Strut invar panel welding method for liquid cargo tank of LNG (Liquefied Natural Gas) ship

Abstract

The embodiment of the invention provides a supporting column invar panel welding method for an LNG ship liquid cargo tank, and relates to the technical field of welding, the process is applied to manual welding of 304L stainless steel supporting column round pipes with the thickness being 6 mm and invar panels with the thickness being 8 mm, and the process comprises the following steps that s100, a welding area is isolated from an external area through a shielding object before welding; and s200, the supporting column invar panel is welded through an invar steel welding wire. According to the design of the welding process, the invar steel welding wire is used as a filling material of the pillar invar panel, and the invar steel material has higher strength and durability at low temperature and high temperature compared with a 308L stainless steel material, so that the problem that the pillar invar panel is easy to have weld cracks and large pores after being welded can be effectively solved, and the welding quality is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a welding method for a support invar panel of a liquid cargo tank of an LNG ship. BACKGROUND

[0002] LNG is the abbreviation of Liquefied Natural Gas, which is liquefied natural gas. Its main component is methane, which is recognized as the cleanest fossil energy in the world. Because it is colorless, odorless, non-toxic and non-corrosive, and its volume is only about 1 / 625 of the volume of equal amount of natural gas, it is considered as an ideal primary energy that can be transported on a large scale.

[0003] LNG ship is a reliable carrier for long-distance transportation of liquefied natural gas. In recent years, the prospect is good. At the same time, LNG ship is also considered as one of the most difficult ship types to build in the world. The biggest difference between LNG ship and ordinary ship is that it is mainly used for large-scale storage and transportation of LNG, and its core is its liquid cargo tank. Because the boiling point of LNG at normal pressure is-161.5℃, it belongs to ultra-low temperature. Therefore, in the LNG shipbuilding industry, the shipyard uses low-temperature-resistant invar steel as the insulation material of the primary and secondary membranes of the cargo tank containment system.

[0004] The tightness of the primary and secondary membranes of the cargo tank containment system, that is, the number of leakage points when doing tightness test, can be used as a major indicator to evaluate the strength of a shipyard in building LNG ships from the perspective of ship owners, ship inspectors and GTT. Large NO.96 type LNG generally has 4 liquid cargo tanks and each tank is divided into 10 faces. In the construction process of the NO.96 type LNG ship 1# liquid cargo tank containment system, in order to better ensure the firmness of the insulation layer of the cargo tank during ship navigation, the shipyard installed a row of supports on the A and C faces of the AE / AH and GC / KC four longitudinal corners respectively to reinforce the insulation layer.

[0005] The bottom end of the support is welded with the hull through a low position knee plate, and the secondary panel of the support is welded with the secondary membrane of the liquid cargo tank. Therefore, the welding quality of the secondary panel of the support will directly affect the firmness of the entire secondary membrane, the secondary insulation layer of the cargo tank, and even the primary and secondary insulation layers.

[0006] The inventor found in the research that the welding method for the support invar panel of the liquid cargo tank of the LNG ship in the prior art at least has the following disadvantages:

[0007] 1. In order to ensure that the product size meets the process requirements and ensure the flatness of the 8mm invar panel of the support, the product needs to be trimmed after the welding is completed. In the trimming process, the 8mm invar panel of the support may be slightly cracked by hammering.

[0008] 2. After the filler weld of the stainless steel pipe of the support column to the 8mm Invar panel has cooled, excessive welding speed during the cover welding may cause fine cold cracks to form on the weld surface.

[0009] 3. During the welding of the support column, the welder was affected by the electric fan or natural wind used by the assembler at the neighboring work station, which affected the argon gas protection and caused large pores in the weld. Summary of the Invention

[0010] The present invention aims to provide, for example, a welding method for Invar panels of struts in LNG carrier cargo tanks, which can effectively improve the problems of weld cracks and atmospheric pores that easily occur after the Invar panels of struts are welded.

[0011] The embodiments of the present invention can be implemented as follows:

[0012] In a first aspect, the present invention provides a method for welding Invar panels for struts in LNG carrier cargo tanks, comprising the following steps:

[0013] Step s100: Before welding, use a shielding material to isolate the welding area from the outside area;

[0014] Step s200: Weld the Invar panels of the support column using Invar steel welding wire.

[0015] In an optional implementation, in step s100, a mark is set in the area to be welded, and a fence is erected along the mark to separate the area to be welded from the outside.

[0016] In an optional implementation, in step s100, the enclosure is formed by detachably engaging multiple sub-plates end to end.

[0017] In an optional embodiment, in step s200, welding is performed sequentially using three welding processes: root pass welding, fill pass welding, and cover pass welding.

[0018] In an optional embodiment, in step s200, when performing the root pass welding, the diameter of the weld formed by the root pass welding is 1.5-1.7 mm.

[0019] In an optional embodiment, during step s200, the diameter of the weld formed by the filler weld is 2.3-2.5 mm.

