Liquefied natural gas (LNG) ship liquid cargo deck construction method

Abstract

The invention discloses an LNG (Liquefied Natural Gas) ship liquid cargo 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, the manufacturing period of the large group on the jig frame is obviously reduced, and the production efficiency is improved. Meanwhile, on the basis that the original total welding length is kept unchanged; a T-shaped seam and a cross-shaped seam formed between a stainless steel plate and a first carbon steel plate, a butt seam in the stainless steel plate, a linear segment weld seam formed between the first carbon steel plate and the stainless steel plate and between a second carbon steel plate and the stainless steel plate, a weld seam at the position where the stainless steel plate is turned into a circular bead and a butt seam between the first carbon steel plate and the second carbon steel plate are sequentially welded through automatic welding. The butt joints between the first carbon steel plate, the second carbon steel plate and the third carbon steel plates and the butt joints between the adjacent third carbon steel plates can remarkably shorten the welding operation time and improve the welding efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of ship construction, and in particular to a method for constructing a liquid cargo 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 liquid dome sections. The stainless steel material of the liquid dome sections is 304L, with a thickness of 16mm to 25mm. The carbon steel material for the docking 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 is low, and the welding quality cannot be well controlled, and multiple repairs often occur.

[0003] The current shortcomings are as follows: ① CO2 gas shielded welding of stainless steel, due to the special nature of the material, the welding deposition rate is low and the welding difficulty is high. It takes 10 minutes for an intermediate welder to weld a one-meter weld, and 6 to 8 welds are required for a 16mm thick stainless steel plate. 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;

[0004] ②Since it is a single-sided forming weld, 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 -4 to +3mm, and the workload of correction is large;

[0005] ③Stainless steel single-sided forming welding is more difficult than carbon steel single-sided forming welding. The welding in this area has been carried out by experts in welding technology, 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 large and it will cause repeated repairs. Turning over the sections once will cause a waste of resources in many aspects;

[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 all the defects are removed, the defects increase after welding. According to the previous statistical flaw detection data, the repair rate of the stainless steel area on the deck has reached more than 40%, and there are even cases where the stainless steel repair time exceeds 20 days, affecting the entire block construction period and dock loading period. Summary of the invention

[0007] In view of this, the present invention provides a method for constructing a liquid cargo deck of an LNG ship to solve the problems existing in the above-mentioned background technology.

[0008] A method for constructing a liquid cargo deck of an LNG carrier, comprising the following steps:

[0009] S1, in the component panel area, splice the U-shaped stainless steel plates, respectively butt the first carbon steel plates on the bow and stern sides of the stainless steel plates, respectively butt the second carbon steel plates on the port and starboard sides of the stainless steel plates, and butt a plurality of third carbon steel plates on the bow sides of the first carbon steel plates and the second carbon steel plates, wherein the butt joint between the second carbon steel plate on the port side and the two first carbon steel plates is aligned with the two butt joints inside the stainless steel plates, the butt joint between the second carbon steel plate on the starboard side and the two first carbon steel plates is staggered with the other two butt joints of the stainless steel plates, and the butt joint between adjacent third carbon steel plates is aligned with the butt 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 the cross seam formed between the stainless steel plate and the first carbon steel plate, the butt seam inside the stainless steel plate, the straight section welds formed between the first carbon steel plate and the second carbon steel plate and the stainless steel plate, the welds at the rounded corners of the stainless steel plate, the butt seam between the first carbon steel plate and the second carbon steel plate, the butt seam between the first carbon steel plate and the second carbon steel plate and the third carbon steel plate, and the butt seams between adjacent third carbon steel plates are welded in sequence;

[0012] 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;

[0013] 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;

[0014] S2, in the FCB assembly line area, the fourth carbon steel plate is welded to the stainless steel area structure, and then the longitudinal bones are welded.

[0015] Preferably, in step S1, when tack welding is performed on all V-shaped welding grooves at the butt joints, 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.

[0016] Preferably, in step S1, when welding the T-shaped seam formed between the stainless steel plate and the first carbon steel plate, CO 2 Gas shielded welding is performed from the butt joint of the stainless steel plate and the first carbon steel plate to the first carbon steel plate and the third carbon steel plate for a step welding of 150 mm.

[0017] When welding the cross seam between the stainless steel plate and the first carbon steel plate, CO 2Gas shielded welding is performed from the butt joint of the stainless steel plate and the first carbon steel plate in four directions, namely, forward, backward, left and right, with a step welding of 150mm respectively, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm.

