JP2000312969A - Outer face buttering process of welding joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent stress corrosion cracks of a welding joint and degradation of an ultrasonic wave flaw detecting characteristic against a weld part. SOLUTION: In this process, after water is poured inside a welding joint R of a nozzle 2 and a pipe 3 of a nuclear reactor pressure container, buttering B is applied to the outer face of the welding joint R by clad welding multiple layers while magnetic agitation is performed. Thereby, inside of the welding joint R is transferred to compressed stress so as to prevent stress corrosion cracks, and a structure is micronized by magnetic agitation so as to improve transmittance of ultrasonic waves. Thus, degradation of an ultrasonic wave flaw detecting characteristic against the welding joint R can be effectively prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buttering method applied to the outer surface of a welded joint between a nozzle of a reactor pressure vessel and a pipe to prevent stress corrosion cracking.

[0002]

2. Description of the Related Art Generally, in a welded structure requiring extremely high safety, such as a reactor pressure vessel, an ultrasonic flaw detection inspection is performed on a welded portion after welding or during a periodic inspection. UT) and the like, the presence or absence of welding defects, stress corrosion cracking (SCC), etc. is non-destructively inspected, and the soundness of the weld is ensured.

For example, as shown in FIGS. 3 and 4, a number of nozzles 2 are integrally formed in a reactor pressure vessel 1,
The pipes 3 corresponding to the respective nozzles 2 are butt-welded and connected, but when the nozzles 2 and the pipes 3 are butt-welded to each other and joint-welded,
Generally, since the nozzle 2 is formed of a low alloy steel such as SFVQ1A and the other pipe 3 is formed of a dissimilar material such as austenitic stainless steel such as SUS304.
After welding a nickel-based alloy such as Inconel (Inconel # 182, etc.) or stainless steel which has good welding familiarity to both materials on the butt surface on the nozzle 2 side, and then performing an appropriate heat treatment, the residual weld joints are left. The stress was removed, and a groove was machined at both ends thereof. Then, the groove was welded to the groove with Inconel such as Inconel # 82 or stainless steel, and then joined together. The integrity of the welded joint is confirmed by performing an ultrasonic inspection.

[0004]

Incidentally, the welded joint between the nozzle 2 and the pipe 3 having such a structure has a slight tensile stress on the inside, so that the inside of the welded joint is subjected to a long-term operation or the like. May cause stress corrosion cracking (SCC).

[0005] Therefore, after the joint welding is performed, a material such as inconel is weld-welded to the outer surface of the welded joint portion to perform buttering, and the inner surface is shifted to an appropriate compressive stress, thereby causing stress corrosion cracking. It has been studied to suppress the occurrence beforehand.

However, in general, a columnar crystal structure of dendrite grows significantly in a welded portion of austenitic stainless steel or a nickel-based alloy as compared with a welded portion of a low alloy steel or the like. Sisters,
There is a problem that the integrity of the weld cannot be sufficiently confirmed, and it has been difficult to apply a reactor pressure vessel requiring extremely high safety to an actual reactor.

Further, when the outer surface of the weld is battered, a heat affected zone (hardened zone) is generated in the base material (low alloy steel) due to the welding heat, but the heat affected zone is tempered and disappears. For this purpose, a long-time heat treatment must be performed after the completion of the buttering, and there is a problem that the compressive stress on the inner surface generated by the outer surface buttering is reduced. Furthermore, aside from constructing a new reactor pressure vessel,
When performing new battering on the outer surface of the welded joint of the existing reactor pressure vessel, since the water has already been filled inside, the above heat treatment is effectively performed after the completion of the buttering. Often it is not possible.

Accordingly, the present invention has been devised in order to effectively solve such a problem, and has as its main objects the stress corrosion cracking of a welded joint and the ultrasonic inspection characteristics of the welded portion. An object of the present invention is to provide a novel outer surface buttering method of a welded joint portion capable of preventing the lowering.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method and a method for spraying water on the inside of a welded joint between a nozzle safe end of a reactor pressure vessel and a pipe, and then forming an outer surface of the welded joint. The layers are welded in layers with magnetic stirring.

By performing this buttering, the inside of the welded joint can be shifted to a compressive stress.
It is possible to effectively prevent stress corrosion cracking (SCC), which is likely to occur in that part, and to improve the ultrasonic characteristics of the buttering welded part because the structure is refined by buttering with magnetic stirring. You.

When at least one of the nozzle safe end and the pipe of the reactor pressure vessel is made of a low alloy steel, a hardened portion is generated inside the reactor pressure vessel due to the welding heat due to the welding heat of the buttering. However, in order to obtain the tempering effect that the welding heat-affected zone on the base metal side is tempered and disappeared by the welding heat of each layer, so that the welding material is welded in multiple layers during this buttering. Generally, the heat treatment required after performing welding on the low alloy steel is also unnecessary.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, the method of the present invention uses SFVQ
A welding material such as Inconel # 82 is multi-layered (4 to 6 layers) on the outer surface of a welding joint R between the nozzle 2 made of a low alloy steel such as 1A and the pipe 3 made of a corrosion-resistant metal such as SUS304.
Buttering B with a thickness of several mm and a width of several cm
The welding is performed over the entire circumference at a dozen cm, and when the layers of the buttering B are overlay-welded, the molten pool is magnetically stirred by a magnetic stir welding method to weld while miniaturizing the structure. It is.

That is, according to this magnetic stir welding method, for example, a current is applied to a magnetic coil attached to a welding torch of a TIG welding apparatus often used for overlay welding to generate a magnetic field of several hundred gauss in a direction perpendicular to the molten pool. This is a method of generating and agitating the molten pool by Lorentz force generated by interaction with welding current. The direction of the magnetic field is alternately changed up and down in the range of 2 to 8 Hz, and the direction in which the Lorentz force works is rotated and reversed. This is a known technique in which the structure of the welded portion is refined by promoting the stirring of the molten pool.

Therefore, first, by performing such a buttering B on the outer surface of the weld joint R between the nozzle 2 and the pipe 3, the inside of the weld joint R is shifted to the compressive stress. Therefore, occurrence of stress corrosion cracking and the like is effectively suppressed. Next, the structure of the portion of the buttering B is refined by applying the buttering B using the magnetic stirring welding method, so that the ultrasonic characteristics are improved and the integrity of the welded joint R by the ultrasonic flaw inspection is improved. Can be reliably inspected, welding defects are reduced by constantly stirring the molten pool, and highly sound buttering can be performed.

When the build-up welding is performed by the magnetic stir welding method, the height of each layer tends to be lower than the height at the time of normal build-up welding. The height of each layer does not become unnecessarily high,
Buttering B having a desired height can be accurately performed.

On the other hand, when such a buttering B is performed, in the case of the nozzle 2 whose base material is made of low alloy steel, when the first layer is build-up welded as shown in FIG. The welding heat may affect the base material and generate a hardened zone around the weld overlay of the first layer.

However, the buttering according to the method of the present invention tends to be lower than the height at the time of normal overlay welding, and the welding material is multi-layer welded. As shown in (4) to (4), the second layer, the third layer, the fourth layer,... Are sequentially superposed on the first layer and overlay welding is performed, so that the hardened region is gradually increased from the outside by the welding heat of each layer. Normal tempering bead welding was carried out by appropriately adjusting the welding heat and the overlay welding thickness, etc., because it can also have a normal temperature temper bead construction method capable of obtaining a tempering effect of being tempered and extinguished. It is also possible to omit the heat treatment required at that time.

When the base material is made of a material other than low-alloy steel and carbon steel, such as the pipe 3 made of a corrosion-resistant metal such as SUS304, a hardened region due to welding heat hardly occurs. There is no need to be aware of such a temper bead method.

[0020]

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

First, as shown in FIG.
13mm, outer diameter 318.5mm, inner diameter 280.5mm,
A pipe made of 19 mm thick SUSF304 (butting section # 82) and a pipe made of SFVQ1A (# 182 overlay) were butt-welded to form a 300A test body according to the present invention. Here, each base material and welding material used had a chemical component and a mechanical property as shown in Tables 1 to 3 below.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

In this state, since the stress on the inner surface is compressed, as shown in FIG. 6, the inner surface of the weld is then back-hanged to a depth of 6 mm. The stress was defined as tensile stress.

Next, in this state, cover both ends of both pipes,
After filling the interior with still water, the outer surface of the welded portion was subjected to external buttering by magnetic stirring welding.

Here, the buttering width is 55 mm or more at both ends from the welding center, and the required thickness of the buttering overlay is 3.5 mm. However, since the room temperature temper bead method is also used, the number of layers is six. And In addition, as a welding material for buttering, a welding material having a chemical composition and a mechanical property as shown in Table 4 was used, and the respective layers were subjected to buttering welding under welding conditions as shown in Table 5. In addition, at the same time as performing the outer surface buttering by the magnetic stirring welding, as shown in Table 6, another 300A was used for UT comparison.
Normal buttering welding, that is, normal buttering welding without magnetic stirring was performed on the test piece.

[0028]

[Table 4]

[0029]

[Table 5]

[0030]

[Table 6]

The thus obtained 300A
(1) Appearance observation (including PT), (2) Residual stress measurement, (3) UT characteristic investigation, and (4) hardness test were performed on the test specimens as shown below.

(1) Appearance Observation Results As a result of observing the appearance of the 300A test specimen according to the present invention by visual observation, it was found that
PT was also defect-free.

(2) Result of Measurement of Residual Stress FIG. 8 shows the result of measurement of the residual stress of a 300A test piece according to the present invention. As can be seen from the drawing, the inner surface of the outer buttering was sufficiently shifted to the compression side by performing the buttering despite the fact that the back was hung and a strong tensile stress was applied. Then, it was confirmed that the stress was sufficiently improved in the still water state. Even in the 0 ° azimuth where the welding was started / stopped, the stress was sufficiently compressed as in the 270 ° side welded upward. From this, it was confirmed that even at the start / stop position of welding, the outer surface battering sufficiently shifted to compressive stress.

(3) Results of UT Characteristics Investigation As a UT characteristics investigation, the ultrasonic transmission characteristics of the 300A test sample according to the present invention and the 300A test sample for UT comparison were measured for the overlay portions in four directions, respectively. did. Here, as for the ultrasonic transmittance, the transmittance (echo height) of SUS304 of 200 mmt was set to 100%, and the transmittance (echo height) at the built-up portion was measured. The result is shown in FIG. Was.

As a result, in the upward (270 °) and downward (0 °) directions, the UT characteristics were significantly improved as compared with the ordinary welding. At 90 ° for downward welding and 180 ° for upward welding, an improvement is seen compared to normal welding, but the transmittance is reduced by about half compared to the base metal,
It is considered that sufficient improvement was not obtained by magnetic stirring. However, there is not enough UT for down and up
Since it has been demonstrated that the characteristics can be improved, if the magnetic method and the welding condition are slightly changed, for example, if the method of welding while rotating the base material side is used if possible, Also, it is considered that a sufficient magnetic stirring effect can be obtained even in the upward direction.

(4) Results of Hardness Test In general, in Ministerial Decree No. 81, heat treatment is required after low-alloy steel is subjected to external battering. However, external battering according to the present invention is performed by watering the inside. Heat treatment is impossible because of the method of improving stress. Therefore, since the method of the present invention is a temper bead method for low alloy steel, a hardness test of a low-alloy steel heat-affected zone is performed to confirm whether or not the tempering effect is actually obtained by this method. Carried out. In this hardness test, Vickers hardness was 9.8 N.

As a result, as shown in FIG. 7 and FIG. 10 to FIG.
It was below 0, and it was confirmed that a sufficient tempering effect was obtained even when the inner surface was filled with water.

