JP2003225763A - Tip end shape of nozzle for pressure vessel and method for build-up welding to tip end part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tip end shape of a nozzle for pressure vessel and a method for build-up welding to the tip end part in which even in the case of arranging the other member, such as an inner pipe, in the inner part of the nozzle, a preventive maintenance work for stress corrosion cracking can be performed by using a welding torch similar to the present used one without removing the other member. <P>SOLUTION: A safe end 8 is cut off without removing the inner pipe 4, and a conical beveling cutting part C at the tip end part of the nozzle 1, is formed over a clad-welding part 2 and a part of a build-up welding part 3. The welding torch 6 is abutted on this conical beveling cutting part C at the inclining angle of 5-60° to the inner surface of a clad-welding part 2 to form a corrosion- resistant improving welded part 9 with the welding. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to overlay welding for improving corrosion resistance on the inner surface of the tip of a nozzle of a pressure vessel having a nickel-based alloy overlay welded portion and other members disposed inside. The present invention relates to a tip shape of a nozzle of a pressure vessel and a welding method for overlaying the tip.

[0002]

2. Description of the Related Art A nozzle of a reactor pressure vessel is internally clad welded with stainless steel or the like, and a nickel-base alloy is welded to the tip of the nozzle to attach a safe end such as stainless steel. There is a product. For a nozzle having this welded connection structure, for example, when performing preventive maintenance of stress corrosion cracking (SCC) in a nickel-base alloy overlay weld, the safe end is cut to provide corrosion resistance to the nickel-base alloy weld inner surface. Improved clad welding has also been performed.

FIG. 6 is a vertical sectional view of a general reactor pressure vessel, and FIG. 7 is an upper sectional view of the nozzle along the axial direction. The reactor pressure vessel is a pressure vessel 10 having a cylindrical body.
And an upper lid 11 that seals the pressure vessel 10. A nozzle 1 for inserting a structure such as an inner pipe 4 inside the pressure vessel 10 is provided on a side portion of the pressure vessel 10. The nozzle 1 that is formed to project by more drawing is welded to the safe end 8 that holds the inner pipe 4 at the butt weld 7. Clad welding 2 for improving corrosion resistance is applied to the inner surface of the nozzle 1, and further nickel-based alloy build-up arc welding 3 is applied to the tip of the nozzle 1,
The safe end 8 which is a connecting pipe made of stainless steel is attached.

By the way, when other members such as the inner pipe 4 are arranged inside the nozzle 1, it is usually necessary to replace the inner structure of the reactor pressure vessel with the inner structure in accordance with the replacement work. After removing other members such as the pipe 4, a cladding weld 9 for improving corrosion resistance is coated. In other words, in the nozzle 1 having the above-described configuration, the welding torch (electrode) 6 indicated by the broken line may not be inserted into the nozzle 1 due to the narrow gap between the nozzle 1 and the internal structure. In such a case, Until the replacement work of the internal structure of the reactor pressure vessel is carried out, the construction of the clad welding 9 for improving the corrosion resistance of the inner surface of the nozzle 1 must be suspended.

[0005]

Therefore, in a reactor pressure vessel equipped with a nozzle 1 which does not require replacement work of internal structures, only to perform preventive maintenance around the nozzle 1, There was an inconvenience that large-scale construction work had to be carried out such as the work of removing the internal structure of the reactor pressure vessel. Therefore, an attempt was made to reduce the size of the welding torch 6 so that it could be inserted into the gap between the nozzle 1 and the internal structure. However, the gap may be 10 mm or less. Since the inner surface of the nozzle 1 is padded to improve the corrosion resistance, it is expected that the gap will be further narrowed. Therefore, at least in the current situation, it is almost impossible for practical technological development.

The present invention has been made to overcome such difficulties in the prior art, and the inner tube 4 is provided inside the nozzle 1.
Welding torch 6 similar to the current one, even if other members such as
It is an object of the present invention to provide a tip shape of a nozzle of a pressure vessel and a method for overlay welding of the tip, which can perform preventive maintenance work of stress corrosion cracking using.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the shape of the tip of the nozzle of the pressure vessel includes at least the inner surface of the weld overlay on the inner surface of the nozzle, and the nozzle moves toward the tip side. A groove-shaped portion having a substantially conical shape is formed by cutting the groove-shaped portion so that the thickness becomes thin. For example, the inclination angle of the groove-shaped portion with respect to the inner surface of the nozzle is set to 5 ° to 60 °, or the nozzle is formed. Of the grooved part on the side opposite to the tip of the groove is formed, or the inclination angle of the grooved part with respect to the inner surface of the nozzle is large on the side opposite to the nozzle tip and small on the nozzle tip side. The method for overlay welding the tip of the nozzle has a multi-stage structure, and the inner surface of the nozzle includes at least the inner surface of the overlay welded portion and is moved to the tip end side of the nozzle without removing other members. Cut the inner surface so that the thickness becomes thinner as After the groove is cut to form a substantially conical shape, overlay welding is performed on the groove processed surface. For example, the direction of the electrode of the welding torch is relative to the radial direction of the nozzle. It is set so as to be tilted at 10 ° to 90 °.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an upper sectional view showing a corrosion resistance improvement welding portion of a nozzle of a pressure vessel according to an embodiment of the present invention, and FIG. 2 is a corrosion resistance improvement welding process procedure diagram of the embodiment as well. A clad weld 2 is formed on the inner surface of the nozzle 1, a build-up weld 3 of a nickel-based alloy is provided on the tip side of the nozzle 1, and an inner pipe 4 is provided inside the clad weld 2. Has been done. A corrosion resistance improving weld 9 made of a nickel-based alloy is formed on the tip of the clad weld 2 and the inner surface of the overlay weld 3. The tip of the nozzle 1 is a butt weld 7.

