JPH067994B2 - Welded pipe manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention effectively prevents generation of a penetrator in a method of manufacturing a welded pipe such as an electric resistance welded steel pipe using a welding technique such as high frequency welding. It proposes a method of manufacturing a welded pipe for improving the welding quality.

[Prior art]

Generally, in a method of manufacturing an electric resistance welded steel pipe, a strip steel is continuously fed to a forming roll group including a plurality of breakdown rolls, side rolls, fin pass rolls, etc., and is first formed into a U-shape, and thereafter, is substantially formed. It is bent into a circular open pipe, and the open pipe is fed to a welding machine.After that, a high frequency current is passed through the end face on the opposite side by an induction coil system or a therma tool system and heated, and then by a squeeze roll. An electric resistance welded steel pipe is manufactured by pressure welding.

This method has a great advantage that it has higher efficiency than other pipe manufacturing methods, and can realize cost reduction of oil well pipes, steel pipes for line pipes, steel pipes for boilers, steel pipes for machine structures, and the like.

However, when the opposite end surface of the open pipe is heated, the high melting point oxides (Mn, Si, Cr, etc.) among the oxides produced by the oxygen in the atmosphere oxidizing the alloy components in the material There is a case where a welding defect called a penetrator occurs, which is not discharged and remains inside the weld. This penetrator significantly deteriorates the mechanical properties confirmed by pipe expansion, flatness, shearpy tests, etc., and reduces the reliability of the electric resistance welded steel pipe, which is one of the factors that limit its use.

Therefore, various methods for preventing the generation of the penetrator have been developed, the main ones of which are a method of stabilizing the welding phenomenon and a method of shielding the periphery of the heating portion with nitrogen gas or the like. The former method pays attention to the fact that a penetrator is apt to be generated when the welding heat input is excessive, and controls the penetrator so as to always obtain an appropriate heat input with respect to variations in plate thickness, V shape, power supply voltage and the like. It is a method to prevent the occurrence,
Even if it is possible to control so as to obtain an appropriate heat input, as long as the penetrator is caused by the oxidation phenomenon of alloy components such as Mn, Si, and Cr in the material, the oxidation phenomenon must be fundamentally prevented. It is impossible to completely eliminate the generation of penetrators, and in reality, only a small amount of penetrator remains by controlling the welding heat input. The latter method is a method of shielding the surroundings of the heating part from the atmosphere with nitrogen gas or the like to prevent oxidation, and it is already known that the generation of penetrators is considerably reduced, but induction heating mounted around the heating part is already known. Since the structure of the coil or the contact power supply is complicated, it is difficult to completely shield the periphery of the heating part from the atmosphere, and the oxidation of alloy components such as Mn, Si and Cr in the material cannot be prevented. The generation of minute penetrators is unavoidable, and the device becomes large-scaled, and its maintenance is troublesome.

〔Purpose〕

The present invention has been made in view of such circumstances, and when producing a welded pipe such as an electric resistance welded steel pipe, substantially completely prevents the oxidation of the material around the heating portion to significantly reduce the generation of the micro penetrator. , To improve the quality of welded pipes.

[Structure of Invention]

In the method of manufacturing a welded pipe according to the present invention, the end portions of the metal strips are bent so as to face each other to form an open pipe, and current is applied to the opposite end portions of the open pipe while heating and pressure is applied from both sides. In the method of manufacturing a welded pipe by press-contacting with, the vicinity of the heating part is sealed with a reducing flame for the purpose of reducing the oxygen partial pressure around the heating part.

〔Example〕

Hereinafter, the method of the present invention will be described in detail with reference to the drawings showing its implementation. FIG. 1 is a schematic plan view showing an electric resistance welded steel pipe production line using the method of the present invention, and FIG. 2 is a vertical cross-sectional view schematically showing an enlarged vicinity of a heating part, which is a main part thereof,
FIG. 3 is a plan view of an open pipe immediately below the vicinity of each heating part and a gas burner arranged in a welded pipe. A strip steel ST whose both edges are finished with a surface suitable for welding by an edging device (not shown)
Is fed in the direction of the hollow arrow and is broken down roll 12
a, 12b and 13a, 13b and side rolls 8l, 8r, 9l, 9r
And 10l and 10r form a U-shape. The upper and lower fin-pass rolls 6 and 7 (only the upper roll is shown in the figure) and the final side rolls 11l and 11r between the fin-pass rolls 6 and 7 are formed into a substantially circular shape. It is formed into an open pipe OP, and both edges facing each other are accurately guided by the fin plate of the upper fin pass roll and fed to the induction heating coil 4. A gas burner for burning the gaseous fuel 2, for example, LP gas, inside the open pipe OP and the welded pipe P formed by welding the open pipe OP over a region from the induction heating coil 4 to a position slightly closer to a welding point A described later. 1 is provided.
This gas burner 1 extends from one end of a tubular U-shape in a plan view toward the other end, and is bent at the intermediate position between the one end and the other end to the side opposite to the U-shaped curved portion, and the other end. Is closed. The gas burner 1 is provided such that the straight portion of the U-shaped portion is in the axial direction of the welded pipe P, and both of the straight portions are directed toward both edges of the open pipe OP and the welding point A. Both edges of OP, welding point A
It has many holes on the side. Regarding the holes that are substantially along the axial direction of the welded pipe P, the flames are inclined so that the flame direction is directed to both edges of the open pipe OP and the welding point A.

The feed pipe 1a, one end of which is connected to the gas burner 1 through a burner mounting jig 1b, has a valve (not shown) attached at an appropriate position, and a gas fuel 2 flowing through the feed pipe 1a
Is adjustable, and the other end of the feed pipe 1a is connected to a gas fuel source (not shown). However, by adjusting the flow rate of the gaseous fuel 2 fed from the gaseous fuel source by the valve as described above, the gaseous fuel 2 discharged from the gas burner 1 is heated by the induction heating coil 4 and is heated to a high temperature as described later. It burns through both edges of the open pipe OP, and the reducing flame portion inside the flame covers the open pipe OP and the vicinity of the welding point A.

Thus, the open pipe OP is fed to the induction heating coil 4 to which the high frequency current is supplied from the high frequency power source 3 while the oxygen partial pressure of the atmosphere is reduced by covering the reducing portion of the combustion flame of the gaseous fuel 2. Then, an induced current is generated in the open pipe OP. This induced current causes the opposite end face 14
Open pipe OP where l and 14r are heated is a squeeze roll
It is pressed from both sides by 5l and 5r and welded at a welding point A to form a welded pipe P.

When the electric resistance welded steel pipe is manufactured by the above method, the opposite side end faces 14l, 14r of the open pipe OP are melted by the above heating and easily react with oxygen in the atmosphere, but the gas fuel 2 released from the gas burner 1 The area around the heating portion is shielded from the atmosphere by the reducing flame portion of the burned flame, and the oxygen partial pressure around the heating portion is significantly reduced. Furthermore, since the reducing flame portion of the flame is strongly reducing, the oxide layer formed on the tube surface is reduced. Therefore, the oxidation of alloy components such as Mn, Si, and Cr in the material is prevented, and the occurrence of penetrators can be effectively prevented,
Conventionally, the number of generated penetrators was 8 / m.

In the above description, a gas burner having a U-shaped gas fuel discharge portion is used, but the present invention is not limited to this and may be any shape as long as it can seal both edges of the open pipe OP and the periphery of the welding point A. Needless to say, it may be annular or bifurcated or trifurcated.

〔effect〕

As described above in detail, in the case of the method of the present invention, when the welded pipe is manufactured, the vicinity of the heating portion can be made into a reducing atmosphere in the reducing flame portion of the combustion flame of the gaseous fuel, and the oxygen partial pressure around the heating portion can be reduced. Oxidation of the alloy components in the raw material can be prevented because the amount is significantly reduced, the occurrence of penetrators can be effectively prevented, and the quality of welded pipes such as ERW steel pipe can be improved. .

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an electric resistance welded steel pipe production line using the method of the present invention, FIG. 2 is an enlarged vertical sectional view schematically showing the vicinity of a heating part, which is a main part thereof, and FIG. 3 is a gas burner. FIG. 1 ... Gas burner 2 ... Gas fuel OP ... Open pipe
P ... Welded pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Kitamura 1850 Minato Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Works (56) References Japanese Patent Publication No. 51-33512 (JP, B1)

Claims (1)

[Claims] 1. A metal strip is bent so as to be opposed to each other at side end faces thereof to form an open pipe, and the opposite side ends of the open pipe are heated by applying a current and pressure is applied from both sides for welding. A method for producing a welded pipe, which comprises sealing the vicinity of a heating section with a reducing flame.