A thick-film high-manganese steel corrugated sheet for polar LNG ships, its manufacturing method and its application

Abstract

This invention discloses a thick-film high-manganese steel corrugated plate for polar LNG ships, its manufacturing method, and its application, belonging to the field of marine technology. The corrugated plate is made of high-manganese steel plate with a manganese content of 22-25 wt%. The high-manganese steel plate substrate has a first protrusion arranged uniformly and parallel along a first direction and a second protrusion arranged uniformly and parallel along a second direction perpendicular to the first direction. A quadruple rotationally symmetrical star-shaped node is pressed at the position where the first and second protrusions intersect perpendicularly. The quadruple rotationally symmetrical star-shaped node includes a surface opening and a recessed bottom surface. Both the surface opening and the recessed bottom surface have a four-lobed symmetrical profile, composed of two alternating arcs with different radii of curvature. The width between the symmetrical lobes of the surface opening is greater than the width between the symmetrical lobes of the recessed bottom surface. This corrugated plate uses an integrated arc transition, which makes it easier for stress to diffuse evenly throughout the entire node area. Results show that the peak stress at the intersection is reduced by more than 35%.

Description

Technical Field

[0001] This invention belongs to the field of marine technology, specifically relating to a thick-film high-manganese steel corrugated plate for polar LNG ships, its manufacturing method, and its application. Background Technology

[0002] The liquefied natural gas (LNG) industry has experienced significant growth over the past few decades, primarily driven by continuously rising energy demand, shifting geopolitical landscapes in the supply chain, and advancements in maritime technology. By 2026, the LNG fleet had surpassed 700 vessels, with a significant increase in icebreakers designed specifically for polar routes—such as those for the Arctic route, which reduces transit time between Asia and Europe by up to 40% compared to traditional routes. This expansion stems from the extremely low temperatures (approximately -162°C) required for LNG transport, where cargo holds must withstand thermal contraction, pressure fluctuations, and external shocks. In polar environments, ships also face additional risks such as ice collisions, frigid temperatures as low as -50°C, and increased liquid sloshing due to harsh sea conditions, necessitating robust membrane designs that prioritize safety, efficiency, and cost-effectiveness. Research indicates that membrane tanks, employing thin metal barriers supported by insulation layers, dominate the market, accounting for over 70% of LNG carriers. Compared to spherical or prismatic tanks, membrane tanks offer significant advantages in evaporation management and space utilization.

[0003] For polar-specific designs, patent US4095546A proposes a novel geometric structure for shipborne LNG storage tanks suitable for the Arctic environment, while recent research focuses on the corrugated steel inner wall technology of membrane tanks. Domestic and international efforts have yielded continuous innovations in corrugated plate node design. Traditional lace-type nodes achieve stress dispersion through multi-layered folding structures, resulting in high manufacturing complexity. Multiple cuts and manual alignment are required at corrugation intersections, leading to welding defects, fatigue cracks, low production efficiency, and cost increases exceeding 20%. W-shaped nodes feature continuous bending, causing stress concentration at sharp corners during application, making them prone to fatigue cracks at extremely low temperatures. Uneven stress distribution at intersections and complex forming processes hinder automation. Overall, while existing node designs have made progress in innovation, they still face limitations such as high manufacturing difficulty, insufficient impact resistance, and high cost. These problems are particularly prominent in polar environments, limiting the safety and economy of LNG transportation. In the process of LNG transportation in polar environments, existing technologies still face the following technical challenges:

[0004] (1) The thin film structure is not resistant enough to ice impact and sway impact, which may lead to plastic deformation or failure—this has been confirmed by studies of thin film fatigue under vibration loads in Arctic conditions. This vulnerability forces frequent inspections and limits operational reliability.

[0005] (2) The traditional node design at the intersection of corrugations increases the manufacturing difficulty, requires precision welding and forming processes, which leads to a 20% increase in construction time and exacerbates the risk of low-temperature welding defects.

[0006] (3) Materials such as Invar alloy or 9% nickel steel are expensive and have a mismatch in thermal expansion coefficients, which leads to stress concentration in the -196℃ environment and weakens long-term stability. In the polar environment, environmental regulations require reduced emissions and increased safety margins, but existing designs still have shortcomings in terms of leak detection efficiency and insulation integrity, which further exacerbates the above problems. Summary of the Invention

[0007] To address the aforementioned shortcomings, this invention proposes a design and manufacturing method for thick-film high-manganese steel corrugated plates using four-corner star-shaped nodes. This method optimizes stress distribution, simplifies the process, and enhances polar adaptability through an integrated arc-shaped structure.

