Method for constructing a liquid cargo deck of an LNG carrier

Abstract

The application discloses a kind of LNG ship liquid cargo deck construction methods, the welding operation of stainless steel plate and carbon steel plate originally carried out on large group cradle is advanced to the stage of splicing plate, can effectively guarantee the continuity of large group operation on large group cradle, significantly reduce the cycle of cradle manufacturing of large group, while the original welding total length remains unchanged, by automatic welding in sequence according to order, T-shaped seam and cross seam formed between stainless steel plate and first carbon steel plate, butt joint seam in stainless steel plate, linear segment weld joint formed between first carbon steel plate and second carbon steel plate and stainless steel plate, round corner weld joint of stainless steel plate, butt joint seam between first carbon steel plate and second carbon steel plate, butt joint seam between first carbon steel plate and second carbon steel plate and third carbon steel plate, and butt joint seam between adjacent third carbon steel plate, can significantly shorten welding operation time, improve welding efficiency.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding technology, and in particular to a method for constructing a liquid cargo deck for an LNG carrier. Background Technology

[0002] One of the challenges in building LNG carriers is the welding of stainless steel plates in the liquid dome sections. The stainless steel used in these sections is 304L, with a thickness ranging from 16mm to 25mm, while the carbon steel used for the mating sections is Grade E, with a thickness ranging from 15mm to 20mm. Both are medium-thickness steel plates. For this area, LNG carriers typically use CO2 gas shielded welding, where the stainless steel and carbon steel plates are pieced together on a large assembly line and welded entirely by hand. This results in low welding speeds and inconsistent weld quality, often leading to multiple rework attempts.

[0003] The current shortcomings are: ① Due to the special nature of the material, stainless steel CO2 gas shielded welding has a low deposition rate and is difficult to weld. It takes an intermediate welder 10 minutes to weld a one-meter weld, and 6 to 8 welds are needed for a 16mm thick stainless steel plate. It takes two intermediate or higher welders 5 to 6 days to weld a stainless steel section of a deck, which takes up a long time.

[0004] ② Because it is a single-sided forming weld, the welding shrinkage is in one direction. Although there are clamps for fixation, there is still considerable welding deformation in the end. The liquid cargo tank surface has a flatness requirement of -4 to +3mm, which requires a large amount of straightening work.

[0005] ③ Stainless steel single-sided forming welding is more difficult to form than carbon steel single-sided forming welding. Even with skilled welders assigned to this area, the weld formation quality is inevitably poor, failing to meet process requirements. Often, sections need to be flipped over for rework, which is extremely difficult and involves repeated adjustments. Each section flip results in significant resource waste.

[0006] ④ Stainless steel welding defects, which is also the biggest pain point. Stainless steel welding defects are very difficult to repair. Sometimes, even after the defects have been cleaned out, the defects actually increase after welding. According to previous flaw detection data, the rework rate of stainless steel areas on the deck has reached more than 40%, and there are even cases where stainless steel rework exceeds 20 days, affecting the entire section construction cycle and the dock loading cycle. Summary of the Invention

[0007] In view of this, the present invention provides a method for constructing a liquid cargo deck for an LNG carrier, in order to solve the problems existing in the background art.

[0008] A method for constructing a liquid cargo deck on an LNG carrier specifically includes the following steps:

[0009] S1, in the component assembly area, stainless steel plates in a U-shape are spliced ​​together. First carbon steel plates are joined to the bow and stern sides of the stainless steel plates respectively, and second carbon steel plates are joined to the port and starboard sides of the stainless steel plates respectively. Multiple third carbon steel plates are joined to the bow sides of the first and second carbon steel plates. The joint between the second carbon steel plate on the port side and the two first carbon steel plates is aligned with the two joints inside the stainless steel plate. The joint between the second carbon steel plate on the starboard side and the two first carbon steel plates is staggered from the other two joints of the stainless steel plate. The joint between adjacent third carbon steel plates is aligned with the joint between the second carbon steel plate and the first carbon steel plate. The thickness of the stainless steel plate is 16mm-25mm, and the thickness of the first carbon steel plate is 15mm-20mm.

[0010] Then, V-shaped welding grooves are made at all the butt joints and tack welds are performed;

[0011] Then, the T-shaped seam and cross seam formed between the stainless steel plate and the first carbon steel plate, the butt joint inside the stainless steel plate, the straight section weld formed between the first carbon steel plate and the second carbon steel plate and the stainless steel plate, the weld at the rounded corner of the stainless steel plate, the butt joint between the first carbon steel plate and the second carbon steel plate, the butt joint between the first carbon steel plate and the second carbon steel plate and the third carbon steel plate, and the butt joint between adjacent third carbon steel plates are welded in sequence.

[0012] Then, the formed stainless steel area structure is turned over, and all welds are plasma arc gouged and ground. Then, the reverse side is welded in the same welding sequence as the front side.

[0013] After the reverse welding is completed, the flatness of the stainless steel area structure is measured, and any areas with excessive flatness are corrected. Once the correction is qualified, the material is sent to the FCB production line area.

[0014] S2, in the FCB production line area, the fourth carbon steel plate is welded to the stainless steel area structure, and then the longitudinal skeleton is welded on.

[0015] Preferably, in step S1, when tack welding is performed on the V-shaped weld grooves at all butt joints, the weld length of the tack weld is greater than 50mm, the weld height is less than 3mm, and the spacing between adjacent tack weld points is 300mm-500mm.

[0016] Preferably, in step S1, when welding the T-shaped seam formed between the stainless steel plate and the first carbon steel plate, CO2 gas shielded welding is used to perform a 150mm stepped weld from the joint between the stainless steel plate and the first carbon steel plate toward the first carbon steel plate and the third carbon steel plate.

[0017] When welding the cross-shaped seam between the stainless steel plate and the first carbon steel plate, CO2 gas shielded welding is used to weld 150mm in each of the four directions (front, back, left, and right) from the joint point between the stainless steel plate and the first carbon steel plate, with the arc ignition and extinguishing points of each layer staggered by 30mm-50mm.

[0018] Preferably, in step S1, when welding the butt joint inside the stainless steel plate, submerged arc welding is used.

[0019] Preferably, in step S1, when welding the straight section weld between the first carbon steel plate and the second carbon steel plate and the stainless steel plate, submerged arc welding is used to weld the joint between the first carbon steel plate and the stainless steel plate and the joint between the second carbon steel plate and the stainless steel plate, but the rounded corners of the stainless steel plate and the 100mm straight section connecting the rounded corners are left unwelded. Step welding is used at the joint, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm.

[0020] Preferably, in step S1, when welding the stainless steel plate at the rounded corner, CO2 gas shielded welding process is used.

[0021] When welding the butt joints between the first carbon steel plate and the second carbon steel plate, the butt joints between the first carbon steel plate and the second carbon steel plate and the third carbon steel plate, and the butt joints between adjacent third carbon steel plates, submerged arc welding is used.

[0022] Preferably, in step S1, mechanical flattening is used to correct the flatness deviation of the stainless steel area structure.

[0023] Preferably, in step S1, the flatness of the stainless steel area structure is controlled within ±3mm / m, and the length, width and diagonal length errors of the stainless steel area structure are controlled within ±3mm.

[0024] The beneficial effects of this invention are:

[0025] This invention moves the welding of stainless steel plates and carbon steel plates, originally performed on the assembly jig, to the plate assembly stage. This effectively ensures the continuity of assembly work on the assembly jig, significantly reducing the assembly cycle on the jig. Furthermore, while maintaining the original total welding length, it utilizes automated welding to sequentially weld the T-joints and cross joints between the stainless steel plate and the first carbon steel plate, the butt joints inside the stainless steel plate, the straight section welds between the first and second carbon steel plates and the stainless steel plate, the welds at the rounded corners of the stainless steel plate, the butt joints between the first and second carbon steel plates, the butt joints between the first and second carbon steel plates and the third carbon steel plate, and the butt joints between adjacent third carbon steel plates. This significantly shortens welding time, improves welding efficiency, reduces welding deformation and defects, and improves welding quality. Consequently, it reduces the rework rate in the stainless steel areas of the deck, greatly shortening the section construction cycle and the dock assembly cycle. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of a V-shaped welding bevel.

[0028] Figure 2 This is a schematic diagram showing the splicing of the first carbon steel plate, the second carbon steel plate, the third carbon steel plate, and the stainless steel plate.

[0029] The meanings of the labels in the diagram are as follows:

[0030] 1 is a stainless steel plate, 2 is a first carbon steel plate, 3 is a second carbon steel plate, 4 is a third carbon steel plate, 5 is a T-shaped seam, 6 is a cross seam, 7 is a butt joint inside the stainless steel plate, 8 is a straight section weld between the first and second carbon steel plates and the stainless steel plate, 9 is a weld at the rounded corner of the stainless steel plate, 10 is a butt joint between the first and second carbon steel plates, 11 is a butt joint between the first and second carbon steel plates and the third carbon steel plate, 12 is a butt joint between adjacent third carbon steel plates, and 13 is a fourth carbon steel plate. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0032] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0033] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information.

[0034] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0035] This invention provides a method for constructing a liquid cargo deck on an LNG carrier, specifically including the following steps:

[0036] S1, in the component panel area, splices the stainless steel area structure.

[0037] Specifically, it includes the following steps:

[0038] S11, Stainless steel plate 1 in the shape of a square is spliced ​​together. The stainless steel plate 1 in the shape of a square is spliced ​​together from four stainless steel plates, two of which are rectangular and the remaining two are U-shaped. The rectangular stainless steel plates are placed symmetrically on the bow and stern sides, and the U-shaped stainless steel plates are placed symmetrically on the port and starboard sides to form a stainless steel plate in the shape of a square. After the stainless steel plates are spliced ​​together, the inner edge of the stainless steel plates is fixed with a weight or clamp (no less than two clamps on each side).

[0039] Then, first carbon steel plates 2 are joined to the bow and stern sides of stainless steel plate 1, and second carbon steel plates 3 are joined to the port and starboard sides of stainless steel plate 1. Both bow and stern first carbon steel plates 2 are rectangular plates, but their widths are different, with the width of the stern first carbon steel plate 2 being greater than that of the bow first carbon steel plate 2. Both port and starboard second carbon steel plates 3 are U-shaped plates with the same dimensions. After the first carbon steel plates 2 and second carbon steel plates 3 are joined, the bow side of the first carbon steel plate on the bow side is flush with the bow side of the second carbon steel plate 3, and the joint between the second carbon steel plate 3 on the port side and the two first carbon steel plates 2 is aligned with the two joints inside stainless steel plate 1. The joint between the second carbon steel plate 3 on the starboard side and the two first carbon steel plates 2 is offset from the other two joints of stainless steel plate 1.

[0040] Then, multiple third carbon steel plates 4 are joined together on the bow sides of the first carbon steel plate 2 and the second carbon steel plate 3, with the joint between adjacent third carbon steel plates 4 aligned with the joint between the second carbon steel plate and the first carbon steel plate.

[0041] The stainless steel plate 1 has a thickness of 16mm-25mm, and all four corners of the stainless steel plate 1 are rounded. The first carbon steel plate 2 has a thickness of 15mm-20mm.

[0042] S12, make V-shaped welding grooves at all butt joints and perform tack welding.

[0043] The tack weld is placed inside the bevel. The length of the tack weld is greater than 50mm and the height is less than 3mm. The distance between adjacent tack welds is 300mm-500mm.

[0044] Among them, 308L welding wire is used for tack welding between stainless steel plates, 309L welding wire is used for tack welding between stainless steel plates and carbon steel plates, and 71NI welding wire is used for tack welding between carbon steel plates.

[0045] S13, sequentially weld the T-shaped seam 5 and cross seam 6 formed between the stainless steel plate 1 and the first carbon steel plate 2, the butt joint 7 inside the stainless steel plate, the straight section weld 8 formed between the first carbon steel plate 2 and the second carbon steel plate 3 and the stainless steel plate 1, the weld 9 at the rounded corner of the stainless steel plate, the butt joint 10 between the first carbon steel plate 2 and the second carbon steel plate 3, the butt joint 11 between the first carbon steel plate 2 and the second carbon steel plate 3 and the third carbon steel plate 4, and the butt joint 12 between adjacent third carbon steel plates 4.

[0046] When welding the T-shaped seam 5 formed between the stainless steel plate 1 and the first carbon steel plate 2, CO2 gas shielded welding is used to perform a 150mm stepped weld from the joint point between the stainless steel plate 1 and the first carbon steel plate 2 toward the first carbon steel plate 2 and the third carbon steel plate 4. The arc ignition and extinguishing points of each layer are staggered by 30mm-50mm, and 71NI welding wire is used as the welding material.

