JPS63160783A - Method for improving residual stress of duplex metallic pipes - Google Patents

Abstract

PURPOSE:To heighten the efficiency of the improvement processing by heating both a duplex pipe part and a simplex pipe part while cooling the duplex metallic pipe inside and then, continuing to heat only the one pipe part to generate the stress to exceed a yield point and afterward, carrying out the cooling. CONSTITUTION:A cooling nozzle 9 is provided to a cylindrical hollow part 6 in the duplex pipes first and second heating means 10 and 11 are arranged to the outside of a base pipe 4 independently respectively. Cooling water is supplied to the inside of the duplex pipes and both the heating means 10 and 11 are operated to form the necessary temperature difference on the wall surface of the base pipe 4. Next, the first heating means 10 is stopped and the heating of only the second heating means 11 is continued and the stress to exceed the yield point is generated in the neighborhood of a weld zone 8 of the base and afterward, the natural cooling is carried out thereon. In this way, the compressive stress remains in the neighborhood of the weld zone 8. The pressing is simplified by only the cooling and heating processing and the efficiency of the improvement processing of the residual stress is heightened.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a method for improving residual stress in double metal pipes, etc.
In particular, the present invention relates to a method for improving residual stress near the weld between the inner surface of the main pipe and the base of the thermal sleeve.

``Prior art'' In general, in metallic materials such as austenitic stainless steel, which is widely used in nuclear power plants, chemical plants, etc., corrosion cracking occurs rapidly when tensile stress and corrosion factors are known to progress.

Conventionally, in order to correct residual stress in austenitic stainless steel pipes, cooling water is passed through the steel pipes and the steel pipes are heated by induction, creating a stress higher than the yield point on the inner and outer surfaces of the main pipe walls. A stress improvement method has been considered in which a temperature level is given to generate residual compressive stress on the inner surface near a welded part such as a joint of a steel pipe.

``Problems to be Solved by the Invention'' However, although this method is applicable when the austenitic stainless steel pipe has a simple shape such as a straight pipe, If it is a double metal pipe made by welding, the combined thickness of the main pipe and the base of the thermal sleeve will be significantly larger than the thickness of the main pipe itself.
``When 4 tubes are induction heated, the temperature distribution on the main tube wall becomes uneven, or the magnitude and direction of the stress generated due to the temperature difference, or the actual dyeing that deviates from the target 1'' occurs. Be able to think.

In addition, it is thought that near the welded part at the base of the thermal sleeve, a part of the structure has become sensitized due to welding heat. If it is not implemented, there is a risk that it will have a negative impact.

The purpose of the present invention is to solve the problems of the prior art, and when the inner surface of the main pipe is treated to improve residual stress by 4 degrees, it simultaneously reduces the residual stress at necessary points at the base of the thermal sleeve. This is intended to improve stress.

[Means for Solving the Problems] The method of improving residual stress in double metal pipes, etc. in the present invention involves making cooling water exist inside the double metal pipe formed by welding the base of the thermal sleeve to the inner surface of the main pipe. As a state, both the double pipe part and the single pipe part located on both sides of the base are heated at the same time, and after the heating process, heating of only one is continued so that the surface of the Y& part on the heating side exceeds the yield point. It is designed to generate stress, then stop all heating and cool down.

``Function'' When the main tube is heated in the presence of cooling water, the temperature difference between the heated part and the cooled part causes the yield point on the main pipe wall of the double pipe part and the single pipe part. Stress exceeding After that, if only one side is heated, a bending moment will act on the vicinity of the base of the thermal sleeve due to the difference in dimensions between the low temperature state of the unheated part and the high temperature state of the heated part. This bending moment creates tensile stresses on the inner surface of the base of the thermal sleeve. After this stress exceeds the yield point, if all heating is stopped i1= and cooled, compressive residual stress will be applied to the inner surface of the main pipe, and the base of the thermal sleeve will be Compressive residual stress can also be applied to the heating side surface.

"Example" Hereinafter, an example of the residual stress compliance method for double metal pipes, etc. according to the present invention will be described based on the drawings.

In this embodiment, as shown in FIG. 1, a double metal pipe is provided with a thermal sleeve 5 inside a main pipe 4 including a nozzle 2 and a safety pipe 3 in a reactor pressure vessel 1, and an upper pipe 11. A cylindrical hollow portion 6 is formed between the thermal sleeve 5 and the thermal sleeve 5 .

Further, the main pipe 4 is connected in the length direction by a butt weld (welded joint) 7, and the base of the thermal sleeve 5 is
It has a structure in which it is attached to the inner surface of the main tube 4 by a base weld 8, and furthermore, this double metal tube is made of austenitic stainless steel J14 (SUS304).

And the equipment used to implement the residual stress improvement method is:
A cooling nozzle 9 for spouting cooling water into the cylindrical hollow part 6 to form a flowing water state;
° By this I: It is composed of a first heating means IO and a second heating means 11 for inductively heating the required portion of the upper tube 4 from the surface side, and is composed of two heating means 10 and 1.
! They are arranged so as to cover the required length of the outer surface of the main pipe 4 at intervals in the longitudinal direction, and are operated independently at a time difference.

[Example of Residual Stress Amendment 2E] Hereinafter, the inner surface of the main pipe 4 including the butt weld part (welded joint) 7 of the main pipe 4 and the base of the thermal sleeve 5 (in Fig. 1, the base of the thermal sleeve 5 is As the center, the first
A case will be described in which residual stress reforming is performed in the range in which the first and second heating means 10 and 11 are arranged on the left and right sides of the figure.

[Supplying cooling water to the main pipe] Fill the inside of the double metal pipe with cooling water, and fill the cylindrical space 6 formed between the main pipe 4 and the thermal sleeve 5 with 6.
Not filled with cooling water. Prior to heating the main tube 4, it is desirable to cause the cooling water to flow as indicated by the arrows in FIG. In this case, if the cylindrical space 6 is formed by a small gap, the cooling water existing in the cylindrical space 6 will hardly be interfered with by the water flow generated in the thermal sleeve 5, so that the cooling water will remain in the stagnation state. It is thought that there may be cases where it is maintained as is.

[Generation of partial water flow] Therefore, the tip of the thin water supply nozzle 9 is inserted into the cylindrical space 6, and the cooling water filled in the cylindrical space G is directed toward the base of the thermal sleeve 5 and the safe end 3. A partial stream of water is ejected inside, as shown by the arrow in FIG. Since this partial water flow hits the base of the thermal sleeve 5 and spreads, a flow of water along the circumferential direction is formed.

In this way, by providing cooling water in a flowing state on the inner surface of the main pipe wall and operating the mountain collapse heating means 0.11, a temperature difference of, for example, 200°C or more is applied to the main pipe wall6. As mentioned above, stress improvement treatment can be applied to the inner surface of the main pipe wall.

However, in order to prevent these stress improvement treatments on the main pipe wall from having a negative effect on the base welded portion 8 of the thermal sleeve 5, the stress improvement treatment on the main pipe wall is performed through the following steps.

[Model near the base welded portion] FIGS. 2(a) to 2(C) show a point A on the inner surface and a point A on the outer surface in contact with the cylindrical space 6 near the base welded portion 8 of the thermal sleeve 5. Point B is set as a model, and changes in shape near the model point in each process are shown. .

Heating of the main pipe by means of E mountain heat disintegration] With cooling water flowing in the thermal sleeve 5 and the cylindrical space G, heating means! 0-11 are activated simultaneously. In FIG. 1, 11 (section 11) includes a carved heating means 10 surrounding the double pipe section located on the left side of the weld section 8;
Right side of base weld 8 1:1. The main pipe wall is heated by induction by the second heating means Il that surrounds the single pipe section where the main pipe is located. The part that is heated by this double-sided heating is mainly the main pipe wall, and most of the thermal sleeve 5 and the vicinity of the base welding part 8 are in contact with cooling water and the temperature rise is suppressed, so that the main pipe wall is heated. Works to prevent thermal expansion of the wall.

That is, the main tube wall, which was in the state shown in FIG. 2(a) before the heating process, is deformed as shown by the broken line in FIG. 2(b) because its thermal expansion is hindered by the base of the thermal sleeve 5. state. By simultaneously heating the cylinder body ■ and the cylinder body ■, the average temperature within the plate thickness increases, so the second
As shown by the broken line in Figure (b), the two rotating cylinders as a whole tend to move outward in the radial direction.

In addition, in this case, if the plate thicknesses of the cylindrical body ■ and the cylindrical body becomes larger, producing a clockwise rotational moment M as shown by the broken line in FIG. 2(b).

Therefore, the vicinity of point A undergoes concave bending deformation, which generates compressive axial stress. The stress strain history of point A up to this point shows that before heating, the 3rd v4 (a
), the stress strain at the zero point is S, as shown by the thick solid line in FIG. 3(b). When it reaches the position of S, the yield point is exceeded, and the increase in stress is small and the strain increases, so it becomes the position of S.

[Heating of the main pipe wall by the second heating means 1 Next, when the second heating means If continues to heat the main pipe wall and the first heating means IO is stopped, the thermal expansion of the single pipe section The deformed state of the main pipe wall becomes as shown in FIG. 2(C) because only the main pipe wall is maintained and the other parts shift to return to their original state by cooling.

Due to this phenomenon, the vicinity of point A protrudes inward, producing tensile stress. The stress strain history at point A up to this point changes from S, to S, and becomes tensile stress, as shown by the thick solid line in Figures 3(C) and 3(d). At the same time, when the yield point is exceeded, it changes into Si2.

[Cooling Step] Next, the operation of the second heating means t' t is stopped, and the temperature is returned to normal temperature by being left to stand naturally. Further, as the cooling time passes, the temperature of the main tube wall returns to a more or less uniform temperature, for example, the temperature of the cooling water (room temperature). By returning it to room temperature like this? As the deformation returns to the point where the strain in the 5th part becomes approximately zero, the stress and strain in the 3rd part move from S1+ to S14, as shown in Figure 3(e), and finally reach a small stress value. Become.

[? Examination of stress improvement effect in Part 5] The residual stress improvement effect on the inner surface of the main pipe wall is shown in Figure 2 (a
), (b), when both or one of the heating means 10-11 is activated, the inner surface of the main pipe wall comes into contact with the cooling water and continues to be cooled, so that the necessary temperature difference between the inner and outer surfaces (for example, austenite If the heating conditions are set to produce a temperature of 200°C or higher in the case of stainless steel, as mentioned above, thermal stress exceeding the yield point will be generated on the main pipe wall, and compressive residual stress will be applied to the inner surface. be able to.

In addition, the point A eventually becomes a compressive residual stress, as shown by S14 in Figure 3(e), and the stress improvement effect has occurred compared to the state in Figure 3(a). Become.

On the other hand, although the explanation for point 13 has been omitted, since it has a reverse relationship with the Δ point, the opposite stress distortion history can be traced.
In the final state, a slight tensile stress is applied as shown at the position of Sb in FIG. 3(e). The stress in this case is set to a level (P'i) that is large enough not to cause problems such as stress corrosion cracking, and is smaller than the threshold stress C at which stress corrosion cracking occurs.

[Supplementary explanation regarding heating conditions] As mentioned above, in order to carry out stress modification on the inner surface of the main pipe wall, it is necessary to satisfy the required temperature and heating time similar to the normal residual stress reforming method. Just do it.

Further, the heating by the first heating means IO is stopped, and the heating by the second heating means IO is stopped.
It is necessary to perform extended heating using only the heating means 11 for a time longer than the time given by the following equation.

τ=0, 71++”/a・・・・・・・・・・
...(i) However, τ: Duration of extended heating of the coil 2 111: Thickness of the welded part of the nozzle and thermal sleeve a: Temperature diffusion coefficient.

Note that, instead of the embodiment described in 117I, the present invention can be applied when the double pipe is a metal pipe other than austenitic stainless steel.

``Effects of the Invention'' As explained hereinafter, the residual stress reforming method for double metal pipes, etc. according to the present invention is such that cooling water is injected into the inside of the double metal pipe, which is formed by welding the base of the thermal sleeve to the inner surface of the main pipe. Both the double pipe part and the single pipe part located on both sides of the J1 (part) are heated at the same time, and after the heating process, only one of the bases on the heated side is heated. Since stress exceeding the yield point is generated on the surface, all heating is then stopped and the device is cooled, resulting in the following excellent effects.

■Residual stress can be improved by actively applying compressive residual stress to the vicinity of the base weld of the thermal sleeve.

■By improving the residual stress on the inner surface of the main pipe wall,
Even if an adverse effect occurs on the base weld, the effect can be reduced.

(2) This can be achieved by switching the heating means, so it is possible to improve the residual stress in the base welded part of the thermal sleeve at the same time as improving the residual stress in the main pipe wall.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of the residual stress reforming method for double metal pipes, etc. according to the present invention applied to a nozzle portion in a reactor pressure vessel, and FIGS. figure(
C) is an explanatory diagram of the residual stress modification process showing a modeled part of the double metal pipe, and Figures 3(a) to 3(0) show the relationship between stress and strain in the modeled part. It is a curve diagram. 1... Reactor pressure vessel, 2... Nozzle, 3... Safe end, 4... Main tube, 5... Thermal sleeve , G... Cylindrical hollow part, -7... Welded part (welded joint), 8... Base welded part, 9... Cooling nozzle, NO ...First heating means, 11...Second heating means. Applicant Ishikawajima Harima Heavy Industries Co., Ltd. Figure 1

Claims (1)

[Claims] A step in which cooling water is present inside a double metal tube formed by welding the base of the thermal sleeve to the inner surface of the main tube, and both the double tube section and the single tube section located on both sides of the base. and a step of continuing heating only one side after the step to generate stress exceeding the yield point on the base surface of the heated side, and a step of stopping all heating and cooling. A method for improving residual stress in double metal pipes, etc., characterized by: