Tank manufacturing method

Abstract

To enhance toughness of a weld part as a whole, more evenly.SOLUTION: A tank manufacturing method, which manufactures a tank by welding joints of plate materials made of steel which constitute the tank, includes a step of performing welding so that a plurality of weld layers are sequentially laminated, between end parts of the plate materials opposing to each other, toward surfaces of the plate materials, and a step of removing a portion of a surface part of a low-level weld layer, before an upper-level weld layer is laminated on the lower-level weld layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a tank. [Background technology]

[0002] Various articles manufactured using metallic materials are required to have the strength and toughness required for each article. For example, Patent Document 1 discloses a configuration in which a modified layer with improved toughness is formed between a front weld layer and a back weld layer of a multi-layer butt welded joint of steel plates by applying an ultrasonic impact treatment to impart compressive residual stress. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-229692 Summary of the Invention [Problem to be solved by the invention]

[0004] For tanks containing low-temperature liquefied gas, such as those with cargo temperatures of -10°C or below, regulations stipulate the thickness, strength, toughness, and other properties of the material forming the tank. Therefore, the welds joining the steel plates forming the tank are also required to have the required toughness. Even if a modified layer with improved toughness is formed using the configuration disclosed in Patent Document 1, there is a possibility that the toughness will not be improved in areas other than the modified layer. To improve the toughness of a weld, it is desirable to increase the toughness more uniformly throughout the entire weld.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing a tank that can increase toughness more uniformly throughout the entire weld. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a method for manufacturing a tank according to the present disclosure is a method for manufacturing a tank by joint-welding steel plates that constitute the tank. The method for manufacturing a tank includes a step of welding and a step of removing a portion of a surface layer of a lower weld layer. The step of welding is performed between the ends of the opposing plates so that multiple weld layers are sequentially stacked toward the surface side of the plates. The step of removing a portion of the surface layer of the lower weld layer removes a portion of the surface layer of the lower weld layer before stacking the upper weld layer on the lower weld layer. In the process of removing a portion of the surface layer of the lower welding layer, the portion of the surface layer of the lower welding layer is removed so that when the upper welding layer is stacked on top of the lower welding layer, the reheating range due to heat input from the upper welding layer extends to the entire lower welding layer after the portion of the surface layer has been removed. [Effects of the Invention]

[0007] According to the tank manufacturing method of the present disclosure, toughness can be increased more uniformly throughout the entire weld. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a tank manufactured by a tank manufacturing method according to an embodiment of the present disclosure. [Figure 2] 1 is a cross-sectional view showing a weld between steel tank plate materials that constitute a tank according to an embodiment of the present disclosure. FIG. [Figure 3] 1 is a flowchart showing the steps of a method for manufacturing a tank according to an embodiment of the present disclosure. [Figure 4] 10A to 10C are diagrams illustrating a process of obtaining a reheating range in a welded layer and a process of setting a range for removing a portion of a surface layer portion of a welded layer, in a method for manufacturing a tank according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a diagram showing a state in which a first welded layer has been formed by a welding process according to an embodiment of the present disclosure. [Figure 6] 10A and 10B are diagrams illustrating a state in which a portion of the surface layer portion of a first welding layer has been removed by a step of removing a portion of the surface layer portion of a lower welding layer according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a diagram showing a state in which a second welded layer has been formed by a welding process according to an embodiment of the present disclosure. [Figure 8]10 is a diagram showing a state in which a portion of the surface layer portion of the second welded layer has been removed by a step of removing a portion of the surface layer portion of the lower welded layer according to an embodiment of the present disclosure. FIG. [Figure 9] FIG. 10 is a diagram showing a state in which an outermost welded layer has been formed by a step of forming an outermost welded layer according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a method for manufacturing a tank according to an embodiment of the present disclosure will be described with reference to FIGS. (Tank configuration) As shown in FIG. 1, the tank 1 of this embodiment is a tank capable of storing liquefied gas such as liquefied carbon dioxide. It is installed in the hull of a ship, the floating body of an offshore floating facility, a liquefied gas storage facility on land, or the like. The tank 1 illustrated in this embodiment is cylindrical. The tank 1 includes a tubular portion 2 and a head portion 3. The tubular portion 2 extends in a central axis direction Dc. In this embodiment, the tubular portion 2 is formed in a cylindrical shape, and a cross section perpendicular to the central axis direction Dc is circular. The head portions 3 are respectively disposed at both ends of the tubular portion 2 in the central axis direction Dc. Each head portion 3 has a spherical shape, such as a hemisphere, and closes an opening of the tubular portion 2 in the central axis direction Dc. Note that the tank 1 is not limited to a cylindrical shape and may be other shapes, such as a spherical shape or a rectangular shape.

