JPS5823582A - Production for welded pipe - Google Patents

Abstract

PURPOSE:To prevent the welding defect due to oxidation from being generated in a welding part, by applying preliminarily carbon, an organic compound, or an organic silicide to the welding part of an open pipe to weld it when a welded steel pipe is produced by high frequency welding. CONSTITUTION:A steel pipe ST is molded to an open pipe OP by many molding roll groups, and side end faces facing to each other of the pipe OP are heated by an induction heating coil 1 to which the high frequency current is flowed from a high frequency power source 2, and the pipe OP is pressurized by squeeze rolls and is welded into a welded pipe P. In this case, carbon of tar or the like, various synthetic resins, an organic solvent, rubber, an organic compound containing a high polymer compound such as cellulose, or an organic silicide such as a silicone resin is applied to side end faces to be welded. These applied materials are vaporized quickly to seal the part near the welding part from air by the vapor pressure, thus preventing the welding defect due to oxidation in the welding part.

Description

[Detailed Description of the Invention] The present invention utilizes welding techniques such as high frequency welding to produce #! Regarding a welded pipe manufacturing method that effectively prevents the occurrence of penetrators and improves welding quality in the manufacturing method of welded pipes. In general, in the method of manufacturing ERW steel pipes, the steel strip is passed through multiple breakdown rolls, It is continuously fed to a group of forming rolls consisting of side rolls, fin pass rolls, etc., first formed into a U-shape, then bent into a substantially circular open pipe, and then fed to a Km welding machine. Electric resistance welded steel pipes are manufactured by passing high-frequency current through the opposite end face of an open pipe to heat and melt that part using the induction coil method or thermage tool method, and then pressure welding with a squeeze sale. ◎ This method is different from other pipe manufacturing methods. The major advantage is that it is highly efficient compared to the open pipe method, and it can reduce the cost of oil country tubular goods, steel pipes for line pipes, steel pipes for boilers, steel pipes for machine structures, etc. During bath melting, the alloy components in the material are oxidized by oxygen in the atmosphere, and among the oxides produced, those with high melting points (oxides such as Mn and 81.Or) are not discharged from the welded part. This penetrator may remain inside the weld and cause a welding defect called a penetrator. This penetrator will significantly deteriorate the mechanical properties confirmed by tube expansion, flattening, and Charpy tests, etc.
Since it reduces the reliability of IaL welded steel pipes, it is one of the factors that limits its uses.For this reason, methods to prevent the occurrence of venetrators have recently been actively researched, and the main method is to stabilize the welding phenomenon. There are two methods: one method is to shield the area around the heated part with nitrogen gas, etc. (The former method is easy to generate venetrators when excessive heat is applied to the bath. This is a method to prevent the occurrence of penetrators by controlling the heat input so as to always obtain an appropriate heat input in response to fluctuations, but even if control is possible to obtain a tentatively appropriate heat input, the penetrator may still be present if the Mn in the material is 81°. As long as the occurrence of penetrators is caused by the oxidation phenomenon of alloy components such as Or, it is impossible to completely eliminate the occurrence of penetrators unless the oxidation phenomenon is fundamentally prevented. The latter method uses nitrogen gas, etc. to shield the area around the heated part from the atmosphere to prevent oxidation, and it is already known that the generation of penetrators is considerably reduced. It is difficult to completely shield the area around the heating part from the atmosphere because the structure of the induction heating coil or contact feeder installed around the heating part is complicated, and Mn in the material.

The oxidation of alloy components such as No. 81 and Or cannot be completely prevented, and the generation of minute venetrators is unavoidable, and the apparatus is large-scale and its maintenance requires baking molds.

The present invention has been developed in view of the above circumstances, and it is possible to substantially completely prevent the oxidation of the material around the heating part when manufacturing welded pipes such as electric resistance welded steel pipes, and to significantly reduce the number of micropenetrators.
A method for manufacturing a welded pipe according to the present invention aims to improve the quality of a welded pipe, which includes bending a metal strip so that one end surface thereof faces each other to form an open pipe;
In a method of manufacturing a welded pipe by applying pressure to the opposing end surfaces of an open pipe by passing an electric current through them and heating them at the same time, applying pressure from the KIIIil@ direction, carbon, an organic compound, or an organosilicon compound is applied to the side end surfaces of the metal strip or the open pipe. The method of the present invention is described in detail below with reference to drawings showing embodiments thereof. FIG. 1 is a plan view schematically showing the main parts of an ERW steel pipe production line using the method of the present invention, and FIG.
0 is a schematic vertical cross-sectional view taken along the line ■-■ in the figure. A steel band 8TFi whose both sides are finished with a surface suitable for welding by an edge device (not shown) is fed in the direction of the white arrow and is fed into a breakdown roll 61a.

61t) and 62a, 62b and side roll 51/
.

