Tank manufacturing method

Abstract

To effectively reduce residual stress in a weld portion caused by multi-layer welding.SOLUTION: Provided is a tank manufacturing method by joint-welding steel sheets which constitute the tank, comprising the steps of: performing multi-layer welding such that a plurality of weld layers are formed successively between opposing ends of the sheets toward an upper surface side of the sheets; and performing a process of locally reducing residual stress only for a part of weld layers that are positioned on the upper surface side.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] When steel materials are joined by welding, residual stress in the tensile direction occurs in the weld, which can lead to defects such as brittle fracture and stress corrosion cracking in the weld. Patent Document 1 discloses a configuration in which a shot peening treatment is performed on a welded portion when manufacturing a marine cryogenic tank. In this configuration, the shot peening treatment imparts compressive stress to the welded portion, thereby offsetting the residual stress in the tensile direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-89802 Summary of the Invention [Problem to be solved by the invention]

[0004] For marine liquefied gas tanks where cargo temperatures fall below -10°C, regulations sometimes require post-weld heat treatment to reduce welding residual stresses to prevent brittle fracture. In this case, the liquefied gas tank is typically placed in a heat treatment furnace and heat treated at the welds all at once. However, due to furnace size limitations, large liquefied gas tanks may not be heat treated in a heat treatment furnace. In such cases, a heat treatment device that performs localized heat treatment, such as a heat treatment device for localized residual stress reduction, is used. For example, for large liquefied gas tanks, the tank plate thickness is large, but residual stress reduction treatment must be performed across the entire thickness of the weld, which can result in a longer construction period.

[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 effectively reduce residual stress in welded portions. [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 performing multi-layer welding and a step of performing a process for locally reducing residual stress. The step of performing multi-layer welding is performed such that multiple weld layers are sequentially stacked between ends of the opposing plates toward the surface side of the plates. The step of performing the process for locally reducing residual stress locally reduces residual stress only in some of the multiple weld layers that are located on the surface side. The step of locally reducing residual stress includes TIG welding to form a TIG weld layer that is thinner than the weld layer located closest to the surface so as to cover the weld layer located closest to the surface, thereby inputting heat to the weld layer located closest to the surface, and removing the TIG weld layer after the TIG welding. Then, peening is performed only on the weld layer located closest to the surface. . [Effects of the Invention]

[0007] According to the tank manufacturing method of the present disclosure, residual stress in the welded portion can be effectively reduced. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an example of a tank manufactured by a tank manufacturing method according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view showing a weld between steel plates constituting the tank according to the first embodiment of the present disclosure. [Figure 3] 1 is a flowchart showing the steps of a tank manufacturing method according to an embodiment of the present disclosure. [Figure 4]1 is a cross-sectional view showing a state in which the outermost weld layer has been removed in a welded portion between plate materials according to a first embodiment of the present disclosure. FIG. [Figure 5] FIG. 10 is a cross-sectional view showing a welded portion between plate materials according to a second embodiment of the present disclosure. [Figure 6] FIG. 10 is a cross-sectional view showing a welded portion between plate materials according to a third embodiment of the present disclosure. [Figure 7] FIG. 10 is a cross-sectional view showing a welded portion between plate materials according to a fourth embodiment of the present disclosure. [Figure 8] FIG. 10 is a cross-sectional view showing a welded portion between plate materials according to a fifth embodiment of the present disclosure. [Figure 9] FIG. 10 is a cross-sectional view showing a welded portion between plate materials in a modified example according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment 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 manufactured by the tank manufacturing method of this embodiment is a tank capable of storing a liquefied gas such as liquefied carbon dioxide. The tank 1 is installed on 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 is, for example, 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 the 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 is hemispherical 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 or rectangular shape.

[0010] FIG. 2 is a cross-sectional view showing a welded portion between steel plates that constitute the tank according to the first embodiment of the present disclosure. 2, the tank 1 is formed by joint-welding a plurality of steel plates 20. Each plate 20 constituting the tank 1 is formed of a metal material such as high-strength tempered steel.

[0011] In this embodiment, the plate materials 20 have a groove portion 21X having an X-shaped cross section, which is an X-shaped groove. The groove portion 21X extends in a direction perpendicular to the opposing direction Da of the plate materials 20 and the thickness direction Dt of the plate materials 20 (a direction perpendicular to the paper surface of FIG. 2). Note that, in this embodiment, a case where the groove portion 21X is an X-shaped groove will be described as an example, but the groove is not limited to an X-shaped groove.

[0012] The opposing ends 20a of the plate materials 20 have inclined surfaces 20s, 20t. The inclined surfaces 20s of the opposing plate materials 20 are formed so that the distance between them in the opposing direction Da gradually decreases from the surface 20f on the first side Dt1 in the plate thickness direction Dt toward the central portion 20c in the plate thickness direction Dt. The inclined surfaces 20t of the opposing plate materials 20 are formed so that the distance between them in the opposing direction Da gradually decreases from the surface 20g on the second side Dt2 in the plate thickness direction Dt toward the central portion 20c in the plate thickness direction Dt.

[0013] 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.

[0014] The welded portion 30 has a plurality of welded layers 31. In this embodiment, the plurality of welded layers 31 includes five welded layers 311 to 315 formed from the central portion 20 c in the plate thickness direction Dt to a first side Dt1 in the plate thickness direction Dt, and five welded layers 316 to 320 formed from the central portion 20 c in the plate thickness direction Dt to a second side Dt2 in the plate thickness direction Dt. The number of the plurality of welded layers 31 is determined depending on the plate thickness of the plate material 20 and can be changed as appropriate.

[0015] In this embodiment, the thickness of the plate material 20 in the plate thickness direction Dt is, for example, about 10 to 100 mm.

[0016] The welded layers 311-315 are stacked in order from the central portion 20c in the plate thickness direction Dt toward the surface 20f on the first side Dt1 in the plate thickness direction Dt. Of the welded layers 311-315, the welded layer 315 located furthest on the first side Dt1 in the plate thickness direction Dt protrudes from the surface 20f of the plate 20 toward the first side Dt1 in the plate thickness direction Dt. The welded layer 315 exemplified in this embodiment is formed closer to the first side Dt1 in the plate thickness direction than the surface 20f of the plate 20.

[0017] The welded layers 316-320 are stacked in order from the central portion 20c in the plate thickness direction Dt toward the surface 20g of the second side Dt2 in the plate thickness direction Dt. Of the welded layers 316-320, the welded layer 320 located furthest from the second side Dt2 in the plate thickness direction Dt protrudes from the surface 20g of the plate 20 toward the second side Dt2 in the plate thickness direction Dt. The welded layer 320 exemplified in this embodiment is formed closer to the second side Dt2 in the plate thickness direction than the surface 20g of the plate 20.

[0018] (Tank manufacturing procedure) FIG. 3 is a flowchart showing the steps of a tank manufacturing method according to an embodiment of the present disclosure. As shown in FIG. 3, a manufacturing method S10 of a tank 1 according to an embodiment of the present disclosure includes a step S11 of multi-layer welding and a step S12 of performing a process of locally reducing residual stress.

[0019] In step S11 of performing multi-layer welding, as shown in Fig. 2, multi-layer welding is performed between the end portions 20a of the opposing plate materials 20 to join the plate materials 20 together. Specifically, welding is performed multiple times between the inclined surfaces 20s of the opposing plate materials 20 from a first side Dt1 in the plate thickness direction Dt in the direction in which the weld extends (a direction perpendicular to the paper surface in Fig. 2), thereby sequentially stacking and forming welded layers 311-315. At this time, the outermost welded layer 315, which is the last to be welded among the welded layers 311-315 and is located closest to the first side Dt1 in the plate thickness direction Dt (closest to the surface 20f), is formed so as to rise from the surface 20f toward the first side Dt1 in the plate thickness direction Dt. Additionally, welding is repeated multiple times from the second side Dt2 in the plate thickness direction Dt between the inclined surfaces 20t of the opposing plate materials 20 along the extension direction of the weld (the direction perpendicular to the paper surface in FIG. 2), thereby sequentially stacking and forming the welded layers 316-320. At this time, the outermost welded layer 320, which is the last to be welded among the welded layers 316-320 and is located closest to the second side Dt2 in the plate thickness direction Dt (closest to the surface 20g), is formed so as to rise from the surface 20g toward the second side Dt2 in the plate thickness direction Dt.

[0020] In this manner, the plate materials 20 are joined together. As a result, a welded portion 30 is formed between the ends 20a of the opposing plate materials 20, in which a plurality of welded layers 31 are stacked. Of the plurality of welded layers 31, residual stress is generated in the outermost welded layer 315, which is formed last on the first side Dt1 in the plate thickness direction Dt, and the outermost welded layer 320, which is formed last on the second side Dt2 in the plate thickness direction Dt. Of the plurality of welded layers 31, the residual stress is relaxed in the other welded layers 311 to 314 and the welded layers 316 to 319 due to heat input when the other welded layers 31 are formed later.

[0021] In step S12, which involves performing a treatment to locally reduce residual stress, the welded portion 30 formed in step S11 is subjected to a treatment to locally reduce residual stress. In this step S12, the treatment to locally reduce residual stress is performed only on the welded portion 30, not on the entire tank 1. In this step S12, the treatment to locally reduce residual stress is performed only on some of the welded layers 31 located on the surface 20f side and the surface 20g side of the multiple welded layers 31. In the treatment to locally reduce residual stress, it is preferable to reduce the residual stress in some of the welded layers 31 located on the surface 20f side and the surface 20g side to a predetermined level (for example, 50% or less of the yield stress of the steel).

[0022] FIG. 4 is a cross-sectional view showing a state in which the outermost welded layer has been removed at a welded portion between plate materials according to the first embodiment of the present disclosure. Specifically, as shown in FIG. 4 , only a portion of the welded layer 31 located on the surface 20f side of the plate material 20 is removed on a first side Dt1 of the welded portion 30 in the plate thickness direction Dt. In this embodiment, the welded layer 315 protruding from the surface 20f toward the first side Dt1 in the plate thickness direction Dt is removed. The removal of the welded layer 315 can be performed using a manual tool such as a grinder. Also, only a portion of the welded layer 31 located on the surface 20g side of the plate material 20 is removed on a second side Dt2 of the welded portion 30 in the plate thickness direction Dt. In this embodiment, the welded layer 320 protruding from the surface 20g toward the second side Dt2 in the plate thickness direction Dt is removed. The removal of the welded layer 320 can also be performed using a manual tool such as a sander, as described above. This removes the welded layer 315 and the welded layer 320, which have not received heat input due to the formation of other welded layers 31 and therefore have not relaxed residual stress.

[0023] (Action and effect) In the manufacturing method S10 of the tank 1 of the above embodiment, a process for reducing residual stress is performed on some welded layers 315, 320, which are located on the surfaces 20f, 20g of the plate material 20, among the multiple welded layers 31 of the welded portion 30. On the other hand, the other welded layers 311-314, 316-319 other than the welded layers 315, 320 are not subjected to a process for reducing residual stress, unlike the process for the welded layers 315, 320, which are located on the surfaces 20f, 20g of the plate material 20. As a result, residual stress can be effectively reduced in the welded portion 30 formed by multi-pass welding.

[0024] Furthermore, in the above embodiment, by locally removing only the welded layers 315, 320 located on the surfaces 20f, 20g of the plate material 20, the local residual stress occurring in the welded portion 30 can be reduced.

[0025] In the above embodiment, step S12 is performed to locally reduce residual stress only in a portion of the tank 1, including the portion where multi-layer welding is performed in step S11. This eliminates the need to perform a process to reduce residual stress on the entire tank 1. Therefore, there is no need to prepare a furnace or the like that can accommodate the entire tank 1 in order to reduce residual stress. Furthermore, in the above embodiment, no local heat treatment is performed, so the construction period for manufacturing the tank 1 can be shortened. As a result, residual stress can be effectively reduced even in a large tank 1. Furthermore, by not performing heat treatment, it is possible to suppress a decrease in toughness and strength at the welded portion 30. As a result, a high-strength material can be used for the plate material 20, and the weight of the tank 1 can be reduced.

[0026] Second Embodiment Next, a second embodiment of the method for manufacturing a tank according to the present disclosure will be described. The second embodiment described below differs from the first embodiment only in the configuration of the step of locally reducing residual stress. Therefore, the same parts as those in the first embodiment will be described with reference to Figures 1 and 3, with the same reference numerals assigned, and redundant description will be omitted. (Tank manufacturing procedure) As shown in FIG. 3, a manufacturing method S20 of the tank 1 according to the embodiment of the present disclosure includes a step S11 of multi-layer welding and a step S22 of performing a treatment to locally reduce residual stress.

