JPH0910984A - Heat treatment method for pressure container nozzle of nuclear reactor - Google Patents

Abstract

PURPOSE: To provide a heat treatment method that enables a continuous annealing operation without lowering a preheating temperature. CONSTITUTION: A nozzle safe end 3 is abutted on the end of a nozzle body 2 provided in the pressure container of a nuclear reactor; also, the nozzle body 2 and the nozzle safe end 3 are wound with a high frequency heating coil 4 and energized with a high frequency current; and while these parts are preheated at a prescribed temperature, the abutting part is welded. After the completion of the welding, continuously with the preheating temperature maintained, the weld zone is wound again with another high frequency heating coil and energized with a high frequency current, so that the weld zone is annealed for prescribed hours with these high frequency heating coils 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a reactor pressure vessel nozzle when welding a nozzle body provided on a reactor pressure vessel and a nozzle safe end.

[0002]

2. Description of the Related Art FIG. 6 shows the structure of a nozzle provided on the side of a reactor pressure vessel 1. As shown in the figure, this nozzle is formed by butt-welding a cylindrical nozzle safe end 3 to the tip of a funnel-shaped nozzle body 2 integrally welded to a pressure vessel 1. By connecting a piping system such as a main steam pipe to the safe end 3, steam, a coolant or the like can be made to flow into or out of the container body 1. A back clad is welded to the inner surfaces of the nozzle body 2 and the nozzle safe end 3 to prevent the base material from being corroded.

Conventionally, the heat treatment of the nozzle has been performed accurately with the pressure vessel 1 in a large gas furnace installed in a factory, but recently, the pressure vessel 1 itself has become large. The portion of the nozzle safe end 3 has come to be welded to the nozzle body 2 later on site.

[0004]

By the way, the nozzle body 2
In order to weld the nozzle safe end 3 locally, before performing the main welding, first use a preheating device including a gas torch that uses oxygen acetylene, propane gas, or city gas as a fuel, and the nozzle body 2 and the nozzle safe end. It is necessary to preheat the end 3. That is, this nozzle body 2
Since the plate thickness reaches 90 mm or more, when the welding work is suddenly started, the heat-affected zone is rapidly hardened to cause welding defects such as under-beat cracking. When the preheating temperature reaches a predetermined temperature, main welding and back clad welding are performed so as to fill the groove formed at the abutting portion of the nozzle body 2 and the nozzle safe end 3.
After that, the welded portion was annealed for a predetermined time by using a heating device including a low-frequency coil to reduce the residual stress due to welding and improve the mechanical properties of the welded portion. However, as described above, since the preheating and the annealing work are performed in different devices, for example,
In order to start the annealing work after the completion of the main welding, it is necessary to remove this preheating device and then install a new annealing device, which requires a lot of time and labor for the work and the annealing work. When starting, the temperature of the welded part had already dropped to near room temperature, and it took a long time to raise the temperature of the nozzle to the annealing temperature again.

In recent pressure vessels and nozzles, new low alloy steels having excellent mechanical properties have been used as materials, but in the conventional heat treatment method, such low alloy steels are not produced. Since the preheating temperature is lowered before annealing, there is a problem that welding defects such as cold cracking occur.

Therefore, the present invention has been devised to solve the above-mentioned problems, and the purpose thereof is to provide a novel heat treatment for a reactor pressure vessel which enables continuous annealing without lowering the preheating temperature. To provide a method.

[0007]

In order to achieve the above object, the present invention provides a nozzle body and a nozzle safe before the nozzle safe end is abutted against the end of the nozzle body provided in the reactor pressure vessel. A high-frequency heating coil is wound around the end to apply a high-frequency current, preheat these to a specified temperature, weld the butt joints after aligning the groove, and after the welding is complete, continuously maintain the preheating temperature. Then, another high-frequency heating coil is wound around the welded portion to energize it, and the welded portion is annealed for a predetermined time by these high-frequency heating coils.

[0008]

As described above, according to the present invention, the main welding is performed while preheating the nozzle body and the nozzle safe end, and then another high-frequency heating coil is wound around this welding portion to anneal. The annealing work can be continuously performed without lowering the preheating temperature. Therefore,
The setup work from preheating to annealing and the time are greatly shortened, and on-site installation work of the nozzle safe end made of low alloy steel with high susceptibility to weld cracking can be easily achieved.
Further, since the high-frequency heating coil is used for such preheating and annealing, there is no inconvenience such as magnetic blowing of the welding arc, and the welding operation is not adversely affected.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

In FIG. 1, 1 is a reactor pressure vessel, 2 is a funnel-shaped nozzle body connected to the reactor pressure vessel 1 side, 3
Is a cylindrical nozzle safe end that is butt-welded to the end of the nozzle body 2, and of these, the pressure vessel 1 side welded portion of the nozzle body 2 has already undergone heat treatment with the pressure vessel 1 by the gas furnace of the factory. doing. In order to carry out the heat treatment method of the present invention, first, a support means (not shown) is used to support the nozzle safe end 3 so as to abut against the end portion of the nozzle main body 2, and the nozzle main body 2 and the nozzle safe end 3 are supported. 3 sets of high frequency heating coils 4, 4, 4
Wrap around these three sets of high frequency heating coils 4, 4, 4
Apply a high-frequency current to these at a predetermined temperature, for example,
Preheat to about 150 ° C. As is well known, the high-frequency heating coil 4 is formed by coating a conductive wire with a covering material such as a ceramic material having an insulating property and heat resistance, and winding this in a coil shape in multiple layers. 1
An induction current is generated in the nozzle base material by passing a high frequency current of 0 to 100 MHz, and the base material is uniformly heated by the Joule heat. Therefore, by this, beat cracks in the subsequent main welding can be prevented and the thermal effect on the nozzle base material can be reduced. In this embodiment, two high frequency heating coils 4 and 4 are wound around the thick nozzle body 2 side, and one high frequency heating coil 4 is wound around the thinner nozzle safe end 3 side. Both heating rates are made uniform. Further, since the heating temperature by the high frequency heating coils 4, 4, 4 is almost proportional to the energization amount of the high frequency current, the heating temperature and speed can be arbitrarily and easily controlled by adjusting the energization amount. .

