JPS63295802A - Repairing of nozzle plate of steam turbine - Google Patents

Abstract

PURPOSE:To improve the working efficiency and reliability in correction by cutting the whole cut part of a nozzle plate due to erosion into straight line form and opened-top-welding a thin plate small piece having the same shape to the original shape. CONSTITUTION:The whole rear edge part of a nozzle plate 1 including a cut part due to particle erosion is cut in straight line form, and the edge surface is finished to an opened top form. Then, a thin plate small piece 6 having the same shape to the original shape of the cut rear edge part is welded onto the cut surface of the nozzle 1. In this case, a copper plate 4 having a prescribed curved shape is attached onto the back side of the butt-joint part between the nozzle plate 1 and the thin plate small piece 6, and the butt-joint top surfaces are tentatively welded 7. Then the butt-joint opened top surfaces are multilayered-welded 7, and further the both edges of the thin plate small piece 6 and the outer and inner rings 2 and 3 of a nozzle are alternately multilayered- padding-welded 8 and 9. After the completion of welding, annealing is performed, and the padded bead part is shaped by a grinder, etc. Using this method, the welding region can be reduced markedly, and the working time for grinder shaping can be shortened, and the working efficiency can be improved markedly.

Description

[Detailed Description of the Invention] Purpose of the Invention (Industrial Field of Application) The present invention is directed to a method for restoring a defective portion to a normal shape when a defective portion occurs at the rear edge of a nozzle plate due to erosion during operation of a steam turbine. This article relates to a nozzle plate repair method for restoration.

(Prior Art) In thermal power plants, carbon dioxide scale often adheres to the inner walls of pipes in boilers. This oxidized scale is mixed into the steam as small solid particles (particles),
It flows into the steam turbine along with the steam.

The steam that has flowed into the turbine rapidly increases in speed while decreasing the pressure at the nozzle, and the direction of the flow changes greatly (amount of turning = about 70° to 75°), but the oxidized school particles P are smaller than the steam. Since the mass is large and is strongly affected by inertial force, it is unable to follow large changes in direction within the turbine nozzle, and as shown by the arrow in Fig. 5, the ventral rear edge of the nozzle plate l collide. As a result, the rear edge of the nozzle plate 1 gradually breaks off as shown in FIG. 2, and so-called particle erosion E occurs.

In the figure, numeral 2 indicates the nozzle outer ring, and 3 indicates the nozzle inner ring.

The steam flow path formed by the nozzle plate that has been damaged due to particle erosion greatly deviates from the designed flow path, which not only significantly reduces the performance of the steam turbine, but also causes an excitation force to act on the turbine rotor blades, causing the steam Reduces turbine reliability.

Therefore, if a nozzle plate having a defect as described above is discovered during a periodic overhaul inspection of a steam turbine, the nozzle plate is repaired to restore it to its normal shape.

Figures 6 and 7 schematically show a conventional nozzle plate repair method, in which a nozzle diaphragm whose outer and inner ends are fixed to the nozzle outer ring 2 and the nozzle inner ring 3, respectively, is attached so that the steam outflow side of the nozzle plate 1 faces upward. First, the defective part of the nozzle plate is shaped with a grinder or the like. Next, a copper plate 4 having the same shape as the ventral side of the nozzle plate 1 is placed on the ventral side of the repaired part.
, and apply the build-up 5 by downward TIG welding in the order shown by symbols ① to ②.

After the build-up is completed, the nozzle plate 1 is annealed, and then the build-up portion 5 is shaped with a grinder or the like and repaired to have a normal nozzle plate shape.

(Problems to be solved by the invention) As mentioned above, in the conventional repair method, the damaged part of the nozzle plate is entirely restored by welding, but the nozzle plate has a curved shape with smoothly connected circular arcs. On the other hand, since the surface of the build-up part is uneven, which is unique to welding, insufficient thickness tends to occur in the build-up weld part. However, it is difficult to detect this lack of thickness until after the fill-up area has been shaped using a grinder, etc., so if it is found that there is a lack of fillet after shaping, work such as build-up welding, annealing, and grinder shaping should be performed again. There was a problem in that work efficiency was lowered.

An object of the present invention is to solve these problems and provide a steam turbine control device that is easy to operate and has high reliability.

[Structure of the Invention] (Means for Solving the Problems) The method for repairing a nozzle plate of a steam turbine according to the present invention is a method for repairing a nozzle plate including the defective portion when a defect occurs at the trailing edge of the nozzle plate due to erosion by solid particles. This method is characterized in that the entire rear edge of the plate is cut and removed in a straight line, and a small piece of thin plate having the same shape as the original shape of the cut and removed rear edge of the nozzle plate is groove-welded thereto.

(Function) As described above, in the steam turbine nozzle plate repair method of the present invention, a small piece of thin plate is inserted into the defective part of the nozzle plate and welded, so the welding area is significantly reduced.
Even if there is a shortage of meat, this can be determined at a glance.

(Example) The present invention will be explained in detail below.

As shown in FIG. 2, when the nozzle plate 1 has a defective part E due to particle erosion, the defective part E
Cut and remove the entire rear edge of the nozzle plate in a straight line as shown by the dash-dotted line, and finish the end face in a beveled shape. Next, as shown in FIGS. 3 and 4, A small thin plate piece 6 having the same shape as the original shape of the rear edge portion of the cut nozzle plate is cut to the same length as the cut portion, and the cut surface is beveled.

After confirming that this small thin plate piece 6 is smoothly joined to the cut surface of the nozzle plate 1, the small thin plate piece 6 is welded.

For this welding, as shown in Fig. 4, a copper plate 4 with a prescribed curved shape is applied to the back side of the butt part between the nozzle plate 1 and the small thin plate piece 6, and the butt groove surfaces are temporarily welded by TIG welding. 7, and then the thin plate pieces and the nozzle outer ring 2 and the nozzle inner ring 3 are temporarily welded by TIG welding.

Next, as shown in FIG. 1, multi-layer welding 7 is performed between the butt groove surfaces using the backward welding method, and then multi-Ra welding 8 is performed alternately between both ends of the thin plate piece 6 and the inner and outer rings of the nozzle. .9
do.

After welding is completed, annealing is performed and the excess bead portion is shaped using a grinder or the like.

[Effects of the Invention] As described above, the nozzle plate repair method of the present invention involves cutting and removing the portion damaged by erosion in a straight line, and butt welding a small thin plate piece having the same dimensions as the cut portion thereto. As is clear from comparing Figures 1 and 8, the welding area can be significantly reduced, the time required for grinder shaping work can be shortened, and the welding process is faster than conventional overlay welding. Sexuality improves dramatically. Also,
The lack of thickness in the entire small piece of thin plate can be confirmed before welding, so
There is no need to repeat the conventional correction work such as weld build-up → annealing → grinder shaping, and work efficiency is greatly improved.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a nozzle diaphragm of a steam turbine repaired by the method of the present invention, Fig. 2 is a perspective view of a nozzle diaphragm with a defective part, and Figs. 3 and 4 show the steps of the method of the present invention. Explanatory diagram: Figure 5 is an explanatory diagram showing the movement of solid particles in the steam turbine; Figures 6 and 7 are explanatory diagrams showing the steps of the conventional method; Figure 8 is a nozzle of a steam turbine repaired by the conventional method. FIG. 3 is a perspective view of a diaphragm. 1... Nozzle plate 2... Nozzle outer ring 3... Nozzle inner ring 4... Copper plate 5... ...Welding section 6... Thin plate small piece 7.8.9... Welding section agent Patent attorney Nori Chika Ken Yudo Ken Daishimaru Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (2)

[Claims] (1) If a defect occurs at the rear edge of the nozzle plate due to erosion by solid particles, cut and remove the entire rear edge of the nozzle plate including the defective part in a straight line, and place the cut and removed part on the rear edge of the nozzle plate. A method for repairing a nozzle plate for a steam turbine, characterized by groove welding a small piece of thin plate having the same shape as the original shape of the edge. (2) A method for repairing a nozzle plate for a steam turbine according to claim 1, characterized in that the inner and outer circumferential surfaces of the thin plate pieces are welded to the nozzle inner ring and the nozzle outer ring.