JP2007190586A - Welding method, and manufacturing method of liquefied gas tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding method for reducing the man-hour of the welding work, and a manufacturing method of a liquefied gas tank. <P>SOLUTION: Laser beam welding is used for welding 9% Ni steel. A groove 20 is formed in the butted part of an annular member 2A and an annular member 2B being members to be welded. The groove 20 is formed in a narrow groove, and a curvature is formed on the bottom part 20B of the groove 20. A root face 21 is formed at the butted part of the annular member 2A and the annular member 2B. In addition, when laminating a weld bead layer, the ratio of the depth of fusion of a molten metal to the width of fusion of the molten metal is set to be ≥1 and ≤1.4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to welding metals together using a laser.

  Tanks for storing liquefied gas such as liquefied natural gas (hereinafter referred to as LNG) and liquefied propane gas (LPG) are classified into so-called ground type and underground type. . The above-ground type LNG tank includes a metal inner tank for storing LNG, and a heat insulating layer and an outer tank are provided outside thereof. Since LNG has a low temperature of −162 ° C., a metal material excellent in low temperature toughness is used for the inner tank directly in contact with LNG. An example of such a metal material is Ni steel containing 9% Ni (hereinafter referred to as 9% Ni steel). Patent Document 1 discloses a technique that uses TIG welding for welding of inner tank side plates that store LNG.

JP-A-9-10931

  However, in TIG welding, it is necessary to make a groove wide to some extent from the viewpoint of welding workability, and it is necessary to provide a multilayer weld bead layer. As a result, there has been a problem that the number of welding processes becomes large. Therefore, the present invention has been made in view of the above, and an object of the present invention is to provide a welding method and a liquefied gas tank manufacturing method that can reduce the number of welding work steps.

  In order to solve the above-described problems and achieve the object, the welding method according to the present invention provides a narrow groove at a butt portion between the welding target members when joining the welding target members using a laser. A curvature is provided at the bottom of the groove, and a root face is provided at the abutting portion between the members to be welded, and when the weld bead layer is laminated, the penetration depth of the molten metal constituting the weld bead layer The ratio of the penetration depth of the molten metal with respect to is set within a predetermined range.

  In this welding method, the number of weld bead layers can be reduced by performing narrow groove welding using a laser having a large penetration depth. As a result, the number of welding operations can be reduced.

  The welding method according to the present invention is characterized in that, in the welding method, a ratio of a penetration depth of the molten metal to a penetration width of the molten metal is 1 or more and 1.4 or less.

  Since this welding method includes the configuration of the welding method, the same effects and advantages as the welding method are achieved. Furthermore, in this welding method, the ratio of the penetration depth of the molten metal to the penetration width of the molten metal is set to 1 or more and 1.4 or less. This can suppress the bonding of the porosity formed by solid solution in the molten metal, so that the reliability of the welded joint is improved.

  The welding method according to the present invention is characterized in that, in the welding method, a dimension of the root face in a penetration depth direction of the molten metal is 1 mm or more and 5 mm or less.

  Since this welding method includes the configuration of the welding method, the same effects and advantages as the welding method are achieved. Further, in this welding method, the dimension of the root face in the depth direction of the molten metal is set to 1 mm or more and 5 mm or less. By using this size and an austenitic welding wire, the structure of the molten metal in the first layer of the weld bead layer becomes austenite, so that toughness at a low temperature can be ensured.

  The welding method according to the present invention is characterized in that, in the welding method, the surface of the welded bead layer that has already been welded on the side of the next welded bead layer to be laminated is a concave shape.

  Since this welding method includes the configuration of the welding method, the same effects and advantages as the welding method are achieved. Furthermore, in this welding method, the next weld bead layer side to be laminated is formed into a concave shape. Thereby, the fusion failure near the boundary between the base material (material of the welding target member) and the molten metal can be suppressed.

  The welding method according to the present invention is characterized in that the input heat amount per unit mass of the welding wire used in the welding method is 10 kJ / cm · g or more and 27 kJ / cm · g or less.

  Since this welding method includes the configuration of the welding method, the same effects and advantages as the welding method are achieved. Furthermore, in this welding method, the input heat amount per unit mass of the welding wire is set to 10 kJ / cm · g or more and 27 kJ / cm · g or less. Thereby, the ratio of the penetration depth of the molten metal to the penetration width of the molten metal can be surely set to 1 or more and 1.4 or less.

