JPH07229878A - Method for forming stress corrosion cracking defect in metal pipe and stress applying device used in the method - Google Patents

Abstract

(57) [Abstract] [Purpose] The required stress corrosion cracking defects are formed in the metal tube so that the waveform of the reflected wave obtained by injecting ultrasonic waves is optimized for use as a criterion. [Structure] A plurality of pressing members 13 are arranged inside a metal pipe 18 in which a defect due to stress corrosion cracking is to be formed.
3 presses the metal pipe 18 from the inside to the outside to generate stress in the metal pipe 18, and the metal pipe 18 in the stressed state
Is immersed in an aqueous solution of magnesium chloride to form a stress corrosion cracking defect in a metal pipe, and a shaft 1 having a tapered portion 3, a sleeve 8, a pressing member 13, and a shaft 1 are used in the axial direction for use in this method. It is a stress applying device 30 provided with a means for moving to.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a stress corrosion cracking defect in a metal pipe for obtaining a waveform as a criterion when detecting the presence or absence of the stress corrosion cracking defect in the metal pipe by an ultrasonic flaw detection test. And a stress applying device used in the method.

[0002]

2. Description of the Related Art Defects due to stress corrosion cracking may occur in metal pipes used in nuclear power plants.

Since it is difficult to visually detect such a defect due to stress corrosion cracking, as a means for confirming whether or not a defect due to stress corrosion cracking has occurred in a metal tube, an ultrasonic flaw detection test has been conventionally used. Is being implemented.

The ultrasonic flaw detection test is performed by injecting an ultrasonic wave directly or through a medium into a metal pipe whose presence or absence of a stress corrosion cracking defect is to be detected, and a waveform of a reflected wave of the incident ultrasonic wave. It is a non-destructive inspection means for determining the presence or absence of stress corrosion cracking defects.

[0005]

In the above-mentioned ultrasonic flaw detection test, the presence or absence of stress corrosion cracking defects is judged from the waveform of the reflected wave of the ultrasonic wave. What kind of waveform is obtained, the metal pipe It is based on many years of experience of the waveform measurer whether or not it is judged that a defect due to stress corrosion cracking has occurred in the, and if the measurer is a different person, even if a reflected wave of similar shape is obtained, Different decisions may be made.

In order to prevent different judgments from being made by different measurers, the required stress corrosion cracking defects are formed in advance on the metal pipe to be sampled, and the reflection obtained by applying ultrasonic waves to this metal pipe is obtained. It has been attempted in the past to form the required stress corrosion cracking defects in the sample metal tube so that the waveform of the wave is used as a criterion, but in the past, the sample was made using thermal stress such as welding stress. Since a stress corrosion cracking defect was formed in the metal pipe to be sampled, the sample metal pipe was plastically deformed, and stress corrosion cracking defects were generated both in the circumferential direction and the axial direction of the sample metal pipe. On the cross section, a stress corrosion cracking defect occurs only on one side of the outer surface or the inner surface of the metal pipe to be sampled, and there is a drawback that a desired stress corrosion cracking defect suitable for use as a criterion cannot be formed. It was.

The present invention eliminates such conventional drawbacks,
Stress corrosion cracking is designed so that the required stress corrosion cracking defects can be reliably formed in the sample metal tube so that the waveform of the reflected wave obtained by injecting ultrasonic waves is optimized for use as a criterion. An object of the present invention is to provide a defect forming method and a stress applying device used in the method.

