Method for manufacturing tank tank

Abstract

A method for manufacturing a tank according to the present invention is a method for manufacturing a tank by joint-welding steel plates constituting the tank, the method comprising: a step for performing multi-layer welding between the ends of the plates facing each other so as to sequentially stack a plurality of welding layers toward the surface side of the plates; and a step for performing a treatment for locally reducing residual stress only on a portion of the plurality of solder layers located on the front surface side.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a storage tank.

[0002] This application claims priority based on patent application No. 2022-118610 filed in Japan on July 26, 2022, and the contents are incorporated herein by reference. Background Art

[0003] When steel materials are joined together by welding, residual stress in the tensile direction is generated at the weld, which can cause problems such as brittle fracture of the weld or stress corrosion cracking.

[0004] Patent Document 1 discloses a structure in which shot peening is performed on welded parts when manufacturing a ship cryogenic tank. In this structure, compressive stress is applied to the welded parts by shot peening, thereby canceling out residual stress in the tensile direction.

[0005] Previous technical literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-89802 Summary of the invention

[0008] Technical issues to be solved by the invention

[0009] However, in the case of marine liquefied gas tanks where the cargo temperature reaches below -10°C, regulations sometimes require heat treatment after welding to reduce welding residual stress from the viewpoint of preventing brittle fracture. In this case, a method is usually adopted in which the liquefied gas tank is placed in a heat treatment furnace to perform heat treatment on the welded portion at one time. However, due to the size limitation of the heat treatment furnace, it is sometimes impossible to perform heat treatment on large liquefied gas tanks using a heat treatment furnace. In this case, a device for performing local residual stress reduction treatment, such as a heat treatment device for performing local heat treatment, is used. For example, in a large liquefied gas tank, the plate thickness of the tank becomes thicker, and residual stress reduction treatment needs to be performed on the entire plate thickness direction of the welded portion, which leads to a problem of extended construction period.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a tank capable of effectively reducing the residual stress of a weld portion.

[0011] Means for solving technical problems

[0012] In order to solve the above-mentioned problems, the manufacturing method of the storage tank involved in the present invention is a storage tank manufacturing method for manufacturing the storage tank by performing joint welding on the steel plates constituting the storage tank. The manufacturing method of the storage tank includes a process of performing multi-layer welding and a process of performing a treatment to locally reduce residual stress. In the process of performing multi-layer welding, multi-layer welding is performed between the ends of the plates facing each other in a manner of stacking a plurality of weld layers in sequence toward the surface side of the plates. In the process of performing a treatment to locally reduce residual stress, the residual stress is locally reduced only for a portion of the weld layers located on the surface side among the plurality of weld layers.

[0013] Effects of the Invention

[0014] According to the method for manufacturing a storage tank of the present invention, the residual stress of the welded portion can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view showing an example of a tank manufactured by the method for manufacturing a tank according to the embodiment of the present invention.

[0016] Figure 2 It is a cross-sectional view showing a welded portion between steel plate materials constituting the storage tank according to the first embodiment of the present invention.

[0017] Figure 3 This is a flowchart showing the procedure of the method for manufacturing a storage tank according to the embodiment of the present invention.

[0018] Figure 4 It is a cross-sectional view showing a state where the outermost weld layer is removed in the welded portion between the plate materials according to the first embodiment of the present invention.

[0019] Figure 5 It is a cross-sectional view showing a welded portion between plate materials according to a second embodiment of the present invention.

[0020] Figure 6 It is a cross-sectional view showing a welded portion between plate materials according to a third embodiment of the present invention.

[0021] Figure 7 It is a cross-sectional view showing a welded portion between plate materials according to a fourth embodiment of the present invention.

[0022] Figure 8 It is a cross-sectional view showing a welded portion between plate materials according to a fifth embodiment of the present invention.

[0023] Fig. 9 It is a cross-sectional view showing a welded portion between plate materials in a modification example according to the embodiment of the present invention. DETAILED DESCRIPTION

[0024] <First embodiment>

[0025] Below, reference Figures 1 to 9 , a method for manufacturing a storage tank according to an embodiment of the present invention is described.

[0026] (Structure of storage tank)

[0027] like Figure 1 As shown, the storage tank 1 manufactured by the manufacturing method of the storage tank of this embodiment is, for example, a storage tank capable of storing liquefied gases such as liquefied carbon dioxide. The storage tank 1 is arranged on the hull of a ship, the floating body of an offshore floating device, a liquefied gas storage facility on land, etc. The storage tank 1 is, for example, cylindrical. The storage tank 1 includes a cylindrical portion 2 and a sealing portion 3. The cylindrical portion 2 extends along its central axis direction Dc. In this embodiment, the cylindrical portion 2 is formed into a cylindrical shape, and the cross-sectional shape orthogonal to its central axis direction Dc is circular. The sealing portion 3 is respectively arranged at both ends of the cylindrical portion 2 in the central axis direction Dc. Each sealing portion 3 is hemispherical and closes the opening of the cylindrical portion 2 in the central axis direction Dc. In addition, the storage tank 1 is not limited to a cylindrical shape, and can also be other shapes such as a sphere and a square.

[0028] Figure 2 It is a cross-sectional view showing a welded portion between steel plate materials constituting the storage tank according to the first embodiment of the present invention.

[0029] like Figure 2 As shown, the tank 1 is formed by welding a plurality of steel plates 20. Each plate 20 constituting the tank 1 is formed of a metal material such as high-strength quenched and tempered steel.

[0030] In the present embodiment, the plate materials 20 have a groove portion 21X with an X-shaped cross section as an X-shaped groove. The groove portion 21X is formed along the opposing direction Da of the plate materials 20 and the direction perpendicular to the plate thickness direction Dt of the plate materials 20 (ie, the groove portion 21X is perpendicular to the plate thickness direction Dt of the plate materials 20). Figure 2 In addition, in this embodiment, the groove portion 21X is an X-shaped groove as an example for description, but it is not limited to the X-shaped groove.

[0031] The ends 20a of the plates 20 facing each other have inclined surfaces 20s and 20t, respectively. The inclined surfaces 20s of the plates 20 facing each other are formed so that the interval in the facing direction Da gradually decreases from the surface 20f of the first side Dt1 of the plate thickness direction Dt toward the center 20c of the plate thickness direction Dt. The inclined surfaces 20t of the plates 20 facing each other are formed so that the interval in the facing direction Da gradually decreases from the surface 20g of the second side Dt2 of the plate thickness direction Dt toward the center 20c of the plate thickness direction Dt.

[0032] The ends 20a of the plates 20 facing each other are joined via the welded portion 30. The welded portion 30 is formed between the ends 20a of the plates 20. The welded portion 30 is formed by multi-layer welding. In the multi-layer welding, the welded portion 30 is formed by repeatedly performing welding a plurality of times between the ends 20a of the plates 20 facing each other. The multi-layer welding is suitable for suppressing the amount of heat input to the plates 20 at each welding.

[0033] The welded portion 30 has a plurality of weld layers 31. In the present embodiment, the plurality of weld layers 31 include five weld layers 311 to 315 formed from the central portion 20c in the plate thickness direction Dt to the first side Dt1 in the plate thickness direction Dt, and five weld layers 316 to 320 formed from the central portion 20c in the plate thickness direction Dt to the second side Dt2 in the plate thickness direction Dt. In addition, the number of the plurality of weld layers 31 is set according to the plate thickness of the plate material 20, etc., and can be appropriately changed.

[0034] In the present embodiment, the thickness of the plate material 20 in the plate thickness direction Dt is, for example, approximately 10 to 100 mm.

[0035] The welding layers 311 to 315 are stacked in sequence 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. Among the welding layers 311 to 315, the welding layer 315 located closest to the first side Dt1 in the plate thickness direction Dt is raised relative to the surface 20f of the plate 20 so as to protrude toward the first side Dt1 in the plate thickness direction Dt. The welding layer 315 illustrated in the present embodiment is formed closer to the first side Dt1 in the plate thickness direction than the surface 20f of the plate 20.

[0036] The welding layers 316 to 320 are stacked in sequence from the central portion 20c in the plate thickness direction Dt toward the surface 20g on the second side Dt2 in the plate thickness direction Dt. Among the welding layers 316 to 320, the welding layer 320 located closest to the second side Dt2 in the plate thickness direction Dt is raised relative to the surface 20g of the plate 20 so as to protrude toward the second side Dt2 in the plate thickness direction Dt. The welding layer 320 illustrated in the present embodiment is formed closer to the second side Dt2 in the plate thickness direction than the surface 20g of the plate 20.

[0037] (Sequence of tank manufacturing methods)

[0038] Figure 3 This is a flowchart showing the procedure of the method for manufacturing a storage tank according to the embodiment of the present invention.

[0039] like Figure 3 As shown, the method S10 for manufacturing the storage tank 1 according to the embodiment of the present invention includes a step S11 of performing multi-layer welding and a step S12 of performing a treatment for locally reducing residual stress.

[0040] In the multi-layer welding process S11, as Figure 2 As shown, the plates 20 are joined by performing multi-layer welding between the ends 20a of the plates 20 facing each other. Specifically, from the first side Dt1 in the plate thickness direction Dt, the inclined surfaces 20s of the plates 20 facing each other are welded along the extending direction of the welded portion ( Figure 2 The welding is repeated multiple times (in a direction perpendicular to the paper surface), thereby sequentially stacking the weld layers 311 to 315. At this time, among the weld layers 311 to 315, the outermost weld layer 315 formed by welding last and located closest to the first side Dt1 (closest to the surface 20f) in the plate thickness direction Dt is formed to bulge from the surface 20f toward the first side Dt1 in the plate thickness direction Dt.

[0041] Furthermore, from the second side Dt2 in the plate thickness direction Dt, between the inclined surfaces 20t of the mutually opposing plate materials 20, along the extending direction of the welded portion ( Figure 2 The welding is repeated multiple times (in a direction perpendicular to the paper surface), thereby sequentially stacking the weld layers 316 to 320. At this time, among the weld layers 316 to 320, the outermost weld layer 320 formed by welding last and located closest to the second side Dt2 (closest to the surface 20g) in the plate thickness direction Dt is formed to bulge from the surface 20g to the second side Dt2 in the plate thickness direction Dt.

[0042] In this way, the plates 20 are joined to each other. Thus, a welded portion 30 in which a plurality of weld layers 31 are stacked is formed between the end portions 20a of the plates 20 facing each other. Among the plurality of weld layers 31, residual stress is generated in the weld layer 315 of the outermost layer formed last on the first side Dt1 in the plate thickness direction Dt and the weld layer 320 of the outermost layer formed last on the second side Dt2 in the plate thickness direction Dt. Among the plurality of weld layers 31, the residual stress of the other weld layers 311 to 314 and the weld layers 316 to 319 is relieved by heat input when the other weld layers 31 are formed later.

[0043] In the step S12 of performing the treatment of locally reducing the residual stress, the treatment of locally reducing the residual stress is performed on the weld 30 formed in the step S11. In the step S12, the treatment of locally reducing the residual stress is performed only on the weld 30, rather than on the entire tank 1. In the step S12, as the treatment of locally reducing the residual stress, the treatment of locally reducing the residual stress is performed only on a portion of the weld layers 31 located on the surface 20f side and the surface 20g side among the plurality of weld layers 31. In the treatment of locally reducing the residual stress, it is preferred to reduce the residual stress in a portion of the weld layer 31 located on the surface 20f side and the surface 20g side to a predetermined level (for example, less than 50% of the yield stress of the steel material).

[0044] Figure 4 It is a cross-sectional view showing a state where the outermost weld layer is removed in the welded portion between the plate materials according to the first embodiment of the present invention.

[0045] Specifically, if Figure 4 As shown, on the first side Dt1 of the plate thickness direction Dt of the welded portion 30, only a portion of the weld layer 31 located on the surface 20f side of the plate 20 is removed. In the present embodiment, the weld layer 315 that is raised to the first side Dt1 of the plate thickness direction Dt more than the surface 20f in the welded portion 30 is removed. The removal of the weld layer 315 can be performed, for example, by a hand tool such as an angle grinder. In addition, on the second side Dt2 of the plate thickness direction Dt of the welded portion 30, only a portion of the weld layer 31 located on the surface 20g side of the plate 20 is removed. In the present embodiment, the weld layer 320 that is raised to the second side Dt2 of the plate thickness direction Dt more than the surface 20g in the welded portion 30 is removed. As described above, the removal of the weld layer 320 can also be performed by a hand tool such as a grinder. Thus, the weld layer 315 and the weld layer 320 whose residual stress is not relieved due to the heat input based on the formation of other weld layers 31 are removed.

[0046] (Effect)

[0047] In the manufacturing method S10 of the storage tank 1 of the above-mentioned embodiment, the residual stress reduction treatment is performed on the partial weld layers 315 and 320 located on the surface 20f and 20g sides of the plate material 20, respectively, among the plurality of weld layers 31 of the weld portion 30. On the other hand, the residual stress reduction treatment is not performed on the other weld layers 311 to 314 and 316 to 319 other than the weld layers 315 and 320, as is the case with the partial weld layers 315 and 320 located on the surface 20f and 20g sides of the plate material 20. As a result, the residual stress can be effectively reduced in the weld portion 30 by multi-layer overlay welding.

[0048] Furthermore, in the above-described embodiment, by partially removing only a portion of the weld layer 315 , 320 located on the surface 20 f , 20 g side of the plate material 20 , it is possible to reduce the local residual stress generated in the weld portion 30 .

[0049] Furthermore, in the above-mentioned embodiment, the step S12 of locally reducing the residual stress is performed only on a portion of the area, and the portion includes the portion where the multi-layer welding is completed by the step S11 of performing the multi-layer welding. As a result, it is not necessary to perform the treatment of reducing the residual stress on the entire tank 1. Therefore, it is not necessary to prepare a furnace that can accommodate the entire tank 1 in order to reduce the residual stress. Moreover, in the above-mentioned embodiment, since the local heat treatment is not performed, the construction period for manufacturing the tank 1 can be shortened. As a result, even a large tank 1 can effectively reduce the residual stress.

[0050] Furthermore, by not performing heat treatment, it is possible to suppress a decrease in toughness or strength in 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.

[0051] <Second embodiment>

[0052] Next, a second embodiment of the method for manufacturing a storage tank according to the present invention will be described. In the second embodiment described below, the structure of the process of only partially reducing the residual stress is different from that of the first embodiment, so Figure 1 , Figure 3 The same components as those in the first embodiment are denoted by the same reference numerals and their repeated descriptions are omitted.

[0053] (Sequence of the method for manufacturing a storage tank)

[0054] like Figure 3 As shown, the method S20 for manufacturing the storage tank 1 according to the embodiment of the present invention includes a step S11 of performing multi-layer welding and a step S22 of performing a treatment for locally reducing residual stress.

[0055] Figure 5 It is a cross-sectional view showing a welded portion between plate materials according to a second embodiment of the present invention.

[0056] In the step S22 of locally reducing the residual stress in the present embodiment, Figure 5 As shown, the weld 30 formed in step S11 is subjected to a treatment for locally reducing residual stress. In this step S22, the treatment for locally reducing residual stress is performed only on the weld 30, rather than on the entire tank 1. In this step S22, as a treatment for locally reducing residual stress, only a portion of the weld layers 31 located on the surface 20f side and the surface 20g side among the plurality of weld layers 31 is subjected to a treatment for locally reducing residual stress. In the treatment for locally reducing residual stress, it is preferred that the residual stress in a portion of the weld layer 31 located on the surface 20f side and the surface 20g side be reduced to a predetermined level (e.g., less than 50% of the yield stress of the steel material).

[0057] In the step S22 of locally reducing the residual stress in the second embodiment, only a portion of the weld layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt is subjected to shot peening. More specifically, in the second embodiment, in the weld portion 30, the surface 315f of the weld layer 315 located closest to the first side Dt1 in the plate thickness direction Dt is subjected to shot peening. In addition, the surface 320f of the weld layer 320 located closest to the second side Dt2 in the plate thickness direction Dt of the weld portion 30 is subjected to shot peening. The shot peening is performed, for example, by needle peening. The shot peening of the weld layer 315 is preferably performed under the following conditions: the influence of the pressure of the needle P of the needle peening is suppressed as much as possible to affect the other weld layers 311 to 314, and the residual stress is concentrated on the weld layer 315 with high residual stress. The shot peening treatment for the weld layer 320 is preferably performed under the following conditions: the influence of the pressure of the needle P of the needle peening is minimized from affecting the other weld layers 316 to 319, and the residual stress is concentrated on the weld layer 320 with high residual stress. As a result, the residual stress generated in the weld layer 315 and the weld layer 320 is reduced.

[0058] (Effect)

[0059] In the manufacturing method S20 of the storage tank 1 of the above embodiment, by performing shot peening only on a portion of the weld layer 31 (315, 320) located on the surface 20f, 20g side of the plate 20, the residual stress of the portion of the weld layer 31 (315, 320) located on the surface 20f, 20g side of the plate 20 can be reduced.

[0060] Furthermore, in the manufacturing method S20 of the storage tank 1 of the above-mentioned embodiment, similarly to the above-mentioned first embodiment, by reducing the residual stress of a portion of the weld layers 31 (315, 320) located on the surface 20f, 20g side of the plate 20 among the multiple weld layers 31, the residual stress of the weld portion 30 based on the multi-layer cladding can be effectively reduced.

[0061] <Third Embodiment>

[0062] Next, a third embodiment of the method for manufacturing the storage tank 1 according to the present invention will be described. In the third embodiment described below, the structure of the process of only partially reducing the residual stress is different from that of the first and second embodiments, so Figure 1 , Figure 3 The same parts as those in the first and second embodiments are denoted by the same reference numerals and their repeated descriptions are omitted.

[0063] (Sequence of tank manufacturing methods)

[0064] like Figure 3 As shown, the method S30 for manufacturing the storage tank 1 according to the third embodiment includes a step S11 of performing multi-layer welding and a step S32 of performing a treatment for locally reducing residual stress.

[0065] In the step S32 of locally reducing residual stress in the present embodiment, the weld 30 formed in the step S11 is locally reduced in residual stress. In the step S32, the process of locally reducing residual stress is performed only on the weld 30, not on the entire tank 1. In the step S32, as a process of locally reducing residual stress, only a portion of the weld layers 31 located on the surface 20f side and the surface 20g side among the plurality of weld layers 31 is locally reduced in residual stress. In the process of locally reducing residual stress, the residual stress in a portion of the weld layer 31 located on the surface 20f side and the surface 20g side is reduced to a predetermined level (for example, less than 50% of the yield stress of the steel material).

[0066] Figure 6 It is a cross-sectional view showing a welded portion between plate materials according to a third embodiment of the present invention.

