JPS61212604A - Turbine nozzle diaphragm - Google Patents

Abstract

PURPOSE:To facilitate joint positioning by electron beam welding the inner and outer rings of a diaphragm and the holding plates from the steam inlet side or effluence side and face-jointing the nonwelded center part. CONSTITUTION:The inner and outer rings 14 and 15 of a diaphragm and the holding plates 11 and 12 are joined and fixed in the closely attached state through the electron beam welding from the steam inflow side A or the effluence side B. In the nonwelded part 17 at the center part in the axial direction, the outer surface of the sealing welded part 13 of each holding plate 11, 12 is formed to have the equal plane to each holding plate 11, 12 and face joining in closely attached state is performed. Therefore, the positioning for the joint between the holding plates and the inner and outer rings of the diaphragm can be easily executed.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a turbine nozzle diaphragm applied to a steam turbine, etc., and in particular to a turbine nozzle diaphragm with an improved joint structure between a contact plate that holds a nozzle blade and the inner and outer rings of the diaphragm. Regarding.

[Technical background of the invention and its problems]

For example, as shown in FIG. 12, a nozzle diaphragm 1, which is a stationary part of an axial flow turbine, is provided closest to a rotor 2 and blades 3, which are rotating parts. Thereby, the steam expanding after passing through the nozzle 4 of the nozzle diaphragm 1 has its flow direction and velocity appropriately determined, and efficiently flows into the blades 3. Therefore, high dimensional accuracy is required of the turbine nozzle diaphragm.

By the way, as shown in FIG. 13, for example, such a turbine nozzle diaphragm includes a pair of annular contact plates 5a and 5b that hold a large number of nozzle blades 4 from their inner and outer peripheries, and is joined to each of the contact plates 5a and 5b. It is composed of a diaphragm inner ring 6 and an outer ring 7. As shown in FIG. 14, each contact plate 5a, 5b and the diaphragm inner ring 6 and outer ring 7 are integrally fixed by welding portions 8, respectively.

In the past, such welding was generally performed by submerged arc welding. That is, first, a large number of nozzles IJI
4 are seal-welded to the contact plates 5a and 5b at a predetermined interval. Then, the diaphragm inner ring 6 and outer ring 7 are attached to the contact plate 5a.
, 5b, and submerged arc welding is performed from the inlet and outlet sides of the driving steam.

In contrast, recently, a structure in which the contact plates 5a, 5b and the diaphragm inner ring 6 and outer ring 7 are welded together by electron beam welding has come into widespread use. This is because electron beam welding has advantages such as less welding deformation, faster welding speed and efficiency, and less weld cracking even when dissimilar metals are combined.

That is, the contact plates 5a and 5b are often made of ferritic stainless steel, and the diaphragm inner ring 6 and outer ring 7 are often made of mild steel, low alloy steel, or the like.

When performing electron beam welding, for example, as shown in FIG. 15, the diaphragm inner ring 6 and outer ring 7 are joined to the contact plates 5a and 5b to which the nozzle blades 4 are fixed in advance by seal welding, and the diaphragm inner ring 6 and outer ring 7 are welded along their joining surfaces. , from the inlet and outlet sides of the driving steam, that is, the nozzle inlet end and outlet end,
Each electron beam 9 is emitted so as to obtain a predetermined penetration.

However, in electron beam welding, various welding defects may occur, as shown in FIG. 16, for example.

The first is the problem of misalignment due to changes in the beam or errors in the beam aiming position (Fig. 16 (A), (B),
(C)). The causes of this are that the welding width of the electron beam is generally narrower than that of arc welding, that alignment at the start of welding is difficult because welding is performed in a vacuum chamber, and that the electron beam is easily deflected between different materials. There are things like that.

For this reason, in the past, as shown in Fig. 16 (C), during welding work, the aim position of the beam was shifted as shown by reference numeral 10, or by using techniques such as giving the beam an inclination θ. Although the groove is positioned, there are problems such as the preparation process before welding requires a lot of time.

The second problem is the occurrence of defects due to weld cracks (No. 16
Figure (D)). In other words, the toe crack 11 that occurs on the weld surface
, defects due to cracks such as vertical cracks 12 and horizontal cracks 13 occurring within the bead may occur. In addition, as other cracks, as shown in FIG. 16(E),
Horizontal cracks, cracks 15, vertical cracks 16, etc. may occur. Although the degree of occurrence is lower than in submerged arc welding, it is still a problem that is difficult to avoid.

The third problem is the occurrence of defects such as voids (FIG. 16(F)). That is, there are problems such as voids 17 occurring within the weld bead, root porosity 18 occurring at the bead tip, and cold shut 19 due to spikes.

The occurrence of such defects can be prevented to some extent by adjusting electron beam welding conditions, ie, beam current, welding speed, beam swing, etc. However, sufficient consideration is required to determine the welding conditions, and according to the results of the inventor's study, the welding conditions for the welding plate 5a.

5b and the diaphragm inner rings 6 and 7 were found to be thick (influenced) on the occurrence of defects. In other words, the farther apart the groove mating surfaces are, the more likely welding defects are to occur.

On the other hand, as a result of examining the strength of electron beam welds, we found that the fracture mechanism is extremely complex and includes factors that cannot be considered in conventional arc welding, such as the fracture toughness of the workpiece and plastic restraint in welding dissimilar materials. understood.

Conventionally, in order to avoid various troubles during electron beam welding caused by such problems, countermeasures have been taken, such as making the joint surfaces between the contact plates 5a and 5b and the diaphragm inner and outer rings 6.7 have a concave-convex fitting structure, for example. is being carried out. However, with such conventional measures, the contact plates 5a, 5b and the diaphragm inner ring 6.
The structure, shape, etc. of 7 etc. have become complicated, and problems have arisen such as the machining process becoming complicated and the alignment of the grooves becoming a national problem.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and it is possible to easily position and weld the joint between the caul plate that holds the inside of the nozzle and the inner and outer rings of the diaphragm, and to minimize the occurrence of welding defects. It is an object of the present invention to provide a highly reliable turbine nozzle diaphragm that can be used in various applications and has sufficient durability.

(Summary of the Invention) In order to achieve the above object, the present invention includes a pair of annular contact plates that hold the inside of a large number of nozzles from the inner and outer periphery sides, and a diaphragm inner ring and outer ring joined to each of the contact plates. and,
In the turbine nozzle diaphragm, which is each made by electron beam welding, the front dividend plate and the inner and outer rings of the diaphragm are
Electron beam welding is performed from at least one of the inflow side and the outflow side of the driving steam in close contact with each other, and the joint portion between the contact plate and the diaphragm inner ring or outer ring, which is left as a non-welded part, is in close contact with each other. It is characterized by a face-to-face meeting.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 5.

The inside of the nozzle 10 is fixedly held by an inner circumference side abutment plate 11 and an outer circumference side abutment plate 12 via a seal weld 13. A diaphragm inner ring 14 and an outer ring 15 are bonded and fixed to each of the contact plates 11 and 12 by an electron beam welding section 16 from the inflow side (A) and the outflow side (B) of driving steam, respectively.

In addition, each contact plate 11.12 and diaphragm inner and outer rings 14.1
5, the central portion along the axial direction remains as a non-welded portion 17 without being subjected to electron beam welding. In this non-welded portion 17, the joint portions of each contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm are in close surface contact with each other.

A preferable value for the degree of closeness of this non-welded portion 17 is that the gap between the grooves when welding each contact plate 11.12 and the diaphragm inner and outer rings 14 and 15 is 0 to 0.5 mm or less. .