[0008]

According to the present invention, a plurality of pressing members are arranged inside a metal pipe in which a defect due to stress corrosion cracking is to be formed, and the metal pipe is pressed from the inside to the outside by the pressing members. A stress corrosion cracking defect forming method for a metal tube, wherein stress is generated in the metal tube, and the metal tube in the stressed state is immersed in an aqueous solution of magnesium chloride, and a stress corrosion cracking method having a tapered portion A shaft to be inserted into the center of a metal pipe to form a defect, a sleeve fitted to the outside of the shaft and inserted into the metal pipe together with the shaft, and an inner surface side of the shaft attached to an end of the sleeve. A plurality of pressing members abutting on the taper portion of the metal pipe and having an outer surface abutting on the inner surface of the metal pipe, and means for moving the shaft in the axial direction. The present invention relates to a stress applying device used in a method of forming a stress corrosion cracking defect against a metal pipe by pressing a metal pipe from the inside to the outside by pressing a part of the pressing portion of the metal pipe, or the outer surface of the pressing member to the inner surface of the metal pipe. Can be formed into a curved surface that can closely contact with each other, a ridge extending in the circumferential direction of the metal tube can be formed on the outer surface of the pressing member, and a ridge extending in the axial direction of the metal tube can be formed on the outer surface of the pressing member.

[0009]

When the shaft is moved in the axial direction, the pressing member is prevented from moving in the axial direction by the sleeve,
It is pushed by the tapered portion of the shaft to push the inner surface of the metal tube outward. When the metal tube is immersed in the magnesium chloride aqueous solution for a predetermined time while being pressed, desired stress corrosion cracking defects are formed in the metal tube.

By injecting an ultrasonic wave into a metal tube having a desired stress corrosion cracking defect in this manner and judging the waveform of the reflected wave as a reference waveform, it is possible to determine whether there is a stress corrosion cracking defect that does not differ among individuals. You can judge.

[0011]

Embodiments of the present invention will now be described with reference to the drawings.

First, an embodiment of the stress applying device of claim 3 for use in the method of the present invention will be described.
It is a front view of the shaft 1 arranged at the center of the stress imparting device of the present invention, in which an upper portion of the shaft 1 is engraved with a male screw portion 2, and a portion near the lower portion of the shaft 1 is directed downward. A tapered portion 3 that expands in diameter is formed.

FIG. 3 is a front view of the base plate 4 fixed to the end portion of a metal tube which will be described later as a sample.
Is a metal disc formed by integrally forming a large diameter portion 5 and a small diameter portion 6, and a through hole 7 through which the shaft 1 of FIG. 2 can be gently inserted is provided at the center. The diameter of the large-diameter portion 5 is made approximately the same as the outer diameter of the metal tube to be sampled, and the diameter of the small-diameter portion 6 is made to the dimension that allows close fitting with the inner surface of the metal tube to be sampled. Has been.

FIG. 4 is a front view of an embodiment of the sleeve 8 fitted to the outside of the shaft 1 shown in FIG. 2, and FIG. 5 is a sectional view taken along line VV of FIG. A center hole 9 into which the shaft 1 shown in FIG. 2 can be gently inserted is bored in the center of the sleeve, and the outer diameter of the sleeve 8 is set to a dimension such that the sleeve 8 can be gently inserted into a metal tube as a sample described later. Has become. At the lower end of the sleeve 8, a fan-shaped protrusion 1
A plurality of 0s and fan-shaped recesses 11 are alternately provided,
A female screw hole 12 is formed from the lower surface of the convex portion 10 toward the upper side.

FIG. 6 is a bottom view showing a state where three pressing members 13 are arranged, FIG. 7 is a sectional view taken along line VII-VII of FIG. 6, and FIG.
6 is a perspective view showing one pressing member 13. The pressing member 13 has a fan-shaped planar shape, and can be fitted into the recess 11 of the sleeve 8 shown in FIG. A tapered surface 14 having a shape along the tapered portion 3 of the shaft 1 shown in FIG. 2 is formed on the inner surface side of the fan-shaped pressing member 13, and the outer surface 1 of the fan-shaped pressing member 13 is formed.
The reference numeral 5 has a curved surface that can be brought into contact with the inner surface of a metal tube which will be described later as a sample.

