JPH0253681B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a membrane wall constituting a water-cooled wall of a furnace such as a boiler, and particularly to a membrane wall suitable for alleviating concentration of stress caused by temperature changes. The present invention relates to a membrane wall having a welded structure.

[Background of the invention]

Fig. 2 is a perspective view showing the configuration of a water cooling wall of a conventional boiler furnace, Fig. 3 is a front view of a conventional membrane wall, Fig. 4 is a sectional view taken along line A-A in Fig. 3, and Fig. 5 is a cross-sectional view of a conventional membrane wall. Figure 6 is an explanatory diagram showing the state of occurrence of cracks in the conventional membrane wall shown in Figure 3. FIG. 6 is an explanatory diagram showing the occurrence of cracks in the conventional membrane wall shown in FIG. 6;

As shown in Figures 2 to 7, natural circulation boilers (NC boilers), supercritical pressure boilers (UP boilers),
A panel-shaped membrane wall 8 in which membrane bars 2 and heat transfer tubes 1 are alternately joined by fillet welds 3 is used for the water-cooled wall of a furnace such as a spiral evaporator tube type once-through boiler (spiral Benson boiler). has been done. The membrane wall 8 is divided into predetermined areas such as the burner opening 14, the access door opening (not shown), and the joints between the water cooling wall 11 and the cage walls 12 and 13.
The end portion 9 of the membrane bar 2 is formed at the separated portion. Therefore, conventionally, the end portion 9
A welded portion 4 was formed by welding at a right angle of the boundary between the heat exchanger tube 1 and the outer surface of the heat exchanger tube 1 .

However, such an end 9 of the membrane bar 2
In this welded structure, thermal stress caused by temperature changes during startup and shutdown of the boiler concentrates on the end portion 9, causing cracks to occur in the welded portion 4. This is because the stress is most concentrated at the welding boundary between the weld metal and the base metal (membrane bar) at the end 9 of the membrane bar 2, and cracks occur particularly from areas where the weld metal has poor penetration or where pinholes are formed. This is considered to occur. And, after many years of boiler use,
The cracks 6 grow and cracks occur in the heat exchanger tube 1, which may cause a leakage accident of the heat exchanger tube 1.

Therefore, in order to prevent a leakage accident of the heat exchanger tube 1 due to the occurrence of a crack 6 in the welded part 4 and the subsequent growth of the crack 6, a groove cut 5 is provided on the end 9 of the membrane bar 2. The aim is to alleviate the concentration of thermal stress in However, thermal stress concentrates at the corner of the tip of the groove cutter 5, causing cracks 7 to occur in the membrane bar 2.
grows and cracks occur in the heat exchanger tubes 1, making it impossible to prevent leakage accidents of the heat exchanger tubes 1, which has been a problem in the past.

[Purpose of the invention]

The present invention was made in order to solve the problems in the above-mentioned prior art, and by providing a welded structure that can alleviate the concentration of thermal stress occurring at the ends of the membrane bar, cracks at the ends can be prevented. An object of the present invention is to provide a membrane wall that can prevent leakage accidents due to cracking of heat exchanger tubes.

[Summary of the invention]

The present invention relates to an improvement in the welded structure of a membrane wall, which constitutes a water-cooled wall of a furnace such as a boiler, by welding adjacent heat exchanger tubes in a panel shape with a membrane bar in the longitudinal direction of the heat exchanger tubes. In the membrane wall of a boiler, the boiler has a structure in which opposing pipes and a membrane bar connecting the pipes are separated, and the membrane bar of the membrane wall is separated. the end of the membrane bar at the point where the end of the membrane bar is entirely covered with a weld between the opposing surfaces of the pipe, and the weld is between the end of the membrane bar and the opposing pipe. This is a boiler membrane wall characterized by a smooth rounded finish.

