JPS599269B2 - Fixed tube circumferential arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixed tube circumferential arc welding method in which the fixed tube to be welded is welded in all circumferential positions by the so-called "TIG welding method."

Conventionally, in circumferential welding of this type of fixed pipe, especially when the fixed pipe to be welded is a small diameter pipe with an outer diameter of 30 m/m or less, and due to the structure of the pipe to be welded, welding can only be done from the inner surface. The "TIG automatic welding method" is used. This "TIG automatic welding method" will be explained with reference to FIG.

1 is a tube plate, 2 is a fixed tube to be welded to the tube plate 1, and 3 is a tungsten electrode for generating an arc 6 between the base metal and the base metal in order to weld the fixed tube 2 and the tube plate 1 together. , 4 is an electrode holder, and 5 is an insulating collar.

However, the inner diameter of the fixed tube 2 is often less than 25 m/m, and due to the structure of the welding torch, it is not possible to insert a filler fire or the like. Therefore, non-filler wire welding is inevitably required, but in such a case, the inner bead (
It is difficult to form both the front bead (front bead) and the outer bead (uranami bead) into a convex shape. In general, this type of weld zone melts and solidifies, so if the molten metal is in a downward position and there is a backing material, the molten metal will shrink as it solidifies and the second
In order to pull the base material on both sides as shown by the arrow 10 in Figure b,
Even in the case of non-filler wire welding, it is possible to form a convex shape on both sides. This state is shown in FIGS. 2a and 2b. In addition, in FIGS. 2a and 2b, 7 is a backing material, 8 is a weld metal, and 9 is a welded material. However, as mentioned above, in welding fixed diameter pipes, the second
Since it is difficult to use the backing material 7 as shown in Figures a and b, the surface tension of the molten metal and the adhesion force with the solid surface support gravity and solidify at a balanced position. As shown in FIGS. 2a and 2b, both sides of the weld bead are not convex, and generally the bead on the outer surface of the tube is concave in the upper part of the tube, and the bead on the inner surface of the tube in the lower part of the tube is likely to be concave. This tendency becomes more pronounced as the wall thickness of the fixed pipe to be welded increases, and this condition is more likely to occur when the wall thickness of the fixed pipe is 1.5 mm or more, and when the wall thickness is 1.5 m/m or less. In this case, the influence of gravity is small and there is no problem in welding. Examples of the above-mentioned problematic weld bead are shown in Figures 3a, b, and c. Figure 3b is a cross-sectional view taken along line AA' of Figure 3a(7), and Figure 3c is a cross-sectional view taken along line AA' of Figure 3a(7). Figure 3 is a cross-sectional view taken along the line AOB-B', which shows that the bead on the outer surface of the tube is depressed in the upper part of the tube, and the bead on the inner surface of the tube is depressed in the lower part of the tube.To prevent this situation, Various efforts have been made to stably form a molten pool to an appropriate size by, for example, controlling heat input. was not obtained.

The present invention has been made with attention to this point, and an object thereof is to provide a novel heat input control means for stably controlling the formation of a molten pool to an appropriate size.

In general, the shape of the molten pool 11 in non-filler wire welding has a cross-sectional shape as shown in FIG. 4 in the case of TIG@ welding.

In other words, Fig. 4a shows a case where the melt has not reached the back surface, and in this case, the hot water is inevitably held well, and depending on the diameter of the molten pool 11 and the depth of penetration, it drips in various positions. is less likely to occur. However, as shown in Fig. 4b, when the melt reaches the back side, the bottom of the molten metal is exposed and the retention of the molten metal is poor, and depending on the diameter of the molten pool 11, the pipe thickness, etc. Easy to melt off. Also, when comparing a stationary arc, that is, a molten pool formed when the electrode is stationary, and a moving arc, that is, a molten pool that is formed when the electrode is moving, the stationary arc has a higher flow of molten metal. Good retention. In the case of a moving arc, a flow 13 of the molten metal occurs within the molten pool 11, as shown in FIG.
This makes it difficult to retain hot water. This invention has been made with attention to the above-mentioned properties, and is intended to perform welding while maintaining the best possible retention of hot water.

That is, assuming that the maximum wall thickness of a pipe that can be welded by TIG non-filler wire is 5 to 6 m/m, the width of the surface bead formed when melting these wall thicknesses in one bath is several meters/m/m.
Let it be m.

In this case, the electrode is moved intermittently in order to continuously form an instantaneous uranami bead with a diameter of 3 to 5 m/m when the uranami bead is formed slightly. This movement distance is up to 3m
/m is desirable. Then, the circumference of the fixed tube to be welded is divided into 30 to 48 equal parts, and the time taken for the electrode to move through each equal part is set to be the same. That is, when forming a molten pool, the tube is melted with a predetermined high-level melting current while the electrode remains stationary, and at the moment when the back side is melted, the melting current is switched to a lower level to solidify the molten pool. , while moving the welding torch. The amount of movement of this welding torch {well, the first division is one division, and the number of divisions is set so that the amount of movement is about 1 to 3 m/m in consideration of the diameter of the Uranami bead. Therefore, as shown in FIG. 6, the arc welding method according to the present invention uses a two-stage pulsating current of high level and low level, and synchronizes this pulsating current with the period of intermittent transition of the electrode. , Moreover, the formation of a molten pool is determined by the stop time of the electrode, that is, the time when a high level current is flowing, "Tlj (1'), and the heat input limit for heat accumulation in the circumferential direction is defined as this time [T1]. , with a high level welding current "Ip", and this "T1" and [Ip
] according to a preset program'1
11 shall be sold wholesale.

Since the purpose of the low-level welding current [B] is to solidify the molten pool, it is set to be low enough to maintain a minimum arc without causing shrinkage cracks in the weld. Further, although the above-mentioned "T1" and "P" are mainly controlled by "T1", it was found that it was more effective to slightly change "Ip" in the latter half of welding. The program at this time preferably controls "T1" or "P" or both, as shown in the characteristic curve shown in FIG. The characteristic curve shown in FIG. 7 is determined by the material, pipe diameter, pipe wall thickness, and electrode tip shape, and is a heat input balance characteristic curve in the case of circumferential pass welding of the pipe. As mentioned above, the arter welding method of this invention melts the back surface of the tube in a static arc state, and when the back surface begins to melt, this unstable state is quickly resolved.
The welding current is lowered, and the electrode is moved during this time to melt the metal again with a stationary arc. This reduces the unstable flow of the molten pool to the tenacity, resulting in stable circumferential single-sided welding of fixed pipes. It has an excellent effect that enables

In addition, although the above-mentioned embodiment described welding the circumference of the tube from the inner surface, it goes without saying that the same effect can be obtained even when electrodes are arranged on the outer surface of the tube (1).

In addition, in order to carry out the arc welding method of the present invention more effectively, the heat input equivalent to the curve A part in FIG. The inventive welding method can also be improved by changing the pipe material, pipe diameter,
Needless to say, this is necessary depending on the wall thickness.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing a conventional welding method for a tube plate and a fixed tube.
Figures 2A and b are explanatory diagrams of weld bead formation when there is a backing material during non-filler wire welding, and Figures 3A and b
, c is an explanatory diagram of weld bead formation that occurs when welding the inner circumferential surface of a pipe, Figures 4A and b are explanatory diagrams of a molten pool during non-filler wire welding, and Figure 5 is an explanatory diagram of a molten pool of a stationary arc and a moving arc. FIG. 6 is a time chart of synchronization of pulsating current and electrode intermittent transition and heat input control, and FIG. 7 is a basic characteristic curve diagram of heat input control program setting. In the drawings, 1 is a tube plate, 2 is a fixed tube, 3 is an electrode, 6 is an arc, 8 is a weld metal, 9 is a welded material, 11 is a molten pool, and 12 is a welding pipe! It is de.

Claims (1)

[Claims] 1 A pulsating current with two levels, high and low, is used as the welding current, and the movement of the non-consumable electrode that moves along the circumference of the fixed pipe to be welded is intermittent movement, and when the current is high, the electrode stops, and when the current is low, When the electrode moves, the pulsating current and the intermittent movement of the electrode are synchronized, and heat input control is performed only during times when high current is flowing and at a high current level, so that the amount of electrode movement is always constant. A fixed tube circumferential arc welding method characterized by: