JPH1038205A - Fin structure of boiler wall pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of the crack of a fin at the coupling part of a wall pipe group and to improve reliability by a method wherein adjoining wall pipes are coupled through a member bent at a specified angle at the final ends of fins in an axial direction of the wall pipe. SOLUTION: In a coupling part, a water wall pipe 6 and a wall pipe 7 on the cage side are welded at a weld part 8 to a final end part welded by a fin 9 and a reinforcing material 14 bent at a bending angle θ in the axial direction of the wall pipe is welded at a weld part 88 to a water wall pipe 6 and a wall pipe 7 on the cage side. Provided a bending angle θ of a reinforcing material 14 is 90 deg., stresses A, B, and C of each part are similarly reduced in a balancing state. Provided the bending angle θ is below 90 deg., lowering of the stressed A and C is slackened and the increase of the stress B is also slackened, whereby it is desirable that the bending angle θ is reduced to a value below 90 deg.. This constitution reduces a stress at the final end of a fin and suppresses the occurrence of the crack of the fin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fin structure for a boiler wall tube in which cracks in fins connecting adjacent boiler wall tubes are prevented.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view showing a wall tube arrangement of a conventional boiler.

[0003] As shown in this figure, a large water pipe boiler for business use is a flat wall pipe group, such as a water wall pipe group 1, a cage side wall pipe group 2, and a cage bottom wall pipe group 3, which are connected by fins. The ceiling wall tube group 4 is formed, and these wall tube groups are combined to constitute the whole. When the boiler is started or stopped, or when the load changes, a temperature difference may occur between the wall tube groups, and when the temperature difference increases, the wall tubes may be thermally deformed, and in particular, the water wall tube group 1
And the joint 5 of the cage side wall tube group 2 often have cracks. Connection part 5 of this water wall tube group 1 and cage side wall tube group 2
Is easy to cause stress concentration due to the discontinuous shape, and when a temperature difference occurs in each wall tube group, a crack is generated because a shear force is applied in addition to a tensile force to open the joint 5 in a complicated manner. Easy to do.

[0004] Such a phenomenon will be described in detail below.

FIG. 5 is an explanatory view showing the structure of a conventional connecting portion of a boiler tube group.

As shown in FIG. 1, a plurality of water wall pipes 6, cage side wall pipes 7, and cage bottom wall pipes 10 are joined to each other by fins 9 for improving the heat transfer performance of the respective wall pipes by welding portions 8. . Each cage side wall tube 7 is connected to a cage side header 11.

[0007] The connecting portion 5 of the water wall tube 6, the cage side wall tube 7, and the cage bottom wall tube 10 is a structure since three types of wall tube groups are three-dimensionally united and have a complicated shape. Forms a shape discontinuity that requires the most attention in terms of strength. Further, since the internal fluid temperature of each of the wall pipe groups of the water wall pipe 6, the cage side wall pipe 7, and the cage bottom wall pipe 10 is different in the connecting portion 5, a difference in elongation of each wall pipe group occurs. Since the internal fluid temperature difference of each wall tube group is large at the time of starting and stopping, a large stress is applied to the joint 5 at the time of starting and stopping.

FIG. 6 is an explanatory view showing the structure of a conventional fin end.

Conventionally, to relieve a large stress applied to the connecting portion 5, an arc-shaped processed portion 12 having an arc-shaped terminal end of the fin 9 is formed as shown in FIG. However, this stress relaxation measure has a small effect if evaluated from operation experience.

[0010]

The crack 13 of the joint 5 shown in FIG. 6, which is found at the time of the periodic inspection, is repaired each time and further necessary reinforcement is performed. Despite such repairs and reinforcements, a new crack 13 is often found at the joint 5 with the same water wall tube group 1 and cage side wall tube group 2 at the next periodic inspection. It is considered difficult to completely prevent the occurrence of 13. When the crack 13 occurs, the combustion gas leaks out of the furnace, or when it propagates to the wall pipe, the steam leaks out, forcing the operation of the boiler to stop, which is an operational problem in a boiler that frequently starts and stops.

An object of the present invention is to suppress a crack of a fin at a joint portion of a wall tube group, and to provide a highly reliable fin structure of a boiler wall tube.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fin structure for a boiler wall tube which has fins interconnecting wall tubes of adjacent boilers and extending in the axial direction of the wall tube. This is achieved by being connected by a member bent at the axial end of the wall tube.

It is desirable that the bending angle of the bent member is 90 ° or less.

According to the above configuration, since the bent member connected to the end of the fin bears the stress applied to the end of the fin, the stress at the end of the fin is reduced, and cracking of the fin is suppressed.

Since the stress applied to the bent member concentrates on the bent portion, the position where the crack is generated is limited, and the inspection and repair become easy.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing the configuration of the embodiment of the present invention.

FIG. 1 is an enlarged view of the connecting portion 5, and the water wall pipe 6 and the cage side wall pipe 7 are bent at the bending end θ in the axial direction of the wall pipe at the terminal end portion where the fin 9 is welded at the welding portion 8. The reinforcing member 14 is welded to the water wall pipe 6 and the cage side wall pipe 7 at a welded portion 88. In the example shown in this figure, the bending angle θ is 90 degrees.

FIG. 2 is a front view showing the structure of another embodiment of the present invention.

This figure shows an example in which the reinforcing member 14 is bent in a U-shape, and the bending angle θ corresponds to 0 degree. With such a configuration in which the reinforcing member 14 having the bent portion in the center is located, the stress generated at the end portion of the fin 9 due to the difference in elongation of each wall tube group can be reduced.
The bent portion 4 is deformed and absorbed, the stress generated at the terminal end portion is reduced, and the generation of the crack 13 in the joint portion 5 is suppressed.
Further, since the position where the stress due to the difference in elongation is applied is concentrated on the bent portion of the reinforcing member 14, the occurrence of the crack 13 is limited to that position. Therefore, during the periodic inspection, the bent portion of the reinforcing member 14 may be mainly inspected, so that labor can be saved. The occurrence of the crack 13 is limited to the reinforcing member 14, so that the repair becomes easy.
As shown in FIG. 1, the reinforcing member 14 may be cut out of a plate material in a bent shape or may be bent.

When the reinforcing member 14 is disposed at the end of the fin 9, the stress generated at the bent portion of the reinforcing member 14 is reduced.
Is always smaller than the stress generated in the welded portion 8 at the terminal end of the fin 9.

The relationship between the bending angle θ of the reinforcing member 14 of the present embodiment and the stress generated in each part was analyzed. The analysis was performed by applying an external force P that would tear the wall tube assuming the start of the boiler, and the stress generated in each part due to the external force P was determined by the finite element method. The analysis conditions are described below.

Temperature: 300 ° C. External force P: 3000 N Outer diameter of water wall tube 6: 50.8 mm Thickness of water wall tube 6: 10.8 mm Material of water wall tube 6: 1Cr-0.5Mo steel Cage side wall tube 7 Outer diameter of: 50.8 mm Thickness of cage side wall tube 1: 10.8 mm Material of cage side wall tube 7: Cr-0.5Mo steel Width of fin 9: 50 mm Thickness of fin 9: 10 mm Material of fin 9: SB410 Thickness of reinforcing member 14: 10 mm Bending radius of reinforcing member 14: 30 mm FIG. 3 is a table showing analysis results of the embodiment of the present invention.

The horizontal axis in this figure is the bending angle θ of the reinforcing member 14, and the vertical axis is when the stress generated in the welding portion 8 of the fin 9 when the bending angle θ of the reinforcing member 14 is 180 degrees is 100%. Is the ratio of The bending angle θ of the reinforcing member 14 of 180 degrees means a straight plate in which the reinforcing member 14 is not bent. A is the stress generated in the weld 8 of the fin 9, B
Is a stress generated at the center bent portion of the reinforcing member 14, and C is a stress generated at the welded portion 88 of the reinforcing member 14. As shown in the figure, when the bending angle θ is increased from 0 degrees to 180 degrees, the stress A generated at the weld 8 of the fin 9 and the stress C generated at the weld 88 of the reinforcing member 14 increase. And reinforcement material 1
The stress B generated at the central bent portion of No. 4 decreases. As is clear from this figure, by setting the bending angle θ of the reinforcing member 14 to 90 degrees, the stresses A, B, and C at the respective portions are similarly balanced and reduced. If the bending angle θ is 90 degrees or less, the stress A and the stress C decrease slowly and the stress B increases slowly, so it is desirable that the bending angle θ be 90 degrees or less.

The stress B generated at the central bent portion of the reinforcing member 14 is the stress A generated at the welded portion 8 of the fin 9 when the bending angle θ is 180 degrees (when the stress is not relaxed by the bent portion of the reinforcing member 14). (Equal to the stress generated in the weld 8 of the conventional fin 9). This suggests that the addition of the reinforcing material 14 reduces the stress generated due to the difference in elongation in the welded portion 8 of the fin 9 and improves the durability against fatigue and creep cracks.

[0026]

According to the present invention, since the bent member connected to the end of the fin bears the stress applied to the end of the fin, the stress at the end of the fin is reduced, and the effect of suppressing cracks in the fin is obtained. .

Since the stress applied to the bent member concentrates on the bent portion, the position where the crack is generated is limited, and an effect that inspection and repair are facilitated is obtained.

[Brief description of the drawings]

FIG. 1 is a front view showing a configuration example of an embodiment of the present invention.

FIG. 2 is a front view showing a configuration example of another embodiment of the present invention.

FIG. 3 is a table showing analysis results of the embodiment of the present invention.

FIG. 4 is a perspective view showing an example of a wall tube arrangement of a conventional boiler.

FIG. 5 is an explanatory diagram showing an example of a configuration of a connecting portion of a conventional boiler tube group.

FIG. 6 is an explanatory view showing a structural example of a conventional fin end.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water wall tube group 2 Cage side wall tube group 3 Cage bottom wall tube group 4 Ceiling wall tube group 5 Joining part 6 Water wall tube 7 Cage side wall tube 8 Welded part 9 Fin 10 Cage bottom wall tube 11 Cage side header 12 Arc shape Processed part 13 Crack 14 Reinforcement 88 Welded part

Claims (2)

[Claims] 1. A fin structure for a boiler wall tube having fins interconnecting wall tubes of adjacent boilers and extending in the axial direction of the wall tube, wherein the adjacent wall tubes are axially terminated to the fins in the wall tube axial direction. A fin structure for a boiler wall tube, wherein the fin structure is connected by a member bent in step (1). 2. The fin structure for a boiler wall tube according to claim 1, wherein a bending angle of the bent member is 90 ° or less.