JPH11218302A - Seal structure of furnace wall through part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of cracks, by simultaneously solving thermal stress and bending stress caused by the difference of thermal expansion. SOLUTION: In the seal structure of a furnace wall through part, a heat conductive pipe 1 of special steel with a sleeve 4 of a specified length set is made to pierce the seal member 3 of a boiler furnace 2 and one end of the sleeve 4 is welded to the seal member 3 of the ferrite material, and the sleeve 4 is made thin by employing the special steel of the same quality as the heat conductive pipe 1 so as to absorb the difference of thermal expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler, and more particularly to a seal structure for a furnace wall penetration portion of a ceiling wall penetrating a heat transfer tube suspended from a ceiling room into a furnace.

[0002]

2. Description of the Related Art A typical structure of a large-sized boiler for power generation is shown in FIG.
Shown in In such a large boiler, a plurality of tubes and membrane bars are alternately welded to form a furnace side wall 22.
And the ceiling wall 2 of the furnace 25, and are supported by being hung from the steel frame 21 by the hanger 19, thereby forming a closed furnace 25.
To form A header 6 and a manifold 15 connected to the heat transfer tube group 11 are installed in a ceiling room 20 above the ceiling wall 2. The heat transfer tube group 11 connected to the header 6 reaches the furnace 25 through the furnace wall penetration of the ceiling wall 2 and becomes a superheater (SH) or a reheater (RH) as a heat exchanger.

In a conventional seal structure for a furnace wall penetration portion, as shown in FIG. 9, a gap between the heat transfer tube 1 penetrating the ceiling wall 2 of the boiler and the ceiling wall 2 is made of a ferrite-based seal plate (seal). A member 3 is used for welding. On the other hand, the heat transfer tube 1 penetrating the ceiling wall 2 is made of carbon steel or Cr-Mo steel in relation to the steam temperature of the internal fluid flowing in the tube, whereas the heat transfer tube 1 near the last stage of the superheater or reheater is used. A heat transfer tube 1 of austenitic stainless steel is used. For this reason, when trying to seal-weld the gap between the heat transfer tube 1 and the ceiling wall 2, there is inevitably a dissimilar joint, and if the boiler is repeatedly started and stopped, the thermal expansion difference of each member causes a thermal stress. This may cause thermal fatigue fracture. Since the thermal fatigue fracture occurs in the heat transfer tube, which is very damaging as a plant, the most suitable means is to use austenitic stainless steel of the same material as the heat transfer tube and to make the sleeve and the seal plate a fillet weld of dissimilar materials. This is a simple sealing means. However, with this method, thermal stress as dissimilar material and stress concentration as fillet welding are superimposed, so that the potential for thermal fatigue fracture becomes very large.

In order to avoid this problem, a means has been developed in which the lengthwise direction of the sleeve is divided into two and the butt welding of the cylinders is made a dissimilar material joint (Japanese Utility Model Laid-Open No. 4-13850).
No. 6). FIG. 11 shows the structure. The heat transfer tube 1 made of austenitic stainless steel is welded to the fillet weld 7 with the sleeve 24 made of austenitic stainless steel. However, since the same material is used for welding, no thermal stress is generated due to a difference in linear expansion coefficient. Is small. Next, the dissimilar material joint in question exists at the butt weld between the austenitic stainless steel sleeve 24 and the ferrite-based material sleeve 5. However, since full penetration welding using a welding groove is possible, the strength against thermal stress is reduced. Can be improved. The welding between the ferrite-based material sleeve 5 and the ferrite-based material sealing plate 3 is fillet welding, but not a dissimilar material joint. The accompanying stress can be reduced.

[0005] However, a large bending load acts on the heat transfer tube penetrating portion due to the difference in thermal expansion between the ceiling wall and the header, in addition to the thermal stress caused by starting and stopping. FIG. 10 shows the mechanism. That is, since the header 6 has a relatively higher internal fluid temperature than the ceiling wall 2, both the header 6 and the ceiling wall 2 thermally expand in the furnace width direction around the center of the pipe serving as a fulcrum. 6 has a larger thermal expansion amount, so that a bending stress due to the bending moment M is generated in the heat transfer tube 1 in the heat transfer tube penetrating portion. Therefore, FIG.
As shown in FIG. 10, even when the dissimilar material joint is provided at the butt-welded portion at the center of the sleeve, as shown in detail D in FIG. 10, a large bending stress is applied to the fillet weld 7 between the heat transfer tube 1 and the sleeve 24. This stress is repeated, which may lead to the generation of fatigue cracks.