  Moreover, the manufacturing method of the liquefied gas tank which concerns on the following this invention welds the welding object member which comprises the tank which stores a liquefied gas at least with the said welding method, It is characterized by the above-mentioned.

  The manufacturing method of this liquefied gas tank welds at least the welding object member which constitutes the tank which stores liquefied gas by the above-mentioned welding method. Thereby, the construction period of the tank for storing the liquefied gas can be shortened.

  The welding method and the manufacturing method of the liquefied gas tank according to the present invention can reduce the number of welding work steps.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the best mode for carrying out the invention (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  In this embodiment, when welding 9% Ni steel, a groove is provided at the abutting portion between the welding target members of 9% Ni steel, a curvature is provided at the bottom of the groove, and the butting between the welding target members is performed. The portion is provided with a root face, and when the weld bead layer is laminated, the ratio of the penetration depth “a” to the penetration width “b” is 1 to 1.4 and laser welding is performed. First, the configuration of the LNG tank will be briefly described.

  FIG. 1 is a schematic cross-sectional view showing an example of a liquefied gas tank. The liquefied gas tank 1 is a so-called ground type liquefied gas tank constructed on the ground. The liquefied gas tank 1 has a double tank structure including an inner tank 2 made of metal and an outer tank 4 made of metal or PC (prestressed concrete) provided outside the inner tank 2. . A liquefied gas such as LNG gas or LPG gas is stored in the inside 2I of the inner tank 2, and a heat insulating material 3 is provided between the inner tank 2 and the outer tank 4, so that the outside air of the outer tank 4 is Heat transfer from the inner tank 2 to the LNG in the inner tank 2 is reduced. In addition, LNG is stored in the inside 2I of the inner tank 2 in a state of extremely low temperature of −162 ° C.

  Since the inner tank 2 is in direct contact with the cryogenic LNG gas, the inner tank 2 is manufactured with a material excellent in low-temperature brittleness. In the liquefied gas tank 1 according to this embodiment, 9% Ni steel containing 9% Ni is used as the material of the inner tank 2. The inner tank 2 is manufactured by welding a 9% Ni steel plate. Although the thickness of the steel plate which comprises the inner tank 2 changes with the scales of the liquefied gas tank 1, it is several mm-several tens mm. Next, an example of the manufacturing method of the liquefied gas tank 1 is demonstrated.

2 and 3 are explanatory views showing an example of a manufacturing method of the liquefied gas tank. 2 and 3 show an example of a procedure for manufacturing the body portion 2C of the inner tank 2 of the liquefied gas tank. The body portion 2C of the inner tub 2 welds a plurality of 9% Ni steel plates (members to be welded) 2P to form the annular members 2 ₁ , 2 _2, etc., which are members to be welded, and then welds the annular members to each other. . In this embodiment, laser welding is used, and for example, an austenitic welding wire (metallurgy) such as a welding wire (metallurgy) containing about 70% Ni is used. In addition, a welding wire (metallurgy) is not restricted to this. FIG. 2 shows an example in which an annular member 2 ₂ made of 9% Ni steel and an annular member 2 ₃ are welded.

In welding the annular member 2 ₂ and the annular member 2 ₃ , the welding apparatus 10 is used. As shown in FIGS. 2 and 3, the welding apparatus 10 is placed on an annular work floor 5 provided on the outer peripheral portion of the inner tank 2. And the welding apparatus 10 welds the annular member 2 ₂ and the annular member 2 ₃ while moving on the work floor 5 in the circumferential direction of the annular member 2 ₃ (direction of arrow R in FIG. 3).

  FIG. 4 is an explanatory view showing a configuration example of the welding apparatus according to this embodiment. The welding apparatus 10 is configured by mounting a welding head 11, a shield gas supply nozzle 12, and a welding wire supply unit 13 on a carriage 14. The carriage 14 is provided with wheels 15 that travel on a guide rail 5 </ b> R laid on the work floor 5. The carriage 14 travels on the guide rail 5R and moves in the circumferential direction of the annular members 2A and 2B, while using the welding wire (metal alloy) W supplied from the welding wire supply unit 13, the annular member 2A and the annular member 2B are welded.

  In this embodiment, a laser is used for welding the annular member 2A and the annular member 2B. Only the welding head 11 is mounted on the welding apparatus 10, and the laser generator 17 and the welding head 11 installed at a place (for example, the ground part) separate from the work floor are connected by an optical cable 18. Then, the laser beam generated by the laser generator 17 is irradiated from the welding head 11 to the welded portion between the annular member 2A and the annular member 2B to weld them together. As the laser, a YAG laser, a CO2 laser, an optical fiber laser, or the like can be used. Use of an optical fiber laser is preferable because the laser generator 17 can be miniaturized.

At the time of welding, the shield gas G supplied from the shield gas cylinder 16 through the gas pipe 19 is injected from the shield gas supply nozzle 12 to the welded portion. The shield gas G is an inert gas and maintains the atmosphere of the welded portion in an inert gas atmosphere during welding. In this embodiment, nitrogen (N ₂ ) is used for the shielding gas G. In this embodiment, by using nitrogen which is easily dissolved in the molten metal as the shielding gas G, the porosity generated in the molten metal or at the boundary between the molten metal and the mother layer can be extremely reduced. The shield gas that can be used in this embodiment is not limited to nitrogen, and, for example, argon (Ar) or helium (H) can also be used. Next, the welding method according to this embodiment will be described.

  FIG. 5 is a sectional view showing a portion to be welded by the welding method according to this embodiment. 5 indicates the inside of the inner tank 2 (see FIG. 1), and OUT indicates the outside of the inner tank 2. Moreover, the arrow G of FIG. 5 shows the action direction of gravity. The annular member 2A and the annular member 2B, which are members to be welded, have a plate thickness t of about several mm to several tens of mm. In this embodiment, a groove 20 is provided at the abutting portion between the annular member 2A and the annular member 2B. In laser welding, in order to make use of keyhole welding, a groove having a shape close to an I groove or an I groove is usually used. In addition, when welding thick plates using laser welding, the root face is enlarged.

  In the welding method according to this embodiment, laser welding is used, but the groove 20 is a narrow groove. Further, a curvature is provided in the bottom portion (groove bottom portion) 20B of the groove 20 (r = 3 mm in this embodiment). Further, a root face 21 is provided at the abutting portion between the annular member 2A and the annular member 2B in order to facilitate skin alignment between the annular member 2A and the annular member 2B. The dimension (hereinafter referred to as root face dimension) s of the root face 21 in the penetration depth direction (plate thickness direction) is made as small as possible. The root face dimension s is preferably as small as possible as long as the skin alignment between the annular member 2A and the annular member 2B is possible. However, in order to facilitate skin matching, it is necessary to secure at least about 1 mm.

  FIG. 6 is an explanatory diagram showing the relationship between the Ni amount (%) and the root face dimension (mm) in the first layer of molten metal. The amount of Ni in FIG. 6 is mass%. When the amount of Ni is less than 25% in the first layer (the first layer of welding) of the molten metal, the molten metal structure becomes a martensitic structure, and the toughness at low temperature is lowered. On the other hand, in the first layer of molten metal, when the Ni content is 25% or more, the structure of the molten metal becomes austenite and the toughness at low temperature is improved. If the root face dimension s is 5 mm or less, the structure of the molten metal is austenite, so that toughness at low temperatures can be improved. If the toughness at low temperature is acceptable, even if a part of the structure of the molten metal is a martensite structure, the root face dimension s does not have to be 5 mm or less, and the dimension corresponding to the allowable range is routed. The face size s may be selected.

  By making the groove 20 in the shape as described above, the base metal dilution of the first layer of welding is reduced and the amount of penetration of the molten metal is increased, so that the joint performance close to the molten metal can be secured, The toughness of the joint part can be secured. Here, although the narrow groove is not strictly defined, a groove having a smaller angle than the groove angle θ of 30 to 50 degrees in the conventional method is called a narrow groove. The opening dimension h of the groove depends on the thickness of the annular member 2A or the like to be welded, but is about 5 mm to 30 mm when the thickness t is several mm to several tens mm. Next, the bead shape of the welded part in this embodiment will be described.

FIG. 7 is a cross-sectional view showing the shape of the weld bead layer of the weld. The welded portion between the annular member 2A and the annular member 2B is formed by laminating a second weld bead layer (weld second layer) 22 ₂ on the first weld bead layer (weld first layer, initial layer) 22 ₁ and The weld bead layers are sequentially laminated, and the annular member 2A and the annular member 2B are welded. In this embodiment, the surface of the weld bead layer that has already been welded on the side of the next weld bead layer to be laminated is formed into a concave shape. This can be realized by providing a curvature at the bottom (groove bottom) 20B of the groove 20.

When welding second weld bead layer 22 ₂ on the first weld bead layer 22 _1, a concave portion C provided on the first weld bead layer 22 ₁ of the surface at the next weld bead layer side to be laminated, the surface concave Shape. Further, in the case of welding a third weld bead layer on the second weld bead layer 22 _2, the recess C formed in the second weld bead layer 22 _second surface in the next weld bead layer side to be laminated, the surface Is a concave shape. By doing in this way, the poor fusion in the vicinity of the boundary between the base material (which is an object to be welded, such as the annular member 2A) and the molten metal can be suppressed.

  8 and 9 are cross-sectional views illustrating the ratio of the penetration depth of the molten metal to the penetration width of the molten metal. In welding, the molten metal melts to form a weld bead layer, and the objects to be welded are joined together. In this embodiment, it is preferable that the ratio a / b of the molten metal penetration depth a to the molten metal penetration width b is 1 or more and 1.4 or less. The reason for this will be explained.

  FIG. 10 is an explanatory diagram showing the relationship of the ratio of the penetration depth of the molten metal to the penetration width of the molten metal. Note that the first layer (first weld bead layer) and the final layer (final bead layer) are excluded because the construction conditions are special. When a / b is 1.43, porosity is generated in the weld bead layer (symbol * 1 in FIG. 10). Further, when a / b is 0.95, a fusion failure occurs near the boundary between the base material (welding target) and the weld bead layer (molten metal) (symbol * 2 in FIG. 10). In the range where a / b is 1 or more and 1.4 or less, no porosity or poor fusion occurs. From this result, a / b is preferably 1 or more and 1.4 or less. Next, the melt penetration width b and the melt penetration depth a will be described.

The penetration depth a of the molten metal is the maximum dimension of the weld bead layer in the direction in which the molten metal is melted when attention is paid to a certain weld bead layer. Further, the penetration depth b of the molten metal is the maximum dimension of the weld bead layer in the direction perpendicular to the direction of the penetration depth of the molten metal in the weld bead layer of interest. The second weld bead layer 22 ₂ shown in FIG. 8 obtains a / b from the contour of the second weld bead layer 22 ₂ according to the above definition when the contour of the weld bead layer is clear.

The second weld bead layer 22 ₂ shown in FIG. 9 is a case where the outline of the second weld bead layer 22 ₂ in the portion in contact with the third weld bead layer 22 ₃ is unclear. In this case, two points of intersections P ₁ and P ₂ between the second weld bead layer 22 ₂ and the adjacent weld bead layer (third weld bead layer 22 ₃ ) and one of the neighboring points of the intersections P ₁ and P ₂ A virtual contour is drawn by drawing a quadratic curve Y connecting a total of three points with P ₃ . And the penetration depth a of a molten metal is determined using this virtual outline. Here, the neighboring point P3 is on the outline of the second weld bead layer 22 ₂ and exists at a position 1 mm away from the intersection point P ₁ or the intersection point P ₂ .

FIG. 11 is an explanatory diagram showing the relationship between the ratio of the penetration depth of the molten metal to the penetration width of the molten metal and the input heat amount. The input heat amount is the input heat amount per unit mass of the welding wire. As can be seen from FIG. 12, in order to obtain the ratio a / b of the penetration depth of the molten metal with respect to the appropriate penetration width of the molten metal, that is, 1 ≦ a / b ≦ 1.4 (hatched portion in FIG. 11), It is preferable to be 10 kJ / cm · g or more and 27 kJ / cm · g or less. Here, the input heat quantity Q can be obtained by equation (1). In the equation (1), P is laser power (kW), v is welding speed (cm / sec.), L is welding wire supply speed (cm / sec.), D is welding wire diameter (cm), and ρ is a welding wire density (g / cm ^3).
Q = (P / v) / (L × π (d / 2) ² × ρ) (1)

  As described above, in this embodiment, a narrow groove is provided at the abutting portion between the members to be welded, a curvature is provided at the bottom of the groove, a root face is provided at the abutting portion between the members to be welded, and welding is performed. When laminating the bead layer, laser welding is performed such that the ratio of the penetration depth a of the molten metal to the penetration width b of the molten metal is 1 or more and 1.4 or less. As a result, the base material dilution in the first layer (the first layer of the weld bead layer) is reduced and the amount of molten metal penetration is increased, so that joint performance close to that of molten metal can be ensured and toughness degradation can be suppressed.

