JPH1043861A - Production of flexible steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce crack or break and to obtain a flexible steel tube having excellent flexibility and the beautiful appearance by mixing a specific amount of helium into an argon and welding butting parts at the time of corrugating a raw tube and producing the flexible steel tube. SOLUTION: A steel strip is formed in a tube shape, its butting parts are welded continuously with a TIG method using an argon as shield gas and a raw tube is formed, the raw tube is corrugated and a flexible steel tube is produced. In this case, helium of 0.5 to 2.0vol% is mixed with argon, and the butted parts are welded. Therefore, crack or break generated on a weld part at the time of corrugating the raw tube is reduced, the yield is improved and an inexpensive flexible steel tube having beautiful appearance can be produced.

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 a flexible steel pipe, and more particularly, to a so-called corrugation for giving elasticity to a base pipe obtained by TIG welding a butt portion of a tubular formed body made of stainless steel. The present invention relates to a welding technique for reducing cracks generated in a welded portion when applying.

[0002]

2. Description of the Related Art Recently, in places where water or gas is used, such as kitchens, bathrooms, washrooms, and the like in buildings, including ordinary households, flexible and beautiful so-called flexible steel pipes are widely used for piping. It became so. This flexible steel pipe is usually
It is manufactured through the line shown in FIG. That is, the coil 1
After the surface of the steel strip 2 unwound from the washing machine is washed by a washing machine 3, the steel strip 2 is formed into a tubular shape by a forming roll 4. Subsequently, a butt portion (commonly referred to as a groove 14) of the tubular molded body 12 formed in the traveling direction of the line is welded by the TIG welding machine 5 to form the raw tube 6. After the raw tube 6 is inspected for flaws by the eddy current flaw detector 7, so-called corrugation processing (hereinafter, simply referred to as corrugation) by rolling in order to impart elasticity and flexibility.
Is applied. The tube body after the corrugation 11 is heat-treated,
An airtightness test and resin coating are performed, and after various inspections, the flexible steel pipe 23 of the product is obtained. It is known that an inert gas such as argon or helium is used as a shielding gas for TIG welding. However, in the industrial production of ERW steel pipes, expensive helium is not used and only argon is used.

[0003] In the method of manufacturing the flexible steel pipe 23, the corrugation 11 is an important step in quality control of the product. The reason for this is that cracks or cracks occur in the welded portion 13 of the raw tube 6 at the time of the corrugation 11, and this is particularly common when the raw tube 6 is made of stainless steel. Since the stainless steel pipe is difficult to form, a problem is likely to occur at the abutting portion of the tubular molded body 12. However, the occurrence of cracks and cracks is the most serious defect for a product in which gas or water flows inside, and also a product. Yield decreases. As a countermeasure, it is conceivable to reduce the welding speed, but this would reduce the productivity of the flexible steel pipe 23 and would be economically disadvantageous.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method for manufacturing a flexible steel pipe which does not cause cracks or cracks in the welded portion when the tube is corrugated even when welding at a normal welding speed. It is intended to provide.

[0005]

In order to achieve the above object, the inventor investigated cracks and causes of cracks in a welded portion 13 of a tubular molded body 12 made of stainless steel. As a result, as shown in FIG. 3, in the case where a crack or a crack is generated in the welded portion 13, the groove 14 is often misaligned because the groove 14 is not correctly abutted. In this case, as the welding speed was increased, the bead width was narrowed, and cracks and cracks in the weld were likely to occur. And the inventor:
This narrow bead width was presumed to be related to the stress-strain at the time of the corrugation, and diligent efforts were made to increase the bead width, thereby completing the present invention.

That is, according to the present invention, a steel strip is formed into a tubular shape, and its butt portion is continuously welded by a TIG method using argon as a shielding gas to form a raw tube, and the raw tube is corrugated. A method for producing a flexible steel pipe, comprising: mixing a helium of 0.5 to 2.0 vol% with the above-mentioned argon and welding the butted portion when producing a flexible steel pipe by performing processing.

Further, the present invention is a method for producing a flexible steel pipe, wherein a stainless steel strip is used as the steel strip. In the present invention, since the flexible steel pipe is manufactured as described above, cracks and cracks generated in the welded portion at the time of corrugation of the raw pipe are significantly reduced as compared with the related art.
As a result, it is possible to increase the welding speed and improve the yield,
High quality flexible steel pipes can be manufactured at low cost.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, taking into account the circumstances leading to the invention. First, FIG.
The state of TIG welding according to the present invention is shown below (however,
The shield box surrounding the torch 16 and the weld 13 is not shown (not shown). According to the present invention, helium is used in a range from 0.5 to helium instead of using only argon as the shield gas 17 flowing into the shield box.
2.0 vol (volume)% was mixed.

The inventor has previously stated that, in TIG welding of a thick plate, when hydrogen gas is mixed with argon, dissociated atomic hydrogen flows on the surface of the thick plate material and is generated when it becomes molecular. Heat spreads the bead with the effect of the residual heat, "he sought to apply this experience to flexible steel pipes. That is, at the beginning of the research on the present technology, the inventor anticipated that welding of the flexible steel pipe would be successful by mixing the above-described hydrogen with argon, and thus added hydrogen. However, in this trial, the amount of penetration was increased, but the electrode was severely consumed, and not only the electrode cost was increased but also the operating rate was reduced due to electrode replacement.

[0010] Therefore, the inventor made various studies and focused on helium, which has a higher ionization energy than argon (see Table 1). This is because helium has a higher ionization energy than argon, and is considered to have a greater residual heat effect. And when I actually ran it,
The results of FIGS. 6 and 7 below were obtained.

[0011]

[Table 1]

FIGS. 6 and 7 show the relationship between the mixing ratio, the increase / decrease in voltage, and the bead width when helium or hydrogen is mixed with argon. As shown in FIGS. 6 and 7, it is clear that the addition of helium increases the bead width. At this time, the state in which the bead width was increased by the addition of helium was compared with the case where only argon was used.
Indicated by 4 is argon only, FIG. 5 is helium 0.5
vol% added (thickness is 0.2m for both)
m), the bead width is from 0.7 mm in FIG. 4 to 1.0 m in FIG.
m to 1.3 times.

In the present invention, the mixing amount of helium is set to 0.1.
The reason for limiting to 5 to 2.0 vol% is that if it is less than 0.5,
This is because the effect of increasing the bead width is small and the cost of a device for maintaining the above-mentioned mixing ratio constant becomes expensive. is there. The concrete performance results of the present invention include stainless steel (S
The welding speed of the tubular molded body made of US304) was increased by 10% as compared with the conventional method, and a flexible steel pipe for 31,900 m was manufactured. At that time, cracking at the time of corrugation was greatly reduced, and the yield at the actual length of the steel pipe was improved by 3%.

[0014]

As described above, according to the present invention, in the production line of flexible steel pipes, the cracks and cracks generated in the welded portion when the raw pipe is corrugated can be greatly reduced as compared with the conventional case. Was. As a result, the welding speed can be increased, and the yield can be improved. Therefore, it is possible to manufacture a flexible steel pipe excellent in flexibility and beautifully at low cost using conventional equipment.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state where a tubular molded body is being welded by a TIG welding machine.

FIG. 2 is a flowchart showing a manufacturing process of a flexible steel pipe.

FIG. 3 is a view showing a groove and a bead of a tubular molded body.

FIG. 4 is a diagram showing a bead width when only argon is used as a shielding gas.

FIG. 5 is a view showing a bead width when 0.5 vol% of helium is added to argon as a shielding gas.

FIG. 6 is a diagram showing a relationship between a mixing ratio of helium and hydrogen to argon and a welding voltage.

FIG. 7 is a diagram showing a relationship between a mixing ratio of helium and hydrogen to argon and a bead width.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coil 2 Steel strip 3 Washing machine 4 Forming roll 5 TIG welding machine 6 Raw tube 7 Eddy current flaw detector 8 Corrugating machine 9 Cylindrical head 10 Dies 11 Corrugated 12 Tubular molded body 13 Welding part 14 Edge 15 Bead 16 Torch 17 Shielding gas 18 Cooling water 19 Arc 20 Filling rod 21 Shielding gas atmosphere 22 Tungsten electrode 23 Flexible steel pipe

Claims (2)

[Claims] 1. A steel strip is formed into a tube, and its butted portion is continuously welded by a TIG method using argon as a shielding gas to form a raw tube, and further, the raw tube is subjected to a corrugating process. A method for manufacturing a flexible steel pipe, comprising mixing 0.5 to 2.0 vol% helium with the argon and welding the butt portion when manufacturing the flexible steel pipe. 2. The method for manufacturing a flexible steel pipe according to claim 1, wherein a stainless steel strip is used as said steel strip.