JP7155816B2 - Manufacturing method and welding equipment for austenitic stainless steel pipe welded joint - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an austenitic stainless steel welded joint for pipes and a welding apparatus used therefor.

In recent years, research toward the practical use of transport equipment using hydrogen has progressed, and there is a demand for the development of an environment in which high-pressure hydrogen and liquefied hydrogen can be stored and transported.

Austenitic stainless steel, which has high strength and excellent resistance to hydrogen embrittlement, has been proposed as a material for use in such equipment. Regarding welded joints of austenitic stainless steel, it has also been proposed to increase the N content of the weld metal to give it a higher tensile strength than the base material (see International Publication No. 2013/005570). ).

Austenitic stainless steel pipes used as piping in hydrogen stations are often welded by gas-tungsten-arc welding (GTAW), and automatic butt welding is often used.

Japanese Patent Application Laid-Open No. 132270/1986 discloses a welding method for preventing depression of a weld bead that occurs when thin members are butt-welded. Specifically, thin-walled members having protrusions provided in the grooves are joined together, and the pressure on the surface side of the joint irradiated with the arc is set below the pressure on the back side to melt the groove including the protrusions. , discloses welding both thin-walled members.

Japanese Laid-Open Patent Publication No. 7-164146 discloses an automatic welding device which prevents the formation of recesses in the back wave layer. Specifically, when welding the objects to be welded with the torch facing upward, the open side of the housing faces the surface of the object to be welded, and the sealing material is brought into contact with the surface of the object to be welded. It is disclosed to seal between the face of the opening edge and introduce an inert gas into the enclosure to increase the pressure and thereby prevent drooping of molten material in the weld pool.

Japanese Patent No. 3496031 discloses a welding method for high-purity gas supply system piping. Specifically, in the circumferential welding of metal tubes by TIG automatic welding, the back shield gas is emitted inward from the opening on the tip side of one metal tube, and the welding current value at the time of arc start is set to It is disclosed that the welding current is maintained at a value lower than the steady-state welding current for a certain period of time from the start of the arc, and then the welding current is increased to the steady-state welding current.

WO2013/005570 JP-A-61-132270 JP-A-7-164146 Japanese Patent No. 3496031

As described in JP-A-61-132270, a method is known in which gas is sealed in a steel pipe to increase the internal pressure and welding is performed from the outside of the pipe. However, with this method, it is difficult to obtain a welded portion in which depressions on the front and back surfaces are suppressed over the entire circumference of the steel pipe.

SUMMARY OF THE INVENTION An object of the present invention is to provide a manufacturing method and a welding apparatus for an austenitic stainless steel pipe welded joint having a welded portion in which depressions on the front and back surfaces are suppressed over the entire circumference.

A method for manufacturing an austenitic stainless steel pipe welded joint according to one embodiment of the present invention comprises supplying a back shield gas to the inside of a pair of steel pipes whose ends are butted against each other, and using a welding torch to circumferentially distribute the gas from the outside. - A step of performing tungsten arc welding is provided, and the internal pressure of the pair of steel pipes is changed based on the attitude of the welding torch.

A welding apparatus according to an embodiment of the present invention is a welding apparatus that performs gas-tungsten-arc welding from the outside in the circumferential direction while supplying a back shield gas to the inside of a pair of steel pipes whose ends are butted against each other. , a welding torch, internal pressure adjusting means for adjusting the internal pressure of the pair of steel pipes, and a control device for driving the internal pressure adjusting means and changing the internal pressure of the steel pipes based on the attitude of the welding torch.

According to the present invention, it is possible to obtain an austenitic stainless steel pipe welded joint having a welded portion in which depressions on the front and back surfaces are suppressed over the entire circumference.

FIG. 1 is a schematic diagram showing the configuration of a welding device according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of the welding head. FIG. 3A is a schematic diagram showing a case where 1.5 circumferences of a steel pipe in the circumferential direction are divided into five regions. FIG. 3B is a schematic diagram showing a case where 1.5 turns of the steel pipe in the circumferential direction are divided into six regions. FIG. 3C is a schematic diagram showing a case where 1.5 turns of the steel pipe in the circumferential direction are divided into nine regions.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same reference numerals are given to the same or corresponding parts in the drawings, and the description thereof will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[Configuration of Welding Device]
FIG. 1 is a schematic diagram showing the configuration of a welding device 1 according to one embodiment of the present invention. A welding apparatus 1 is a welding apparatus that performs gas-tungsten-arc welding from the outside in the circumferential direction while supplying a back shield gas to the inside of steel pipes P1 and P2 whose ends are butted against each other. The welding device 1 includes an introduction line 11 , a discharge line 21 , a shield gas supply line 31 , a welding head 40 , a welding torch 41 and a control device 50 .

