JPS61258902A - Repairing method for turbine wheel - Google Patents

Abstract

PURPOSE:To aim at improvement in operatability, by inserting each blade formed into a single structure after installing a nick in a shroud, in a separate disc in regular sequence, and connecting these blades together as one body. CONSTITUTION:Nicks are installed in shroud 5 of each blade 1 set to a shrinkage-fit disc, forming these blades into a single structure blade 1. This unitized blade 1 is inset in a disc 8 in order. Electron beams are irradiated to an end edge where these shrouds 5 face each other, from the outside of these shrouds 5, and these shrouds 5 are solidly connected together as one body. With this constitution, it becomes unnecessary to remove these shrouds, so that operatability in removal and assembling is improvable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a repair method used in a steam turbine when a partial defect in a turbine impeller found during inspection is removed and the turbine impeller is used again.

[Technical Background of the Invention and Problems Therewith] Generally, a steam turbine has an impeller for transmitting the kinetic energy of steam from a nozzle to the blades to obtain power. The size of this impeller increases in proportion to the increase in the capacity of the steam turbine, with some impellers in the low pressure section exceeding 3 meters in diameter. Normally, there are various difficulties in manufacturing such large impellers, so the axle disc into which the blades are implanted and the axle are manufactured separately, and then the axle disc is heated before being integrated with the axle. An impeller based on a so-called shrink-fit disc is used.

FIG. 8 shows an example of such an impeller, that is, an impeller constructed of shrink-fitted disks. That is, the shrink-fitting disc 2 into which the blade 1 is implanted is fixed to the axle 3 by shrink-fitting. Furthermore, as shown in FIGS. 9 and 10, the shrink-fit disc 2 and the axle 3 are constructed with a key 4 placed between them in case the above-mentioned shrink-fit fixation becomes loose. ing.

Note that the reference numeral 5 in FIG. 8 is a shroud for binding the blades 1 together.

However, in this type of impeller that has been used for many years,
Cracks shown by reference numeral C in FIG. 1 and FIG. 10 may be discovered during regular inspections, and the strength of some of the shrink-fitted discs 2 may be impaired. In general, this type of cracking occurs during the process of increasing or decreasing the load on a steam turbine, because the temperature change on the metal side of the steam turbine is gentler than the sudden temperature change on the steam side. The difference occurs when the groove area of the shrink-fit disc 2 into which the key 4 is inserted is repeatedly kept dry or wet, and furthermore, due to centrifugal force and shrink-fit surface pressure, the inner diameter portion of the shrink-fit disc 2 Stress acts in the circumferential direction, which acts as a so-called stress concentration in the groove, and corrosive factors such as chlorine ions contained in a fine layer of steam gather, creating a corrosive environment. This is called stress corrosion cracking.

If the steam turbine continues to operate with such cracks generated, the cracks will gradually develop and grow, and there is a fear that the entire shrink-fitted disk 2 may suddenly break down at some point.

Therefore, in order to prevent such accidents, measures are taken to find cracks while they are small through inspection and replace the shrink-fitted disc 2 with a newly manufactured one. It is extremely difficult to remove the blade 1 bound by 5 from the shrink-fitted disk 2, and on the other hand, when reusing the removed blade 1, a reduction in performance due to a reduction in effective length is a major problem. .

[Object of the Invention] An object of the present invention is to provide a novel method for repairing a turbine impeller, which allows removal of a blade from a shrink-fitted disk relatively easily, and which does not cause deterioration in steam turbine performance. be.

[Summary of the Invention] The present invention involves making notches in the shroud binding the vanes to form a single vane configuration, and then removing this single vane from a shrink-fit disc and sequentially inserting it into another shrink-fit disc. The shrouds are then integrally connected again using metallurgical bonding means to match the original number of sheets.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3.

(I) First step In FIG. 1, four blades 1 are arranged in a row in the circumferential direction on a shrink-fitting disc 2. In order to make the four blades 1 into a single blade 1, a cut 6 is made by applying, for example, a cutting wheel from the outside of the shroud 5. By repeating this operation three times for each blade 1, each blade 1 is separated from each other with the shroud 5 attached as shown in FIG. You can remove them one by one.

