JP2003136130A - Method for manufacturing inner and outer surface submerged arc welded steel pipe excellent in toughness characteristics of seam welded portion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe excellent in toughness characteristics of the welded portion of a high strength steel pipe, especially a tensile strength of 800 MPa or more. SOLUTION: The method for manufacturing the inner and outer surface submerged arc welded steel pipe excellent in toughness characteristics of the seam welded portion is characterized in that a steel plate is formed like a steel pipe and the seam portion is tack-welded, and in the steel pipe manufactured by submerged arc welding from the inner and outer surface, submerged arc welding is performed from the opposite surface against a tack welded portion and after a part of tack welded bead existing inside the groove in the opposite surface against the tack welding is cut and removed, submerged arc welding is performed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to improving the toughness of a seam welded portion of a high-strength line pipe manufactured by submerged arc welding of a seam welded portion widely used as a natural gas / crude oil transport line pipe from the inner and outer surfaces. And a manufacturing method.

[0002]

2. Description of the Related Art In recent years, pipelines have become increasingly important as long-distance transportation methods for natural gas and crude oil.
Large-diameter line pipes are required for long-distance main line pipes, but most of them are steel pipes manufactured by UO forming steel plates and then submerged arc welding on the inner and outer surfaces (hereinafter UOE-D).
SAW steel pipe) is used, but low temperature toughness is required according to the laying environment, and in steel plate manufacturing, products with excellent low temperature toughness by adjusting chemical composition, applying controlled rolling method, and applying accelerated cooling method. Is being developed.

On the other hand, the controlled rolling method and the accelerated cooling method cannot be applied in order to improve the toughness of the seam welded portion. Therefore, the chemical composition must be adjusted. Particularly, as the strength increases, it becomes difficult to improve the low temperature toughness. For such a problem, for example, in Japanese Patent Laid-Open No. 2001-113374, an ultra-high strength steel pipe excellent in low temperature toughness of a seam weld and a manufacturing method thereof are provided by optimizing a chemical composition of a steel plate and a chemical composition of a seam weld metal. Although disclosed, 800 MPa
The high toughness of the seam welded portion of the high-strength steel pipe as described above has not been stably ensured, and the need for improvement of the seam welding method itself is required for further high toughness.

[0004]

The present invention has a tensile strength of 530 MPa (API standard X65 or more), especially 80
Provided is a method for manufacturing an inner-outer surface submerged arc welded steel pipe having excellent toughness at a seam welded portion by improving a seam welding method for a high-strength steel pipe having a pressure of 0 MPa or more (equivalent to API standard X100 or more).

[0005]

The present invention has been made to solve the above problems, and its gist is as follows. (1) In a method of manufacturing a steel pipe, which comprises forming a steel plate into a steel tube, and temporarily welding the seam portion thereof, and then performing submerged arc welding from the inner surface and the outer surface, in the method of producing a steel pipe, after the temporary welding, from the side opposite to the side where the temporary welding is performed, submerge Perform arc welding, then cut and remove part of the tack weld bead in the groove on the tack welded side, and then perform submerged arc welding so that it overlaps with the weld metal part that was previously submerged arc welded. A method for manufacturing an inner and outer surface submerged arc welded steel pipe excellent in toughness of a seam welded portion. (2) In (1) above, 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 a submerged arc welded steel pipe having excellent toughness at a seam weld, which is characterized by performing submerged arc welding later. (3) The method for producing an inner / outer surface submerged arc welded steel pipe excellent in toughness of a seam welded portion according to (1) or (2) above, wherein the steel pipe is formed by a UO method. (4) In any of the above items (1) to (3), the steel pipe after welding has a tensile strength of 800 MPa or more, and a method for producing an inner / outer surface submerged arc welded steel pipe having excellent seam weld toughness. .

[0006]

DETAILED DESCRIPTION OF THE INVENTION The contents of the present invention will be described in detail below.

The present invention has a tensile strength of 530 MPa (AP
I standard X65 or more) 800 MPa or more (API
It is an invention relating to a method for producing an inner-outer surface submerged arc welded steel pipe excellent in seam weld toughness by improving a seam welding method for a high strength steel pipe of standard X100 or more).

Generally, in the production of UOE-DSAW steel pipe,
As shown in Fig. 1 (a), the seam welded part is formed into a steel pipe shape and then restrained to reduce the seam gap, and as shown in Fig. 1 (b), tack welding is performed from the outer surface to prevent the seam part from opening. After that, submerged arc welding is performed from the inner and outer surfaces as shown in FIGS. 1 (c) and 1 (d). At this time, the quality of the tack weld metal often changes and the quality is not always high. Therefore, it is necessary to re-melt the temporary weld metal by submerged arc welding so that the submerged arc weld metals on the inner and outer surfaces overlap each other. The low temperature toughness of the submerged arc weld metal and the heat affected zone of the weld becomes higher as the welding heat input is lower, that is, the faster the cooling rate is. This is because the faster the cooling rate is, the more the γ → α transformations occur at a low temperature all at once, so that a more homogeneous structure can be obtained. In particular, when the tensile strength exceeds 800 MPa, both the heat-affected zone of the welding and the weld metal have a bainite structure, but if the bainite structure is made into a lower bainite structure by increasing the cooling rate, the toughness is more significantly improved. However, in order to remelt the tack welding and fill the inside of the groove with the weld metal, heat input above a certain limit is required, and there is a limit to lowering the heat input.

As a result of a detailed study of the factors of the heat input reduction limit, the inventors of the present invention have made it possible to reduce the cross-sectional area of re-melted tack welding and to reduce the groove cross-sectional area (space portion where there is no material). It was found that the heat input can be reduced by reducing the fluctuation.

However, reducing the tack weld metal itself makes it difficult to secure the strength required for tack welding, and is limited in preventing meltdown of the first submerged arc welded portion before tack welding. It turns out that there is. The present inventor, as a result of diligent studies to solve this technical deadlock, found a method of cutting and removing a part of tack welding.

Further, even if the groove is accurately cut, the groove cross-sectional area before welding varies in the longitudinal direction due to fluctuations in the butt angle when the ends of the steel plates are butted against each other after forming the steel pipe. Therefore, it is necessary to select the welding heat input amount according to the maximum groove cross-sectional area, but the obstacle of low heat input must be solved. Therefore, if the groove surface is cut and removed at the same time as cutting and removing the tack, or after that, welding can be performed under the limit condition because the groove shape is constant.

The ratio of cutting and removing tack weld metal is
The lower limit is not specified because it is effective even if a small amount is cut and removed, but the upper limit is determined by this because cutting and removing even the initial submerged arc welding part is completely out of purpose.

Any method may be used for cutting and removing, and mechanical cutting is generally preferable from the viewpoint of accuracy.

[0014]

EXAMPLES Examples of the present invention and their effects will be specifically described below.

Tensile strength is 900 MPa and plate thickness is 16 m
As shown in FIG. 2, the end portion of the thick steel plate of m was groove-processed, and this was molded into a steel pipe having an outer diameter of 36 inches by the UO method, and
As shown in (a), the butt portion was tack-welded by gas metal arc welding from the outer surface, and then submerged arc welding was performed from the inner surface. After that, as shown in FIGS. 3B to 3D, after cutting the tack welding portion or cutting the tack welding portion and the groove portion, the outer surface was subjected to submerged arc welding.
Note that FIG. 3B shows the head welding portion of the tack welded portion removed, and the cutting amount corresponds to approximately 50% of the cross-sectional area of the tack welded portion existing above the groove surface. . Figure 3
(C) is a cut of the entire tack weld portion existing above the groove surface, and FIG. 3 (d) is a cut of the tack weld portion and a part of the groove portion around the tack weld portion. Is. The results are shown in Table 1.

[0016]

[Table 1]

In Table 1, it is a necessary condition that the submerged arcs on the inner and outer surfaces overlap, that is, the tack welding is completely melted by the submerged arc welding. The "-" sign indicates that the submerged weld metals on the inner and outer surfaces are separated, and the "+" sign indicates that they overlap. Considering industrial variations, it is considered necessary to have an overlap of about 2 mm or more.

The method of the present invention enables welding with a smaller heat input as compared with the conventional method of leaving the temporary attachment as it is. Further, the weld zone toughness (melting line (FL) +1 mm position and Charpy value in weld metal) is also good.

[0019]

According to the present invention, the toughness of the welded portion of the high strength line pipe can be remarkably improved as compared with the conventional method.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a method for manufacturing a UOE-DSAW steel pipe.

FIG. 2 is a view showing a groove processing of an end portion of a UOE steel pipe.

FIG. 3 is a view showing a shape before outer surface submerged arc welding according to the present invention, in which (a) to (c) show cutting and removal of a tack weld portion, and (d) shows a tack weld portion and a groove portion. Cutting
The figure which shows removal.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 37/08 B23K 37/08 E (72) Inventor Shigeru Ohkita 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares Company Technology Development Headquarters (72) Inventor Koichi Shinada 20-1 Shintomi Steel, Futtsu City, Chiba Prefecture Nippon Steel Corporation Stock (72) Inventor Yu Morimoto 20-1 Shintomi Futtsu City, Chiba Prefecture Nippon Steel Stock Company Technology Development Division (72) Inventor Tatsuya Yoshida 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Stock company Kimitsu Steel Company (72) Inventor Hideki Miyazaki 1 Kimitsu, Chiba Shin Nippon Steel Co., Ltd. Kimitsu Works F-term (Ref) 4E001 AA04 BB05 CA02 CC03 DG02 EA02 4E028 CB04 CB06 4E081 AA01 BA19 BB04 CA05 FA03

Claims (4)

[Claims] 1. A method of manufacturing a steel pipe, comprising forming a steel plate into a steel tube, and temporarily welding the seam portion thereof, and then performing submerged arc welding from the inner surface and the outer surface thereof. After the temporary welding, the side opposite to the temporarily welded side. After performing submerged arc welding from the above, after cutting and removing a part of the tack weld bead existing in the groove on the tack welded side, the submerge arc so that it overlaps with the weld metal part that was previously submerged arc welded. A method for manufacturing an inner-outer surface submerged arc welded steel pipe excellent in toughness of a seam weld, which is characterized by welding. 2. The method 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 so that the groove shape in the longitudinal direction of the steel pipe is made uniform. A method for producing a submerged arc welded steel pipe having excellent toughness at a seam welded portion, which is characterized by performing submerged arc welding after the welding. 3. The method for producing a submerged arc welded steel pipe having an inner and outer surface excellent in toughness of a seam welded portion according to claim 1, wherein the steel pipe is formed by a UO method. 4. The method for producing an inner / outer surface submerged arc welded steel pipe excellent in seam weld zone toughness according to any one of claims 1 to 3, wherein the steel pipe after welding has a tensile strength of 800 MPa or more. .