JPS5932262B2 - Method and device for shot peening of curved pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shot peening method and apparatus for removing residual tensile stress on the outer surface of a curved pipe to prevent so-called stress corrosion cracking, and in particular to improving the shot peening effect,
This is a measure to prevent the scattering of fine powder materials.

It is generally known that if tensile stress remains in a steel material, cracks and corrosion cracks will progress from that part. Therefore, fine powder such as glass beads is sprayed on the surface of the steel material under high pressure to reduce the residual tensile stress on the surface of the steel material. Shot peening is used for the purpose of converting stress into compressive stress and preventing corrosion cracking of steel materials.

Among steel materials with such residual stress, for example, curved pipes used in heat exchangers for nuclear power generation are exposed to extremely high temperatures and are subject to strong thermal stress and corrosion, so it is necessary to remove the stress after bending. Although sintering is commonly used for this purpose, stress relief methods using shots have recently begun to be used.

In the conventional shot peening method, which aims to relieve stress, fine powder is sprayed all at once onto the outer periphery of the circular tube from a large number of nozzles installed around the tube. The jetting force is reduced, leading to a reduction in the shot peening effect.

In addition, in curved pipes for heat exchangers, the curved part and straight pipe part are generally continuous, but the distribution of residual stress is completely different between the curved part and the straight pipe part, so it is difficult to It is very difficult to perform shot peening on a curved portion and a straight pipe portion continuously using one nozzle set.

Therefore, it is desirable to treat the curved portion and the straight pipe portion separately using nozzle sets arranged according to the respective residual stress distribution states.

Furthermore, since shot peening uses fine powder as mentioned above, if the fine powder flow interferes with each other or stagnates as in the conventional method, the fine powder leaks to the outside, causing many problems in terms of worker health management. .

The present invention aims to solve the drawbacks and inconveniences inherent in the conventional shot peening methods as described above, and provides a shot peening means optimal for curved pipes where the residual stress distribution is concentrated in a specific place. In order to prevent nozzles from interfering with each other and to ensure an orderly flow of fine powder, all the nozzles are divided into multiple nozzle groups, each nozzle group is made to spray in turn, and the fine powder is discharged from the discharge port on the downstream side. It is.

Hereinafter, embodiments embodying the present invention will be described in detail with reference to the accompanying drawings.

Here, FIG. 1 is a front cross-sectional view of the nozzle part of a shot peening apparatus that is an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line X-X in FIG. 1, and FIG. A plan view of the entire peening device, FIG. 4 is a side view of the same, FIG. 5 is an enlarged side view of the nozzle stand with the nozzle attached, and FIG. 6a
, b, c are for explaining the residual stress state of the curved pipe section, a is a plan view of the curved pipe, and c is Y
-Y cross section stress distribution diagram, Figure 7 ayb is a plane cross-sectional view of the nozzle part showing other nozzle arrangement states, Figure 8
Figure ayb is a plan view and a side view showing another mounting device for the nozzle stand, and FIG. 9 is a side view of the nozzle stand showing still another mounting device.

First, in FIGS. 1 to 5, an upper nozzle cover 1 having a semicircular front shape divided into an upper part and a lower part, and a lower nozzle cover 2 are connected by a hinge 3, and the lower nozzle cover 2 is , is fixed to a nozzle stand 5 placed on a swivel arm 4 forming a part of a swivel device, tilted at 45 degrees from the horizontal line.

The upper nozzle cover 1 is connected by a link 8 to a piston rod 7 of an opening/closing cylinder 6 fixed to the nozzle stand 5, and opens and closes as shown by solid lines or broken lines (fifth (see figure).

A through hole 10 is provided at the center of the upper and lower nozzle covers 1 and 2, through which the curved pipe 9 is inserted, and four nozzles N1. N
2. N3. Of N4, N, , N3 are on the vertical line 11, N
2. N4 is provided on the horizontal line 12, and nozzles N1. N2
A first nozzle group consisting of nozzles N3. The second nozzle group consisting of N4 is fixed to the lower nozzle cover 2, and all the nozzles are oriented toward the center of the through hole 10, that is, toward the center of the curved tube 9 inserted into the through hole 10. .

The reason why the four nozzles are arranged on a horizontal line or a vertical line with a phase of 90 degrees is to direct the spray direction of the nozzles toward the tensile stress remaining portion of the curved pipe, as will be described later.