FIG. 2 shows the state of each member before welding to obtain such a welded joint structure of the contact plate and the inner and outer rings of the diaphragm. The nozzle 1110 and each seal welding part 13 of each backing plate 11.12 are welded in advance with a slightly raised bead on the outside of each backing plate 11.12, and then the seal welding part 13 is machine finished. The outer surface is molded to be flush with each of the contact plates 11 and 12. The diametric relationship between each contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm is as follows. That is, if the inner diameter of the inner circumferential side contact plate 11 is 02, and the outer diameter of the outer circumferential side contact plate 12 is 02, then the diaphragm inner ring 14 is O. The gap δ between the joint surfaces of each contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm is set within 0-0.5 m.

Figure 3 shows the gap δ (am) between the contact surface of the contact plate and the inner and outer rings of the diaphragm, and the electron beam welded part 16 during use.
The graph shows the relationship between the load concentration rate on the tip portion 16a and the load concentration rate on the tip portion 16a. Here, the load concentration ratio is the force F1 that acts toward the outer circumferential side on the outer circumferential side contact plate 12 due to thermal expansion or the like.
This is the ratio of the concentrated load F2 acting on the end portion 16a of the electron beam welding portion 16 to

As is clear from FIG. 3, when the gap between the contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm, that is, δ, is O, the force E1 pushing the nozzle [10] is entirely transmitted through the contact plates 11 and 12. It was confirmed that the load was transmitted to the inner and outer rings of the diaphragm, the load concentration ratio became smaller, the load action and distribution characteristics became uniform, and the structural strength became stable. On the other hand,
If the gap δ is 0.51
The contact plates 11 and 12 are deformed in some areas, and the deformation tends to concentrate at the end of the electron beam welding part 16 located at the end of the gap. For this reason, the contact plates 11 and 12 and the diaphragm inner and outer rings 14
．． As a result, a part of the joint surface with 15 has a low strength.

FIG. 4 shows the electron beam welding part 16 due to concentrated load F2.
This shows the degree to which the fatigue strength of As shown, the contact plate 11.12 and the diaphragm inner and outer rings 14.15
When the gap δ becomes 0.5 mm or more, the degree of load concentration at the end of the 111 portion increases, and it is recognized that the fatigue strength of the nozzle diaphragm ultimately decreases. If a steam turbine is operated with such reduced fatigue strength, the number of repeated operations and stops of the turbine will increase, increasing the possibility of cracks, etc.
Turbine operation has to be limited to three times, resulting in serious operational problems. Therefore, it can be seen that controlling the FIA distance δ between the contact plates 11 and 12 and the inner and outer rings 14 and 15 of the diaphragm within 0 to 0.5 mm has a very significant meaning in reducing the possibility of crack occurrence. .

FIG. 5 shows the relationship between the defect occurrence rate due to electron beam welding and the gap δ. As shown in the figure, as the gap δ becomes wider, the incidence of the aforementioned voids, root porosity, and other defects increases. In particular, F.J.I.
When liIδ exceeds 0.5 mm, the defect occurrence rate increases rapidly and welding becomes difficult. The maximum defect rate of electron beam welded parts is set to a range that does not cause any practical problems, that is, 5
In order to set the gap within %, it is desirable that the gap δ be within 0.5 mm.

As described above, the contact plates 11, 12 and the diaphragm inner and outer rings 14.
When welding with No. 15, the interval between the groove mating surfaces is set to 0 to 0.
By setting the weight to 5mg+ or less, the contact plate 11.12 and the inner and outer rings of the diaphragm 14.15 remaining as non-welded parts
According to the turbine nozzle diaphragm according to the above-mentioned embodiment, in which the joint portions are closely surface-joined with each other, it is possible to minimize the occurrence of welding defects, and it is also possible to provide sufficient strength and improve reliability. Moreover, the welding and combination structure is simplified, so construction can be easily performed.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the outer diameter D2 of the abutment plate 12 on the outer circumference side of the nozzle 1110 is made larger than the inner diameter D4 of the diaphragm outer ring 15 joined thereto, and the abutment plate 12 on the inner circumference side of the nozzle blade 10
The inner diameter D1 of the diaphragm 14 is joined to the diaphragm inner ring 14.
It is made smaller than the outer diameter D3 of. And each plate 11
．． 12 was cold fitted to the inner and outer rings 14 and 15 of the diaphragm before electron beam welding.