FIG. 9 is a plan view of the pressing ring 16, and the ring 16 presses the pressing member 13 so that the pressing member 13 fitted in the recess 11 of the sleeve 8 does not fall out of the recess 11. The holding ring 16 is formed in a flat ring shape, and a bolt insertion hole 17 is formed at a position corresponding to the female screw hole 12 shown in FIG. The outer diameter of the pressing ring 16 is approximately equal to the outer diameter of the sleeve 8 shown in FIG. 5, and the ring-shaped inner diameter of the pressing ring 16 is slightly larger than the diameter of the central hole 9 of the sleeve 8. It has become.

The above-mentioned members of FIGS. 2 to 9 constitute the stress applying device of the present invention. Next, a method of using the stress applying device will be described.

FIG. 1 is a vertical sectional front view showing a usage state of an embodiment of a stress applying device 30 of the present invention, and FIG.
X cross-sectional view is shown, and 18 is a sample metal tube, which is obtained by cutting a metal tube having the same material, the same outer diameter and the same plate thickness as the metal tube used in the nuclear power plant etc. to an appropriate length. Is.

The small-diameter portion 6 of the base plate 4 shown in FIG. 3 is fitted to one end (upper end in FIG. 1) of the metal tube 18 and the base plate 4 is fixed to one end of the metal tube 18.

On the other hand, the sleeve 8 shown in FIGS. 4 and 5 is fitted on the outer side of the shaft 1 of FIG. 2, and the pressing ring 16 of FIG. After inserting the bolt 19 shown in FIGS. 1 and 10 into the insertion hole 17, the bolt 19 is screwed into the female screw hole 12 of the sleeve 8 shown in FIGS. 4 and 5, and the pressing ring 16 is attached to the convex portion of the sleeve 8. When the pressing member 13 shown in FIGS. 6 to 8 is fixed from the outer peripheral side while being fixed to the lower surface of the sleeve 10, the sleeve 8 is attached to the outside of the shaft 1.
The pressing member 13 and the pressing ring 16 are assembled.

The shaft 1, the sleeve 8, the pressing member 13, and the pressing ring 16 assembled in this manner are connected to the metal tube 18
Is inserted into the inside of the metal tube 18 from the other end (lower end in FIG. 1), and the upper portion of the shaft 1 is projected above the base plate 4 through the through hole 7 of the base plate 4 fixed to one end of the metal tube 18. .

Next, as shown in FIG. 1, when the nut 20 is screwed onto the male screw portion 2 of the shaft 1, the assembling of the stress applying device 30 is completed. Then, when the nut 20 is tightened, after the lower surface of the nut 20 contacts the upper surface of the base plate 4, the shaft 1 moves above the axis. As described above, the male screw portion 2, the base plate 4, and the nut 20 are means for moving the shaft 1 in the axial direction.

When the shaft 1 moves above the axis, the tapered portion 3 of the shaft 1 comes into close contact with the taper surface 14 on the inner surface of the pressing member 13, and the shaft 1 further moves above the axis, so that the pressing member is moved. 13 tapered surface 14
Is pushed outward by the tapered portion 3 of the shaft 1,
As shown in FIGS. 1 and 10, the outer surface 15 of the pressing member 13 comes into contact with the inner surface of the metal tube 18 and presses the metal tube 18 from the inside to the outside.

For this reason, the metal pipe 18 has a portion which is pushed outward by the pressing member 13 and a portion which is not pushed between the portions, and the metal pipe 18 is deformed from the solid line state in FIG. 11 to the broken line state. And the tensile stress indicated by +,
A compressive stress indicated by-is generated.

At this time, a strain gauge is attached on the outer circumference of the metal tube 18 between the pressing members 13, and the stress generated is measured so that the stress falls within the elastic limit of the metal tube 18. To do.

