A method of welding a head and a method of welding a liquid cargo tank

Abstract

The application discloses a head welding method and a liquid cargo tank welding method. The head welding method preliminarily fixes the head by positioning welding, hoists the head to the cylinder section for positioning welding, preliminarily fixes the head and the cylinder section to form an assembly, offsets the gravity center of the assembly relative to the gravity center of the single head towards the cylinder section, provides conditions for the shift welding of the connecting joint of the head on the rolling support, turns over the assembly and hoists the assembly to the rolling support, makes the axis of the assembly horizontal, rotates the assembly, and makes the first connecting joint or the second segmented weld or the third segmented weld on the head located in the horizontal welding range, so that horizontal welding or flat welding can be performed. Compared with the traditional process which adopts the horizontal welding and vertical welding mode all the time, the head weld welding mode is changed, horizontal welding or flat welding of the connecting joint is realized, the heat input and the welding difficulty are greatly reduced, and the mechanical properties and the welding quality of the welding joint are improved.

Description

Technical Field

[0001] This application relates to the field of liquid cargo tank assembly and welding technology, and particularly to a head welding method, as well as a liquid cargo tank welding method. Background Technology

[0002] Small and medium-sized liquefied natural gas (LNG) carriers and liquefied petroleum gas (LPG) carriers often use C-type tank designs for their cargo tanks. C-type cryogenic cargo tanks have spherical heads at both ends of the hull. The heads consist of multiple arc-shaped temperate plates and a circular crown plate on top. The butt joints between adjacent temperate plates are arc-shaped, while the butt joints between the crown plate and the temperate plates are circular. When welding the heads, welders need to perform irregular welding movements in the vertical direction, which increases the difficulty of welding. During the welding process, problems such as incomplete fusion of the bevel surface, slag inclusions in the weld, and failure to meet design requirements in mechanical properties are prone to occur.

[0003] In related technologies, due to the large size of the end cap, the end cap is constructed horizontally with the equatorial seam (the periphery of the end circle of the hemispherical end cap) as the base surface, with the equatorial seam facing the ground. A temporary support frame is built into the inner side of the end cap to temporarily fix the temperate plate. Welders use scaffolding or hoisting cages on the inner and outer sides to move and perform welding operations, so as to achieve the welding of vertical arc-shaped butt joints at different positions between multiple adjacent temperate plates and the circular butt joints between the temperate plate and the crown plate. After the large-sized end cap is welded, the end cap is then welded and assembled with the cylinder section.

[0004] The above process has the following problems:

[0005] 1. The vertical arc weld of the temperate plate is welded in both vertical and overhead positions (the upper part of the arc butt joint). The crown plate is welded to the temperate plate on one side in the overhead position and on the other side in the flat position. The welding in the vertical and overhead positions is more difficult and requires higher skills from the welders.

[0006] 2. Furthermore, the arc-shaped and long weld seams, coupled with the poor welding environment caused by welders moving on scaffolding or suspended cages, easily lead to problems such as incomplete fusion of the bevel surface and slag inclusions in the butt joints between the end caps and temperate zone plates. This necessitates extensive weld rework, and repeated heating or excessive heat input is detrimental to the low-temperature mechanical properties of the C-shaped cryogenic liquid cargo tank welds. Additionally, according to standards, the butt joints of C-type cryogenic liquid cargo tanks require the welding of a test plate under equivalent welding conditions. This test plate must undergo tensile, bending, and low-temperature impact mechanical property testing. Vertical welding positions have higher heat input than other welding positions. Excessive heat input reduces the strength, plasticity, and low-temperature impact resistance of the weld, easily leading to the failure of the mechanical property tests for the vertical butt joint test plates between temperate zone plates. This necessitates the rework of all welds represented by the test plates or replacement of the plates, resulting in significant losses. Summary of the Invention

[0007] This application aims to at least partially solve one of the aforementioned technical problems in the prior art. To this end, embodiments of this application provide a head welding method and a liquid cargo tank welding method, which change the welding method of the head weld, reduce heat input and welding difficulty, thereby improving the mechanical properties and welding quality of the weld.

[0008] According to an embodiment of the first aspect of this application, a method for welding a head is provided for welding a head to a cylindrical section. The head is hemispherical and includes a circular crown plate and multiple arc-shaped temperate plates. Each temperate plate is circumferentially connected to the circumferential edge of the crown plate. The weld between the head and the cylindrical section is an equatorial weld. The method for welding the head includes the following steps:

[0009] Steps for creating bevels: Create inner bevels on the four sides of the temperate plate and the circumferential edge of the crown plate, with each inner bevel facing the inside of the end cap;

[0010] Head assembly steps: The head is constructed horizontally using the equatorial seam as the base surface. A temporary support frame is built in to temporarily fix each of the temperate plates and the crown plate. The connecting weld between each pair of adjacent temperate plates is the first connecting seam, and the connecting weld between the crown plate and the temperate plate is the second connecting seam. The second connecting seam includes a second segment weld that is connected end to end in sequence. The equatorial seam includes a third segment weld that is connected end to end in sequence. Positioning welds are performed on the first connecting seam and the second connecting seam to assemble the crown plate and each of the temperate plates into the head.

[0011] Head hoisting steps: Hoist the head, place the head on the cylindrical section, perform tack welding on the equatorial seam, and assemble the head and the cylindrical section into a combined assembly;

[0012] Assembly flipping step: Flip the assembly and hoist it onto the rolling support so that the axis of the assembly is horizontal. The assembly is rotatably set on the rolling support. A workbench is set up on the inner and / or outer side of the end cap.

[0013] Welding steps: Rotate the assembly so that the first connecting seam, the second segment weld, or the third segment weld on the end cap is within the horizontal welding range, and weld the first connecting seam, the second segment weld, or the third segment weld on the workbench.

[0014] Repeat the welding steps until all the first joint, second segment welds, and third segment welds are completed.

[0015] In an optional or preferred embodiment, the end cap includes the temperate plate divided into n equal parts, where n is an even number. The first connecting seam and another first connecting seam on the opposite side are on the same plane. The two opposing first connecting seams form a first welding group. The welding step includes welding each of the first connecting seams, and welding each of the first connecting seams includes the following steps:

[0016] Rotate the assembly so that the two first connecting seams of one of the first welding groups are respectively located in the horizontal welding range, and weld the two first connecting seams of the first welding group respectively.

[0017] Rotate the assembly so that the two first connecting seams of the adjacent first welding group are in the horizontal welding range, and weld the two first connecting seams of the first welding group respectively; repeat the rotation of the assembly n / 2 times to complete the welding of all the first welding groups in sequence.

[0018] In an optional or preferred embodiment, the second segmented weld is set to an even number of welds, and two opposite second segmented welds form a second welding group. The welding step further includes welding the second connecting seam, which includes the following steps:

[0019] The two first connecting seams of the first welding group are in a horizontal position. The two second segment welds located at the top and bottom respectively are selected as the first welding group of the second welding group. The two second segment welds of the second welding group are welded respectively.

[0020] Rotate the assembly so that the two second segment welds of the adjacent second welding group are located in the horizontal welding range, and weld the two second segment welds of the second welding group respectively;

[0021] Repeatedly rotate the assembly to complete the welding of all second welding groups in sequence.

[0022] In an optional or preferred embodiment, the third segment weld is set to an even number of welds, and the two opposite third segment welds form a third welding group. The welding step further includes welding the equatorial seam, which includes the following steps:

[0023] The two first connecting seams of the first welding group are in a horizontal position. The two third segment welds located at the top and bottom respectively are selected as the first third welding group to be welded. The two third segment welds of the third welding group are welded respectively.

[0024] Rotate the assembly so that the two third segment welds of the adjacent third welding group are located in the horizontal welding range, and weld the two third segment welds of the third welding group respectively;

[0025] Repeatedly rotate the assembly to complete the welding of all third welding groups in sequence.

[0026] In an optional or preferred embodiment, the steps of welding the second connecting seam and welding the equatorial seam are performed simultaneously.

[0027] In an optional or preferred embodiment, the number of the second segment weld and the third segment weld are the same, both being n+2 or n+4. In the steps of welding the second connecting seam and welding the equatorial seam, the angle of rotation of the assembly is 360 / (n+2) degrees or 360 / (n+4) degrees.

[0028] In an optional or preferred embodiment, the positioning welding performed on the first connecting seam, the second connecting seam, and the equatorial seam in the head assembly step and the head hoisting step are performed on the back side of the corresponding inner bevel.

[0029] In optional or preferred embodiments, the thickness of the temperate plate and the crown plate is T. When 15mm ≤ T < 16mm, a V-shaped bevel is formed, which is the inner bevel; when 16mm ≤ T < 20mm, a Y-shaped bevel is formed, which is the inner bevel; when T ≥ 20mm, an X-shaped double-sided bevel is formed, and the one facing the inside of the end cap is the inner bevel.

[0030] In an optional or preferred embodiment, the welding step involves a double-sided welding process for the first connecting seam, the second connecting seam, and the equatorial seam. The double-sided welding process includes the following steps: welding at least one weld layer on the reverse side, performing carbon arc gouging to clean the root on the front side, grinding the front side, and finally sealing the bottom with welding. The inner bevel side is the reverse side.

[0031] According to an embodiment of the second aspect of this application, a liquid cargo tank assembly and welding method is provided, wherein two heads are assembled and welded using the above-described head assembly and welding method to form two assemblies, and the two assemblies and the remaining cylindrical section are joined and welded together to form the liquid cargo tank.