[0067] like Figure 6 As shown, in this embodiment, specifically, a TIG welding layer 35 is formed in order to input heat to a portion of the welding 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 welding layer 35 includes: a TIG welding layer 351 covering the outermost welding layer 315 located closest to the first side Dt1 in the plate thickness direction Dt; and a TIG welding layer 352 covering the outermost welding layer 320 located closest to the second side Dt2 in the plate thickness direction Dt. The thickness T1 of the TIG welding layer 351 is smaller than the thickness T2 of the outermost welding layer 315 in the plate thickness direction Dt. The thickness T3 of the TIG welding layer 352 is smaller than the thickness T4 of the outermost welding layer 320 in the plate thickness direction Dt. The TIG welding layers 351 and 352 are formed by TIG (Tungsten Inert Gas) welding. In addition, the construction position, thickness, etc. of the TIG welding layers 351 and 352 are not limited to the above, and can be properly managed so that the residual stress generated by the presence of the TIG welding layers 351 and 352 does not become a problem. For example, when the residual stress of the TIG welding layers 351 and 352 becomes a problem, the TIG welding layers 351 and 352 can be removed after TIG welding.

[0068] The residual stress of the welding layer 315 is reduced by the heat input during welding when forming the TIG welding layer 351. The welding when forming the TIG welding layer 351 is preferably performed under the following conditions: the influence of the heat input generated by welding is suppressed as much as possible to spread to other welding layers 311 to 314, and the residual stress is concentrated on the welding layer 315 with high residual stress.

[0069] Furthermore, the residual stress of the weld layer 320 is reduced by the heat input during welding when forming the TIG weld layer 352. Welding when forming the TIG weld layer 352 is preferably performed under the following conditions: the influence of the heat input generated by welding is suppressed as much as possible from spreading to other weld layers 316 to 319, and the heat input is concentrated on the weld layer 320 with high residual stress.

[0070] (Effect)

[0071] In the manufacturing method S30 of the storage tank 1 of the above-mentioned embodiment, heat is applied to reduce the residual stress of the weld layer 31 (315, 320) located on the side closest to the surface 20f, 20g to a predetermined level by TIG welding for forming the TIG weld layers 351, 352. As a result, the residual stress of a portion of the weld layer 315, 320 located on the side of the surface 20f, 20g of the plate 20 can be reduced. Furthermore, when the TIG weld layer 35 is formed by TIG welding, the TIG weld layer 35 can be formed thinner than the weld layers 315, 320, and sufficient heat input can be performed, so that the residual stress can be locally reduced with respect to the weld layer 31 (315, 320) located on the side of the outermost surface 20f, 20g, and the residual stress in the tensile direction generated in the TIG weld layer 35 can be suppressed to a small value. Therefore, the residual stress in the weld portion 30 can be reduced in the end.

[0072] Furthermore, in the method S30 for manufacturing the tank 1 according to the above embodiment, the residual stress of the welded portion 30 by multi-layer build-up welding can be effectively reduced, similarly to the above-mentioned first and second embodiments.

[0073] <Fourth embodiment>

[0074] Next, a fourth embodiment of the method for manufacturing the tank 1 according to the present invention will be described. In the fourth embodiment described below, the structure of the process of partially reducing the residual stress is different from that of the first to third embodiments, so Figure 1 , Figure 3 The same parts as those in the first to third embodiments are denoted by the same reference numerals and their description will be omitted.

[0075] (Sequence of tank manufacturing methods)

[0076] like Figure 3As shown, the method S40 for manufacturing the tank 1 according to the fourth embodiment includes a step S11 of performing multi-layer welding and a step S42 of performing a treatment for locally reducing residual stress.

[0077] In the step S42 of locally reducing residual stress in the present embodiment, the weld 30 formed in the step S11 is locally reduced in residual stress. In the step S42, the process of locally reducing residual stress is performed only on the weld 30, not on the entire tank 1. In the step S42, as a process of locally reducing residual stress, only a portion of the weld layers 31 located on the surface 20f side and the surface 20g side among the plurality of weld layers 31 is locally reduced in residual stress. In the process of locally reducing residual stress, it is preferred to reduce the residual stress in a portion of the weld layer 31 located on the surface 20f side and the surface 20g side to a predetermined level (for example, less than 50% of the yield stress of the steel material).

[0078] Figure 7 It is a cross-sectional view showing a welded portion between plate materials according to a fourth embodiment of the present invention.

[0079] like Figure 7 As shown, in the present embodiment, specifically, the laser beam Lb is irradiated to a portion of the weld layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt. In the present embodiment, the laser beam Lb is irradiated from the first side Dt1 in the plate thickness direction Dt to the outermost weld layer 315 located closest to the first side Dt1 in the plate thickness direction Dt. Furthermore, the laser beam Lb is irradiated from the second side Dt2 in the plate thickness direction Dt to the outermost weld layer 320 located closest to the second side Dt2 in the plate thickness direction Dt. The irradiation of the laser beam Lb is performed by directing the laser irradiation portion (not shown) irradiated with the laser beam Lb along the extension direction ( Figure 7 The laser beam Lb of the welding layers 315 and 320 can be irradiated with a laser device (in other words, a laser scanner) that can scan the laser beam Lb using a galvanometer mirror. In addition, as the laser device, for example, a welding device for laser welding can be used.

[0080] By irradiating the laser beam Lb, the weld layers 315 and 320 are heated, and the residual stress of the weld layers 315 and 320 is reduced. The irradiation of the laser beam Lb is preferably performed under the following conditions: the influence of the heating generated by the irradiation of the laser beam Lb is suppressed as much as possible from spreading to other weld layers 311 to 314 and 316 to 319, and the residual stress is concentrated on the weld layers 315 and 320 with high residual stress.

[0081] (Effect)

[0082] In the manufacturing method S40 of the storage tank 1 of the above-mentioned embodiment, by irradiating the weld layer 315, 320 located on the outermost surface 20f, 20g side with the laser beam Lb, the residual stress of a part of the weld layer 315, 320 located on the surface 20f, 20g side of the plate material 20 can be locally reduced. In addition, the heating based on the irradiation of the laser beam Lb is performed on the outermost weld layer 315, 320 as a part of the plate thickness direction Dt of the weld portion 30. Therefore, it is not necessary to heat the entire plate thickness direction Dt of the weld portion 30, and the required thermal energy can be less. Therefore, the local residual stress generated in the weld portion 30 can be reduced more easily and at a low cost.

[0083] Furthermore, in the method S40 for manufacturing the tank 1 according to the above embodiment, the residual stress of the welded portion 30 by multi-layer build-up welding can be effectively reduced, similarly to the above-described first to third embodiments.

[0084] <Fifth embodiment>

[0085] Next, a fifth embodiment of the method for manufacturing the storage tank 1 according to the present invention will be described. In the fifth embodiment described below, the structure of the process of partially reducing the residual stress is different from that of the first to fourth embodiments, so Figure 1 , Figure 3 The same parts as those of the first to fourth embodiments are denoted by the same reference numerals and descriptions thereof will be omitted.

[0086] (Sequence of tank manufacturing methods)

[0087] like Figure 3 As shown, the method S50 for manufacturing the tank 1 according to the fifth embodiment includes a step S11 of performing multi-layer welding and a step S52 of performing a treatment for locally reducing residual stress.

[0088] In the step S52 of performing the process of locally reducing the residual stress in the present embodiment, the process of locally reducing the residual stress is performed on the welded portion 30 formed in the step S11. In the step S52, the process of locally reducing the residual stress is performed only on the welded portion 30, not on the entire tank 1. In the step S52, as the process of locally reducing the residual stress, the process of locally reducing the residual stress is performed only on a portion of the welded layers 31 located on the surface 20f side and the surface 20g side among the plurality of welded layers 31.

[0089] Figure 8 It is a cross-sectional view showing a welded portion between plate members according to a fifth embodiment of the present invention.

[0090] like Figure 8 As shown, in this fifth embodiment, a portion of the weld layer 31 located on the surface 20f, 20g side of the plate material 20 in the plate thickness direction Dt is heated by the heating mechanism 50. In this embodiment, the heating mechanism 50 heats the outermost weld layer 315 located closest to the first side Dt1 in the plate thickness direction Dt from the first side Dt1 in the plate thickness direction Dt. In addition, the heating mechanism 50 heats the outermost weld layer 320 located closest to the second side Dt2 in the plate thickness direction Dt from the second side Dt2 in the plate thickness direction Dt. As the heating mechanism 50, for example, a panel heater, a high-frequency heating device, etc. can be used. The heating based on the heating mechanism 50 is performed by causing the heating mechanism 50 to extend along the extension direction ( Figure 8 It is done by moving in sequence in the direction perpendicular to the paper surface).

[0091] The residual stress of the weld layers 315 and 320 is reduced by heating by the heating mechanism 50. The heating by the heating mechanism 50 is preferably performed under the following conditions: the influence of the heating by the heating mechanism 50 is minimized from spreading to other weld layers 311 to 314 and 316 to 319, and the residual stress is concentrated on the weld layers 315 and 320 with high residual stress.

[0092] (Effect)

[0093] In the manufacturing method S50 of the storage tank 1 of the above embodiment, the welding layers 315 and 320 located closest to the surface 20f and 20g are heated by the heating mechanism 50 opposed to the welding layers 315 and 320 located closest to the surface 20f and 20g, thereby reducing the residual stress of a portion of the welding layers 315 and 320 located on the surface 20f and 20g of the plate 20. In addition, the heating by the heating mechanism 50 only needs to be performed on the outermost welding layers 315 and 320 as a portion of the plate thickness direction Dt of the welded portion 30, so it is not necessary to heat the entire plate thickness direction Dt of the welded portion 30, and the required heat energy can be less. Therefore, the local residual stress generated in the welded portion 30 can be reduced more easily and at a low cost.

[0094] Furthermore, in the method S50 for manufacturing the tank 1 according to the above embodiment, the residual stress of the welded portion 30 by multi-layer overlay welding can be effectively reduced, similarly to the above-described first to fourth embodiments.

[0095] (Other Implementations)

[0096] As mentioned above, although the embodiment of the present invention is described in detail with reference to the drawings, the specific structure is not limited to this embodiment, and design changes and the like that do not depart from the scope of the gist of the present invention are also included.

[0097] In addition, in the above-mentioned embodiment, the groove portion 21X is set to have an X-shaped cross section, but it is not limited to this. Fig. 9 As shown, the groove portion 21V can be set to a V-shaped cross section. In the weld portion 30V, as a plurality of weld layers 31, weld layers 321 to 327 are stacked from the second side Dt2 to the first side Dt1 in the plate thickness direction Dt. In this case, the residual stress of the weld layer 327 located closest to the surface 20f is reduced. As a result, the residual stress of the weld layer 327 of the outermost layer generated locally in the weld portion 30V formed by multi-layer cladding can be effectively reduced.

[0098] Furthermore, the structures described in the first to fifth embodiments may be appropriately combined. For example, the shot peening described in the second embodiment may be combined with the structures described in the first and third to fifth embodiments.

[0099] <Note>

[0100] The manufacturing methods S10, S20, S30, S40, and S50 of the storage tank 1 described in each embodiment can be understood, for example, as follows.

[0101] (1) The manufacturing method S10, S20, S30, S40, S50 of the storage tank 1 involved in the first embodiment manufactures the storage tank 1 by performing joint welding on the steel plate 20 constituting the storage tank 1. The manufacturing method S10 of the storage tank 1 includes the following steps: a step S11 of performing multi-layer welding between the plates 20 whose end portions 20a are opposite to each other in a manner of sequentially stacking a plurality of weld layers 31 toward the surfaces 20f, 20g of the plates 20; and a step S12 of locally performing a treatment to reduce residual stress only on a portion of the weld layers 31 located on the surfaces 20f, 20g of the plurality of weld layers 31.

[0102] The manufacturing methods S10, S20, S30, S40, and S50 of the storage tank 1 can reduce the residual stress of a portion of the weld layer 31 located on the surface 20f and 20g side of the plate 20 among the plurality of weld layers 31. On the other hand, the influence of the treatment for reducing the residual stress can be suppressed with respect to the other weld layers 31 except for the portion of the weld layer 31 located on the surface 20f and 20g side of the plate 20. As a result, the residual stress of the weld portion 30 by multi-layer overlay welding can be effectively reduced.

[0103] (2) The second embodiment of the method S10 for manufacturing a tank 1 is the method S10 for manufacturing a tank 1 according to (1), wherein in the step S12 of locally reducing the residual stress, only a portion of the weld layer 31 located on the surface 20f, 20g side is removed.

[0104] Thus, by removing only a portion of the weld layer 31 located on the surfaces 20 f and 20 g of the plate material 20 , the residual stress in the portion of the weld layer 31 located on the surfaces 20 f and 20 g can be locally reduced.

[0105] (3) The method S20 for manufacturing a storage tank 1 according to the third embodiment is the method S20 for manufacturing a storage tank 1 according to (1) or (2), wherein, in the step S22 of performing the treatment for locally reducing the residual stress, shot peening is performed only on a portion of the weld layer 31 located on the side of the surfaces 20f, 20g.

[0106] Thus, by subjecting only a portion of the weld layer 31 located on the surfaces 20 f and 20 g of the plate material 20 to shot peening, the residual stress of the portion of the weld layer 31 located on the surfaces 20 f and 20 g of the plate material 20 can be locally reduced.

[0107] (4) The manufacturing method S30 of the storage tank 1 involved in the fourth embodiment is any one of the manufacturing methods S30 of the storage tank 1 (1) to (3), wherein, in the step S32 of performing the treatment for locally reducing the residual stress, heat input is performed by performing TIG welding on the welding layer 31 located closest to the surface 20f, 20g.

[0108] In this structure, by performing TIG welding on the weld layer 31 located closest to the surfaces 20 f and 20 g to input heat, the residual stress of a portion of the weld layer 31 located on the surfaces 20 f and 20 g of the plate material 20 can be locally reduced.

