JPS63266295A - Crack progress inhibiting method of piping - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application) The present invention relates to a method for inhibiting crack growth in piping used in atomic couplants, chemical plants, and the like.

(Prior art) Austenitic stainless steel, which is mainly used for piping in atomic couplants and chemical plants, has an austenitic structure, so it has high toughness and is susceptible to rapid and unstable fractures caused by cracks, etc. Even if cracks such as stress corrosion cracking occur, leakage tends to occur before pipe rupture occurs. However, in order to enhance the reliability of plants and improve their operating rates, various methods for inhibiting pipe crack growth have been developed. Among these pipe crack propagation inhibiting methods, a typical one is the high-frequency heating residual stress improvement method, which has been widely practiced in the past. This method uses a high-frequency induction coil to repair the outer periphery of piping, where there is a risk of small cracks that do not penetrate inside or outside, such as the location of butt welded joints, to a temperature that exceeds the operating temperature of the piping. The pipe is heated to a desired temperature, and at the same time, water is passed through the pipe to cool it, creating a large temperature difference between the inner and outer circumferences of the pipe, and the thermal stress caused by this temperature difference reduces the residual stress at the location where the crack is likely to exist. is changed to the compression side, thereby inhibiting crack propagation.

(Problems to be Solved by the Invention) The conventional method for suppressing pipe crack growth using high-frequency heating residual stress improvement method requires a high-frequency induction heating device as a heating source and a water cooling device, resulting in major damage to the device. There were drawbacks.

This invention was made in order to solve the above-mentioned problems of the conventional piping crack propagation prevention method. The purpose is to provide a method.

[Structure of the invention]

(Means for Solving the Problems) The method of the present invention involves sandwiching the cracked portion of a pipe in which there is a minute crack that does not penetrate inside or outside in the middle, and placing a predetermined interval in the axial direction of the outer circumference of the pipe. A fixing member is removably attached to the portion of the piping, and the portion of the piping that is sandwiched by the fixing member, including the cracked portion, is heated to a predetermined temperature higher than the operating temperature of the piping, and a fixing member is attached to the portion of the piping in a predetermined axial direction. After applying a tensile load of a magnitude of , the above purpose is achieved by releasing the tensile load and lowering the temperature of the portion below the operating temperature of the pipe.

(Function) According to the method of the present invention, in austenitic stainless steel piping, by heating the portion of the piping where there is a minute crack that does not penetrate inside and outside, and the portion adjacent thereto, to a predetermined temperature, the piping can be improved. Since the toughness of the material is increased, a larger tensile load can be applied to the portion before heating. Heating said section of the piping to a predetermined temperature higher than its service temperature, and applying a predetermined tensile load to that section, which is greater than the permissible tensile load at the pipe's service temperature, by a simple means detailed below. At this time, the piping undergoes some plastic deformation and is strengthened. If the temperature of the piping is subsequently lowered and the tensile load is released, the residual stress at the location where the crack exists becomes compressive stress, so even if the piping is put into service and a service tensile load is applied, the crack will continue to grow. It is suppressed without any problem.

(Embodiment) An embodiment of the present invention is shown in FIGS. 1 to 4. Pipes 1.1 are butt-welded at welded portions 2. In FIGS. Welding part 2
has a minute crack 3 on its inner periphery that does not penetrate outward. The piping 1.1 is recessed at an approximately equidistant distance from the welded portion 2 of the pipe 1.1 in the axial direction. 4 retaining ring grooves 4
An inner peripheral portion of a C-shaped concentric retaining ring 5 having a circular cross section is fitted into each of the retaining rings 5. The fixing members 6.6, each of which is a pair, are each divided into two equal parts along a plane that includes the center axis thereof, and when assembled at the dividing plane, the outer periphery forms a taper 7 on the same axis as the inner periphery. It is formed into a short cylindrical shape. The inner periphery of the fixing member 6 is a right cylindrical shape that can be fitted onto the outer periphery of the pipe 1, and the inner periphery has two strips into which approximately the outer half of each of the two retaining rings 5 is fitted. A retaining ring groove 8 is recessed. The wedge cylinder 9° 10 is divided into two equal parts along a plane including its center axis, and when assembled at the dividing plane, the inner periphery forms a tapered hole 11 that fits into the taper 7, and the outer periphery forms an annular hole. It is formed into a short cylindrical shape with a right cylindrical surface except for the retaining groove 12. The wedge cylinder 9.10 has five through screw holes 13.10 in its annular interior parallel to the central axis and at equal pitches in the circumferential direction. A bottom hole 14 is provided, and a threaded portion of an adjustment bolt 15 is provided in the screw hole 13 and the bottom hole 14 .

The rod-shaped part is fitted. The tightening ring 16 is made by dividing an annular body having irregular protrusions on a part of its outer periphery into two equal parts in a plane including its central axis, and tightening the two parts with four tightening bolts 17 to form an annular shape. However, since the shapes of the two portions to be tightened differ only in the shape of the attachment portion of the tightening bolt 17, the two portions will not be distinguished and will be described together as the tightening ring 16. A retaining groove 1 is provided on the inner circumference of the tightening ring 16.
An annular removal stop protrusion 18 that fits into 2 is integrally provided.

Reference numeral 19 denotes a heating device that is detachably installed between the fixing members 6, 6 and surrounding the outer periphery of the welded portion 2.

The implementation steps of the method of this invention will now be described.

Fixing members 6, 6 are fixed to the outer periphery of the pipes 1, 1.

To do this, first, connect the four stopper pipes 5 to each pipe 1.
into each of the retaining ring grooves 4. Align the two equally divided parts of the fixing member 6 so that the retaining ring groove 8 fits into the retaining ring 5, cover the outer periphery of the piping 1, put the two equally divided parts together, and temporarily secure the sides with adhesive tape or the like. Attach it and hold it in a ring shape. At that time, the pair of fixing members 6, 6 are attached such that the small ends of the tapers 7.7 are opposed to each other. Wedge cylinders 9, 10, taper holes 11°11
is aligned with the taper 7.7, mounted on the taper 7.7, and held in an annular shape in the same manner as the fixing member 6. 10
Each of the adjusting bolts 15 is passed through the threaded hole 13 of the wedge cylinder 9, and the rod-shaped tip thereof is fitted into the bottomed hole 14.

The adjustment bolt 15 is a wedge cylinder 9. When the IO is in a half-split state, it may be passed through the wedge cylinder 9.10 in advance and covered with a lid so as not to interfere with the subsequent assembly work. Tightening ring 16
゜16 is the removal prevention protrusion 18. 18 is removed from the removal prevention groove 1.
2. Fitted with 12, wedge cylinder 9. It is placed over the outer periphery of the lO and tightened in an annular manner with four tightening bolts 17. Next, remove the adhesive tape used for tacking. By tightening the tightening bolt 17, the fixing member 6. 6,
<The rust cylinders 9, 10 and the tightening rings 16, 16 sandwich the welded part 2, which has a small crack 3 that does not penetrate to the outside, in the middle, and can be freely attached and detached at two locations not far in the axial direction of the pipe 1.1. can be added to.

In this state, if the 10 adjustment bolts 15 are uniformly tightened one after another, the tip of the left rod-shaped part of the adjustment bolt 15 will be in place of the bottom hole 14 in FIG. 15, the tightening force applies force to the fixing members 6.6 through the wedge cylinders 9, 10 in the direction of separating them from each other. Fixing members 6, 6 are attached to piping 1, 1
On the other hand, since the relative movement in the axial direction is restrained by two retaining rings 5 each, the portion of the pipe 1.1 that is held between the fixing members 6, 6 is connected to the adjustment bolt 15 and the wedge cylinder 9.1.
A tensile load is applied through 0.

The magnitude of the load can be freely adjusted using a torque wrench or the like used to turn the adjustment bolt 15.

By loosening the adjustment bolt 15 and removing the tightening bolt 17, the tightening ring 16, wedge cylinder 9, 10, fixing member 6, and retaining ring 5 can be easily removed from the pipe 1.

Figure 3 shows a pipe 1 with a minute crack 3 that does not penetrate inside or outside.
In (Fig. 1), crack 3 at a location close to crack 3
This is a schematic representation of the relationship between the distance from the center and the residual stress of the pipe 1 at that location. Fig. 3(a) shows a case where the pipe 1 has a crack 3 and is left in a used state naturally, and residual tensile stress is acting on the pipe 1 near the crack 3, and the pipe 1 is used as is. Then, there is a possibility that the crack 3 will grow.

The heating device 19 heats the pipe 1.1, including the welded portion 2 where the crack 3 exists, between the fixing members 6, 6 to a predetermined temperature higher than the operating temperature of the pipe 1.1. In this state, if the adjustment bolts 15 are tightened uniformly, the fixing member 6.
A predetermined tensile load larger than the allowable tensile load of the piping 1.1 can be applied to the portion between the fixing members 6.6 of the piping 1.1 in the direction in which the piping 1.1 opens. The pipes 1, 1 are made of austenitic stainless steel, and their toughness improves with heating, so even if a predetermined tensile load greater than the allowable tensile load is applied, the crack 3 will grow and the pipe 1. 1 will not be damaged. Furthermore, the piping 1.1 is
Due to the application of the tensile load, the material is slightly plastically deformed and strengthened, so that it can withstand a larger tensile load than before the application of the tensile load.

Figure 3(b) shows the state of the piping 1,1 when the piping 1.1 is heated and a tensile load is applied to the piping 1.1 as described above.
The residual tensile stress generated in the vicinity of the crack 3 is shown, and it is shown that this residual stress is larger than that in FIG. 3(a).

A pipe 1゜1 with a small crack 3 that does not penetrate inside or outside is heated to a temperature higher than its operating temperature as described above,
After applying a tensile load larger than the allowable tensile load for use in the axial direction, loosen the adjustment bolt 15 to release the tensile load, stop heating by the heating device 19, and lower the temperature of the pipes 1, 1 to below their operating temperature. If so, the residual stress in the pipe 1.1 in the vicinity of the crack 3 becomes compressive stress, as shown in FIG. 3(C), and the growth of the crack 3 is suppressed.

In FIG. 4, curve i1#(d) shows the relationship *a between the temperature T and the tensile load P in the pipe 1 (FIG. 1). When the piping 1 is not heated and the tensile load described above is not applied, the crack 3 (FIG. 1) in the piping 1 begins to grow under the tensile load P1 when the piping 1 is at its operating temperature T1. Since the pipe 1 has the characteristic that its toughness increases as the temperature rises up to a certain temperature, the tensile load P at which the crack 3 begins to grow increases along the curve ((1)) as the temperature of the pipe 1 rises. The pipe 1 is heated to a predetermined temperature T2 higher than its operating temperature T1, and the predetermined tensile load is lower than the tensile load P2 when the crack 3 starts to grow at the temperature T2 of the pipe 1 and is larger than the tensile load P1. Piping P3 1
, the piping 1 is slightly plastically deformed and strengthened by processing.If the temperature of the piping 1 is lowered to the temperature TI, then the tensile load P at the time when the crack 3 starts to grow becomes approximately P3.
increase to.

This increase in tensile load enhances the effect of inhibiting the propagation of cracks 3 caused by heating and applying a tensile load to the piping 1, followed by lowering the temperature of the piping 1 and releasing the tensile load.

Next, other embodiments of the invention will be described.

In this embodiment, the adjustment bolt 15 in the embodiment shown in FIGS. 1 and 2 is replaced with an adjustment bolt 15a (not shown), and the heating device 19 heats the welded portion 2 of the pipe 1.11. In addition, one straight bolt 15a can be heated. The adjustment bolt 15a is made of a shape memory alloy). ! At a predetermined temperature higher than the operating temperature at which fl, 1 is heated, it expands to a predetermined dimension with a predetermined stretching force, and at a low operating temperature of the pipes 1, 1, it has the characteristic of shrinking to a predetermined short dimension.

When the pipe 1.1 is at a low operating temperature, the adjusting bolt 15a
Tighten the wedge cylinder 9 degrees 104 degrees without being too tight or loose, and tighten the adjustment bolt 15 along with the welded part 2 and piping 1.1.
a to the pipe 1.a by the heating device 19. When the pipes 1, 1 are heated to a predetermined temperature higher than the operating temperature of the pipes 1, 1, the wedge cylinders 9, 10 and the fixing members 6, 6 are tightened by the adjusting bolt 15a, which attempts to expand with a predetermined tension force as the temperature rises. .Fixing member 6゜6 through four retaining rings 5
A tensile local load of a predetermined magnitude is applied in the axial direction between the two. Stop the heating by the heating device 19, and adjust the temperature of the adjustment bolt 15a along with the pipes 1 and 1 to the pipe l.

If the temperature is lowered to below the operating temperature of 1.1, the adjustment bolt 15a will shorten, thereby stopping the application of tensile load to the pipe 1.1, and the residual stress in the pipe 1.1 in the vicinity of the crack 3 will become compressive stress. , the growth of crack 3 is inhibited.

In the embodiment described above, in order to apply a tensile load to the pipes 1, 1, the pipes 1. 1. It is necessary to tighten the adjustment bolt 15 during heating, but in this embodiment, since a shape memory alloy is used for the adjustment bolt 15a, the tightening adjustment of the adjustment bolt 15a can be made by tightening the adjustment bolt 15a. There is no need to carry out heating at high temperature in step 1.

From pipes 1 and 1 where the crack 3 growth prevention method was implemented,
By removing the tightening bolt 17 was used to carry out this method. All members including the tightening ring 16 and the retaining ring 5 can be easily removed.

〔Effect of the invention〕

The method of the present invention is to removably attach a fixing member to the outer periphery of the pipe, sandwiching the crack existing part of the pipe in the middle, and fixing the part of the pipe that is sandwiched by the fixing member. After heating the piping to a predetermined temperature higher than the operating temperature of the piping and applying a predetermined amount of tensile load in the axial direction of that part, the tensile load is released and the temperature of that part of the piping is increased. By lowering the temperature to below the operating temperature, the residual stress in the piping near the crack can be made into compressive stress, and this method can be carried out using a simple device as detailed above to prevent crack propagation in the piping. This has the effect of easily suppressing this.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing an embodiment of this invention,
Fig. 1 is a longitudinal cross-sectional view, Fig. 2 is a side view, Fig. 3 is a residual stress diagram of the pipe 1 near the crack 3 in Fig. 1, and Fig. 4 is a
It is a temperature T-tensile load P relationship curve diagram in the piping 1 of FIG. 1. 1... Piping, 3... Crack, 6... Fixed member.

Claims (1)

[Claims] A fixing member is removably attached to two locations at a predetermined interval in the direction of the outer circumferential axis of the piping, sandwiching the crack existing part in the middle of the piping where there is a minute crack that does not penetrate inside or outside, and fixing the crack in the piping. heating the part sandwiched by the fixing member, including the existing location, to a predetermined temperature higher than the operating temperature of the piping;
After applying a tensile load of a predetermined magnitude to the portion of the piping in the axial direction, the tensile load is released, and
A method for inhibiting crack growth in piping, comprising lowering the temperature of the portion below the operating temperature of the piping.