JPH07151295A - Suppression for growth of crack on piping - Google Patents

Abstract

PURPOSE:To suppress the generation and growth of a crack due to the fatigue, stress erosion cracks, etc. CONSTITUTION:Semiannular fixing members 6 and 6' each of which has a taper surface on the inner surface, setting a part having a crack 3 of a pipe 1 interposed, are installed, and a taper member 7 is press-fitted into the fixing members 6 and 6', and the tensile load in the axial direction of the pipe 1 is applied and then released. Tightening rings 8 and 8' are tightened by a tightening bolt 9 and fixed on the fixing members 6 and 6'. Further, the stress in the vicinity of the crack 3 is applied on a compression side by loading the compression load. Accordingly, the residual stress on the compression side is generated at the top end part of the crack 3, and the generation and the growth of the crack can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing crack propagation in piping used in nuclear power plants, chemical plants and the like.

[0002]

2. Description of the Related Art Austenitic stainless steel, which is mainly used for piping in nuclear power plants and chemical plants, has a toughness because its base is an austenite structure, and rapid unstable fracture starting from cracks and the like. It is a material that is unlikely to cause cracking, and even if cracks such as stress corrosion cracking occur, there is a tendency for leakage to occur before pipe breakage occurs.

In order to improve the reliability of the plant and improve its operating rate, various methods for suppressing the growth of cracks in pipes have been developed. Among these methods for suppressing crack propagation in pipes, a method that has been widely and conventionally performed is known as a high frequency heating residual stress improving method.

This method uses a high-frequency induction coil on the outer circumference of the pipe where a small crack that does not penetrate inside and outside may exist inside the pipe at a location such as a butt-welded joint location of the piping. In locations where the cracks may exist due to thermal stress due to the temperature difference between the inner and outer circumferences of the pipe, by heating the pipe to a desired temperature exceeding the operating temperature and simultaneously cooling the pipe with water. The residual stress is changed to the compression side, thereby suppressing crack growth.

[0005]

The conventional method for suppressing pipe cracks by the high frequency heating residual stress improving method requires a high frequency induction heating device as a heating source and a water cooling device, and therefore has a problem that the device becomes large-scale. .

The present invention has been made to solve the above problems, and in a pipe used in a nuclear power plant, a chemical plant, or the like, the stress at a location where a crack exists is changed to a compression side so that the crack progresses. In a method for suppressing cracks, it is an object to provide a crack growth suppressing method for a pipe that does not require a large-scale device and that can suppress the occurrence of cracks during use of a pipe having a minute crack that does not penetrate inside and outside. To do.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and two places are provided at a predetermined interval in the axial direction of the outer periphery of the pipe. A pair of taper fixing members are attached, a taper-shaped semi-annular member is attached between the pair of fixing members, and the semi-annular member is mechanically contracted so that the fixing members are axially aligned. After a tensile load of a predetermined magnitude is applied to, the contraction is released and the tensile load is removed.

[0008]

[Operation] By applying a certain amount of tensile stress to a crack existing part of a pipe having a small crack that does not penetrate inside and outside and unloading, a compressive residual stress is generated at the crack tip and Generation is suppressed and crack propagation is delayed due to crack opening.

Therefore, even when the pipe is in use,
Generation and propagation of cracks due to fatigue and SCC are suppressed. Further, the compressive stress is generated in the vicinity of the crack of the pipe having the crack to suppress the propagation of the crack due to fatigue and SCC.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for suppressing crack propagation in a pipe according to the present invention will be described with reference to FIGS. 2 is a sectional view taken along the line AA in FIG.

That is, in FIG. 1, the pipe 1 is abutted and welded at the welded portion 2. In the welded portion 2, a minute crack 3 that does not penetrate to the outside is formed near the innermost periphery thereof.

A retaining ring groove 4 having a substantially semicircular cross section is provided on the outer periphery of the pipe 1 at a position that is substantially equidistant from the welded portion 2 in the axial direction and is not far from the welded portion 2 in the axial direction. It is recessed. The inner circumferential portion of a C-shaped concentric retaining ring 5 having a circular cross section is fitted into each of the two retaining ring grooves 4.

The two fixing members 6 forming a pair are each divided into two equal parts in a plane including the central axis thereof, and when combined at the dividing surfaces, the outer circumference is a short cylinder on the same axis as the inner circumference. It is formed to have a shape.

The inner circumference of the fixing member 6 is a right cylinder so that it can be fitted into the outer circumference of the pipe 1, and the outer half of each retaining ring 5 fits into the inner circumference.
A single retaining ring groove is recessed.

Further, the surfaces sandwiching the fixing members 6 and 6'are tapered. The tightening ring 8 is an annular body having an irregular projection on a part of its outer circumference in a plane including its central axis.
The two parts of the equally divided shape are tightened with four tightening bolts 9 to form an annular shape. On the inner circumference of the tightening ring 8, a retaining protrusion 11 is integrally provided in an annular shape that fits in the retaining groove 10.

The taper member 7 is 2 in a plane including the center thereof.
It is divided, and when combined at the dividing surface, the outer circumference is formed into a short cylindrical shape on the same axis as the inner circumference, the inner circumference is larger than the pipe outer circumference, and the taper angle is the fixing member. The taper angle of 6 matches.

Thereafter, the taper member 7 is mechanically tightened in the radial direction to fix the fixing members 6 and 6'in FIG.
Forces are applied in the directions away from each other via the tapered surfaces of.
Since the fixing members 6, 6'are restrained from moving relative to the pipe 1 in the axial direction by the retaining ring 5, the portion sandwiched by the fixing members 6, 6'fixed to the pipe 1 is loaded with a tensile load. To be done.

The magnitude of the load can be adjusted by mechanically adjusting the tightening amount of the taper member 7. Further, since the fixing members 6 and 6'and the taper member 7 are each divided into two parts, they can be easily separated from the pipe 1 by removing the tightening bolt 9.

When a tensile stress larger than the stress that is normally applied to a pipe having a minute crack in this way is applied, a compressive residual stress is generated at the crack tip to suppress the occurrence of cracks, and The crack opening delays the crack growth. Therefore, even when the pipe is in use, the generation and propagation of cracks due to fatigue and stress corrosion cracking (SCC) are suppressed.

Further, in the first, as the material of the taper member 7, Ti 50% and Ni 50% as atomic% are used.
50%, Ni 20%, Cu 30%, Au 52.5%, Cd 4
A shape memory alloy that undergoes thermoelastic-plastic martensitic transformation such as 7.5% is used.

These alloys that undergo the thermo-elasto-plastic martensant transformation have the property of becoming a martensite phase by cooling from the shape memory matrix phase and returning to the matrix phase by heating from the martensite phase.

The use of the shape memory alloy is to memorize an arbitrary shape in the alloy in the parent phase state, then cool the parent phase to the martensant phase and change the shape of the alloy in this martensant phase. In this state, the shape memory alloy is restored to the original shape when it is heated and returned to the parent phase state.

The stress generated during this shape recovery is large enough to deform the Martensanto phase alloy. The taper material 7 is stored and set so that a predetermined tightening force for the pipe 1 can be obtained in the state of the heated mother phase. Then, the taper material 7 is cooled to undergo martensite transformation, and is deformed and stored in the martensite phase state so that its inner diameter corresponds to the taper surface.

When the taper material 7 made of the shape memory alloy thus constructed is heated and the alloy returns to the parent phase state, the taper material 7 is restored to the memorized size in the parent phase state, and the pipe is piped through the tapered surface. No. 1 is loaded with tensile stress.

Next, referring to FIG. 3, another embodiment of the method for suppressing crack propagation in a pipe according to the present invention will be described. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and overlapping description will be omitted. That is, in this embodiment, as shown in FIG. 3, when a jig composed of two fixing members 12 and 13 and one taper member 14 is arranged with the crack 3 of the pipe interposed therebetween. Is.

In FIG. 3, a crack 3 is formed in the weld 2 of the pipe 1.
Is occurring. Retaining ring grooves 4 are formed on both surfaces of the pipe 1 on both sides of the welded portion 3, and retaining rings 5 are fitted into the retaining ring grooves 4. Fixing members 12 and 13 are attached to the retaining ring 5, fastening rings 15 and 16 are attached to the fastening members 12 and 13, and the fastening rings 15 and 16 are fixed with fastening bolts 17. The taper member 14 is pushed into the fixing members 12 and 13.