[0027] FIG. 5 is a cross-sectional view showing a welded portion between plate materials according to the second embodiment of the present disclosure. In this embodiment, in step S22 of performing a treatment to locally reduce residual stress, as shown in Fig. 5, the treatment to locally reduce residual stress is performed on the welded portion 30 formed in step S11. In step S22, the treatment to locally reduce residual stress is performed only on the welded portion 30, not on the entire tank 1. In step S22, the treatment to locally reduce residual stress is performed only on some of the welded layers 31 located on the surface 20f side and the surface 20g side of the multiple welded layers 31. In the treatment to locally reduce residual stress, it is preferable to reduce the residual stress in some of the welded layers 31 located on the surface 20f side and the surface 20g side to a predetermined level (for example, 50% or less of the yield stress of the steel).

[0028] In this second embodiment, in step S22 of performing a treatment to locally reduce residual stress, the peening treatment is performed only on some of the welded layers 31 located on the surfaces 20f, 20g side of the plate material 20 in the plate thickness direction Dt. More specifically, in this second embodiment, the peening treatment is performed on the surface 315f of the welded layer 315 located on the first side Dt1 in the plate thickness direction Dt of the welded portion 30. Also, the peening treatment is performed on the surface 320f of the welded layer 320 located on the second side Dt2 in the plate thickness direction Dt of the welded portion 30. The peening treatment is performed, for example, by needle peening. The peening treatment of the welded layer 315 is preferably performed under conditions such that the influence of the pressure from the needle P of the needle peening on the other welded layers 311 to 314 is minimized and the pressure is concentrated on the welded layer 315 with high residual stress. The peening treatment of the welded layer 320 is preferably performed under conditions that minimize the influence of the pressure from the needle P of the needle peening on the other welded layers 316 to 319 and concentrate the pressure on the welded layer 320, which has high residual stress. This reduces the residual stress generated in the welded layer 315 and the welded layer 320.

[0029] (Action and effect) In the manufacturing method S20 of the tank 1 of the above embodiment, by performing peening treatment only on a portion of the welded layer 31 (315, 320) located on the surface 20f, 20g side of the plate material 20, the residual stress of the portion of the welded layer 31 (315, 320) located on the surface 20f, 20g side of the plate material 20 can be reduced.

[0030] Furthermore, in the manufacturing method S20 of the tank 1 of the above embodiment, as in the first embodiment, the residual stress of some of the multiple welded layers 31 (315, 320) located on the surface 20f, 20g side of the plate material 20 can be reduced, thereby effectively reducing the residual stress of the welded portion 30 due to multi-layer welding.

[0031] Third Embodiment Next, a third embodiment of the method for manufacturing the tank 1 according to the present disclosure will be described. The third embodiment described below differs from the first and second embodiments only in the configuration of the step of locally reducing residual stress, and therefore, the same parts as those in the first and second embodiments will be described with reference to Figures 1 and 3, with the same reference numerals assigned to them, and redundant description will be omitted. (Tank manufacturing procedure) As shown in FIG. 3, a manufacturing method S30 of the tank 1 according to the third embodiment includes a step S11 of multi-layer welding and a step S32 of performing a process of locally reducing residual stress.

[0032] In this embodiment, in step S32 of performing a treatment to locally reduce residual stress, the treatment to locally reduce residual stress is performed on the welded portion 30 formed in step S11. In this step S32, the treatment to locally reduce residual stress is performed only on the welded portion 30, not on the entire tank 1. In this step S32, the treatment to locally reduce residual stress is performed only on some of the welded layers 31 located on the surface 20f side and the surface 20g side of the multiple welded layers 31. In the treatment to locally reduce residual stress, the residual stress in some of the welded layers 31 located on the surface 20f side and the surface 20g side is reduced to a predetermined level (for example, 50% or less of the yield stress of the steel).

[0033] FIG. 6 is a cross-sectional view showing a welded portion between plate materials according to a third embodiment of the present disclosure. As shown in FIG. 6 , in this embodiment, specifically, a TIG welded layer 35 is formed to input heat to a portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt. In this embodiment, the TIG welded layer 35 includes a TIG welded layer 351 covering the outermost welded layer 315 located on the first side Dt1 in the plate thickness direction Dt, and a TIG welded layer 352 covering the outermost welded layer 320 located on the second side Dt2 in the plate thickness direction Dt. The thickness T1 of the TIG welded layer 351 is smaller than the thickness T2 of the outermost welded layer 315 in the plate thickness direction Dt. The thickness T3 of the TIG welded layer 352 is smaller than the thickness T4 of the outermost welded layer 320 in the plate thickness direction Dt. The TIG welded layers 351, 352 are formed by TIG (Tungsten Inert Gas) welding. The application positions, thicknesses, etc. of the TIG welded layers 351, 352 are not limited to those described above, and may be appropriately controlled so as to prevent residual stress due to the presence of the TIG welded layers 351, 352. For example, if the residual stress of the TIG welded layers 351, 352 is a problem, the TIG welded layers 351, 352 may be removed after TIG welding.

[0034] Residual stress in the welded layer 315 is reduced by the heat input during welding to form the TIG welded layer 351. It is preferable that welding to form the TIG welded layer 351 be performed under conditions that minimize the influence of the heat input from welding on the other welded layers 311 to 314 and concentrate the heat input on the welded layer 315, which has high residual stress. Furthermore, residual stress in the welded layer 320 is reduced by the heat input during welding when forming the TIG welded layer 352. It is preferable that welding when forming the TIG welded layer 352 be performed under conditions that minimize the influence of the heat input from welding on the other welded layers 316 to 319 and concentrate the heat input on the welded layer 320, which has high residual stress.

[0035] (Action and effect) In the manufacturing method S30 of the tank 1 according to the above embodiment, heat sufficient to reduce the residual stress of the welded layer 31 (315, 320) closest to the surfaces 20f, 20g to a predetermined level is applied by TIG welding to form the TIG welded layers 351, 352. This reduces the residual stress of the welded layers 315, 320 located closest to the surfaces 20f, 20g of the plate material 20. Furthermore, when the TIG welded layer 35 is formed by TIG welding, the TIG welded layer 35 can be formed thinner than the welded layers 315, 320 and sufficient heat input is possible. This reduces the residual stress locally in the welded layer 31 (315, 320) closest to the surfaces 20f, 20g, while minimizing the tensile residual stress generated in the TIG welded layer 35. Consequently, the residual stress in the welded portion 30 can ultimately be reduced.

[0036] Also, in the manufacturing method S30 of the tank 1 of the above embodiment, similarly to the first and second embodiments, the residual stress in the welded portion 30 due to multi-pass welding can be effectively reduced.

[0037] <Fourth embodiment> Next, a fourth embodiment of the manufacturing method for the tank 1 according to the present disclosure will be described. The fourth embodiment described below differs from the first to third embodiments only in the configuration of the step of locally reducing residual stress, and therefore, the same parts as those in the first to third embodiments will be described with reference to Figures 1 and 3, with the same reference numerals assigned to them, and redundant description will be omitted. (Tank manufacturing procedure) As shown in FIG. 3, a method S40 for manufacturing a tank 1 according to the fourth embodiment includes a step S11 of multi-layer welding and a step S42 of performing a process for locally reducing residual stress.

[0038] In this embodiment, in step S42 of performing a treatment to locally reduce residual stress, the treatment to locally reduce residual stress is performed on the welded portion 30 formed in step S11. In this step S42, the treatment to locally reduce residual stress is performed only on the welded portion 30, not on the entire tank 1. In this step S42, the treatment to locally reduce residual stress is performed only on some of the welded layers 31 located on the surface 20f side and the surface 20g side of the multiple welded layers 31. In the treatment to locally reduce residual stress, it is preferable to reduce the residual stress in some of the welded layers 31 located on the surface 20f side and the surface 20g side to a predetermined level (for example, 50% or less of the yield stress of the steel).

[0039] FIG. 7 is a cross-sectional view showing a welded portion between plate materials according to a fourth embodiment of the present disclosure. As shown in FIG. 7 , in this embodiment, specifically, a laser beam Lb is irradiated onto a portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt. In this embodiment, the laser beam Lb is irradiated from a first side Dt1 in the plate thickness direction Dt to the outermost welded layer 315 located on the first side Dt1 in the plate thickness direction Dt. The laser beam Lb is also irradiated from a second side Dt2 in the plate thickness direction Dt to the outermost welded layer 320 located on the second side Dt2 in the plate thickness direction Dt. The laser beam Lb is irradiated by sequentially moving a laser irradiation unit (not shown) that irradiates the laser beam Lb in the direction in which the welded portion 30 extends (a direction perpendicular to the plane of the drawing in FIG. 7 ). The laser beam Lb can be irradiated onto the welded layers 315, 320 using, for example, a laser device capable of scanning the laser beam Lb using a galvanometer mirror (in other words, a scanner laser device). As the laser device, for example, a welding device for performing laser welding may be used.

[0040] The irradiation of the laser beam Lb heats the welded layers 315, 320, reducing the residual stress of the welded layers 315, 320. The irradiation of the laser beam Lb is preferably performed under conditions that minimize the influence of the heating caused by the irradiation of the laser beam Lb on the other welded layers 311-314, 316-319, and concentrate the heating on the welded layers 315, 320, which have high residual stress.

[0041] (Action and effect) In the manufacturing method S40 of the tank 1 according to the above embodiment, residual stress in some of the welded layers 315, 320 located closest to the surfaces 20f, 20g of the plate material 20 can be locally reduced by irradiating the welded layers 315, 320 closest to the surfaces 20f, 20g with laser light Lb. Furthermore, heating by irradiation with laser light Lb targets the outermost welded layers 315, 320, which are part of the welded portion 30 in the thickness direction Dt. Therefore, heating does not need to be performed on the entire welded portion 30 in the thickness direction Dt, and less heat energy is required. Therefore, local residual stress occurring in the welded portion 30 can be reduced more easily and at low cost.

[0042] Also, in the manufacturing method S40 of the tank 1 of the above embodiment, similarly to the first to third embodiments, the residual stress in the welded portion 30 due to multi-pass welding can be effectively reduced.

[0043] Fifth Embodiment Next, a fifth embodiment of the manufacturing method for the tank 1 according to the present disclosure will be described. The fifth embodiment described below differs from the first to fourth embodiments only in the configuration of the step of locally reducing residual stress, and therefore, the same parts as those in the first to fourth embodiments will be described with reference to Figures 1 and 3, with the same reference numerals assigned to them, and duplicated explanations will be omitted. (Tank manufacturing procedure) As shown in FIG. 3, a method S50 for manufacturing a tank 1 according to the fifth embodiment includes a step S11 of multi-layer welding and a step S52 of performing a process for locally reducing residual stress.

[0044] In this embodiment, in step S52 of performing a treatment to locally reduce residual stress, the treatment to locally reduce residual stress is performed on the welded portion 30 formed in step S11. In this step S52, the treatment to locally reduce residual stress is performed only on the welded portion 30, not on the entire tank 1. In this step S52, the treatment to locally reduce residual stress is performed only on some of the welded layers 31 located on the surface 20f side and the surface 20g side out of the multiple welded layers 31.

[0045] FIG. 8 is a cross-sectional view showing a welded portion between plate materials according to a fifth embodiment of the present disclosure. As shown in FIG. 8 , in the fifth embodiment, a portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt is heated by a heating means 50. In this embodiment, the heating means 50 heats the outermost welded layer 315 located on the first side Dt1 in the plate thickness direction Dt from a first side Dt1 in the plate thickness direction Dt. The heating means 50 also heats the outermost welded layer 320 located on the second side Dt2 in the plate thickness direction Dt from a second side Dt2 in the plate thickness direction Dt. For example, a panel heater, a high-frequency heating device, or the like can be used as the heating means 50. Heating by the heating means 50 is performed by sequentially moving the heating means 50 in the direction in which the welded portion 30 extends (a direction perpendicular to the plane of the paper in FIG. 8 ).

[0046] Heating by the heating means 50 reduces the residual stress in the welded layers 315 and 320. Heating by the heating means 50 is preferably performed under conditions that minimize the influence of the heating by the heating means 50 on the other welded layers 311-314 and 316-319 and concentrate the heating on the welded layers 315 and 320, which have high residual stress.

[0047] (Action and effect) In the manufacturing method S50 of the tank 1 according to the above embodiment, the welded layers 315, 320 closest to the surfaces 20f, 20g are heated by a heating means 50 facing the welded layers 315, 320 closest to the surfaces 20f, 20g, thereby reducing residual stress in some of the welded layers 315, 320 closest to the surfaces 20f, 20g of the plate material 20. Furthermore, since the heating by the heating means 50 only targets the outermost welded layers 315, 320, which are part of the welded portion 30 in the thickness direction Dt, it is not necessary to heat the entire welded portion 30 in the thickness direction Dt, and less heat energy is required. Therefore, localized residual stress occurring in the welded portion 30 can be reduced more easily and at low cost.