[0010] FIG. 2 is a cross-sectional view showing a welded portion between steel plates that constitute a tank according to an embodiment of the present disclosure. 2, the tank 1 is formed by joint-welding a plurality of steel plates 20. The plates 20 constituting the tank 1 are formed of a metal material such as high-strength tempered steel. In this embodiment, the thickness of the plate 20 in the thickness direction Dt is, for example, about 10 to 100 mm.

[0011] In this embodiment, the plate materials 20 have a groove portion 21V having a V-shaped cross section, which is a V-groove. In the groove portion 21V, the end portions 20a of the plate materials 20 facing each other have inclined surfaces 20s. The inclined surfaces 20s of the facing plate materials 20 are formed so that the distance between them in the facing direction Da gradually decreases from the surface 20f on the first side Dt1 in the plate thickness direction Dt to the surface 20g on the second side Dt2 in the plate thickness direction Dt. The groove portion 21V extends in a direction perpendicular to the facing direction Da of the plate materials 20 and the plate thickness direction Dt of the plate materials 20 (a direction perpendicular to the plane of the paper in FIG. 2).

[0012] The ends 20a of the opposing plate materials 20 are joined together via a welded portion 30. The welded portion 30 is formed between the ends 20a of the plate materials 20. The welded portion 30 is formed by multi-layer welding. In multi-layer welding, the welded portion 30 is formed between the ends 20a of the opposing plate materials 20 by repeating welding multiple times. Multi-layer welding is suitable for reducing the amount of heat input to the plate materials 20 during each welding.

[0013] The welded portion 30 has a plurality of welded layers 31. In this embodiment, six welded layers 311 to 316 are formed as the welded layers 31 of the welded portion 30 (see FIG. 9). Note that FIG. 2 illustrates only five welded layers 311 to 315 out of the six welded layers 311 to 316. The welded layers 311 to 316 are stacked in order from the second side Dt2 in the plate thickness direction Dt toward the surface 20f of the first side Dt1 in the plate thickness direction Dt. Note that the number of layers of the plurality of welded layers 31 is determined depending on the plate thickness of the plate material 20, etc., and can be changed as appropriate. A portion of the surface layer 31a of each of the welded layers 311 to 315 is removed, as will be described in detail later.

[0014] (Tank manufacturing procedure) Fig. 3 is a flowchart showing the steps of a method for manufacturing a tank according to an embodiment of the present disclosure. Fig. 4 is a diagram schematically showing a step of obtaining a reheating range in a welded layer and a step of setting a range for removing a part of a surface layer portion of the welded layer in the method for manufacturing a tank according to an embodiment of the present disclosure. As shown in FIG. 3, the manufacturing method S10 of the tank 1 according to this embodiment includes a step S11 of obtaining a reheat range in the welded layer, a step S12 of setting a range for removing a portion of the surface layer of the welded layer, a step S13 of performing welding, a step S14 of removing a portion of the surface layer of the lower welded layer, a step S15 of forming the outermost welded layer, and a step S16 of removing at least a portion of the outermost welded layer.

[0015] In step S11 of acquiring a reheat range in a welded layer, the reheat range in the lower welded layer 31 is acquired. Here, in step S13 of performing welding, which will be described later, welding is repeated multiple times from the second side Dt2 toward the first side Dt1 in the plate thickness direction Dt to sequentially stack and form welded layers 311-315 and the outermost welded layer 316. At this time, welding heat is input to the lower welded layer 31, which is formed first, when welding the upper welded layer 31 thereafter. In step S11 of acquiring a reheat range in a welded layer, as shown in FIG. 4, a reheat range A in the lower welded layer 31A due to heat input from the upper welded layer 31B is acquired when the upper welded layer 31B is stacked on the lower welded layer 31A. That is, the heat input from the upper welded layer 31B does not necessarily extend to the entire lower welded layer 31A, and the range of the lower welded layer 31A that extends from the portion that contacts (actually, partially overlaps) with the upper welded layer 31B to the portion that the heat input from the upper welded layer 31B extends to is taken as reheat range A. Reheat range A is a region where the toughness of the lower welded layer 31A is increased by the heat input from the upper welded layer 31B, and the toughness is restored to a predetermined standard or higher.

[0016] In step S12 of setting the range for removing a portion of the surface layer portion of the welded layer, a range for removing a portion of the surface layer portion 31a of the lower welded layer 31 is set based on the reheating range A acquired in step S11 of acquiring the reheating range for the welded layer. The portion of the surface layer portion 31a of the lower welded layer 31 is removed in step S14 of removing a portion of the surface layer portion of the lower welded layer, which will be described in detail later. The range for removing the portion of the surface layer portion 31a of the lower welded layer 31 is set so that the toughness of the entire lower welded layer 31 remaining after removing this range is increased (recovered) to a standard level or higher due to heat input from the upper welded layer 31B. In this embodiment, the range for removing the portion of the surface layer portion 31a of the lower welded layer 31 is set based on the thickness T in the plate thickness direction Dt of the range B other than the reheating range A in the lower welded layer 31. Note that the removal of the surface layer portion 31a can be performed, for example, by cutting using a tool such as a disc grinder.

[0017] In the welding step S13, welding is performed between the end portions 20a of the opposing plate materials 20. Specifically, welding is performed from the second side Dt2 in the plate thickness direction Dt between the inclined surfaces 20s of the opposing plate materials 20 in the direction in which the welded portion 30 extends (the direction perpendicular to the paper surface in FIG. 2).

[0018] In step S14 of removing a portion of the surface portion of the lower weld layer, a portion of the surface portion 31a of the lower weld layer 31 is removed before the upper weld layer 31 is laminated on the lower weld layer 31. In step S14 of removing a portion of the surface portion of the lower weld layer, the weld layer 31 formed by welding in step S13 of welding is designated as the lower weld layer 31. In step S14 of removing a portion of the surface portion of the lower weld layer, a portion of the surface portion 31a of the lower weld layer 31 is removed based on the dimension T set in step S12 of setting the range over which the portion of the surface portion of the weld layer is to be removed. A grinder, for example, is used to remove the portion of the surface portion 31a of the lower weld layer 31.

[0019] The above-mentioned step S13 of performing welding and step S14 of removing a part of the surface layer of the lower welded layer are repeated a predetermined number of times to form welded layers 311 to 315 in succession.

[0020] Fig. 5 is a diagram showing a state in which a first welded layer is formed by a step of performing welding according to an embodiment of the present disclosure, and Fig. 6 is a diagram showing a state in which a part of the surface layer portion of the first welded layer is removed by a step of removing a part of the surface layer portion of the lower welded layer according to an embodiment of the present disclosure. 5, in a welding step S13, welding is performed between the ends 20a of the opposing plate materials 20 at a position on the second side Dt2 in the plate thickness direction Dt to form a first welded layer 311. Next, in a part-removing step S14 of the surface layer portion of the lower welded layer as shown in FIG. 6, before a second welded layer 312 (corresponding to the upper welded layer 31) is laminated on the first welded layer 311 (corresponding to the lower welded layer 31), a part of the surface layer portion 31a of the first welded layer 311 is removed by a dimension T.

[0021] Fig. 7 is a diagram showing a state in which a second welded layer is formed by a step of performing welding according to an embodiment of the present disclosure, and Fig. 8 is a diagram showing a state in which a part of the surface layer portion of the second welded layer is removed by a step of removing a part of the surface layer portion of the lower welded layer according to an embodiment of the present disclosure. Next, as shown in Fig. 7, in a welding step S13, welding is performed between the ends 20a of the opposing plate materials 20 such that a second welded layer 312 (corresponding to an upper welded layer 31) is stacked on a first side Dt1 in the plate thickness direction Dt relative to a first welded layer 311 (corresponding to a lower welded layer 31). At this time, the first welded layer 311 is reheated by heat input when welding the second welded layer 312. A portion of the surface layer 31a of the first welded layer 311 has been removed. Therefore, the heat input from the second welded layer 312 increases (in other words, restores) the overall toughness of the first welded layer 311 from which a portion of the surface layer 31a has been removed.

[0022] Next, as shown in FIG. 8, in step S14 of removing a portion of the surface layer of the lower welding layer, before the third welding layer 313 (corresponding to the upper welding layer 31) is stacked on the second welding layer 312 (corresponding to the lower welding layer 31), a portion of the surface layer 31a of the second welding layer 311 is removed by a dimension T.

[0023] Thereafter, the third welded layer 313 to the fifth welded layer 315 are sequentially stacked by repeating the welding step S13 and the step S14 of removing a part of the surface layer of the lower welded layer in the same manner.

[0024] FIG. 9 is a diagram showing a state in which the outermost welded layer has been formed by the step of forming the outermost welded layer according to the embodiment of the present disclosure. 9, a sixth welded layer 316, which is located closest to the first side Dt1 (closest to the surface 20f) in the thickness direction Dt, is formed by welding it onto the fifth welded layer 315. The outermost welded layer 316, which is located closest to the first side Dt1 (closest to the surface 20f) in the thickness direction Dt, is formed so as to rise from the surface 20f to the first side Dt1 in the thickness direction Dt.

[0025] Next, in step S16 of removing at least a portion of the outermost welded layer, at least a portion of the welded layer 31 located closest to the surface 20f of the plate material 20 is removed. Among the multiple welded layers 31, the welded layers 311-314 have their toughness restored and residual stress alleviated by the heat input when the other welded layers 31 are subsequently formed. The welded layer 315 has its toughness restored and residual stress alleviated by the heat input when the outermost welded layer 316 is subsequently formed. In contrast, residual stress occurs in the outermost welded layer 316, which is formed last on the first side Dt1 in the plate thickness direction Dt. Therefore, at least a portion of the outermost welded layer 316 located closest to the surface 20f of the plate material 20 is removed. This removes the portion of the outermost welded layer 316 that has not been reheated, thereby locally reducing residual stress. Note that FIG. 2 illustrates a case in which all of the welded layer 316 is removed. In this manner, the plate materials 20 in this embodiment are joined together. As a result, a welded portion 30 in which a plurality of weld layers 31 are stacked is formed between the end portions 20a of the plate materials 20 facing each other.

[0026] (Action and effect) In the tank manufacturing method S10 of the above embodiment, before the upper welded layer 31 is laminated on the lower welded layer 31, a portion of the surface layer 31a of the lower welded layer 31 is removed. As a result, when the upper welded layer 31 is welded to be laminated on the lower welded layer 31, heat is input from the upper welded layer 31 to the lower welded layer 31. Because a portion of the surface layer 31a of the lower welded layer 31 has been removed, the lower welded layer 31 is reheated by the heat input from the upper welded layer 31, thereby increasing the toughness of the lower welded layer 31. Each time multiple welded layers 31 are sequentially laminated, the heat input from the upper welded layer 31 ultimately reheats the entire welded portion 30, thereby increasing its toughness. As a result, the toughness can be more uniformly increased throughout the entire welded portion 30. Furthermore, reheating the entire welded portion 30 can also reduce residual stress in the welded portion 30.

[0027] Furthermore, in the above embodiment, when the upper welding layer 31 is laminated by welding, the lower welding layer 31 from which part of the surface layer 31a has been removed can be reheated by heat input from the upper welding layer 31, thereby reheating the entire lower welding layer 31.

[0028] Furthermore, in the above embodiment, when the upper welding layer 31 is stacked on the lower welding layer 31, the reheat range A due to the heat input from the upper welding layer 31 extends to the entire lower welding layer 31 after removing a portion of the surface layer 31a, thereby increasing the overall toughness of the lower welding layer 31.

[0029] In the above embodiment, the reheat range A in the lower welding layer 31 due to the heat input from the upper welding layer 31 is acquired. This makes it possible to appropriately set the range in which the part of the surface layer 31a of the lower welding layer 31 is to be removed so that the heat input from the upper welding layer 31 covers the entire lower welding layer 31 after the part of the surface layer 31a has been removed.

[0030] In addition, in the above embodiment, by removing at least a portion of the welded layer 316 located on the surface 20f side of the plate material 20, the portion of the welded layer 316 located on the surface 20f side that has not been reheated can be removed, and residual stress can be locally reduced.

[0031] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure. In the above embodiment, the groove portion 21V has a V-shaped cross section, but is not limited to this. For example, the groove portion may have an X-shaped cross section.

[0032] <Additional Notes> A method for manufacturing the tank 1 according to the embodiment can be understood, for example, as follows.

[0033] (1) A manufacturing method of a tank 1 according to a first aspect is a manufacturing method of a tank 1 in which the tank 1 is manufactured by joint-welding steel plates 20 that constitute the tank 1, and includes a step S13 of welding between the ends 20a of the plates 20 facing each other so that a plurality of welded layers 31 are sequentially stacked toward the surface 20f of the plates 20, and a step S14 of removing a portion of the surface layer 31a of the lower welded layer 31 before stacking the upper welded layer 31 on the lower welded layer 31.

[0034] In this manufacturing method of the tank 1, before the upper weld layer 31 is laminated on the lower weld layer 31, a portion of the surface layer 31a of the lower weld layer 31 is removed. This allows heat to be input to the entire lower weld layer 31 when the lower weld layer 31 is reheated, thereby increasing the toughness of the lower weld layer 31. As a result, the toughness of the welded portion 30 can be more uniformly increased. Furthermore, by reheating the welded portion 30, residual stress in the welded portion 30 can also be reduced.

[0035] (2) A manufacturing method of a tank 1 according to a second aspect is the manufacturing method of a tank 1 according to (1), and in the welding step S13, when the upper welding layer 31 is laminated on the lower welding layer 31 by welding, the lower welding layer 31 from which a portion of the surface layer 31a has been removed is reheated by the heat input from the upper welding layer 31.

[0036] As a result, when the upper welded layer 31 is laminated by welding, the lower welded layer 31 from which part of the surface layer 31a has been removed can be reheated by heat input from the upper welded layer 31. Therefore, each time a plurality of welded layers 31 are sequentially laminated, heat is input from the upper welded layer 31, and ultimately the entire welded portion 30 is reheated, thereby increasing the toughness of the entire welded portion 30.

[0037] (3) A manufacturing method of a tank 1 according to a third aspect is a manufacturing method of a tank 1 according to (1) or (2), in which in step S14 of removing a portion of the surface layer 31a of the lower welding layer 31, the portion of the surface layer 31a of the lower welding layer 31 is removed so that when the upper welding layer 31 is stacked on the lower welding layer 31, the reheat range A due to the heat input from the upper welding layer 31 covers the entire lower welding layer 31 after the portion of the surface layer 31a has been removed.

[0038] As a result, when an upper welding layer 31 is stacked on a lower welding layer 31, the reheat range A due to heat input from the upper welding layer 31 extends to the entire lower welding layer 31 after removing part of the surface layer 31a, thereby increasing the overall toughness of the lower welding layer 31.

[0039] (4) A manufacturing method of a tank 1 according to a fourth aspect is a manufacturing method of a tank 1 according to any one of (1) to (3), further including: a step S11 of acquiring a reheating range A in the lower welding layer 31 due to heat input from the upper welding layer 31 when the upper welding layer 31 is stacked on the lower welding layer 31; and a step S12 of setting a range for removing a portion of the surface layer 31a of the lower welding layer 31 based on the reheating range A acquired in the step S11 of acquiring the reheating range A, in a step S14 of removing a portion of the surface layer 31a of the lower welding layer 31.

[0040] This allows the range in which the portion of the surface layer 31a of the lower welding layer 31 is removed to be appropriately set so that the heat input from the upper welding layer 31 reaches the entire lower welding layer 31 after removing a portion of the surface layer 31a.

[0041] (5) The manufacturing method of the tank 1 according to the fifth aspect is a manufacturing method of any one of the tank 1 according to (1) to (4), in which at least a portion of the welding layer 316, which is located closest to the surface 20f of the plate material 20 among the plurality of welding layers 31, is removed.

[0042] This allows removing at least a portion of the welded layer 316 located on the surface 20f side of the plate material 20, thereby removing the portion of the welded layer 316 located on the surface 20f side that has not been reheated, and locally reducing residual stress. [Explanation of symbols]

[0043] DESCRIPTION OF SYMBOLS 1...tank 2...cylindrical portion 3...end plate portion 20...plate material 20a...end portion 20f...surface 20g...surface 20s...inclined surface 21V...groove portion 30...weld portion 31...weld layer, 311-316...weld layers 31A...lower weld layer 31B...upper weld layer 31a...surface portion A...reheat range Da...opposing direction Dc...central axis direction Dt...plate thickness direction Dt1...first side Dt2...second side K...range to be removed S10...tank manufacturing method S11...process of obtaining reheat range in weld layer S12...process of setting range to remove part of surface portion of weld layer S13...process of welding S14...process of removing part of surface portion of lower weld layer S15...process of forming outermost weld layer S16...process of removing at least part of outermost weld layer

Claims

1. A manufacturing method of a tank in which a steel plate material constituting the tank is joint-welded to manufacture the tank, a step of welding between the opposing ends of the plate materials so that a plurality of weld layers are sequentially stacked toward the surface side of the plate materials; a step of removing a part of a surface layer of the lower welding layer before the upper welding layer is laminated on the lower welding layer; Including, In the step of removing a portion of the surface layer of the lower welding layer, the portion of the surface layer of the lower welding layer is removed so that, when the upper welding layer is laminated on the lower welding layer, a reheat range due to heat input from the upper welding layer will cover the entire lower welding layer after the portion of the surface layer is removed. Tank manufacturing method.

2. In the welding step, when the upper welding layer is laminated on the lower welding layer by welding, the lower welding layer from which a portion of the surface layer has been removed is reheated by heat input from the upper welding layer. A method for manufacturing the tank of claim 1.

3. acquiring a reheat range in the lower welding layer due to heat input from the upper welding layer when the upper welding layer is stacked on the lower welding layer; and a step of removing a portion of the surface layer portion of the lower welded layer based on the reheating range acquired in the step of acquiring the reheating range, the step of removing a portion of the surface layer portion of the lower welded layer further includes a step of setting a range for removing a portion of the surface layer portion of the lower welded layer. A method for manufacturing the tank according to claim 1 or 2.

4. At least a part of the welded layer located closest to the surface of the plate material among the plurality of welded layers is removed. A method for manufacturing the tank according to claim 1 or 2.

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