JP6025620B2 - Submerged arc welding method, method of manufacturing steel pipe using the submerged arc welding method, welded joint, and steel pipe having the welded joint - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a submerged arc welding method in which steel plates are formed into a tubular shape and welded on both sides, a method for manufacturing a steel pipe using the submerged arc welding method, a welded joint, and a steel pipe having the welded joint.

  Conventionally, as a method for automatically welding a steel pipe, a method using submerged arc welding (SAW) which is a kind of arc welding method has been developed (see Patent Document 1). In this technique, the groove cross-sectional area on the outer surface side of the X-groove-shaped element pipe is made smaller than the groove cross-sectional area of the inner area of the element pipe, and the outer surface of the element pipe seam part (joint part) is also used for tack welding. After the main welding by submerged arc welding, the inner surface is finally welded.

  As a method for automatically welding a steel pipe, a method using gas shield arc welding (Gas Metal Arc Welding: GMAW), which is a kind of arc welding method, has been developed (see Patent Document 2). In this technique, a groove is provided on both the inner surface and the outer surface of the tube, the root gap of the groove is maintained at 2 mm or less, the tube is fixed, and the first first layer welding with low heat input is performed from either the inner surface or the outer surface. Apply. Subsequently, the second first layer welding with high heat input that causes the first first layer welding to melt from the other of the inner surface or the outer surface is performed. And the inner and outer surfaces of the pipe are subjected to multilayer welding at the same time.

Japanese Patent No. 4259376 JP-A-8-57641

  However, none of the techniques described in Patent Documents 1 and 2 assume a steel pipe exceeding a predetermined plate thickness. Here, the predetermined plate thickness is, for example, more than 40 mm.

Patent Document 1 describes a method of efficiently manufacturing a steel pipe having a thickness of about 19 mm using a submerged arc welding method. The technique described in Patent Document 1 is not studied at all from the viewpoint of hot cracking and cold cracking, although the number of welding processes is reduced in order to reduce welding defects, that is, the efficiency is studied. Patent Document 1 describes that a steel pipe is welded in one pass and one layer, and paragraph [0021] describes that multilayer welding does not impair the effect. However, there has been no idea of combining single layer welding and multilayer welding when the plate thickness exceeds 40 mm.
In general, when a predetermined plate thickness (over 40 mm) is welded using the submerged arc welding method, a multilayer welding method using gouging is known. Hereinafter, this technique will be described with reference to FIG. In addition, the code | symbol t in FIG. 10 shows the board thickness of the bent steel plate.

  In the multilayer welding method using the submerged arc welding method, first, the first layer on the 1st side is welded with low heat input (low current / low speed). This is to avoid hot cracking. Subsequently, the second and subsequent layers on the 1st side are subjected to multilayer welding by providing a heat input limit (for example, 175 kJ / cm or less) so that the heat input does not become extremely large. This is to avoid cold cracking. Subsequently, an operation for widening the groove by gouging or machining is performed on the 2nd side. This is to solve the lack of penetration due to the low heat input of the first layer on the 1st side and the 2nd side. Subsequently, the 2nd side is welded in the same procedure as the 1st side. Therefore, there is a problem that a gouging process is required and the number of passes increases.

  The technique described in Patent Document 2 uses a gas shield arc welding method. Here, the gas shielded arc welding method has a lower welding current than the submerged arc welding method, so the welding amount is small, and when performing welding that requires a large amount of welding, such as a steel sheet having a plate thickness exceeding 40 mm. ineffective. Therefore, in general, when welding a steel sheet having a thickness exceeding 40 mm, the submerged arc welding method is used, and the gas shielded arc welding method is not used.

  The present invention has been made in view of the above problems, and it is possible to reduce the number of passes and eliminate the gouging process as compared with the conventional multi-layer welding method. Further, the submerged arc welding method can extremely reduce hot cracks and cold cracks. It is an object of the present invention to provide a method of manufacturing a steel pipe using the submerged arc welding method, a welded joint, and a steel pipe having the welded joint.

In order to solve the above-mentioned problem, a submerged arc welding method according to the present invention is a submerged arc welding method in which a steel plate formed into a tubular shape having a plate thickness exceeding 40 mm is welded on both sides, and the steel plate is a first one on one side. It has a groove-shaped joint portion in which the cross-sectional area in the groove portion is larger than the cross-sectional area in the second groove portion on the other surface side, and the first opening is performed in one pass and one layer with low heat input. Applying to the tip and forming the first welded portion, and further welding the high heat input to the second groove until the weld metal in the second groove exceeds the surface of the steel plate. subjected Te, and forming a second weld, subjected to multilayer welding in the first groove portion, viewed including the step of forming a third welded portion, the first weld portion, the second weld portion, The third weld is formed by submerged arc welding .

