Method for building a gas dome deck of an LNG carrier

Abstract

The application discloses a LNG ship gas dome deck construction method, which can effectively ensure the continuity of the large group on the large group jig, significantly reduce the large group jig cycle, and shorten the welding operation time, improve the welding efficiency, reduce the welding deformation and welding defects, improve the welding quality, reduce the repair rate of the deck stainless steel area, and greatly shorten the section construction cycle and the dock loading cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shipbuilding, in particular to a LNG ship gas dome deck construction method. BACKGROUND

[0002] One of the difficulties in LNG transport ship construction is the welding of stainless steel plates in the gas dome section. The stainless steel material of the gas dome section is 304L, and the thickness distribution is 16mm-25mm. The carbon steel material to be connected is E-grade, and the thickness distribution is 15mm-20mm. Both belong to medium-thickness steel plates. For this area, the LNG ship adopts CO2 gas shielded welding. In the large assembly position, the stainless steel plates and carbon steel plates are scattered and assembled for manual welding. The welding speed of manual welding is low, and the welding quality cannot be well controlled, and multiple repairs often occur.

[0003] The disadvantages of current manual welding are:

[0004] 1. The CO2 gas shielded welding of stainless steel has low welding deposition rate and high welding difficulty due to the particularity of the material. It takes 10 minutes for a middle-level welder to weld one meter of weld. Six to eight passes are needed for 16mm thick stainless steel plates. Two middle-level welders need to weld for 5-6 days in the stainless steel area of a deck section, which occupies a long period of assembly position.

[0005] 2. Since it is single-sided forming welding, the welding shrinkage is in one direction, although there is a Kama fixing, but there is still a lot of welding deformation. The liquid cargo tank deck has a flatness requirement of-4mm to +3mm, and the correction workload is large.

[0006] 3. The single-sided forming welding of stainless steel is more difficult than that of carbon steel. The welding in this area has been carried out by good welders, but it is difficult to form a good weld with poor quality, which cannot meet the process requirements. Therefore, the section needs to be turned over for repair, which is difficult to repair and causes repeated repair, section turning over, and waste of resources.

[0007] 4. Stainless steel welding defects, which are the biggest pain point, are very difficult to repair. Sometimes after cleaning the defects and welding again, the defects increase. According to the previous inspection data, the repair rate of the deck stainless steel area is more than 40%, and even the stainless steel repair time exceeds 20 days, which seriously affects the construction period of the section and the docking period of the ship. SUMMARY

[0008] Therefore, the present application provides a LNG ship gas dome deck construction method to solve the problems in the background art.

[0009] A LNG ship gas dome deck construction method, specifically comprising the following steps:

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

[0011] Then, V-shaped welding grooves are opened at the butt joint of the stainless steel plate and the first carbon steel plate, and positioning welding is performed.

[0012] Then, the T-shaped seam formed between the stainless steel plate and the first carbon steel plate, the bow and stern weld, the longitudinal weld, the weld at the rounded corner of the stainless steel plate, and the carbon steel butt joint are sequentially welded.

[0013] Then, the formed stainless steel area structure is turned over, after plasma arc planing and polishing of all welds, reverse welding is performed in the same welding sequence as the front welding.

[0014] After the reverse welding is completed, the flatness of the stainless steel area structure is measured, and the positions with excessive flatness are corrected, and after the correction is qualified, it is sent to the FCB flow line area.

[0015] S2, in the FCB flow line area, the second carbon steel plate is butt welded with the stainless steel area structure, and the longitudinal frame is assembled and welded.

[0016] Preferably, in step S1, when positioning 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 positioning welding is greater than 50 mm, the weld height is less than 3 mm, and the spacing between adjacent positioning welding points is 300-500 mm.

[0017] 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 step welding 150 mm from the butt joint of the stainless steel plate and the first carbon steel plate to the first carbon steel plate, and the arc extinguishing points of each layer are staggered by 30-50 mm.

[0018] Preferably, in step S1, when welding the bow and stern weld formed between the stainless steel plate and the first carbon steel plate, submerged arc welding is used to weld the joint between the bow and stern side of the stainless steel plate and the corresponding first carbon steel plate, and the arc extinguishing points of each layer are staggered by 30-50 mm, but the rounded corner of the stainless steel plate and the 100 mm straight line segment connecting the rounded corners are not welded.

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

[0020] Preferably, in step S1, the weld at the fillet radius of the stainless steel plate is welded by CO2 gas shielded welding.