(It) In the second step, as shown in Fig. 3(a), this single blade 1
are inserted into a new shrink-fitting disk 8 through a notch (not shown) and sequentially fed in the circumferential direction to form four consecutive disks (only two are shown in the figure). This causes the edge of the shroud 5 to face the edge of the adjacent shroud, ready for the next process.

(III) Third step An electron beam is irradiated from the outside of the shroud 5 to the edges of the shrouds 5 facing each other.
join them together. By repeating this welding three times in each group (the welds are indicated by 9), the single blade 1 is reconstituted into its original four-bladed configuration.

The present invention, which is composed of the above-mentioned steps, can be completed by the simplest butt welding process in which the shrouds 5 are joined together at the welded portion 9, and is effective in promoting automation of the process and obtaining high quality products. This is extremely convenient.

In addition, the method of the present invention for joining the shroud 5 is different from the conventional method in that the tenon portion is regenerated at the tip of the blade 1 and the shroud 5 is
This method makes it possible to eliminate welds from the tenon part, which is exposed to severe stress conditions, increasing the strength margin and improving the reliability of the impeller.

Needless to say, since each blade 1 can be treated as a single blade, there is no problem in removing and assembling the blade, and on the other hand, there is no possibility that the effective length of the blade will be reduced, and the shrink-fit disk can be replaced. There is no adverse effect on performance associated with this.

Next, another embodiment of the present invention different from the above embodiment will be described. In the embodiment shown in FIGS. 4 and 5, the cut shape of the shroud 5 is matched to the cross-sectional shape of the blade 1,
Any of these methods is recommended as a method that minimizes damage to the tip portion of the blade 1 when cutting the shroud 5.

Further, in the embodiment shown in FIG. 6, when cutting the shroud 5, the shroud 5 is cut into an annular shape that includes the entire blade cross section of the blade 1. Such processing can be easily performed using a core drill or the like. This annular cutting method allows the start and end points of welding work to be in one place, and is effective against welding defects that tend to appear at the start and end points. This is a way to prevent it. Note that the notch 6 of the shroud 5 shown in each of the above embodiments is provided with a welding groove 1 on the outside of the shroud 5 as shown in FIG. 7, except when electron beam welding is applied.
0 to obtain sufficient joint strength.

[Effects of the Invention] As explained above, according to the present invention, when replacing the shrink-fitted disc of a steam turbine, it is possible to treat the shroud as a single blade without removing the shroud, which is the binding member of the blade. Therefore, the workability in removal and assembly can be improved, and the welding part required for repair is the shroud instead of the conventional tenon part, and the welding work can be performed relatively easily.

[Brief explanation of the drawing]

1, 2, and 3 are step-by-step process explanatory diagrams showing the method of the present invention, and FIGS. 4, 5, and 6 are process explanatory diagrams showing other different methods of the present invention. Figure, 7th
Figure 8 is a process explanatory diagram showing a special example of the welding method of the present invention, Figure 8 is a cross-sectional view showing an example of a conventional steam turbine impeller, and Figure 19 is a cross-sectional view showing a fixing means for a shrink-fitted disk. 10 are cross-sectional views taken along the line x-xsi in FIG. 9. 1...Blade 2.8...Shrink fitting disc 3...Axle 4...Key 5...・・・Shroud 6・・・・・・Notch 7・・・・・・Notch 9・・・・・・・・・Welded portion 10・・・・・・・・・Welding groove agent patent attorney Noriyuki Chika (and 1 other person) Figure 11 Figure 3 Figure 6 Figure 71 Figure 8

Claims (1)

[Claims] A method of repairing a turbine impeller in which a shrouded vane is removed from a shrink-fit disc and the removed vane is subsequently assembled to another shrink-fit disc, the vane being first of a unitary configuration. A cut is made in the shroud as shown in FIG. A method for repairing a turbine impeller, characterized in that the turbine impellers are integrally connected using metallurgical connection means.