JP2001079663A - Surface treatment method for welded structure in nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve intergranular corrosion resistance property of a nickel base alloy. SOLUTION: An end side of a nozzle pipe 28 inserted in an opening 26 of a vessel body 22 is welded to the vessel body 22 with a build-up weld metallic part 30 of a nickel base alloy and a butt welded metallic part 32 of the nickel base alloy, and Nb powder is applied on the surfaces of these structures in the nuclear reactor so that the Nb powder coating layer 44 may be formed, and the surfaces are irradiated with laser beam 58 and a molten metal is made to be the alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating the surface of a welded structure in a nuclear reactor, and more particularly to a method for treating the surface of a welded structure in a nuclear reactor which is in contact with reactor water in a nuclear reactor pressure vessel. The present invention relates to a surface treatment method for a welded structure in a nuclear reactor, which is suitable for improving interfacial corrosion.

[0002]

2. Description of the Related Art Conventionally, a reactor pressure vessel as shown in FIG. 5 has been known as a nuclear reactor. In this reactor pressure vessel, a reactor internal structure 2, various instrumentation nozzles 3, a control rod drive mechanism pipe 4, and the like are mounted in a low alloy steel pressure vessel main body 1. As shown in FIG. 6, the reactor pressure vessel is composed of a low-alloy steel pressure vessel main body 1 and a stainless steel overlay weld metal 5 constituting an inner wall surface of the reactor. An instrumentation nozzle pipe 7 is inserted into the opening 1a of the pressure vessel main body 1. And the tip side of the nozzle pipe 7
It is welded to the pressure vessel main body 1 by a build-up weld metal part 6 of a nickel-based alloy and a butt weld metal part 8 of a nickel-based alloy which have been subjected to stress relief annealing in a groove of welding.

In the prior art, as a nickel-based alloy of a weld metal portion 6 and a butt weld metal portion 8 in a groove of welding,
Welding rod ENiCr according to AWS A 5.11-76 standard
Fe-1 or ENiCrFe-3 is used. As an example of the composition of these alloys, ENiCrFe
Heat A: 0.041% by weight C;
46 wt% Mn, 72.13 wt% Ni, 14.73 wt% Cr, 8.01 wt% Fe, 2.33 wt% Nb,
0.03% by weight of Ti, and the material corresponding to ENiCrFe-3 is heat B: 0.039% by weight C, 6.32% by weight
Mn, 65.89% by weight Ni, 15.26% by weight Cr,
9.54 wt% Fe, 1.67 wt% Nb, and 0.54 wt% Ti.

[0004] However, it is clear from the test results shown in FIG. 7 that the nickel-base alloy according to the prior art has a low intergranular corrosion susceptibility due to the low Nb content.

FIG. 7 shows an improved ASTM of a nickel-based alloy.
It shows the results of the intergranular corrosion test by the G28 test, so-called sulfuric acid / ferric sulfate corrosion test. Of the materials shown in the figure, those referred to as Type 82 are AWS A5.14.
A material equivalent to ERNiCr-3 in the -76 standard, and Type 182 is a welding rod ENiCrFe-1 or ENiCrFe in the AWS A 5.11-76 standard.
−3. Further, Type 600 is an ordinary nickel-based 600 alloy. In FIG. 7, the results of the intergranular corrosion test are represented by the relationship of the amount of carbon (C), the amount of niobium, and the amount of twice as much titanium (Ti) (Nb + 2Ti) wt% in the material. The symbols in black in the figure indicate that the criterion for determining intergranular corrosion resistance was 0.5 mm / d or more, and the white symbols indicate the criterion for determining intergranular corrosion resistance 0.5 mm / d.
/ D or less.

As apparent from FIG. 7, a component region in which the value of N (= O.13 (Nb + 2Ti) / C), which is referred to as a stabilization parameter, is 12 or more is a region in which the intergranular corrosion resistance is excellent. The mechanism of the excellent corrosion resistance is that, in a nickel-based alloy, a sufficient amount of Nb fixes and stabilizes C as NbC, so that C and Cr react at the crystal grain boundaries and Cr depletion segregates. This is because there is no so-called sensitization. In addition, there is only one point of black coating data in the area where the intergranular corrosion resistance is excellent.
It contains a larger amount of Si than other heats, and may be considered an exceptional heat.

Thus, what is clear from FIG. 7 is that when the amount of C is constant, it is necessary to include a large amount of Nb in order to improve intergranular corrosion resistance. .

[0008] Further, according to the AWS A 5.11-76 standard, the type of the welding rod is ENiCrFe-1 or ENiCrFe-1.
Most of the CrFe-3 weld metal has a low Nb content, as in Heat A and Heat B, and has a stabilization parameter N (= 0.13 (Nb + 2Ti) / C) value of 12 or less in FIG. And does not have intergranular corrosion resistance. Therefore, it is considered necessary to apply some surface treatment to the nickel-base alloy welded part in contact with the reactor water.

As a surface treatment method, for example, as described in Japanese Patent Publication No. 2654235, the welding of a long housing such as an austenitic stainless steel neutron flux monitor housing fixed to a welding portion of a reactor vessel is described. It has been proposed that the surface of the inner peripheral surface within the range affected by heat is directly melted, the delta ferrite structure is precipitated here, and then the shot affected area is subjected to shot peening. .

Considering the case where this method is applied to a nickel-based alloy, the ferrite structure does not appear due to the metallurgical conditions even if the surface is melted, and the nickel-based alloy has no specific effect. Become.

As another surface treatment method, for example, as described in Japanese Patent Publication No. 2672613, an austenitic stainless steel reactor internal structure installed in reactor water in a reactor pressure vessel is disclosed. And the melting process of melting the surface of the welded part of the equipment by laser in the furnace water,
A method has been proposed in which the surface of the melted weld is treated with furnace water in accordance with a quenching step of quenching. However, even if this method is used, in the case of a nickel-based alloy that does not contain Nb, such as a weld metal, or when the Nb content is small, the intergranular corrosion resistance is reduced only by the melting step and the rapid cooling step. It cannot be improved. The reason for this is that the nickel-based alloy has a very low solid solubility of C as compared with austenitic stainless steel, and it is difficult to prevent sensitization even by cooling with water.

Further, as another surface treatment method, as described in JP-A-3-63128, a surface of a stainless steel base material is coated with Cr: 15 to 50% by weight and Ni:
5-30% by weight, Fe: 40-60% by weight, Mo: 1-
One that forms a cladding layer having a composition of 4% by weight has been proposed. According to this method, corrosion resistance can be improved. However, this technique is directed to stainless steel, and does not take into consideration the formation of a clad by focusing on Nb. Therefore, even if the above technique is used, it is not expected that the intergranular corrosion resistance of the nickel-based alloy is much improved.

[0013]

As described above, in the prior art, in a nickel-based alloy having a low C solid solubility, N
It is not considered that if the b content is low, it is not enough to secure intergranular corrosion resistance, and surface treatment technology to improve this is only applicable to austenitic stainless steel. However, no consideration is given to the treatment method for nickel-based alloys.

An object of the present invention is to provide a surface treatment method for a welded structure in a nuclear reactor, which can improve the intergranular corrosion resistance of a nickel-based alloy.

[0015]

In order to achieve the above object, the present invention provides a method for welding a welding object inserted into an opening of a reactor pressure vessel to an inner wall surface of the pressure vessel with a nickel-based alloy. When treating the surface of the welded structure formed in the pressure vessel by the above, Nb is supplied to the surface of the welded structure, and thermal energy is applied to the surface layer metal of the welded structure and the supplied Nb to provide both. And a method for surface-treating a welded structure in a nuclear reactor, characterized by melting and fusing the alloy.

In adopting the surface treatment method for a welded structure in a nuclear reactor, the following elements can be added.

(1) When applying thermal energy to the surface layer metal of the welded structure and the supplied Nb, thermal energy due to arc discharge or thermal energy due to laser light is used.

(2) When supplying Nb to the surface of the welded structure, a turbid body of powder of metal Nb and a volatile solvent is applied to the surface of the welded structure.

(3) N supplied to the surface of the welded structure
b is Nb: 4 to 20% by weight, Cr: 15 to 35% by weight,
Ni: an alloy containing 60% by weight or more.

According to the above-described means, Nb is supplied to the surface of the welded structure, and the supplied Nb is supplied to the surface layer metal of the welded structure.
b is melt-fused to form an alloy by applying thermal energy to the alloy b, so that the intergranular corrosion resistance of the nickel-based alloy can be improved, and the nickel-based alloy placed in the furnace water of the pressure vessel can be used. Damage due to corrosion of the welded structure in the reactor can be prevented beforehand, and the operation rate of the nuclear power plant can be maintained.

More specifically, as shown in FIG. 4, when the composition of the surface layer of the nickel-based alloy constituting the welded structure in the reactor is in the grain boundary corrosion susceptibility area at point A, When Nb atoms are melted in the surface layer of the composition using arc discharge or laser, the Nb content of the surface layer at point B increases. Then, Nb reacts with C present in the nickel-based alloy, fixes this C as a stable carbide at high temperature of NbC, and stabilizes the material. Therefore, in the process of cooling the molten layer on the material surface, C and Cr do not react with each other at the crystal grain boundaries to form chromium carbides. It does not decline.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a view for explaining an application step in a surface treatment method for a welded structure in a nuclear reactor according to an embodiment of the present invention. In FIG. 1, a reactor pressure vessel 20 includes a vessel body 22 made of a low alloy steel, and a stainless steel overlay welding metal 24 is welded to an inner wall surface (a surface facing the reactor water) of the body 22. . An instrumentation nozzle pipe 28 to be welded is inserted into the opening 26 of the main body 22. The tip end side of the nozzle pipe 28 is provided with a build-up weld metal portion 30 of a nickel-based alloy within the groove of the weld, then annealed after removing the stress, and thereafter, a butt weld metal portion 32 of the nickel-based alloy is removed. It is formed and welded to the nozzle pipe 28. As the nickel-based alloy of the build-up weld metal part 30 and the butt weld metal part 32 within the welding groove, the type of welding rod ENiCrFe-1 is used in accordance with the AWS A 5.11-76 standard. The alloy composition is as follows: 0.041 wt% C, 2.46 wt% M
n, 72.13 wt% Ni, 14.73 wt% Cr,
8.01 wt% Fe, 2.33 wt% Nb, and 0.03 wt% Ti.

A nozzle pipe 28 is attached to a tip side (inner wall surface) of the opening 26 with a build-up weld metal part 30 and a weld metal part 32.
After the welding structure is formed by welding in the nuclear reactor, the turbid body 34 of the Nb powder and the volatile solvent is sprayed in the application step of the turbid body of the Nb powder and the volatile solvent in the application step.
Injected from 6. The spray 36 is inserted into the nozzle pipe 28, and the end of the spray nozzle 36 is connected to a nozzle rotation driving device 38. The nozzle rotation driving device 38 includes an Nb powder coating control device 40 and a nozzle rotation driving control device 4.
2 are connected. Then, the spray nozzle 36 moves the turbid body 34 according to the driving of the nozzle rotation driving device 38.
Is sprayed toward the butt weld metal part 30 and the butt weld metal part 32, and a turbid body 34 of Nb powder and a volatile solvent is applied to the surfaces of these welded structures in the nuclear reactor. When the turbid body 34 is applied to the surfaces of these welded structures, an Nb powder coating layer 44 is formed on the surfaces of these welded structures. The average particle size of the Nb powder is 0.5 μm or less, and the thickness of the Nb powder coating layer 44 is suitably at least 5 μm.

In the step of applying the turbid body 34 of the Nb powder and the volatile solvent, Nb is made into a powder having a small particle size of 0.5 μm or less because the overlay welding metal portion 30 in the welding groove and the butt welding are used. This is for facilitating the dissolution of Nb in the molten portion of the nickel-based alloy surface layer of the metal part 32 and for facilitating the transport of Nb by a spray method.

Next, a first embodiment of the melting step in the present invention will be described with reference to FIG. In the present embodiment, a laser control drive pipe 46 is inserted into the nozzle pipe 28, and one end of the drive pipe 46 is connected to a laser mechanism drive 48,
The other end is connected to the arm 50, and the laser transmitter 52 and the mechanism drive control unit 54 are connected to the drive unit 48.
A lens / mirror storage section 56 is connected to the distal end of the laser beam 58 and a laser beam 58 is directed from the lens / mirror storage section 56 toward the welded structure.
Is irradiated.

That is, in the present embodiment, after the coating step shown in FIG. 1, the Nb powder coating layer 44 is irradiated with the laser beam 58 and the Nb powder coating layer 44 is melted by the thermal energy of the laser beam 58. A melting step is performed. When the Nb powder coating layer 44 is melted by the thermal energy of the laser beam 58, the surface melting treatment layer 6
0 is formed.

In this embodiment, the laser emitted from the laser oscillator 52 is a YAG laser, and the laser output from the laser oscillator 52 is a laser mechanism drive unit 48, a laser control drive tube 46, an arm 50, a lens mirror storage unit. 5
The laser light 58 is transmitted to the Nb powder coating layer 44 from the lens / mirror storage unit 56. The laser light is transmitted by a glass fiber. Also, Y
The conditions of the AG laser irradiation are as follows: output: 0.45 kW, pulse frequency: 30 Hz, laser irradiation speed: 1 mm / s, shielding gas: argon.

In this embodiment, the Nb powder coating layer 4
When Nb is melted by irradiating the surface layer of No. 4 with the laser beam 58, the Nb content of the welded structure surface layer increases, and Nb reacts with C present in the nickel-based alloy, fixing C as NbC. And stabilize the material. Therefore, in the subsequent cooling process of the material surface molten layer, C and C
Since r does not react to form Cr carbide, the Cr deficiency phenomenon, that is, sensitization does not occur, and the intergranular corrosion resistance does not decrease.

Therefore, according to this embodiment, it is possible to prevent damage due to corrosion of a welded structure in a reactor made of a nickel-based alloy placed in the reactor water of a pressure vessel, and to maintain the operation rate of a nuclear power plant. Can be.

Next, another embodiment of the melting step in the present invention will be described with reference to FIG.

In the present embodiment, a stainless steel housing tube 62 is inserted into the opening 26 of the container body 22, and a halfway of the housing tube 62 is overlaid with a nickel-based alloy forming the inner wall surface of the pressure container 20. A butt weld metal portion 66 made of a nickel-based alloy is welded to the metal portion 64, and a stub tube 68 is attached to a surface of the housing tube 62 that comes into contact with the reactor water. The welding is performed by the butt weld metal portion 66 of the nickel base metal and the butt weld metal portion 70 of the nickel base alloy. In this case, each nickel-based weld metal portion 64, 66
Is melted by the arc discharge 74 from the TIG torch 72. The wire supplied to the TIG torch 72 is an alloy containing Nb: 4 to 20% by weight, Cr: 15 to 30% by weight, and Ni: 60% by weight or more. A small amount of the Nb-enhanced alloy is melted into the surface layers of the butt weld metal portions 66 and 70. TIG welding conditions at this time are: average current: 50 A, arc voltage: 12 V, welding speed: 50 mm / MIN, shield gas: Ar.

