JPS59206171A - Welding method of turbine nozzle diaphragm - Google Patents

Abstract

PURPOSE:To improve strength, toughness and the reliability of a weld zone by joining a nozzle plate and supporting straps by groove welding and eliminating the unwelded part on the front surface and rear surface of the nozzle plate. CONSTITUTION:A supporting strap 4 on the inside ring side and a nozzle plate 3 are subjected to groove welding 9 in addition to the conventional type constituted by sealing welding 5 of inside and outside supporting straps 4, 4' and the plate 3. The unwelded part of welding is therefore eliminated and the strap 4' on the outside ring side is fitted thereto then an outside ring 1 and an inside ring 2 are joined by welding 6, by which a nozzle diaphragm is produced. The presence of the unwelded part of welding which is previously the point for generating a crack and has a significant influence on the decreased strength is thus obviated and the rigidity and strength are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for fixing a nozzle plate of a turbine nozzle diaphragm to an inner ring and an outer ring by welding.

[Technical background of the invention and its problems]

The turbine nozzle diaphragm thermally expands the steam passing through the nozzle blades, determines the flow direction and speed of the steam, and allows it to flow efficiently into the turbine rotor blades.As shown in Figure 1, it consists of a semicircular ring-shaped outer ring. 1 and the inner ring 2 (- constituted by radially disposing a plurality of nozzle plates 3.

A conventional nozzle diaphragm has an inner support plate 4 and an outer support plate 4' placed concentrically as shown in FIG. After fitting the nozzle plate into the nozzle plate, and then fixing both ends of the nozzle plate 3 and the two support plates 4 and 4' by seal welding 5 and 5', respectively, the inner support plate 4 is connected to the inner ring 2, Outer support plate 4
' and the outer ring 1 respectively to form a joint 6, thereby assembling. Therefore, the conventional nozzle diaphragm has non-welded parts 7' and 7 between the inner and outer rings 2 and 1 and the inner and outer support plates 4 and 4', respectively, as shown in FIG.
Also, there are non-welded parts 8a, 8b and 8'a, 8') between the inner and outer support plates 4, 4' and the nozzle plate 3, respectively.
It was common for there to be. Figure 3 shows the results of a finite element method elastic-plastic analysis performed on a nozzle diaphragm with such a structure.When the design differential pressure is loaded (AO), 160% of the design differential pressure is loaded. If (A
1), and when 200% of the design differential pressure is loaded (A2
) represents the plastic deformation region at each stage. As is clear from FIG. 3, the area where the stress is high and the plastic deformation is significant is near the non-welded portion 8a at the root of the nozzle plate at the steam inlet on the inner ring side. Even when a fatigue test was actually carried out using repeated loads on a full-scale model, cracks mainly occurred at the tip of the inner ring side non-welded part 8a, and the existence of the non-welded part affected the strength and rigidity of the nozzle diaphragm. It is clear that this is the cause of the decrease in Vt. The nozzle diaphragm is installed with minimum axial and radial gaps between the rotating parts of the turbine, such as the rotor and moving blades, in order to increase the efficiency of the turbine. This may lead to an increase in the amount of deflection, and there is a risk of serious accidents occurring.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a welding method for a turbine nozzle diaphragm that has excellent strength and high rigidity, and also allows easy welding work and improves the reliability of the welded part. shall be.

[Summary of the invention]

In order to achieve the above object, the present invention integrates the nozzle plate and the support plate by fitting the end of the nozzle plate into a hole provided in the support plate, sealing the end face, and then groove welding the side surface. Then, the support plate and the inner and outer rings are groove welded.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7. FIG. 4 shows a state in which the nozzle diaphragm is welded together according to the present invention. Inner/outer support plate 4
, 4' and the nozzle plate 3, a groove weld 9 is performed between the inner ring side support plate 4 and the nozzle plate 3, thereby reducing the welded non-welded area shown in FIG. 8a and 8b are removed, and the outer ring side support plate 4 is added.
' are fitted and joined to the outer ring 1 and inner ring 2 by welding 6 to manufacture a nozzle diaphragm. As a result, the non-welded portion 8a, which conventionally becomes a point where cracks occur and has a significant effect on strength reduction, is no longer present, resulting in a significant improvement in rigidity and strength. Figure 5 shows the structure (ao) according to the conventional method and the structure (a, a,
) and the amount of deflection (point B in Figure 3).

The horizontal axis is the ratio (l/L) of the length l of the non-welded part 7 to the width of the nozzle plate 3, and a is slightly smaller than ao, allowing for improved blade rigidity. On the other hand, as shown in FIG. 6, the stress intensity factor at the zero point on the steam inlet side on the inner ring side of the valve welded portion 7 is much lower in the structure according to the present invention (bl) than in the conventional structure (bo). Recognize. This tendency is particularly noticeable in regions where l/L is large. However, as shown in this figure, when l/L becomes 0.7 or more, the stress intensity factor increases rapidly, so it is desirable that this value is 0.7 or less.

FIG. 7 shows another embodiment of the present invention, in which groove welding 9' is also performed on the outer ring side support plate 4' and the nozzle plate 3, so that the non-welded part 8'a in FIG. In this case, the strength and rigidity are further increased, and the deflection at point B is also reduced as shown in Figure 5a.

Moreover, FIGS. 8 and 9 show other different embodiments of the present invention, and FIG. 8 shows a groove fillet between the nozzle plate and the support plate without providing a hole in the inner ring side support plate. how to weld,
FIG. 9 shows a method of groove fillet welding the nozzle plate directly to the inner ring without using the inner ring side support plate. In this case as well, the strength is further improved and the amount of deflection at point B is reduced as shown in FIGS. 5a and a4.

〔Effect of the invention〕

As described above, according to the present invention, the nozzle plate and the support plate are joined by groove welding to eliminate unwelded parts on the front and rear surfaces of the nozzle plate (secondly, the strength and rigidity are excellent, and the welded part is reliable). A method for welding a turbine nozzle diaphragm with improved properties is obtained.

[Brief explanation of drawings]

Figure 1 is a front view of the turbine nozzle diaphragm, Figure 2 is an enlarged cross-sectional view taken along the line X-X in Figure 1, and Figure 3 is plastic deformation based on the results of finite element analysis of the nozzle diaphragm using the conventional welding method. FIG. 4 is a cross-sectional view showing one embodiment of the present invention, FIG. 5 is a curve diagram showing the results of rigidity analysis of a nozzle diaphragm, and cross-sectional views showing other different embodiments of the present invention. 1... Outer ring, 2... Inner ring, 3... Nozzle plate, 4... Inner ring side support plate, 4'... Outer ring side support plate, 5, 5'... Seal welded part , 6...
Groove welded part, 7.8a, 8b, 8'a, 8'b - welded non-welded part, 9
．． 9', 10... Groove fillet weld. Agent Patent attorney Noriyuki Chika (one idiot) Figure 1 Figure 3 Ao: ■ Al: Mouth A2; Mouth Figure 4 Figure 5 Figure 6 Jl/L'・6 /, θ Figure 7

Claims (2)

[Claims] (1) In a welding method for a turbine nozzle diaphragm in which at least one of an inner ring and an outer ring and a nozzle plate are welded together via an annular support plate, the end of the nozzle plate is inserted into a hole provided in the support plate. A welding method for a turbine nozzle diaphragm, characterized by integrating a nozzle plate and a support plate by fitting and seal welding the end faces, and then groove welding the support plate and the inner and outer rings. (2) A method for welding a turbine nozzle diaphragm according to claim 1, characterized in that the inner ring side support plate and the nozzle plate are groove-fillet welded. r3) The method for welding a turbine nozzle diaphragm according to claim 1, characterized in that the inner ring and the nozzle plate are directly groove fillet welded.