JP2017177215A - Method for production of electric resistance welded steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for an electric resistance welded steel tube capable of surely preventing generation of oxides during electric resistance welding.SOLUTION: An objective method for production of an electric resistance welded steel tube 15 comprises: previously making a polymeric material 2 generating a reductive gas by combustion adhere to both circumferential end parts (parts 11 to be welded) of a tubular body prior to heating when heating and butting both end parts of the tubular body while molding a steel belt into the tubular body (elemental tube 10) and electric resistance-welding; shielding the heating range from the heating start points 12 of both circumferential end parts of the tubular body to a welding point 13 by a non-oxidative gas; and electric resistance-welding the tubular body in the oxygen concentration range of 0.01-10 vol.%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an electric resistance welded steel pipe, in particular, an electric resistance welded steel pipe that requires high mechanical properties in a welded part, such as for oil well line pipes and automobile parts.

  ERW steel pipe is an electric seam welding method in which the width of the ERW pipe is rounded while discharging the steel plate (the meaning of the steel strip, the same shall apply hereinafter), and the end of the rounded width is subjected to high-frequency energization or induction heating to the melting point or higher, butting up and welding In general, it is said that the mechanical properties of welds are inferior to those of the base metal, and guaranteeing the toughness, strength, and elongation of welds has always been a problem for each application when using ERW pipes. .

  The cause of the deterioration of the mechanical properties of welded parts made by ERW welding is that an oxide-based welding defect called a penetrator is caused by welded parts (more specifically, open pipes made by rolling steel strips) during ERW welding. An example where the pipe end butt is a part where both ends of the pipe in the circumferential direction are abutted and remains, and due to this residual penetrator, the toughness is reduced or the strength is insufficient. There were many.

  Therefore, in order to remove the penetrator, which is the main cause of ERW welding failure, from the welded portion as a conventional technique, it is possible by means of gas shield welding method or upset to prevent the welded portion from being oxidized by blowing gas onto the welded portion. There have been many proposals for ways to discharge outside.

  For example, in Patent Document 1, in order to prevent the formation of oxides, the joining end portion of the steel strip is heated in a non-oxidizing atmosphere, the joining failure is prevented, and the non-metallic inclusions are on the surface of the welded portion. In order to prevent the occurrence of the above, a technique is disclosed in which the upset amount is 25 to 125% of the wall thickness and electro-welding is performed to ensure excellent toughness and SSC resistance of the welded portion. It is described that nitrogen and argon are used as the atmospheric gas and a sealed box is provided to keep the welded portion non-oxidizing.

  In addition, in Patent Document 2, the edge part with which the tubular body is attached is melted by irradiating with a laser beam and is upset and welded to discharge the oxide generated at the time of welding to the outside of the molten steel. Has disclosed a technique for reducing the oxygen content of the part to 200 ppm or less.

  Further, in Patent Document 3, when manufacturing an electric resistance welded steel pipe, a welded portion is covered with a gas shield box during welding (pressure welding), and a gas (for example, argon gas or nitrogen gas) is injected and shielded to reduce the amount of oxygen. While reducing the amount of oxide generated, the end to be pressed is heated by irradiating a laser beam or plasma arc to the welding site during high frequency heating, and the liquid oxide at the end is heated. A technique has been disclosed in which welding defects are remarkably reduced and the toughness and workability of an electric-welded welded part are improved by making it easy to discharge and discharging by subsequent pressure welding.

  Patent Document 4 discloses a method of preventing the occurrence of a penetrator by applying carbon, an organic compound or an organosilicon compound to the side end face of an open tube and then welding.

JP 63-241116 A JP-A-9-194998 JP-A-5-23867 JP 58-23582 A

  However, the method of installing the seal box described in Patent Document 1 or the gas shield box described in Patent Document 3 and gas-shielding the welded portion with a non-oxidizing gas is not sufficient for shielding and can be performed during ERW welding. In some cases, oxides are generated and remain in the welded portion, thereby deteriorating the mechanical properties of the welded portion.

  Also, a method of discharging the oxide generated at the time of welding by melting, upsetting, and welding the edge portions brought together by laser beam irradiation described in Patent Document 2, or described in Patent Document 3 The method of increasing the temperature of the welded portion by irradiating the laser beam or plasma arc to facilitate discharge of the liquid oxide, or carbon, organic compound or organic silicon on the side end face of the open tube described in Patent Document 4 Any of the methods to prevent the generation of the penetrator by applying the compound and then welding may leave the generated oxide in the welded part without being completely discharged, such as the strength and toughness of the welded part. There was a problem that the mechanical properties varied and the quality of the welded portion could not be guaranteed over the entire length of the pipe.

  As described above, in these conventional techniques, there is a problem in that the welded part at the time of ERW welding cannot be reliably suppressed by using a non-oxidizing atmosphere, and generation of a penetrator cannot be prevented.

  An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing an electric resistance welded steel pipe that can reliably prevent the formation of oxides during electric resistance welding.

The present inventors have intensively studied to solve the above-mentioned problems, and as a result, after pre-adhering a polymer material that burns to generate a reducing gas to the end portion to be subjected to ERW welding, ERW welding is performed. In addition, the present inventors have found that the formation of oxides in the welded portion can be prevented by performing a specific gas shield during electric resistance welding. That is, the present invention is as follows.
(1) In a method for producing an electric resistance steel pipe, a polymer that burns to generate a reducing gas when forming a steel strip into a tubular body and heating and butt-welding both ends in the circumferential direction of the tubular body The material is preliminarily attached to both ends in the circumferential direction of the tubular body before heating, and is then subjected to electric resistance welding, and at least during the electric resistance welding, reaches the welding point from the heating starting points at both ends in the circumferential direction of the tubular body. A method for producing an ERW steel pipe, wherein the heating range is shielded with a non-oxidizing gas, and the oxygen concentration is in the range of 0.01 to 10 vol.%.
(2) In the method (1), the reducing gas contains any one or more of methane, ethylene, acetylene, and ethane.
(3) In the method (2), the polymer material is any one of polyester, polyethylene, polypropylene, and a thermosetting acrylic resin.
(4) In any one of said (1)-(3), the adhesion amount of the said polymeric material shall be 10-1000 micrometers in adhesion thickness, The manufacturing method of the electric resistance steel pipe characterized by the above-mentioned.
(5) In any one of (1) to (4), the non-oxidizing gas used for the shield is an inert gas.
(6) In any one of the above (1) to (5), the non-oxidizing gas used for the shield is caused to flow in the shield box, and the non-oxidizing gas flow rate in the shield box is set to 50 to 3000 l / min. A method for producing an ERW steel pipe.
(7) In any one of the above (1) to (6), the outer diameter of the tubular body immediately after ERW welding is 10 to 700 mm.
(8) In any one of the above (1) to (7), the steel strip has a thickness of 0.5 to 30 mm.

  According to the present invention, the amount of oxide generated in the ERW welded portion can be maintained at a sufficiently low level, and the welded portion characteristics of the ERW steel pipe can be reliably improved from the conventional level.

It is the schematic which shows embodiment of this invention. It is the schematic which shows the coating method (an example) of the polymeric material by a gas spraying method.

  FIG. 1 is a schematic view showing an embodiment of the present invention. The steel strip, which is a steel pipe material, is continuously discharged by an uncoiler (not shown), corrected by a leveler (not shown), and fed in the pipe forming direction 20, while the width of the steel strip is rounded by a roll forming machine (not shown) to form a tubular body (Open pipe) 10 and the welded part 11 which is a raw pipe edge butting portion formed by abutting both ends in the circumferential direction of the raw pipe 10 is shown in an electric resistance welding machine (not shown) The squeeze roll 16 for pressure welding is used to perform electric resistance welding to obtain an electric resistance steel pipe 15. Here, the plate | board thickness of the steel strip employ | adopted is 0.5-30 mm. Moreover, the outer diameter immediately after the electric resistance welding of the tubular body is 10 to 700 mm. Examples of steel types of the steel strip include low carbon low alloy steel, steel for machine structure, steel for welded structure, steel for boiler / heat exchanger, stainless steel for piping, and the like.

  Reference numeral 12 denotes an element pipe edge heating start point, and reference numeral 13 denotes a welding point indicating a pipe passing direction position where the welded part 11 is joined by the pressure welding. In addition, an impeller (not shown) may be disposed on the inner surface side of the base tube 10 to the ERW steel tube 15. The outer diameter of the ERW steel pipe 15 exiting the ERW welder is adjusted by a sizer (not shown).

  In the present invention, the polymer material 2 is applied to both ends by the polymer material applicator 1 at a position upstream of the raw tube edge heating start point 12 (a position on the exit side of the fin pass roll not shown) is desirable. Do (attach). The polymer material 2 is desirably a polymer material that generates a reducing gas such as methane, ethylene, acetylene, or ethane as a combustion product during combustion. However, from the viewpoint of environmental safety, it is desirable to use a polymer material that contains few toxic substances such as hydrogen chloride, hydrogen cyanide, ammonia, and hydrogen sulfide as combustion products. Specifically, polyester, polyethylene, polypropylene, thermosetting acrylic resin, and the like are preferable.

  Examples of the coating method of the polymer material include a thermal spraying method (gas spraying, plasma spraying, etc.), a thermocompression bonding method, and a welding method. The polymer material coating apparatus 1 may be an apparatus suitable for carrying out the above coating method.

  Further, the coating thickness (adhesion thickness) of the polymer material is preferably 10 to 1000 μm because an excessively large thickness causes a welding failure, and an excessively small coating thickness has a poor effect on suppressing the formation of oxides. More preferably, it is 50-500 micrometers.

  Next, the entire range of the pipe passage direction from the raw tube edge heating starting point 12 to the welding point 13, or an area within the range where oxides are likely to be generated in the welded part (this area can be specified by preliminary investigation) It is preferable to shield with non-oxidizing gas during welding. It is desirable to install a shield box 3. Moreover, as the non-oxidizing gas, an inert gas such as argon gas or nitrogen gas is preferable. The oxygen concentration of the non-oxidizing gas is preferably in the range of 0.01 to 10 vol.%. If the oxygen concentration is less than 0.01 vol.%, The polymer material that remains unburned remains in the welded portion, and the strength of the welded portion is reduced. Therefore, the oxygen concentration is preferably 0.01 vol.% Or more. On the other hand, if it exceeds 10 vol.%, An oxide is generated in the welded portion, and the strength of the welded portion is lowered, so that 10 vol.% Or less is preferable.

  If the non-oxidizing gas flow rate in the shield box 3 is too small, the oxygen concentration exceeds 10 vol. On the other hand, if it is excessive, the polymer material that does not burn easily remains in the weld. Therefore, it is preferable to set it as 50-3000 l / min.

  The steel strip is passed through a pipe making facility in which an uncoiler, leveler, roll forming machine, electric seam welder, and sizer are arranged in this order, and a low carbon low alloy with an outer diameter of 152.4 mm and a wall thickness of 6.4 mm In the process of manufacturing an electric resistance welded steel pipe, pipe forming is performed under the conditions shown in Table 1 in the embodiment shown in FIG. Defect area ratio of welds (area ratio of oxides and inclusions, etc.) for steel pipes manufactured by coating (examples of the present invention) and steel pipes manufactured without applying polymer material to both edges (comparative examples) Was measured.

  The polymer material was applied by the following method with a target application thickness of 200 μm. That is, it applied by gas spraying method (schematic diagram is shown in FIG. 2) to both edge end faces before the heating starting point 12. For gas spraying, a propane and oxygen combustion flame was used. A polymer material powder pre-heated to 80 ° C. and having an average particle diameter of 0.1 mm is conveyed by a carrier gas (air is used here) to be supplied at a supply rate of 50 g / min. Thermal spraying was performed under the conditions of a flow rate: 20 l / min, a propane pressure: 0.4 MPa, an oxygen flow rate: 55 l / min, and an oxygen pressure: 0.4 MPa. The shield gas flow rate when the shield gas (non-oxidizing gas used for the shield) was used was 800 l / min.

  Here, the defect area ratio of the welded portion means the area ratio of the portion including foreign matter such as oxide inside the dimple in the dimple region other than the cleavage or pseudo-cleavage region in the fracture surface by the impact fracture test. To do. This defect area ratio was determined by the following method. In other words, the brittle fracture surface ratio (visual judgment) was made by a Charpy test with a notch so that the seam welded part (the joint interface where the welded parts were welded and joined, which is substantially perpendicular to the pipe circumferential direction) is the fracture surface. ) Is observed with a scanning electron microscope (SEM) at least 10 fields of view at a magnification of 500 times and oxidized from the dimple region in the fracture surface. The total area of the dimples containing foreign substances such as oxide is measured by selecting the dimples containing foreign substances such as objects, and the percentage of the total area of the visual field [= the total number of dimples containing foreign substances such as oxides] Area / total field of view × 100 (%)] was defined as the defect area ratio. The groove shape of the welded end face was a straight shape. The results are shown in Table 1.

  As shown in Table 1, in the example of the present invention, the defect area ratio of the welded portion was remarkably reduced as compared with the comparative example, and a welded portion having excellent strength and toughness was obtained. If the defect area ratio of the welded portion is 5% or less, preferably 2% or less, the strength and toughness are excellent.

1 Polymer Material Coating Device 2 Polymer Material 3 Shield Box 10 Elementary Tube (Open Tube)
11 Welded part (element tube edge butt part)
12 Element pipe edge heating starting point 13 Welding point 15 ERW steel pipe 16 Squeeze roll 20 Pipe making direction

Claims (8)

  In the method for producing an electric resistance steel pipe, a polymer material that burns to generate a reducing gas when the steel strip is formed into a tubular body and both ends in the circumferential direction of the tubular body are heated and butt-welded to perform electric resistance welding. After preliminarily adhering to both ends in the circumferential direction of the tubular body before heating, and at least during the electric resistance welding, a heating range from the heating starting point of the both ends in the circumferential direction of the tubular body to the welding point is set. A method for producing an ERW steel pipe, characterized by shielding with a non-oxidizing gas and adjusting the oxygen concentration to a range of 0.01 to 10 vol.%.   2. The method for producing an ERW steel pipe according to claim 1, wherein the reducing gas contains one or more of methane, ethylene, acetylene, and ethane.   The method for producing an electric resistance welded steel pipe according to claim 2, wherein the polymer material is any one of polyester, polyethylene, polypropylene, and thermosetting acrylic resin.   The method for producing an electric-welded steel pipe according to any one of claims 1 to 3, wherein an adhesion amount of the polymer material is 10 to 1000 µm in terms of adhesion thickness.   The non-oxidizing gas used for a shield is an inert gas, The manufacturing method of the ERW steel pipe of any one of Claims 1-4 characterized by the above-mentioned.   The non-oxidizing gas used for the shield is made to flow in the shield box, and the non-oxidizing gas flow rate in the shield box is set to 50 to 3000 l / min. The manufacturing method of the electric resistance steel pipe of description.   The outer diameter immediately after the electric resistance welding of the tubular body is 10 to 700 mm, The method for manufacturing the electric resistance steel pipe according to any one of claims 1 to 6.   The thickness of the steel strip is 0.5 to 30 mm, and the method for producing an ERW steel pipe according to any one of claims 1 to 7.

Images