Next, the MIZ is attached to the nozzle safe end 3.
Automatic welding robots 6 and 6 that apply an arc welding machine such as G or TIG are installed, and welding material is fleshed from the outside to the narrow groove formed at the abutting end of the nozzle body 2 and the nozzle safe end 3. After they are piled up and welded together, as shown in FIG. 2, a cladding material is welded to the inner surface of the welded portion to form a back cladding.
The automatic welding robots 6 and 6 can be used as they are, and the automatic welding robots 6 and 6 can be installed together with the high-frequency heating coil 4 before preheating. You may stay. Then, by such welding, the nozzle body 2 and the nozzle safe end 3 are integrally connected for the time being,
A large residual stress due to welding heat exists in this weld. Therefore, when this welding is completed, immediately after removing the automatic welding robots 6 and 6, as shown in FIG. 3, a high frequency heating coil 5 is further wound around the welding portion, and these four high frequency heating coils 4 and 4 are wound. The heating temperature is raised by gradually increasing the energization amount of the high-frequency current flowing through 4, 4, and 5. After that, the heating temperature is an annealing temperature, for example, about 6
If it reaches 15 ℃, keep that temperature for a few minutes ~
Annealing is performed for several hours to remove the residual stress in the weld. By performing this annealing, in addition to removal of residual stress, dimensional deviation prevention, increase in resistance to corrosion, temper softening of heat-affected zone, increase in ductility due to release of hydrogen contained in weld, impact value ( Toughness) or
An effect such as an increase in strength (precipitation hardening) can be obtained.

Next, FIG. 4 shows the relationship between the heat treatment of the nozzle according to the present invention and the time, and FIG. 5 shows the relationship between the conventional heat treatment and the time. As shown in the figure, in the conventional method, the temperature of the nozzle is lowered after the welding is completed in the setup for annealing after performing the welding by preheating the periphery of the welded portion to about 150 ° C. In order to prevent inconvenience due to deterioration, immediately after completion of welding, for example, after performing post-weld heat treatment at about 350 ° C.,
The temperature was lowered and the annealing work was started, and the temperature was raised again to around 600 ° C. On the other hand, according to the present invention, since it is not necessary to remove the preheating device as in the conventional case, the preheating temperature does not decrease, and the annealing work can be immediately started after the welding is completed. Therefore, the operations from preheating to annealing can be continuously performed, and the labor and time for heat treatment can be reduced. Further, as described above, since it is not preferable to lower the preheating temperature for the nozzle material having high susceptibility to welding cracks, the conventional method cannot be used, and the method of the present invention enables annealing for the first time. Furthermore, since the preheating and the annealing heat are obtained by the high-frequency heating coil, there is no inconvenience such as magnetic blowing of the welding arc during welding of the automatic welding machine, and there is no adverse effect on the welding work. That is, a heating coil using a low frequency adversely affects the welding arc and cannot perform good welding. In this embodiment, three sets of high frequency heating coils are used for preheating,
Although high-frequency heating coils were additionally added during annealing, it is needless to say that the number of installed high-frequency heating coils, preheating by these high-frequency heating coils and annealing temperature and time may be appropriately changed according to the intended heat treatment.

[0013]

In summary, according to the present invention, since the local annealing work can be continuously performed without lowering the preheating temperature, the labor and time required for the whole heat treatment and the preheating are reduced. It has excellent effects such as on-site welding of nozzle safe end made of unfavorable material.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment of a preheating method and a welding method according to the present invention.

FIG. 2 is a partially cutaway side view showing an embodiment of a welding method according to the present invention.

FIG. 3 is a side view showing an embodiment of an annealing method according to the present invention.

FIG. 4 is a graph showing the relationship between temperature and time of heat treatment according to the method of the present invention.

FIG. 5 is a graph showing a relationship between temperature and time of heat treatment according to a conventional method.

FIG. 6 is a sectional view showing an example of a conventional nozzle.

[Explanation of Codes] 1 pressure vessel 2 nozzle body 3 nozzle safe end 4,5 high frequency heating coil 6 automatic welding robot

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G21C 13/00 G21C 13/00 X

Claims (1)

[Claims] 1. A nozzle safe end is butted against an end of a nozzle body provided in a reactor pressure vessel,
A high-frequency heating coil is wound around the nozzle body and nozzle safe end, and a high-frequency current is passed through them, and the butt joints are welded while preheating these to a specified temperature.After the welding is completed, the preheating temperature is maintained and continuous. A heat treatment method for a reactor pressure vessel nozzle, which further comprises winding another high-frequency heating coil around the welded portion to energize the welded portion, and annealing the welded portion for a predetermined time by the high-frequency heating coil.