[0047] When welding the cross joint 6 formed between the stainless steel plate 1 and the first carbon steel plate 2, CO2 gas shielded welding is used to weld 150mm in each of the four directions (front, back, left, and right) from the joint point between the stainless steel plate 1 and the first carbon steel plate 2. The arc ignition and extinguishing points of each layer are staggered by 30mm-50mm. 71NI welding wire is selected as the welding material.

[0048] When welding the butt joint 7 inside the stainless steel plate, the submerged arc welding process is used, and the welding material is GWS-308L / GXS-300 welding wire.

[0049] When welding the straight section weld 8 formed between the first carbon steel plate 2 and the second carbon steel plate 3 and the stainless steel plate 1, submerged arc welding is used to weld the joint between the first carbon steel plate 2 and the stainless steel plate 1, and the joint between the second carbon steel plate 3 and the stainless steel plate 1. However, the rounded corners of the stainless steel plate 1 and the 100mm straight section connecting the rounded corners are left unwelded. Step welding is used at the joint, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm. Avesta309L / Flux805 welding wire is selected as the welding material.

[0050] When welding the stainless steel plate at the rounded corner of weld seam 9, CO2 gas shielded welding process is used, and 309L welding wire is selected as the welding material.

[0051] When welding the butt joint 10 between the first carbon steel plate 2 and the second carbon steel plate 3, the butt joint 11 between the first carbon steel plate 2 and the second carbon steel plate 3 and the third carbon steel plate 4, and the butt joint 12 between adjacent third carbon steel plates 4, the submerged arc welding process is used for welding, and GLES-44 / SJ101A welding wire is selected as the welding material.

[0052] S14 involves flipping the formed stainless steel area structure over, performing plasma arc gouging and grinding on all welds, and then welding the reverse side in the same welding sequence as the front side welding.

[0053] After the reverse welding is completed, the flatness of the stainless steel area structure is measured, and any areas with excessive flatness are corrected. Once the flatness is corrected and the area is qualified, it is sent to the FCB production line area.

[0054] Mechanical flattening was used to correct the flatness deviations of the stainless steel area structure.

[0055] The flatness of the stainless steel area structure is controlled within ±3mm / m, and the length, width and diagonal length errors of the stainless steel area structure are controlled within ±3mm.

[0056] S2, in the FCB production line area, the fourth carbon steel plate 13 is spliced ​​and welded to the stainless steel area structure, and then the longitudinal skeleton is welded on.

[0057] Due to the special nature of the stainless steel plates used in LNG carriers, which are exposed to environments below -20°C for extended periods, it is crucial to prevent contamination from carbon, oil, and other impurities. Simultaneously, it is essential to control the deformation of the assembled plates, as this could affect the installation of insulation boxes in the cargo hold area of ​​the LNG carrier. Therefore, before welding, the bevels and surfaces of the stainless steel plates must be cleaned to remove rust. The weld surface must be protected with lime water before welding. Welding operations must be strictly performed according to the aforementioned welding procedures. Self-inspection and mutual inspection, as well as process records, must be conducted during welding. All welds must be symmetrically welded to minimize welding deformation.

[0058] In the component assembly area, after the stainless steel plates are welded, the flatness of the weld seam is controlled within ±3mm / m, and the length, width, and diagonal after welding are controlled within ±3mm. After the component assembly weld seam is completed, non-destructive testing is performed. Only after the weld seam is free of defects is it transported to the FCB production line area for the next welding step. If the flatness, main dimensions, or non-destructive testing are not up to standard, relevant process methods are adopted for correction.

[0059] When the flatness of the stainless steel plate exceeds the standard and needs to be repaired, hot work is generally prohibited. Uncontrolled hot work can easily cause carbonization, significantly reducing the mechanical properties of the stainless steel and potentially leading to disastrous consequences for LNG transportation. Mechanical flattening can be used to level the stainless steel plate.

[0060] When repairing welds that fail flaw detection, plasma arc gouging should be used to remove the weld seams. Carbon gouging is prohibited because it can also cause stainless steel to carburize. After plasma arc gouging, stainless steel grinding discs should be used to clean the weld bead, removing all debris and polishing it to reveal the metallic luster of the stainless steel plate before proceeding with further repairs.

[0061] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method of constructing a cargo deck of an LNG carrier, characterized by, Specifically comprising the following steps: S1, in the component panel area, splice the back-shaped stainless steel plate (1), respectively butt joint the first carbon steel plate (2) on the bow and stern side of the stainless steel plate (1), respectively butt joint the second carbon steel plate (3) on the left and right side of the stainless steel plate (1), butt joint multiple third carbon steel plates (4) on the bow side of the first and second carbon steel plates (2) and (3), wherein the butt joint seam between the second carbon steel plate on the left side and the two first carbon steel plates is aligned with the two butt joint seams inside the stainless steel plate, the butt joint seam between the second carbon steel plate on the right side and the two first carbon steel plates is staggered with the other two butt joint seams of the stainless steel plate, the butt joint seam between adjacent third carbon steel plates (4) is aligned with the butt joint seam between the second carbon steel plate and the first carbon steel plate, the thickness of the stainless steel plate (1) is 16-25mm, and the thickness of the first carbon steel plate (2) is 15-20mm. Then, open V-shaped welding grooves at all butt joints and perform positioning welding. Then, weld the T-shaped seam (5) and the cross seam (6) formed between the stainless steel plate (1) and the first carbon steel plate (2), the butt joint seam (7) inside the stainless steel plate, the straight line seam (8) formed between the first and second carbon steel plates (2) and (3) and the stainless steel plate (1), the fillet weld (9) at the rounded corner of the stainless steel plate, the butt joint seam (10) between the first and second carbon steel plates (2) and (3), the butt joint seam (11) between the first and second carbon steel plates (2) and (3) and the third carbon steel plate (4), and the butt joint seam (12) between adjacent third carbon steel plates (4) in sequence. Then, turn over the formed stainless steel area structure, after plasma arc planing and polishing of all welds, perform reverse welding in the same welding sequence as the front welding. After the reverse welding is completed, measure the flatness of the stainless steel area structure, correct the positions with excessive flatness, and send to the FCB flow line area after the correction is qualified. S2, in the FCB flow line area, splice and weld the fourth carbon steel plate (13) with the stainless steel area structure, and then weld the longitudinal rib.

2. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, when positioning welding is performed on the V-shaped welding grooves at all butt joints, the weld length of the positioning welding is greater than 50mm, the weld height is less than 3mm, and the spacing between adjacent positioning welding points is 300-500mm.

3. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, when welding the T-shaped seam (5) formed between the stainless steel plate (1) and the first carbon steel plate (2), CO2 gas shielded welding is used to perform step welding 150mm from the butt joint of the stainless steel plate (1) and the first carbon steel plate (2) to the direction of the first carbon steel plate (2) and the third carbon steel plate (4). When welding the cross seam (6) between the stainless steel plate (1) and the first carbon steel plate (2), CO2 gas shielded welding is used to perform step welding 150mm in four directions of front, back, left and right from the butt joint of the stainless steel plate (1) and the first carbon steel plate (2), and the arc extinguishing points of each layer are staggered by 30-50mm.

4. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, when welding the butt joint seam (7) inside the stainless steel plate, submerged arc welding process is used for welding.

5. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, when welding the linear segment weld joint (8) formed between the first carbon steel plate (2) and the second carbon steel plate (3) and the stainless steel plate (1), the joint between the first carbon steel plate (2) and the stainless steel plate (1) and the joint between the second carbon steel plate (3) and the stainless steel plate (1) are welded by using submerged arc welding, but the fillet of the stainless steel plate (1) and the 100mm linear segment connecting the fillet are not welded, and the joint is welded by using step welding, and the arc extinguishing points of each layer are staggered by 30mm-50mm.

6. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, when welding the weld joint (9) at the fillet of the stainless steel plate, CO2 gas shielded welding process is used for welding. When welding the butt joints (10) between the first carbon steel plate (2) and the second carbon steel plate (3), the butt joints (11) between the first carbon steel plate (2) and the second carbon steel plate (3) and the third carbon steel plate (4), and the butt joints (12) between adjacent third carbon steel plates (4), submerged arc welding process is used for welding.

7. The LNG carrier cargo deck construction method according to claim 1, characterized by, In step S1, the mechanical flattening method is used to correct the positions where the flatness of the stainless steel area structure exceeds the tolerance.

8. The LNG carrier cargo deck construction method according to claim 1 or 7, characterized by, In step S1, the flatness of the stainless steel area structure is controlled within ±3mm / m, and the length, width and diagonal length error of the stainless steel area structure is controlled within ±3mm.

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