JPH0562026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for circumferential welding of pipes, and particularly to prevention of oxide film formation on the inner surface of the pipe.

[Prior Art] In piping where pipes are butted together and joined by circumferential welding, such as hydraulic piping, cooling water piping, etc.
In order to prevent damage to equipment that uses piping, it is necessary to remove the oxide film on the inner surface of the pipe at the welded part after welding.

Conventionally, welded pipes were pickled to remove the oxide film on the inner surface of the pipes after welding.

[Problems to be Solved by the Invention] When removing the oxide film from the inner surface of a tube in the above-mentioned conventional method, a pickling step was required after welding, which caused a problem in that the efficiency of the work process was reduced.

This invention has been made to solve these problems, and its purpose is to propose a circumferential welding method for pipes that prevents the formation of an oxide film on the inner surface of the welded pipe during welding. be.

[Means for Solving the Problems] The method for circumferential welding of pipes according to the present invention, when welding pipes together by circumferential welding, sets the oxygen concentration in the inner part of the pipe to 50 to 200 ppm, and It is characterized by maintaining the pressure inside the pipe at 1 mmAq or less.

[Function] In the present invention, the oxygen concentration inside the tube is reduced during circumferential welding of the tube, thereby preventing the formation of an oxide film on the back corrugated portion of the inner surface of the tube during welding.

[Embodiment] Fig. 1 is an explanatory diagram showing an embodiment of the present invention. In the figure, 1a and 1b are pipes whose ends are butted and welded, and the pipes 1a and 1b are line-up clamps (not shown). ) is used for centering.
2 is a groove with a predetermined gap provided at the welded portion of the pipes 1a and 1b; 3 is a closing lid attached to the end of one of the tubes 1a by a clamp mechanism (not shown); 4 is a closing lid 3 The inert gas supply pipe 5 attached to the inert gas supply pipe 5 is an inert gas cylinder to which the tip of the inert gas supply pipe 4 is connected. 6 is a closing lid attached to the end of the other tube 1b, 7 is an electrode provided on the welding head, and 8 is a wire. 9 is the closing lid 6
The valve 10 attached to the valve 9 is an oxygen concentration meter attached to the diffusion tube of the valve 9 via a probe.

When arranging the pipes 1a and 1b to be welded as described above and welding oil well piping, for example, first open the valve of the inert gas cylinder 5, and then
Supply inert gas inside. At this time, groove 2
The gap is covered with heat-resistant adhesive tape 11 from the outside. Then, the valve 9 is opened, the probe of the oxygen concentration meter 10 is inserted into the diffusion pipe section, and the oxygen concentration within the pipe is measured.

When the pointer of the oxygen concentration meter 10 stabilizes within 50 to 200 ppm, the heat-resistant adhesive tape 11 is peeled off by about 50 to 70 mm, and an arc is generated from the electrode 7 on the groove 2.
Welding is performed in all positions along the entire circumference of the groove 2 while feeding the wire 8, or in one position by rotating the tube. At this time, if the heat-resistant adhesive tape 11 is not welded while being gradually peeled off, the oxygen concentration will be 50~
Care must be taken as it is not stable within the 200ppm range.

The pressure inside the pipe, the flow rate of inert gas, and the appropriate gap during welding greatly affect the quality and quality of welding. Second
An example is shown in the figure, in which the supply pipe is a 200A steel pipe, the welding method is TIC welding, and the gap is 3mm.
This figure shows the range of good welding when the peeling length of the heat-resistant adhesive tape is 100 mm and the nominal diameter of the valve 9 is 50 mm. From FIG. 2, the pressure inside the pipe is within 1 mmAq, and the inert gas flow rate n10 ¹⁹ P/T (1) is in a good range of 50 to 200/min. If the pressure inside the pipe is more than 1mmAq, it will be difficult to start the arc of TIG welding, and if it is less than 50/min, the shielding will be poor and the Uranami will oxidize. And 200/min
If this is the case, care must be taken as problems such as difficulty in generating back waves will occur when the gap is closed during welding in the first layer.

[Effects of the Invention] As explained above, this invention makes the oxygen concentration in the Uranami part about 50 to 200 ppm and the pressure inside the pipe to 1 mmAq.
Since the pipes are welded with the pipes maintained at , it is possible to improve the efficiency of the work process.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention;
The figure shows the correlation between inert gas flow rate and pipe pressure in a 200A steel pipe. 1a, 1b...Pipe, 2...Bevel, 3, 6...Closing lid, 4...Vacuum piping, 5...Vacuum pump, 7...
...Electrode, 8...Wire.

Claims (1)

[Claims] 1 Circumferential welding of pipes, which is characterized by butt welding between pipes, in which the oxygen concentration in the inner part of the pipe is maintained in the range of 50 to 200 ppm, and the pressure inside the pipe is maintained at 1 mmAq or less. Method.