Method for assembling and positioning low-temperature pipe of large LNG (Liquefied Natural Gas) transport ship

Abstract

A large LNG transport ship low-temperature pipe assembling and positioning method includes the steps that in the low-temperature pipe unit manufacturing and unit butt joint stage, a plurality of target tools are arranged at all pipe openings at equal intervals, a space coordinate system of a single datum point is established, the coplanarity of pipe end openings can be calibrated through positioning information of all target points, and the positioning precision of the low-temperature pipes is improved; meanwhile, the axis three-dimensional coordinates of a plurality of pipe orifices at the end part of the pipe unit are accurately calculated. Before unit butt joint, the position information of the adjacent low-temperature pipe units is measured and calculated through the same method, virtual butt joint of all the units is achieved under a single space coordinate system through coordinate system conversion, the position adjustment of the closing opening of the low-temperature pipe units is completed before closing, and the construction efficiency is improved. The clamping type design is adopted, and the problem that traditional magnetic target paper cannot be attracted due to the weak magnetism characteristic of a low-temperature tube is solved. The application range of the target tool can cover the low-temperature stainless steel pipe with the pipe diameter phi ranging from 100 mm to 762 mm and the wall thickness ranging from 3.4 mm to 30 mm to be used for positioning the low-temperature stainless steel pipe. The assembly precision and the construction efficiency of the special-shaped pipe unit of the LNG transport ship can be improved.

Description

Technical Field

[0001] This invention belongs to the field of LNG ship design and construction with sails, and specifically relates to a method for assembling and positioning cryogenic pipes on a large LNG carrier. Background Technology

[0002] LNG carriers feature a complex and extensive cryogenic piping system on their decks, known as the Cargo Handling System. This system is used for LNG cargo loading and unloading operations and for controlling cargo tank pressure during navigation. It primarily includes liquid phase piping, gas phase piping, volatile gas piping, and tank cleaning spray piping. Due to the presence of ultra-low temperature media in the piping, extremely high welding quality is required. Alignment and assembly precision control of welded components are crucial for ensuring welding quality. Currently, LNG carrier cryogenic piping typically employs modular design and construction, dividing the cargo handling system into several cryogenic piping units. After each unit is fabricated, it must be joined and assembled on the ship's deck. Each unit contains multiple cargo systems, resulting in a complex and irregular structure. Adjacent cryogenic piping units have multiple connection points, requiring simultaneous positioning and alignment of these multiple cryogenic ports during unit fabrication and assembly, making the unit assembly and positioning work quite challenging. The traditional construction method involves placing two adjacent pipe units in close proximity, using a plumb bob to locate the center of the pipe opening, and then adjusting the closure one by one to achieve centering. This method is limited by the selection of the plumb bob position and can only be used for a single pipe opening, making it impossible to locate the positions of multiple pipe openings simultaneously. This results in long positioning time and repeated adjustments to the closure during the closure process of low-temperature pipe units, leading to low construction efficiency. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for assembling and positioning cryogenic pipes on large LNG carriers, aiming to achieve rapid positioning and closure of two adjacent cryogenic pipe units. The technical solution adopted is as follows: A method for assembling and positioning cryogenic pipes for large LNG carriers, wherein the cryogenic pipe unit has multiple pipe openings at both ends, and a set of targets is fixed at each pipe opening. The set of targets consists of three targets, which are equally spaced along the circumference of the pipe opening. The three targets are denoted as A, B, and C, and the targets and pipe openings are located on the same plane.

[0004] A total station is placed on the ground. The position of the total station can measure all the targets on all pipe openings. Combined with the ground survey line, the X-axis is taken as the axial direction of the pipe, the Y-axis is the horizontal direction of the pipe perpendicular to the axial direction of the pipe, and the Z-axis is the vertical direction to establish a coordinate system.

[0005] The spatial coordinates of each target point are measured using a total station. The spatial coordinates of a single pipe opening target are denoted as A(x1,y1,z1), B(x2,y2,z2), and C(x3,y3,z3). Based on the spatial coordinates of points A, B, and C, the axial center position coordinates O(x0,y0,z0) of the pipe opening end are obtained through formulas (1), (2), and (3).

[0006] (1) (2) (3) Because calculating the center of a circle from three points in space is quite complex, the above formula includes process parameters A1, B1, C1, D1, A2, B2, C2, D2, A3, B3, C3, and D3, which have no actual physical meaning. A1=y1z2–y2z1–y1z3+y3z1+y2z3–y3z2; B1=-(x1z2–x2z1–x1z3+x3z1+x2z3–x3z2); C1=x1y2–x2y1–x1y3+x3y1+x2y3–x3y2; D1 = -(x1y2z3 – x1y3z2 – x2y1z3 + x2y3z1 + x3y1z2 – x3y2z1); A2 = 2(x2 – x1); B2=2(y2–y1); C2=2(z2–z1); D2=x1 ² +y1 ² +z1 ² -x2 ² –y2 ² –z2 ² ; A3 = 2(x3 – x1); B3 = 2(y3 – y1); C3=2(z3–z1); D3=x1 2 +y1 2 +z1 2 -x3 2 -y3 2 -z3 2 ; After calculating the axial center coordinates O of each pipe opening, adjacent cryogenic pipe units are docked and joined together. One cryogenic pipe unit is a fixed reference section, and the other cryogenic pipe unit is the docking section. By referring to the axial center coordinates of each docking opening of the reference section, the corresponding docking opening positions of the docking section are adjusted one by one to make the corresponding position coordinates of the docking openings of the two cryogenic pipe units consistent, thereby realizing the simulated positioning and rapid assembly of the LNG carrier's irregularly shaped pipe units.

[0007] In the above-mentioned method for assembling and positioning cryogenic pipes for large LNG carriers, preferably, the target is fixed at the pipe opening by a clamping component. The main body of the clamping component is a U-shaped groove, the pipe opening wall is inserted into the U-shaped groove and fixed by bolts. The outer groove wall of the U-shaped groove has an arc that matches the pipe opening wall, and the bolt passes through the inner groove wall of the U-shaped groove and presses against the inner wall of the pipe opening.

[0008] In the above-mentioned method for assembling and positioning cryogenic pipes on a large LNG carrier, preferably, the end openings of the cryogenic pipe units are of different sizes.

[0009] In the above-mentioned method for assembling and positioning cryogenic pipes for large LNG carriers, preferably, when the coordinates of the axial position of the fixed section pipe opening are inconsistent with the coordinates of the corresponding axial position of the docking section pipe opening, a hand-cranked hoist is used to pull the docking section so that its coordinates are consistent with the coordinates of the corresponding position of the fixed section's closing opening.

[0010] In the above-mentioned method for assembling and positioning cryogenic pipes on a large LNG carrier, preferably, multiple bolts pass through the wing plates of the U-shaped main body.

[0011] In the above-mentioned method for assembling and positioning cryogenic pipes for large LNG carriers, preferably, the target is fixed to the outer surface of the clamping component by a target base and is set perpendicular to the clamping component.

[0012] Compared to traditional methods such as plumb bob and bottom-point measurement to deduce axis coordinates, this invention avoids positioning errors caused by placement errors of the plumb bob and single-point target, thus improving measurement accuracy. Target fixation using fasteners overcomes the problem of weak magnetism in the low-temperature stainless steel pipes used in LNG carriers preventing the magnetic target paper from adhering. By establishing a spatial coordinate system with a single reference point, the spatial coordinates of the center points of multiple pipe fitting joints within a non-standard pipe unit can be measured simultaneously without moving the total station. By comparing the spatial coordinates of the interfaces between adjacent pipe units, the simulated mounting and rapid assembly of non-standard pipe units for LNG carriers can be achieved. Attached Figure Description

[0013] Figure 1 This is a schematic diagram showing a set of targets installed at the nozzle. Figure 2 This is a schematic diagram of the base section structure; Figure 3 This is a schematic diagram of the docking section structure; Figure 4 This is a schematic diagram of the merging structure of the reference section and the docking section. Detailed Implementation

[0014] The invention will be further described with reference to the accompanying drawings.

[0015] A method for assembling and positioning cryogenic pipes on a large LNG carrier, wherein the cryogenic pipe unit has multiple openings at both ends, and a set of targets is fixed at each opening, such as... Figure 1 As shown, a set of targets consists of three targets, which are equally spaced along the circumference of the pipe opening. The three targets are denoted as A, B, and C, and the targets and the pipe opening are located on the same plane.

[0016] A total station is placed on the ground. The position of the total station can measure all the targets on all pipe openings. Combined with the ground plot, the X-axis is taken as the axial direction of the pipe, the Y-axis is the horizontal direction of the pipe perpendicular to the axial direction of the pipe, and the Z-axis is the vertical direction to establish a coordinate system. The spatial coordinates of each target point are measured using a total station. The spatial coordinates of a single pipe opening target are denoted as A(x1,y1,z1), B(x2,y2,z2), and C(x3,y3,z3). Based on the spatial coordinates of points A, B, and C, the axial center position coordinates O(x0,y0,z0) of the pipe opening end are obtained through formulas (1), (2), and (3).

[0017] (1) (2) (3) Because calculating the center of a circle from three points in space is quite complex, the above formula includes process parameters A1, B1, C1, D1, A2, B2, C2, D2, A3, B3, C3, and D3, which have no actual physical meaning. A1=y1z2–y2z1–y1z3+y3z1+y2z3–y3z2; B1=-(x1z2–x2z1–x1z3+x3z1+x2z3–x3z2); C1=x1y2–x2y1–x1y3+x3y1+x2y3–x3y2; D1 = -(x1y2z3 – x1y3z2 – x2y1z3 + x2y3z1 + x3y1z2 – x3y2z1); A2 = 2(x2 – x1); B2=2(y2–y1); C2=2(z2–z1); D2=x1 ² +y1 ² +z1² -x2 ² –y2 ² –z2 ² ; A3 = 2(x3 – x1); B3 = 2(y3 – y1); C3=2(z3–z1); D3=x1 2 +y1 2 +z1 2 -x3 2 -y3 2 -z3 2 .

[0018] After calculating the axial center coordinates O of each pipe opening, adjacent cryogenic pipe units are docked and joined together. One cryogenic pipe unit is a fixed reference section, and the other cryogenic pipe unit is the docking section. By referring to the axial center coordinates of each docking opening of the reference section, the corresponding docking opening positions of the docking section are adjusted one by one to make the corresponding position coordinates of the docking openings of the two cryogenic pipe units consistent, thereby realizing the simulated positioning and rapid assembly of the LNG carrier's irregularly shaped pipe units.

[0019] like Figure 2 As shown, the ZD22-A unit of the actual ship is used as a fixed reference section, such as... Figure 3 As shown, the ZD22-B unit is the docking section, with a total of 8 closure joints (O1 to O8) at the beginning of the reference section. A total station is set up near the unit and the spatial coordinate zero point is set.

[0020] Three targets are installed on each closure opening. The coordinates of the target center (A1, B1, C1) of the O1 pipe opening are measured. The coordinates of the axial center position O1 of the pipe opening are calculated using formulas (1)(2)(3).

[0021] coordinate X Y Z A1 1617 280 2534 A2 1618 482 2878 A3 1618 174 2658 o1 1618 366 2715 Using this method, the center coordinates of the eight closure pipe openings were obtained, as shown in the table below: X Y Z O1 1618 366 2715 O2 1610 186 2715 O3 1610 -14 2730 O4 1608 191 2418 O5 1610 -480 2622 O6 1610 -1605 2714 O7 1610 -2470 2486 O8 1610 -3280 2709 Using the same method, the coordinates of the center of each closure joint at the tail of the ZD22-B docking section were measured, as shown in the table below: X Y Z O1’ 1119 864 2713 O2’ 1110 686 2715 O3’ 1110 486 2730 O4’ 1108 693 2418 O5’ 1110 22 2622 O6’ 1114 -1106 2714 O7’ 1110 -1970 2487 O8’ 1110 -2780 2709 By transforming the coordinates, using point O1 of the reference segment ZD22-A as the origin, the coordinates of the two cryogenic tube units are converted into a single coordinate system, as shown in the table below: By comparing the coordinates of each pipe opening in the two sets of cryogenic tube units, the position of the ZD22-B unit's pipe opening is adjusted using a traction device such as a hand-operated hoist to align with the coordinates of the reference section. For example, at point O1, the closing opening of the ZD22-B unit O1' needs to be adjusted 1mm in the negative X-axis direction. This process is repeated until all closing openings are adjusted, thus completing the virtual overlap between the closing unit and the reference unit. The unit closing work can then commence, saving time spent adjusting the pipe openings on-site.

Claims

1. A method for positioning cryogenic pipe assemblies of a large LNG carrier, characterized in that, the cryogenic pipe unit has a plurality of pipe openings at both ends, a set of targets is fixed at each pipe opening, the number of targets in a set is three, the three targets are arranged at equal intervals along the circumference of the pipe opening, the three targets are respectively marked as A, B and C, and the targets and the pipe opening are located in the same plane; a total station is placed on the ground, the position of the total station can measure all the targets on all the pipe openings, combined with the ground sample line, the X axis is taken as the axial direction of the pipe, the Y axis is taken as the horizontal direction perpendicular to the axial direction of the pipe, and the Z axis is taken as the vertical direction to establish a coordinate system; the spatial coordinates of each target point are measured by the total station, the spatial coordinates of the targets of a single pipe opening are respectively marked as A(x1, y1, z1), B(x2, y2, z2) and C(x3, y3, z3), and the coordinates of the axial center of the end of the pipe opening are obtained through formulas (1), (2) and (3) according to the spatial coordinates of points A, B and C; (1) (2) (3) wherein, A1 = y1z2 - y2z1 - y1z3 + y3z1 + y2z3 - y3z2; B1 = -(x1z2 - x2z1 - x1z3 + x3z1 + x2z3 - x3z2); C1 = x1y2 - x2y1 - x1y3 + x3y1 + x2y3 - x3y2; D1 = -(x1y2z3 - x1y3z2 - x2y1z3 + x2y3z1 + x3y1z2 - x3y2z1); A2 = 2(x2 - x1); B2 = 2(y2 - y1); C2 = 2(z2 - z1); D2 = x1 ² + y1 ² + z1 ² - x2 ² - y2 ² - z2 ² ; A3 = 2(x3 - x1); B3 = 2(y3 - y1); C3 = 2(z3 - z1); D3 = x1 2 + y1 2 + z1 2 - x3 2 - y3 2 - z3 2 ; after the axial center coordinates of each pipe opening are obtained through calculation, the adjacent two cryogenic pipe units are butted and folded, one of the two cryogenic pipe units is a fixed reference section, and the other is a butt section, the axial center coordinates of the folding openings of the reference section are compared, the positions of the corresponding folding openings of the butt section are adjusted one by one, the corresponding position coordinates of the folding openings of the two cryogenic pipe units are made consistent, the simulation positioning and rapid folding assembly of the special pipe unit of the LNG carrier are realized.

2. A method of positioning cryogenic piping assemblies for a large LNG carrier as defined in claim 1, wherein The targets are fixed at the pipe openings by clamping members, the main body of the clamping member is a U-shaped groove, the pipe opening wall is inserted into the U-shaped groove, and the U-shaped groove is fixed by bolts, the outer groove wall of the U-shaped groove has an arc matched with the pipe opening wall, and the bolts pass through the inner groove wall of the U-shaped groove and are in contact with the inner wall of the pipe opening.

3. The method of claim 1, wherein, The sizes of the pipe openings at the ends of the cryogenic pipe unit are different.

4. The method of claim 1, wherein, When the axial center coordinates of the pipe opening of the fixed section and the corresponding pipe opening of the butt section are inconsistent, the butt section is pulled by a hand-operated hoist to make the corresponding position coordinates of the folding openings of the fixed section and the butt section consistent.

5. The method of claim 2, wherein, There are a plurality of bolts passing through the wings of the U-shaped main body.

6. The method of positioning cryogenic piping assemblies for a large LNG carrier of claim 2, wherein, The targets are fixed on the outer surface of the clamping member by target bases, and are arranged perpendicularly to the clamping member.

Images