JP7748926B2 - Tank manufacturing method - Google Patents

Description

This disclosure relates to a method for manufacturing a tank.

Various articles manufactured using metallic materials are required to have the required strength and toughness depending on the article. For example, Patent Document 1 discloses a configuration in which a multi-layer butt-welded joint of steel plates is subjected to ultrasonic impact treatment to impart compressive residual stress between the front and back weld layers, thereby forming a modified layer with improved toughness.

Japanese Patent Application Laid-Open No. 2008-229692

For tanks containing low-temperature liquefied gas, where the cargo temperature falls to -10°C or below, regulations stipulate the thickness, strength, toughness, etc. of the material that makes up the tank. Therefore, the welds that join the steel plates that make up 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 increase the toughness of welds, it is desirable to increase the toughness more uniformly throughout the entire weld.

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.

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 welding step and a step of removing a portion of a surface layer of a lower-layer welded layer. The welding step involves welding between ends of the opposing plates so that multiple welded layers are sequentially stacked toward the surface side of the plates. The step of removing a portion of the surface layer of the lower-layer welded layer involves removing a portion of the surface layer of the lower-layer welded layer before stacking an upper-layer welded layer on the lower-layer welded layer. The step of removing a portion of the surface layer of the lower-layer welded layer involves removing a portion of the surface layer of the lower-layer welded layer so that, when the upper-layer welded layer is stacked on the lower-layer welded layer, the reheat range due to heat input from the upper-layer welded layer will cover the entire lower-layer welded layer after the portion of the surface layer has been removed.

The tank manufacturing method disclosed herein allows for more uniform toughness to be achieved throughout the entire weld.

FIG. 1 is a cross-sectional view of a tank manufactured by a tank manufacturing method according to an embodiment of the present disclosure. 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. 1 is a flowchart showing the steps of a method for manufacturing a tank according to an embodiment of the present disclosure. 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. 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. 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. 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. 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. 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.

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 land-based liquefied gas storage facility, 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. The tank 1 is not limited to a cylindrical shape, and may be other shapes, such as a spherical shape or a rectangular shape.

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 plates 20 in the thickness direction Dt is, for example, about 10 to 100 mm.

In this embodiment, the plate materials 20 have a groove portion 21V with a V-shaped cross section, which is a V-groove. In the groove portion 21V, the end portions 20a of the opposing plate materials 20 each have an inclined surface 20s. 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 of the first side Dt1 in the plate thickness direction Dt to the surface 20g of the second side Dt2 in the plate thickness direction Dt. The groove portion 21V 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 plane of the paper in Figure 2).

The ends 20a of opposing plate materials 20 are joined via welds 30. The welds 30 are formed between the ends 20a of the plate materials 20. The welds 30 are formed by multi-layer welding. In multi-layer welding, the welds 30 are formed between the ends 20a of 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.

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 the plurality of welded layers 31 is determined depending on the plate thickness, etc. of the plate material 20 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.

(Tank manufacturing method procedure)
Fig. 3 is a flowchart showing the procedure of the method for manufacturing a tank according to an embodiment of the present disclosure. Fig. 4 is a diagram schematically showing a process for obtaining a reheating range in a welded layer and a process for setting a range for removing a part of a surface layer 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 reheating 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.

In step S11 of acquiring the reheat range in the welded layer, the reheat range in the lower welded layer 31 is acquired. In step S13 of performing welding, which will be described later, welding is repeated multiple times from the second side Dt2 to 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 later. In step S11 of acquiring the reheat range in this welded layer, as shown in FIG. 4, when the upper welded layer 31B is stacked on the lower welded layer 31A, the reheat range A in the lower welded layer 31A is acquired due to the heat input from the upper welded layer 31B. In other words, the heat input from the upper welded layer 31B does not necessarily extend to the entire lower welded layer 31A; the area of the lower welded layer 31A that contacts (actually overlaps) with the upper welded layer 31B and into which the heat input from the upper welded layer 31B extends is taken as reheat area A. Reheat area A is the region where the toughness of the lower welded layer 31A is increased by the heat input from the upper welded layer 31B, and it recovers to above a preset standard.

In step S12, which sets the area for removing a portion of the surface portion of the welded layer, the area for removing a portion of the surface portion 31a of the lower welded layer 31 is set based on the reheating area A acquired in step S11, which acquires the reheating area of the welded layer. The portion of the surface portion 31a of the lower welded layer 31 is removed in step S14, which will be described in detail later, for removing a portion of the surface portion of the lower welded layer. The area for removing a portion of the surface 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 area is increased (recovered) to a standard level by the heat input from the upper welded layer 31B. In this embodiment, the area for removing a portion of the surface portion 31a of the lower welded layer 31 is set based on the thickness T in the plate thickness direction Dt of the area B outside the reheating area A of the lower welded layer 31. The surface portion 31a can be removed, for example, by cutting using a tool such as a disc grinder.

In the welding process 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 plane of the paper in Figure 2).

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

The above-mentioned welding process S13 and process S14, in which a portion of the surface layer of the lower welding layer is removed, are repeated a predetermined number of times to form the welding layers 311-315 in sequential layers.

Fig. 5 is a diagram illustrating 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 illustrating 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 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 31a of the first welded layer 311 is removed by a dimension T.

Fig. 7 is a diagram illustrating 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 illustrating a state in which a portion of the surface layer of the second welded layer is removed by a step of removing a portion of the surface layer 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 opposing ends 20a of the plate materials 20 such that a second welded layer 312 (corresponding to the 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 the lower welded layer 31). At this time, the first welded layer 311 is reheated by the 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.

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

After this, the third welded layer 313 to the fifth welded layer 315 are sequentially stacked by repeating the welding process S13 and the process S14 of removing part of the surface of the lower welded layer.

FIG. 9 is a diagram illustrating 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 , in step S15 of forming the outermost welding layer, a sixth welding layer 316 located closest to the first side Dt1 (closest to the surface 20f) in the plate thickness direction Dt is formed by welding the sixth welding layer 316 onto the fifth welding layer 315. The outermost welding layer 316 located closest to the first side Dt1 (closest to the surface 20f) in the plate thickness direction Dt is formed so as to protrude from the surface 20f toward the first side Dt1 in the plate thickness direction Dt.

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 relieved by the heat input when the other welded layers 31 are subsequently formed. The welded layer 315 has its toughness restored and residual stress relieved by the heat input when the outermost welded layer 316 is subsequently formed. In contrast, residual stress is generated 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 an example 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.

(Action and effect)
In the tank manufacturing method S10 of the above embodiment, a portion of the surface layer 31 a of the lower welded layer 31 is removed before the upper welded layer 31 is laminated on the lower welded layer 31. As a result, when the upper welded layer 31 is welded to 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 31 a 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 of the entire welded portion 30 can be more uniformly increased. Furthermore, reheating the entire welded portion 30 can also reduce residual stress in the welded portion 30.

In addition, in the above embodiment, when the upper welded layer 31 is laminated by welding, the heat input from the upper welded layer 31 reheats the lower welded layer 31 from which part of the surface layer 31a has been removed, thereby reheating the entire lower welded layer 31.

Furthermore, in the above embodiment, when the upper welded layer 31 is laminated on the lower welded layer 31, the reheat range A due to the heat input from the upper welded layer 31 extends to the entire lower welded layer 31 after removing part of the surface layer 31a, thereby improving the overall toughness of the lower welded layer 31.

In addition, in the above embodiment, the reheat range A in the lower welding layer 31 due to heat input from the upper welding layer 31 is acquired. This makes it possible to appropriately set the range in which the portion of the surface layer 31a of the lower welding layer 31 is removed so that the heat input from the upper welding layer 31 covers the entire lower welding layer 31 after removing that portion of the surface layer 31a.

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, thereby locally reducing residual stress.

(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.

<Additional Notes>
A manufacturing method of the tank 1 described in the embodiment can be understood, for example, as follows.

(1) The manufacturing method of the tank 1 according to the first aspect is a manufacturing method of the tank 1 in which the tank 1 is manufactured by joint-welding the steel plates 20 that constitute the tank 1, and includes a process S13 of welding between the ends 20a of the opposing plates 20 so that multiple welded layers 31 are sequentially stacked toward the surface 20f of the plates 20, and a process 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.

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

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

As a result, when the upper weld layer 31 is laminated by welding, the heat input from the upper weld layer 31 can reheat the lower weld layer 31 from which part of the surface layer 31a has been removed. Therefore, each time multiple weld layers 31 are laminated in sequence, heat is input from the upper weld layer 31, and ultimately the entire welded portion 30 is reheated, thereby increasing the toughness of the entire welded portion 30.

(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), wherein in step S14 of removing a portion of the surface layer 31a of the lower welded layer 31, the portion of the surface layer 31a of the lower welded layer 31 is removed so that when the upper welded layer 31 is laminated on the lower welded layer 31, the reheat range A due to the heat input from the upper welded layer 31 covers the entire lower welded layer 31 after the portion of the surface layer 31a has been removed.

As a result, when the upper weld layer 31 is stacked on top of the lower weld layer 31, the reheat range A due to heat input from the upper weld layer 31 extends to the entire lower weld layer 31 after removing part of the surface layer 31a, thereby improving the overall toughness of the lower weld layer 31.

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

This allows the extent to which the surface layer 31a of the lower welded layer 31 is removed to be appropriately set so that the heat input from the upper welded layer 31 reaches the entire lower welded layer 31 after removing that portion of the surface layer 31a.

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

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.

1...Tank 2...Cylindrical portion 3...Head plate portion 20...Plate material 20a...End portion 20f...Surface 20g...Surface 20s...Inclined surface 21V...Groove portion 30...Weld portion 31...Welded layer, 311-316...Welded layers 31A...Lower welded layer 31B...Upper welded layer 31a...Surface portion A...Reheating area Da...Opposing direction Dc...Central axis direction Dt...Plate thickness direction Dt1...First side Dt2...Second side K...Removal area S10...Tank manufacturing method S11...Process for determining the reheating area in the welded layer S12...Process for setting the area for removing a portion of the surface portion of the welded layer S13...Process for performing welding S14...Process for removing a portion of the surface portion of the lower welded layer S15...Process for forming the outermost welded layer S16...Process for removing at least a portion of the outermost welded layer

Claims (4)

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. The method for manufacturing a tank according to claim 1, wherein, in the welding step, when the upper weld layer is welded to the lower weld layer, the lower weld layer from which a portion of the surface layer has been removed is reheated by heat input from the upper weld layer. 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;
3. The method for manufacturing a tank according to claim 1, further comprising: a step of setting a range in which a portion of the surface portion of the lower welded layer is to be removed, in a step of removing a portion of the surface portion of the lower welded layer, based on the reheating range acquired in the step of acquiring the reheating range. 3. The method for manufacturing a tank according to claim 1, wherein at least a portion of the welded layer located closest to the surface of the plate material among the plurality of welded layers is removed.