[0048] Also, in the manufacturing method S50 of the tank 1 of the above embodiment, similarly to the first to fourth embodiments, the residual stress in the welded portion 30 due to multi-pass welding can be effectively reduced.

[0049] (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 21X has an X-shaped cross section, but this is not limiting. For example, as shown in FIG. 9, the groove 21V may have a V-shaped cross section. In the welded portion 30V, welded layers 321-327 are stacked as multiple welded layers 31 from the second side Dt2 to the first side Dt1 in the plate thickness direction Dt. In this case, the residual stress in the welded layer 327 located closest to the surface 20f is reduced. This effectively reduces the residual stress that occurs locally in the outermost welded layer 327 in the welded portion 30V formed by multi-layer welding.

[0050] Furthermore, it is also possible to combine the configurations shown in the first to sixth embodiments as appropriate. For example, the configurations shown in the first embodiment and the third to sixth embodiments may be combined with the peening treatment shown in the second embodiment.

[0051] <Additional Notes> The manufacturing methods S10, S20, S30, S40, and S50 of the tank 1 described in each embodiment can be understood, for example, as follows.

[0052] (1) Manufacturing methods S10, S20, S30, S40, and S50 of a tank 1 according to a first aspect are a manufacturing method S10 of a tank 1 for manufacturing the tank 1 by joint-welding steel plates 20 constituting the tank 1, and include a process S11 of performing multi-layer welding between the plates 20 whose ends 20a face each other so that a plurality of welded layers 31 are sequentially stacked toward the surfaces 20f and 20g of the plates 20, and a process S12 of performing a process to locally reduce residual stress only on some of the welded layers 31 located on the surfaces 20f and 20g of the plurality of welded layers 31.

[0053] The manufacturing methods S10, S20, S30, S40, and S50 of the tank 1 can reduce residual stress in some of the multiple welded layers 31 located on the surfaces 20f and 20g of the plate material 20. On the other hand, the effects of the treatment to reduce residual stress on the other welded layers 31 other than the some of the welded layers 31 located on the surfaces 20f and 20g of the plate material 20 can be suppressed. As a result, the residual stress in the welded portion 30 due to multi-layer welding can be effectively reduced.

[0054] (2) The manufacturing method S10 of the tank 1 according to the second aspect is the manufacturing method S10 of the tank 1 of (1), and in the step S12 of performing the treatment to locally reduce the residual stress, only a portion of the welded layer 31 located on the surface 20f, 20g side is removed.

[0055] As a result, by removing only a portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20, the residual stress in the portion of the welded layer 31 located on the surface 20f, 20g side can be locally reduced.

[0056] (3) The manufacturing method S20 of the tank 1 according to the third aspect is the manufacturing method S20 of the tank 1 according to (1) or (2), and in the step S22 of performing the treatment to locally reduce the residual stress, the peening treatment is performed only on a portion of the weld layer 31 located on the surface 20f, 20g side.

[0057] As a result, by performing the peening treatment only on a portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20, the residual stress of the portion of the welded layer 31 located on the surface 20f, 20g side of the plate material 20 can be locally reduced.

[0058] (4) The manufacturing method S30 of the tank 1 according to the fourth aspect is any one of the manufacturing methods S30 of the tank 1 according to (1) to (3), and in the step S32 of performing the treatment to locally reduce residual stress, heat is input by TIG welding to the weld layer 31 located closest to the surfaces 20f, 20g.

[0059] In this configuration, by applying heat by TIG welding to the weld layer 31 located closest to the surfaces 20f, 20g, the residual stress of some of the weld layers 31 located on the surfaces 20f, 20g of the plate material 20 can be locally reduced.

[0060] (5) The manufacturing method S40 of the tank 1 according to the fifth aspect is any one of the manufacturing methods S40 of the tank 1 according to (1) to (4), and in the step S42 of performing the treatment to locally reduce residual stress, laser light Lb is irradiated to the welded layer 31 located closest to the surfaces 20f, 20g.

