JPS591064A - Uranami welding of fixed tube - Google Patents

Abstract

PURPOSE:To perform all position plasma welding of fixed tubes at high accuracy, by attaching a ring having sectional area larger than the thickness of fixed tubes and a step for alignment to fixed tubes so that the step protrudes from fixed tubes, and then welding them. CONSTITUTION:A ring 9C is attached to the end of fixed tubes 8A, 8B to be welded provided to arrest rotation. The ring 9C has radial sectional area larger than the thickness D of fixed tubes 8A, 8B, and steps 10A, 10B for centering are provided on the outer periphery and inner periphery respectively. The steps 10A, 10B are made to protrude from inner wall and outer wall of fixed tubes 8A, 8B. By performing plasma keyhole welding under this condition, depression of uranami of welding bead and undercut can be prevented. Dripping of molten metal can be prevented by changing welding current intermittently and alternately to high and low.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for welding fixed tubes that are non-rotatable during welding.

In general, in plasma keyhole welding, the arc penetrates to the back surface, so it is possible to weld a thicker root face in one pass than with TIG welding, and the back wave produced is also stable. However, since the molten pool is large, it is difficult to hold the molten metal in order to be usable in all positions, and the range of conditions under which welding is possible is also narrow.

In particular, when welding the keyhole 5 of the base material 1 with the plasma torch 2 in an upright upward position as shown in FIG. Because it hangs downward (behind the arc), it cannot hold the molten metal necessary to form a good bead. As a result, as shown in FIG. 1(b), an undercut 6 may be generated on the surface of the weld bead 3, and a dent 7 may be formed in the back of the weld bead 3.

The present invention aims to eliminate the above-mentioned drawbacks.
A ring having a cross section (in the radial direction) larger than the wall thickness of the fixed tube and provided with a step for center alignment on both or one of the inner and outer circumferences, the step being located on the inner and outer walls of the fixed tube. The ring is attached to a fixed tube so as to project upward, and the ring and the fixed tube are welded together by plasma keyhole welding.

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 2 (→ to (C)), 8a and 8b are fixed pipes to be welded that are non-rotatable during welding, and 9A to 9C are rings attached to each end of the pair of fixed pipes 8A and 8B. , these rings 9A to 9C have the wall thickness DJ of the fixed tubes 8A and 8B.
t) The rings 9A to 9C are formed to have a large radial cross section, and are provided with centering steps 10A and IOB on both or one of the inner and outer circumferences of the rings 9A to 9C.

The ring 9 in FIG. 8(a) has a step 10A on both end faces of its outer circumference, and this step 10A is connected to the fixed tubes 8A and 8B.
Fixed pipe 8A so as to protrude from the outer wall.

It is installed on 8B. The ring 9B shown in FIG. 8(b) is provided with a step 10B on both end faces of its inner circumference.
0B is attached to the fixed tubes 8A, 8B so as to protrude from the inner walls of the fixed tubes 8A, 8B.

The ring 9C in FIG. 8(C) is provided with a step 10A and an IOB on opposing end surfaces of its outer and inner circumferential parts, respectively, and the step 10A protrudes from the outer wall of the fixed tube 8A, and the step 10B is formed on the fixed tube 8B. Fixed pipe 8 so as to protrude from the inner wall of
It is attached to A and 8B respectively. The above step difference 10A,
The IOB can be easily provided by mechanical processing or plastic processing such as pressing.

All-position plasma welding of fixed tubes, i.e. downward.

When performing welding in upward, sideways, vertical upward movement, vertical upward movement, and intermediate positions between these positions, the steps 10A of rings 9A to 9C, as shown in FIG.
By fitting the ends of the 10BK tubes 8A and 8B, the centers of the two tubes 8A and 8B can be aligned with high accuracy. If plasma keyhole welding is performed in such a state, it is possible to prevent partial ridges protruding from the inner and outer walls of the pipes 8A and 8B of the rings 9A to 9C, dents and undercuts of the weld bead. In addition, since molten metal having a low ring temperature is supplied to the Uranami forming section, the holding force (surface tension) of the Uranami increases.

On the other hand, as a method to prevent molten metal from dripping during welding, the welding current is alternately switched between high and low current intermittently, and the molten pool that is large during high waves is partially solidified during low current. By lowering the temperature of the molten pool in this way, the molten metal in the bath can be easily held and dripping can be prevented. In this case, in plasma keyhole welding, the keyhole is formed or not formed depending on the current value, so to obtain a continuous Uranami bead,
It is necessary to set the current switching time and cycle in consideration of the welding speed.

Next, an experimental example will be explained.

For full circumference welding of a stainless steel pipe with an outer diameter of 60.5 m+ and a wall thickness of 9 m, a ring 9A having the shape shown in Fig. 2 (→) is used, and this ring 9A is attached to the pipes 8A and 8B from the inner and outer walls. Next, in the upright upward position where the most defects occur, the plasma current was 100 A, 0.311 ElO and 35 A, 0.4 (6
), the plasma gas flow rate is 3. OL/
wa, nozzle outer diameter is 3m+, shield gas component is Ar+
The weld bead observed under the conditions of 70% Ha mixed gas and a welding speed of 100 m/1 m was in good condition with no undercut and no dent in the back wave. In addition, Ring 9 varied the protruding portions toward the inner walls of the tubes 8A and 8B to a height of 0.5 to Z, Owm, and a thickness of 1 to 2 ws, but the protruding portion of the ring 9A forms a keyhole. It was completely melted by the plasma arc, and no unmelted parts remained.

As explained above, according to the present invention, in all-position plasma welding of fixed pipes, molten metal is added to the bead forming part and molten metal is Since the retention force of the pond can be increased, defects such as the undercut and the dent in the back wave can be prevented. Further, according to the present invention, there is an advantage that center positioning of the tubes can be easily and precisely performed.

[Brief explanation of drawings]

FIG. 1 (aXb) is a weld cross-sectional view and a bead cross-sectional view of a conventional fixed pipe using the Uranami welding method, and FIGS. 2 (a) to (C) are embodiments of the Uranami welding method of a fixed pipe according to the present invention. FIG. 3 is a partially cutaway view showing the temporal change in current in this embodiment. 8A, 8B--Fixed tube, 9A-9C--Ring, I
O.A. 10...step. 1st■ z121 -339-゛3f2]

Claims (1)

[Claims] 1. Having a cross section (radial direction) larger than the wall thickness of the fixed pipe,
and a ring having a step for center positioning on both or one of the inner circumference and the outer circumference is attached to the fixed tube so that the step protrudes from the inner and outer walls of the fixed tube, and the ring and the fixed tube are connected to each other. Uranami welding method for fixed tubes, which is characterized by welding by plasma keyhole welding. 2. When performing the plasma keyhole welding described above, the welding current is alternately switched to a high current that forms a keyhole and a low current that does not form a keyhole at a predetermined time and period at which the uranami bead is continuously observed. A method for welding fixed pipes according to claim 1, characterized in that: