Liquefied natural gas (LNG) ship gas dome deck construction method

Abstract

The invention discloses an LNG (liquefied natural gas) ship dome deck building method, which is characterized in that the original welding operation of a stainless steel plate and a carbon steel plate on a large-group jig frame is advanced to a plate splicing stage, so that the continuity of the operation of a large group on the large-group jig frame can be effectively ensured, and the manufacturing period of the large group on the jig frame is obviously reduced; meanwhile, on the basis that the original total welding length is kept unchanged, a T-shaped seam, a bow and stern welding seam, a longitudinal welding seam, a stainless steel plate fillet welding seam and a carbon steel butt seam which are formed between the stainless steel plate and the first carbon steel plate are sequentially welded through automatic welding, the welding operation time can be remarkably shortened, the welding efficiency is improved, and the production cost is reduced. Meanwhile, welding deformation and welding defects can be reduced, the welding quality is improved, and therefore the repair rate of a deck stainless steel area is reduced, and the segmented construction period and the dock carrying period are greatly shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of ship construction, and in particular to a method for constructing an air dome deck of an LNG ship. Background Art

[0002] One of the difficulties in building LNG carriers is the welding of stainless steel plates in the gas dome sections. The stainless steel material of the gas dome sections is 304L, with a thickness of 16mm to 25mm. The carbon steel material for the gas dome sections is E-grade, with a thickness of 15mm to 20mm. Both are medium-thickness steel plates. For this area, LNG carriers use CO2 gas shielded welding. In the large group position, stainless steel plates and carbon steel plates are assembled and welded manually. The welding speed of manual welding is low, and the welding quality cannot be well controlled, and multiple repairs are often required.

[0003] The shortcomings of current manual welding are:

[0004] 1. CO2 gas shielded welding of stainless steel, due to the special nature of the material, has a low welding deposition rate and is difficult to weld. It takes 10 minutes for an intermediate welder to weld a one-meter weld. A 16mm thick stainless steel plate requires 6 to 8 passes. Two intermediate or above welders need 5 to 6 days to weld a stainless steel section of a deck, which takes a long period of time.

[0005] 2. Due to the single-sided forming welding, the welding shrinkage is in one direction. Although it is fixed by the card, there is still a lot of welding deformation in the end. The flatness of the liquid cargo tank surface is required to be -4mm~+3mm, and the workload of correction is large;

[0006] 3. Stainless steel single-sided forming welding is more difficult than carbon steel single-sided forming welding. Welding in this area has been performed by skilled welders, but it is inevitable that the quality of the weld forming layer is poor and does not meet the process requirements. It is often necessary to turn over the sections for repair, because the difficulty of repairing the sections is quite high, and it will also cause repeated trimming and turning over the sections, resulting in a waste of resources in many aspects.

[0007] 4. Stainless steel welding defects, which is also the biggest pain point, are very difficult to repair. Sometimes, even after all the defects are removed, more defects may occur after welding. According to previous statistics of flaw detection data, the repair rate of stainless steel area on deck has reached more than 40%, and there are even cases where stainless steel repairs take more than 20 days, which seriously affects the entire block construction period and dock loading period. Summary of the invention

[0008] In view of this, the present invention provides a method for constructing an LNG ship gas dome deck to solve the problems existing in the above-mentioned background technology.

[0009] A method for constructing a gas dome deck of an LNG ship, comprising the following steps:

[0010] S1, in the component panel area, four first carbon steel plates are butt-jointed around the stainless steel plate, wherein two first carbon steel plates are butt-jointed at the bow and stern sides of the stainless steel plate, and the remaining two first carbon steel plates are butt-jointed at the port and starboard sides of the stainless steel plate, the width of the two first carbon steel plates butt-jointed at the bow and stern sides of the stainless steel plate is less than the width of the stainless steel plate, the length of the two first carbon steel plates butt-jointed at the port and starboard sides of the stainless steel plate is equal to the sum of the length of the stainless steel plate and the length of the two first carbon steel plates butt-jointed at the bow and stern sides of the stainless steel plate, the thickness of the stainless steel plate is 16mm-25mm, and the thickness of the first carbon steel plate is 15mm-20mm;

[0011] Then, a V-shaped welding groove is formed at the joint between the stainless steel plate and the first carbon steel plate and positioning welding is performed;

[0012] Then, the T-shaped seam, the bow and stern welds, the longitudinal welds, the welds at the rounded corners of the stainless steel plate and the carbon steel butt seams formed between the stainless steel plate and the first carbon steel plate are welded in sequence;

[0013] Then, the formed stainless steel area structure is turned over, and after all welds are plasma arc planed and polished, the reverse side welding is carried out in the same welding sequence as the front side welding;

[0014] After the reverse side welding is completed, the flatness of the stainless steel area structure is measured, and the position where the flatness exceeds the tolerance is corrected. After the correction is qualified, it is sent to the FCB assembly line area;

[0015] S2, in the FCB assembly line area, the second carbon steel plate is welded to the stainless steel area structure, and then the longitudinal bones are welded.

[0016] Preferably, in step S1, when tack welding is performed on the V-shaped welding groove between the stainless steel plate and the first carbon steel plate, the weld length of the tack welding is greater than 50 mm, the weld height is less than 3 mm, and the spacing between adjacent tack welding points is 300 mm-500 mm.

[0017] Preferably, in step S1, when welding the T-seam formed between the stainless steel plate and the first carbon steel plate, CO2 gas shielded welding is used to perform step welding 150mm from the butt joint of the stainless steel plate and the first carbon steel plate toward the first carbon steel plate, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm.

[0018] Preferably, in step S1, when welding the bow and stern welds formed between the stainless steel plate and the first carbon steel plate, submerged arc welding is used to weld the joints between the bow and stern sides of the stainless steel plate and the corresponding first carbon steel plate, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, but the fillet of the stainless steel plate and the 100mm straight line segment connecting the fillet are retained without welding.

[0019] Preferably, in step S1, when welding the longitudinal weld formed between the stainless steel plate and the first carbon steel plate, submerged arc welding is used to weld the seams between the left and right sides of the stainless steel plate and the corresponding first carbon steel plate, and the weld extends 100mm-150mm toward the first carbon steel plate located at the bow and stern sides, but the fillet of the stainless steel plate and the 100mm straight line segment connecting the fillet are retained.

[0020] Preferably, in step S1, CO2 gas shielded welding is used to weld the weld at the fillet of the stainless steel plate;

[0021] Submerged arc welding is used to weld the carbon steel butt joints between adjacent first carbon steel plates.

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

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

[0024] The beneficial effects of the present invention are:

[0025] The present invention advances the welding operation of the stainless steel plate and the carbon steel plate originally carried out on the large assembly tire frame to the splicing stage, which can effectively ensure the continuity of the large assembly operation on the large assembly tire frame, significantly reduce the tire production cycle of the large assembly, and at the same time, on the basis of keeping the original total welding length unchanged, the T-seam, bow and stern welds, longitudinal welds, welds at the rounded corners of the stainless steel plate and the carbon steel butt seam formed between the stainless steel plate and the first carbon steel plate are welded in sequence by automatic welding, which can significantly shorten the welding operation time and improve the welding efficiency, and also reduce the welding deformation and welding defects, improve the welding quality, thereby reducing the rework rate of the stainless steel area of ​​the deck, and greatly shortening the segmented construction period and the dock loading period. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a structural schematic diagram of a V-shaped welding groove.

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

[0029] The meanings of the numbers in the figure are:

[0030] 1 is a stainless steel plate, 2 is a first carbon steel plate, 3 is a T-seam, 4 is a bow and stern weld, 5 is a longitudinal weld, 6 is a weld at a rounded corner of the stainless steel plate, 7 is a carbon steel butt joint, and 8 is a second carbon steel plate. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

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

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

[0034] The present application is further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0035] The present invention provides a method for constructing a gas dome deck of an LNG ship, which specifically comprises the following steps:

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

[0037] Specifically, the steps include:

[0038] S11, butt-join four first carbon steel plates 2 around the stainless steel plate 1, wherein two first carbon steel plates 2 are butt-jointed at the bow and stern sides of the stainless steel plate 1, and the remaining two first carbon steel plates 2 are butt-jointed at the port and starboard sides of the stainless steel plate 1,

[0039] The width of the two first carbon steel plates 2 butted at the fore and stern sides of the stainless steel plate 1 is smaller than the width of the stainless steel plate 1, and the port side or starboard side thereof is aligned with the port side or starboard side of the stainless steel plate 1, and the length of the two first carbon steel plates 2 butted at the port and starboard sides of the stainless steel plate 1 is equal to the sum of the length of the stainless steel plate 1 and the length of the two first carbon steel plates 2 butted at the fore and stern sides of the stainless steel plate 1, such as Figure 2 As shown, the port side edges of the two first carbon steel plates 2 butted at the bow and stern sides of the stainless steel plate 1 are aligned with the port side edge of the stainless steel plate 1, so that the starboard side of the stainless steel plate 1 is embedded in the second carbon steel plate 2 located on its starboard side, and both ends of the starboard side edge of the stainless steel plate 1 are provided with rounded corners;

[0040] The thickness of the stainless steel plate 1 is 16 mm to 25 mm, and the thickness of the first carbon steel plate 2 is 15 mm to 20 mm;

[0041] S12, a V-shaped welding groove is formed at the joint between the stainless steel plate 1 and the first carbon steel plate 2 and positioning welding is performed.

