JPS6119281Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement in the structure of a smooth plate in a water-cooled pipe wall of a combustion chamber of a boiler or the like and a peripheral wall of a combustion gas passage.

The combustion chamber 1 of the boiler shown in FIG. 1 is made up of a pipe wall formed by connecting water-cooled pipes 3 with fins 4, as shown in FIG. A smooth plate covers the concave surface of the fin to form a smooth surface.

As structures of conventionally known smooth plates, there are several structures shown in FIGS. 3 to 9. In the case shown in FIGS. 3 and 4, the water-cooled pipes 3 and 3 are connected by smooth plates 5 and 6, and the method shown in FIG. The end of the pipe 5 is a straight line, and the method shown in Fig. 4 (hereinafter referred to as method B) has a structure processed into an arc shape. This is a method in which the pipe is welded 7 so that it becomes flat on the surface. In these structures, stress concentration tends to occur at the ends of the smooth plates 5 and 6, as shown in FIG. If the temperature difference and temperature change between the smooth plates 5 and 6 becomes large, or if the external force from the metal fittings attached to the smooth plate parts is large, it will be unsafe and undesirable.

On the other hand, the method shown in FIGS. 7 to 9 (hereinafter referred to as method C) is a method for reducing the drawbacks of the former two methods, and in order to eliminate discontinuity at the end of the smooth plate 8, Bend the part of the pipe wall toward the center of the pipe axis of the water-cooled pipe 3 (Fig. 8), and weld the tip to the fin (B
This is the method of mounting in the section).

This method is similar to the former two methods (Figures 3 and 4).
Compared to the smooth plate method shown in Figure 10, the stress σ3 at the end of the smooth plate 8 is lower than the stress _σ3 at the bent portion 10 of the smooth plate 8 (C
part) and σ _{4 '} at the tip (part B), which are considerably reduced compared to σ ₁ in method A and σ ₂ in method B.

However, in recent or future boiler plants for thermal power generation, due to the development of nuclear power generation, rapid load fluctuations and frequent starting and stopping are required, unlike when they were operated for conventional base load purposes. Furthermore, with the trend toward energy conservation, boilers are becoming larger and require variable voltage operation. For these reasons, in the conventionally known method, although the stress concentration was considerably alleviated in the C method, it was not possible to provide a sufficiently safe device against such severe repeated thermal stress and stress caused by excessive external force. do not have.
Furthermore, if the smooth plate is applied to the part connecting the furnace walls, one side of the smooth plate 8 will come into contact with the combustion gas, and the central part of the curved part 10 will be heated, further increasing the thermal stress. Therefore, it is not practical.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional structure and to provide a smooth plate structure having sufficient strength against fatigue failure due to repeated thermal stress and excessive stress due to increase in external force.

In other words, the present invention bends both ends of a smooth plate disposed between the water-cooled tubes forming the tube wall in the direction of the center of the tube axis, and then bends its tip in the direction of the tube axis to form a fin. The smooth plate structure is characterized in that the peripheral edge of the smooth plate is welded and attached to a water-cooled pipe, and a hole is bored approximately in the center of the bent part of the plate to relieve stress concentration at the welded part.

The present invention will now be described in detail with reference to preferred embodiments of the present invention, which are illustrated in FIG. 11 of the accompanying drawings.

Reference numeral 3 indicates a water-cooled pipe forming the peripheral wall of the combustion chamber 1 and the combustion gas passage 2; 4 indicates a fin for gas-sealing between the water-cooled pipes 3; 11 indicates a smooth plate;
2 is a round hole drilled in the bent portion of the water-cooled pipe 3 at the end of the smooth plate 11; 13 is the smooth plate 1;
1 shows a part that is bent in an S shape so that the part attached to the fin is approximately in the axial direction of the water-cooled pipe. That is, both ends of the smooth plate 11
As shown with a curvature R in FIGS. 2 and 14, it is first bent toward the center of the tube axis, and then its tip is bent toward the tube axis and welded to the fin 4. 14 is the attachment weld between the smooth plate 11 and the water-cooled pipe 3, 15 is the thickness of the water-cooled pipe 3, 16 is the thickness of the smooth plate 11, 1
Reference numerals 2' and 12'' show other embodiments of the shape of the holes formed in the bent portion of the water-cooled tube 3 at the end of the smooth plate 11 of the present invention.

Compared to methods A and B, conventionally known method C eliminates discontinuities in welding when attaching the smooth plate, bends the curved plate in an arc from the surface of the water-cooled pipe to the fin, and eliminates corners. This method alleviates concentrated stress, but it is quite effective when the action of the force is mainly an external force. In this case, a temperature difference occurs between the water-cooled pipe 3 and the smooth plate 8, and thermal stress occurs when the outside diameter of the water-cooled pipe 3 attempts to deform due to the internal pressure. The effect is not sufficient against such thermal stress. That is, since the end portion 10 of the smooth plate 8 is bent, the smooth plate becomes soft in the vertical direction, but its rigidity in the horizontal direction increases.
As a result, displacement of the water-cooled pipe 3 in the circumferential direction is restrained, and the welded part (C
It was found that the stress increases in the section) and the effect of stress concentration due to the curve decreases.