By mechanically tightening the taper member 14 simultaneously in the radial direction, a tensile stress is generated in the axial direction in the region between the fixing members 12 and 13 as in the above-described embodiment. Further, due to the generation of tensile stress, compressive stress is generated in this vicinity.

Therefore, two pairs of taper members sandwiching the crack 3 are provided.
In the case of having 14, the stress distribution in the axial direction as shown in FIG. 4 is generated, so that the propagation of the crack 3 is suppressed. Piping 1
A compressive stress will be generated at the crack existing location.

Similarly, by using a shape memory alloy as the material of the taper member 14 and utilizing thermoelastic-plastic Martensant transformation, the location of the crack 3 in the pipe 1 is as shown in FIG.
A compressive stress in the axial direction is generated as shown in.

In any case, since the fixing members 12 and 13 and the taper member 14 are each divided into two parts, they can be easily separated from the pipe 1 by removing the tightening bolt 17.

As described above, the method of the present invention does not have a one-piece structure, but has a divided structure that can be easily disassembled and assembled. Therefore, it is not necessary to cut the pipe when repairing or replacing the pipe.

[0032]

According to the present invention, a crack existing portion of a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and two portions are tapered at a predetermined interval in the axial direction of the outer circumference of the pipe. After applying a tensile load of a predetermined magnitude between the fixing members by arranging them and mechanically or heating them, a residual compressive stress is generated near the crack by releasing the tensile load, or Press the taper processed member. As a result, compressive stress is generated between the fixing members. Therefore, there is an effect that crack propagation of the pipe can be easily suppressed without requiring a large-scale device.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of a method for suppressing crack propagation in a pipe according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a vertical cross-sectional view showing a second embodiment of the crack growth inhibiting method for a pipe according to the present invention.

FIG. 4 is a stress distribution diagram in the axial direction of the pipe when the tapered member is pressed.

[Explanation of symbols]

1 ... Piping, 2 ... Weld, 3 ... Crack, 4 ... Retaining groove, 5 ...
Retaining ring, 6 ... fixing member, 7 ... taper member, 8, 15, 16 ... tightening ring, 9, 17 ... tightening bolt, 10 ... retaining groove, 11 ... retaining protrusion, 12, 13 ... fixing member, 14 ... Tapered material.

Front page continuation (72) Masahiro Saito, Inventor Masahiro Saito, 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Ltd. Within the Toshiba Yokohama office In the office

Claims (4)

[Claims] 1. A pair of fixings, wherein the crack-existing portion of a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and tapering is performed at two places at a predetermined interval in the axial direction of the outer periphery of the pipe. A member is attached, a tapered semi-annular member is attached between the pair of fixing members, the semi-annular member is mechanically contracted, and a tensile load of a predetermined size is axially applied between the fixing members. Is applied, and then the contraction is released to unload the tensile load. 2. A pair of fixings in which the crack-existing portion of a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and taper processing is performed at two places at a predetermined interval in the axial direction of the outer periphery of the pipe. After attaching a member and combining a semi-annular ring made of a shape memory alloy that has been subjected to taper processing between the pair of fixing members, the semi-annular ring made of a shape memory alloy is heated to shrink the axis line between the fixing members. A method for suppressing crack propagation in a pipe, which comprises cooling after applying a predetermined tensile load in a direction. 3. A semi-annular ring in which the crack-existing portion of a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and two portions are tapered at predetermined intervals in the axial direction of the outer periphery of the pipe. A method for suppressing crack propagation in a pipe, characterized in that a fixing member for sandwiching a member is attached, and the semi-annular member is mechanically contracted to apply a compressive stress in the axial direction between the fixing members. 4. A shape memory alloy in which the crack-existing portion of a pipe having a minute crack that does not penetrate inside and outside is sandwiched in the middle, and two portions are tapered at a predetermined interval in the axial direction of the outer periphery of the pipe. A crack growth of a pipe, characterized in that a fixing member sandwiching a manufacturing semi-annular ring is attached and heated to shrink the shape memory alloy semi-annular ring to apply an axial compressive stress between the fixing members. Deterrence method.