  Moreover, by setting a / b to 1 or more and 1.4 or less, it is possible to suppress the bonding of porosity formed by solid solution in the molten metal. Furthermore, by providing a curvature at the bottom of the groove, the shape of the bead can be made concave, and fusion failure near the boundary between the base material and the molten metal can be suppressed. Further, by using laser welding that can generate high-density energy, deep penetration and high-speed welding are possible. Moreover, the number of the weld bead layers can be reduced by using a narrow groove. By these actions, the number of welding processes can be shortened.

  FIG. 12 is an explanatory diagram showing the results of one example of the present invention. In this example, 9% Ni steel was welded using the welding method of the present invention, and RT was determined. The conditions were as follows: the plate thickness to be welded was 30 mm, the groove opening dimension was 8 mm, the groove bottom radius was 2 mm, and the root face dimension was 3 mm. Nitrogen was used as the shielding gas. In addition, the welding was made up of six layers, and the laser output, welding speed, etc. were controlled so that each of the weld bead layers was in the range of 1 to 1.4. The construction conditions of each weld bead layer are as shown in FIG. As can be seen from the RT determination result of FIG. 12, all weld bead layers are at the pass level of RT1 type 1 type. Here, the RT1 type 1 class is defined in JIS Z 3106 (2001).

  As described above, the welding method and the method for manufacturing a liquefied gas tank according to the present invention are useful for welding 9% Ni steel, and are particularly suitable for reducing the number of man-hours for welding work.

It is a section schematic diagram showing an example of a liquefied gas tank. It is explanatory drawing which shows the example of a manufacturing method of a liquefied gas tank. It is explanatory drawing which shows the example of a manufacturing method of a liquefied gas tank. It is explanatory drawing which shows the structural example of the welding apparatus which concerns on this embodiment. It is sectional drawing which shows the part welded with the welding method which concerns on this embodiment. It is explanatory drawing which shows the relationship between Ni amount (%) and root face dimension (mm) in the first layer of molten metal. It is sectional drawing which shows the shape of the weld bead layer of a welding part. It is sectional drawing explaining the ratio of the penetration depth of molten metal with respect to the penetration width of molten metal. It is sectional drawing explaining the ratio of the penetration depth of molten metal with respect to the penetration width of molten metal. It is explanatory drawing which shows the relationship of the ratio of the penetration depth of molten metal with respect to the penetration width of molten metal. It is explanatory drawing which shows the relationship between the ratio of the penetration depth of a molten metal with respect to the penetration width of a molten metal, and input heat amount. It is explanatory drawing which shows the result of one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 liquefied gas tank 2 inner tank 2A annular member 2B annular member 2C trunk | drum 2I inside 3 heat insulation material 4 outer tank 10 welding apparatus 11 welding head 16 shield gas cylinder 17 laser generator 18 optical cable 19 gas piping 20 groove 20B groove bottom 21 route Face 22 ₁ First weld bead layer 22 ₂ Second weld bead layer 22 ₃ Third weld bead layer

Claims (6)

When joining members to be welded using a laser,
While providing a narrow groove at the abutting portion between the members to be welded and providing a curvature at the bottom of the groove,
Also, a root face is provided at the butting portion between the members to be welded, and
A welding method characterized in that, when the weld bead layer is laminated, a ratio of a penetration depth of the molten metal to a penetration width of the molten metal constituting the weld bead layer is set within a predetermined range.   The welding method according to claim 1, wherein a ratio of a penetration depth of the molten metal to a penetration width of the molten metal is 1 or more and 1.4 or less.   The welding method according to claim 1 or 2, wherein a dimension of the root face in a penetration depth direction of the molten metal is 1 mm or more and 5 mm or less.   The welding method according to any one of claims 1 to 3, wherein a surface of the weld bead layer that has already been welded is formed in a concave shape on the side of the next weld bead layer to be laminated.   The welding method according to claim 1, wherein a heat input per unit mass of the welding wire used in the welding method according to claim 1 is 10 kJ / cm · g or more and 27 kJ / cm · g or less.   A manufacturing method of a liquefied gas tank characterized by welding at least a member to be welded constituting a tank for storing liquefied gas by the welding method according to any one of claims 1 to 5.

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