JPH0745113B2 - Laser welding method for pipe inner surface - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for welding a pipe inner surface by a laser, which is applied to repair a steam generator heat transfer tube in a nuclear power plant or a heat transfer tube of a general heat exchanger. .

[Prior Art] A conceptual diagram of a steam generator heat transfer section used in a nuclear power plant is shown in FIG. In FIG. 2, the steam generator barrel 1
There is an inlet nozzle 2 into which the primary coolant of the nuclear reactor, that is, high-temperature water, flows into the lower part of After passing through and exchanging heat with the extra-pipe water, the exit nozzle 5 returns to the reactor. The water supply is supplied from the water supply nozzle 6, descends, flows upward on the outer surface of the heat transfer tube 4, rises while exchanging heat with the high-temperature water as described above, and is discharged as steam 7. The heat transfer tube 4 is supported by the support plate 8 at several points in the axial direction.

When the heat transfer tube 4 is damaged by corrosion or vibration, it is repaired. One of the repair methods is a sleeve repair method, and the principle thereof is shown in FIG. Damaged part 9 of heat transfer tube 4
A tubular repair member, that is, the sleeve 10 is inserted so as to cover the above, and the upper and lower portions thereof are fixed by the welded portion 11. Various methods are adopted for the fixing method.

[Problems to be solved by the invention]

Since the heat transfer tube as described above is a tube with a general small diameter, when trying to weld and fix the sleeve with a general laser welding device, the tip optical system and the reflection mirror approach the welded part, so it occurs during welding. Spatters and fumes that adhere to the tip optical system deteriorate optical performance (lens transmittance, reflection mirror reflectance, etc.). In addition, when laser welding the inner surface of a small-diameter tube, the diameter of the tube that contains the condensing optical system and the reflection mirror used for this is also small, and water cooling is not possible, resulting in insufficient cooling of the optical system and overheating. And so on
There is a problem that the quality of welding varies and welding defects easily occur.

Therefore, the present invention provides a high-quality laser tube inner surface welding method in which cooling is not performed, overheating does not occur in the laser light transmission system, and contamination by spatter or fume does not occur in the laser light transmission system. To aim.

[Means for solving problems]

In order to achieve the above object, the method for welding a pipe inner surface according to the present invention is to guide a laser beam in an elongated tube by an optical fiber to advance the laser beam in the longitudinal direction, to focus the laser beam through a condensing optical system, and to a reflecting mirror. When the laser beam is reflected and deflected outward in the radial direction and laser welding is performed on the inner surface of the pipe, cooling gas is guided in parallel with the laser light to cool the condensing optical system and the reflecting mirror, and adjacent to the welded portion. It is characterized by forming a curtain of cooling gas.

[Action]

Laser light travels through an optical fiber in an elongated tube,
The light is condensed by the condensing optical system and then reflected by the reflecting mirror to focus on the welded portion on the inner surface of the pipe. The light energy of the laser light is concentrated on this focal point to increase the energy density and welding is performed. At this time, most of the cooling air is guided along with the laser light, and after cooling the optical components and the reflecting mirror of the condensing optical system, it covers the welded portion to form the air curtain portion and shields spatter and fumes. .

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 shows the structure of a welding apparatus used for carrying out the method of the present invention, and FIG. 1 (a) is a longitudinal sectional view showing the vicinity of a welded portion.
Figure (b) is a longitudinal sectional view showing the rear end portion of Figure (a).

In FIGS. 1A and 1B, an optical fiber 18 extends in the heat transfer tube 4 in the longitudinal direction, and laser light is guided from the fiber emitting portion 19 to the tip optical system 12. The guided laser light is condensed by the condensing optical system 14 and enters the reflection mirror 15. This laser light is reflected by the reflection mirror 15, changes its course by 90 degrees, passes through the emission hole 16, and forms a focal point on the welded portion 11.

The tip optical system 12 is built in the rotary cylinder 13 and
When is rotated, the focal point of the laser light moves in the circumferential direction, and a circumferential welded portion by the laser light is formed between the sleeve 10 and the heat transfer tube 4.

Spatters and fumes generated from welded parts are the tip optical system 12
If it adheres to, the function will be deteriorated, so this measure is necessary. In the present invention, a cooling gas or gas is flowed through conduit 17 extending along optical fiber 18. Gas is
The gas flows in the rotary cylinder 13 as shown by the arrow and crosses the emission hole 16 to form a gas curtain.

As a result, spatter and fumes from the weld 11 are prevented from entering the rotary cylinder 13 even though the tip optical system 12 is extremely close to the weld 11. In principle, a gas having a large molecular weight is advantageous, but an argon gas, a helium gas, or the like used as a shield gas for welding is also effective.

The above-mentioned gas is guided to the tip portion, and at that time, it is also used for cooling the tip optical system 12 as described above. A notch is formed in the periphery of each lens of the condensing optical system 14 that constitutes the distal end optical system 12 at a position facing the adjacent lens by 180 degrees, and the gas flows along each lens. In this way, the condensing optical system 14 is effectively cooled.

This gas further flows along the reflection surface of the reflection mirror 15 of the front end optical system and the spiral cooling fin 20 provided on the back surface side thereof, and is used for cooling the reflection mirror 15.

〔The invention's effect〕

As described above in detail, according to the present invention, even in a small-diameter pipe, laser light can be used to perform inner surface pipe welding without quality defects.

[Brief description of drawings]

FIG. 1 is a structural diagram of an apparatus for carrying out a laser in-pipe welding method according to the present invention. FIG. It is a longitudinal cross-sectional view showing an end portion. FIG. 2 is a vertical sectional view showing an internal structure of a steam generator to which the method of the present invention is applied, and FIG. 3 is a vertical sectional view showing a conventional heat transfer tube repairing procedure. 1 …… Steam generator barrel, 2 …… Inlet nozzle, 3 …… Tube plate, 4 ……
Heat transfer tube, 5 …… Exit nozzle, 6 …… Water supply nozzle, 7 …… Steam, 8
…… Support plate, 9 …… Break point, 10 …… Sleeve, 11 …… Welded part, 12 …… Tip optical system, 13 …… Rotating cylinder, 14 …… Condensing optical system,
15 …… Reflecting mirror, 16 …… Exit hole, 17 …… Conduit, 18 …… Optical fiber, 19 …… Fiber exit part, 20 …… Cooling fin.

Front Page Continuation (72) Inventor Takashi Ishide 2-1-1, Niihama, Arai-cho, Takasago, Hyogo Prefecture Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Shoichi Urushibata, 1-chome, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo No. 1-1 Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Masatoshi Sato 1-1-1, Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Mitsubishi Heavy Industries Ltd., Kobe Shipyard (72) Inventor Nagashima, Kobe Kobe, Hyogo Prefecture 1-1 1-1 Wadasaki-cho, Hyogo-ku, Yokohama, Kobe Shipyard, Mitsubishi Heavy Industries, Ltd. (56)

Claims (1)

[Claims] 1. A laser beam is guided into an elongated tube by an optical fiber and travels in the longitudinal direction. The laser beam is converged through a condensing optical system, reflected by a reflecting mirror and deflected radially outward. When performing laser welding on the inner surface of the pipe, cooling gas is guided in parallel with the laser light to cool the condensing optical system and the reflecting mirror, and a curtain of cooling gas is formed adjacent to the welding portion. Laser welding method for pipe inner surface.