The reason why the Nb content of the Nb alloy in the wire is increased is to provide a surface layer having a sufficient Nb content even if the composition is diluted in the surface layer of the nickel-base weld metal. That is, the amounts of Cr and Ni are adjusted to the composition in the surface layer of the nickel-based weld metal.

In this embodiment, the Nb powder coating layer 4
When Nb of the surface layer of No. 4 is melted by arc discharge 74, the Nb content of the surface layer of the welded structure increases, and Nb reacts with C present in the nickel-based alloy to fix C as NbC, Stabilize. Therefore, in the subsequent cooling process of the material surface molten layer, C and C
Since r does not react to form Cr carbide, the Cr deficiency phenomenon, that is, sensitization does not occur, and the intergranular corrosion resistance does not decrease.

Therefore, according to the present embodiment, it is possible to prevent damage due to corrosion of the welded structure in the reactor of the nickel-based alloy placed in the reactor water of the pressure vessel, and to maintain the operation rate of the nuclear power plant. Can be.

[0035]

As described above, according to the present invention,
Nb was supplied to the surface of the welded structure, and thermal energy was applied to the surface layer metal of the welded structure and the supplied Nb to melt and fuse the two to form an alloy. Can be improved, and damage due to corrosion of the welded structure in the reactor made of nickel-based alloy placed in the reactor water of the pressure vessel can be prevented beforehand, and the operation rate of the nuclear power plant can be maintained.

[Brief description of the drawings]

FIG. 1 is a view for explaining an Nb powder application step according to an embodiment of the present invention.

FIG. 2 is a view for explaining a melting step using a laser according to one embodiment of the present invention.

FIG. 3 is a view for explaining a melting step by arc discharge in another embodiment of the present invention.

FIG. 4 is a characteristic diagram for explaining a change in the composition of Nb in a nickel-based alloy surface layer.

FIG. 5 is a sectional view of a conventional reactor pressure vessel.

FIG. 6 is a sectional view of a main part of a welded portion of a conventional instrumentation nozzle.

FIG. 7 is a characteristic diagram showing the results of an intergranular corrosion test of a nickel-based alloy by an improved ASTM G28 test.

[Explanation of symbols]

 Reference Signs List 20 Reactor pressure vessel 22 Vessel main body 24 Stainless steel overlay welding metal part 26 Opening 28 Nozzle pipe 30 Nickel based alloy overlay welding metal part 32 Nickel based alloy butt welding metal part 34 Turbid body 36 Spray nozzle 38 Nozzle rotary drive Apparatus 40 Nb powder application control device 42 Nozzle rotation drive control device 44 Nb powder application layer 46 Laser control drive tube 48 Laser mechanism drive 50 Arm 52 Laser transmitter 54 Laser mechanism drive control 56 Lens / mirror storage 58 Laser Hikari 60 surface melting layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G21D 1/00 G21D 1/00 W

Claims (4)

[Claims] An object to be welded inserted into an opening of a reactor pressure vessel is welded to an inner wall surface of the pressure vessel with a nickel-based alloy, and a surface of a welded structure formed in the pressure vessel is treated by the welding. In the nuclear reactor, Nb is supplied to the surface of the welded structure, and thermal energy is applied to the surface layer metal of the welded structure and the supplied Nb to melt and fuse the two. Surface treatment method for welded structures. 2. The method according to claim 1, wherein when applying heat energy to the surface layer metal of the welded structure and the supplied Nb, heat energy by an arc discharge or heat energy by a laser beam is used. Surface treatment method for welded structures in reactors. 3. The method according to claim 1, wherein when supplying Nb to the surface of the welding structure, a turbid body of powder of metal Nb and a volatile solvent is applied to the surface of the welding structure.
Or the surface treatment method for a welded structure in a nuclear reactor according to item 2. 4. Nb supplied to the surface of the welded structure is Nb: 4 to 20% by weight, Cr: 15 to 35% by weight,
4. The surface treatment method for a welded structure in a nuclear reactor according to claim 1, wherein i is an alloy containing 60% by weight or more.