JP3509187B2 - Header structure - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a header structure of a boiler into which steam flows, and in particular, to prevent a crack from being generated at an edge of an opening for connection with a stub. Related to header structure. [0002] Boiler superheater tubes and reheater tubes are collected in headers. FIG. 3 shows an external view of such a header.
The header 1 includes a large-diameter header 2 and a plurality of stubs 3 connected to the header 2. The stub 3 refers to a portion of the small-diameter tube such as a superheater tube or a reheater tube that engages with the tube barrel 2. FIG. 4 is a diagram showing a structure for connecting the header 2 and the stub 3. An opening 4 having the same diameter as the inner diameter of the stub 3 is provided for each stub 3 in the header 2 and the stub 3 is fillet welded to the header 2 by matching the opening 4 and the inner diameter of the stub 3. Is done. The surface of the tube barrel 2 that engages with the stub 3 is flat counterbore-worked so that the end surface of the stub 3 contacts the entire circumference. The welded portions are indicated by crossed diagonal lines. FIG. 6 is a diagram showing an example of a change in the temperature of steam passing through the stub 3 and the temperature of the header 2 during the operation of the boiler. The horizontal axis shows time, and the vertical axis shows temperature. When the boiler is ignited, the steam temperature of each stub 3 varies, and in one stub 3, steam having a higher temperature than the other stub 3 flows as shown by a solid line and flows into the header 2. The temperature of the header 2 shown by a broken line coincides with the average value of the temperature of the steam flowing from each stub 3. The maximum temperature difference ΔT between the steam of the stub 3 and the header 2 at the time of this start is about 100 ° C. When the boiler load fluctuates, the steam temperature changes immediately following the change, but the temperature of the header 2 follows with a delay. When the steam temperature decreases during the stop, the temperature of the header barrel 2 decreases with a delay. Note that “parallel” means that the generator coupled to the turbine driven by the steam from the boiler starts supplying power to the power system, and “parallel” means that power supply is stopped. Assuming that one cycle from start to stop is one cycle per day,
Alternatively, it is operated at a rate of one cycle a week. [0004] The temperature of the header 2 will be described in detail. The surface of the opening that comes into contact with the steam flowing from the stub 3 approaches the steam temperature, and the inside of the header 2 is closed. Average temperature. Due to this temperature difference, a large thermal stress is generated around the opening 4 of the header 2 due to stress concentration. During one cycle, the header 2 is heated by steam at startup and cooled at shutdown. When the load changes, heating and cooling are repeated. If 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 2, so that thermal fatigue as shown in FIG. Cracks occur. When such a crack is generated, it is necessary to cut the stub 3 and replace the tube shell 2 as a repair method, and the cost of this repair work is considerably high. For this reason, measures to prevent the crack before it occurs are desired. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a header structure in which a countermeasure for preventing the occurrence of a crack can be taken before a crack occurs around an opening of an existing header body. The purpose is to provide. In order to achieve the above object, a stub having the same inner diameter as the opening provided in the header is welded to the outer surface of the header so that the inner diameter matches the opening. in a tube pulling structure comprising Te, through said opening, one end protrudes a predetermined length pipe pulling the cylinder, the other end is provided a sleeve which is welded to the stub inner surface, an outer periphery of the sleeve the hole
And a predetermined gap, and a vibration having almost the same height as this gap
The protrusion for preventing movement is located at the position
It is provided . A sleeve is provided extending through the opening of the header to extend to the inner surface of the stub. One end of the sleeve projects into the header and the other end is welded to the inner surface of the stub. I have. Since the steam passing through the stub enters the sleeve and is discharged from the end of the sleeve protruding from the opening of the header, 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 opening and its surroundings become substantially the same as the temperature of the tube shell, so that the thermal stress is reduced and the occurrence of cracks due to thermal fatigue is prevented. Although the temperature of the sleeve in contact with the steam is almost the same as the temperature of the steam, the temperature of the sleeve is almost equal to the steam temperature due to the small thickness, and the generation of thermal stress is small. The outer diameter of the sleeve is made smaller than the diameter of the opening of the header to create a gap. The gap further prevents the heat of the steam from being transferred to the surface of the opening, reducing the difference between the surface temperature and the internal temperature, and reducing the thermal stress. This can prevent cracks around the opening due to thermal fatigue. In addition, since the protrusion having substantially the same height as the gap is provided around the sleeve at the position where the opening penetrates, vibration of the sleeve is prevented. 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 header 1 has a large number of stubs 3 composed of small-diameter pipes connected to a header 2 of a large-mouth pipe. Existing header 1
In FIG. 1, a header 2 and a stub 3 are configured as shown in FIG. 4, and a repair work having a structure as shown in FIG. The existing header 1 is in a state in which no crack is generated in the opening of the header body due to thermal fatigue. Referring to FIG. 1, an opening 4 is provided in a tube barrel 2, and a stub 3 having the same inner diameter as the opening 4 is provided.
However, it is welded to the header 2 in a state where the inner diameter and the opening match. At the welding position, the tube barrel 2 is counter-sunk flat so that the tip of the stub 3 is in close contact. A sleeve 5 penetrating the opening 4 and extending into the stub 3 is provided, one end of which protrudes from the inner surface of the header 2 and the other end is welded to the inner surface of the stub 3. The outer diameter of the sleeve 5 is smaller than the opening 4 and varies depending on the size of the stub 3. For example, the outer diameter of the sleeve 5 is set to have a gap of about 1 mm (difference of 2 mm in diameter). 1
It should be about 0 mm. On the outer surface of the sleeve 5 facing the opening 4, a protrusion 6 having substantially the same height as the gap between the opening 4 and the sleeve 5 is provided in a circumferential shape to prevent vibration of the sleeve 5 caused by steam. The projections 6 are circumferentially continuous, but may be intermittent.
FIG. 2 shows the engagement between the projection 6 and the opening 4. Referring to FIG. 1, a method of attaching the sleeve 5 will be described. The stub 3 is cut at the position of the welding line 7, and the sleeve 5 is inserted from the cut opening. The length L1 between the welding line 7 and the inner surface of the header 2 is measured, and the length L2 of the sleeve 5 is measured.
L3 is determined from the protrusion length H, and the inner surface of the stub 3 and one end of the sleeve 5 are welded such that one end of the sleeve 5 is located at a position L3 from the welding line 7. After attaching the sleeve 5 in this manner, the groove of the welding line 7 is processed and welded. The welded portions are indicated by crossed diagonal lines. Next, the operation of the sleeve 5 will be described.
The steam passing through the stub 3 passes through the inside of the sleeve 5 and is discharged from an end protruding from the inner surface of the header 2. Since the steam does not come into contact with the inner surface and the periphery of the opening 4, the temperature is substantially the same as the temperature of the tube barrel 2. Thereby, the thermal stress on the inner surface of the opening and around the edge is small, and the occurrence of cracks due to thermal fatigue is prevented. In addition, since the sleeve 5 and the inner surface of the opening 4 are in contact over the entire circumference by the protrusion 6 provided on the outer periphery of the sleeve 5, the sleeve 5 is prevented from vibrating due to the flow of steam. In the present 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 has been described. As shown in FIG. As is apparent from the above description, according to the present invention, the sleeve is provided in the opening of the header and the stub so that the surface of the opening and the periphery of the edge do not come into contact with the steam flowing from the stub. By doing so, the thermal stress on the surface of the opening and around the edge is reduced, and the occurrence of cracks due to thermal fatigue is prevented. Also the sleeve
A protrusion approximately the same height as the gap between the
Since it is provided around the sleeve, vibration of the sleeve
Is prevented. The present invention is suitable for repairing existing headers, but can also be applied to newly manufactured headers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a configuration of an embodiment of the present invention. FIG. 2 is a diagram illustrating a relationship between a protrusion of a sleeve and an opening of a tube approach cylinder. FIG. 3 is an external view of a header. FIG. 4 is a cross-sectional view showing a conventional opening of a header body and a stub. FIG. 5 is a diagram showing cracks generated by thermal fatigue in the opening of the header body. FIG. 6 is a diagram illustrating a temperature of a steam passing through a stub and a temperature of a tube barrel during operation of the boiler. [Description of Signs] 1 Header 2 Header 3 Stub 4 Opening 5 Sleeve 6 Projection 7 Welding line H Projection length

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F22B 37/22 F22B 37/00 F16L 59/00-59/22

Claims (1)

(57) [Claim 1] A header which is formed by welding a stub having the same inner diameter as the opening provided in the header to the outer surface of the header while adjusting the inner diameter to the opening. In the structure, there is provided a sleeve that penetrates the opening, one end protrudes into the header barrel at a predetermined length, and the other end is welded to the inner surface of the stub , and the outer periphery of the sleeve has a predetermined gap with the opening. Or
The protrusion for preventing vibration of approximately the same height as the gap is
A header structure , which is provided at a position where the opening of the outer periphery of the sleeve penetrates .