[0020] In an optional embodiment, in step s200, when performing the cover weld, the diameter of the weld formed by the cover weld is 2.3-2.5 mm.

[0021] In an optional embodiment, in step s200, the Invar panel of the support column is welded with a spot welding distance set to 10-15mm.

[0022] In an optional embodiment, in step s200, the welding currents for the root pass, fill pass, and cover pass are 130A, 150A, and 145A, respectively.

[0023] In an optional embodiment, in step s200, the Invar panel of the support is welded at a welding speed of 60 mm / min.

[0024] The beneficial effects of the embodiments of the present invention include, for example:

[0025] In summary, the Invar panel welding method for LNG carrier cargo tank supports provided in this embodiment isolates the construction site with shielding materials during the welding process to prevent external factors from affecting argon protection and improve welding quality. Furthermore, when straightening the Invar panels for flatness after welding, avoid forceful hammering to prevent structural damage. Additionally, using Invar steel welding wire as the filler material for the support Invar panels effectively addresses the issues of weld cracks and large porosity that often occur after welding, resulting in high welding quality. Invar steel, compared to 308L stainless steel, possesses higher strength and durability at both low and high temperatures. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the welded workpiece of this application;

[0028] Figure 2 This is a flowchart illustrating the welding method of the Invar panel for the support structure of an LNG carrier cargo tank, as described in this application.

[0029] icon:

[0030] 100-304L stainless steel support tube; 200-Invar panel. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0033] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0034] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0035] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0036] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0037] This embodiment provides a welding method for Invar panels 200 used in LNG carrier cargo tank struts, applied to the manual welding of 6mm thick 304L stainless steel strut round tubes 100 and 8mm thick Invar panels 200, including the following steps:

[0038] Step s100: Before welding, use a shielding material to isolate the welding area from the outside area;

[0039] Step s200: Weld the Invar panel 200 of the support column using Invar steel welding wire.

[0040] Specifically, when isolating the welding area from the outside world, choose appropriate shielding materials, such as fireproof cloth or heat insulation boards, to ensure that the shielding materials can effectively isolate the welding area from the external environment. At the same time, clean the welding area to remove oil, dust, and other impurities to ensure that the welded surface is clean.

[0041] It should be understood that placing shielding objects around the welding area is necessary to ensure that the shielding objects can completely cover the welding area and prevent the external environment from affecting the welding process.

[0042] It should be noted that by preparing for welding and performing the welding operation, the welding quality of the Invar 200 support panels of the LNG carrier's cargo tank can be ensured, thus guaranteeing the safety and reliability of the cargo tank. Before welding, ensuring the control of the welding environment and the accuracy of welding parameters provides a good foundation for subsequent non-destructive testing and grinding. This welding method is particularly suitable for the construction of LNG carrier cargo tanks, ensuring the safety and stability of the ship during the transportation of liquefied natural gas.

[0043] The following embodiments illustrate the details of the welding method for the Invar panel 200 of the support structure for the liquid cargo tank of an LNG ship according to this application by way of example.

[0044] In this embodiment, optionally, in step s100, markings are set on the area to be welded, and a fence is erected along the markings to isolate the area to be welded from the outside. The outer markings of the welding area can be made with a pen or powder, which is convenient and simple. The fence design is based on the markings, making the operation convenient and the fence position accurate and reliable.

[0045] In this embodiment, optionally, in step s100, a barrier is formed by detachably engaging multiple sub-plates end to end.

[0046] It should be understood that the structure of the fence is simple, and since the fence is made of multiple sub-panels spliced ​​together, the number of fences can be selected as needed to adapt to the usage requirements of different scenarios. During on-site construction, it can also be adjusted according to the situation, making it flexible and convenient.

[0047] In addition, since the sub-boards are detachably connected, they can be disassembled into individual structures during transport or storage. They are small in size, stackable to prevent compact structures, occupy little space, are easy to store, and reduce operating and storage costs.

[0048] It should be understood that sub-panels come in various forms and materials, and can be selected according to needs. When designing the fencing on-site, different styles can be constructed according to requirements, including but not limited to square, round, etc. Furthermore, to improve the fencing's sturdiness, widening components can be installed at the bottom, increasing the contact area with the ground and enhancing stability.

[0049] In this embodiment, optionally, in step s200, welding is performed sequentially using three welding processes: root pass welding, fill pass welding, and cap pass welding. By employing these three welding processes sequentially, the welding quality of the Invar panels 200 supporting the LNG carrier's cargo tank can be ensured, improving the reliability and safety of the welding. Strict control over each step before welding provides a good foundation for subsequent non-destructive testing and polishing. The combination of multiple welding methods significantly improves the overall welding quality.

[0050] In this embodiment, optionally, in step s200, when performing the root pass welding, the diameter of the weld formed by the root pass welding is 1.5-1.7mm.

[0051] It should be understood that in the actual welding process, the diameter of the weld formed by the root pass can be set to 1.5mm, 1.6mm or 1.7mm, etc.

[0052] It should be understood that by controlling the weld diameter of the root pass to 1.5-1.7 mm, the size and shape of the molten pool can be better controlled, ensuring complete fusion at the weld root. This is crucial for preventing incomplete penetration and lack of fusion defects at the root. Simultaneously, it helps reduce porosity formation because a smaller molten pool allows for easier gas expulsion, reducing porosity. Furthermore, this weld diameter range design results in a smoother, more uniform weld, improving its appearance quality.

[0053] In this embodiment, optionally, in step s200, during the filler welding, the diameter of the weld formed by the filler welding is 2.3-2.5 mm.

[0054] It should be understood that in the actual welding process, the diameter of the filler weld can be set to 2.3mm, 2.4mm or 2.5mm, etc.

[0055] It is worth noting that a weld diameter of 2.3-2.5 mm can ensure uniform filling of the weld, avoid welds that are too thick or too thin, thereby improving the stability and consistency of the weld; in addition, it also helps to reduce the formation of interpass porosity, because a larger molten pool can better expel gas and reduce the generation of porosity.

[0056] In this embodiment, optionally, in step s200, when performing the cover weld, the diameter of the weld formed by the cover weld is 2.3-2.5 mm.

[0057] It should be noted that the diameter of the weld formed by the cover weld can be 2.3mm, 2.4mm or 2.5mm, etc.

[0058] Controlling the weld diameter of the cap weld to between 2.3-2.5mm ensures a smooth weld surface, preventing excessively thick or thin welds and improving its aesthetics. It also helps ensure weld uniformity, reducing surface irregularities and resulting in a smoother weld. Furthermore, it allows for more flexible welding operations, making it easier for welders to control weld formation, especially in longer welds or complex structures. Additionally, it reduces welding spatter, minimizes cleanup work, and improves overall efficiency.

[0059] In this embodiment, optionally, in step s200, the support Invar panel 200 is welded with a spot welding distance set to 10-15mm.

[0060] It should be noted that during welding, the spot welding distance can be controlled at 10mm, 12.5mm, or 15mm, etc. This ensures the uniform distribution of weld spots, avoiding excessively dense or sparse weld spots, thereby improving the uniformity and stability of the weld; it also reduces the heat input of each weld spot, thereby reducing the width of the weld heat-affected zone, reducing thermal deformation and residual stress, and improving the overall performance of the welded structure.

[0061] In this embodiment, optionally, in step s200, the welding currents for the root pass, fill pass, and cap pass are 130A, 150A, and 145A, respectively. It should be understood that controlling the welding current satisfies welding requirements while also reducing costs.

[0062] In this embodiment, optionally, in step s200, the Invar panel 200 of the support column is welded at a welding speed of 60 mm / min. By setting a reasonable welding speed, the stability of the welding can be ensured, thereby improving the welding quality.

[0063] The welding method for the Invar panel 200 support structure of the LNG carrier cargo tank provided in this embodiment has at least the following advantages:

[0064] 1. Invar steel welding wire is used as the filler material for the Invar panel 200 of the support column. Since Invar steel has higher strength and durability than 308L stainless steel at both low and high temperatures, it can fundamentally solve the problem of weld cracks and large air holes that are easy to occur after the Invar panel 200 of the support column is welded.

[0065] 2. For welders on site, Invar steel welding wire has a lower hardness than 308L stainless steel welding wire, making it easier to weld the Invar 200 panels of the support columns, resulting in better welding quality and higher welding efficiency.

[0066] 3. The weld formation after welding with Invar steel welding wire is good, the macroscopic metallographic structure of the weld is free of defects, and the welding quality is high.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for welding Invar panels for struts in LNG carrier cargo tanks, characterized in that, Includes the following steps: Step s100: Before welding, use a shielding material to isolate the welding area from the outside area; Step s200: Weld the Invar panels of the support column using Invar steel welding wire.

2. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 1, characterized in that: In step s100, markings are set in the area to be welded, and a fence is erected along the markings to separate the area to be welded from the outside world.

3. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 2, characterized in that: In step s100, the enclosure is formed by detachably fitting multiple sub-plates end to end.

4. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 1, characterized in that: In step s200, welding is performed sequentially using three welding processes: root pass welding, fill pass welding, and cover pass welding.

5. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, when performing the root pass welding, the diameter of the weld formed by the root pass welding is 1.5-1.7 mm.

6. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, during the filler welding, the diameter of the weld formed by the filler welding is 2.3-2.5 mm.

7. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, when performing the cover weld, the diameter of the weld formed by the cover weld is 2.3-2.5 mm.

8. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, the Invar panel of the support column is welded with a spot welding distance of 10-15mm.

9. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, the welding currents for the root pass, fill pass, and cover pass are 130A, 150A, and 145A, respectively.

10. The welding method for Invar panels of struts in LNG carrier cargo tanks according to claim 4, characterized in that: In step s200, the Invar panel of the support is welded at a welding speed of 60 mm / min.

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