Further, as shown in FIG. 2 (a), a clad weld portion is formed by clad welding on the inner surface of the nozzle 1 before the preventive maintenance work, and a nickel-base alloy overlay is formed on the tip thereof. A weld 3 is provided. Butt welding is performed by forming a groove at the tip end side of the build-up welded portion 3 and the tip end of the companion safe end 8. Therefore, first, the safe end 8 is removed by cutting the butt weld 7 without removing the inner pipe 4. Next, a conical groove cutting portion C is formed by hanging a part of the clad welding portion 2 and the overlay welding portion 3 at the tip of the nozzle 1 (b). That is, the inner surface is tapered. Then, the welding torch 6 is brought into contact with the conical groove cutting portion C obliquely from below to form the corrosion resistance improving welding portion 9 by welding (c). As a result,
The corrosion resistance improvement welded portion 9 shown in is formed. Further nozzle 1
It is possible to restore the original nozzle by taking a groove at the tip of and then butt welding it to the safe end that also has a groove.
The corrosion resistance improving weld 9 is also formed of a nickel-based weld metal.

FIG. 3 shows a conical groove cutting portion C and a welding torch 6.
FIG. 3 is a conceptual diagram showing the relationship between the posture and the movement direction of FIG. The conical groove cutting portion C is 5 ° with respect to the inner surface of the clad welding portion 2.
It is formed so as to form an inclination angle θ of -60 °. If the inclination angle θ is smaller than 5 °, the effect of facilitating the formation of the corrosion resistance improving weld 9 can hardly be expected, and if the inclination angle θ is larger than 60 °, the formation range of the corrosion resistance improving weld 9 becomes too wide. . The direction of the electrodes of the welding torch 6 is set to 10 ° to 90 ° with respect to the radial direction of the nozzle 1. If the inclination angle φ of the electrode with respect to the radial direction of the nozzle 1 is smaller than 10 °, the distance between the nozzle 1 and the inner pipe 4 is too narrow, and the corrosion resistance improving weld 9
Formation becomes difficult.

The direction of the welding arc is set to be the same as the direction of the electrodes of the welding torch 6, but it does not have to be the same depending on the relationship with the welding shape and welding conditions.
The welding torch 6 is provided with a drive mechanism that can move independently in both the axial direction and the radial direction of the nozzle 1. The range of forming the conical groove cutting portion C is basically about 5 to 40 mm because it is sufficient that at least the inner peripheral surface of the overlay welding portion 3 can be covered to form the corrosion resistance improving welding portion 9.

As described above, in this embodiment, the thickness of the tip of the nozzle 1 inside the clad weld 2 and the overlay weld 3 becomes thinner as it moves to the tip side. Since the cut conical groove cutting portion C is formed, the nozzle 1
Inner surface of clad weld 2 and inner pipe 4 that is not removed
The welding torch 6 was used because a space for receiving the welding torch 6 expanded in the radial direction of the nozzle 1 is formed below the conical groove cutting portion C on the tip side even if the space between the welding torch 6 and It is possible to easily form the corrosion resistance improving welded portion 9 for preventive maintenance of stress corrosion cracking. Further, by inclining the direction of the electrode of the welding torch 6 by a predetermined angle with respect to the radial direction of the nozzle 1,
Even if the welding torch 6 is not downsized so much, the corrosion resistance improving welding can be performed relatively easily.

FIG. 4 is a front view (a) and a partially enlarged view (b) showing a corrosion resistance improving weld of a nozzle of a pressure vessel according to another embodiment in which the conical groove cutting portion C has a different shape. . In this embodiment, the inner peripheral side of the nozzle 1, that is, the end of the conical groove cutting portion C on the side opposite to the tip is formed into an annular cutting portion C '(annular groove). By forming the shape of the conical groove cutting portion C in this way, a slightly wide gap can be formed inside the annular cutting portion C ′, and thus the corrosion resistance improving welding can be easily performed. .

FIG. 5 is a front view showing a corrosion resistance improving weld portion of a nozzle according to still another embodiment in which the conical groove cutting portion C has a different shape. In this example, the large-angled cutting portion C is formed on the inner side of the shape of the conical groove cutting portion C and has a slightly large inclination angle θ1 with respect to the inner surface of the clad welded portion 2.
1 and a small-inclined cutting portion C2 that is connected to this and has a slightly small inclination angle θ2. By forming the shape of the conical groove cutting portion C in this way, the amount of molten metal required to form the corrosion resistance improvement welding portion 9 can be saved.

[0015]

As described above, according to the first aspect of the present invention, including the inner surface of the overlay welding portion, the substantially conical shape is cut so that the thickness becomes thinner as it moves to the tip side. Since the groove processing part that forms the is formed, the welding torch receiving space that is expanded in the radial direction of the nozzle is formed below the groove processing part, so other members disposed inside the nozzle are removed. Without doing so, a preventive maintenance work for stress corrosion cracking of the weld can be performed using a welding torch similar to the current one.

According to the second aspect of the present invention, since the inclination angle of the grooved portion with respect to the inner surface of the nozzle is set to 5 ° to 60 °, a welded torch similar to the existing one is used to form a corrosion resistance improved welded portion. It can be easily formed.

According to the third aspect of the present invention, since the circular annular groove is formed at the edge of the grooved portion on the side opposite to the tip of the nozzle, the welding is performed to improve the corrosion resistance of the inner surface of the tip of the nozzle. It can be done easily.

According to the fourth aspect of the present invention, since the inclination angle of the groove processed portion with respect to the inner surface of the nozzle is large on the side opposite to the tip of the nozzle and small on the tip side of the nozzle, a multi-step refraction structure is adopted, so that corrosion resistance improving welding is performed. The amount of molten metal required to form the part can be saved.

According to the fifth aspect of the present invention, the inner surface is cut so that the thickness becomes thinner as it moves to the tip side of the nozzle without removing other members arranged in the nozzle. After performing the groove processing that forms a substantially conical shape, the welded surface is subjected to overlay welding, so preventive maintenance work can be performed easily, and the time required for the work can be shortened. , The cost can be reduced.

According to the sixth aspect of the invention, the direction of the electrode of the welding torch is 10 ° to 90 ° with respect to the radial direction of the nozzle.
Since it is set to be tilted, it is possible to easily perform overlay welding on the groove processed surface using the welding torch.

[Brief description of drawings]

FIG. 1 is a front view showing a corrosion resistance improving welded portion of a nozzle of a pressure vessel according to an embodiment of the present invention.

FIG. 2 is likewise a flow chart of the corrosion resistance improving welding process.

FIG. 3 is a conceptual diagram showing the relationship between the orientation and operation direction of the conical groove processed portion and the welding torch.

FIG. 4 is a front view (a) and a partially enlarged view (b) showing a corrosion resistance improvement welded portion of a nozzle of a pressure vessel according to another embodiment in which a conical groove processed portion has a different shape.

FIG. 5 is a front view showing a corrosion resistance improvement welding portion of a nozzle of a pressure vessel according to still another embodiment, in which the conical groove processed portion has a different shape.

FIG. 6 is a vertical sectional view of a general reactor pressure vessel.

FIG. 7 is likewise an upper sectional view taken along the axial direction of the nozzle.

[Explanation of symbols]

1 nozzle 2 Clad weld 3 Overlay weld 4 inner tube 6 welding torch 7 Butt weld 8 Safe end 9 Corrosion resistance improved weld C Conical groove processing part

Claims (6)

[Claims] 1. A pressure vessel in which another member such as an inner pipe is disposed, and a corrosion resistance improving weld portion for preventing stress corrosion cracking is formed inside a tip portion including a nickel-based alloy overlay weld portion. In the tip shape of the nozzle, a groove-shaped portion having a substantially conical shape including at least the inner surface of the build-up welded portion on the inner surface of the nozzle and being cut so that the thickness becomes thinner as it moves to the tip side. The tip shape of the nozzle of the pressure vessel is characterized in that a clad weld is formed to improve corrosion resistance. 2. The tip shape of the nozzle of the pressure vessel according to claim 1, wherein an inclination angle of the groove processing portion with respect to the inner surface of the nozzle is set to 5 ° to 60 °. 3. The shape of the tip of the nozzle of the pressure vessel according to claim 1, wherein a circular annular groove is formed on the edge of the grooved portion on the side opposite to the tip of the nozzle. 4. The tip shape of a nozzle, wherein the groove angle of the groove processing portion with respect to the inner surface of the nozzle is large on the side opposite to the tip of the nozzle and small on the tip side of the nozzle. 5. Another member such as an inner pipe is arranged inside, and overlay welding for improving corrosion resistance is performed on an inner surface of a tip of a nozzle of a pressure vessel including a nickel-based alloy overlay welding portion. In the overlay welding method of the tip of the nozzle of the pressure vessel, the inner surface of the nozzle includes at least the inner surface of the overlay welded portion without removing the other member, and the process proceeds to the tip side of the nozzle. Of the nozzle of the pressure vessel, characterized in that the inner surface is cut so that the thickness becomes thin, and the groove is formed into a substantially conical shape, and then the overlay welding is performed on the groove processed surface. Overlay welding method at the tip. 6. The overlay welding method for a tip of a nozzle of a pressure vessel according to claim 5, wherein the direction of the electrode of the welding torch is set to be tilted by 10 ° to 90 ° with respect to the radial direction of the nozzle. .