Regarding this construction method, for example, the inside of the nozzle 10 and the backing plate 1
After performing seal welding and surface processing of the seal welded portion 13 in combination with 1.12, set the diameters of the diaphragm inner and outer rings 14.15 as described above according to the dimensions of the contact plate 11.12. It is something to be processed. When performing cold fitting, the diaphragm inner ring 14 is first cooled with, for example, dry ice, and then fitted to the inner peripheral side contact plate 11.
The best part is to heat the diaphragm outer ring 15 and
2.

In the case of such a heating and cold fitting structure, the contact plate 11, 12 and the inner and outer rings 14 and 15 of the diaphragm are in close contact with each other, and the gap therebetween is completely zero.

Therefore, there are fewer problems when performing electron beam welding.
In addition, an electron beam welding structure with fewer welding defects can be achieved, and during operation, the force acting on the nozzle blade 10 and the contact plates 11, 12 is reduced to the diaphragm inner and outer rings 14.
15, and the strength characteristics are extremely good.

In addition, the above 1. According to the second embodiment, sufficient fatigue strength can be obtained even if the electron beam welding depth is reduced to some extent. This will be explained with reference to FIG. The figure shows welding vI
Characteristics based on dimensional relationships such as width and gap, and fatigue strength are shown. L is the axial height of the nozzle blade 10, O is the welding depth inward from the end of the nozzle blade 10, J13 is the overall welding depth dimension, and δ does not indicate a gap. In the figure, the horizontal axis shows the 1st/L1, and the vertical axis shows the fatigue strength ratio. Here, the fatigue strength ratio is a value of fatigue strength in an arbitrary state with respect to a reference fatigue strength. That is, in the fatigue strength ratio diagram, the curves Il 2 are δ−0°δ−0, respectively.
The values in the case of 5, 6-0, 75, 6-1, 0 are shown. From the above conditions, as shown by curve A, when δ#0 and /L is 0.5, the fatigue strength ratio is 1.0. As is clear from the figure, in order to obtain a constant fatigue strength ratio,
It was observed that the value of /L tends to be smaller as δ is smaller.

Therefore, in the case of the above embodiment in which the Fli distance δ is set to O-0.5 m, sufficient fatigue strength can be obtained even if the welding depth 13 of electron beam welding is made small. In particular, as shown in the second embodiment, when the gap δ is set to O by using a cold-fit structure, sufficient fatigue strength can be obtained with a relatively small welding depth. As a result, the number of welding steps is reduced, and welding defects can also be reduced.

Next, a third embodiment of the present invention will be described with reference to FIGS. 8 to 11.

In this embodiment, electron beam welding is performed only from the inlet side of the driving steam. FIG. 8 shows the external shape of the nozzle diaphragm, and FIG. 9 shows the joint structure between the contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm.

Nozzle I! 10 is the support hole 11a, 1 of the backing plate 11.12
2a, and is fixedly held by a seal weld 13. These respective contact plates 11 and 12 and the diaphragm inner and outer rings 14
．． The joint surfaces with 15 have slopes of constant angles θ and θ2 with respect to the axial direction, respectively. The directions of the gradients θ 1 and θ 2 are such that, for example, the gap between the joint surfaces is wide on the inflow side of the driving steam. As a result, during electron beam welding, each contact plate 11.12 and the diaphragm inner and outer rings 14.
15 are joined so that their slopes match, so that the joint surface gap δ becomes 0. Then, the electron beam welding section 16 is applied to each joint surface between the contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm at a height of 50 mm in the axial direction of the nozzle blade 10 from the drive steam inflow side.
For solutions of % or more, inclusion is set.

Note that the above-mentioned gradient is determined to be 0≦θ, θ2≦15, taking into consideration the beam inclination angle of electron beam welding, the processing of the contact plate 11, 12, etc.
It is desirable to set the temperature to about 1°.

Even with this configuration, the gap δ of the non-welded portion 17 is 0, as in the second embodiment, and the joint surfaces of the contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm can be joined in a tight state. and has sufficient fatigue strength.

Furthermore, since electron beam welding is performed only from one direction, the work is easy and welding defects can be reduced.

FIG. 10 shows the fatigue strength ratio characteristics of the embodiment shown in FIG. 3 in comparison with the first and second embodiments. Note that θ and θ2 were set to 5°. Moreover, the fatigue strength ratio here shall be in accordance with the definition of the above formula.

Fatigue strength ratio...-(1) As is clear from Fig. 10, in the nozzle diaphragm according to the third embodiment, the steam is welded by electron beam welding (one bus) only from the inflow side of the driving steam. Despite the presence of the non-welded portion 17 on the outflow side, the fatigue strength ratio of this third embodiment, as shown by the constant chain line (e), is higher than the first one, as shown by the solid line (e). It was observed that the values were almost the same as those of the second example. Note that the third embodiment is similar to the first embodiment. Compared to the second example, there is a slight decrease in strength in areas where δ is 0.5 or less, but the rate of strength decrease is extremely small, considering the difference in machining error and welding error. , which is sufficiently acceptable at the ankylosing design stage.

FIG. 11 is a characteristic diagram showing the influence of electron beam welding depth on fatigue strength in the nozzle diaphragm according to the third embodiment. In FIG. 11, the horizontal axis shows the ratio between the nozzle blade height and the welding depth 11 from the nozzle blade tip, and the vertical axis shows the fatigue strength ratio. Here, the fatigue strength ratio follows the definition below.

Fatigue strength ratio...(2) In Fig. 11, the second is the first. The distance from the nozzle blade tip to the tip side of the electron beam welding depth on the steam outlet side in the case of the second embodiment is shown. In the case of the third embodiment shown by the dashed line (g), the first embodiment shown by the dotted line (g). Compared to the case of the second example, it is recognized that the fatigue strength is almost unchanged in a range where the ratio of the weld depth to the nozzle blade length is 0.5 or more. In particular, in this range of /L≧0.5, a change in 11/L does not particularly affect the change in fatigue strength ratio.

This behavior occurs because the groove 11w1 of the weld between the contact plate 11.12 and the inner and outer rings 14.15 of the diaphragm is sufficiently narrow, so that the stress acting on the weld due to the load due to steam pressure is compressed by surface contact transmission. It is thought that this is to transmit stress. If the groove mwA is wide, the compressive stress cannot be transmitted from the contact plate 11.12 to the inner and outer rings 14.15 of the diaphragm, so the strength is significantly reduced. That is, in the one-sided welding from the steam inflow side in the third embodiment, the precision of the groove size plays an extremely important role. Therefore, by creating a joining structure between the contact plate 11° 12 and the diaphragm inner and outer rings 14 and 15, which are sloped in the axial direction as described above, the gap can be reduced. 1 wA is set to almost 0, thereby making it possible to reduce the distribution of vertical stress in the non-wJ@ portion.

In the third embodiment, the contact plates 11 and 12 and the inner and outer rings 14 and 15 of the diaphragm are provided with a slope, but this is the easiest means when the gap δ is set to O, and the slope is By performing welding from the widening side, even if M (I!1. #J steam outflow side), which is narrow due to the slope, is not welded, no stress component is applied in that direction, and welding is performed from the widening side. This is the most suitable case for increasing the effect, and the present invention is not necessarily limited to such a case. , it is not necessarily necessary to provide a slope.