In the membrane wall having the welded structure of the present invention, the entire surface of the end of the membrane bar is sufficiently covered with the welded part, and then rounded into a smoothly continuous arc shape to avoid stress concentration. Stress concentration at the end of the membrane bar, where stress tends to be concentrated, is alleviated, and at the same time, there is no boundary between the weld metal and the base material (membrane bar) on the end face of the end, resulting in poor penetration and pins. Almost no cracks will occur from that part due to the formation of holes. Furthermore, the material for the welded part covering the end of the membrane bar, which is subject to the most severe conditions in terms of thermal stress, can always be appropriately selected and welded, resulting in a welded structure with excellent strength. It is possible to do so.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail based on FIG. 1. FIG. 1 is a front view of a membrane wall showing a situation in which the welded portion is rounded.

As shown in FIG. 1, membrane bars 2 and heat exchanger tubes 1 are alternately joined by fillet welds 3 to form a panel-shaped membrane wall 8. Then, the end 9 of the membrane bar 2 and the outer surface of the heat exchanger tube 1 are continuously welded, and the welded portion 1
5 is formed. As shown in the figure, the end surface of the end portion 9 of the membrane bar 2 is continuously covered over the entire surface by a welded portion 15 and is not exposed. Further, the welded portion 15 is subjected to a grinder processing as shown in the figure, and a rounded portion 16 having a smooth circular arc shape is formed. This rounded portion 16 needs to be finished as smoothly as possible using a grinder or the like so that there are no concave or convex portions to avoid concentration of thermal stress.

In this way, in the present invention, the entire end of the membrane bar, where stress is most likely to concentrate, is formed with a welded part that is rounded into a smooth arc shape, so that the stress concentration is alleviated and at the same time, the occurrence of weld defects is prevented. The welding boundary between the weld metal and the base metal (membrane bar) is not exposed to the surface, and a sound weld is obtained, and there are almost no defects in weld metal penetration or pinholes that occur with conventional technology. Therefore, it was possible to eliminate a location where thermal stress is concentrated at the end of the membrane bar and where cracks are likely to occur, and the service life of the heat exchanger tube could be further improved.

〔Effect of the invention〕

As explained in detail above, the membrane wall having the welded structure of the present invention covers the entire surface between the end of the membrane bar and the surface of the adjacent heat exchanger tube with a welded part, and further reduces thermal stress. Because the welding structure is rounded into a smooth arc shape that is difficult to concentrate, there is no boundary between the weld metal and the base metal (membrane bar), which could cause welding defects at the end of the membrane bar, and Since a healthy weld is obtained by forming a weld, cracks from the boundary due to poor penetration are almost eliminated. In addition, it is possible to appropriately select welding materials that are resistant to thermal stress concentration as necessary, and the heat exchanger tubes can be welded without cracking due to temperature changes when starting and stopping a furnace such as a boiler. A membrane wall with a long service life and high reliability without leakage accidents can be obtained.

[Brief explanation of drawings]

Fig. 1 is a front view of the membrane wall showing the situation where the end of the membrane bar is covered with a rounded welded part, Fig. 2 is a perspective view showing the configuration of the water cooling wall of a conventional boiler furnace, and Fig. Figure 3 is a front view of a conventional membrane wall, and Figure 4 is A- in Figure 3.
A sectional view, Figure 5 is an explanatory diagram showing the occurrence of cracks in the conventional membrane wall shown in Figure 3, and Figure 6 is the situation where grooves are cut at the end of the conventional membrane wall shown in Figure 3. An explanatory diagram showing
FIG. 7 is an explanatory diagram showing the occurrence of cracks in the conventional membrane wall shown in FIG. 6. 1... Heat exchanger tube, 2... Membrane bar, 3...
Fillet welded part, 4... Welded part, 5... Groove cut, 6,
7...Crack, 8...Membrane wall, 9...
End, 11... Water cooling wall, 12, 13... Cage wall, 14... Burner opening, 15... Welding part, 1
6... R processing part, 17... Stop hole.

Claims (1)

[Claims] 1. A membrane wall for a boiler, which includes opposing pipes and a membrane bar that connects the pipes, and has a structure in which the pipes and the membrane bar are separated. The end of the membrane bar where the membrane bar is separated is
The entire surface between the opposing surfaces of the tube is covered with a welded part, and the welded part is rounded smoothly between the end of the membrane bar and the opposing pipe. A boiler membrane wall characterized by: