JP3773631B2 - TIG welding method for stainless steel pipe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a TIG welding method for joining circumferential joints of austenitic stainless steel pipes, and particularly to improvement of welding efficiency.
[0002]
[Prior art]
Welding of the pipe ends at the pipeline laying site of austenitic stainless steel pipes, after applying groove processing to the pipe ends of both pipes to be joined, with both pipes abutted and fixed with an internal clamp or the like, This is done by all-position welding along the circumferential joint formed. The all-position automatic welding method is adopted to save labor in the welding work and stabilize the welding quality. The problem with all-position automatic welding of this austenitic stainless steel pipe is that even if an attempt is made to secure a good back wave by providing a root interval, the root interval fluctuates due to heating during welding and a stable back wave cannot be obtained. It is. In particular, in an austenitic stainless steel pipe, the thermal conductivity is as small as about 1/3 that of carbon steel and the thermal expansion coefficient is as large as about 1.5 times that of carbon steel. For this reason, for the austenitic stainless steel pipe, in order to be able to ignore the shrinkage of the root interval during welding, for example, as shown in FIG. 4, a U-shaped groove 41 having a groove angle α of 30 degrees to 60 degrees. Is formed by machining, and TIG automatic welding is adopted with a route interval of 0 mm as standard. In this case, in order to obtain a good back wave over the entire circumference, the thickness t ₀ of the root surface is set to 1.0 mm to 1.5 mm, and the width w of the root surface is set to 2.0 mm to 3.0 mm. The first layer back wave welding is performed by this method.
[0003]
Further, for example, the joint joint method of a fixed pipe described in JP-A-9-19767 is a V-shaped groove having a groove angle α of 90 degrees to 110 degrees and a route interval of 0 mm to 0.5 mm. It is the method of joining with a wire-type TIG automatic welding apparatus. This welding method is characterized by a V-shaped and wide-angle groove that is easy to groove, and with a hot wire type TIG automatic welding device that is heated by energizing the filler wire, with a route interval of 0 mm to 0.5 mm. It is in the point that the fluctuation of can be ignored. That is, this method reduces the substantial thickness of the root portion by widening the groove angle α to 90 to 110 degrees in order to ensure the melting of the root portion and ensure a good back wave, By heating the wire with electric resistance, the thermal efficiency of the arc for the welding of the root portion is increased.
[0004]
[Problems to be solved by the invention]
As described above, the TIG welding method with the U-shaped groove 41 having a root interval of 0 mm can ignore the fluctuation (shrinkage) of the root interval, but the groove shape is complicated and high-precision management is required for the machining dimensions. For this reason, a dedicated groove processing machine was required. For this reason, equipment costs will become expensive. Pipelines are not only straight pipes that are easy to beveled, but fittings such as elbows are used everywhere, but these are difficult to hold and fix when machining due to shape problems, and have high precision. The groove processing is difficult, and the application range of TIG automatic welding is limited.
[0005]
In addition, pipe ends that are grooved for U-shaped grooves have a high risk of damage during pipe transportation and butt centering operations, and pipe end protection and work management must be carefully performed. The management was not easy. In addition, once damaged, it could not be corrected by a simple method such as a grinder, which caused problems on site construction.
[0006]
Further, in the welding method described in Japanese Patent Laid-Open No. 9-19767, the V-shaped angle of the V-shaped groove is greatly expanded from 90 degrees to 110 degrees, so that the groove sectional area increases and the number of weld layers increases. Therefore, it takes a lot of time for the welding work. For example, if a U-shaped groove with a groove angle of 40 degrees is used for the same plate thickness of 7 mm, as shown in FIG. 5, the four-layer finish is used, but a V-shaped groove with a groove angle of 100 degrees is used. If the tip is used, it will be a five-layer finish. Furthermore, as shown in the change characteristic chart of the tube thickness and the groove cross-sectional area of FIG. 6, the increase in the groove cross-sectional area of the V-shaped groove having a groove angle of 100 degrees increases the thickness of the pipe. As the number of weld layers increases, the number of weld layers increases as compared with a U-shaped groove having a groove angle of 40 degrees.
