A method for constructing the inner bottom section of an LNG carrier

Abstract

This invention discloses a method for constructing LNG carrier inner bottom sections, comprising the following steps: fabricating the inner bottom plate during the initial assembly stage; during the intermediate assembly stage, installing the longitudinal and transverse structures onto the inner bottom plate to form the intermediate assembly; and during the final assembly stage, inverting the intermediate assembly onto the outer plate, welding the joints between the longitudinal and transverse structures and the outer plate, and welding the reverse side of the joints between the second carbon steel plate and the first carbon steel plate and the stainless steel plate to form a complete inner bottom section. This invention completes the splicing of the stainless steel and carbon steel plates of the inner bottom plate during the initial assembly stage and optimizes the welding process at this stage. While ensuring controllable deformation of the inner bottom plate, it significantly shortens the jig cycle during the final assembly stage, does not affect the assembly and forming of the sections during the final assembly stage, meets the required segment accuracy, and greatly shortens the jig cycle during the final assembly stage, thus improving the efficiency of section construction.

Description

Technical Field

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

[0002] As is well known, LNG carriers are specialized vessels used for transporting cryogenic liquefied natural gas. A typical 174,000 cubic meter LNG carrier usually has four cargo tanks, which store cryogenic liquefied natural gas. Although LNG carriers have a mature containment system that can ensure the cryogenic state is maintained during transportation, further reinforcement is still needed at the pump outlet of the cargo tank during the stage where liquefied natural gas is pumped into the cargo tank. This reinforcement is necessary to withstand the cryogenic shock of the cryogenic liquefied natural gas. This area on the inner bottom plate is usually designed with stainless steel plates to improve the cryogenic resistance of the local structure.

[0003] Currently, for sections with stainless steel inner base plates, the conventional construction method involves placing the stainless steel inner base plate during the main assembly stage. The stainless steel and carbon steel plates are then spliced ​​together after the main frame of the inner base plate is hoisted, in order to control welding deformation between the stainless steel and carbon steel. While this method can minimize welding deformation at the stainless steel plates and avoid cutting the stainless steel, the section has an excessively long on-site cycle during the main assembly stage, resulting in low production efficiency. Summary of the Invention

[0004] In view of this, the present invention provides a method for constructing LNG ship inner bottom sections. By splicing the stainless steel and carbon steel plates of the inner bottom plate during the initial assembly stage and optimizing the welding process at this stage, the jig cycle of the main assembly stage can be greatly shortened while ensuring that the deformation of the inner bottom plate is controllable. This method does not affect the closure and forming of the sections in the main assembly stage, and the section accuracy meets the requirements. At the same time, it significantly shortens the main assembly jig cycle and improves the efficiency of section construction.

[0005] A method for constructing the inner bottom section of an LNG carrier specifically includes the following steps:

[0006] S1, Make the inner bottom plate;

[0007] Specifically, firstly, two first carbon steel plates are laid on both sides of the stainless steel plate and joined together with the two sides of the stainless steel plate. The front side of the butt joint between the first carbon steel plate and the stainless steel plate is welded using a submerged arc automatic welding machine. After welding, the entire steel plate is flipped over, and the back side of the butt joint is planed using a plasma air planer. Then, the back side of the butt joint is welded using a submerged arc automatic welding machine.

[0008] Then, place the second carbon steel plate horizontally on one side of the first carbon steel plate and stainless steel plate, and keep a 2-3mm butt joint between the second carbon steel plate and the first carbon steel plate and stainless steel plate. Then, use the FCB welding method to weld the front side of the butt joint between the second carbon steel plate and the first carbon steel plate and stainless steel plate. Do not weld the back side of the butt joint for the time being to form the inner bottom plate.

[0009] S2, the middle assembly stage, involves installing the longitudinal and transverse structures onto the inner base plate to form the middle assembly;

[0010] S3, the main assembly stage, the middle assembly is flipped onto the outer plate, the joints between the longitudinal and transverse structures and the outer plate are welded, and the reverse side of the joint between the second carbon steel plate and the first carbon steel plate and the stainless steel plate is welded to form a complete inner bottom segment.

[0011] Preferably, after the inner bottom plate is manufactured in step S1, the flatness of each joint is checked with a level to determine whether welding deformation has occurred. If the welding deformation exceeds ±3mm, the hydraulic press is placed at the joint to flatten the plate surface.

