JP2525695B2 - Welding method of thick-wall ERW steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing thick-walled electric resistance welded steel pipe.

[0002]

As is well known, in the manufacture of ERW steel pipe,
The edge (end) of the pipe material (steel strip) to be welded is heated by electric resistance or induction, and then pressure welding (welding) is performed by a squeeze roll. The welded portion of the electric resistance welded steel pipe manufactured in this manner often has defects such as cold welding defects due to insufficient melting and welding defects due to residual oxide, which also deteriorates toughness and workability. In electric resistance welding, "Steelmaking Research" No. As announced in 277 "Experiment on ERW Pipe Welding Mechanism", it is effective to control the welding phenomenon to prevent the occurrence of welding defects, and there are appropriate welding conditions of high speed and large heat input. It has been clarified that welding defects are unlikely to occur even with slight variations in welding conditions. These are disclosed in JP-B-54-33784 and JP-B-54-40454.
As "monitoring and controlling method of high frequency electric resistance welding phenomenon" and "monitoring and controlling device of high frequency electric resistance welding phenomenon",
It is disclosed. In the welding of thick-walled electric resistance welded steel pipes, in order to satisfy the above-mentioned appropriate welding conditions of high speed and large heat input, high welding electric power is required, and therefore it is necessary to perform welding with a welding machine with high output. For example, in welding a thick-walled electric resistance welded steel pipe having a wall thickness of 8 mm, a welding speed of 20 m / min or more is required to obtain proper welding conditions in which welding defects are less likely to occur, and welding is performed in order to perform welding under proper welding conditions. Heat input 1000
kW or more is required. That is, in the welding of a thick-walled electric resistance welded steel pipe having a wall thickness of 8 mm, in order to prevent the occurrence of welding defects, it is necessary to perform welding with a welding machine having an output of 1000 kW or more. On the other hand, the high-frequency welder has a characteristic that the welding frequency is lowered when the output is increased due to its structure. The welding frequency of the welder having an output of 1000 kW or more is generally 2 when the manufacturing cost of the welder is taken into consideration.
It is less than 00 kHz. However, this output is 1000k
With a welding machine of W or more and a welding frequency of less than 200 kHz,
When welding thick ERW steel pipes with a wall thickness of 8 mm or more,
Welding speed 2 which is considered to be proper welding condition in the prior art
Even under welding conditions of 0 m / min or more and a welding heat input of 1000 kW or more, the welding phenomenon is not stable and welding defects frequently occur.
The inconvenience occurred that excellent weld quality could not be obtained.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been invented to solve the above-mentioned problems, and when welding a thick ERW steel pipe at a welding frequency of 200 kHz or more and a welding machine output of 1000 kW or more. Welding significantly reduces welding defects in thick-walled ERW steel pipes with a wall thickness of 8 mm or more,
At the same time, it is intended to improve the toughness and workability of the electric resistance welded portion and manufacture a thick-walled electric resistance welded steel pipe of excellent quality.

[0004]

The gist of the present invention is, when welding an electric resistance welded steel pipe, welding at a welding frequency of 200 kHz or more and a welding machine output of 1000 kW or more. Is the way. The present inventors
Based on the prediction that the disadvantages of the prior art in the thick-walled electric resistance welded steel pipe having a wall thickness of 8 mm or more described above are related to the welding frequency, the output is 1000 kW or more and the welding frequency is 2
A welding machine with a frequency of 00 kHz or higher was made as a prototype by disregarding the manufacturing cost of the welding machine, and the following research was conducted. Wall thickness 8mm
For the thick ERW steel pipes above, the welding frequency, welding speed,
The relationship between the welding phenomenon and the welding frequency was observed with a high-speed camera, observing a series of phenomena of heating → melting → pressurization that occurred on both edges between the power feeding position and the center of the squeeze roll when the welding heat input was changed. As a result of research, they found that there is a phenomenon that is completely different from the conventional wisdom. The present invention was made based on these findings, and the details will be described below.

[0005]

Function In the electric resistance welding, the high frequency current is generated by the skin effect and the proximity effect as shown in FIG.
Flow concentratedly at the corners 3, 4, 5, 6 of the welded steel pipe, and as a result, a drum-shaped heat effect mark remains on the welded portion of the electric resistance welded steel pipe as shown in FIG. This indicates that heating at the central portion of the wall thickness is delayed compared to the upper and lower surfaces. The delay in heating the upper and lower surfaces of the thickness center portion can be known by the difference between the thickness center and the upper and lower surfaces of the heat affected width. In FIG. 2, a is the heat-affected width of the upper surface, and b is the heat-affected width of the thickness center. Therefore, the heating delay with respect to the upper and lower surfaces of the wall thickness center can be expressed by the heating delay ratio (b / a). When the heating delay ratio (b / a) is 1.0, there is no heating delay, and the smaller the heating delay ratio (b / a) is, the more severe the heating delay is. It was found in this study that the heating delay at the center of the wall thickness becomes more severe as the wall thickness becomes thicker and the welding frequency becomes lower. This state is shown in FIG.
As shown in FIG. Further, it can be seen from FIGS. 3 and 4 that the heating delay at the center portion of the wall thickness becomes remarkable when the wall thickness is 8 mm or more and when the welding frequency is lower than 200 kHz. Furthermore, as a result of observing the welding phenomenon with a high-speed camera, it was confirmed that this heating delay at the center of the wall thickness makes the welding phenomenon non-uniform in the wall thickness direction and causes instability of the welding phenomenon. As a result of the above research, the wall thickness is 8m
It has been found that a welding frequency of 200 kHz or more is necessary in order to stabilize the welding phenomenon in the electric resistance welding having a thickness of m or more. In the electric resistance welding with a thickness of 8 mm or more, in order to stabilize the welding phenomenon and perform welding under proper welding conditions, it is necessary to weld at a welding frequency of 200 kHz or more and a welding machine output of 1000 kW or more. Is. Next, examples of the present invention are shown in Table 1.

[0006]

【Example】

[Table 1]

[0007]

EFFECTS OF THE INVENTION According to the present invention, it is very effective in preventing welding defects, and the excellent effect of improving the product yield and also improving the toughness of the welded portion is obtained, which is extremely large. Is.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a heating state of an edge portion of an electric resistance welded portion immediately before joining,

FIG. 2 is an explanatory view showing a heat affected state of an electric resistance welded portion,

FIG. 3 is a diagram showing the relationship between wall thickness and heating delay ratio (b / a),

FIG. 4 is a diagram showing a relationship between a welding frequency and a heating delay ratio (b / a).

[Explanation of symbols]

 1,2 Edges 3,4,5,6 Edges and corners a Upper surface heat affected width b Wall thickness center heat affected width

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Takashi Nakamura and two others “Modern Welding Technology Series 8 Resistance Welding” (SHO 55-1-23) P.P. 179, P.I. 185-P. 186

Claims (1)

(57) [Claims] 1. A method for welding a thick-walled electric resistance welded steel pipe, which comprises welding at a welding frequency of 200 kHz or higher and a welding machine output of 1000 kW or higher when welding the electric resistance welded steel pipe.