The introduction line 11 is connected to the steel pipe P1 and introduces the back shield gas inside the steel pipes P1 and P2. A valve 12, a regulator 13, a flow meter 14, and a valve 15 are connected to the introduction line 11 in this order from the upstream side of the back shield gas.

The discharge line 21 is connected to the steel pipe P2 and discharges the back shield gas from inside the steel pipes P1 and P2. A pressure gauge 22 and a valve 23 are connected to the discharge line 12 in this order from the upstream side of the back shield gas.

A shield gas supply line 31 supplies shield gas to the welding torch 41 . A valve 32 , a regulator 33 , a flow meter 34 , and a valve 35 are connected to the shielding gas supply line 31 in order from the upstream side of the shielding gas.

FIG. 2 is a schematic diagram showing the configuration of the welding head 40. As shown in FIG. The welding head 40 includes a welding torch 41 , a base 42 and a stage 43 . Welding head 40 may additionally comprise a welding material supply device for supplying welding material.

A welding torch 41 is fixed to the stage 43 of the welding head. The stage 43 is configured to be rotatable around the axial directions of the steel pipes P1 and P2. As the stage 43 rotates, the welding torch 41 also rotates around the steel pipes P1 and P2.

The welding torch 41 sprays the shield gas supplied from the shield gas supply line 31 and generates an arc to melt the welded portion (the contact position between the steel pipe P1 and the steel pipe P2). Welding torch 41 is, for example, a laser torch. By welding while rotating the welding torch 41, the steel pipe P1 and the steel pipe P2 can be welded in the circumferential direction.

Controller 50 controls valves 15 , 23 and 35 and weld head 40 . Specifically, the control device 50 opens and closes the valve 15 to start or stop the supply of the back shield gas to the steel pipes P1 and P2, and opens and closes the valve 35 to start the supply of the shield gas to the welding torch 41. or stop. The control device 50 also adjusts the opening of the valve 23 to adjust the internal pressure of the steel pipes P1 and P2. The controller 50 further rotates the stage 43 at a predetermined speed and controls the current supplied to the welding torch 41 .

[Method for manufacturing an austenitic stainless steel pipe welded joint]
A method for manufacturing an austenitic stainless steel pipe welded joint using the welding apparatus 1 will be described below.

The steel pipes P1 and P2 are fixed to the welding device 1 with their ends facing each other. Steel pipes P1 and P2 are austenitic stainless steel pipes. The chemical composition of the steel pipes P1 and P2 is not limited to this, but for example, in mass %, C: 0.10% or less, Si: 1.0% or less, Mn: 3 to 7%, Cr: 15 to 30% , Ni: 10 to 17%, Al: 0.10% or less, N: 0.10 to 0.50%, Mo: 0 to 5.0%, V: 0 to 1.0%, Nb: 0 to 1 .0%, balance: Fe and impurities. The steel pipes P1 and P2 may contain elements other than those mentioned above.

Valves 15 and 35 are opened to start the supply of shield gas and back shield gas. The shield gas and back shield gas are argon gas, for example. Preferably, valves 15 and 35 are opened and closed automatically by controller 50 .

Pressure gauge 22 measures the internal pressure of steel pipes P<b>1 and P<b>2 and transmits the measured value to control device 50 . The controller 50 adjusts the opening degree of the valve 23 based on this measured value to control the internal pressures of the steel pipes P1 and P2. The internal pressure of the steel pipes P1 and P2 is preferably controlled at 0.1-0.9 kPa.

Gas-tungsten-arc welding is performed while supplying shield gas and back shield gas. At this time, the controller 50 changes the internal pressures of the steel pipes P1 and P2 based on the attitude of the welding torch 41 .

Preferably, the internal pressure of the steel pipes P1 and P2 when the tip of the welding torch 41 faces downward is higher than the internal pressure of the steel pipes P1 and P2 when the tip of the welding torch 41 faces the other direction. This control can be performed, for example, by dividing the welding path into a plurality of regions and setting a target value of internal pressure for each region.

FIG. 3A is a schematic diagram showing a case where 1.5 circumferences of the steel pipes P1 and P2 in the circumferential direction are divided into five regions. In FIG. 3A, the z direction is the vertical direction. The same applies to FIGS. 3B and 3C. In the case of the diagram of FIG. 3A, it is preferable to set the internal pressure of the third region (region [3]) to a value greater than the internal pressure of the other regions.

