JPS6233032B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing welded pipes such as electric resistance welded steel pipes using welding techniques such as high frequency welding, which effectively prevents the generation of penetrators and improves weld quality. In general, in the method of manufacturing ERW steel pipes, a steel strip is continuously fed to a group of forming rolls consisting of a plurality of breakdown rolls, side rolls, fin pass rolls, etc., and is first formed into a U-shape, and then approximately It is bent into a circular open pipe, and then fed to a welding machine, where a high frequency current is passed through the opposing end face of the open pipe using an induction coil method or a thermal tool method to heat and melt that part.
An electric resistance welded steel pipe is manufactured by pressure welding with a squeeze roll. The great advantage of this method is that it is highly efficient compared to other pipe manufacturing methods, and it is possible to reduce the cost of oil country tubular goods, steel pipes for line pipes, steel pipes for boilers, steel pipes for machine structures, etc. However, when the opposing end face of the open pipe is heated and melted, the alloy components in the material are oxidized by oxygen in the atmosphere, resulting in oxides with high melting points (oxides of Mn, Si, Cr, etc.). may not be discharged from the weld and may remain inside the weld, resulting in a welding defect called a penetrator. This penetrator significantly deteriorates the mechanical properties confirmed by tube expansion, flattening, and shear py tests, and lowers the reliability of the ERW steel pipe, which is one of the reasons for limiting its uses. For this reason, methods for preventing the occurrence of penetrators have recently been actively researched, and the main methods include a method of stabilizing the welding phenomenon and a method of shielding the area around the heated part with nitrogen gas or the like. The former method focuses on the fact that penetrators are likely to occur when there is excessive welding heat input, and the method is controlled so that an appropriate heat input is always obtained despite changes in plate thickness, V shape, power supply voltage, etc. This is a method to prevent this from occurring, but even if the penetrator can be controlled to obtain an appropriate heat input, the
As long as it is caused by the oxidation phenomenon of alloy components such as Si and Cr, it is impossible to completely eliminate the occurrence of penetrators unless the oxidation phenomenon is fundamentally prevented. A tiny penetrator remains. The latter method is a method in which the area around the heating part is shielded from the atmosphere using nitrogen gas, etc. to prevent oxidation, and it is already known that the generation of penetrators is considerably reduced. Because the structure of the coil or contact feeder is complex, it is difficult to completely shield the area around the heating part from the atmosphere, and it is difficult to prevent the oxidation of alloy components such as Mn, Si, and Cr in the material. The generation of microscopic penetrators is unavoidable, and
There are disadvantages in that the device is large-scale and its maintenance is also cumbersome. In addition, in the production of clad pipes, a medium with a cooling function using latent heat of vaporization and an oxidation prevention function using a non-oxidizing atmospheric gas, specifically lower alcohols and amines, is ejected into the welded part to prevent oxidation and prevent oxidation of the clad material. A method is known (Japanese Patent Publication No. 52-22945) aimed at preventing the melting and outflow of flammable liquid, but in this method, the flammable liquid evaporates before it reaches the part to be shielded because it is sprayed onto the high-temperature heating area. Alternatively, as a result of combustion, there is a disadvantage that shielding from these vapors or combustion flames is insufficient. The present invention has been made in view of the above circumstances, and it is possible to substantially completely prevent material oxidation around the heating part when manufacturing welded pipes such as ERW steel pipes, to significantly reduce micropenetrators, and to improve welded pipes. The aim is to improve the quality of The method for manufacturing a welded pipe according to the present invention includes bending a metal strip so that its side end surfaces face each other to form an open pipe, heating the opposite end surfaces of the open pipe, and applying pressure from both sides. In the method of manufacturing welded pipes by pressure welding, carbon,
After applying the organic compound or organosilicon compound,
Characterized by welding. Hereinafter, the method of the present invention will be explained in detail based on the drawings showing examples thereof. FIG. 1 is a plan view schematically showing a main part of an electric resistance welded steel pipe manufacturing line using the method of the present invention, and FIG. 2 is a schematic longitudinal cross-sectional view taken along the line --- in FIG. The steel strip ST, whose both edges have been finished with a surface suitable for welding by an edging device (not shown), is fed in the direction of the white arrow to the breakdown roll 6.
1a, 61b and 62a, 62b and side rolls 51l, 51r, 52l, 52r and 53
It is formed into a U-shape by 1 and 53r. And fine pass rolls 41, 42 arranged vertically oppositely.
(Only the upper roll is shown in the figure) Furthermore, the final side rolls 54l and 54r between the fin pass rolls 41 and 42 form the open pipe OP into a substantially circular shape, and the upper fin pass roll OP is formed into a substantially circular shape. The opposing edges are accurately guided by the fin plates of the roll and fed to the induction heating coil 1. Glycerin to be applied to the opposite end surfaces 8l and 8r of the open pipe OP is stored above the open pipe OP located between the induction heating coil 1 and the last fine pass roll 42, and the glycerin is to be discharged. Opening 7 at the bottom
A container 71 provided with 1a is provided. The conduit 73 whose one end is connected to the opening 71a has a valve 72 attached at an appropriate position.
The amount of glycerin exuded from inside can be adjusted. The other end of the conduit 73 is divided into two openings 73l and 73r, and brushes 74l and 74r are attached to the tips of the openings 73l and 73r, and brushes 74l and 74r are attached to the tips of the openings 73l and 73r to remove the glycerin exuding from the container 71 to the opposite end surface 8l of the open pipe OP. , 8r. The open pipe OP whose side end face is coated with glycerin in this way is fed from the high frequency power supply 2 to the induction heating coil 1 to which a high frequency current of about 200 to 500 KHz is supplied, and the open pipe OP
An induced current is generated. The open pipe OP whose opposing end surfaces 8l and 8r are heated by this induced current is pressurized from both sides by the squeeze rolls 3l and 3r and welded at the welding point A to form the pipe P. When manufacturing electric resistance welded steel pipes by such a method, when the opposing end surfaces 8l and 8r of the open pipe OP are heated, the glycerin applied to the opposing end surfaces 8l and 8r has a melting point of 17°C and a boiling point of 17°C. is 290℃
Because the pressure is so low, it easily vaporizes, and its vapor pressure shields the area around the heating area from the atmosphere. Therefore, the oxidation of alloy components such as Mn, Si, and Cr in the material is prevented, and the generation of penetrators can be effectively prevented. In this example, glycerin was applied to the opposite end surfaces 8l and 8r of the open pipe OP because glycerin is in a liquid state at room temperature (20°C), so it is convenient to apply it using the method described above. It is. In addition, since the boiling point of glycerin is over 200℃, the vaporization is not completed in the early stages of heating, and the area around the heating area can be sufficiently shielded from the atmosphere.For this reason, it is recommended as a material to be applied. It is desirable that the boiling point is 200℃ or higher. In addition, the following carbon, organic compounds, or organosilicon compounds are the opposite end surface 8 of the open pipe OP.
As a substance to be applied to 1 and 8r, it can be expected to have the same penetrator prevention effect as glycerin. (1) Carbon polymers such as carbon and tar. (2) Acrylonitrile resin, acetyl cellulose, vinylidene chloride resin, vinyl chloride resin, nylon, nitrocellulose, polyethylene, polycarbonate, polystyrene, Teflon, polypropylene, methyl methacrylate resin, aniline/formaldehyde resin, epoxy resin, phenol resin, urea/formaldehyde Resins, phenol/formaldehyde resins, polyester resins, melamine/formaldehyde resins, hydrocarbons such as paraffin, xylene, nitro compounds such as nitrobenzene, glycerin, organic solvents such as acetone, alcohol, rubber, cellulose, etc. Organic compounds such as molecular substances. (3) Organosilicon compounds such as silicone resins. Some of these substances are not liquid at room temperature, and in such cases it is difficult to use the coating method described in the examples, but other suitable coating methods, such as melt spray coating, can be used. Penetrator generation can be prevented by welding the material after applying it. In addition, it is undesirable for these substances to contain oxygen elements, but if they contain hydrogen elements, even if water vapor is generated by reacting with oxygen in the atmosphere when it evaporates, the amount of water vapor generated is In addition, since non-oxidizing gas such as hydrogen gas is continuously generated, a non-oxidizing atmosphere can be maintained as a whole, and the effect of the method of the present invention will not be impaired due to the hydrogen element contained in the above substance. do not have. As shown in the embodiments, it is desirable to apply carbon, an organic compound, or an organosilicon compound between the induction heating coil 1 and the final fine pass roll 42. This is because if carbon, organic compound, or organosilicon compound is applied before the open pipe OP passes through the fin pass rolls 41 and 42, it will be peeled off by the fin plates of the fin pass rolls above, and the above-mentioned action will occur. This is because the effect of preventing penetrator generation is reduced. However, even if the pre-process, for example, carbon, organic compound, or organosilicon compound is applied to the end face of the metal strip while it is in a coiled state, and the metal strip is sent to the ERW steel pipe production line and welded, no effect is observed. It will be done. Note that the same applies even if a direct current type welding machine is used. Furthermore, it goes without saying that the method of the present invention may be used in combination with a method of shielding the periphery of the heating section with nitrogen gas or the like. Next, examples of the method of the present invention will be described. Chemical components are C: 0.14%, Si: 0.30%, Mn: 0.50%,
Cr: 1.0% test material plate thickness: 3.2mm, outer diameter: 48.6mm
The steel pipe was manufactured at a pipe manufacturing speed of 50 m/min. Table 1 compares the occurrence of penetrators between the conventional method and the method of the present invention, and Table 2 summarizes the occurrence of penetrators when the method of the present invention is used. Even when welding under welding heat input conditions that would result in frequent penetrators using conventional methods,

【table】

【table】

【table】

[Table] In the case of the method of the present invention, the generation of penetrators could be significantly reduced, and the effectiveness of the method of the present invention in preventing the generation of penetrators was sufficiently confirmed. As detailed above, in the case of the method of the present invention, when manufacturing a welded pipe, carbon, an organic compound, or an organosilicon compound is applied to the side end surface of a metal strip or an open pipe, and then welded, so that the applied material can be easily removed. The vapor pressure shields the area around the heating part from the atmosphere, preventing the alloy components in the material from oxidizing and effectively preventing the generation of penetrators. In addition, in the present invention, since the side end surface of the open pipe is covered with a coating material, even in the low-temperature heating range up to the welding temperature, the coating provides a direct atmospheric removal effect, and oxidation occurs before vaporization. It also has a high prevention effect. Further, the present invention requires only a simple device for coating and does not require the large-scale device used in the prior art.The present invention has a great effect on improving the quality of welded pipes such as electric resistance welded steel pipes.

[Brief explanation of the drawing]

FIG. 1 is a plan view schematically showing a main part of an electric resistance welded steel pipe manufacturing line using the method of the present invention, and FIG. 2 is a schematic vertical sectional view taken along the line - - in FIG. 1. P...pipe, OP...open pipe, ST...
...Strip steel, A...Welding point, 1...Induction heating coil,
2... High frequency power supply, 3l, 3r... squeeze roll, 71... container, 72... valve, 73... conduit, 74l, 74r... brush.

Claims (1)

[Claims] 1. A method of manufacturing a welded pipe by bending metal strips so that their side end surfaces face each other to form an open pipe, heating the opposing end surfaces of the open pipe by passing an electric current through them, and pressurizing them from both sides to weld them together. A method for manufacturing a welded pipe, comprising applying carbon, an organic compound, or an organosilicon compound to a side end surface of a metal strip or an open pipe, and then welding the same.