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

[0019] Preferably, in step S1, when welding the straight-line welds formed 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 joints between the first carbon steel plate and the stainless steel plate and the joints between the second carbon steel plate and the stainless steel plate, but the fillet of the stainless steel plate and the 100 mm straight-line segment connecting the fillet are not welded, and step welding is used at the joints, with the arc initiation and extinguishing points of each layer staggered by 30 mm to 50 mm.

[0020] Preferably, in step S1, when welding the fillet weld of the stainless steel plate, CO 2 Welding is performed using the gas shielded arc welding process;

[0021] When welding 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, a submerged arc welding process is used for welding.

[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 operation of the large assembly 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 and the cross seam formed between the stainless steel plate and the first carbon steel plate, the butt seam inside the stainless steel plate, the straight section weld seam formed between the first carbon steel plate and the second carbon steel plate and the stainless steel plate, the weld seam at the rounded corner of the stainless steel plate, the butt seam between the first carbon steel plate and the second carbon steel plate, the butt seam between the first carbon steel plate and the second carbon steel plate and the third carbon steel plate, and the butt seam between adjacent third carbon steel plates are welded in sequence by automatic welding, which can significantly shorten the welding operation time and improve the welding efficiency, and at the same time can also reduce welding deformation and welding defects, improve 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, the third 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 second carbon steel plate, 4 is a third carbon steel plate, 5 is a T-seam, 6 is a cross seam, 7 is a butt seam inside the stainless steel plate, 8 is a straight weld formed between the first carbon steel plate, the second carbon steel plate and the stainless steel plate, 9 is a weld at the rounded corner of the stainless steel plate, 10 is a butt seam between the first carbon steel plate and the second carbon steel plate, 11 is a butt seam between the first carbon steel plate, the second carbon steel plate and the third carbon steel plate, 12 is a butt seam between adjacent third carbon steel plates, and 13 is a fourth 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, third, 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 the same type of information from each other. For example, without departing from the scope of the present disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information.

[0034] In order to better understand the technical solution of the present invention, the present invention is described in detail below with reference to the accompanying drawings.

[0035] The present invention provides a method for constructing a liquid cargo 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, splicing a U-shaped stainless steel plate 1, the U-shaped stainless steel plate 1 is spliced ​​by four stainless steel plates, two of which are rectangular and the remaining two are U-shaped, the rectangular stainless steel plates are symmetrically placed on the bow and stern sides, and the U-shaped stainless steel plates are symmetrically placed on the port and starboard sides to form a U-shaped stainless steel plate. After the stainless steel plates are spliced, the inner edge of the stainless steel plates is fixed with a pressure iron or a card (no less than two cards on a single side);

[0039] Then, the first carbon steel plate 2 is butt-jointed at the bow and stern sides of the stainless steel plate 1, and the second carbon steel plate 3 is butt-jointed at the port and starboard sides of the stainless steel plate 1, respectively. The two first carbon steel plates 2 at the bow and stern are both rectangular plates, but their widths are different, wherein the width of the first carbon steel plate 2 at the stern side is greater than the width of the first carbon steel plate 2 at the bow side; the two second carbon steel plates 3 on the left and right are both U-shaped plates, and the two have the same size; when the first carbon steel plate 2 and the second carbon steel plate 3 are butt-jointed, the bow side edge of the first carbon steel plate on the bow side is flush with the bow side edge of the second carbon steel plate 3, and the butt 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 butt joints inside the stainless steel plate 1, and the butt joint between the second carbon steel plate 3 on the starboard side and the two first carbon steel plates 2 is staggered with the other two butt joints of the stainless steel plate 1;

[0040] Then, a plurality of third carbon steel plates 4 are butt-jointed on the bow side of the first carbon steel plate 2 and the second carbon steel plate 3, and the butt joints between adjacent third carbon steel plates 4 are aligned with the butt joints between the second carbon steel plate and the first carbon steel plate.

[0041] The thickness of the stainless steel plate 1 is 16 mm to 25 mm, and the four corners of the stainless steel plate 1 are all provided with rounded corners. The thickness of the first carbon steel plate 2 is 15 mm to 20 mm.

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

[0043] The positioning welding is done in the groove, 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 300mm-500mm.

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

[0045] S13, sequentially weld the T-seam 5 and the cross seam 6 formed between the stainless steel plate 1 and the first carbon steel plate 2, the butt seam 7 inside the stainless steel plate, the straight section weld 8 formed between the first carbon steel plate 2, 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 seam 10 between the first carbon steel plate 2 and the second carbon steel plate 3, the butt seam 11 between the first carbon steel plate 2, the second carbon steel plate 3 and the third carbon steel plate 4, and the butt seam 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, CO 2 Gas shielded welding is performed for 150mm step welding 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 third carbon steel plate 4. The arc initiation 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 seam 6 formed between the stainless steel plate 1 and the first carbon steel plate 2, CO 2 Gas shielded welding is performed from the butt joint of the stainless steel plate 1 and the first carbon steel plate 2 in four directions of 150mm in front, back, left and right, with the arc initiation and extinguishing points of each layer staggered by 30mm-50mm. 71NI welding wire is used as the welding material.

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

[0049] When welding the straight 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 joints between the first carbon steel plate 2 and the stainless steel plate 1 and the joints between the second carbon steel plate 3 and the stainless steel plate 1, but the fillet of the stainless steel plate 1 and the 100mm straight segment connecting the fillet are retained without welding, step welding is used at the joints, and the arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, and Avesta309L / Flux805 welding wire is selected as the welding material.

[0050] When welding stainless steel plates at the rounded corners, use CO2 The welding is carried out by gas shielded welding process, and the welding material is 309L welding wire.

[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, submerged arc welding technology is used for welding, and GLES-44 / SJ101A welding wire is selected as the welding material.

[0052] S14, turn over the formed stainless steel area structure, plasma arc planer and grind all welds, and then perform reverse side welding in the same welding sequence as the front side welding.

[0053] 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.

[0054] Mechanical flattening is used to correct the flatness deviation 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 assembly line area, the fourth carbon steel plate 13 is welded to the stainless steel area structure, and then the longitudinal bones are welded.

[0057] 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.

[0058] 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.

[0059] 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 temperature control 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.

[0060] 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.

[0061] 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 a liquid cargo deck of an LNG carrier, characterized in that: The specific steps include: S1, in the component panel area, a U-shaped stainless steel plate (1) is spliced, a first carbon steel plate (2) is respectively butted on the bow and stern sides of the stainless steel plate (1), a second carbon steel plate (3) is respectively butted on the port and starboard sides of the stainless steel plate (1), and a plurality of third carbon steel plates (4) are butted on the bow sides of the first carbon steel plate (2) and the second carbon steel plate (3), wherein a butt joint between the second carbon steel plate on the port side and the two first carbon steel plates is aligned with two butt joints inside the stainless steel plate, a butt joint between the second carbon steel plate on the starboard side and the two first carbon steel plates is staggered with the other two butt joints of the stainless steel plate, and a butt joint between adjacent third carbon steel plates (4) is aligned with a butt joint between the second carbon steel plate and the first carbon steel plate, the thickness of the stainless steel plate (1) is 16 mm-25 mm, and the thickness of the first carbon steel plate (2) is 15 mm-20 mm; Then, V-shaped welding grooves are made at all the butt joints and tack welds are performed; Then, 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 seam (7) inside the stainless steel plate, the straight 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 seam (10) between the first carbon steel plate (2) and the second carbon steel plate (3), the butt seam (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 seam (12) between adjacent third carbon steel plates (4) 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 fourth carbon steel plate (13) is welded to the stainless steel area structure, and then the longitudinal bones are welded.

2. The method for constructing a liquid cargo deck of an LNG carrier according to claim 1, characterized in that: In step S1, when tack welding is performed on all V-shaped welding grooves at the butt joints, 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 a liquid cargo deck of an LNG carrier according to claim 1, characterized in that: 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 150 mm from the butt joint 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). When welding the cross seam (6) formed between the stainless steel plate (1) and the first carbon steel plate (2), CO2 gas shielded welding is used to perform step welding of 150 mm in four directions, namely, forward, backward, left and right, from the butt joint of the stainless steel plate (1) and the first carbon steel plate (2), and the arc initiation and extinguishing points of each layer are staggered by 30 mm to 50 mm.

4. The method for constructing a liquid cargo deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the butt joint (7) inside the stainless steel plate, a submerged arc welding process is used for welding.

5. The method for constructing a liquid cargo deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the straight 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), but the fillet of the stainless steel plate (1) and the 100 mm straight segment connecting the fillet are not welded, and step welding is used at the joint, with the arc initiation and extinguishing points of each layer staggered by 30 mm to 50 mm.

6. The method for constructing a liquid cargo deck of an LNG carrier according to claim 1, characterized in that: In step S1, when welding the weld (9) at the rounded corner of the stainless steel plate, a CO2 gas shielded welding process is used for welding; 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), a submerged arc welding process is used for welding.

7. The method for constructing a liquid cargo 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 a liquid cargo deck of an LNG carrier 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.

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