[0042] When tack welding is performed on the V-shaped welding groove between the stainless steel plate 1 and the first carbon steel plate 2, the weld length of the tack welding is greater than 50 mm, the weld height is less than 3 mm, and the spacing between adjacent tack welding points is 300 mm-500 mm.

[0043] The 309L welding wire is used for the tack welding between the stainless steel plate 1 and the first carbon steel plate 2 , and the 71NI welding wire is used for the tack welding between the first carbon steel plate 2 and the first carbon steel plate 2 .

[0044] S13, sequentially welding the T-seam 3, the bow and stern weld 4, the longitudinal weld 5, the stainless steel plate fillet weld 6 and the carbon steel butt seam 7 formed between the stainless steel plate 1 and the first carbon steel plate 2.

[0045] When welding the T-seam 3 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 toward the first carbon steel plate 2. The arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, and 71NI welding wire is used as the welding material.

[0046] When welding the bow and stern welds 4 formed between the stainless steel plate 1 and the first carbon steel plate 2, submerged arc welding is used to weld the joints between the bow and stern sides of the stainless steel plate 1 and the corresponding first carbon steel plate 2. The arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, but the fillet of the stainless steel plate 1 and the 100mm straight line segment connecting the fillet are retained without welding, and the welding material is Avesta309L / Flux805 welding wire.

[0047] When welding the longitudinal weld 5 formed between the stainless steel plate 1 and the first carbon steel plate 2, submerged arc welding is used to weld the seams between the left and right sides of the stainless steel plate 1 and the corresponding first carbon steel plate 2, and the weld extends 100mm-150mm to the first carbon steel plate located on the bow and stern sides. The arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, but the fillet of the stainless steel plate 1 and the 100mm straight line segment connecting the fillet are retained without welding, and the welding material is Avesta309L / Flux805 welding wire.

[0048] CO2 gas shielded welding is used to weld the weld 6 at the rounded corner of the stainless steel plate, and the welding material is 309L welding wire.

[0049] Submerged arc welding is used to weld the carbon steel butt joint 7 between adjacent first carbon steel plates 2. The welding consumables for the inner deck area are GLES-44 / SJ101A, and the welding consumables for the well deck area are GLES-40 / SJ101.

[0050] S14, turn over the formed stainless steel area structure, plasma arc gouge and grind all welds, and then perform reverse side welding in the same welding sequence as the front side welding.

[0051] After the reverse side welding is completed, the flatness of the stainless steel area structure is measured, and the position where the flatness exceeds the tolerance is corrected. After the correction is qualified, it is sent to the FCB assembly line area.

[0052] Mechanical flattening is used to correct the flatness deviation of the stainless steel area structure.

[0053] The flatness of the stainless steel area structure should be controlled within ±3mm / m, and the length, width and diagonal length errors of the stainless steel area structure should be controlled within ±3mm.

[0054] S2, in the FCB assembly line area, the second carbon steel plate 8 is welded to the stainless steel area structure, and then the longitudinal bones are welded.

[0055] Due to the particularity of the stainless steel plate 1 of the LNG carrier, it is kept in an environment below -20℃ for a long time. It is very important to prevent the stainless steel plate from being contaminated by carbon, oil and other impurities. At the same time, the deformation of the plate should be controlled, otherwise it will affect the installation of the insulation box in the cargo hold area of ​​the LNG carrier. Therefore, the stainless steel plate groove and surface should be rust-free and cleaned before welding, and the weld surface should be coated with lime water for protection before welding. The welding operation should be carried out strictly in accordance with the above welding process, and self-inspection and process records should be carried out during the welding process. All welds should be welded symmetrically to reduce welding deformation.

[0056] In the component panel area, after the stainless steel plate is welded, the flatness of the panel weld is controlled within ±3mm / m, and the length, width and diagonal after welding are controlled within ±3mm; after the component panel weld is completed, non-destructive testing is carried out, and after the weld is tested without defects, it is transported to the FCB assembly line area for the next step of welding. If the flatness, main dimensions and flaw detection are unqualified, relevant process methods are adopted for repair.