[0008] This invention provides a thick-film high-manganese steel corrugated sheet for polar LNG ships, comprising a high-manganese steel plate substrate plane, and a first protrusion and a second protrusion protruding from the substrate plane; the first protrusion is uniformly and parallelly arranged along a first direction in the substrate plane, and the second protrusion is uniformly and parallelly arranged along a second direction perpendicular to the first direction in the substrate plane; a quadruple rotationally symmetrical star-shaped node is pressed at the position where the first protrusion and the second protrusion intersect perpendicularly; the quadruple rotationally symmetrical star-shaped node includes a surface opening and a recessed bottom surface, both of which are four-lobed symmetrical contours, formed by two alternating arcs with different radii of curvature; the width between the symmetrical lobes of the surface opening is greater than the width between the symmetrical lobes of the recessed bottom surface.

[0009] Furthermore, the thickness of the high-manganese steel corrugated plate is 1.2~3mm; the manganese content of the high-manganese steel corrugated plate is 22wt%~25wt%.

[0010] Furthermore, both the first and second protrusions are arc-shaped protrusions, and the cross-section of the arc-shaped protrusion is a single-segment circular arc; the corresponding structural parameters of the first and second protrusions are the same; the distance between adjacent protrusions is 600~1000mm.

[0011] Furthermore, the vertical height H from the highest point of the arc-shaped protrusion to the base plane is 50~60mm, and the length L of a single arc-shaped protrusion is 75~85mm.

[0012] Furthermore, the groove depth of the quadruple rotationally symmetric star node is equal to the height H of the first and second protrusions.

[0013] Furthermore, the width d1 at both ends of the surface opening is 2.8 to 3.8 times the width d2 at both ends of the bottom plane; the surface opening and the recessed bottom surface are connected by an inclined transition surface; the connection between the inclined transition surface and the surface opening and the recessed bottom surface is set as an arc transition or an angular transition; the included angle between the inclined transition surface and the recessed bottom surface and the surface opening is 110° to 115°; among the arcs with different radii of curvature, the radius of curvature R1 of the outwardly convex arc segment is 1.2 to 1.4 times the radius of curvature R2 of the inwardly concave arc segment.

[0014] Furthermore, the width d1 at both ends of the surface opening is 25~30mm, and the width d2 at both ends of the bottom plane is 85~95mm; among the arcs with different radii of curvature, the radius of curvature R1 of the outwardly convex arc segment is 5~10mm, and the radius of curvature R2 of the inwardly concave arc segment is 4~8mm; among the arcs with different radii of curvature, the central angle corresponding to the radius of curvature R1 of the outwardly convex arc segment is 120~130°, and the central angle corresponding to the radius of curvature R2 of the inwardly concave arc segment is 30~40°.

[0015] This invention also provides a method for producing thick-film high-manganese steel corrugated sheets for polar LNG ships, comprising the following steps:

[0016] Step 1: Cut and pre-treat high manganese steel plates with a manganese content of 22wt%~25wt% to form an equiaxed austenitic microstructure;

[0017] Step 2: Preheat the high manganese steel plate from Step 1, and then stamp it using a hydraulic press equipped with a four-corner star-shaped mold and a cross-shaped arch mold;

[0018] Step 3: Align the multiple stamped high-manganese steel plates and perform laser welding along the linear lap joint.

[0019] Further, in step 1, the material pretreatment is as follows: the high manganese steel plate is heated to 1150~1200℃ and held for 2~3 hours, the initial rolling temperature is ≥1100℃, the final rolling temperature is 830~850℃, the water immersion temperature is 790~810℃, and then cooled to room temperature by ultra-fast water cooling to form an equiaxed austenitic microstructure; in step 2, the preheating temperature is 200~300℃; the hydraulic press pressure is 60~120MPa.

[0020] The present invention also provides an application of thick-film high-manganese steel corrugated plate for polar LNG ships, used in the membrane storage tank of the cargo hold of polar LNG ships, as the innermost layer of the liquid cargo maintenance system closely attached to the insulation layer, and can withstand hydrostatic pressure up to 7 bar.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) This invention is the first to design a four-pointed star node on a thick-film high-manganese steel corrugated plate. The corrugated plate of this invention uses arc-shaped protrusions with the same curvature, and a four-pointed star node is pressed at the vertical intersection of the protrusions. The arc-shaped protrusions and the four-pointed star node are far superior to the existing mainstream node forms in terms of structural performance. In polar environments, when subjected to external forces of swaying impact loads, the four-pointed star node can quickly disperse the force from the central area to various parts through the multi-path force transmission formed by the arc-shaped four-pointed star node, avoiding excessive stress concentration at the intersection, reducing the risk of local yielding, fatigue cracking and plastic deformation, and improving the reliability of the structure under cyclic loads, impact loads and complex working conditions. At the same time, when external forces act on the surface openings and the bottom concave arc of the four-pointed star node, they will be uniformly transmitted along the curved surface, unlike sharp corners and flat surfaces that concentrate the force in a certain place. The four-pointed star node of this invention adopts an integrated arc transition, and the stress is more easily diffused evenly to the entire node area. The results show that the peak stress at the intersection is reduced by more than 35%. In polar environments, the optimized thick film structure significantly enhances resistance to shaking and ice impact.

[0023] (2) The manufacturing method of this invention adopts an integral stamping process, which simplifies the production process by forming unified nodes and reduces the complexity of the cross-shaped structure that requires precise manual alignment. This process saves materials by reducing cutting steps and supports straight-line welding that is easier to automate, saving labor costs. When splicing traditional cross-shaped or horizontal and vertical corrugated nodes with different heights, the node positions are often complex three-dimensional curved surfaces or the horizontal and vertical wave heights are inconsistent. It is difficult for the robot to stably track the weld, and it can only rely on manual welding, resulting in a high welding defect rate and a lot of time consumption, which greatly affects production efficiency. In this invention, all corrugations have the same height and the nodes are on the same horizontal plane as the planar area. Only straight lap welds are needed along the edge of the plate. The robot can automatically track the entire process, improving the consistency of welding quality without the need for manual intervention. Attached Figure Description

[0024] Figure 1 This is a top view of the nodal area of ​​the thick-film high-manganese steel corrugated plate of the present invention;

[0025] Figure 2 This is an overall view of the thick-film high-manganese steel corrugated plate of Embodiment 1 of the present invention;

[0026] Figure 3 This is a partial view of the nodal area (the connection is arc-shaped) of the thick-film high-manganese steel corrugated plate of the present invention;

[0027] Figure 4 This is a side view of the nodal area of ​​the thick-film high-manganese steel corrugated plate of the present invention;

[0028] Figure 5 This is a top view of the nodal area of ​​the thick-film high-manganese steel corrugated plate of the present invention.

[0029] Figure 6 This is a comparison image before and after the deformation of a thick-film high-manganese steel corrugated plate.

[0030] In the attached figures, 1 is the first protrusion, 2 is the second protrusion, 3 is the planar area, 4 is the four-cornered star node, 5 is the longitudinal splicing weld, 6 is the transverse splicing weld, 7 is the crest position, 8 is the insulation layer, 9 is the recessed bottom surface, and 10 is the corner at the connection between the inclined transition surface and the surface opening. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] This invention provides a design and manufacturing method for a thick-film high-manganese steel corrugated sheet for polar LNG carriers, comprising: a thick-film structure optimizing strength and anti-sway performance, using a high-manganese steel sheet with a thickness ranging from 1.2 to 3 mm to withstand ice impact (this condition improves bending stiffness and impact absorption capacity, while relying on the low coefficient of thermal expansion and excellent low-temperature toughness of high-manganese steel, it maintains the flexibility brought by the corrugations, and avoids the thermal expansion mismatch and high cost of Invar or 9% nickel steel); a four-pointed star-shaped node design is adopted at the corrugation intersections to simplify the forming and installation process; the integration of high-manganese steel material improves low-temperature toughness and reduces the coefficient of thermal expansion, achieving approximately 30% cost savings. The sheet is formed by a single integral stamping of the high-manganese steel plate using a customized mold, forming longitudinal and transverse corrugations with four-pointed star-shaped arc nodes, and then assembled into a membrane shell component through linear welds.

[0033] A thick-film high-manganese steel corrugated sheet for polar LNG ships includes a high-manganese steel plate substrate plane and a first protrusion and a second protrusion raised on the substrate plane. The first protrusion is uniformly and parallelly arranged along a first direction in the substrate plane, and the second protrusion is uniformly and parallelly arranged along a second direction perpendicular to the first direction in the substrate plane. The corrugated protrusions are integrally formed with the substrate plane and are protrusion structures formed by stamping the substrate plane. At the position where the first and second protrusions intersect perpendicularly, a fourfold rotationally symmetric star-shaped node (quadrangular star-shaped node) is pressed. The fourfold rotationally symmetric star-shaped node includes a surface opening and a recessed bottom surface. Both the surface opening and the recessed bottom surface have a four-lobed symmetrical profile, which is composed of two alternating arc segments with different radii of curvature. The width between the symmetrical lobes of the surface opening is greater than the width between the symmetrical lobes of the recessed bottom surface.

[0034] All dimensional parameters of thick-film high-manganese steel corrugated sheets are measured based on the original flat base surface of the metal sheet.

[0035] Both the first and second protrusions are arc-shaped, with a single-segment circular arc cross-section. The corresponding structural parameters of the first and second protrusions are identical. The arc-shaped protrusions extend beyond the base plane, and multiple arc-shaped protrusions are arranged at intervals along a predetermined direction, with gaps between adjacent protrusions. The distance between adjacent protrusions is 600-1000 mm. The vertical height H from the highest point of the arc-shaped protrusion to the base plane is 50-60 mm, and the length L of a single arc-shaped protrusion is 75-85 mm. The radius of curvature of the circular arc is determined by H and W.

[0036] The groove depth of the quadruple rotationally symmetric star node is equal to the height H of the first and second protrusions. The width d1 of the two ends of the symmetrically outward-protruding arc of the surface opening of the quadruple rotationally symmetric star node is 2.8 to 3.8 times the width d2 of the two ends of the bottom plane. The surface opening and the recessed bottom surface are connected by an inclined transition surface. The connection between the inclined transition surface and the surface opening and the recessed bottom surface is set as an arc transition or an angular transition. The included angle between the inclined transition surface and the recessed bottom surface and the surface opening is 110° to 115°. Among the arcs with different radii of curvature, the radius of curvature R1 of the outward-protruding arc segment is 1.2 to 1.4 times the radius of curvature R2 of the inward-recessed arc segment. The width d1 of the two ends of the symmetrically outward-protruding arc of the surface opening is 25 to 30 mm, and the width d2 of the two ends of the symmetrically outward-protruding arc of the bottom plane is 85 to 95 mm. When the connection between the inclined transition surface and the surface opening and the recessed bottom surface is set as an arc transition (as shown in the arc transition cross-section diagram...), Figure 3 The radius of curvature R of the transition segment is 5~8mm, and the central angle is 65~70°. Among the arcs with different radii of curvature, the radius of curvature R1 of the outwardly convex arc segment is 5~10mm, and the radius of curvature R2 of the inwardly concave arc segment is 4~8mm. Among the arcs with different radii of curvature, the central angle corresponding to the radius of curvature R1 of the outwardly convex arc segment is 180°-θ1, and the central angle corresponding to the radius of curvature R2 of the inwardly concave arc segment is 180°-θ2. θ1 is the angle of the outward convex arc (50°~60°), and θ2 is the angle of the inward concave arc (140°~150°). The radius of curvature and central angle of the arcs at the surface opening and the concave bottom surface remain consistent. As the thickness of the high-manganese steel plate increases, the radius of curvature of the arcs with different curvatures increases, and the widths at both ends of the symmetrical outward convex arcs at the surface opening and the concave bottom surface decrease. If an arc transition is used at the connection between the inclined transition surface and the surface opening and the concave bottom surface, the radius of curvature of this arc increases. The above adjustments are made to avoid the influence of the plate thickness on the arc dimensions during stamping and to reduce the processing difficulty.

[0037] A design and manufacturing method for a thick-film high-manganese steel corrugated sheet for polar LNG ships includes the following steps:

[0038] (1) Material preparation: Low-temperature certified high manganese steel plate is selected as the base material. The manganese content of the high manganese steel plate is 22~25%, the thickness is 1.2~3mm, and it is cut into rectangular blanks with a length of 600~1000mm and a width of 600~1000mm to meet the modular assembly requirements.