[0021] The carbon steel butt joints between adjacent first carbon steel plates are welded by submerged arc welding.

[0022] Preferably, in step S1, the flatness of the stainless steel area structure is corrected by mechanical flattening.

[0023] Preferably, 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.

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

[0025] The present application advances the welding operation of the stainless steel plate and the carbon steel plate originally performed on the large group jig to the plate assembly stage, which can effectively ensure the continuity of the large group operation on the large group jig, significantly reduce the large group manufacturing cycle, and on the basis of maintaining the original total welding length, sequentially weld the T-shaped joint, the bow and stern weld, the longitudinal weld, the weld at the fillet radius of the stainless steel plate and the carbon steel butt joint between the stainless steel plate and the first carbon steel plate by automatic welding, which can significantly shorten the welding operation time, improve the welding efficiency, reduce the welding deformation and welding defects, and improve the welding quality, thereby reducing the repair rate of the deck stainless steel area, greatly shortening the segmented construction period and the dock loading period. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

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

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

[0029] The meanings of the reference numerals in the drawings are as follows:

[0030] 1 is a stainless steel plate, 2 is the first carbon steel plate, 3 is a T-shaped seam, 4 is a bow and stern weld, 5 is a longitudinal weld, 6 is a weld at the rounded corner of the stainless steel plate, 7 is a carbon steel butt joint, and 8 is the second 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," 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] The present application will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0035] This invention provides a method for constructing an air dome 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, four first carbon steel plates 2 are joined around the stainless steel plate 1, with two first carbon steel plates 2 joined on the bow and stern sides of the stainless steel plate 1, and the remaining two first carbon steel plates 2 joined on the port and starboard sides of the stainless steel plate 1.

[0039] The width of the two first carbon steel plates 2 joined on the bow and stern sides of the stainless steel plate 1 is less than the width of the stainless steel plate 1, and their port or starboard sides are aligned with the port or starboard sides of the stainless steel plate 1. The length of the two first carbon steel plates 2 joined on 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 joined on the bow and stern sides of the stainless steel plate 1. Figure 2 As shown, the port side of the two first carbon steel plates 2 that are docked on the bow and stern sides of the stainless steel plate 1 are aligned with the port side 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 the two ends of the starboard side of the stainless steel plate 1 are provided with rounded corners.

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

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

[0042] When tack welding is performed on the V-shaped weld groove between the stainless steel plate 1 and the first carbon steel plate 2, 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.

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

[0044] S13, sequentially weld the T-shaped seam 3 formed between the stainless steel plate 1 and the first carbon steel plate 2, 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 joint 7.

[0045] 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 a 150mm stepped weld from the joint point of the stainless steel plate 1 and the first carbon steel plate 2 toward 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.

[0046] When welding the bow and stern weld 4 between the stainless steel plate 1 and the first carbon steel plate 2, the bow and stern sides of the stainless steel plate 1 and the corresponding first carbon steel plate 2 are welded by submerged arc welding. The arc initiation and extinguishing points of each layer are staggered by 30mm-50mm, but the rounded corners of the stainless steel plate 1 and the 100mm straight section connecting the rounded corners are left unwelded. The welding material is Avesta309L / Flux805 welding wire.

[0047] When welding the longitudinal weld 5 between the stainless steel plate 1 and the first carbon steel plate 2, the 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 100-150 mm to the first carbon steel plate located at the bow or stern side, the arc extinguishing points of each layer are staggered by 30-50 mm, but the fillet radius of the stainless steel plate 1 and the 100 mm straight line segment connected to the fillet radius are not welded, and the welding material is selected from Avesta309L / Flux805 welding wire.

[0048] The CO2 gas shielded welding is used to weld the weld 6 at the fillet radius of the stainless steel plate, and the welding material is selected from 309L welding wire.

[0049] The submerged arc welding is used to weld the carbon steel butt seams 7 between adjacent first carbon steel plates 2, the welding material selected for the inner deck area is GLES-44 / SJ101A, and the welding material selected for the surrounding trap deck area is GLES-40 / SJ101.

[0050] S14, the formed stainless steel area structure is turned over, after plasma arc planing and polishing of all welds, back welding is performed in the same welding sequence as the front welding.

[0051] After the back welding is completed, the flatness of the stainless steel area structure is measured, and the out-of-tolerance position is corrected, and after the correction is qualified, it is sent to the FCB flow line area.

[0052] The out-of-tolerance position of the flatness of the stainless steel area structure is corrected by mechanical flattening.

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

[0054] S2, in the FCB flow line area, the second carbon steel plate 8 is welded with the stainless steel area structure, and the longitudinal rib is assembled.

[0055] Because the stainless steel plate 1 of the LNG transport ship has its particularity, it is in the environment below -20℃ for a long time, it is very important to prevent the stainless steel plate from being polluted by carbon, oil and other impurities, and the deformation amount of the plate assembly should also be controlled, otherwise it will affect the installation of the insulation tank in the cargo hold area of the LNG transport ship, therefore, the bevel and surface of the stainless steel plate should be cleaned before welding, the weld surface should be coated with lime water for protection before welding, the welding operation should be strictly carried out according to the above welding process, the self-inspection and process record should be done well during the welding process, and all welds are symmetrically welded to reduce the welding deformation.

[0056] In the component panel area, after the stainless steel plate welding is finished, 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 welding is finished, non-destructive testing is carried out, and after the weld is detected without defects, it is transported to the FCB flow line area for the next step of welding. When the flatness, main size and flaw detection are unqualified, relevant process methods are taken for trimming.

[0057] When the flatness exceeds the standard and needs to be trimmed, the stainless steel plate is prohibited from using firework in principle, because the firework that does not control the time of fire easily causes the carbonization of the stainless steel plate, thereby greatly reducing the mechanical properties of the stainless steel plate, which will bring disastrous consequences to the LNG transportation. The mechanical flattening method can be used to straighten the stainless steel plate.

[0058] When the flaw detection is unqualified and needs to be repaired, the plasma arc planing method is used to remove the weld, and the carbon planing method is prohibited, because the carbon planing also causes the carbonization of the stainless steel. After the plasma arc planing, the stainless steel grinding piece is used to clean the weld, remove all impurities, polish and leave the metal luster of the stainless steel plate, so that the subsequent repair can be carried out.

[0059] It should be clear that the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.

Claims

1. A method for constructing an air dome deck for an LNG carrier, characterized in that, Specifically, the following steps are included: S1, in the component assembly area, four first carbon steel plates (2) are joined around the stainless steel plate (1), two of which are joined on the bow and stern sides of the stainless steel plate (1) and the remaining two are joined on the port and starboard sides of the stainless steel plate (1). The width of the two first carbon steel plates (2) joined on the bow and stern sides of the stainless steel plate (1) is less than the width of the stainless steel plate (1). The length of the two first carbon steel plates (2) joined on 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) joined on the bow and stern sides of the stainless steel plate (1). The thickness of the stainless steel plate (1) is 16mm-25mm and the thickness of the first carbon steel plate (2) is 15mm-20mm. Then, a V-shaped welding groove is opened at the joint between the stainless steel plate (1) and the first carbon steel plate (2) and tack welding is performed; Then, the T-shaped seam (3), bow and stern weld (4), longitudinal weld (5), stainless steel plate rounded corner weld (6), and carbon steel butt joint (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 all welds are plasma arc gouged and ground. Then, the reverse side is welded in the same welding sequence as the front side. 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. 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 skeleton is 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 weld groove between the stainless steel plate (1) and the first carbon steel plate (2), the weld length of the tack weld is greater than 50mm, the weld height is less than 3mm, and the distance between adjacent tack weld points is 300mm-500mm.

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 a 150mm stepped weld from the joint point of the stainless steel plate (1) and the first carbon steel plate (2) toward the first carbon steel plate (2), with the arc ignition and extinguishing points of each layer staggered by 30mm-50mm.

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 weld (4) formed between the stainless steel plate (1) and the first carbon steel plate (2), the joint between the bow and stern sides of the stainless steel plate (1) and the corresponding first carbon steel plate (2) is welded by submerged arc welding. The arc ignition and extinguishing points of each layer are staggered by 30mm-50mm, but the rounded corners of the stainless steel plate (1) and the 100mm straight section connecting the rounded corners are left unwelded.

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), the joint between the port and starboard sides of the stainless steel plate (1) and the corresponding first carbon steel plate (2) is welded by submerged arc welding and the weld extends 100mm-150mm towards the first carbon steel plate located on the bow and stern sides, but the rounded corner of the stainless steel plate (1) and the 100mm straight section connecting the rounded corner 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 stainless steel plate at the rounded corner (6); The carbon steel butt joint (7) between adjacent first carbon steel plates (2) is welded by submerged arc welding.

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

8. The method for constructing the gas dome 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 ±3mm / m, and the length, width and diagonal length errors of the stainless steel area structure are controlled within ±3mm.

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