[0057] When the flatness exceeds the standard and needs to be trimmed, the stainless steel plate is generally prohibited from being pyrotechnic, because pyrotechnics without good control of the temperature can easily cause carbonization of the stainless steel plate, thereby greatly reducing the mechanical properties of the stainless steel plate and bringing disastrous consequences to LNG transportation. Mechanical flattening can be used to flatten the stainless steel plate.

[0058] When repairing unqualified products, plasma arc planing is used to clean the welds. Carbon planing is prohibited because carbon planing can also cause carbonization of stainless steel. After plasma arc planing, stainless steel grinding pads are used to clean the welds, remove all debris, polish, and leave the metallic luster of the stainless steel plate before subsequent repairs can be carried out.

[0059] It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for constructing an LNG ship air dome deck, characterized in that: The specific steps include: S1, in the component panel area, four first carbon steel plates (2) are butt-jointed around the stainless steel plate (1), wherein two first carbon steel plates (2) are butt-jointed at the bow and stern sides of the stainless steel plate (1), and the remaining two first carbon steel plates (2) are butt-jointed at the port and starboard sides of the stainless steel plate (1), the width of the two first carbon steel plates (2) butt-jointed at the bow and stern sides of the stainless steel plate (1) is smaller than the width of the stainless steel plate (1), the length of the two first carbon steel plates (2) butt-jointed at the port and starboard sides of the stainless steel plate (1) is equal to the sum of the length of the stainless steel plate (1) and the length of the two first carbon steel plates (2) butt-jointed at the bow and stern sides of the stainless steel plate (1), the thickness of the stainless steel plate (1) is 16 mm-25 mm, and the thickness of the first carbon steel plates (2) is 15 mm-20 mm; Then, a V-shaped welding groove is formed at the joint between the stainless steel plate (1) and the first carbon steel plate (2) and positioning welding is performed; Then, the T-shaped seam (3), the bow and stern weld (4), the longitudinal weld (5), the weld at the rounded corner of the stainless steel plate (6) and the carbon steel butt seam (7) formed between the stainless steel plate (1) and the first carbon steel plate (2) are welded in sequence; Then, the formed stainless steel area structure is turned over, and after all welds are plasma arc planed and polished, the reverse side welding is carried out in the same welding sequence as the front side welding; After the reverse side welding is completed, the flatness of the stainless steel area structure is measured, and the position where the flatness exceeds the tolerance is corrected. After the correction is qualified, it is sent to the FCB assembly line area; S2, in the FCB production line area, the second carbon steel plate (8) is welded to the stainless steel area structure, and then the longitudinal bones are welded.

2. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, when tack welding is performed on the V-shaped welding groove between the stainless steel plate (1) and the first carbon steel plate (2), the weld length of the tack welding is greater than 50 mm, the weld height is less than 3 mm, and the spacing between adjacent tack welding points is 300 mm-500 mm.

3. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the T-shaped seam (3) formed between the stainless steel plate (1) and the first carbon steel plate (2), CO2 gas shielded welding is used to perform step welding 150 mm from the butt joint of the stainless steel plate (1) and the first carbon steel plate (2) toward the first carbon steel plate (2), and the arc initiation and extinguishing points of each layer are staggered by 30 mm-50 mm.

4. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the bow and stern welds (4) formed between the stainless steel plate (1) and the first carbon steel plate (2), submerged arc welding is used to weld the joints between the bow and stern sides of the stainless steel plate (1) and the corresponding first carbon steel plate (2), and the arc starting and extinguishing points of each layer are staggered by 30 mm to 50 mm, but the rounded corners of the stainless steel plate (1) and the 100 mm straight line segments connecting the rounded corners are retained without welding.

5. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the longitudinal weld (5) formed between the stainless steel plate (1) and the first carbon steel plate (2), submerged arc welding is used to weld the seams between the left and right sides of the stainless steel plate (1) and the corresponding first carbon steel plate (2), and the weld extends 100 mm to 150 mm toward the first carbon steel plate located at the bow and stern sides, but the fillet of the stainless steel plate (1) and the 100 mm straight line segment connecting the fillet are retained.

6. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, CO2 gas shielded welding is used to weld the weld (6) at the rounded corner of the stainless steel plate; Submerged arc welding is used to weld the carbon steel butt joint (7) between adjacent first carbon steel plates (2).

7. The method for constructing the gas dome deck of an LNG carrier according to claim 1, characterized in that: In step S1, a mechanical flattening method is used to correct the flatness deviation position of the stainless steel area structure.

8. The method for constructing an LNG carrier air dome deck according to claim 1 or 7, characterized in that: In step S1, the flatness of the stainless steel area structure is controlled within ±3 mm / m, and the length, width and diagonal length errors of the stainless steel area structure are controlled within ±3 mm.

Images