JP6769276B2 - Manufacturing method of hot-dip galvanized steel pipe and hot-dip galvanized steel pipe - Google Patents

Description

The present invention relates to a hot-dip galvanized steel pipe and a method for manufacturing a hot-dip galvanized steel pipe.

In the production of hot-dip galvanized steel pipes, the steel pipes are immersed in a flux tank (FL tank) to prevent surface oxidation of the steel pipes, and after removing dirt and rust on the surface, the steel pipes are dried in a drying furnace and placed in a plating bath. (See Patent Document 1 and FIG. 1).

In addition, immersion in a flux tank (flux immersion treatment) is performed by a batch process in which a plurality of steel pipes are immersed at once, and drying in a drying furnace (drying process) is performed by a continuous process in which steel pipes are continuously inserted one by one. It is known. In this case, since there is a time difference in the processing time between the flux dipping treatment and the drying treatment, a subloader for adjusting the time is provided between the flux tank and the drying furnace to adjust the time.

The subloader temporarily holds the steel pipe taken out from the flux tank by the arm, and sends the steel pipe to the conveyor that conveys the steel pipe to the drying furnace in a timely manner. Since a plurality of steel pipes are placed in a bundle in the subloader, the steel pipes come into contact with each other and streak-like rust may occur at the contact portion.

International Publication No. 2013/161122

By the way, as described above, when the steel pipe is dried and hot-dip galvanized with rust on the contact portion or the like, there is a problem that the plating does not sufficiently adhere to the rusted portion. Further, it is preferable that the plating adheres as uniformly as possible in the circumferential direction, but if there is rust, it is difficult to adhere uniformly, and quality problems may occur.

Further, when the flux dries after the flux immersion treatment, the flux falls off from the surface of the steel pipes due to contact between the steel pipes or between the steel pipes and equipment such as a conveyor. Then, this dropped portion causes rust and plating failure.

The present invention has been made in view of the above circumstances, and is a method for producing a hot-dip galvanized steel pipe capable of suppressing plating defects and producing a hot-dip galvanized steel pipe having a uniform plating thickness, and a hot-dip galvanized steel pipe having a uniform plating thickness. The purpose is to provide.

In order to achieve the above object, the method for producing a hot-dip galvanized steel pipe of the present invention includes a flux dipping treatment step of immersing a plurality of raw pipes in a flux to attach the flux to the raw pipes, and a flux dipping treatment step. A method for producing a hot-dip galvanized steel pipe, comprising a drying treatment step of drying the raw pipe in a drying furnace after the above, and a hot-dip galvanizing treatment step of performing a hot-dip galvanizing treatment on the raw pipe after the drying treatment step. It is characterized in that the raw pipe to which the flux is adhered by the flux dipping treatment step is conveyed to the drying furnace by a conveyor, and the flux is sprayed from above the conveyor toward the raw pipe.

According to such a configuration, the raw pipe immersed in the flux and to which the flux is attached is conveyed by a conveyor and dried in a drying oven. Then, a hot-dip galvanized steel pipe is manufactured by performing a hot-dip galvanizing treatment on the raw pipe. Further, during the transportation by the conveyor, the flux is sprayed from above the conveyor toward the raw pipe. Therefore, the rust generated before the flux is sprayed can be removed. In addition, the flux that has fallen off due to natural drying or the like before the flux is sprayed can be regenerated. Therefore, it is possible to suppress plating defects and to produce a hot-dip galvanized steel pipe having a uniform plating thickness by uniformly adhering the plating to the raw pipe.

Further, in the configuration of the present invention, it is preferable to blow flux toward the raw pipe with a width equal to or larger than the circumference of the raw pipe with respect to the transport direction of the raw pipe conveyed by the conveyor.

According to such a configuration, the flux is sprayed with a width equal to or larger than the circumference of the raw pipe with respect to the carrying direction of the raw pipe conveyed by the conveyor. The raw pipe conveyed by the conveyor is conveyed while rolling on the conveyor, but since the flux is sprayed toward the raw pipe with a width equal to or larger than the circumference of the raw pipe, it covers the entire circumference of the rolling raw pipe. , Can be sprayed with flux. Therefore, the rust generated before the flux is sprayed can be removed more reliably. In addition, it is possible to more reliably regenerate the flux that has fallen off by natural drying or the like before spraying the flux. Therefore, it is possible to more reliably suppress plating defects, and to uniformly adhere the plating to the raw pipe to produce a hot-dip galvanized steel pipe having a uniform plating thickness.

Further, in order to achieve the above object, the hot-dip galvanized steel pipe of the present invention has a plating layer at a pitch of 30 ° in the circumferential direction of the steel pipe at three locations, the central portion in the longitudinal direction of the steel pipe and 250 mm from each of the ends of both pipes. The standard deviation of the plating thickness when the plating thickness of the above is measured is 3.5 or less.

According to such a configuration, it is possible to provide a hot-dip galvanized steel pipe having a uniform plating thickness.

According to the present invention, it is possible to suppress plating defects, produce a hot-dip galvanized steel pipe having a uniform plating thickness, and provide a hot-dip galvanized steel pipe having a uniform plating thickness.

The embodiment of the present invention is shown, and it is a figure for demonstrating the manufacturing method of a hot-dip galvanized steel pipe. It is a figure for demonstrating the flux spraying process, and is the figure which looked at the flux shower apparatus from above of the conveyor. It is a figure for demonstrating the flux spraying process, and is the figure which looked at the flux shower apparatus from the side of the conveyor. It is a figure for demonstrating the measuring method of the plating thickness.

Hereinafter, embodiments of the present invention will be described.

The method for producing a hot-dip galvanized steel pipe according to the present embodiment includes a degreasing treatment step of performing a degreasing treatment, a pickling treatment step of performing a pickling treatment, a flux dipping treatment step of performing a flux dipping treatment, and a flux spraying treatment. It includes a flux spraying treatment step to be performed, a drying treatment step to perform a drying treatment, and a hot-dip galvanizing treatment step to perform a hot-dip galvanizing treatment.

In manufacturing the hot-dip galvanized steel pipe, first, a raw pipe 10 (see FIGS. 1 to 3) formed to a predetermined size is prepared. The size of the raw tube 10 is not particularly limited. The hot-dip galvanized steel pipe manufacturing apparatus used in carrying out the present invention may prepare a raw pipe 10 having a size capable of performing a series of plating treatments.

In addition, any steel pipe may be used for the raw pipe 10, for example, SGP steel pipe (steel pipe for general piping) specified in JIS G3452, STPG steel pipe (steel pipe for pressure piping) specified in JIS G3454, and the like. Should be used.
The method for manufacturing the SGP steel pipe and the STPG steel pipe is not particularly limited. That is, any of a forged pipe, an electric resistance welded pipe, a hot electric resistance welded pipe, a seamless pipe, and the like can be used as the raw pipe 10.
The forge-welded pipe is a steel pipe in which the end portions of the strip steel are forge-welded after hot roll forming of the strip steel. The electric resistance welded pipe is a steel pipe in which the ends of steel strips are cold and electric resistance welded to each other. Further, the hot electric resistance welded pipe is a steel pipe in which the ends of the strip steel are hot and electric resistance welded to each other. The seamless pipe is a steel pipe obtained by rolling and rolling a billet into a hollow pipe with a drilling machine.

In the production of hot-dip galvanized steel pipe, first, degreasing treatment is performed. In the degreasing treatment, first, the raw tube 10 is immersed in a degreasing solution to degrease. For degreasing, for example, alkaline degreasing or solvent degreasing may be performed. After degreasing, the raw tube 10 is washed with water to remove the degreasing liquid. This completes the degreasing process.
By degreasing in this way, the oil and fat adhering to the surface of the raw pipe 10 can be removed.

Following the degreasing treatment, the degreased raw tube 10 is pickled. In the pickling treatment, first, the raw tube 10 is immersed in a pickling solution to perform pickling. The pickling time may be determined according to the adhesion state of the scale and the like, and may be, for example, about 10 to 60 minutes. After pickling, the base tube 10 is washed with water to remove the pickling solution. This completes the pickling process.
In the pickling treatment, for example, sulfuric acid, hydrochloric acid or the like may be used as the pickling solution. Further, by incorporating an appropriate amount of an acid corrosion inhibitor (inhibitor) in the pickling solution, it is possible to suppress over-pickling and intergranular corrosion of the raw tube 10.
By such pickling, the scale on the surface of the raw tube 10 can be removed.

Following the pickling treatment, the pickled raw pipe 10 is subjected to a flux dipping treatment. In the flux dipping treatment, as shown in FIG. 1, a plurality of raw tubes 10 are immersed in the flux liquid in the flux tank 11 (FL tank).
By immersing in the flux liquid, a film of the flux liquid is formed on the raw tube 10, and this film protects the surface of the raw tube 10 and also involves zinc oxide during the hot-dip galvanizing treatment described later, resulting in poor plating. Is suppressed. Further, the wettability of the molten zinc can be improved by forming a film of the flux liquid.
As shown in FIG. 1, the flux dipping process may be performed by a batch process in which a plurality of raw tubes 10 are immersed at one time. A film of the flux liquid can be formed by pulling up the raw tube 10 from the flux liquid after 1 to 5 minutes of immersion.
As the flux liquid, for example, an aqueous solution of zinc chloride and ammonium chloride may be used. The quantitative ratio (molar ratio) of zinc chloride and ammonium chloride is preferably 1: 1 to 1: 6, and more preferably 1: 2 to 1: 4.
Further, in the flux dipping treatment, the flux liquid is used by heating it to 50 to 90 ° C. As the flux liquid, the higher the concentration (the total mass (g) of zinc chloride and ammonium chloride contained in 1 liter (L) of water) is preferable, and for example, the flux liquid having a high concentration of 400 g / L or more. Should be used.

Following the flux dipping treatment, the flux spraying treatment is performed on the raw pipe 10 after the flux dipping. The raw pipe 10 after the flux immersion treatment is temporarily stored in the subloader 12, and then sent to the conveyor 13 in a timely manner. Then, the raw pipes 10 are arranged on the conveyor 13 with the longitudinal direction of the raw pipe 10 oriented in a direction substantially perpendicular to the transport direction, and are conveyed to the drying furnace 16 by the conveyor 13. At this time, a flux spraying process is performed in which the flux is sprayed onto the raw pipe 10 by the flux shower device 14 from above the conveyor 13. That is, the raw pipes 10 immersed in the flux tank 11 and to which the flux is attached are conveyed side by side on the conveyor 13 and the flux is blown onto the raw pipe 10 from above the conveyor until it is inserted into the drying furnace 16.

After the flux immersion treatment, the tubes are placed together on the subloader 12 or conveyed in parallel on the conveyor 13, so that the tubes 10 come into contact with each other and streaky rust due to electric field corrosion is generated on the surface of the tubes 10. Or flux dropout occurs. Further, since the flux dipping treatment is performed by heating the flux liquid to 50 ° C. or higher, the flux liquid is partially dried and the powdery flux falls off on the conveyor 13 before the subsequent drying treatment. By performing the flux spraying treatment, the streak-like rust formed on the surface of the raw pipe 10 after the flux immersion treatment is removed, and the flux partially removed from the surface of the raw pipe 10 due to drying is repaired (recovered). It is possible to reduce the occurrence of plating defects. By arranging the flux shower device 14 immediately before the drying furnace 16, it is possible to remove the rust formed from the subloader 12 to the drying furnace 16 and to repair the flux that has fallen off. At the same time, it is possible to more reliably prevent rust from being generated again and the flux from falling off after the flux is sprayed and before the drying treatment is performed.

The flux shower device 14 is provided above the conveyor 13. Further, as shown in FIG. 2, the flux shower device 14 has a direction perpendicular to the width direction of the conveyor 13 (direction perpendicular to the transport direction (indicated by arrows D in FIGS. 2 and 3), that is, raw pipes arranged on the conveyor 13. A plurality of filled conical nozzles 15 arranged at equal intervals in a row toward a direction substantially parallel to the longitudinal direction of the 10 are provided. Further, the spray surfaces P of the flux blown out from the adjacent nozzles 15 partially overlap each other. Here, the spray surface P is a range (circular surface) where the flux blown from the nozzle 15 reaches, and refers to a surface in contact with the upper end of the raw pipe 10 flowing on the conveyor 13 (see FIG. 2). As a result, the flux can be sprayed on the conveyor 13 without gaps in the longitudinal direction of the raw pipes 10 arranged in a state where the longitudinal direction is directed to the direction perpendicular to the transport direction.
Further, the flux spraying width W with respect to the transport direction of the raw pipe 10 conveyed on the conveyor 13 is a width equal to or larger than the circumference length of the raw pipe 10. Here, as shown in FIG. 3, the spray width W is the width at which the flux sprayed from the flux shower device 14 reaches the raw pipe 10 transported on the conveyor, and refers to the width in the transport direction.
Since the raw pipe 10 is conveyed while rotating on the conveyor 13, if the spray width W is set to a width equal to or larger than the circumferential length of the raw pipe 10 in this way, the flux is evenly sprayed in the entire circumference direction of the raw pipe 10. It is possible to surely eliminate plating defects.
In the present embodiment, as shown in FIG. 2, the width from the rear end portion in the transport direction to the front end portion in the transport direction of the overlapping portion of the spray surface P of the flux ejected from the adjacent nozzles 15 of the flux shower device 14. Is the spray width W. By doing so, the flux can be sprayed over the entire longitudinal direction of the raw pipe 10 with a width equal to or larger than the circumference of the raw pipe 10 with respect to the transport direction of the raw pipe 10, and the flux is sprayed in the longitudinal direction of the raw pipe 10. Flux can be sprayed evenly in the circumferential direction of the raw pipe 10 over the entire area.
The flux shower device 14 may include only one nozzle 15 instead of a plurality of nozzles 15. Further, in FIGS. 2 and 3, adjacent raw pipes 10 are shown at regular intervals for easy understanding, but in the actual flux spraying process, the raw pipes 10 are shown like the raw pipes 10 on the conveyor 13 shown in FIG. Are usually in contact or transported with little distance.

Following the flux spraying treatment, the raw pipe 10 after the flux spraying treatment is subjected to a drying treatment. The drying treatment is performed by continuously inserting the raw pipes 10 into the drying furnace 16 one by one. The temperature inside the drying furnace 16 is adjusted to 70 to 150 ° C. according to the season and the diameter of the steel pipe. Further, the raw pipe 10 is discharged from the outlet 5 to 10 minutes after being inserted from the inlet of the drying furnace 16.
If water remains in the raw tube 10, it vaporizes when it comes into contact with the hot-dip galvanizing bath 17, and scatters the hot-dip zinc, causing plating failure. Therefore, it is necessary to sufficiently dry the raw pipe 10, but the water remaining in the raw pipe 10 can be sufficiently removed by the drying treatment.

Following the drying treatment, the hot-dip galvanizing treatment is performed on the raw pipe 10 after the drying treatment. The hot-dip galvanizing treatment is performed by immersing the raw tube 10 in the hot-dip galvanizing bath 17. The hot-dip galvanizing bath 17 may be made by melting a metal having a purity of one or more kinds of distilled zinc ingots, and is preferably made by melting the purest zinc ingot in consideration of the environment. ..
The temperature of the hot-dip galvanizing bath 17 is 440 to 490 ° C., the immersion time is 25 to 360 seconds, and the temperature and immersion time of the hot-dip galvanizing bath 17 may be adjusted according to the required thickness of the plating layer.
Further, when the raw tube 10 is taken out from the hot-dip galvanizing bath 17 after the elapse of a predetermined immersion time, excess molten zinc may be attached to the raw tube 10. In this case, air may be blown onto the raw tube 10 after the hot-dip galvanizing treatment to adjust the amount of hot-dip galvanizing.
Then, the hot-dip galvanized steel pipe is manufactured by cooling the hot-dip galvanized pipe 10.

The hot-dip galvanized steel pipe manufactured by the manufacturing method of the present embodiment has a more uniform plating thickness than the hot-dip galvanized steel pipe manufactured by the conventional method. This is because the rust on the raw pipe 10 can be removed by performing the flux spraying treatment after the flux dipping treatment and before the drying treatment, and the flux coating becomes more uniform than when the flux spraying treatment is not performed. Conceivable.
Therefore, according to the manufacturing method of the present invention, the plating thickness of the hot-dip galvanized steel pipe becomes uniform, and the quality of the hot-dip galvanized steel pipe can be improved.
Further, by the flux spraying treatment, the rust generated before the flux is sprayed can be removed, and the flux that has fallen off by natural drying or the like can be regenerated before the flux is sprayed, so that plating defects can be suppressed.

Whether or not the entire steel pipe is stably and uniformly plated can be determined by measuring the plating thickness at three points, the central portion in the longitudinal direction of the steel pipe and 250 mm from each of the ends of both pipes. That is, if the plating thickness is examined at the center of the steel pipe in the longitudinal direction (1 / 2L position) and at the position near the pipe end excluding the very vicinity of the pipe end corresponding to the threaded portion in some products, the steel pipe It can be determined whether the whole is uniformly plated. For example, the standard deviation σ of the plating thickness when the plating thickness of the plating layer is measured at a pitch of 30 ° in the circumferential direction of the steel pipe at three locations, the central part in the longitudinal direction of the steel pipe and 250 mm from each of the ends of both pipes, is 3. If it is 5 or less, it can be said that it is a high-quality hot-dip galvanized steel pipe in which the entire steel pipe is uniformly plated.

In the production of hot-dip galvanized steel pipes, the plating failure rate when the flux shower device 14 is provided above the conveyor 13 for transporting the raw pipe 10 installed between the flux tank 11 and the drying furnace 16 and when the flux shower device 14 is not provided is determined. investigated.

The flux shower device 14 includes a plurality of conical nozzles 15 arranged in a row along the width direction of the conveyor 13 (longitudinal direction of hot-dip galvanized steel pipes arranged on the conveyor 13). Further, these plurality of nozzles 15 are arranged apart so that a part of the spray surface P of the adjacent nozzles 15 overlaps.
Further, the height of the nozzle 15 is adjusted so that the width W of the spray surface of the nozzle 15 in the transport direction of the raw tube 10 is equal to or larger than the circumference of the raw tube 10.

The hot-dip galvanized steel pipe is a 15A to 100A (outer diameter 21.7 to 114.3mm) raw pipe 10 produced by hot electric resistance welding, which is degreased, pickled, and flux-immersed. Was performed, the drying treatment was performed in the drying furnace 16, and the hot-dip galvanizing treatment was performed to produce the product. Further, the hot-dip galvanized steel pipe is manufactured before and after the installation of the flux shower device, that is, when the flux spraying process by the flux shower device 14 is performed or not between the flux dipping process and the drying process. 2 patterns were performed.

As a result of investigating the plating defects of the manufactured hot-dip galvanized steel pipes, before the flux shower device 14 was installed (when the flux spraying treatment was not performed), 37769 of the 4617667 pipes were manufactured. Yes, the plating defect rate was 0.818%. On the other hand, after the flux shower device 14 was installed (when the flux spraying treatment was performed), out of 1715309 manufactured pieces, 8136 pieces had plating defects, and the plating failure rate was 0.474%. It was. The plating defect is so-called non-plating (JIS H8641).
From the above, it was confirmed that the plating defect can be reduced by providing the flux shower device 14 and performing the flux spraying process of spraying the flux from above the conveyor 13.

Further, with respect to the non-defective product before and after the installation of the flux shower device 14, the plating thickness of the plating layer was measured at three points, the central portion in the longitudinal direction of the steel pipe and the position 250 mm from the ends of both pipes. As shown in FIG. 4, the plating thickness of the plating layer was measured at a pitch of 30 ° in the circumferential direction of the steel pipe (points 1 to 12 in FIG. 4) so as to include the welded joint. Further, in order to measure the plating thickness more accurately, a V-shaped attachment was attached to the probe of the electromagnetic film thickness meter so that the tip of the probe was substantially perpendicular to the steel pipe.

Tables 1 to 3 show the plating thickness measurement results of plated steel pipes having outer diameters of 25A, 80A, and 100A. From Tables 1 to 3, the standard deviation σ of the plating thickness before the installation of the flux shower device 14 was 3.616 to 4.718, whereas the standard deviation σ of the plating thickness after the installation of the flux shower device 14 was 2. It was 397 to 3.492, which was 3.5 or less. As a result, it was confirmed that by using the method for producing a hot-dip galvanized steel pipe of the present invention, a plated steel pipe having a more uniform plating thickness can be obtained, which contributes to improving the quality of the hot-dip galvanized steel pipe.

10 Raw pipe 11 Flux tank 12 Subloader 13 Conveyor 14 Flux shower device 15 Nozzle 16 Drying furnace 17 Plating bath W Spray width

Claims (2)

A flux dipping treatment step of immersing a plurality of raw pipes in flux to attach flux to the raw pipes, a drying treatment step of drying the raw pipes in a drying furnace after the flux dipping treatment step, and this drying treatment step. A method for producing a hot-dip galvanized steel pipe, comprising a hot-dip galvanizing treatment step of performing a hot-dip galvanizing treatment on the raw pipe after the above.
A hot-dip galvanized steel pipe characterized in that the raw pipe to which the flux is adhered by the flux dipping treatment step is conveyed to the drying furnace by a conveyor and the flux is sprayed from above the conveyor toward the raw pipe. Production method. The hot-dip galvanized steel pipe according to claim 1, wherein the flux is blown toward the raw pipe with a width equal to or larger than the circumference of the raw pipe with respect to the transport direction of the raw pipe conveyed by the conveyor. Manufacturing method.

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