JP3702216B2 - Manufacturing method for inner and outer surface submerged arc welded steel pipes with excellent seam weld toughness - Google Patents

Description

【００１７】
表１において、内外面のサブマージアークが重なる、すなわち仮付け溶接がサブマージアーク溶接で完全溶融することが必要条件である。“−”符号は内外面のサブマージ溶接金属が離れていることを示しており、“＋”符号は重なっていることを示している。工業的ばらつきを考慮すると２ｍｍ程度以上の重なりが必要であると考えられる。
【００１８】
本発明法では従来の仮付けをそのまま残す方法と比較してより小入熱で溶接が可能である。また溶接部靭性（溶融線（ＦＬ）＋１ｍｍ位置および溶接金属でのシャルピー値）も良好である。
【００１９】
【発明の効果】
本発明によれば、高強度ラインパイプの溶接部靭性を従来法に比べて格段に向上させることが可能となる。
【図面の簡単な説明】
【図１】ＵＯＥ−ＤＳＡＷ鋼管の製造方法の概略を示す図。
【図２】ＵＯＥ鋼管端部の開先加工を示す図。
【図３】本発明による外面サブマージアーク溶接する前の形状を示す図で、（ａ）〜（ｃ）は仮付け溶接部の切削、除去を、（ｄ）は仮付け溶接部及び開先部の切削・除去を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method for improving the toughness of a seam welded portion of a high-strength linepipe produced by submerged arc welding of a seam welded portion widely used as a natural gas / crude oil transportation linepipe from the inner and outer surfaces. .
[0002]
[Prior art]
In recent years, pipelines have become increasingly important as a long-distance transportation method for natural gas and crude oil. Large-diameter line pipes are required for long-distance transport main line pipes, but most of them use steel pipes (hereinafter referred to as UOE-DSAW steel pipes) manufactured by UO molding of steel plates and then by submerged arc welding on the inner and outer surfaces. However, low temperature toughness corresponding to the laying environment is required, and in steel plate production, products having excellent low temperature toughness have been developed by adjusting chemical components, applying a controlled rolling method, and applying an accelerated cooling method.
[0003]
On the other hand, in order to improve the toughness of the seam welded portion, the application of the controlled rolling method and the accelerated cooling method cannot be applied, and therefore, it must be dealt with by adjusting the chemical composition. In particular, as the strength increases, it becomes difficult to improve the low temperature toughness. For example, Japanese Patent Application Laid-Open No. 2001-113374 discloses an ultra-high-strength steel pipe excellent in low-temperature toughness of a seam welded portion and a method for producing the same by optimizing a steel plate chemical component and a seam weld metal chemical component. Although disclosed, the high toughness of seam welds of high-strength steel pipes of 800 MPa or more has not been stably secured, and there is a need for improvement of the seam welding method itself for further toughness. It has been.
[0004]
[Problems to be solved by the invention]
The present invention provides an inner / outer surface submerged arc with excellent seam weld toughness by improving the seam welding method for high strength steel pipes having a tensile strength of 530 MPa (API standard X65 or higher), particularly 800 MPa or higher (API standard X100 or higher). A method for manufacturing a welded steel pipe is provided.
[0005]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the gist thereof is as follows. (1) In a steel pipe manufacturing method in which a steel plate is formed into a steel tube and the seam portion is tack welded and then submerged arc welded from the inner surface and the outer surface , the tensile strength of the steel pipe after welding is 800 MPa or more, After welding, submerged arc welding is performed from the side opposite to the tack welded side, and then a part of the tack weld bead in the groove on the tack welded side is cut and removed, and then the submerged arc first. Submerged arc welding is performed so as to overlap the welded metal part welded, and the weld heat affected zone and the weld metal structure are the lower bainite structure. . (2) In the above (1), a part of the tack weld bead is cut and removed, and the groove on the side where the tack is present is adjusted and cut to make the groove shape uniform in the longitudinal direction of the steel pipe. A method for manufacturing an inner / outer surface submerged arc welded steel pipe excellent in seam weld toughness, characterized in that submerged arc welding is performed later.
(3) A method for producing an inner / outer surface submerged arc welded steel pipe excellent in seam welded portion toughness, characterized in that, in the above (1) or (2), the method of forming the steel pipe is a UO method .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the contents of the present invention will be described in detail.
[0007]
INDUSTRIAL APPLICABILITY The present invention is suitable for high-strength steel pipes having a tensile strength of 530 MPa (API standard X65 or higher), particularly 800 MPa or higher (API standard X100 or higher), and improved the seam welding method to improve the toughness of the seam welded portion. It is invention regarding the method of manufacturing a steel pipe.
[0008]
In general, in the manufacture of UOE-DSAW steel pipes, the seam welded part is formed into a steel pipe shape as shown in FIG. 1 (a) and then constrained to reduce the seam gap, and as shown in FIG. 1 (b), temporary welding is performed from the outer surface. Then, the seam portion is prevented from opening, and then submerged arc welding is performed from the inner and outer surfaces as shown in FIGS. At this time, the quality of the tack weld metal often fluctuates, and the quality is not necessarily high. Therefore, it is necessary to remelt by submerged arc welding so that the inner and outer surface submerged arc weld metals overlap. The low-temperature toughness of the submerged arc weld metal and the weld heat-affected zone is higher as the welding heat input is lower, that is, the cooling rate is higher. This is because the faster the cooling rate, the more the γ → α transformation is performed at a low temperature, so that a homogeneous structure can be obtained. In particular, when the tensile strength exceeds 800 MPa, both the weld heat-affected zone and the weld metal have a bainite structure, but when the bainite structure is changed to a lower bainite structure by increasing the cooling speed, the improvement in toughness becomes more remarkable. However, in order to re-melt tack welding and fill the groove with weld metal, heat input beyond a certain limit is required, and there is a limit to lowering heat input.
[0009]
As a result of examining the factors of the heat input reduction limit in detail, the inventors of the present invention reduced the cross-sectional area of the tack weld to be remelted and reduced the fluctuation of the groove cross-sectional area (space portion without material). I learned that heat input can be reduced.
[0010]
However, reducing the size of the tack weld metal itself makes it difficult to secure the strength of the tack, and there are limits to preventing the first submerged arc weld from being melted before tack welding. I understand. As a result of intensive studies to solve this technical deadlock, the present inventor has found a method of cutting and removing a part of the tack welding.
[0011]
Furthermore, even if the groove is cut accurately, the groove cross-sectional area before welding varies in the longitudinal direction due to a variation in the butting angle when the steel plate ends are butted after the steel pipe is formed. Therefore, it is necessary to select the amount of heat input for welding in accordance with the maximum groove cross-sectional area, but the problem of low heat input must be solved. Therefore, if the groove surface is cut and removed at the same time as or after the tacking is cut and removed, the groove shape is constant, so that welding under a limit condition becomes possible.
[0012]
The ratio of cutting and removing the tack weld metal is effective if it is cut and removed even with a small amount, so the lower limit is not particularly specified, but cutting and removing to the initial submerged arc welding part is completely out of purpose. Therefore, the upper limit is determined by this.
[0013]
Further, any method may be used for cutting and removing, and mechanical cutting is generally preferable from the viewpoint of accuracy.
[0014]
【Example】
Examples of the present invention and effects thereof will be specifically described below.
[0015]
The end of a thick steel plate having a tensile strength of 900 MPa and a plate thickness of 16 mm is grooved as shown in FIG. 2, and this is formed into a steel pipe having an outer diameter of 36 inches by the UO method, as shown in FIG. As shown, the butt portion was tack welded from the outer surface by gas metal arc welding, and then submerged arc welded from the inner surface. Thereafter, as shown in FIGS. 3B to 3D, after cutting the tack welded portion or cutting the tack welded portion and the groove portion, the outer surface was subjected to submerged arc welding. In FIG. 3B, the head portion of the tack welded portion is deleted, and the amount of cutting corresponds to approximately 50% of the cross-sectional area of the tack welded portion existing above the groove surface. . FIG. 3 (c) is a cut of the entire tack welded portion existing above the groove surface, and FIG. 3 (d) is an adjustment cut of a part of the peripheral groove portion along with the tack welded portion. It is a thing. The results are shown in Table 1.
[0016]
[Table 1]

[0017]
In Table 1, it is a necessary condition that the submerged arcs on the inner and outer surfaces overlap, that is, tack welding is completely melted by submerged arc welding. The “−” sign indicates that the inner and outer surface submerged weld metals are separated, and the “+” sign indicates that they are overlapping. Considering industrial variation, it is considered that an overlap of about 2 mm or more is necessary.
[0018]
In the method of the present invention, welding can be performed with a smaller heat input as compared with the conventional method of leaving the tacking as it is. Moreover, the weld zone toughness (melting line (FL) +1 mm position and Charpy value in the weld metal) is also good.
[0019]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to improve the weld part toughness of a high intensity | strength line pipe markedly compared with the conventional method.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a method for producing a UOE-DSAW steel pipe.
FIG. 2 is a view showing groove processing of an end portion of a UOE steel pipe.
FIGS. 3A and 3B are views showing shapes before external submerged arc welding according to the present invention, wherein FIGS. 3A to 3C show cutting and removal of a tack welded portion, and FIG. 3D is a tack welded portion and a groove portion; FIG.

Claims (3)

In the steel pipe manufacturing method in which the steel sheet is formed into a steel tube, and the seam portion is tack welded, and the submerged arc welding is performed from the inner surface and the outer surface , the tensile strength of the steel pipe after welding is 800 MPa or more, and after the tack welding, Submerged arc welding is performed from the side opposite to the tack welded side, and then a part of the tack weld bead in the groove on the tack welded side is cut and removed, and then the first submerged arc welding is performed. A method for producing an inner / outer surface submerged arc welded steel pipe having excellent seam weld toughness, characterized in that submerged arc welding is performed so as to overlap with a metal part, and the structure of the weld heat affected zone and the weld metal is a lower bainite structure .   The submerged arc according to claim 1, wherein a part of the tack weld bead is cut and removed, and the groove on the side where the tack is present is adjusted and cut to make the groove shape uniform in the longitudinal direction of the steel pipe. A method for producing an inner / outer surface submerged arc welded steel pipe excellent in seam weld toughness, characterized by welding.   3. The method for manufacturing an inner / outer surface submerged arc welded steel pipe excellent in seam welded portion toughness according to claim 1, wherein the steel pipe is formed by a UO method.

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