However, the number of nozzles and their mounting angles may be varied depending on the stress distribution state of the curved pipe.

Discharge port E1 provided around each nozzle. FJ7. E3
゜E4 are for discharging the fine powder material injected from the nozzles, respectively. The discharge ports E1 and E2 are connected to the communication pipe 13, and the discharge ports E3 and E4 are connected to the communication pipe 14.
are connected to discharge pipes 15 and 16, respectively (see FIGS. 1 and 2).

The nozzle stand 5 on which these nozzle groups are placed is
As is clear from FIGS. 3 to 5, the swing arm 4 is provided on the swing arm 4, which swings around a center stand 17 by a variable speed motor M.

It is slidably mounted on the guide groove 18 and is connected to a piston rod 20 of a hydraulic cylinder 19 installed on an extension of the swing arm 4, so that it can slide on the guide groove 18 by the operation of the hydraulic cylinder 19. It moves to change its turning radius and hangs.

21 is a wheel that rolls on the rail 22 while supporting the swing arm 4.

On both sides of the nozzle turning device as described above, drum-shaped guide rolls 23, 23 for supporting and guiding the curved tube 9 and crumb rolls 24 for fixing the curved tube are installed on the straight part 25 of the curved tube 9.
A hydraulic cylinder 28 having a two-pronged stopper 26 attached to a piston rod 27 is fixed on a pedestal 29 in front of the swing device.

It is desirable that the guide rolls 23 and crumb rolls 24 be able to change their positions in accordance with the bending radius of the curved pipe 9.

Next, the operation of the above embodiment will be explained.

First, place the nozzle covers 1 and 2 at position 02 (see Figure 3). In order to insert the curved tube 9 into the through hole 10 of the nozzle covers 1 and 2, operate the opening/closing cylinder 6 and move the upper nozzle cover 1 as indicated by the broken line. Open to position 1' as shown (see Figure 5).

Then the curved tube 9 is placed on the guide roll 23.23,
When moved in the direction of arrow 30, the tip 3 of the R section of the curved pipe 9
1 hits the stopper 26 pushed out by the hydraulic cylinder 6 to the position 26' indicated by the broken line, and the clamp roll 24 moves semicircularly to fix the curved tube 9 at that position, guiding the straight section of the curved tube 9. It is held between the roll 23 and the roll 23.

Subsequently, the stopper 26 is moved back to its original position by the action of the hydraulic cylinder 28, and the upper nozzle case 1 is closed by the operation of the opening/closing cylinder 6 as shown by the solid line in FIG. The tip 31 is gripped in the through hole 10.

Then, the rotating arm 4 is rotated by the motor M, and the nozzle covers 1 and 2 are moved to the end C1 of the R section.

Subsequently, the nozzle covers 1 and 2 are moved by the arrow 32 by the motor M.
Shot peening is performed while rotating along the curved pipe 9 in the direction of , but in the first half-circle rotation process from C1 to C3 via 02, the first nozzle group consisting of nozzles N, , N2 At the same time, a discharge port E3 provided downstream of the fine powder flow discharged from these nozzles N, N2. E4 is subjected to negative pressure by a floor (not shown) through the discharge pipe 16 and the communication pipe 14, and the fine powder material discharged from the first nozzle group intensively collides with the upper surface A1 and inner surface A2 of the curved pipe 9. After that, the discharge ports E3. It is discharged from E4 to the outside.

In this way, only one side of the curved pipe 9 is processed,
When the position of the nozzle cover C3 is reached, the turning device is subsequently reversed, and the next half-round turning from C3 to C1 via 02 begins.

Simultaneously with the start of this rotation, the first nozzle group N1. N2 stops, and the second nozzle group N3. As soon as the N4 starts to blow out, the exhaust port E3. The negative pressure of E4 is released, and the outlet E1°N2 is instead exposed to negative pressure.

Therefore, in the return half-circle process, the lower surface A of the curved pipe 9
3 and the outer surface A4 are exclusively exposed to shot pressure.

Residual stress is distributed in the curved tube 9 as shown by the broken line in FIG. 6, depending on various conditions such as its bending radius, wall thickness, and material.

In other words, if the dashed line is inside the circle P with the circle P as the boundary, it indicates compressive stress, and if the dashed line is outside the circle P, it indicates that tensile stress remains, and the distance between the dashed line and the circle P indicates that each It shows the magnitude of stress.

Therefore, in the case of Fig. 6, the point A where the y-axis intersects the curved pipe 9
2 and A4, the compressive stress is maximum at point A2 on the inside of the curved part, the tensile stress is maximum at point A4 on the outside, and the intersection A1. A3 has a slight compressive stress distribution.

In such an example, it is natural that the stress distribution in the vicinity of point P4 must be converted to the compressive side by shot peening in the vicinity of point P4, but if the residual compressive stress is It is desirable to obtain a larger residual compressive stress by further shot peening the areas where the corrosion resistance is insufficient due to the small surface area. Depending on the situation, it may be necessary to perform shot peening to further increase the compressive stress.

In the case shown in FIG. 6C, the y-axis and the y-axis intersect with the curved pipe 9, A1tA21 A3t, respectively.
If tensile stress is concentrated and remains in A4, it is possible to convert the residual stress into compression over the entire outer circumference of the R part of the curved pipe by intensively shot peening these parts. It is.

Therefore, by performing shot peening intensively on the parts where only tensile stress or compressive stress insufficient for corrosion resistance remains through the above-mentioned reciprocating process, corrosion resistance can be improved over the entire outer circumference of the R section of the curved pipe. Sufficient residual compressive stress is ensured.

In terms of heat, since shot peening cannot be applied any further to areas where the necessary compressive stress has already been secured, appropriate nozzles may be stopped in the forward or backward process as necessary.

Also, depending on the curved pipe, the shape shown in Fig. 6a may not always be the same. In some cases, the stress is not concentrated on the y-axis or on the y-axis, as in b.
In such cases, change the installation direction of the nozzle as necessary.
It is also possible to use a nozzle set in which the number of nozzles is variously changed, and it is desirable to change the positions of the discharge ports El, etc. accordingly.

When the reciprocating shot process of half a circle is completed in this way, nozzle group N3. N4 injection and discharge ports E, N
2 is stopped, the upper nozzle case 1 is opened by the opening/closing cylinder 6, the clamp roll 24 is moved in a semicircle to remove it from the straight pipe part of the curved pipe 9, and the curved pipe 9 is inserted into the through hole 10.
Then, the shot peening of the curved portion is completed.

It is desirable that all of the above steps be performed automatically.

The peak value of the tensile residual stress in the distribution of residual stress in the curved portion, the width of the distribution, and the shape of the distribution curve vary depending on conditions such as the wall pressure, material, bending radius, and heating temperature of the curved pipe.

Therefore, it is desirable to be able to change the peening amount, peening width, shot pressure, etc. according to the state of residual stress.
It is desirable to be able to freely adjust the nozzle pressure, change the peening width by slightly swinging the nozzle case in the direction of the arrow 33, and freely change the nozzle pressure.

In addition, in order to process curved pipes with different bending radii, the hydraulic cylinder 19 is operated to change the nozzle's turning radius. Such a turning radius change is shown by the two-dot chain line in FIG. A screwdriver 34 like the one shown in FIG.
may be omitted.

A further improved device for varying the radius of gyration of such a nozzle is shown in FIGS. 8a and 8b.

In this case, the hydraulic cylinder 19 and carrying screw 34 are omitted, and instead, a stand mounting base 38 with the nozzle stand 5 integrated thereon is provided on the swing arm 4, and the stand is attached to the center 39 of the swing arm 4 by a fixing member 40. The mounting base 38 may be fixed, and in this case, a stand mounting base 38 having a different distance from the center of rotation to the center of the nozzle is used depending on the radius of curvature of the R section (turning radius) of the curved pipe. It turns out.

Further, as shown in FIG. 9, a plurality of stand mounting pedestals 41 are provided in advance at suitable locations on the swing arm 4, and the nozzle stand 5
Place the nozzle stand 5 on the appropriate pedestal 41 according to the turning radius.
may be attached by bolts 42 or the like.

Furthermore, it is desirable to supply compressed air to the nozzle and apply negative pressure to the outlet using a flexible tube such as a rubber tube.

This is to accommodate the 180 degree rotation of the nozzle stand 5 and the opening/closing of the nozzle cover 1.

The above-mentioned opening/closing mechanism of the upper nozzle cover 1 can be constructed by omitting the link 8 and using the opening/closing cylinder 6 as shown in FIG. It is also possible to directly engage the piston rod 7 of No. 6 to the upper nozzle cover 1.

In the above embodiment, the discharge ports E1 to E4 are provided around each nozzle, but the positions of the discharge ports E1 to E4 are not limited to the above as long as they are on the downstream side of the fine powder flow where the fine powder flow does not interfere with the fine powder flow. Two outlets E1°F2 and F3. Each nozzle case has one F4 at the bottom F, , F2 or a position F3 . There is no problem even if it is installed in F4.

The present invention avoids nozzle interference by dividing the nozzle rotation process into a reciprocating forward and return process and shifting the injection timing of each nozzle group as described above, but as shown in FIG. By shifting the phase of the nozzle groups Nx and Ny in the longitudinal direction and partitioning them with a partition wall 36, interference between the nozzle groups can be prevented, and the width l of the entire nozzle can be prevented from increasing as in this example. As shown in Fig. 7, the nozzles Nx and Ny are provided on the same plane or slightly out of phase, and a partition wall such as 37 is provided between the nozzle groups Nx and Ny to prevent interference between both nozzle groups. may be prevented.

In this case, since both nozzle groups can eject at the same time, shot peening around the entire circumference of the curved portion is completed with only a process for a semicircle.

In the present invention, the nozzle covers 1 and 2 cover all the processing parts, so there is almost no scattering of the fine powder to the outside, but in order to further prevent scattering, it is necessary to adjust the radius of the curved pipe.
It is desirable to cover the entire county.

As described above, the present invention allows shot peening to be carried out extremely efficiently because the nozzles are directed toward the tensile stress residual portion or the compressive stress residual portion with insufficient corrosion resistance of the curved pipe. All the nozzles are divided into multiple nozzle groups, and the nozzle groups are alternately used for each rotation process of the nozzle half-round, so there is no disadvantage such as a decrease in peening effect due to interference between nozzles, and peening spots. We are able to avoid a decrease in the amount of peening, and by providing a fine powder discharge port downstream of each nozzle group, we eliminate turbulence in the fine powder flow and achieve an orderly flow, which further eliminates interference between nozzles and improves the fine powder flow. The scattering and leakage of fine powder materials to the outside due to turbulence is prevented.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of a nozzle part of a shot peening device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line X-X in FIG. The overall plan view, Figure 4 is a side view of the same, Figure 5 is an enlarged side view of the nozzle stand with the nozzle attached, Figures 6a and b
yc explains the state of residual stress in the curved pipe section, a is a plan view of the curved pipe, b and c are stress distribution diagrams in the Y-Y cross section, and Figures 7a and l) are respectively A plan sectional view of the nozzle part showing another nozzle arrangement state, FIG. 8a,
b is a plan view and a side view showing another mounting device for the nozzle stand, and FIG. 9 is a side view of the nozzle stand showing still another mounting device. Explanation of symbols 9...Curved pipe, N, ~N4...Nozzle,
A, ~A4...Tensile stress residual portion, E1~E4. F,
, F2...Exhaust port.

Claims (1)

[Scope of Claims] 1. In a shot peening method for a curved pipe in which shot peening is performed while rotating a nozzle along the curved pipe, each of the plurality of nozzles is compressed to the extent that the tensile stress remains or the corrosion resistance of the curved pipe is insufficient. In addition to injecting toward the stress residual area, all the nozzles are divided into two or more nozzle groups, and the nozzle rotation process along the curved pipe is further divided into a reciprocating rotation process every half circle, and the forward or return The shot peening is performed by alternately ejecting the nozzle groups for each process, staggering the injection time of each nozzle group, and discharging the fine powder material injected from each nozzle group from the downstream side of the fine powder flow. A shot peening method for curved pipes. 2. In a shot peening device for a curved tube in which a plurality of nozzles arranged toward the curved tube are rotated by a rotation device along the curved tube, each nozzle is attached to a portion of the curved tube where tensile stress remains or where the corrosion resistance is insufficient. At the same time, all the nozzles are divided into two or more nozzle groups, and each nozzle group is made to alternately inject in accordance with the reciprocating movement of the turning device every half circumference, and each nozzle group A shot peening device with a curved tube, characterized in that a fine powder discharge port corresponding to the above is provided on the downstream side of the fine powder flow.