[0007]
Furthermore, since the welding method described in Japanese Patent Application Laid-Open No. 9-19767 employs hot wire type TIG welding for the first layer, wire heating equipment is required, and an energizing terminal is provided near the torch for heating. Since the cable is installed, not only the equipment cost becomes expensive, but also the structure of the torch part becomes complicated and the cable processing during welding becomes troublesome.
[0008]
An object of the present invention is to provide a TIG welding method for a stainless steel pipe which can efficiently form a high-quality welded joint with simple equipment to improve such disadvantages.
[0009]
[Means for Solving the Problems]
In the TIG welding method for stainless steel pipes according to the present invention, the end faces of austenitic stainless steel pipes to be joined together have a V-shaped angle in the range of 65 to 80 degrees and the thickness of the root surface in the range of 0.1 to 1.5 mm. Groove processing is performed to form a V-shaped groove, the pipe ends are butted so that the root interval is in a range of 0 mm to 2.0 mm, and the depth of the abutted pipe end is deep inside the V-shaped groove. While fixing a backing having a groove with a width of 0.5 mm to 1.5 mm and a width of 10 mm to 40 mm, and supplying argon gas mixed with 1 to 7% hydrogen gas from a welding gas nozzle, V type TIG automatic welding is performed along the groove.
[0010]
Further, it is desirable to supply a back shield gas from the backing to the inner surface of the V-shaped groove.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the TIG welding method for a stainless steel pipe of the present invention, argon gas mixed with 1 to 7% hydrogen is used as a shielding gas, and the arc is converged to increase the energy density of the arc. Here, the reason why the hydrogen gas mixing ratio of the shielding gas is set to 1 to 7% is that the arc convergence effect is obtained from the hydrogen gas mixing ratio of the shielding gas of 1%, and the austenite type when the hydrogen gas mixing ratio of the shielding gas is 7%. This is because stainless steel is not a problem in terms of joint quality.
[0012]
In this case, the groove dimensions of the V-shaped groove are a root surface thickness t ₀ of 0.1 mm to 1.5 mm, and an appropriate range of the V-shaped angle is 65 degrees to 80 degrees. In other words, if the V-shaped angle exceeds 80 degrees, the required amount of deposited metal increases and the efficiency is inferior, and the back wave tends to dent in an upward orientation, and if the V-shaped angle is narrower than 65 degrees, it melts into the root part. Since defects are likely to occur, the appropriate groove angle range is set to 65 to 80 degrees.
[0013]
Further, by fixing a backing having a groove with a depth d in the range of 0.5 mm to 1.5 mm and a width w _{1 in} the range of 10 mm to 40 mm inside the V-shaped groove, the molten metal is removed from the TIG arc. Hold and cool on the back side to ensure a uniform back wave in all positions. By this backing, the dimensional tolerance of the root interval of the V-shaped groove was expanded to 0 to 2.0 mm, and good welding could be performed.
[0014]
Further, by supplying the back shield gas from the backing, the back wave is prevented from being oxidized, the quality of the back wave is improved, and a better quality welded joint can be formed.
[0015]
【Example】
FIG. 1 is a sectional view showing a groove shape according to an embodiment of the present invention. As shown in the figure, when the austenitic stainless steel pipes 1a and 1b having a thickness t are abutted and joined, the V-type angle α is in the range of 65 to 80 degrees, and the root surface thickness t ₀ is 0.1 to 1.5 mm. The tube ends of the tubes 1a and 1b are grooved so as to form a V-shaped groove having a range of mm. The V-shaped groove 2 is formed by butting the pipe ends of the pipes 1a and 1b that have been grooved so that the root interval L is in the range of 0 mm to 2.0 mm. A backing 4 having a groove 3 having a depth d in the range of 0.5 mm to 1.5 mm and a width w _{1 in} the range of 10 mm to 40 mm is fixed by an internal clamp device 6 having a plunger 5 inside the V-shaped groove 2. To do.
[0016]
The pipes 1a and 1b are welded by a TIG automatic welding apparatus. As shown in FIG. 2, the TIG automatic welding apparatus supplies an argon gas mixed with 1 to 7% of hydrogen from the welding gas nozzle 12 of the welding torch 11 as a shielding gas, and between the tungsten electrode 13 and the stainless steel pipe. In the cold wire method in which an arc 14 is generated in the wire 14 and no electric heating is performed by a wire feeding device 18 having a wire reel 15, a wire feeding motor 16 and a wire feeding roller 17. The V-shaped groove 2 is filled and welded while melting and feeding. The welding torch 11 and the wire feeding device 18 are mounted on a welding carriage (not shown), rotate in one direction while traveling on a guide rail provided along the outer periphery of one pipe 1b, and have a V-shaped groove over all positions. Automatic welding is performed so as to fill 2. On the welding carriage, there is a biaxial drive mechanism that can move the welding torch in the pipe axis direction and the pipe radial direction. The operation of these drive shafts, the welding current, the welding voltage, the wire feed speed, and the like are controlled by a control device (not shown). In FIG. 2, 21 is a welding power source, and 22 is a gas supply device.
[0017]
The reason for using the argon gas mixed with 1 to 7% hydrogen as the shielding gas as described above and determining the conditions of the V-shaped groove 2 will be described.
[0018]
In TIG welding generally used, argon gas is used as a shielding gas. When the root distance is set to 0 mm with this shielding gas, a groove of about 100 degrees is used in the same manner as the welding method disclosed in Japanese Patent Laid-Open No. 9-19767 in order to ensure a good back wave with a V-shaped groove. An angle is required. This is because if the groove angle is smaller than about 100 degrees, molten metal is formed on the outer surface side of the tube and the root portion remains undissolved. Further, if the welding heat input is increased to melt the root portion, excessive melting occurs in an upward posture, and the back wave becomes concave, so that a good weld joint cannot be obtained.
[0019]
On the other hand, when argon gas in which hydrogen gas is mixed with the shielding gas is used, the arc is converged and the energy density of the arc is increased. When the arc is converged, the potential gradient of the arc changes, and when argon gas is actually mixed with 3% hydrogen, the arc voltage increases by 1.0V to 1.2V at the same arc length when compared with 100% argon gas. Confirmed to do. Various welding conditions were set in consideration of the increase in the arc energy density, and welding experiments were conducted. As a result, a shield gas in which 1 to 7% hydrogen gas is mixed with argon gas is used, the thermal energy of the TIG arc is converged, and the root portion is good even with the V-shaped groove 2 having a V-shaped angle smaller than 100 degrees. It was confirmed that a good back wave was obtained in all positions. Here, the reason why the hydrogen gas mixing ratio of the shielding gas is set to 1 to 7% is that the arc convergence effect is obtained from the hydrogen gas mixing ratio of the shielding gas of 1%, and the austenite type when the hydrogen gas mixing ratio of the shielding gas is 7%. This is because stainless steel is not a problem in terms of joint quality.
[0020]
In this case, the groove size of the V-shaped groove 2 is 65 to 80 degrees when the root surface thickness t ₀ is 0.1 mm to 1.5 mm. If the V-shaped angle α exceeds 80 degrees, the amount of required metal to be deposited increases and the efficiency is inferior, and the back wave tends to dent in an upward posture. Further, if the V-shaped angle α is narrower than 65 degrees, a poor penetration is likely to occur in the root portion. Therefore, 65 to 80 degrees was determined as a proper range of the groove angle α.
[0021]
Further, by fixing a copper or ceramic backing 4 having a groove 3 with a depth d in the range of 0.5 mm to 1.5 mm and a width w _{1 in} the range of 10 mm to 40 mm inside the V-shaped groove 2, melting is performed. The finished metal could be held and cooled on the back side of the TIG arc, and a uniform back wave could be secured in all positions. Furthermore, with this backing 4, the dimensional tolerance of the route interval L of the V-shaped groove 2 was expanded to 0 to 2.0 mm, and good welding could be performed. By pressing the backing 4 from the inner surface of the tube in this way, it is possible to secure a good back wave that only slightly oxidizes without supplying the back shield gas, but further prevents the back wave from being oxidized. In order to improve the back wave quality, a gas supply hole is provided in the backing 4 and the internal clamp device 6, and if TIG automatic welding is performed while a back shield gas such as argon gas is supplied from the gas supply hole, a better quality welded joint is obtained. Can be formed.
[0022]
[Specific example] For example, a specific example in the case of welding the circumferential joint of the pipes 1a and 1b having a pipe diameter of 300A of austenitic stainless steel (SUS304) and a plate thickness t = 6.5 mm will be described.