[0039] (2) Integral stamping: A hydraulic press equipped with a four-pointed star and cross-arch mold is used to stamp the high manganese steel plate blank in one pass to form longitudinal and transverse corrugated structures and intersection nodes; the nodes adopt a four-pointed star design to simplify the node structure, optimize stress distribution and reduce welding defects; optionally, the blank is heated to 200~300℃ before stamping to improve formability and ensure uniform thickness without thinning;

[0040] (3) Quality inspection: The stamped sheet is inspected by ultrasonic testing or X-ray flaw detection to verify that there are no cracks, deformations or uneven thicknesses, and that it meets the International Maritime Organization liquefied natural gas membrane standards;

[0041] (4) Welding assembly: Align multiple stamped plates and perform laser welding or arc welding along the linear lap joint. The welding length covers the entire edge of the plate to ensure a leak-free seal. Optionally, a guide groove can be added at the node to improve the automation accuracy of robot welding. This replaces the traditional lace-shaped or W-shaped node, reduces the complexity of cutting and manual alignment, and improves installation efficiency by more than 20%.

[0042] (5) System integration: The assembled corrugated plate is bonded to the insulation layer and tested for anti-sway and anti-impact performance in a simulated polar environment.

[0043] High-manganese steel possesses low-temperature toughness and a low coefficient of thermal expansion, enhancing structural stability at -162℃. Its cost is approximately 30% lower than Invar alloys or 9% nickel steel. The chemical composition of high-manganese steel includes C: 0.35~0.55wt%, Si: 0.10~0.50wt%, S: ≤0.005wt%, P: ≤0.02wt%, Ni: 0.20~0.30wt%, Cr: 3.00~4.00wt%, Mn: 22~25%, Cu: 0.30~0.70wt%, with the balance being Fe.

[0044] An application of a thick-film high-manganese steel corrugated sheet for polar LNG carriers is described. This sheet serves as the innermost layer of the LNG cargo protection system, acting as a primary barrier that directly contacts the LNG cargo. Below this primary barrier, a primary insulation layer composed of reinforced polyurethane foam and plywood is tightly attached. Further outwards is a secondary barrier, made of a composite material of glass cloth, aluminum foil, and resin film, which is ultimately connected to the ship's steel hull. This "closely attached to the hull + multi-layer composite" design maximizes the use of hull space, lowers the center of gravity, and reduces steel consumption.

[0045] Example 1

[0046] This embodiment provides a basic design and manufacturing method for thick-film high-manganese steel corrugated sheets for polar LNG carriers, emphasizing the material's low-temperature toughness and structural impact resistance to meet the LNG transportation needs in extreme environments such as the Arctic shipping route. This method achieves uniform forming and balanced stress distribution of the corrugated sheet by optimizing the high-manganese steel composition and the overall stamping process. The manufacturing steps are described in detail below:

[0047] (1) Material preparation: High-manganese steel plate with low-temperature certification is selected as the base material. The manganese content of the high-manganese steel plate is 22~25wt% to ensure excellent impact toughness and low coefficient of thermal expansion in an environment of -162℃ to -196℃. The chemical composition of the high-manganese steel is controlled as follows: C: 0.35~0.55wt%, Si: 0.10~0.50wt%, S: ≤0.005wt%, P: ≤0.02wt%, Ni: 0.20~0.30wt%, Cr: 3.00~4.00wt%, Cu: 0.30~0.70wt%, Mn: 22~25wt%, with the balance being Fe and unavoidable impurities.

[0048] The sheet material is 2mm thick, with a yield strength ≥400MPa, tensile strength 800~970MPa, elongation ≥22%, and impact absorption energy at -196℃ ≥27J. The high-manganese steel sheet is cut into rectangular blanks, 600mm in length and 600mm in width. This size references the standard corrugated sheet of the Mark III system, facilitating integration with polyurethane foam insulation. Laser cutting is used to ensure smooth, burr-free edges, avoiding stress concentration points. Material pretreatment includes heating to 1150~1200℃ and holding for 2~3 hours, initial rolling temperature ≥1100℃, final rolling temperature 830~850℃, water immersion temperature 790~810℃, and ultra-fast water cooling to room temperature to form an equiaxed austenitic microstructure, improving formability and low-temperature performance.