In this state, as shown in FIG. 1, a lock nut 21 is screwed onto the male thread portion 2 of the shaft 1 to prevent the nut 20 from rotating so that the shaft 1 is prevented from moving in the axial direction, and the stress applying device 30 is provided. The inner surface of the pressing member 13
Metal tube 18 that is pressed outward by
Is immersed in an aqueous solution of 42% magnesium chloride at a temperature of 143 ° C. defined by JIS for a predetermined time, stress corrosion cracking defects are formed in the metal pipe 18, and the method of the invention of claim 1 is carried out. Will be.

The pressing member 13 shown in FIG. 8 is an embodiment of the invention of claim 4 in which the outer surface 15 of the pressing member 13 is the metal tube 1.
The pressing member 1 has a curved surface that closely contacts the inner surface of the pressing member 1.
If the axial dimension h of 3 and the circular dimension l of the outer surface 15 of the pressing member 13 are made equal, stress corrosion cracking defects are formed in the circumferential direction and the axial direction of the metal tube 18.

If there is a portion of the plurality of portions extruded by the pressing member 13 of the metal tube 18 to the outside that does not want to cause stress corrosion cracking defects, as shown in FIG. The coatings 22 and 23 are applied to the inner surface and the outer surface of the portion where it is desired not to generate the above by means such as coating epoxy resin or the like. In this case, the metal tube 1
The coating 23 applied to the outer surface of 8 may be a resin coating material, and may be attached to the outer surface of the metal tube 18 by a mounting bracket 24.

In this way, the inner surface and the outer surface are covered with the coatings 22, 23.
When the metal tube 18 subjected to the treatment is immersed in an aqueous solution of 42% magnesium chloride at a temperature of 143 ° C. for a predetermined time, the coating 2
No stress corrosion cracking defects are formed even if the portions provided with Nos. 2 and 23 are extruded to the outside by the pressing member 13, and stress corrosion is caused only to the portions extruded to the outside with the pressing member 13 without providing the coatings 22 and 23. Since the crack defect is formed, the stress corrosion crack defect can be formed at any place.

The above method is the embodiment of claim 2.

FIG. 13 shows a pressing member 13 according to the invention of claim 5.
15 is a perspective view of the embodiment of FIG.
A horizontal ridge 25 is formed at the bottom. Metal tube 18
When the center radius of R is Rmm and the plate thickness of the metal tube 18 is tmm, the axial dimension h of the protrusion 25 in the horizontal direction is 0.5√ (R
It is preferable that the size is smaller than t) and the arc-direction size 1 of the horizontal projection 25 is larger than √ (Rt). The pressing member 13 shown in FIG. 13 is used in FIGS. The stress applying device 30 is configured as shown, and the metal pipe 1
While pressing 8 from the inside to the outside, move the metal tube 18 to 143 ° C.
When immersed in an aqueous solution of 42% magnesium chloride at a temperature of, for a predetermined time, a circumferential stress corrosion cracking defect is formed in the metal tube 18.

FIG. 14 shows a pressing member 13 of the invention of claim 6.
15 is a perspective view of the embodiment of FIG.
A vertical ridge 26 is formed at the bottom. When the center radius of the metal tube 18 is Rmm and the plate thickness of the metal tube 18 is tmm, the axial dimension h of the longitudinal ridge 26 is set to a dimension larger than √ (Rt), and the arc of the vertical ridge 26 is set. It is preferable that the directional dimension 1 is smaller than 0.5√ (Rt),
1 and 10 by using the pressing member 13 of FIG.
The stress applying device 30 is configured as shown in FIG. 3, and the metal pipe 18 is immersed in an aqueous solution of 42% magnesium chloride at a temperature of 143 ° C. for a predetermined time while the metal pipe 18 is pressed from the inside to the outside. A stress corrosion cracking defect is formed in the axial direction.

Pressing member 13 when constructing the stress applying device
Is not limited to three, but can be any other number.

[0034]

According to the first aspect of the present invention, it is ensured that the required stress corrosion cracking defects, which are optimum for using the waveform of the reflected wave obtained by injecting ultrasonic waves on the metal tube as a sample, as a criterion for judgment. There is an effect that can be formed.

According to a second aspect of the present invention, when there is a portion where stress corrosion cracking defect is not desired to be generated among a plurality of portions extruded outward by the pressing member of the metal pipe, the stress corrosion cracking defect is present at that portion. There is an effect that it becomes possible not to cause.

When the invention of claim 3 is used in the method of claims 1 and 2, there is an effect that a stress corrosion cracking defect can be easily formed at an arbitrary position without plastically deforming the metal tube.

The invention of claim 4 has an effect that stress corrosion cracking defects can be formed in the circumferential direction and the axial direction of the metal tube.

The invention of claim 5 has an effect of forming a stress corrosion cracking defect in the circumferential direction of the metal tube.

The invention of claim 6 has an effect that a stress corrosion cracking defect can be formed in the axial direction of the metal tube.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing a usage state of an embodiment of a stress applying device of the present invention.

FIG. 2 is a front view of an embodiment of a shaft.

FIG. 3 is a front view of a base plate used in the stress applying device of the present invention.

FIG. 4 is a front view of an embodiment of a sleeve.

5 is a sectional view taken along line VV of FIG.

FIG. 6 is a bottom view of an example of a pressing member.

7 is a sectional view taken along line VII-VII in FIG.

FIG. 8 is a perspective view of an example of a pressing member.

FIG. 9 is a plan view of a pressing ring used in the stress applying device of the present invention.

10 is a cross-sectional view taken along line XX of FIG.

FIG. 11 is a plan view showing a state where stress is applied to the metal tube.

FIG. 12 is a partial vertical sectional front view when performing the method of claim 2.

FIG. 13 is a perspective view of an embodiment of a pressing member used in the stress applying device according to the present invention.

FIG. 14 is a perspective view of an example of a pressing member used in the stress applying device of claim 6;

[Explanation of symbols]

 1 shaft 2 male screw part (means for moving shaft in axial direction) 3 taper part 4 base plate (means for moving shaft in axial direction) 8 sleeve 13 pressing member 15 outer surface 18 metal tube 20 nut (moving shaft in axial direction) 22) coating 23 coating 25 ridges 26 ridges 30 stress applying device

Claims (6)

[Claims] 1. A plurality of pressing members are arranged inside a metal pipe in which a defect due to stress corrosion cracking is to be formed, and the pressing members press the metal pipe from the inside to the outside to generate stress in the metal pipe. A method of forming a stress corrosion cracking defect in a metal tube, wherein the metal tube in the stressed state is immersed in an aqueous solution of magnesium chloride. 2. The method of forming a stress corrosion cracking defect for a metal pipe according to claim 1, wherein a part of the pressed portion of the metal pipe that presses the metal pipe from the inside to the outside is covered with a pressing member. 3. A shaft which has a tapered portion and is inserted into the center of a metal pipe in which a defect due to stress corrosion cracking is to be formed, and a sleeve which is fitted to the outside of the shaft and is inserted inside the metal pipe together with the shaft. A plurality of pressing members mounted on the end of the sleeve, the inner surface of which contacts the tapered portion of the shaft and the outer surface of which contacts the inner surface of the metal tube; and means for moving the shaft in the axial direction. A stress applying device for use in a method for forming a stress corrosion cracking defect in a metal pipe, which is characterized by 4. The stress applying device used in the stress corrosion cracking defect forming method for a metal pipe according to claim 3, wherein the outer surface of the pressing member is a curved surface that can be brought into close contact with the inner surface of the metal pipe. 5. The stress applying device used in the method of forming a stress corrosion cracking defect for a metal pipe according to claim 3, wherein a protrusion extending in the circumferential direction of the metal pipe is formed on the outer surface of the pressing member. 6. The stress applying device used in the stress corrosion cracking defect forming method for a metal pipe according to claim 3, wherein a protrusion extending in the axial direction of the metal pipe is formed on the outer surface of the pressing member.