JPH085005A - Structure of header - Google Patents

Abstract

PURPOSE:To prevent crack due to thermal fatigue generated around the rim of an opening on a header cylinder. CONSTITUTION:In the structure of a header consisting of a stub 3, having the same diameter as the inner diameter of an opening 4 provided on a header cylinder 2 and welded to the outer surface of the header cylinder 2 while aligning the inner diameter with the inner diameter of the opening 4, a sleeve 5, penetrating the opening 4 and one end of the same is projected into the header cylinder by a predetermined length while the other end is welded to the inner surface of the stub, is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler pipe advancing structure into which steam flows, and more particularly to a pipe advancing structure for preventing cracks generated at an edge of an opening hole for coupling with a stub.

[0002]

2. Description of the Related Art Boiler superheater tubes and reheater tubes are gathered together. FIG. 3 shows an external view of such a header.
The header 1 comprises a large diameter barrel 2 and stubs 3 connected to the barrel 2. The stub 3 refers to a portion to be fitted with the pipe shifting cylinder 2 of a small diameter pipe such as a superheater pipe or a reheater pipe. FIG. 4 is a view showing a joint structure of the pipe shifting cylinder 2 and the stub 3. An opening 4 having the same diameter as the inner diameter of the stub 3 is provided in the pipe shifting cylinder 2 for each stub 3. The stub 3 and the inner diameter of the stub 3 are combined so that the stub 3 is fillet welded to the pipe shifting barrel 2. To be done. The surface of the pipe shifting cylinder 2 which is fitted with the stub 3 is flatly counterbored so that the end surface of the stub 3 is in full contact. The welded portions are indicated by crossed diagonal lines.

FIG. 6 is a diagram showing an example of changes in the temperature of steam passing through the stub 3 and the temperature of the header cylinder 2 during boiler operation. The horizontal axis represents time and the vertical axis represents temperature. When the boiler is ignited, the steam temperature of each stub 3 varies, and a certain stub 3 has a higher temperature than the other stubs 3 and flows into the header cylinder 2. The temperature of the header cylinder 2 shown by the broken line corresponds to the average value of the temperature of the steam flowing in from each stub 3. The maximum temperature difference ΔT between the steam of the stub 3 and the pipe shifting cylinder 2 at the time of starting is about 100 ° C. When the boiler load fluctuates and the load changes, the steam temperature immediately changes and changes, but the temperature of the pipe shifting cylinder 2 follows with a delay. When the steam temperature is lowered at the time of stop, the temperature of the pipe shifting cylinder 2 is lowered after that. The parallel line represents that the generator coupled to the turbine driven by the steam of the boiler starts supplying power to the power system, and the parallel line represents that the supply of power is stopped. In this way, if the cycle from start to stop is 1 cycle, usually 1 cycle per day,
Alternatively, it is operated at a rate of 1 cycle per week.

[0004]

The temperature of the header cylinder 2 will be described in detail. The surface of the opening which comes into contact with the steam flowing from the stub 3 approaches the steam temperature, and the inside is the average temperature of the header cylinder 2. Has become. Due to this temperature difference, a large thermal stress is generated around the opening 4 of the tube drawing cylinder 2 due to stress concentration. During one cycle, the pipe shifting cylinder 2 is heated by steam at the time of starting and cooled at the time of stopping. When the load changes, heating and cooling are repeated. When such a cycle is performed a certain number of times, for example, one cycle per day for 15 years or more, the above-mentioned thermal stress is generated around the opening 4 of the header cylinder 2, so the thermal fatigue as shown in FIG. Caused by cracking. If such a crack occurs, it is necessary to cut the stub 3 and replace the pipe shifting cylinder 2 with a new one as a repair method, and the cost of this repair work becomes considerably high. For this reason, there is a demand for measures to prevent this before cracks occur.

The present invention has been made in view of the above-mentioned problems, and a structure of a pipe header in which measures for preventing crack generation can be taken before a crack is generated around an opening of an existing pipe header cylinder. The purpose is to provide.

[0006]

In order to achieve the above object, a pipe formed by welding a stub having the same inner diameter as that of an opening provided in a pipe shifting cylinder to the outer surface of the pipe shifting cylinder so that the inner diameter is aligned with the opening. In the shifting structure, a sleeve is provided which penetrates the opening, one end of which projects into the tube shifting barrel for a predetermined length, and the other end of which is welded to the inner surface of the stub.

Further, the outer diameter of the sleeve has a predetermined gap with the opening, and a protrusion having substantially the same height as the gap is provided at a position where the sleeve penetrates the opening.

[0008]

A sleeve is provided which extends through the opening of the tube transfer cylinder and extends to the inner surface of the stub. One end of the sleeve projects into the tube transfer cylinder and the other end is welded to the inner surface of the stub. Since the steam passing through the stub enters the sleeve and is discharged from the sleeve end protruding from the opening of the pipe drawing cylinder, the steam does not come into contact with the surface of the opening and its surroundings. As a result, the temperature of the surface of the aperture and its surroundings becomes almost the same as the temperature of the pipe barrel, so that the thermal stress is reduced and the occurrence of cracks due to thermal fatigue is prevented. The temperature of the sleeve in contact with the steam is almost the same as the temperature of the steam, but since the thickness of the sleeve is thin, the temperature of the sleeve is almost the steam temperature and thermal stress is less likely to occur.

The outer diameter of the sleeve is made smaller than the opening diameter of the pipe shifting cylinder so that a gap is formed. This gap further prevents the heat of the steam from being transferred to the surface of the opening, reduces the difference between the surface temperature and the internal temperature, and reduces the thermal stress. This can prevent the occurrence of cracks around the openings due to thermal fatigue. Further, since the protrusions having substantially the same height as this gap are provided around the sleeve at the through hole penetrating position, vibration of the sleeve is prevented.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of the present embodiment, and FIG. 2 is a detailed view of a protrusion of a sleeve. As shown in FIG. 3, the pipe header 1 has a large number of stubs 3 each having a small diameter pipe connected to a pipe barrel 2 of a large pipe. Existing guide 1
4, the header cylinder 2 and the stub 3 are configured as shown in FIG. 4, and the existing header 1 is subjected to repair work having the structure shown in FIG. It should be noted that the existing header 1 is in a state where no crack due to thermal fatigue is generated in the opening of the header cylinder.

In FIG. 1, an opening 4 is provided in the pipe shifting cylinder 2, and a stub 3 having the same inner diameter as the opening 4 is formed.
Is welded to the pipe shifting cylinder 2 with the inner diameter and the opening aligned. At the welding position, the pipe shifting cylinder 2 is countersunk flat so that the tips of the stubs 3 are in close contact with each other. A sleeve 5 is provided which penetrates through the opening 4 and extends into the stub 3, one end of which projects from the inner surface of the displacement cylinder 2 and the other end of which is welded to the inner surface of the stub 3. The outer diameter of the sleeve 5 is smaller than that of the opening 4 and varies depending on the size of the stub 3, but for example, the size is such that a gap of about 1 mm (difference of 2 mm in diameter) is generated. 1
It should be about 0 mm. On the outer surface of the sleeve 5 facing the opening 4, a protrusion 6 having a height substantially equal to the gap between the opening 4 and the sleeve 5 is circumferentially provided to prevent vibration of the sleeve 5 caused by steam. The projections 6 are circumferentially continuous, but may be intermittent.
FIG. 2 shows the connection between the protrusion 6 and the opening 4.

A method of attaching the sleeve 5 will be described with reference to FIG. The stub 3 is cut at the position of the welding line 7, and the sleeve 5 is inserted through this cutting port. The length L1 between the welding line 7 and the inner surface of the pipe shifting cylinder 2 is measured, and the length L2 of the sleeve 5 is measured.
Then, L3 is obtained from the protrusion length H, and the inner surface of the stub 3 and one end of the sleeve 5 are welded so that one end of the sleeve 5 comes to the position from the welding line 7 to L3. After mounting the sleeve 5 in this way, the groove of the welding line 7 is processed and welded. The welded portions are indicated by crossed diagonal lines.

Next, the function of the sleeve 5 will be described.
The steam that has passed through the stub 3 passes through the inside of the sleeve 5 and is discharged from the end portion projecting from the inner surface of the pipe drawing cylinder 2. Since the steam does not come into contact with the inner surface of the opening 4 and the periphery of the edge, the temperature is almost the same as the temperature of the pipe shifting cylinder 2. As a result, the thermal stress on the inner surface of the aperture and around the edge is small, and the occurrence of cracks due to thermal fatigue is prevented. Further, since the sleeve 5 and the inner surface of the opening 4 are in contact with each other over the entire circumference by the projection 6 provided on the outer circumference of the sleeve 5, the sleeve 5 is prevented from vibrating due to the flow of steam.

In this embodiment, the case where the existing header 1 shown in FIG. 4 is repaired and the sleeve 5 is attached as shown in FIG. 1 is explained. Alternatively, the sleeve 5 may be attached as shown in FIG.

[0015]

As is apparent from the above description, according to the present invention, the sleeve is provided in the opening and the stub of the pipe drawing cylinder so that the steam flowing from the stub does not come into contact with the surface of the opening and the periphery of the rim. This reduces the thermal stress on the surface of the aperture and the periphery of the edge, and prevents the occurrence of cracks due to thermal fatigue. The present invention is suitable for repairing existing headers, but can also be applied to newly manufactured headers.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a protrusion of a sleeve and an opening of a pipe shifting cylinder.

FIG. 3 is an external view of a header.

FIG. 4 is a cross-sectional view showing a connection between a conventional pipe shifting cylinder opening and a stub.

FIG. 5 is a diagram showing cracks generated by thermal fatigue in an opening of a pipe drawing cylinder.

FIG. 6 is a diagram showing a temperature of steam passing through a stub and a temperature of a header cylinder when the boiler is in operation.

[Explanation of symbols]

 1 Pipe pulling 2 Pipe pulling barrel 3 Stub 4 Opening hole 5 Sleeve 6 Protrusion 7 Welding line H Protrusion length

Claims (2)

[Claims] 1. A pipe header structure in which a stub having the same inner diameter as that of an opening provided in the pipe body is welded to the outer surface of the pipe body so that the inner diameter of the stub is aligned with the opening, and the piercing hole penetrates the hole. A structure of a pipe drawer characterized in that one end projects into the pipe draw cylinder for a predetermined length, and the other end is provided with a sleeve welded to the inner surface of the stub. 2. The outer diameter of the sleeve has a predetermined gap with the opening, and a protrusion having substantially the same height as the gap is provided at the opening penetrating position of the sleeve. The pipe header structure according to claim 1.