[0006]

In the conventional sealing structure for a furnace wall penetration, not only the thermal stress caused by starting and stopping but also a large bending moment in the heat transfer tube due to the difference in thermal expansion between the ceiling wall and the header. Occurs. For this reason, a large bending stress is generated in the fillet welding between the heat transfer tube and the sleeve, and the bending stress may be repeated to cause fatigue cracks.

An object of the present invention is to provide a sealing structure for a through-hole of a furnace wall which simultaneously solves thermal stress and bending stress caused by a difference in thermal expansion and prevents cracks from occurring.

[0008]

In order to achieve the above object, a sealing structure for a furnace wall penetration according to the present invention comprises a special steel heat transfer tube fitted with a sleeve of a predetermined length and a furnace wall sealing member. In the seal structure of the furnace wall penetration portion in which one end of the sleeve is welded to a seal member made of a ferrite-based material, the sleeve is thinly formed of special steel so as to absorb a difference in thermal expansion.

The sleeve is 1/1 of the thickness of the heat transfer tube.
A structure in which a special steel ring having the thickness described above is fitted to each end and each ring is welded to a heat transfer tube and a seal member, or the thickness is formed so that the thickness is 0 to 1/5. May be formed, and the ends having the respective thicknesses may be welded to the heat transfer tube and the seal member.

Further, in the boiler, at least one of the above-mentioned furnace wall penetrating portions is provided with a seal structure, and at least an overheat is provided by a heat transfer tube group including a plurality of heat transfer tubes and a header connected to the heat transfer tube group. And the reheater are housed in a furnace.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, a heat transfer tube 1 made of a special steel such as austenitic stainless steel in which the other end of a sleeve 4 having a predetermined length is welded and fitted is attached to a seal member (seal plate) 3 of a boiler furnace wall 2. A seal structure of a heat transfer tube penetrating portion which penetrates and welds one end of a sleeve 4 to a seal member 3 made of a ferrite material. The sleeve 4 is made of a special steel made of the same material as the heat transfer tube 1 so as to absorb a difference in thermal expansion. To make it thinner. As shown in FIG. 2, the sleeve 4 is formed as thin as 1/10 to 1/5 of the thickness of the heat transfer tube 1 and has a special steel plate having substantially the same thickness as the heat transfer tube 1 at each end. Of the heat transfer tube 1 and the seal member 3 are welded.

That is, it is better to reduce the thickness of the sleeve from the viewpoint of reducing the bending stress. However, considering the weldability with the heat transfer tube and the handling at the time of installation work, the thickness of the heat transfer tube is reduced. A thin thickness of 1/10 to 1/5 is ideal. That is, the thickness of the heat transfer tube is about 5 to 10 mm, and the thickness of the sleeve is 0.5 to 2 mm.

Hereinafter, a manufacturing procedure of this embodiment will be described. When the thin (thin) sleeve 4 and the heat transfer tube 1 are directly welded, only the sleeve 4 is melted and the heat transfer tube 1 is not melted, so that sound welding is difficult. Therefore, first, it is necessary to previously weld a special steel ring 8 having the same thickness as that of the heat transfer tube 1 to both ends of the thin-walled sleeve 4. FIG. 3 is an enlarged view of a portion B in FIG. 2, and a TIG welding method having low heat input is formed by forming a welding groove 9 on the other end of the ring 8 at the end face where the heat transfer tube 1 and the ring 8 are fitted. Can be welded more easily. Next, welding of the resulting one end of the sleeve and the seal plate or the other end of the sleeve and the heat transfer tube can be easily welded without requiring special consideration.

FIG. 4 shows another embodiment of the present invention. The sleeve 14 is formed as thin as 1/10 to 1/5 of the thickness of the heat transfer tube 1, and each end portion having substantially the same thickness as the heat transfer tube 1 is formed. The configuration is such that the portion is welded to the heat transfer tube 1 and the seal member 3.
That is, by using a cylinder having a thick wall at each end and a thin wall at the center formed by machining or plastic working, an effect equivalent to that of the sleeve 4 shown in FIG. 1 can be exerted. The length of the sleeve is not specified, but the longer the sleeve, the greater the resistance to the above-mentioned thermal fatigue fracture.

Next, the operation of the present invention will be described with reference to FIG. Focusing on the rigidity of the sleeve, as a means to simultaneously solve the problem of thermal stress and bending stress due to dissimilar joints,
FIG. 5 shows a model of the effect of reducing the thickness of the sleeve as a means for simply reducing the rigidity. As shown in (a), when the sleeve 24 is as thick as the heat transfer tube 1, the austenitic stainless steel sleeve 24 expands more thermally at startup than the seal plate 3 made of ferrite material (FIG. (Indicated by the middle dotted line) is constrained by the welded portion, so that it must be locally bent and deformed in the vicinity of the welded portion, so that a large stress is generated. On the other hand, as shown in FIG. When the thickness is thin, the stress at the dissimilar joint becomes small because it can be easily deformed at a portion away from the weld.

As described above, the thermal stress as a dissimilar joint between the sleeve made of austenitic material and the seal plate made of ferrite material can be reduced by reducing the thickness of the sleeve. A case where a bending load caused by a difference in thermal expansion acts on the heat transfer tube can also be reduced by reducing the wall thickness as shown in FIGS. That is, when the sleeve 24 has the same thickness as the heat transfer tube 1 as in the conventional structure, the difference in rigidity between the portion where the sleeve 24 is fitted and the portion where it is not fitted becomes large, Bending stress concentrates on the weld toe, whereas when a thin sleeve 4 is used as in the present invention, the difference in rigidity between the portion where the sleeve 4 is fitted and the portion where it is not fitted is small. Therefore, bending deformation occurs evenly in the entire portion where the sleeve 4 is fitted, and the stress concentration at the welded portion is slight.

According to the present invention, thermal stress as a dissimilar material acting between the sleeve and the seal plate and bending stress acting between the heat exchanger tube and the sleeve can be reduced with respect to the stainless steel heat exchanger tube. The occurrence of a crack in the portion can be prevented.

[0018]

According to the present invention, the sleeve is made of the same material as the heat transfer tube made of special steel and is thin, so that the thermal stress between the sleeve and the seal plate and the heat transfer between the heat transfer tube and the sleeve are exerted. The bending stress is reduced, and the occurrence of cracks in the welded portion can be prevented.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view showing a portion A in FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing a portion B of FIG. 2;

FIG. 4 is a cross-sectional view showing another embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a bending stress of a thick and thin sleeve.

FIG. 6 is a cross-sectional view illustrating a bending stress of a thick sleeve.

FIG. 7 is a cross-sectional view illustrating the bending stress of a thin sleeve.

FIG. 8 is a sectional view showing a structure of a conventional boiler.

FIG. 9 is a diagram showing a conventional technique.

FIG. 10 is an enlarged sectional view of a part of FIG. 9;

FIG. 11 is a diagram illustrating generation of bending stress.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 heat transfer tube 2 ceiling wall 3 seal plate 4, 14 sleeve 5, 24 sleeve 6 header 7 fillet weld 8 ring 9 weld groove 11 heat transfer tube group 20 ceiling room 25 furnace

 ──────────────────────────────────────────────────の Continuing from the front page (72) Kang Inventor 6-9 Takara-cho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory

Claims (3)

[Claims] 1. A furnace wall penetration seal for penetrating a heat transfer tube made of a special steel having a sleeve of a predetermined length fitted thereinto through a seal member of a furnace wall and welding one end of the sleeve to the seal member made of a ferrite material. In the structure, the sleeve is formed thinly of the special steel so as to absorb a difference in thermal expansion, and a seal structure for a furnace wall penetration portion. 2. The sealing structure for a furnace wall penetration according to claim 1, wherein the sleeve has a thickness of 1/1 of a thickness of the heat transfer tube.
It is formed in a thin thickness of 0 to 1/5, and a ring of special steel having the above thickness is fitted to each end, and each ring is welded to the heat transfer tube and the seal member. Seal structure of the furnace wall penetration. 3. A sealing structure for a furnace wall penetration according to claim 1, wherein the sleeve has a thickness of 1/1 of a thickness of the heat transfer tube.
A furnace wall characterized in that each end is formed to have a thickness of 0 to 1/5 and has the thickness described above, and the end of each thickness is welded to the heat transfer tube and the seal member. Sealing structure of the penetrating part.