FIG. 3B is a schematic diagram showing a case where 1.5 circumferences of the steel pipes P1 and P2 in the circumferential direction are divided into six regions. In the case of FIG. 3B, it is preferable to set the internal pressures of the third and fourth regions (regions [3] and [4]) to values higher than those of the other regions. FIG. 3C is a schematic diagram showing a case where 1.5 circumferences of the steel pipes P1 and P2 in the circumferential direction are divided into nine regions. In the case of FIG. 3C, it is preferable to set the internal pressure of the fifth region (region [5]) to a value greater than the internal pressure of the other regions.

In FIGS. 3A to 3C, each region is evenly divided, but each region may have a different length. The number of divided regions is arbitrary, and the internal pressure may be changed continuously. Also, in FIGS. 3A to 3C, 1.5 turns in the circumferential direction are welded, but welding may be performed for one turn or more, and may be just one turn or two or more turns.

FIGS. 3A to 3C illustrate the case where welding is started from a position where the tip of the welding torch faces the horizontal direction, and then the welding torch 41 is rotated downward of the steel pipes P1 and P2. However, the welding start position and rotation direction are arbitrary.

The magnitude of the current supplied to the welding torch 41 is preferably 15-50A. It is preferable to change the magnitude of the current supplied to the welding torch 41 based on the elapsed time from the start of welding. Specifically, immediately after the start of welding, it is preferable to reduce the current supplied to the welding torch 41 in order to stabilize the arc. Further, after the current is set to a predetermined magnitude, it is preferable to reduce the current in order to prevent overheating of the welded portion due to temperature rise of the steel pipes P1 and P2. That is, it is preferable to increase the current from a small value immediately after the start of welding, and then decrease the current again.

After welding is completed, the valves 15 and 35 are closed to stop the supply of shield gas and back shield gas. Through the above steps, an austenitic stainless steel welded joint in which the steel pipe P1 and the steel pipe P2 are circumferentially welded is manufactured.

[Effect of this embodiment]
In circumferential welding of steel pipes, the weld metal may sag under the influence of gravity. In this embodiment, back shield gas is supplied to the inside of the steel pipes P1 and P2 to increase the internal pressure, thereby preventing the weld metal from sagging inside the steel pipes P1 and P2. On the other hand, if the internal pressure is too high, the back surface of the weld metal (inside the steel pipes P1 and P2) may be dented. Due to the influence of gravity, the optimum internal pressure differs depending on the welding posture.

In this embodiment, the internal pressures of the steel pipes P1 and P2 are changed according to the attitude of the welding torch 41. FIG. As a result, an austenitic stainless steel pipe welded joint having a welded portion in which depression is suppressed over the entire circumference can be obtained.

Preferably, the internal pressure of the steel pipes P1 and P2 when the tip of the welding torch 41 faces downward is higher than the internal pressure of the steel pipes P1 and P2 when the tip of the welding torch 41 faces the other direction. That is, the internal pressure is relatively increased when the weld metal tends to hang down inside the steel pipes P1 and P2 under the influence of gravity.

The welded joint for austenitic stainless steel pipes manufactured according to the present embodiment preferably does not have depressions of 30 μm or more on the front and back surfaces over the entire circumference of the weld. More preferably, the austenitic stainless steel pipe welded joint manufactured according to the present embodiment does not have depressions of 20 μm or more on the front and back surfaces over the entire circumference of the welded portion.

The welded joint for austenitic stainless steel pipes manufactured according to the present embodiment has high strength because it has welded portions in which depressions are suppressed over the entire circumference. The austenitic stainless steel pipe welded joint produced according to this embodiment preferably has a tensile strength of 690 MPa or more at room temperature. The austenitic stainless steel pipe welded joint manufactured according to this embodiment more preferably has a tensile strength of 700 MPa or more at room temperature.

The method for manufacturing an austenitic stainless steel pipe welded joint according to the present embodiment is particularly suitable when the steel pipes P1 and P2 are relatively small diameter steel pipes. The steel pipes P1 and P2 preferably have an outer diameter of 30 mm or less, more preferably 20 mm or less, although the steel pipes P1 and P2 are not limited to this.

In the above embodiment, the case where the control device 50 controls the internal pressures of the steel pipes P1 and P2 has been described. However, the internal pressures of the steel pipes P1 and P2 may be controlled manually. That is, the internal pressure of the steel pipes P1 and P2 may be controlled by manually adjusting the opening of the valve 23 while checking the attitude of the welding torch 41 and the pressure gauge 22 .

In the above, the case where the internal pressure of the steel pipes P1 and P2 is adjusted by adjusting the opening of the valve 23 connected to the discharge line 21 has been described. However, any method may be used to adjust the internal pressure of the steel pipes P1 and P2, and the welding apparatus 1 may be provided with some pressure adjusting means. For example, the internal pressures of the steel pipes P<b>1 and P<b>2 may be adjusted by adjusting the opening degrees of the regulator 13 and the valve 15 .

The configuration of the welding apparatus and the manufacturing method of the austenitic stainless steel pipe welded joint according to one embodiment of the present invention have been described above. According to this embodiment, it is possible to obtain an austenitic stainless steel pipe welded joint having a welded portion in which depressions on the front and back surfaces are suppressed over the entire circumference.

EXAMPLES The present invention will be described in more detail below with reference to examples. The invention is not limited to these examples.

% by mass, C: 0.03%, Si: 0.4%, Mn: 4%, Ni: 12%, Cr: 22%, Mo: 2%, Nb: 0.2%, N: 0.3 %, V: A steel containing 0.2% was melted to produce an ingot. The produced ingot was subjected to hot forging, hot rolling, heat treatment and machining to produce a steel plate having a thickness of 15 mm, a width of 110 mm and a length of 300 mm. A steel pipe having an outer diameter of 9.53 mm, a wall thickness of 2.3 mm, and a length of 100 mm was produced from this steel plate by hollowing. An I groove was applied to the end of the steel pipe.

The produced steel pipes were butted against each other and welded 1.5 turns by automatic GTAW without using a welding material to produce a welded joint. Argon gas was used as both the shield gas and the back shield gas. During welding, 1.5 turns of the steel pipe in the circumferential direction were divided into 5 to 9 regions, and the internal pressure and current supplied to the welding torch were changed for each region. In each case, welding was started from a position where the tip of the welding torch faced the horizontal direction, and then the welding torch was rotated toward the bottom of the steel pipe (same as explained using FIGS. 3A to 3C). Table 1 shows the current and internal pressure set in each region.

The produced welded joint was cut at 45° intervals in the circumferential direction, and eight vertical cross sections were observed with a stereoscopic microscope to observe the size of the recesses on the front and back surfaces of the welded portion. The size of the largest dent in the eight longitudinal sections observed was defined as the "maximum amount of dent."

A tensile test was performed on each welded joint. Specifically, each welded joint was cut to a length of 100 mm and subjected to a tensile test at room temperature in a tubular form.

Table 2 shows the maximum dent and tensile strength of each welded joint.

The welded joints of test numbers J1 to J6 were manufactured by changing the internal pressure based on the attitude of the welding torch during welding. These welded joints had no weld defects, had a maximum weld recess of 30 μm or less, and had a tensile strength of 690 MPa or more at room temperature.

The welded joint of test number J7 had a maximum recession of more than 30 μm. It is considered that this is because the internal pressure during welding was kept constant.

Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the scope of the invention.

Claims (4)

A method for manufacturing an austenitic stainless steel pipe welded joint, comprising:
A step of performing gas-tungsten-arc welding in the circumferential direction from the outside using a welding torch while supplying back shield gas to the inside of a pair of steel pipes whose ends are butted against each other,
changing the internal pressure of the pair of steel pipes based on the attitude of the welding torch ;
A method for producing an austenitic stainless steel pipe welded joint, wherein the produced welded joint for austenitic stainless steel pipe does not have a dent of 30 μm or more on the front and back surfaces over the entire circumference of the welded part, and has a tensile strength of 690 MPa or more . A method for manufacturing an austenitic stainless steel pipe welded joint according to claim 1,
A welded joint for austenitic stainless steel pipes, wherein the internal pressure of the pair of steel pipes when the tip of the welding torch is oriented downward is greater than the internal pressure of the pair of steel pipes when the tip of the welding torch is oriented in another direction. manufacturing method. A method for manufacturing an austenitic stainless steel pipe welded joint according to claim 1 or 2,
A method for manufacturing an austenitic stainless steel pipe welded joint, wherein the internal pressure of the pair of steel pipes is 0.1 to 0.9 kPa. A method for manufacturing an austenitic stainless steel pipe welded joint according to any one of claims 1 to 3 ,
A method for manufacturing an austenitic stainless steel pipe welded joint, wherein the magnitude of the current supplied to the welding torch is changed based on the elapsed time from the start of welding.

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