[0109] (5) The method S40 for manufacturing a tank 1 according to the fifth aspect is any one of the methods S40 for manufacturing a tank 1 according to (1) to (4), wherein, in the step S42 of performing the treatment for locally reducing the residual stress, the weld layer 31 located closest to the surfaces 20f, 20g is irradiated with the laser beam Lb.

[0110] Thus, by irradiating the weld layer 31 located on the outermost surfaces 20 f and 20 g with the laser beam Lb, the residual stress of a portion of the weld layer 31 located on the outer surfaces 20 f and 20 g of the plate material 20 can be locally reduced.

[0111] (6) The manufacturing method S50 of the storage tank 1 involved in the sixth embodiment is any one of the manufacturing methods S50 of the storage tank 1 (1) to (5), wherein, in the step S52 of performing the treatment for locally reducing the residual stress, the welding layer 31 located closest to the surface 20f, 20g is heated by the heating mechanism 50 opposite to the welding layer 31 located closest to the surface 20f, 20g.

[0112] The heating mechanism 50 is a panel heater or a high-frequency heating device.

[0113] Therefore, the welding layer 31 located closest to the surface 20f, 20g is heated by the heating mechanism 50 opposite to the welding layer 31 located closest to the surface 20f, 20g, thereby locally reducing the residual stress of a portion of the welding layer 31 located on the surface 20f, 20g side of the plate material 20.

[0114] (7) The manufacturing method S10, S20, S30, S40, S50 of the storage tank 1 involved in the seventh embodiment is any one of the manufacturing methods S10, S20, S30, S40, S50 of the storage tank 1 in (1) to (6), which includes the steps S12, S22, S32, S42, S52 of locally reducing the residual stress only for a portion of the area including the multi-layer welding completed by the step S11 of performing multi-layer welding.

[0115] Thus, in the tank 1, only a partial area including the welded portion 30 as a portion where multi-layer welding is completed is subjected to treatment for locally reducing residual stress. Thus, it is not necessary to reduce residual stress in the entire tank 1. Therefore, it is not necessary to prepare a furnace that can accommodate the entire tank 1 in order to reduce residual stress. Furthermore, since heat treatment is not performed, the manufacturing period for the tank 1 can be shortened. As a result, even a large tank 1 can effectively reduce residual stress.

[0116] Furthermore, by not performing heat treatment, it is possible to suppress a decrease in toughness or strength in 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.

[0117] Industrial Applicability

[0118] According to the method for manufacturing a storage tank of the present invention, the residual stress of the welded portion can be effectively reduced.

[0119] Explanation of symbols

[0120] 1-storage tank, 2-cylindrical part, 3-end part, 20-plate, 20a-end part, 20c-central part, 20f, 20g-surface, 20s, 20t-inclined surface, 21X, 21V-groove part, 30, 30V-welding part, 31, 311~315, 315f, 316~320, 320f, 321~327-welding layer, 35, 351, 352-TIG welding layer, 50-adding Thermal mechanism, Da-opposing direction, Dc-center axis direction, Dt-plate thickness direction, Dt1-first side, Dt2-second side, Lb-laser beam, S10, S20, S30, S40, S50-tank manufacturing method, S11-multilayer welding process, S12, S22, S32, S42, S52-process for locally reducing residual stress, T1, T2, T3, T4-thickness.

Claims

1. A method for manufacturing a storage tank, wherein the storage tank is manufactured by welding a joint of steel plates constituting the storage tank, the method comprising the following steps: A step of performing multi-layer welding between the ends of the plates facing each other by sequentially stacking a plurality of welding layers toward the surface side of the plates; and A step of performing a treatment for locally reducing residual stress on only a portion of the solder layers located on the surface side among the plurality of solder layers.

2. The method for manufacturing a storage tank according to claim 1, wherein: In the step of performing the treatment for locally reducing the residual stress, only a portion of the solder layer located on the surface side is removed.

3. The method for manufacturing a storage tank according to claim 1 or 2, wherein: In the step of performing the treatment for locally reducing the residual stress, shot peening is performed only on a portion of the weld layer located on the surface side.

4. The method for manufacturing a storage tank according to claim 1 or 2, wherein: In the step of performing the treatment for locally reducing the residual stress, heat is input to the weld layer located closest to the surface by TIG welding.

5. The method for manufacturing a storage tank according to claim 1 or 2, wherein: In the step of performing the treatment for locally reducing the residual stress, the weld layer located closest to the surface is irradiated with a laser beam.

6. The method for manufacturing a storage tank according to claim 1 or 2, wherein: In the step of performing the treatment for locally reducing the residual stress, the solder layer located closest to the surface is heated by a heating mechanism that faces the solder layer located closest to the surface.

7. The method for manufacturing a storage tank according to claim 1 or 2, wherein: In the tank, the step of performing the treatment to locally reduce the residual stress is performed only on a partial region including a portion where the multi-layer welding is completed by the step of performing the multi-layer welding.

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