〔Effect of the invention〕

As described above, according to the turbine nozzle diaphragm according to the present invention, the contact plate and the inner and outer rings of the diaphragm are kept in close contact with each other, so that the driving steam is not affected by the inflow side and the outflow side.
Electron beam welding is performed from either side of the diaphragm, and the remaining unwelded parts of the contact plate and the diaphragm inner ring or outer ring are brought into close surface contact with each other, so there is no opening for electron beam welding. M construction is simple and allows man-hours to be reduced, and sufficient strength can be maintained even with M4 construction at close joints in non-welded parts, so it can be used with relatively few welding man-hours and with a small welding depth. , it has sufficient fatigue strength. Moreover, since the number of welded parts is reduced, the incidence of welding defects can be reduced. Therefore, an excellent effect is achieved in that a highly reliable turbine nozzle diaphragm can be obtained with a relatively simple structure.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view showing a state of the turbine nozzle diaphragm shown in FIG. 1 before welding, and FIGS. 3 to 5 are similar to FIG. FIG. 6 is a cross-sectional view showing the assembled state before welding, showing the second embodiment of the present invention, and FIG. 7 is a characteristic diagram showing the characteristics of the turbine nozzle diaphragm shown in FIG. 6. FIG. 8 is a perspective view showing the third embodiment of the present invention, FIG. 9 is an enlarged sectional view of FIG. 8, and FIGS. 10 and 11 are characteristic diagrams of the third embodiment. Fig. 12 is a sectional view of a steam turbine to explain a conventional example, and Fig. 13 is an exploded oblique view of the turbine nozzle diaphragm. Figures 1 and 14 are perspective views that do not show conventional welding structures, Figure 15 is a perspective view that shows conventional electron beam welding structures, and Figures 16 (A) to (F) are explanations showing the shapes of welding defects. It is a diagram. 10... Nozzle blade, 11.12... Backing plate, 14...
・Diaphragm inner ring, 15...Diaphragm outer ring, 1
6...Electron beam welding section. Applicant's agent Hisashi Hatano Figure 3 Figure 4 Gap 6 (mm) /L Figure 8 Figure 9 Gap δ (mm) f+/L Figure 12 Figure 13 Figure 14 Figure 15 Figure 16

Claims (1)

[Claims] 1. A pair of annular contact plates that hold a large number of nozzle blades from their inner and outer periphery sides, and a diaphragm inner ring and outer ring joined to each of the contact plates are each made by electron beam welding. In the turbine nozzle diaphragm, the contact plate and the inner and outer rings of the diaphragm are electron beam welded in close contact with each other from at least one of the inflow side and the outflow side of driving steam, and the contact plate and the inner and outer rings of the diaphragm are welded with an electron beam from at least one of the inflow side and the outflow side of the driving steam, and the contact plate and the inner and outer rings of the diaphragm are welded with an electron beam from at least one of the inflow side and the outflow side of the driving steam, and the contact plate and the inner and outer rings of the diaphragm are welded in close contact with each other from at least one of the inflow side and the outflow side of the driving steam. A turbine nozzle diaphragm characterized in that a joint portion between a plate and an inner ring or an outer ring of the diaphragm is in close surface contact with each other. 2. The turbine nozzle diaphragm according to claim 1, wherein the gap between the groove mating surfaces during welding between the contact plate and the inner and outer rings of the diaphragm is set to 0 to 0.5 mm or less. 3. The outer diameter of the contact plate on the outer circumferential side of the nozzle blade is larger than the inner diameter of the outer ring of the diaphragm to which it is joined, and the inner diameter of the contact plate on the inner circumferential side of the nozzle blade is smaller than the outer diameter of the inner ring of the diaphragm to be joined to it; 2. The turbine nozzle diaphragm according to claim 1, wherein each of the contact plates is heated or cold fitted to the inner and outer rings of the diaphragm before electron beam welding. 4. The electron beam welding part has a penetration depth of 50% or more of the axial height of the nozzle blade from the drive steam inlet side to the joint surfaces of each contact plate and the inner and outer rings of the diaphragm. A turbine nozzle diaphragm according to claim 1. 5. Claim 1, wherein the joint surfaces between each contact plate and the inner and outer rings of the diaphragm have a slope of a certain angle with respect to the axial direction.
Turbine nozzle diaphragm as described in section.