[0061] As a result, by irradiating the laser light Lb onto the welded layer 31 located closest to the surfaces 20f, 20g, the residual stress of some of the welded layers 31 located closest to the surfaces 20f, 20g of the plate material 20 can be locally reduced.

[0062] (6) The manufacturing method S50 of the tank 1 according to the sixth aspect is any one of the manufacturing methods S50 of the tank 1 according to (1) to (5), and in the step S52 of performing the treatment to locally reduce the residual stress, the welding layer 31 located closest to the surfaces 20f, 20g is heated by a heating means 50 facing the welding layer 31 located closest to the surfaces 20f, 20g. The heating means 50 is a panel heater or a high-frequency heating device.

[0063] As a result, by heating the welded layer 31 located closest to the surfaces 20f, 20g using a heating means 50 facing the welded layer 31 located closest to the surfaces 20f, 20g, the residual stress in some of the welded layers 31 located closest to the surfaces 20f, 20g of the plate material 20 can be locally reduced.

[0064] (7) The manufacturing methods S10, S20, S30, S40, and S50 of the tank 1 according to the seventh aspect are any one of the manufacturing methods S10, S20, S30, S40, and S50 of the tank 1 according to (1) to (6), in which steps S12, S22, S32, S42, and S52 of performing the process of locally reducing residual stress are performed only on a portion of the tank 1 including a portion where multi-layer welding is performed by step S11 of performing the multi-layer welding.

[0065] As a result, a process for locally reducing residual stress is performed only on a portion of the tank 1, including the welded portion 30, where multi-layer welding is performed. This eliminates the need to reduce residual stress throughout the entire tank 1. Therefore, there is no need to prepare a furnace or the like that can accommodate the entire tank 1 in order to reduce residual stress. Furthermore, because heat treatment is not performed, the construction period for manufacturing the tank 1 can be shortened. As a result, residual stress can be effectively reduced even in large tanks 1. Furthermore, by not performing heat treatment, it is possible to suppress a decrease in toughness and strength at the welded portion 30. As a result, a high-strength material can be used for the plate material 20, and the weight of the tank 1 can be reduced. [Explanation of symbols]

[0066] DESCRIPTION OF SYMBOLS 1...tank 2...cylindrical portion 3...end plate portion 20...plate material 20a...end portion 20c...center portion 20f, 20g...surface 20s, 20t...inclined surface 21X, 21V...groove portion 30, 30F, 30V...welded portion 31, 311 to 315, 315F, 316 to 320, 320F, 321 to 327...welded layer 35, 351, 352...TIG welded layer 50...heating means Da...Face direction Dc...Central axis direction Dt...Plate thickness direction Dt1...First side Dt2...Second side Lb...Laser light S10, S20, S30, 40, S50...Tank manufacturing method S11...Process for multi-layer welding S12, S22, S32, S42, S52...Process for locally reducing residual stress T1, T2, T3, T4...Thickness

Claims

1. A manufacturing method of a tank, in which a steel plate material constituting the tank is joint-welded to manufacture the tank, performing multi-layer welding between the opposing ends of the plate materials such that a plurality of weld layers are sequentially stacked toward the surface side of the plate materials; and performing a process of locally reducing residual stress only on some of the welded layers located on the surface side among the plurality of welded layers, In the step of locally reducing the residual stress, a TIG welding layer thinner than the welded layer located closest to the surface is formed by TIG welding so as to cover the welded layer located closest to the surface, and heat is input to the welded layer located closest to the surface, and after the TIG welding, the TIG welding layer is removed and a peening treatment is performed only on the welded layer located closest to the surface. Tank manufacturing method.

2. In the step of locally reducing the residual stress, only a part of the weld layer located on the surface side is removed. A method for manufacturing the tank of claim 1.

3. In the step of locally reducing the residual stress, a laser beam is irradiated onto the weld layer located closest to the surface. A method for manufacturing the tank according to claim 1 or 2.

4. In the step of locally reducing residual stress, the welded layer located closest to the surface is heated by a heating means opposed to the welded layer located closest to the surface. A method for manufacturing the tank according to claim 1 or 2.

5. The step of locally reducing residual stress is carried out only on a partial region of the tank including a portion where multi-layer welding is performed in the step of performing multi-layer welding. A method for manufacturing the tank according to claim 1 or 2.

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