[0023]
The tubes 1a and 1b are formed so as to form a V-shaped groove in which the V-shaped angle α of the V-shaped groove 2 shown in FIG. 1 is 70 degrees and the thickness t ₀ of the root surface is in the range of 0.5 mm to 1.5 mm. The edge is grooved. The V-shaped groove 2 is formed by butting the pipe ends of the pipes 1a and 1b that have been grooved so that the root interval L is in the range of 0 mm to 2.0 mm. A backing 4 having a groove 3 having a depth d of 1.0 mm and a width w ₁ of 15 mm inside the V-shaped groove 2 is fixed by an internal clamp device 6, and the TIG automatic welding device shown in FIG. As a shielding gas, a mixed gas of 3% hydrogen and 97% argon gas is used, and with JIS Z 3321 Y308L 1.0mm welding wire, the average welding current is 110-150A, and the average wire feed speed is 110- Welding was performed under a welding condition of 160 cm / min and a welding speed of 70 to 100 mm / min. The number of weld layers at this time was finished in two layers as shown in FIG. After welding, visual inspection and X-ray inspection were conducted as non-destructive inspection, but both the inner and outer surfaces had a good appearance, and no harmful defects were generated inside the joint. In addition, a tensile test and a bending test were performed as mechanical tests. In the tensile test, a strength higher than that of the base material standard was obtained, and in the bending test, good joint performance could be obtained without generation of defects.
[0024]
【The invention's effect】
As described above, the present invention uses argon gas mixed with 1 to 7% hydrogen as a shielding gas and converges the arc to increase the energy density of the arc, so there is no need to heat the wire. The structure of the welding apparatus can be simplified.
[0025]
In addition, by using a V-shaped groove on the circumferential joint, it is possible to easily perform groove processing for fittings such as straight pipes and elbows on-site without using a special machine, thereby reducing welding costs. Can do.
[0026]
Furthermore, by reducing the V-shaped angle of the V-shaped groove to 65 degrees to 80 degrees, the amount of deposited metal required can be reduced, and the welding efficiency can be increased.
[0027]
In addition, the molten metal is held behind the TIG arc by fixing a backing having a groove with a depth of 0.5 mm to 1.5 mm and a width of 10 mm to 40 mm inside the V-shaped groove. , Cool, ensure a uniform back wave in all postures, can perform good welding.
[0028]
In addition, the dimensional tolerance of the root spacing of the V-shaped groove is expanded to 0 to 2.0 mm, the V-shaped angle is narrow, and the arc energy density using a shielding gas of argon gas mixed with 1 to 7% hydrogen. Therefore, circumferential welding of an austenitic stainless steel pipe having a large route interval variation can be reliably performed.
[0029]
Further, by supplying the back shield gas from the backing, the back wave is prevented from being oxidized, the quality of the back wave is improved, and a better quality welded joint can be formed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a groove shape according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a TIG automatic welding apparatus.
FIG. 3 is a cross-sectional view showing the number of weld layers according to the embodiment.
FIG. 4 is a cross-sectional view showing a conventional U-shaped groove.
FIG. 5 is a cross-sectional view showing the number of weld layers of a U-shaped groove of a conventional example.
FIG. 6 is a graph showing changes in the plate thickness and groove cross-sectional area of the tube.
[Explanation of symbols]
1 Austenitic stainless steel pipe 2 V-shaped groove 4 Backing

Claims (2)

A groove is formed at the ends of the austenitic stainless steel pipes to be joined to each other so that a V-shaped groove having a V-shaped angle in the range of 65 to 80 degrees and a root surface thickness in the range of 0.1 to 1.5 mm is formed. Apply the processing, but the tube ends are butted so that the root interval is in the range of 0 mm to 2.0 mm,
A backing having a groove with a depth in the range of 0.5 mm to 1.5 mm and a width in the range of 10 mm to 40 mm is fixed to the inside of the V-shaped groove at the end of the butted tube,
A TIG welding method for a stainless steel pipe, characterized in that TIG automatic welding is performed along a V-shaped groove while supplying argon gas mixed with 1 to 7% hydrogen gas from a welding gas nozzle. The TIG welding method for a stainless steel pipe according to claim 1, wherein a back shield gas is supplied from the backing to the inner surface of the V-shaped groove.

Images