[0049] (2) Integral stamping: Using a hydraulic press equipped with a four-pointed star-shaped node mold 1 and a cross-arch mold, the high-manganese steel sheet blank is stamped in one pass using the cross-arch mold to form a longitudinal and transverse corrugated structure; then, the four-pointed star is used to stamp the intersection of the corrugations (protruding surface) to form a fourfold rotationally symmetrical star-shaped intersection node. The hydraulic press pressure is controlled at 60~120MPa, and the blank is heated to 250℃ to improve formability and avoid thickness reduction. Subsequently, a single stamping is performed to form a longitudinal and transverse corrugated structure with a corrugation height of 55mm, and a node with a four-pointed star at the center. Figure 1As shown, the node position adopts a four-pointed star design, with the inclined transition surface tangentially connected to the upper and lower planes to ensure no stress concentration. This process replaces the traditional multi-step forming, reduces cutting processes, and supports uniform thickness. During the stamping process, strain distribution is monitored to ensure optimized stress distribution at the corrugation intersections, improving anti-shaking ability. After forming, it is naturally cooled to room temperature to avoid residual thermal stress. Specific node dimensions: corrugation height is 55mm, corrugation width is 80mm; the arcs with different radii of curvature on the surface opening and the concave bottom surface, the outward convex arc segment has a curvature radius R1 of 7mm, the corresponding central angle of R1 is 123°, and the included angle θ1 is 57°; the inward concave arc segment has a curvature radius R2 of 5mm, the corresponding central angle of R2 is 33°, and the included angle θ2 of the top concave part is 147°; the surface opening and the concave bottom arc and their central angles are consistent, the plane width d1 at both ends of the surface opening is 95mm, and the plane width d2 at both ends of the inward concave bottom is 30mm. The depth of the four-pointed star-shaped nodes should match the height of the corrugations to ensure that the bottom surface of the nodes is on the same horizontal plane as the corrugated plate. Figure 4 and Figure 5 As shown.

[0050] (3) Quality Inspection: The sheet metal is inspected using an ultrasonic testing instrument to confirm that there are no cracks or deformations and that it meets the IMO liquefied natural gas membrane standards. Specific tests include tensile / impact tests at room temperature and -196°C, CTOD tests, fatigue SN curve analysis, and corrosion tests. X-ray flaw detection is also used to verify internal defects and ensure the integrity of the sheet metal. If minor unevenness is found, local repairs are carried out to avoid overall scrapping.

[0051] (4) Welding and Assembly: Align multiple stamped sheet metal pieces and perform laser welding along the linear lap joint. The welding speed should be controlled at 0.5~1m / min to ensure sealing. (See attached...) Figure 2 As shown, weld positions 1 and 2 follow a straight path, facilitating robot operation. Guide grooves are added at the nodes to improve automation accuracy. After welding, penetrant testing and vacuum leak detection are performed.

[0052] (5) System Integration: The corrugated board was assembled and bonded to the polyurethane foam insulation layer, and its anti-sway performance was tested in a simulated -162℃ polar environment. Low-temperature resistant adhesive was used for bonding to ensure that there were no air bubbles at the interface. The tests included fatigue analysis under vibration load, impact simulation, and thermo-fluid-structure interaction analysis.

[0053] like Figure 1 The structure and node locations of the thick-film high-manganese steel corrugated sheet are shown. The nodes feature a four-pointed star design, highlighting the curved transitions to alleviate stress concentration.

[0054] like Figure 2The image shows the linear welding paths at positions 5 and 6 of the longitudinal splice weld, as well as the details of the four-corner star-shaped node. The arc-shaped structure at the intersection of multiple corrugations simplifies the complexity of traditional nodes and facilitates automated welding.

[0055] like Figure 3 The structural relationship between the thick-film high-manganese steel layer, the node locations, and the insulation material layer is shown. The node locations adopt a four-pointed star-shaped node design, highlighting the arc transition to alleviate stress concentration. The insulation material layer is represented by a diagonal texture. The overall structure is designed for use in extremely low temperature environments.

[0056] Figure 6 To simulate the before-and-after deformation comparison, the displacement and stress distribution of the node under polar sway loads are displayed based on finite element analysis results. The comparison before and after deformation shows that the maximum displacement in the x and y directions is only 1.2~1.8mm (mainly concentrated at the intersection), far lower than the 3.5~5mm of traditional arc-shaped / W-shaped nodes. Stress is effectively released through the arc-shaped node, with peak stress controlled below 250MPa (lower than the yield strength of high-manganese steel, 400MPa), while the local stress of traditional nodes often reaches above 350MPa, easily leading to fatigue. This simulation result verifies the advantages of the four-pointed star-shaped node: optimized stress distribution, minimized deformation risk, and improved overall structural durability in extremely low-temperature environments.

[0057] The 2mm thick high-manganese steel corrugated plate with four-pointed star-shaped nodes, verified by ANSYS finite element simulation, exhibits excellent performance under typical polar LNG loads: under 7 bar hydrostatic pressure, the maximum von Mises stress is only 168 MPa, the maximum displacement is 0.72 mm, and the safety factor is 2.38; with swaying impact parameters set to 0.5g, the stress is 242 MPa and the displacement is 1.55 mm; under ice impact (50 J energy), the local stress is 265 MPa and the local displacement is 2.10 mm, with a post-impact structural recovery rate >95%. Compared with traditional Mark III stainless steel films, this invention reduces stress by 30-40% and displacement by more than 60%, fully meeting the IMO and CCS polar specifications and the requirements of 7 bar + swaying + ice impact composite loads at -196℃, while achieving approximately 30% cost reduction.

[0058] Example 2

[0059] (1) Material preparation: High-manganese steel plates with a manganese content of 22-25 wt% and a thickness of 2.5 mm were selected to cope with extreme ice environments. The chemical composition was the same as in Example 1, but microalloying elements such as Cr and Ni were added to improve low-temperature toughness. The plates were cut into rectangular billets with a length of 1000 mm and a width of 1000 mm. The pretreatment process was the same, but the final rolling temperature was adjusted to 820-840℃ to optimize the grain size.

[0060] (2) Integral stamping: The radius of curvature R1 of the outwardly convex arc segment is adjusted to 10mm, and the radius of curvature R2 of the inwardly concave arc segment with the surface opening is adjusted to 8mm. θ1, θ2 and their corresponding central angles remain unchanged from Example 1. d1 and d2 are reduced to 85mm and 25mm, respectively, to avoid the influence of the plate thickness on the arc size during stamping and reduce the processing difficulty. This adjustment adapts to different thickness requirements. As the plate thickness increases, the arc radii R1 and R2 need to be increased accordingly, while ensuring that θ1, θ2 and their corresponding central angles remain unchanged, and at the same time reducing the dimensions of d1 and d2. This step monitors the temperature gradient to ensure no thinning phenomenon. After forming, annealing is performed to release residual stress.

[0061] (3) Quality inspection: X-ray flaw detection combined with ultrasonic testing is used to verify the integrity of the board.

[0062] (4) Welding assembly: Align multiple stamped sheet metal pieces and perform laser welding along the linear lap joint. The welding speed is controlled at 0.5~1m / min to ensure sealing.

[0063] (5) System integration: After being connected to the insulation layer, an ice impact test was conducted in a simulated -196℃ environment. The test results showed that the deformation risk of the 2.5mm thick film was reduced by 25%~30% compared with that of the 2mm film. After the radius of the arc of the node structure was appropriately increased with the thickness of the high manganese steel plate, it still fully complied with the sloshing specification.

[0064] In summary, this invention forms a uniform corrugated and node structure through a single pressing process, reducing cutting and manual alignment steps, supporting automated welding, and enabling robotic linear welding throughout the entire process. Under polar sway loads, the x and y displacements of the thick-film high-manganese steel corrugated plate are controlled within the range of 1-2 mm, mainly concentrated at the intersections; stress is effectively released at the intersections, avoiding localized damage. In extremely low-temperature environments, stress distribution is optimized, deformation risk is minimized, and the overall structural durability is improved.

[0065] This embodiment is merely a further explanation of the present invention and is not intended to limit the present invention. Those skilled in the art can make non-inventive modifications to this embodiment as needed after reading this specification, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A thick-film high-manganese steel corrugated sheet for polar LNG ships, characterized in that, The device includes a high-manganese steel plate substrate plane, and a first protrusion and a second protrusion raised on the substrate plane. The first protrusion is arranged uniformly and parallelly along a first direction in the substrate plane, and the second protrusion is arranged uniformly and parallelly along a second direction perpendicular to the first direction in the substrate plane. A four-fold rotationally symmetric star-shaped node is pressed at the position where the first protrusion and the second protrusion intersect perpendicularly. The four-fold rotationally symmetric star-shaped node includes a surface opening and a recessed bottom surface. Both the surface opening and the recessed bottom surface are four-lobed symmetrical contours, which are composed of two alternating arcs with different radii of curvature. The width between the symmetrical lobes of the surface opening is greater than the width between the symmetrical lobes of the recessed bottom surface.

2. The thick-film high-manganese steel corrugated plate for polar LNG ships according to claim 1, characterized in that, The thickness of the high-manganese steel corrugated plate is 1.2~3mm; the manganese content of the high-manganese steel corrugated plate is 22wt%~25wt%.

3. The thick-film high-manganese steel corrugated plate for polar LNG ships according to claim 1, characterized in that, Both the first and second protrusions are arc-shaped protrusions, and the cross-section of the arc-shaped protrusion is a single-segment circular arc; the corresponding structural parameters of the first and second protrusions are the same; the distance between adjacent protrusions is 600~1000mm.

4. The thick-film high-manganese steel corrugated sheet for polar LNG ships according to claim 3, characterized in that, The vertical height H from the highest point of the arc-shaped protrusion to the base plane is 50~60mm, and the length L of a single arc-shaped protrusion is 75~85mm.

5. The thick-film high-manganese steel corrugated plate for polar LNG ships according to claim 1, characterized in that, The groove depth of the quadruple rotationally symmetric star node is equal to the height H of the first and second protrusions.

6. The thick-film high-manganese steel corrugated plate for polar LNG ships according to claim 1, characterized in that, The width d1 at both ends of the surface opening is 2.8 to 3.8 times the width d2 at both ends of the bottom plane; the surface opening and the recessed bottom surface are connected by an inclined transition surface; the connection between the inclined transition surface and the surface opening and the recessed bottom surface is set as a rounded transition or an angular transition; the included angle θ between the inclined transition surface and the recessed bottom surface and the surface opening is 110° to 115°; among the arcs with different radii of curvature, the radius of curvature R1 of the outwardly convex arc segment is 1.2 to 1.4 times the radius of curvature R2 of the inwardly concave arc segment.

7. The thick-film high-manganese steel corrugated sheet for polar LNG ships according to claim 6, characterized in that, The width d1 at both ends of the surface opening is 25~30mm, and the width d2 at both ends of the bottom plane is 85~95mm; among the arcs with different radii of curvature, the radius of curvature R1 of the outwardly convex arc segment is 5~10mm, and the radius of curvature R2 of the inwardly concave arc segment is 4~8mm; among the arcs with different radii of curvature, the central angle corresponding to the radius of curvature R1 of the outwardly convex arc segment is 120~130°, and the central angle corresponding to the radius of curvature R2 of the inwardly concave arc segment is 30~40°.

8. A method for preparing the thick-film high-manganese steel corrugated sheet for polar LNG ships according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Cut and pre-treat high manganese steel plates with a manganese content of 22wt%~25wt% to form an equiaxed austenitic microstructure; Step 2: Preheat the high manganese steel plate from Step 1, and then stamp it using a hydraulic press equipped with a four-corner star-shaped mold and a cross-shaped arch mold; Step 3: Align the multiple stamped high-manganese steel plates and perform laser welding along the linear lap joint.

9. The method for using thick-film high-manganese steel corrugated plates for polar LNG ships according to claim 8, characterized in that, In step 1, the material pretreatment is as follows: the high manganese steel plate is heated to 1150~1200℃ and held for 2~3 hours, the initial rolling temperature is ≥1100℃, the final rolling temperature is 830~850℃, the water immersion temperature is 790~810℃, and then cooled to room temperature by ultra-fast water cooling to form an equiaxed austenitic microstructure; in step 2, the preheating temperature is 200~300℃; the hydraulic press pressure is 60~120MPa.

10. The application of the thick-film high-manganese steel corrugated sheet for polar LNG ships as described in any one of claims 1 to 7, characterized in that, Membrane tanks used in the cargo holds of polar LNG ships serve as the innermost layer of the liquid cargo maintenance system, closely attached to the insulation layer, and can withstand hydrostatic pressures up to 7 bar.

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