Further, the submerged arc welding method according to the present invention is a submerged arc welding method for performing double-side welding on a steel sheet formed into a tubular shape having a plate thickness exceeding 40 mm, wherein the steel sheet is cut in a first groove portion on one side. It has a groove-shaped joint portion formed with an area larger than the cross-sectional area in the second groove portion on the other surface side, and welds with low heat input in one pass and one layer to the first groove portion. And a step of forming a first welded portion, a step of applying multilayer welding to the first groove portion to form a third welded portion, and a weld metal in the second groove portion exceeding the surface of the steel plate. until subjected to further welding high heat input to the second groove portion, it viewed including the step of forming a second weld, said first weld portion, the second weld portion, and said third welding The part is formed by submerged arc welding .

  Here, in the submerged arc welding method according to the present invention, the joint portion may have a root face of 2 to 15 mm. Preferably, the root face is 3 mm or more and 12 mm or less. If the root face is less than 2 mm, meltdown may occur. If the root face exceeds 15 mm, the melt may be insufficiently melted. From the viewpoint of preventing melt-down, the root face is preferably 3 mm or more, and from the viewpoint of preventing insufficient melting, the root face is preferably 12 mm or less.

  In the submerged arc welding method according to the present invention, in the step of forming the first welded portion, the low heat input is 15 to 50 kJ / cm, and the step of forming the second welded portion is the high input. The heat is 55 to 175 kJ / cm, and the step of forming the third welded portion may have a heat input of 30 to 175 kJ / cm. Preferably, the low heat input is 20 kJ / cm or more and 45 kJ / cm or less, and the step of forming the second welded portion is the high heat input is 60 kJ / cm or more and 160 kJ / cm or less, In the step of forming the three welds, the heat input is preferably 45 kJ / cm or more and 160 kJ / cm or less.

That is, if the low heat input is less than 15 kJ / cm, the amount of weld metal is small and the efficiency is poor. Moreover, when the said low heat input exceeds 50 kJ / cm, a hot crack and a melt-down may generate | occur | produce. Therefore, from the viewpoint of efficiently performing welding, the low heat input is preferably 20 kJ / cm or more, and from the viewpoint of preventing hot cracking and melting, the low heat input is preferably 45 kJ / cm or less. Good.
Further, if the high heat input is less than 55 kJ / cm, the penetration may be insufficient. Further, when the high heat input exceeds 175 kJ / cm, melt-down may occur. Therefore, from the viewpoint of preventing insufficient melting, the high heat input is preferably 60 kJ / cm or more, and from the viewpoint of preventing melting, the high heat input is preferably 160 kJ / cm or less.
The heat input is less efficient if it is less than 30 kJ / cm. Moreover, when the said heat input exceeds 175 kJ / cm, the thickness for every pass will become thick and a cold crack may generate | occur | produce. Therefore, from the viewpoint of efficiently performing welding, the heat input is preferably 45 kJ / cm or more, and from the viewpoint of preventing low temperature cracking, the heat input is preferably 160 kJ / cm or less.

According to such a configuration, the submerged arc welding method performs high-heat-input single-layer welding on the second groove portion until the weld metal exceeds the surface of the steel plate. Therefore, according to the submerged arc welding method according to the present invention, it is possible to increase the width of the weld metal and extremely reduce the hot cracking.
In the submerged arc welding method, multilayer welding is performed on the first groove portion. Therefore, according to the submerged arc welding method according to the present invention, it is possible to adjust the thickness of each layer and extremely reduce the low temperature cracking.

  The submerged arc welding method according to the present invention is characterized in that, in the first groove portion, a part of the third weld portion is formed before the second weld portion. Here, the total height of the first welded part and the third welded part may be 4 to 30 mm.

  According to the structure which concerns, a submerged arc welding method forms a part of 3rd weld part before the process of forming a 2nd weld part. Therefore, according to the submerged arc welding method which concerns on this invention, it can avoid that a melt-down generate | occur | produces in the process of forming a 2nd weld part.

  Further, in the submerged arc welding method according to the present invention, the joining portion is formed on the outer surface of the steel plate in which the first groove portion is formed into a tubular shape, and the second groove portion is formed on the inner surface of the steel plate. It is characterized by being.

  According to this configuration, the submerged arc welding method performs multilayer welding on the first groove portion formed on the outer surface and performs one-pass one-layer welding on the second groove portion formed on the inner surface. . Therefore, according to the submerged arc welding method according to the present invention, the inner surface that is difficult to weld is performed in one pass, and the outer surface that is relatively easy to weld is performed in multiple passes, so that the welding operation is easy.

  Moreover, the submerged arc welding method according to the present invention is characterized in that the second welded portion is applied so as to melt into at least a part of the first welded portion.

  According to this configuration, the submerged arc welding method causes the second welded portion to melt into at least a part of the first welded portion. Therefore, according to the submerged arc welding method according to the present invention, lack of penetration does not occur in the step of forming the second welded portion, and thus it is necessary to perform gouging as a previous stage of the step of forming the second welded portion. Absent.

  Moreover, the method for manufacturing a steel pipe according to the present invention is characterized by using any one of the submerged arc welding methods described above.

  According to the structure which concerns, the method of manufacturing a steel pipe uses the submerged arc welding method which concerns on this invention for the process of welding a steel plate. Therefore, according to the method for manufacturing a steel pipe according to the present invention, high temperature cracks and low temperature cracks can be extremely reduced in the step of welding steel plates.

Moreover, the welded joint according to the present invention is a welded joint in which a groove-shaped joint is formed, and the joint is welded on both sides using a submerged arc welding method, and the thickness of the steel sheet exceeds 40 mm, The joint portion has a cross-sectional area in the first groove portion on one surface side larger than a cross-sectional area in the second groove portion on the other surface side, and the weld metal in the first groove portion forms a multilayer and the first The weld metal in the second groove portion forms a single layer , and the weld metal in the first groove portion and the weld metal in the second groove portion are formed by submerged arc welding, and the weld in the second groove portion. The metal exceeds the surface of the steel sheet.

According to such a configuration, in the welded joint according to the present invention, the weld metal in the second groove portion exceeds the surface of the steel plate. Therefore, according to the welded joint according to the present invention, it is possible to increase the width of the weld metal in the manufacturing process, and extremely reduce hot cracking.
In this welded joint, the weld metal in the first groove has a multilayer structure. Therefore, according to the welded joint according to the present invention, it is possible to adjust the thickness of each layer in the manufacturing process, and extremely reduce low temperature cracking.

  The weld joint according to the present invention is characterized in that the weld metal in the second groove portion is melted into at least a part of the weld metal in the first groove portion.

  According to this configuration, in the welded joint according to the present invention, the weld metal in the second groove portion is melted into at least a part of the weld metal in the first groove portion. Therefore, according to the welded joint according to the present invention, lack of penetration does not occur in the manufacturing process, so that it is not necessary to gouging as a stage before welding the second groove portion.

  Moreover, the steel pipe which concerns on this invention has the said weld joint, It is characterized by the above-mentioned.

  According to the structure which concerns, the steel pipe which concerns on this invention uses the welded joint which concerns on this invention for the part which joins a steel plate. Therefore, according to the steel pipe which concerns on this invention, in a welded joint, a high temperature crack and a low temperature crack can be reduced extremely.

  The submerged arc welding method and the method of manufacturing a steel pipe using the submerged arc welding method according to the present invention do not require a gouging process as compared with the conventional multilayer welding method, and can generate hot cracks and cold cracks even if the number of passes is small. Extremely reduced. Further, the welded joint according to the present invention and the steel pipe having the welded joint do not require a gouging process as compared with the conventional steel pipe, and can extremely reduce hot cracking and cold cracking even if the number of passes is small.

It is an external appearance perspective view which shows the structural example of the welding mechanism for implement | achieving the submerged arc welding method which concerns on this invention. It is a figure for demonstrating the junction part welded with the submerged arc welding method which concerns on this invention. It is a figure for demonstrating the submerged arc welding method which concerns on this invention. It is a figure for demonstrating the welding method which concerns on Example 1, (a) is a process of forming a 1st weld part, (b) is a process of forming a part of 3rd weld part, c) is a step of forming the second welded portion, and (d) is a step of forming the remaining portion of the third welded portion. It is a figure for demonstrating the welding method which concerns on Example 2, (a) is a process of forming a 1st weld part, (b) is a process of forming a 3rd weld part, (c) is a process. This is a step of forming a second weld. It is a figure which shows the example of welding in the welding method which concerns on Example 1 and Example 2. FIG. It is a figure which shows the comparative example of the submerged arc welding method which concerns on this invention. It is a figure for demonstrating the groove shape in an Example. It is a figure for demonstrating arrangement | positioning of the electrode in an Example. It is a figure for demonstrating the modification of a steel plate. It is a figure for demonstrating the multilayer welding method which welds the junction part of the steel plate which plate | board thickness exceeds 40 mm using a submerged arc welding method as a prior art example.

[Embodiment]
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate.
Each figure is only schematically shown so that the invention can be fully understood. Therefore, the present invention is not limited to the illustrated example. In the drawings to be referred to, dimensions of members constituting the present invention may be exaggerated for clarity of explanation. Moreover, in each figure, the same code | symbol is attached | subjected about the common component and the same component, and those overlapping description is abbreviate | omitted.

<< Configuration Example of Welding Mechanism for Realizing Submerged Arc Welding Method According to the Present Invention >>
A welding mechanism 1 shown in FIG. 1 is a configuration example of a welding mechanism for realizing a submerged arc welding method according to the present invention (hereinafter sometimes referred to as “the present welding method”). That is, the welding mechanism 1 is merely an example, and the present welding method described later is not limited to the welding operation realized by the welding mechanism 1. This welding method can be realized by a general welding mechanism.

  The welding mechanism 1 automatically welds a steel plate 80 formed into a tubular shape using a submerged arc welding method described later. The welding mechanism 1 includes two welding machines 10 that weld the outer surface side or the inner surface side of the steel plate 80. Each welding machine 10 includes a plurality of (two in FIG. 1) torches (nozzles) 12 and a flux discharge portion 13. Each torch 12 includes an electrode 12a through which a wire is inserted. Hereinafter, the electrode 12a that precedes the welding direction is referred to as an L pole, and the electrode 12a that follows the welding direction is referred to as a T pole. Here, the polarity of the electrode 12a is not particularly limited. For example, the polarity of the electrode 12a may be a combination of alternating currents or a combination of direct current and alternating current. Further, in the case of a combination of alternating currents, the method for connecting the electrodes 12a is not particularly limited. For example, the connection method may be reverse V connection, V connection, Scott connection, or the like. Preferably, since the penetration becomes deep, a combination of alternating currents using reverse V connection or a combination of direct current and alternating current is preferable. In addition, the welding mechanism 1 rotates the steel plate 80 appropriately so that each welding machine 10 can weld the steel plate 80 downward.

  The steel plate 80 has a joint portion 81 where both sides that are faced with each other formed by groove processing are joined. The joining part 81 is a part welded by the submerged arc welding method according to the present invention. The kind of the steel plate 80 is not particularly limited. For example, the steel plate 80 may be mild steel, high-tensile steel, low-temperature steel, or the like. With reference to FIG. 2, the shape and dimension of the steel plate 80 and the junction part 81 are demonstrated.

  As shown in FIG. 2, the steel plate 80 has a cylindrical shape. Hereinafter, the thickness of the steel plate 80 is represented by “t”. The steel plate 80 according to the present embodiment assumes a case where the thickness t is larger than 40 mm (t> 40 mm). The joint portion 81 has an X groove shape in a side view and is formed in parallel with the axial direction of the steel plate 80 bent in a plan view. A direction (axial direction) in which the joint 81 is formed in plan view may be referred to as a welding direction.

  The joint portion 81 includes an outer surface side groove portion 82 (first groove portion), an inner surface side groove portion 83 (second groove portion), and a route face (route surface) 84. The outer surface side groove portion 82 has a V shape in a side view, and represents a groove depth as “d1 (mm)” and a groove angle as “θ1 (°)”. The inner surface side groove portion 83 has a V shape in a side view, and represents a groove depth as “d2 (mm)” and a groove angle as “θ2 (°)”. Further, the distance in the radial direction of the route face 84 is represented by “r”.

  In the joining portion 81 of the steel plate 80 according to the present embodiment, the cross-sectional area in the outer surface side groove portion 82 is formed larger than the cross sectional area in the inner surface side groove portion 83. Moreover, even when the thickness t becomes 50 mm or 60 mm, the joining portion 81 fixes the dimension of the groove depth d2 within a range of, for example, 0 to 20 (mm), and only the dimension of the groove depth d1. Increase Thereby, although details will be described later, the inner surface side groove portion 83 can be formed by one-pass one-layer welding. The groove depth d2 is preferably 2 mm or more and 18 mm or less. The route face 84 is preferably designed so that the distance r is in the range of 2 to 15 (mm). The root face 84 is preferably 3 mm or more and 12 mm or less.

≪Submerged arc welding method according to the present invention≫
The outline of the submerged arc welding method according to the present invention will be described with reference to FIG. In the present welding method, three welds of a first weld 91, a second weld 92, and a third weld 93 are formed in the joint 81. Here, the 1st welding part 91 and the 3rd welding part 93 are comprised with the weld metal by welding mainly. The second welded portion 92 is mainly composed of a weld metal obtained by welding and a portion of the base material (steel plate 80) that is affected by the heat.

  In this welding method, the first welded portion 91 is formed in the outer surface side groove portion 82 by low heat input of one pass and one layer. Further, in the present welding method, high-heat input single-layer welding is applied to the inner surface side groove portion 83 until the weld metal in the inner surface side groove portion 83 exceeds the surface of the steel plate 80. Thus, in the present welding method, the second welding portion 92 is formed on the inner surface side groove portion 83. In the present welding method, multilayer welding is performed on the outer surface side groove portion 82, and a third weld portion 93 is formed on the upper portion of the first weld portion 91.

  Here, the main welding method is “the formation of the first welding portion 91 → the formation of the second welding portion 92 → the third” as the order of forming the first welding portion 91, the second welding portion 92, and the third welding portion 93. There are two ways: “formation of welded portion 93” and “formation of first welded portion 91 → formation of third welded portion 93 → formation of second welded portion 92”. Below, the welding method by the former order is demonstrated as Example 1, and the welding method by the latter order is demonstrated as Example 2. FIG.

  In the following, referring to FIG. 4 (refer to FIGS. 1 to 3 as appropriate), “formation of first welded portion 91 → formation of second welded portion 92 → formation of third welded portion 93” according to Example 1. The welding method in order will be described. In this welding method, in the step of forming the second welded portion 92, a part of the third welded portion 93 is formed prior to the formation of the second welded portion 92 in order to prevent the weld metal from being burned out. To do.

<Step of forming the first welded portion>
First, in this welding method, the outer surface side groove portion 82 of the joint portion 81 is welded with a low heat input of one pass and one layer. As a result, a “first welded portion 91” made of a single layer of weld metal is formed in the outer surface side groove portion 82 (see FIG. 4A). The process of forming the 1st welding part 91 is good to carry out with the L pole (leading pole) of the welding machine 10 of the outer surface side, for example. However, the process of forming the 1st welding part 91 may use a T pole (following pole), and is not limited to a L pole.

<Step of forming a part of the third welded portion>
Then, this welding method changes a welding condition with the process of forming a 1st welding part, and forms a part of 3rd welding part 93 in the outer surface side groove part 82 of the junction part 81. FIG. This welding operation is performed in multiple passes until the weld metal in the outer surface side groove portion 82 has a height of 4 to 30 mm. As a result, a “part of the third welded portion 93” is formed on the upper portion of the first welded portion 91 in the outer surface side groove portion 82 to a height of 4 to 30 mm (see FIG. 4B). The step of forming a part of the third welded portion 93 may be performed by, for example, the L pole (leading pole) and the T pole (following pole) of the welding machine 10 on the outer surface side. However, the process of forming a part of the third welded portion 93 may use only one of the L pole and the T pole, and is not limited to the tandem welding of the L pole and the T pole.

<Step of forming the second welded portion>
Subsequently, in the present welding method, the inner surface side groove portion 83 of the joint portion 81 is welded with high heat input of one pass and one layer. Here, the groove depth d2 (see FIG. 2) of the inner surface side groove portion 83 is designed to be a dimension that the inner surface side groove portion 83 is filled with the weld metal by one welding operation. For this reason, in this welding method, by performing a single welding operation, extra filling appears in the inner surface side groove portion 83 (the weld metal in the inner surface side groove portion 83 exceeds the surface of the steel plate 80). Moreover, a part of the first welded portion 91 is melted by the heat effect of the welding. In this way, a “second welded portion 92” composed of one layer of the weld metal and the portion affected by the heat caused by the welding is formed in the inner surface side groove portion 83 (FIG. 4 (c). )reference). The step of forming the second welded portion 92 includes, for example, appropriately rotating the steel plate 80 so that the inner surface side groove portion 83 is at the welding position, and then the L pole (leading electrode) and T of the inner surface side welding machine 10. It is good to carry out by the pole (following pole). However, the process of forming the second welded portion 92 may use only one of the L pole and the T pole, and is not limited to the tandem welding of the L pole and the T pole.

<The process of forming the remaining part of a 3rd weld part>
Subsequently, in the present welding method, the outer surface side groove portion 82 of the joint portion 81 is welded. This welding operation is performed in a plurality of passes until the outer surface side groove portion 82 has a surplus (until the weld metal in the outer surface side groove portion 82 exceeds the surface of the steel plate 80). As a result, a “third welded portion 93” made of a plurality of layers of weld metal is formed in the outer surface side groove portion 82 (see FIG. 4D). The step of forming the remaining portion of the third welded portion 93 includes, for example, appropriately rotating the steel plate 80 so that the outer surface side groove portion 82 is at the welding position, and then the L pole (preceding) of the outer surface side welding machine 10. It is good to carry out on the welding conditions similar to the process of forming a part of the 3rd welding part 93 using a pole) and a T pole (following pole). However, the process of forming the remaining part of the 3rd welding part 93 may use only any one of a L pole and a T pole, and is not limited to the tandem welding of a L pole and a T pole.

  A welding example in the welding method according to Example 1 is shown in FIG. 6A. The content of the symbol column is information for identifying the welding method. In FIG. 6A, “T1”, “T2”... “T6” are shown. The welding method according to the first embodiment corresponds to “T1” to “T5”. The content of the groove shape column is information for identifying the shape of the groove formed in the joint portion 81. In FIG. 6A, “G1” to “G3” are shown. The groove shapes G1 to G3 correspond to FIGS. 7 (a) to 7 (c). The contents of the pass field are information for identifying the welding operation. The content of the side field is information for identifying a groove to be welded. In FIG. 6A, “outer surface” and “inner surface” are shown.

  The contents of the welding condition column are information indicating conditions for performing welding corresponding to the pass column. The welding condition column includes an L pole current column, an L pole voltage column, a T pole current column, a T pole voltage column, a speed column, and a heat input column. The contents of the L pole current column indicate the current of the leading electrode. The contents of the L pole voltage column indicate the voltage of the leading electrode. The contents of the T pole current column indicate the current of the trailing electrode. The contents of the T pole voltage column indicate the voltage of the trailing electrode. The content of the speed column indicates the welding speed. The heat input indicates the amount of heat given to the weld. The arrangement of the L and T poles is shown in FIG. Here, in the welding example shown in FIG. 6A, “SACG1” defined in “JIS Z 3352” is used as the flux. Further, “YS-S6” defined in “JIS Z 3351” was used as a wire.

The content of the hot crack column is information indicating whether or not a hot crack has occurred in the weld metal.
The content of the cold crack column is information indicating whether or not a cold crack has occurred in the weld metal.
The content of the burnout column is information indicating whether or not a burnout has occurred.
The content of the unmelted column is information indicating whether or not unmelted has occurred.
The confirmation of hot cracking and cold cracking was carried out in accordance with the ultrasonic flaw detection test method for steel welds specified in “JIS Z 3060”. Undissolved residue was judged by visual observation of a cross-sectional macrostructure test piece.

  In the symbol “T1”, the welding methods “1” to “2” of the welding method indicate the welding operation in the step of forming the first welded portion 91, and the pass “3” in the step of forming a part of the third welded portion 93. The welding operation is shown, the path “4” shows the welding operation in the step of forming the second welded portion 92, and the paths “5” to “12” show the welding operation in the step of forming the remaining third welded portion 93. . As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  Also, the welding method passes “1” to “2” in the symbol “T2” indicate the welding operation in the process of forming the first welded portion 91, and the pass “3” forms part of the third welded portion 93. The welding operation in the process is shown, the path “4” shows the welding operation in the process of forming the second welded portion 92, and the paths “5” to “14” show the welding operation in the process of forming the remaining third welded portion 93. Indicates. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  Also, the welding method passes “1” to “2” in the symbol “T3” indicate welding operations in the process of forming the first welded portion 91, and the pass “3” forms part of the third welded portion 93. The welding operation in the process is shown, the path “4” shows the welding operation in the process of forming the second welded part 92, and the paths “5” to “10” show the welding operation in the process of forming the remaining third welded part 93. Indicates. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  Further, the welding method passes “1” to “2” in the symbol “T4” indicate welding operations in the process of forming the first welded portion 91, and the passes “3” to “6” are ones of the third welded portion 93. Shows the welding operation in the step of forming the portion, the path “7” shows the welding operation in the step of forming the second welded portion 92, and the passes “8” to “12” form the remaining third welded portion 93. The welding operation in a process is shown. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  In addition, the welding method pass “1” at the symbol “T5” indicates a welding operation in the step of forming the first welded portion 91, and the path “2” is a welding operation in the step of forming a part of the third welded portion 93. The path “3” indicates the welding operation in the process of forming the second welded portion 92, and the paths “4” to “9” indicate the welding operation in the process of forming the remaining third welded portion 93. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  In the following, referring to FIG. 5 (see FIGS. 1 to 3 as appropriate), “Formation of the first welding part 91 → Formation of the third welding part 93 → Formation of the second welding part 92” according to the second embodiment. The welding method in order will be described.

<Step of forming the first welded portion>
First, in this welding method, the outer surface side groove portion 82 of the joint portion 81 is welded with a low heat input of one pass and one layer. As a result, a “first welded portion 91” made of one layer of weld metal is formed in the outer surface side groove portion 82 (see FIG. 5A). The process of forming the 1st welding part 91 is good to carry out with the L pole (leading pole) of the welding machine 10 of the outer surface side, for example. However, the process of forming the 1st welding part 91 may use a T pole (following pole), and is not limited to a L pole.

<Step of forming the third welded portion>
Subsequently, the present welding method changes the welding conditions as compared with the step of forming the first welded portion, and forms the third welded portion 93 on the upper portion of the first welded portion 93 of the outer surface side groove portion 82. This welding operation is performed in a plurality of passes until the outer surface side groove portion 82 has a surplus (until the weld metal in the outer surface side groove portion 82 exceeds the surface of the steel plate 80). As a result, a “third welded portion 93” made of a plurality of layers of weld metal is formed in the outer surface side groove portion 82 (see FIG. 5B). The step of forming the third welded portion 93 may be performed by, for example, the L pole (leading pole) and the T pole (following pole) of the welding machine 10 on the outer surface side. However, the process of forming the third welded portion 93 may use only one of the L pole and the T pole, and is not limited to the tandem welding of the L pole and the T pole.

<Step of forming the second welded portion>
Subsequently, in the present welding method, the inner surface side groove portion 83 of the joint portion 81 is welded with high heat input of one pass and one layer. Here, the groove depth d2 (see FIG. 2) of the inner surface side groove portion 83 is designed to be a dimension that the inner surface side groove portion 83 is filled with the weld metal by one welding operation. For this reason, in this welding method, by performing a single welding operation, extra filling appears in the inner surface side groove portion 83 (the weld metal in the inner surface side groove portion 83 exceeds the surface of the steel plate 80). Moreover, a part of the first welded portion 91 is melted by the heat effect of the welding. In this way, a “second welded portion 92” composed of one layer of the weld metal and the portion affected by the heat due to this welding is formed in the inner surface side groove portion 83 (FIG. 5C). )reference). The step of forming the second welded portion 92 includes, for example, appropriately rotating the steel plate 80 so that the inner surface side groove portion 83 is at the welding position, and then the L pole (leading electrode) and T of the inner surface side welding machine 10. It is good to carry out by the pole (following pole). However, the process of forming the second welded portion 92 may use only one of the L pole and the T pole, and is not limited to the tandem welding of the L pole and the T pole.

A welding example in the welding method according to Example 2 is shown in FIG. 6A (symbol “T6”).
Steps “1” to “2” of the welding method at symbol “T6” indicate welding operations in the step of forming the first welded portion 91, and steps of “3” to “11” form the third welded portion 93. The path “12” indicates the welding operation in the process of forming the second welded portion 92. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

  The path “1” of the welding method at symbol “T7” indicates a welding operation in the process of forming the first welded portion 91, and the paths “2” to “8” indicate the welding operation in the process of forming the third welded portion 93. A path “9” indicates a welding operation in the process of forming the second welded portion 92. As a result of actual welding by this welding method, none of hot cracking, cold cracking, melt-down, and unmelted residue occurred.

As described above, in the submerged arc welding method according to the present invention, the inner surface side groove portion 83 (second groove portion) has a surplus in the inner surface side groove portion 83 (the weld metal is the steel plate 80). High-heat-input single-layer welding is applied. Therefore, according to the submerged arc welding method according to the present invention, it is possible to increase the width of the second welded portion 92 and extremely reduce the occurrence of hot cracks in the weld metal.
Moreover, the submerged arc welding method according to the present invention performs multilayer welding on the outer surface side groove portion 82 (first groove portion). Therefore, according to the submerged arc welding method according to the present invention, the thickness of each layer of the third welded portion 93 can be adjusted, and the occurrence of cold cracks in the weld metal can be extremely reduced.

[Comparative example]
A comparative example of the welding method according to the embodiment of the present invention is shown in FIG. 6B.
The groove shape G4 of the welding method at symbol “T8” corresponds to FIG. In the welding method according to this comparative example, since the inner surface side groove portion 83 is not welded in one pass and one layer unlike the main welding method, hot cracking occurs. The welding method in symbols “T9” to “T12” is the same as the welding method in groove shape G1 in symbol “T1” in Example 1 (see FIG. 6A). The welding method according to these comparative examples is a reference when setting the welding conditions of the present welding method.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can implement in the range which does not change the meaning. The modification of embodiment is shown below.

  In the embodiment, the steel plate 80 is assumed to be cylindrical, but the shape of the steel plate 80 is not limited to the cylindrical shape. As shown in FIG. 9A, a steel plate 380 having a polygonal shape (a quadrangle is illustrated in FIG. 9A) in a side view may be used. Further, as shown in FIGS. 9B and 9C, steel plates 480 and 580 on which a plurality of joints 81 are formed may be bent into a cylindrical shape or a rectangular tube shape.

  Moreover, although the junction part 81 which concerns on embodiment assumed X groove shape, it is not limited to this. The shape of the joint portion 81 may be, for example, a Y groove shape, a V groove shape, an H groove shape, or the like. Further, in the embodiment, the joint portion 81 is formed such that the cross-sectional area in the outer surface side groove portion 82 is larger than the cross sectional area in the inner surface side groove portion 83, but conversely in the inner surface side groove portion 83. May be formed larger than the cross-sectional area in the outer surface side groove portion 82. In that case, the first welded portion 91 and the third welded portion 93 are formed on the inner surface side groove portion 83, and the second welded portion 92 is formed on the outer surface side groove portion 82.

DESCRIPTION OF SYMBOLS 1 Welding mechanism 10 Welding machine 12a Electrode 80,380,480,580 Steel plate 81 Joint part 82 Outer surface side groove part (1st groove part)
83 Inner surface side groove (second groove)
84 Route face 91 First welded portion 92 Second welded portion 93 Third welded portion

Claims (16)

A submerged arc welding method in which a steel plate formed into a tubular shape with a plate thickness exceeding 40 mm is welded on both sides,
The steel sheet has a groove-shaped joint portion in which the cross-sectional area in the first groove portion on one side is larger than the cross-sectional area in the second groove portion on the other surface side,
Applying low heat input welding in one pass and one layer to the first groove portion to form a first weld portion;
Until the weld metal in the second groove portion exceeds the surface of the steel plate, a step of applying a single layer of high heat input to the second groove portion to form a second weld portion;
Subjected to multilayer welding in the first groove portion, it viewed including the steps of forming a third welded portion,
The first merged part, the second welded part, and the third welded part are formed by submerged arc welding. In the first groove portion, a part of the third welded portion is formed before the second welded portion.
The submerged arc welding method according to claim 1. The joining portion is formed on the outer surface of the steel plate in which the first groove portion is formed into a tubular shape, and the second groove portion is formed on the inner surface of the steel plate.
The submerged arc welding method according to claim 1 or 2, wherein the submerged arc welding method is provided. The joint portion has a root face of 2 to 15 mm.
The submerged arc welding method according to any one of claims 1 to 3.   5. The submerged arc welding method according to claim 1, wherein the second welded portion is applied so as to melt into at least a part of the first welded portion. A submerged arc welding method in which a steel plate formed into a tubular shape with a plate thickness exceeding 40 mm is welded on both sides,
The steel sheet has a groove-shaped joint portion in which the cross-sectional area in the first groove portion on one side is larger than the cross-sectional area in the second groove portion on the other surface side,
Applying low heat input welding in one pass and one layer to the first groove portion to form a first weld portion;
Applying multilayer welding to the first groove portion to form a third weld portion;
Until said weld metal of the second groove portion is greater than the surface of the steel sheet, subjected to the second groove portion further welding high heat input, seen including a step of forming a second weld portion,
The first merged part, the second welded part, and the third welded part are formed by submerged arc welding. The joining portion is formed on the outer surface of the steel plate in which the first groove portion is formed into a tubular shape, and the second groove portion is formed on the inner surface of the steel plate.
The submerged arc welding method according to claim 6. The joint portion has a root face of 2 to 15 mm.
The submerged arc welding method according to claim 6 or 7, wherein:   The submerged arc welding method according to any one of claims 6 to 8, wherein the second welded portion is applied so as to melt into at least a part of the first welded portion. In the step of forming the first weld, the low heat input is 15 to 50 kJ / cm.
The submerged arc welding method according to any one of claims 1 to 9, wherein: In the step of forming the second weld, the high heat input is 55 to 175 kJ / cm.
The submerged arc welding method according to any one of claims 1 to 10, wherein: In the step of forming the third weld, the heat input is 30 to 175 kJ / cm.
The submerged arc welding method according to any one of claims 1 to 11, wherein the method is a submerged arc welding method.   A method for manufacturing a steel pipe, wherein the submerged arc welding method according to any one of claims 1 to 12 is used. A welded joint in which a groove-shaped joint is formed and the joint is welded on both sides using a submerged arc welding method,
The thickness of the steel sheet exceeds 40 mm,
The joining portion has a cross-sectional area in the first groove portion on one surface side larger than a cross-sectional area in the second groove portion on the other surface side, and the weld metal in the first groove portion forms a multilayer and the first portion. 2 The weld metal in the groove forms a single layer,
The weld metal in the first groove portion and the weld metal in the second groove portion are formed by submerged arc welding,
The weld joint in which the weld metal in a said 2nd groove part has exceeded the surface of the said steel plate.   The weld joint according to claim 14, wherein the weld metal in the second groove portion is dissolved in at least a part of the weld metal in the first groove portion.   A steel pipe comprising the welded joint according to claim 14 or 15.

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