[0012] Preferably, in step S2, the T-shaped profiles in contact with the stainless steel plate in the longitudinal and transverse structure are made of multiple profiles spliced ​​together front and back. When installing the T-shaped profile, the panel splicing seams of the multiple profiles spliced ​​front and back are welded first, the web splicing seams of the multiple profiles spliced ​​front and back are welded, and finally the splicing seams between the profile web and the stainless steel plate are welded.

[0013] Each joint between the profile web and the stainless steel plate retains a 100mm unwelded area during welding, which is reserved for welding during the final assembly stage.

[0014] Preferably, when welding the joint between the profile web and the stainless steel plate, the weld is symmetrically welded using the back-welding method.

[0015] Preferably, in step S3, before the welding operation in the large assembly stage, wooden blocks are placed in the area where the stainless steel plate is located on the inner base plate, and then pressure irons are placed on the wooden blocks to prevent the stainless steel plate from deforming during the welding process.

[0016] The beneficial effects of this invention are:

[0017] This invention completes the splicing of the stainless steel and carbon steel plates of the inner bottom plate during the small-scale assembly stage and optimizes the welding process at this stage. While ensuring that the deformation of the inner bottom plate is controllable, it can greatly shorten the jig cycle of the large-scale assembly stage, without affecting the closure and forming of the segments in the large-scale assembly stage. The segmentation accuracy meets the requirements, and at the same time, it significantly shortens the jig cycle of the large-scale assembly and improves the segment construction efficiency. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a structural diagram of the inner bottom plate.

[0020] Figure 2 This is a schematic diagram of the assembled structure.

[0021] Figure 3 This is a schematic diagram of the segmented inner sole structure.

[0022] The meanings of the labels in the diagram are as follows:

[0023] 1 is the first carbon steel plate, 2 is the second carbon steel plate, 3 is the stainless steel plate, 4 is the inner bottom plate, 5 is the middle assembly, 6 is the longitudinal and transverse structure, 7 is the T-shaped profile, 8 is the first splice joint, 9 is the second splice joint, 10 is the third splice joint, 11 is the fourth splice joint, and 12 is the outer plate. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] This invention provides a method for constructing the inner bottom section of an LNG carrier, specifically including the following steps:

[0029] S1, Make the inner bottom plate;

[0030] Specifically, firstly, at the submerged arc welding plate splicing station, two first carbon steel plates 1 are laid on both sides of stainless steel plate 3 and joined together with the two sides of stainless steel plate 3. The front side of the butt joint between the first carbon steel plate 1 and stainless steel plate 3 is welded using a multi-layer, multi-pass back-welding method with a submerged arc automatic welding machine. After welding, the entire steel plate is flipped over, and the back side of the butt joint is planed using a plasma gouging machine. Then, the back side of the butt joint is welded using a submerged arc automatic welding machine. After welding, an ultrasonic flaw detector is used to inspect the weld formation quality. A 1m level is used to check the flatness of each butt joint to determine whether welding deformation has occurred. If the welding deformation exceeds ±3mm, a hydraulic press is placed at the butt joint to flatten the plate surface.

[0031] Then, place the second carbon steel plate 2 horizontally on one side of the first carbon steel plate 1 and stainless steel plate 3, and maintain a 2-3mm butt joint between the second carbon steel plate 2 and the first carbon steel plate 1 and stainless steel plate 3. Then, use the FCB welding method to weld the front side of the butt joint between the second carbon steel plate 2 and the first carbon steel plate 1 and stainless steel plate 3. The back side of the butt joint is not welded for the time being (the back side of the butt joint will be welded in the large assembly stage) to form the inner bottom plate 4.

[0032] When welding the butt joints of ordinary steel plates using the FCB welding method, a 0mm butt joint is typically required, meaning the two steel plates are completely butted together without any gaps. However, since the inner bottom plate of this application contains a stainless steel plate, considering the special properties of stainless steel, a 2-3mm butt joint is maintained between the second carbon steel plate 2 and the first carbon steel plate 1 and stainless steel plate 3 when placing the second carbon steel plate 2 to prevent shrinkage deformation during welding.

[0033] S2, the middle assembly 5 production stage, where the longitudinal and transverse structures 6 are installed onto the inner base plate 4 to form the middle assembly.

[0034] Each component in the longitudinal and transverse structure 6 is hoisted onto the inner bottom plate 4 in sequence. Welding can only proceed if the ends of the longitudinal truss structure 6 are vertical and the end faces that intersect the inner bottom plate 4 perpendicularly.