[0032] Based on the above technical solution, the embodiments of this application have at least the following beneficial effects:

[0033] The above technical solution initially uses the equatorial seam as the base surface for horizontal construction. By performing tack welding on the head, the temperate plate and crown plate are initially fixed. Then, it is hoisted onto the cylindrical section for tack welding to initially fix the head and the cylindrical section, forming an assembly. This makes the center of gravity of the assembly offset from the center of gravity of the individual head towards the cylindrical section, thus providing conditions for displacement welding of the head's connecting seam on the rolling support. The assembly is then flipped and hoisted onto the rolling support, making the axis of the assembly horizontal. The assembly can rotate on the rolling support. By rotating the assembly, the first connecting seam, second segment weld, or third segment weld on the head is placed within the horizontal welding range, allowing for horizontal or flat welding of the first connecting seam, second segment weld, or third segment weld. Compared to the traditional method of horizontal construction throughout, this solution uses an initial horizontal construction to temporarily fix the head and cylinder into a combined assembly. Then, it is flipped onto a rolling support, changing the axis of the head from vertical to horizontal. The head can be easily moved by rotation, placing each joint within the horizontal welding range. This enables horizontal or flat welding of the joints, changing the welding method of the head weld. Compared to the traditional vertical welding, this greatly reduces heat input and welding difficulty, and improves the mechanical properties and welding quality of the weld. Attached Figure Description

[0034] The present application will be further described below with reference to the accompanying drawings and embodiments;

[0035] Figure 1 This is a schematic diagram of the structure of the end cap according to an embodiment of this application;

[0036] Figure 2 This is a schematic diagram of the structure in this application embodiment, showing the end cap being hoisted onto the cylindrical section;

[0037] Figure 3 This is a schematic diagram of the structure of the assembly of the present application placed on the rolling support;

[0038] Figure 4 This is an embodiment of the present application. Figure 1 Bottom view of the center head;

[0039] Figure 5 This is an embodiment of the present application. Figure 4 A schematic diagram of the structure of the middle head after all the first joints have been welded;

[0040] Figure 6 This is a schematic diagram of the V-shaped inner bevel in an embodiment of this application;

[0041] Figure 7 This is a schematic diagram of the structure of the X-type inner bevel in an embodiment of this application;

[0042] Figure 8 This is a structural schematic diagram of the liquid cargo tank in an embodiment of this application.

[0043] Figure label:

[0044] 100 end cap, 110 crown plate, 120 temperate plate, 130 inner bevel, 140 first connecting seam, 150 second connecting seam, 151 second segment weld, 160 equatorial seam, 161 third segment weld, 170 temporary fixing seam, 200 cylinder section, 300 assembly, 400 rolling support, 500 worktable. Detailed Implementation

[0045] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0046] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application 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 application.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0048] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0049] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0051] Reference Figure 1 and Figure 8 The liquid cargo tank includes two hemispherical shell-shaped heads 100 and several cylindrical sections 200. The head 100 includes a circular crown plate 110 and multiple arc-shaped temperate plates 120, with each temperate plate 120 circumferentially connected to the circumferential edge of the crown plate 110.

[0052] The following reference Figures 1 to 8 This embodiment describes a method for welding a head, wherein a crown plate 110 is welded and fixed to multiple temperate plates 120 to form a head 100, and the head 100 is then welded to a cylindrical section 200. The weld connecting the head 100 and the cylindrical section 200 is an equatorial weld 160.

[0053] The head assembly and welding method includes the following steps:

[0054] S100, Beveling steps: Inner bevels 130 are made on the four sides of the temperate plate 120, the circumferential edge of the crown plate 110, and the end circumferential edge of the cylindrical section 200, with each inner bevel 130 facing the inside of the end cap 100.

[0055] In some specific embodiments, the thickness of the temperate plate 120 and the crown plate 110 is T. When 15mm ≤ T < 16mm, a V-shaped bevel is formed, which is the inner bevel 130, as shown in the reference. Figure 6When 16mm ≤ T < 20mm, a Y-shaped bevel is formed, which is the inner bevel 130; when T ≥ 20mm, an X-shaped double-sided bevel is formed, and the one facing inward towards the end cap 100 in the X-shaped double-sided bevel is the inner bevel 130, as shown in the reference. Figure 7 Different bevel shapes are designed according to the thickness of the different temperate plates 120 and crown plates 110, which helps to improve the welding quality.

[0056] S200, Head Assembly Steps: Refer to... Figure 1 A head 100 is constructed horizontally with the equatorial seam 160 as the base surface. A temporary support frame is built on the inner side to temporarily support and fix the crown plate 110 and each temperate plate 120 in a hemispherical shape, forming the head 100. The axis of the head 100 is vertical. The connecting weld between any two adjacent temperate plates 120 is the first connecting weld 140, which is arc-shaped. The connecting weld between the circumferential edge of the crown plate 110 and the top edges of the multiple temperate plates 120 is the second connecting weld 150, which is located on top of the first connecting weld 140 and is annular. The second connecting weld 150 includes second segment welds 151 connected end to end, and the equatorial seam 160 includes third segment welds 161 connected end to end. Position welding is performed on the first connecting seam 140 and the second connecting seam 150 to form a temporary fixing seam 170. The temperate plates 120 and the crown plate 110 are assembled into a head 100, which facilitates the hoisting, transfer and flipping of the head 100 in steps S300 and S400.

[0057] S300, head hoisting steps: Refer to Figure 2 Lifting lugs are welded and fixed to the outside of the head 100. The head 100 is then lifted using these lugs and placed on the cylindrical section 200. The equatorial seam 160 is located at the bottom of the first connecting seam 140 and is annular. Tack welding is performed on the equatorial seam 160 to assemble the head 100 and the cylindrical section 200 into a composite assembly 300.

[0058] S400, Assembly Flipping Steps: Refer to... Figure 3 The assembly 300 is flipped and hoisted onto the rolling support 400, making its axis horizontal. The assembly 300 is rotatably mounted on the rolling support 400. Specifically, the rolling support 400 can be a roller frame, with several rollers or shafts supporting the main body of the cylindrical section 200, enabling rotatable operation of the assembly 300, including the end cap 100, with the axis of the assembly 300 as the center of rotation. A workbench 500 is erected on the inner and / or outer side of the end cap 100; a horizontal scaffold can be used as the workbench 500.

[0059] This solution uses tack welding to temporarily fix the end cap 100 itself, and then temporarily fixes the end cap 100 and the cylindrical section 200 to form an assembly 300. The center of gravity of the assembly 300 is offset from the center of gravity of the individual end cap 100 towards the cylindrical section 200. The center of gravity of the assembly 300 is on the main body of the cylindrical section 200. Since the main body of the cylindrical section 200 is a regular cylindrical shape, it is convenient to operate the assembly 300 so that it is placed horizontally with the axis horizontal. This provides conditions for the displacement welding of the butt joint of the end cap 100 on the rolling support 400, so that the horizontal or flat welding of the butt joint of the end cap 100 can be performed subsequently.

[0060] Traditional welding processes for cargo tank heads, due to their large size and weight, involve horizontal construction with the equatorial seam as the base surface, ensuring the head axis remains vertical throughout. After welding the head, the entire cargo tank is assembled by welding the head onto the cylindrical section 200, and then welding the head and section 200 together. A single head 100, being hemispherical, is inconvenient for support, fixation, and relocation. This solution pre-positions and welds the head 100 and section 200, transforming the individual welding of the head into a comprehensive welding of both, facilitating operation and significantly improving the overall welding efficiency of the cargo tank.

[0061] S500, Welding Procedure: Refer to... Figure 4 and Figure 5 Rotate the assembly 300 so that the first connecting seam 140, the second segment weld 151, or the third segment weld 161 on the end cap 100 is within the horizontal welding range. The operator welds the first connecting seam 140, the second segment weld 151, or the third segment weld 161 on the workbench 500. Specifically, horizontal welding or flat welding can be performed.

[0062] Repeat the welding steps until all the first connecting seams 140, the second segment welds 151, and the third segment welds 161 are completed. Specifically, welding is performed on the inner bevel 130 corresponding to each connecting seam to complete the welding of the end cap 100.

[0063] It is understood that the horizontal welding range refers to the range within which the worker can perform horizontal or flat welding on the weld seam. Specifically, it includes the first connecting seam rotated to a generally horizontal (not necessarily completely horizontal) position, the second segment weld 151 with its top and bottom generally horizontal, and the third segment weld 161 with its top and bottom generally horizontal.

[0064] Those skilled in the art will understand that a flat weld refers to a weld with a weld inclination angle of 0° to 5° and a weld turn angle of 0° to 10°, welded in a horizontal position; a transverse weld refers to a weld with a weld inclination angle of 0° to 5° and a butt weld turn angle of 70° to 90°, welded in a horizontal position; and a vertical weld refers to a weld with a weld inclination angle of 80° to 90° and a weld turn angle of 0° to 180°, welded in a vertical position. Both horizontal and flat welding methods involve arrangements in a horizontal plane or parallel to the ground plane, and the molten metal tends to flow downwards or to lower areas due to its own weight. These two welding methods are significantly superior to vertical or overhead welding. The horizontal welding range can be further understood as the range of horizontal operating positions where the weld inclination angle is 0° to 5° and the molten pool metal is not vertical or inverted.

[0065] The assembly 300 is flipped so that the axis of the head 100 is horizontal, which facilitates the welding of the head 100 and enables horizontal or flat welding of the butt joint on the head 100.

[0066] Specifically, the first connecting seam 140 is arc-shaped, and each first connecting seam 140 surrounds the crown plate 110 and is also circumferentially distributed around the axis of the end cap 100 / assembly 300. Therefore, by rotating the assembly 300 to the 3 o'clock or 9 o'clock position, the corresponding first connecting seam 140 can be made horizontal and located within the horizontal welding range, allowing workers to perform horizontal welding. The second connecting seam 150 is annular, and the plane of the second connecting seam 150 is perpendicular to the axis of the assembly 300. By dividing the second connecting seam 150 into multiple second segment welds 151 for welding, when the assembly 300 is rotated to a certain position, the second segment welds 151 directly above (12 o'clock position) or directly below (6 o'clock position) the axis are roughly horizontal. Although they have a certain curvature, they are still within the horizontal welding range, basically enabling horizontal welding. Similarly, the equatorial seam 160 is annular. By dividing the equatorial seam 160 into multiple third segment welds 161 for welding, when the assembly 300 is rotated to a certain position, the third segment welds 161 directly above (12 o'clock position) or directly below (6 o'clock position) the axis are located in the horizontal welding range, which can achieve flat welding.

[0067] It should be noted that those skilled in the art will understand that the aforementioned 6 o'clock and 12 o'clock positions are based on clock times. The 6 o'clock position refers to the lower position, but it is not limited to exactly 6 o'clock; it can also be in the range between 4 o'clock and 8 o'clock, to facilitate welding. Therefore, when interpreting the scope of protection of this application, the 6 o'clock position should be understood as the range between 4 o'clock and 8 o'clock, with the optimal position during operation being closer to 6 o'clock. Similarly, the 12 o'clock position refers to the upper position. Likewise, when interpreting the scope of protection of this application, the 12 o'clock position should be understood as the range between 10 o'clock and 2 o'clock, with the optimal position during operation being closer to 12 o'clock.

[0068] Compared to traditional vertical welding, where workers need to move vertically along scaffolding or a suspended cage, and each weld joint requires extensive movement around the inner or outer circumference of the head 100, this solution uses horizontal or flat welding. By rotating the assembly 300, the position of each weld joint on the head 100 can be changed, placing each weld joint within a horizontal welding range. Workers can perform horizontal or flat welding on the workbench 500, greatly reducing heat input and welding difficulty, thereby improving the mechanical properties and welding quality of the weld joint.

[0069] It is understandable that the number of temperate plates 120 can be set according to the size of the end cap 100. When the size of the end cap 100 is large, the number of temperate plates 120 can be set to be larger.

[0070] Reference Figure 4 and Figure 5 In some specific embodiments, the end cap 100 includes n equally divided temperate plates 120, where n is an even number. The first connecting seam 140 and another first connecting seam 140 on the opposite side are on the same plane. The two opposing first connecting seams 140 form a first welding group. Step S500 includes step S510, welding each first connecting seam 140. Step S510 includes:

[0071] S511, Rotate the assembly 300 so that the two first connecting seams 140 of one of the first welding groups are respectively located in the horizontal welding range, specifically at 3 points or 9 points, and weld the two first connecting seams 140 of the first welding group respectively.

[0072] S512, Rotate assembly 300, rotate 360 / n degrees, so that the two first connecting seams 140 of the adjacent first welding group are located in the horizontal welding range, specifically at 3 points or 9 points, and weld the two first connecting seams 140 of the first welding group respectively.

[0073] S513. Repeat step S512, rotate assembly 300 repeatedly, rotate n / 2 times, and complete the welding of all first welding groups in sequence, thereby completing the welding of all first connecting seams 140.

[0074] In some embodiments, the number of second segment welds 151 is even, and two opposite second segment welds 151 constitute a second welding group. Step S500 further includes step S520, welding the second connecting seam 150, which includes:

[0075] S521. The two first connecting seams 140 of the first welding group are in a horizontal position. The two second segment welds 151 located at the top and bottom respectively are selected as the first welding group of the second welding group. The two second segment welds 151 are located in the horizontal welding range, specifically at the 6 o'clock position or the 12 o'clock position. The two second segment welds 151 of the second welding group are welded respectively.

[0076] S522, Rotate assembly 300 to place the two second segment welds 151 of the adjacent second welding group in the horizontal welding range, and weld the two second segment welds 151 of the second welding group respectively.

[0077] S523. Repeat step S522, rotate assembly 300 repeatedly, and complete the welding of all second welding groups in sequence, thereby completing the welding of the second connecting seam 150.

[0078] In some embodiments, the number of third segment welds 161 is even, and two opposite third segment welds 161 constitute a third welding group. Step S500 further includes step S530, welding the equatorial weld 160, which includes:

[0079] S531. The two first connecting seams 140 of the first welding group are in a horizontal position. The two third segment welds 161 located at the top and bottom respectively are selected as the first welding third welding group. The two third segment welds 161 are located in the horizontal welding range, specifically at the 6 o'clock position or the 12 o'clock position. The two third segment welds 161 of the third welding group are welded respectively.

[0080] S532, Rotate assembly 300 to place the two third segment welds 161 of the adjacent third welding group in the horizontal welding range, and weld the two third segment welds 161 of the third welding group respectively.

[0081] S533. Repeat step S532, rotate assembly 300 repeatedly, and complete the welding of all third welding groups in sequence, thereby completing the welding of equatorial seam 160.

[0082] Specifically, in step S531, welding the two third segment welds 161 of the third welding group can be performed by first flat welding the bottom third segment weld 161, then rotating it 180 degrees so that the third segment weld 161 originally located at the top is rotated to the bottom, and then flat welding is performed on it again, thus avoiding overhead welding. The two opposite third segment welds 161 are welded symmetrically and sequentially to reduce welding stress and improve the overall welding quality of the equatorial seam 160. When the thickness of the temperate plate 120 and the cylindrical section 200 is relatively thick, multiple layers of welds are required. The above method can be used to weld three to four layers of welds on the inner bevel 130 corresponding to the equatorial seam 160. Then, root cleaning is performed on the back side of the inner bevel 130, that is, on the outer side. Next, the bottom third segment weld 161 is flat welded. At the same time, the top third segment weld 161 can be flat welded on the outer side of the inner bevel 130. That is, the bottom third segment weld 161 and the top third segment weld 161 can be flat welded on the inner and outer sides of the head 100 at the same time.

[0083] In some embodiments, steps S520 and S530 can be performed simultaneously, meaning that when the assembly 300 rotates to a certain position, the second segment weld 151 and the third segment weld 161 can be welded simultaneously. Along the axial / length direction of the assembly 300, the second segment weld 151 and the third segment weld 161 are located in different vertical plane positions. The second segment weld 151 and the third segment weld 161 are welded simultaneously by two workers, thereby greatly improving welding efficiency and thus improving the overall assembly and welding efficiency of the head 100.

[0084] In some embodiments, the number of second segment welds 151 and third segment welds 161 is the same, both being n+2 or n+4. The second segment welds 151 and third segment welds 161 are arc-shaped. In this embodiment, the number of second segment welds 151 and third segment welds 161 is greater than the number of first connecting seams 140 to avoid their large curvature affecting horizontal or flat welding. Furthermore, the number of second segment welds 151 and third segment welds 161 should not be excessive to avoid low welding efficiency. In this scheme, the number of second segment welds 151 and third segment welds 161 is preferably n+2 or n+4. Correspondingly, in steps S522 and S532, the angle of rotation of the assembly 300 is 360 / (n+2) degrees or 360 / (n+4) degrees.

[0085] Reference Figure 4 and Figure 5This plan uses six temperate zone plates (120) as an example to illustrate the welding sequence of the first connecting seam (140), the second connecting seam (150), and the equatorial seam (160). The numbers 1# to 7# in the diagram indicate the welding order for each weld segment. Welds with the same number are welded simultaneously or symmetrically, and can be welded by multiple workers at the same time. The arrows in the diagram indicate the welding direction. The specific welding sequence is as follows:

[0086] (1) The number of the first connecting seams 140 is 6. (Refer to...) Figure 4 Rotate assembly 300 to rotate the No. 1 segment weld to the 3 o'clock position. The No. 1 segment weld on the opposite side is located at the 9 o'clock position. Both are within the horizontal welding range. The worker moves on the workbench 500 to perform horizontal welding on the two No. 1 segment welds.

[0087] (2) Rotate the assembly 300 by 60 degrees, rotate the No. 2 segment weld to position 3 o'clock, and the No. 2 segment weld on the opposite side to position 9 o'clock. Both are within the horizontal welding range. The worker performs horizontal welding on the two No. 2 segment welds. Refer to Figure 5 Continue to rotate the assembly 300, rotate 60 degrees, and perform horizontal welding on the two No. 3 segment welds to complete the welding of each first connecting seam 140;

[0088] (3) The second connecting seam 150 is divided into eight second segment welds 151, and the equatorial seam 160 is divided into eight third segment welds 161. The second connecting seam 150 and the equatorial seam 160 are welded simultaneously. (Refer to...) Figure 5 Select two 4# segment welds and two 4'# segment welds located in the horizontal welding range at the bottom (6 o'clock position) and top (9 o'clock position) of the 3# segment weld. The workers perform horizontal welding on the two 4# segment welds and flat welding on the two 4'# segment welds.

[0089] (4) Rotate assembly 300 by 45 degrees and perform horizontal welding on the two 5# segment welds and flat welding on the two 5'# segment welds. Repeat rotating assembly 300 by 45 degrees and welding the remaining 6# segment weld, 6'# segment weld, 7# segment weld, and 7'# segment weld in sequence to complete the welding of the second connecting seam 150 and the equatorial seam 160.

[0090] Reference Figure 6 and Figure 7 In some embodiments, in steps S200 and S300, the tack welding at the first connecting seam 140, the second connecting seam 150, and the equatorial seam 160 is performed on the back side of their respective inner bevels 130, i.e., on the outside of the end cap 100. The temporary fixing seams 170 formed by the tack welding can be spaced out on each connecting seam, using short welds.

[0091] The tack weld is placed on the back of the inner bevel 130, so that the heat-affected zone of the tack weld can be removed by carbon gouging, thereby achieving uniformity of the outer root bevel and reducing the number of heating cycles. This improves the uniformity of the cross-section and mechanical properties of the butt joint of the head 100 in the length direction, making it easier to maintain consistency in the weld cross-sectional shape and weld properties in the length direction, thus improving the welding quality and ensuring the consistency of the overall weld performance, thereby making it easier to ensure the overall safety of the liquefied tank.

[0092] Furthermore, in step S500, the first connecting seam 140, the second connecting seam 150, and the equatorial seam 160 adopt a double-sided welding process. The double-sided welding process includes the following steps: welding at least one weld layer on the reverse side, performing carbon arc gouging to clean the root on the front side (located on the outside of the head 100), grinding the front side, and finally sealing the bottom with welding. One side of the inner bevel 130 (located on the inside of the head 100) is the reverse side.

[0093] This embodiment also provides a method for welding a liquid cargo tank. Two end caps 100 are welded together using the aforementioned end cap welding method to form two assemblies 300. The two assemblies 300 and the remaining cylindrical section 200 are then joined and welded together to form the liquid cargo tank. (Refer to...) Figure 8 .

[0094] Compared to the traditional process of first welding the end cap, then hoisting the end cap onto the cylindrical section 200, welding the end cap and cylindrical section 200 together to form a composite body 300, and finally assembling and welding the two composite bodies 300 together to form a liquid cargo tank, this solution simultaneously welds the end cap 100 and the composite body 300 of the end cap 100 and cylindrical section 200, thereby greatly improving the welding efficiency.

[0095] In summary, this technical solution initially uses the equatorial seam 160 as the base surface for horizontal construction. By performing tack welding on the end cap 100, the temperate plate 120 and the crown plate 110 are initially fixed. Then, it is hoisted onto the cylindrical section 200 for tack welding, initially fixing the end cap 100 and the cylindrical section 200 to form the assembly 300. This makes the center of gravity of the assembly 300 offset from the center of gravity of the individual end cap 100 towards the cylindrical section 200, thereby providing conditions for the displacement welding of the connecting seam of the end cap 100 on the rolling support 400. The assembly 300 is flipped over and hoisted onto the rolling support 400, so that the axis of the assembly 300 is horizontal. The assembly 300 can rotate on the rolling support 400. By rotating the assembly 300, the first connecting seam 140, the second segment weld 151, or the third segment weld 161 on the end cap 100 is located within the horizontal welding range, so that the first connecting seam 140, the second connecting seam 150, or the equatorial seam 160 can be horizontally or flatly welded.

[0096] Compared to the traditional method of horizontal construction throughout, this solution uses an initial horizontal construction to temporarily fix the head 100 and the cylinder section 200 into a combined body 300. Then, it is flipped onto the rolling support 400, and the head 100 can be easily moved by rotation, thereby realizing horizontal or flat welding of each connection seam. This changes the welding method of the head 100 weld seam. Compared with the traditional vertical and overhead welding, it greatly reduces heat input and welding difficulty, improves the mechanical properties and welding quality of the weld seam, and enables easy welding of the first, second, and equatorial seams at different positions on the plane, thus improving welding efficiency.

[0097] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A method for welding a head to a cylindrical section, wherein the head is hemispherical in shape, the head includes a circular crown plate and multiple arc-shaped temperate plates, each of the temperate plates being circumferentially connected to the circumferential edge of the crown plate, and the weld connecting the head and the cylindrical section is an equatorial weld, characterized in that... The head welding method includes the following steps: Steps for creating bevels: Create inner bevels on the four sides of the temperate plate and the circumferential edge of the crown plate, with each inner bevel facing the inside of the end cap; Head assembly steps: The head is constructed horizontally using the equatorial seam as the base surface. A temporary support frame is built in to temporarily fix each of the temperate plates and the crown plate. The connecting weld between each pair of adjacent temperate plates is the first connecting seam, and the connecting weld between the crown plate and the temperate plate is the second connecting seam. The second connecting seam includes a second segment weld that is connected end to end in sequence. The equatorial seam includes a third segment weld that is connected end to end in sequence. Positioning welds are performed on the first connecting seam and the second connecting seam to assemble the crown plate and each of the temperate plates into the head. Head hoisting steps: Hoist the head, place the head on the cylindrical section, perform tack welding on the equatorial seam, and assemble the head and the cylindrical section into a combined assembly; Assembly flipping step: Flip the assembly and hoist it onto the rolling support so that the axis of the assembly is horizontal. The assembly is rotatably set on the rolling support. A workbench is set up on the inner and / or outer side of the end cap. Welding steps: Rotate the assembly so that the first connecting seam, the second segment weld, or the third segment weld on the end cap is within the horizontal welding range, and weld the first connecting seam, the second segment weld, or the third segment weld on the workbench. Repeat the welding steps until all the first joint, the second segment weld, and the third segment weld are completed. The end cap includes the temperate plate divided into n equal parts, where n is an even number. The first connecting seam and another first connecting seam on the opposite side are on the same plane. The two opposite first connecting seams form a first welding group. The welding step includes welding each of the first connecting seams. Welding each of the first connecting seams includes the following steps: Rotate the assembly so that the two first connecting seams of one of the first welding groups are respectively located in the horizontal welding range, with one of the first connecting seams located at the 3 o'clock position and the first connecting seam on the opposite side located at the 9 o'clock position, and perform horizontal welding on the two first connecting seams of the first welding group respectively. Rotate the assembly so that the two first connecting seams of the adjacent first welding group are in the horizontal welding range, and weld the two first connecting seams of the first welding group respectively; repeat the rotation of the assembly n / 2 times to complete the welding of all the first welding groups in sequence.

2. The head welding method according to claim 1, characterized in that, The second segmented weld is configured with an even number of welds, and two opposite second segmented welds form a second welding group. The welding step also includes welding the second connecting seam. Includes the following steps: The two first connecting seams of the first welding group are in a horizontal position. The two second segment welds located at the top and bottom respectively are selected as the first welding group of the second welding group. The two second segment welds of the second welding group are welded respectively. Rotate the assembly so that the two second segment welds of the adjacent second welding group are located in the horizontal welding range, and weld the two second segment welds of the second welding group respectively; Repeatedly rotate the assembly to complete the welding of all second welding groups in sequence.

3. The head welding method according to claim 2, characterized in that, The third segment weld is configured with an even number of welds, and the two opposite third segment welds form the third welding group. The welding step also includes welding the equatorial weld. Includes the following steps: The two first connecting seams of the first welding group are in a horizontal position. The two third segment welds located at the top and bottom respectively are selected as the first third welding group to be welded. The two third segment welds of the third welding group are welded respectively. Rotate the assembly so that the two third segment welds of the adjacent third welding group are located in the horizontal welding range, and weld the two third segment welds of the third welding group respectively; Repeatedly rotate the assembly to complete the welding of all third welding groups in sequence.

4. The head welding method according to claim 3, characterized in that: The steps of welding the second connecting seam and welding the equatorial seam are performed simultaneously.

5. The head welding method according to claim 4, characterized in that: The number of the second segment weld and the third segment weld are the same, both being n+2 or n+4. In the steps of welding the second connecting seam and welding the equatorial seam, the angle of rotation of the assembly is 360 / (n+2) degrees or 360 / (n+4) degrees.

6. The head welding method according to any one of claims 1 to 5, characterized in that: In the head assembly step and the head hoisting step, the positioning welding at the first connecting seam, the positioning welding at the second connecting seam, and the positioning welding at the equatorial seam are performed on the back side of the corresponding inner bevel.

7. The head welding method according to claim 6, characterized in that: The thickness of the temperate plate and the crown plate is T. When 15mm ≤ T < 16mm, a V-shaped bevel is made, which is the inner bevel; when 16mm ≤ T < 20mm, a Y-shaped bevel is made, which is the inner bevel; when T ≥ 20mm, an X-shaped double-sided bevel is made, and the one facing the inside of the end cap is the inner bevel.

8. The head welding method according to claim 6, characterized in that, In the welding process, the first connecting seam, the second connecting seam, and the equatorial seam adopt a double-sided welding process. The double-sided welding process includes the following steps: welding at least one weld layer on the reverse side, performing carbon arc gouging to clean the root on the front side, grinding the front side, and finally sealing the bottom with welding. The inner bevel side is the reverse side.

9. A method for welding liquid cargo tanks, characterized in that: The two heads are welded together using the head welding method described in any one of claims 1 to 8 to form two assemblies. The two assemblies and the remaining cylindrical section are then joined together to form the liquid cargo tank.

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