U by 51r, 52/, 52r and 551,53r
formed into a letter shape. Then, the fin pass rolls 41 and 42 which are arranged vertically opposite each other (in the figure, upper a-ruf>mi are shown). The open pipe OP is formed into a substantially circular shape by r, and the opposing edges are accurately guided by the fin plate of the upper fin pass roll, and the pipe is fed to the induction heating coil l.
Glycerin to be applied to the opposite end surfaces 81 and 8r of the open pipe OP is stored above the open pipe OP placed between the induction heating coil l and the last fin pass roll 42, and the glycerin is discharged. A container is equipped with a container with an opening at its bottom. The conduit 13 to which one end 1aK is connected is provided with a valve 2 at an appropriate position so that the amount of glycerin oozing out from the inside of the conduit 3 can be adjusted. Another conduit? The other end of 3 is divided into two parts and has an opening '/3/
, 3r and 9, with a brush 41. at the tip. A pipe 4r is attached so that glycerin exuding from the container 11 can be applied to the opposite end surfaces 8/, 8rlC of the open pipe OP. In this way, the open pipe OP whose side end face is coated with glycerin is powered by a high frequency power source 2 to 200
~! A high frequency current of approximately SOOkHg is fed to the induction heating coil l, and an induced current is generated in the open pipe OP.This induced current causes the opposing end face 8! ,
The open pipe OP where 8r is heated is squeeze roll 3! , 3rK from both sides and are bath-welded at the welding point AK to form the pipe P.

When producing an electric resistance welded steel pipe by such a method, the glycerin applied to the opposing end surfaces 8/, 8r of the open pipe OP during the gap where the opposing end surfaces 81, 8r are heated has a melting point of 17° C. Because it has a very low boiling point of 290°C, it easily vaporizes, and its vapor pressure shields the area around the heating section from the atmosphere. Therefore, Mn, Si, Cr in the material
The oxidation of the alloy components such as
, 8r was coated with glycerin because glycerin is in liquid form at room temperature (20C) K, so it is convenient to apply it using the method described above. This prevents vaporization from being completed in the early stages of heating, and provides sufficient shielding from the atmosphere around the heated area.For this reason, substances that should be coated should have a boiling point of 200°C or higher. 0 is desirable, and the following carbon, organic compounds, or organosilicon compounds are expected to have the same penetrator generation prevention effect as glycerin as substances to be applied to the opposite end surface 81°8rvc of the open pipe OP.◇(1) Carbon, tar Carbon polymer C: 4ypvo nitrile resin, acetyl cellulose, vinylidene chloride resin, vinyl chloride resin, nylon, nitrocellulose, polyethylene, polycarbonate, polystyrene, Teflon, polyglobylene, methyl methacrylate resin, aniline/formaldehyde resin, epoxy resin, phenol resin, urea Φ formaldehyde resin,
Phenol/formaldehyde resin, polyester resin, melamine. Formaldehyde, fat, etc. +7) Resins, hydrocarbons such as paraffin, xylene, nitro compounds such as nitrobenzene, glycerin, organic solvents such as acetone, alcohol, and organic compounds such as polymeric substances such as rubber and cellulose (3) Organosilicon compounds such as silicone resins Some of these substances are not liquid at room temperature, in which case it is difficult to use the coating method explained in the examples, but others Venetrator formation can be prevented by applying the material using a suitable application method, such as melt spray application, and then welding.

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 continues to be generated, a non-oxidizing atmosphere can be maintained as a whole.
The effect of the method of the present invention is not impaired by the presence of hydrogen element in the above substance.

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 last fin pass roll 42. This means that when the open pipe OF passes through the fin pass roll 41.42, applying carbon, organic compounds or organosilicon compounds,
This is because the particles are peeled off by the fin rate of the upper fin pass roll, reducing the effect of preventing the formation of venetrators due to the above-mentioned action. However, even if the previous process, for example, when the metal strip is in a coiled state, is coated with carbon, an organic compound, or an organic compound, then the metal strip is sent to an ERW steel pipe production line and welded, the effect is still high. Acceptable ◇ 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, an example of the method of the present invention will be explained.
: 0.14%%81 : 0.30%,'! 1:
0.50 inch, Cr: 1.0% sample material plate thickness: s,
A steel pipe of 2 m and an outer diameter of 48.61111 was manufactured at a pipe manufacturing speed of 5 o in town. Table 1 compares the occurrence of penetrators between the conventional method and the method of the present invention, and Table 2 shows the state of penetrator occurrence when the method of the present invention is used. When welding is carried out under welding heat input conditions that would result in frequent penetrators when using the method, the number of penetrators is significantly reduced when using the method of the present invention. We were able to confirm its effectiveness in preventing this.

As described above, in the case of the method of the present invention, when manufacturing a welded pipe, carbon,
By welding after applying an organic compound or organosilicon compound, the applied substance is easily vaporized, and the area around the heating area is shielded from the atmosphere due to its vapor pressure, preventing oxidation of the alloy components in the material. It can effectively prevent the occurrence of penetrators, and has a great effect on improving the quality of welded pipes such as electric resistance welded steel pipes.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. The side end surfaces of the metal strips are bent to face each other to form an open pipe, and the opposite side ends 1 of the open pipe are bent.
In the method of manufacturing a welded pipe by heating it with an iK current and pressurizing it from both sides, welding is performed after applying carbon, an organic compound, or an organosilicon compound to the side end surface of a metal strip or open pipe. Characteristic welded pipe manufacturing method O