsequent welding. The welding method used is flux-cored wire gas shielded welding (FCAW). T-beams 401 do not need to be welded to the intermediate cylinder 107 or the lower cylinder 108.

[0047] Step 2: Mark the cross lines and arrange the jig; Draw the crosshair centerline of the cylinder on the ground according to the drawing. Arrange jigs II504 approximately every 30° along the circumference, for a total of 12 jigs (the number can be increased on-site as needed), evenly distributed circumferentially. This evenly distributed jig arrangement helps to evenly distribute the load on the contact surfaces of the hull components, reduce component deformation and vibration, provide unified support, and improve construction precision. These effects increase the durability and stability of the hull components, improving overall performance and safety. Fix the jigs II504 to the ground. After the jigs II504 are arranged, check their levelness to ensure the jig surface is level (1mm). Step 3: Fabrication of the lower cylinder in a 108-degree normal configuration; S31: After the pre-processed 600mm reinforced arc plate is hoisted onto the jig II504 in sequence, the cylinder is adjusted to be level, the level accuracy requirement is ≯3mm, and the bottom is firmly shimmed with the jig II504. S32: Weld horizontal clamps at the joint. After pre-welding self-inspection and approval, the cylinder diameter accuracy requirement is ≤2mm, and the cylinder levelness requirement is 1mm. Preheat to a certain temperature according to the welding process before welding, and weld the four vertical seams symmetrically. Pay attention to the welding sequence to control deformation. After welding, check the roundness. The diameter deviation should be controlled within ±2mm. If it exceeds the tolerance, it needs to be corrected. Step 4: Inspection and sandblasting; After the lower cylinder 108 is completed and inspected, and the weld tightness and NDT tests are completed, it will be moved to the sand room. On the original jig II 504, the upper cylinder 106 and the intermediate cylinder 107 will continue to be manufactured. Step 5: Marking lines for pre-assembly of the cylinder; Use a total station to complete the crosshair, φ11800mm inspection line, φ111 inner diameter, and φ12000 outer diameter inspection lines, and mark the weld positions on the drawings, with a line marking accuracy of 1mm. Complete the tooling jig layout based on the ground plot lines, and use a total station to check the levelness of the upper surface of the tooling, with a levelness standard of ±1mm. Step Six: Positioning the lower cylinder at 108; During positioning, align the crosshairs of the lower cylinder 108 with the ground sampling line. Use a plumb bob to check the matching degree between the lower opening of the lower cylinder 108 and the ground sampling line. Use a total station to measure the horizontality of the upper and lower openings of the lower cylinder 108. The horizontal accuracy requirements for the lower opening are: ±3mm; the verticality of the lower cylinder 108 itself is ≤3mm; the deviation between the actual center of the lower cylinder 108 and the center of the ground sampling is ≤3mm. Step 7: Positioning of the intermediate cylinder 107; Before positioning the intermediate cylinder 107, first set up a screed (the screed's range should be <170°) at the top of the lower cylinder 108, placing one screed within each 170° angle. After the sections are in place, use the 150mm inspection lines at the top and bottom and the bow and stern crosshairs to complete the initial positioning of the sections. After the initial positioning is completed, use a total station to measure the horizontality of the top of the intermediate cylinder 107, the verticality of the intermediate cylinder 107 itself, and the deviation between the center of the intermediate cylinder 107 and the center of the ground sample. During the initial positioning process, the key is to control the misalignment of the cylinder walls between the lower cylinder 108 and the intermediate cylinder 107, with a maximum misalignment of ≤2mm. The positioning scheme for the upper cylinder 106 is the same as that for the intermediate cylinder 107.

[0048] A small misalignment of the cylinder wall can effectively improve the sealing performance of the cylinder; a small misalignment of the cylinder wall means that the contact area between the two cylinders is increased, the connection is tighter, thereby enhancing the overall structural stability and strength.

[0049] During the installation of the upper cylinder 106, middle cylinder 107, and lower cylinder 108, a total station is used to ensure correct alignment of the centers of the two cylinders. A reference point is selected within the measurement area, and a benchmark measurement is performed using the total station. This reference point can be a fixed point or a point with known coordinates. The total station is correctly installed in the measurement position, and basic calibration and adjustments are performed. The position of each cylinder is measured using the total station. This can be done by measuring the center point, edge, or other specific marker points of the cylinder. Measurement data is collected using the total station. This data can include horizontal angles, vertical angles, slope distances, coordinates, etc. The measurement data is compared and analyzed to compare the measurement results between the two cylinders. Differences in distance, deviations, and angles between the cylinders can be calculated.

[0050] like Figures 18-19 The diagram illustrates the assembly process of the moon pool upper cylinder section 800 of the present invention. It includes the assembly of the upper reinforcing structure 300, the moon pool upper cylinder 102, and the connecting assembly 400. The connecting assembly includes a T-beam 401 and a lifting lug 402. The upper reinforcing structure 300 includes segments IX 301, X 302, XI 303, and XII 304; the assembly sequence is moon pool upper cylinder 102 → segment IX 301 → segment X 302 → segment XI 303 → segment XII 304. During the assembly of the moon pool upper cylinder section 800, the assembly is divided into upper and lower parts according to the sequence of moon pool upper cylinder 102 → segment IX 301 → segment X 302 → segment XI 303 → segment XII 304, following the principle of bottom-to-top assembly. Sequential segmental installation ensures a safe working environment. Each segment can be completed in a defined sequence, reducing the potential hazards of assembling multiple segments simultaneously. This ensures that appropriate safety measures are taken at the right time to protect workers and equipment. Sequential segment installation ensures each segment is correctly installed and connected. This reduces the risk of incorrect combinations and connections, ensuring proper matching and alignment between segments. Precise segment installation helps maintain the strength and stability of the structure and reduces the need for subsequent maintenance and repairs. Sequential segment installation simplifies quality control and inspection. Each segment can be independently documented and evaluated to ensure assembly quality and standards are met. Any errors or quality issues can be detected and corrected early, preventing subsequent segments from being affected and improving work efficiency.

[0051] Before assembly, the upper cylinder 102 of the moon pool needs to be positioned. After positioning, the remaining sections are hoisted according to the overall assembly sequence to ensure the overall dimensions of the section. Welding is carried out strictly according to the welding process. After the overall assembly is completed, 16 lifting lugs 402 are welded to the upper surface of the platform of the upper cylinder section 800. Then, a gantry crane is used to hoist the upper cylinder section 800 into place. The upper surface formed by the combination of sections IX301, X302, XI303, and XII304 forms a rectangular platform surface. This rectangular platform surface is the upper surface of the upper cylinder section 800. Due to the large weight of the upper cylinder section 800, multiple lifting points are needed to evenly distribute the load, making the weight of the load more evenly distributed across different lifting points. This reduces the pressure on each lifting point, reduces the load on the lifting points and connecting components, and reduces deformation and damage to materials and equipment during hoisting. Multiple lifting points increase the number of connection points between the load and the hook, improving the load's stability. When the load is secured to multiple lifting points, the possibility of swaying or rotation is reduced, making the lifting movement easier to control. Welding multiple lifting points is intended to enhance lifting safety.

[0052] Four lifting lugs 402 are welded in a rectangular pattern at each corner of the upper surface of the lower cylinder section 800 of the moon pool. The lifting lugs 402 at each corner are symmetrically distributed, for a total of 16 lifting lugs. The number of lifting lugs can be adjusted according to the size of the moon pool structure. If the structure size is small, the number of lifting lugs 402 can be reduced accordingly.

[0053] After the lifting lug 402 is welded, it is used for hoisting operations. Sixteen steel wire ropes are pulled by the hook of the gantry crane and connected to the lifting lug 402 in sequence for hoisting. After the upper cylinder section 800 of the moon pool is hoisted into place, the lifting lug 402 is removed. The lower cylinder sections 700 and 800 of the moon pool are then hoisted into place as a whole and welded together, one above the other, to form the moon pool structure.

[0054] The moon pool structure of this FPSO is a section of a large vessel, and the moon pool section is further divided into sub-sections for construction. Because the moon pool structure is relatively simple, with an outer reinforcing structure in the shape of a cuboid and a central cylindrical body, the method of subdividing the sub-sections is quite diverse. It can be divided according to the size of the production site and the lifting capacity; if the site is limited or the lifting capacity is limited, the sub-sections can be smaller to facilitate operations; if the site is ample and the lifting capacity is excellent, larger sub-sections can be formed to improve construction efficiency. Therefore, the FPSO moon pool sub-section construction method mentioned in this application is applicable to enterprises with different operating sites and different production capacities, offering high construction flexibility.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for constructing an FPSO moon pool structure, characterized in that, The installation of the moon pool cylinder, lower reinforcing structure, upper reinforcing structure, and connecting components includes the following steps: Step 1: Marking and positioning the lower and upper cylinders and arranging the jig I; Step Two: Reverse fabrication of the lower cylinder; Step 3: Sandblasting; Step 4: Marking and positioning the sliding ring and arranging the tire frame; Step 5: Assemble the lower sliding ring and the lower cylinder; Step Six: Turning Over and Hoisting; After the welding of the lower sliding ring and the lower cylinder is completed and inspected, lifting lugs are welded on the corresponding positions of the lower sliding ring and the lower cylinder. The cylinder is then hoisted and turned over into the main assembly jig to prepare for the assembly of cylinder component I. Step 7: Assemble the lower sliding ring and the upper cylinder; Step 8: Final assembly inspection; The moon pool lower cylinder includes cylinder assembly I and connecting assemblies; the moon pool lower cylinder assembly is installed on the moon pool lower cylinder; the assembly process of the moon pool lower cylinder assembly includes the assembly of the moon pool lower cylinder, the lower reinforcing structure, and the connecting assemblies. The lower reinforcing structure consists of segments I, II, III, IV, V, VI, VII, and VIII; the connecting assemblies include lifting lugs; the assembly sequence is: moon pool lower cylinder → segment I → segment II → segment III → segment IV → segment V → segment VI → segment VII → segment VIII; After the completion of the entire assembly of the lower cylinder section of the moon pool, four lifting lugs are welded in a rectangular distribution on each corner of the upper surface of the lower cylinder section of the moon pool, and the lifting lugs in each corner are symmetrically distributed. The upper cylinder of the moon pool includes cylinder assembly II and connecting assemblies; the upper cylinder of the moon pool is installed on the upper cylinder of the moon pool; the connecting assemblies include T-beams and lifting lugs; cylinder assembly II includes an upper cylinder, an intermediate cylinder, and a lower cylinder; the assembly process of the upper cylinder of the moon pool includes the assembly of the upper reinforcing structure, the upper cylinder of the moon pool, and the connecting assemblies; the connecting assemblies include T-beams and lifting lugs, and the upper reinforcing structure includes segments IX, X, XI, and XII; the assembly sequence is upper cylinder of the moon pool → segment IX → segment X → segment XI → segment XII; Four lifting lugs are welded in a rectangular pattern at each corner of the upper surface of the lower cylinder section of the moon pool, with the lifting lugs at each corner being symmetrically distributed.

2. A method for constructing an FPSO moon pool structure according to claim 1, characterized in that, In step six, after the hoisting and turning is completed, a T-shaped beam is welded around the outside of the lower cylinder.

3. A method for constructing an FPSO moon pool structure according to claim 1, characterized in that, This also includes the fabrication of the cylindrical body above the moon pool, which involves the following steps: Step 1: Machining the arc-shaped plate; S11: Construct a raised-type jig II based on the ground line; jig II is a template jig. S12: The arc-shaped panels are positioned with reference to the ground line. Positioning accuracy requirements: ±2mm in the length direction of the panels, ±1mm in the width direction, ≤3mm in the fit gap between the jig II and the arc-shaped panels, and ≤3mm in the end difference of the panel seams; long strips are added to the joint of the panels, with a length of ≥600mm and a spacing of ≤500mm. The convex surface welding of the arc-shaped panels and the spot welding of the vertical stiffeners are completed on the convex jig; the positioning wooden templates are used for installation during structural installation, and the wooden templates are used for support and positioning; double-sided diagonal supports are added to the joint after installation. S13: After the arc-shaped plate is spliced ​​and welded on the convex tire, it is turned over. The tire moves with the section and is turned over to complete the welding of the reverse side of the spliced ​​plate. Step 2: Mark the cross lines and arrange the jig; Draw the cross center line of the cylinder on the ground according to the position on the drawing, and arrange the jig II along the circumference; Step 3: Normal fabrication of the lower cylinder; S31: After reinforcing the processed arc plate, hoist it onto the jig II in sequence, adjust the cylinder to be level, and ensure that the level accuracy is ≤3mm. Make sure the bottom is properly shimmed with the jig II. S32: Weld horizontal clamps at the joint, the cylinder diameter accuracy requirement is ≤2mm, and the four vertical seams are welded symmetrically. Step 4: Inspection and sandblasting; After the lower cylinder is completed and inspected, and the weld tightness and NDT tests are completed, it will be moved to the sand room; the upper cylinder and the intermediate cylinder will continue to be manufactured on the original jig II; Step 5: Marking lines for pre-assembly of the cylinder; Use a total station to complete the crosshair, inspection line, inner diameter, and outer diameter inspection line, and mark the weld position on the drawing; complete the tooling jig layout with reference to the ground layout line. Step Six: Positioning the lower cylinder; During positioning, align the crosshairs of the lower cylinder with the ground sample line, check the matching degree between the lower opening of the lower cylinder and the ground sample line, measure the horizontality of the upper and lower openings of the lower cylinder, the horizontal accuracy requirement of the lower opening is ±3mm, the verticality of the lower cylinder itself is ≤3mm, and the deviation between the actual center of the lower cylinder and the center of the ground sample is ≤3mm. Step 7: Positioning the intermediate cylinder; Before positioning the intermediate cylinder, a code plate is first set at the top of the lower cylinder. The code plate is set within a range of less than 170°. After the sections are in place, the initial positioning of the sections is completed using the inspection lines at the top and bottom and the cross lines at the bow and stern. After the initial positioning is completed, the horizontality of the top of the intermediate cylinder, its verticality, and the deviation between the center and the center of the ground sample are measured. The positioning scheme of the upper cylinder is the same as that of the intermediate cylinder.

4. A method for constructing an FPSO moon pool structure according to claim 3, characterized in that, In step two, a frame II is arranged at approximately 30° intervals along the circumference.

5. A method for constructing an FPSO moon pool structure according to claim 3, characterized in that, In step seven, the key point in the initial positioning process is to control the misalignment of the cylinder walls between the lower cylinder and the middle cylinder, with the maximum misalignment ≤ 2mm; the positioning scheme for the upper cylinder is the same as that for the middle cylinder.

6. A method for constructing an FPSO moon pool structure according to claim 2, characterized in that, The lower cylinder of the moon pool is set up with the main section of the lower cylinder. Before assembly, the lower cylinder of the moon pool needs to be positioned. After positioning, the sections are hoisted in the following order: lower cylinder of moon pool → section I → section II → section III → section IV → section V → section VI → section VII → section VIII. During the welding process, the welding process is strictly followed. After the main assembly is completed, multiple lifting lugs are welded on the upper surface of the platform of the lower cylinder of the moon pool according to the position required by the drawings.

7. A method for constructing an FPSO moon pool structure according to claim 3, characterized in that, The upper cylinder of the moon pool is set up with the main section of the upper cylinder. Before assembly, the upper cylinder of the moon pool needs to be positioned. After positioning, the upper cylinder of the moon pool is hoisted in the order of the main assembly of the upper cylinder of the moon pool → section IX → section X → section XI → section XII to ensure the overall size of the main section. The welding process is strictly followed. After the main assembly is completed, multiple lifting lugs are welded on the upper surface of the platform of the upper cylinder of the moon pool.

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