In order to reduce the rigidity of the smooth plate in such areas,
According to the present invention, a round hole 12 is formed approximately in the center of the curved portion of the smooth plate 11. This alleviates stress concentration.

Ideally, the shape of the hole 12 is desirably circular, but in consideration of ease of processing and stress concentration at the edge of the hole due to drilling, a round hole is preferred. It has also been found that oval and triangular circular shapes have almost the same stress relaxation effect as circular holes. That is, by making a hole approximately in the center of the bend in order to reduce the lateral rigidity of the bend, stress concentration can be extremely effectively alleviated without interfering with the continuity of welding.

Furthermore, in the conventionally known method C, it has been found that considerable stress concentration occurs in the part (B part) where the tip of the smooth plate 8 is attached and welded to the fin 4, although no attention was paid to stress concentration. .

This is because the smooth plate 8 is tapered, and is generally safe when there is little repeated stress such as external force, but as mentioned above, when frequent repeated stress such as thermal stress occurs, it is extremely dangerous from the perspective of fatigue failure. It becomes a state.

In the present invention, in order to relieve stress at the tip, the tip of the smooth plate is bent in a direction opposite to the bending direction of the surface of the water-cooled tube and brought closer to the 3-axis direction of the water-cooled tube.

That is, as shown in FIGS. 12 and 14, at the end 13 of the smooth plate 11, the surface of the water-cooled pipe 3 is made into an S-shape from the beginning of the bend 10', thereby reducing stress in all parts of the attachment weld 14 of the smooth plate. This has reduced concentration to the point where it can be completely ignored in practical terms.

FIG. 16 shows a comparison of the reduction of stress concentration by the smooth plate of the present invention with Method C. The reduction in generated stress is several tenths lower than that of the C method, but in terms of the lifespan of fatigue failure due to repeated stress, the safety level is several to several orders of magnitude, and it is a smooth surface that is completely safe in practice. Can be provided as a board.

Furthermore, as shown in Figures 19 and 20, at the joint between the peripheral wall of the combustion chamber and the peripheral wall, one end of the smooth plate comes into contact with the combustion gas, so the temperature of the central part of the smooth plate is heated, causing excessive thermal stress. However, according to the present invention,
The substantially central portion of the heated portion of the smooth plate 11 has a hole 12 to reduce heat reception, and has a stress concentration relaxation structure as described above, which has a remarkable effect.

When applied to a gas seal structure, since the external force is relatively small, the generated stress can be reduced by drilling only the bent part on the side that comes into contact with the gas, and keeping the other end fairly far away from the welding of the sealing surface. is reduced and is not at all unreasonable in practice.

More specifically, it is desirable that the thickness of the smooth plate 11 be approximately equal to or greater than the thickness 15 of the water-cooled tube 3. If the pipe thickness is considerably thicker than 15, a large concentrated stress will occur at the attachment weld 14 between the smooth plate 11 and the water-cooled pipe 3, which is not preferable. or,
On the other hand, if it is considerably thinner than the pipe thickness, it is not preferable because the average stress generated in its cross section becomes large.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of the boiler, Figure 2 is a cross-sectional view of the peripheral wall in Figure 1, Figure 3 is a front view of a conventional example using a flat plate as the smooth hardware, and Figure 4 shows the end of the flat plate. A front view of the conventional example processed into an arc shape, Fig. 5 is a side sectional view of Figs. 3 and 4, Fig. 6 is a plan sectional view of Figs. Front view of the plate bending method with the part bent toward the center of the tube axis, No. 8
7 is a side sectional view of FIG. 7, FIG. 9 is a plan sectional view of FIG. 7, and FIG.
Figure 11: Comparison graph of stress distribution in the welded area of smooth metal and pipe for the flat plate method (A method), the flat plate arc method (B method) in Figure 4, and the plate bending method (C method) in Figure 7, respectively. is a front view of a preferred embodiment of the present invention;
Fig. 12 is a side sectional view taken along line XII-XII of Fig. 11, Fig. 13 is a - plane sectional view of Fig. 11, Fig. 14 is a sectional view of the bent smooth plate with holes of the present invention, and Fig. 15 is a sectional view taken from the side of Fig. 11. Its front view, FIG. 16 is a stress distribution comparison graph between the method of the present invention and the conventionally known method in FIG. FIG. 19 is an enlarged view of section A in FIG. 1, showing an embodiment of the sealing system of the device of the present invention, and FIG. 20 is a sectional view taken along the line -- in FIG. 19. 1... Boiler combustion chamber, 2... Combustion gas passage,
3... Water-cooled pipe, 4... Fin, 5, 6... Smooth plate,
7... Mounting welded part, 8... Smooth plate, 9... Mounted welded part, 10... Plate bent part, 11... Smooth plate, 1
2, 12', 12''... Hole, 13... S-shaped bent part, 14... Mounting welded part, 15... Pipe thickness, 16
...Plate thickness.

Claims (1)

[Scope of utility model registration request] A smooth plate disposed between the water-cooled tubes constituting the tube wall and forming a smooth surface is bent at both ends toward the center of the tube axis, and further bent at its tip toward the tube axis and welded to the fin, and A smooth plate structure characterized in that the peripheral edge of the smooth plate is attached to a water-cooled pipe by welding, and a hole is bored approximately in the center of the bent part of the plate to relieve stress concentration at the welded part.