[0038]

In summary, according to the present invention, the following excellent effects can be obtained.

(1) By subjecting the outer surface of the welded joint to buttering, the inner surface of the welded joint can be shifted to compressive stress, so that the occurrence of stress corrosion cracking at that portion can be suppressed.

(2) By performing buttering by magnetic stir welding, the structure of the welded portion is refined and the UT characteristics are improved, so that the soundness of the welded joint by ultrasonic waves can be accurately inspected.

(3) By performing overlaid welding on the outer surface of the welded joint in multiple layers and performing buttering, a temper beat effect such that the hardened region is gradually eliminated can be obtained. Even in the case of using a base material that is likely to be hardened due to the thermal influence of steel or the like, heat treatment after the buttering work is not required, and workability is also improved.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of a welded joint showing one embodiment of the method of the present invention.

FIG. 2 is a partially enlarged view of a portion A in FIG. 1, and is a conceptual diagram showing a tempering effect by a temper beat method.

FIG. 3 (1) is a partial view showing a welded joint between a nozzle and a pipe of a conventional reactor pressure vessel. (2) is FIG.
FIG. 2 is a partially enlarged cross-sectional view showing a portion A in (1).

FIG. 4 is a partially enlarged sectional view showing a portion A in FIG. 3 (2).

FIG. 5 is a partially enlarged cross-sectional view showing a welded joint portion of a 300A specimen according to an example of the method of the present invention.

FIG. 6 is a partially enlarged cross-sectional view showing a state in which a back is suspended on the inside of a welded joint portion of the 300A specimen shown in FIG. 5;

FIG. 7 is a table showing the results of a hardness test according to an example of the method of the present invention.

FIG. 8 is a graph showing a residual stress measurement method and results according to an example of the method of the present invention.

FIG. 9 is a graph showing the results of an examination of ultrasonic characteristics (comparison of ultrasonic transmittances) of the cladding according to an example of the method of the present invention.

FIG. 10 is a graph showing an external battering effect confirmation test by magnetic stirring (hardness test result of heat-affected zone of low alloy steel: 0 ° cross section, downward welding).

FIG. 11 is a graph showing an outer surface battering effect confirmation test by magnetic stirring (hardness test result of heat-affected zone of low alloy steel: 90 ° cross section, downward welding).

FIG. 12 is a graph showing an outer surface battering effect confirmation test by magnetic stirring (hardness test result of heat-affected zone of low alloy steel: 180 ° cross section, upward welding).

FIG. 13 is a graph showing an outer surface battering effect confirmation test by magnetic stirring (hardness test result of heat-affected zone of low alloy steel: 270 ° cross section, upward welding).

[Explanation of symbols]

 1 Reactor pressure vessel 2 Nozzle 3 Piping B Buttering R Weld joint

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Claims (4)

[Claims] After water is applied to the inside of a welded joint between a nozzle of a reactor pressure vessel and a pipe, the outer surface of the welded joint is clad by multi-layer welding with magnetic stirring to perform buttering. An outer surface buttering method for a weld joint, wherein an inner surface is made to have a compressive stress. 2. After water is applied to the inside of the welded joint between the nozzle and the pipe of the reactor pressure vessel, the outer surface of the welded joint is magnetically stirred and multi-layer build-up welded and buttered, An outer surface buttering method for a welded joint, wherein the weld heat affected zone on the base material side is tempered by the welding heat of each layer to be extinguished. 3. The nozzle and piping of a reactor pressure vessel,
The outer joint buttering method for a weld joint according to claim 2, wherein at least one of the base material and the base material is hardened by the influence of welding heat during the overlay welding. 4. The reactor pressure vessel according to claim 1, wherein the nozzle of the reactor pressure vessel is mainly made of low alloy steel, and the pipe is made of stainless steel, nickel base alloy or carbon steel. An outer surface buttering method for a welded joint according to any one of the above.