[0035] The T-shaped profile 7 of the longitudinal and transverse structure 6, which is in contact with the stainless steel plate 3, is made up of multiple profile sections spliced ​​together. When installing the T-shaped profile 7, the panel splicing seams of the multiple profile sections spliced ​​together are welded first, then the web splicing seams of the multiple profile sections spliced ​​together are welded, and finally the splicing seam between the web of the profile and the stainless steel plate 3 is welded.

[0036] There are four splicing seams between the web of the T-shaped profile and the stainless steel plate, namely the first splicing seam 8, the second splicing seam 9, the third splicing seam 10, and the fourth splicing seam 11. These four splicing seams are symmetrically welded using the back-welding method, and the welding current and voltage are controlled to ensure that the structure at this point does not deform. In addition, a 100mm unwelded area is left for each of these four splicing seams during welding. This 100mm unwelded area is reserved for welding during the large assembly stage.

[0037] S3, the main assembly stage: the middle assembly 5 is flipped onto the outer plate 12 to form a complete inner bottom segment. At this time, the inner bottom plate 4 is facing upwards. Wooden blocks are placed on the area where the stainless steel plate 3 is located on the inner bottom plate 4, and then 5T weights are placed on the wooden blocks to prevent the stainless steel plate 3 from deforming during the welding process in the main assembly stage. Then, the butt joints between the longitudinal and transverse structures 6 and the outer plate 12 are welded, the reverse side of the butt joints between the second carbon steel plate 2 and the first carbon steel plate 1 and the stainless steel plate 3 are welded, and the 100mm unwelded areas on the first splice joint 8, the second splice joint 9, the third splice joint 10, and the fourth splice joint 11 are welded.

[0038] 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 for constructing the inner bottom section of an LNG carrier, characterized in that, Specifically, the following steps are included: S1, Make the inner bottom plate; Specifically, firstly, two first carbon steel plates are laid on both sides of the stainless steel plate and joined together with the two sides of the stainless steel plate. The front side of the butt joint between the first carbon steel plate and the stainless steel plate is welded using a submerged arc automatic welding machine. After welding, the entire steel plate is flipped over, and the back side of the butt joint is planed using a plasma air planer. Then, the back side of the butt joint is welded using a submerged arc automatic welding machine. Then, place the second carbon steel plate horizontally on one side of the first carbon steel plate and stainless steel plate, and keep a 2-3mm butt joint between the second carbon steel plate and the first carbon steel plate and stainless steel plate. Then, use the FCB welding method to weld the front side of the butt joint between the second carbon steel plate and the first carbon steel plate and stainless steel plate. Do not weld the back side of the butt joint for the time being to form the inner bottom plate. S2, the middle assembly stage, involves installing the longitudinal girder structure onto the inner bottom plate to form the middle assembly; S3, the main assembly stage, the middle assembly is reversed and fastened onto the outer plate, the joint between the longitudinal girder structure and the outer plate is welded, and the reverse side of the joint between the second carbon steel plate and the first carbon steel plate and the stainless steel plate is welded to form a complete inner bottom segment. Before welding during the assembly phase, place wooden blocks in the area where the stainless steel plate is located on the inner base plate, and then place weights on the wooden blocks to prevent the stainless steel plate from deforming during the welding process.

2. The method for constructing the inner bottom section of an LNG carrier according to claim 1, characterized in that, After the inner bottom plate is made in step S1, use a level to check the flatness of each joint to determine whether there is welding deformation. If the welding deformation exceeds ±3mm, place the hydraulic press at the joint to flatten the plate surface.

3. The method for constructing the inner bottom section of an LNG carrier according to claim 1, characterized in that, In step S2, the T-shaped profile of the longitudinal girder structure that contacts the stainless steel plate is made up of multiple profile sections spliced ​​together. When installing the T-shaped profile, the panel splicing seam of the multiple profile sections spliced ​​together is welded first, the web splicing seam of the multiple profile sections spliced ​​together is welded then, and finally the splicing seam between the profile web and the stainless steel plate is welded. Each joint between the profile web and the stainless steel plate retains a 100mm unwelded area during welding, which is reserved for welding during the final assembly stage.

4. The method for constructing the inner bottom section of an LNG carrier according to claim 3, characterized in that, When welding the joint between the web of the profile and the stainless steel plate, the weld is symmetrically welded using the back-welding method.

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