JP2013039596A - Repair method of metal component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate repairing damage generated on a cast steel metal component used in a high-temperature and high-pressure environment.SOLUTION: A repair method of a metal component includes steps of: mechanically removing a damaged part of the metal component; filling a part where the damaged part is removed with a brazing filler metal having a lower melting point than a metal material which forms the metal component; and polishing a surface of a part filled with the brazing filler metal to be smooth.

Description

  The present invention relates to a method for repairing metal parts, and more particularly to a method for repairing metal parts suitable for repairing cast steel metal parts used in high temperature and high pressure environments.

  For example, a steam turbine device installed in a power plant or the like has a casing of a turbine, a high-temperature and high-pressure (for example, a supercritical pressure turbine used in a coal-fired power plant has a temperature of about 600 ° C. and about 25 MPa. There are many parts such as a valve device for controlling the steam flow. The components such as the passenger compartment and the valve device are generally manufactured as a cast steel metal part in order to realize a complicated shape required for the design in order to form a smooth steam flow path. .

  The above components of the steam turbine apparatus are continuously exposed to high temperature and high pressure environments during operation. For this reason, cracks are generated on the surface of the parts due to elongation deformation due to creep, in which a tensile force is applied for a long time in a high-temperature / high-pressure environment, and thermal stress due to a rapid temperature change at the start and stop of the steam turbine equipment. May occur. If this crack is found at an occasion such as periodic inspection of the steam turbine equipment, measure it against the maintenance standards such as whether the crack depth exceeds the predetermined maintenance standard value, and repair if necessary. Is called.

  Repair of cracks in cast steel metal parts is generally performed by the following method. That is, the crack portion where the crack of the part is generated is ground with a grinding tool such as a grinder so that the crack is completely removed. When a crack is generated again in the crack part once removed, the crack can be ground and removed repeatedly within a range in which the thickness of the target part does not fall below a specified value. If the plate thickness of the target part falls below a predetermined value by removing the crack, the target part is updated.

  Recently, in place of the above-described conventional repairing method by grinding and removing a crack, a repairing method using a welding technique has been studied. This is an attempt to not only remove the crack, but also to repair the shape of the removed part, thereby extending the useful life of the target part and reducing the resistance to vapor flow in the device. It is.

  As a repair method applying the welding technique, first, as a first method, there is a method of completely removing a crack portion generated in a target part with a grinder or the like and then welding a welding material. After removing the crack, groove processing is performed to form a recess for welding the welding material. Next, overlay welding is performed on the grooved portion, and the welded portion is smoothly finished with a grinder or the like. According to the first method, it is possible to completely remove the crack generated in the target part and to restore the shape of the part from which the crack has been removed by welding.

  Further, as a second method, there is a method in which a crack portion of the target part is melted with a high-temperature arc and a crack opening on the surface of the target part is sealed. According to the second method, although a crack remains in the target part, the crack opening is sealed and the remaining crack is shielded from the oxidizing environment, so that the progress of the crack due to oxidation is prevented. There is an effect.

  Alternatively, as a third method, there is a method in which a welding material is welded to an opening of a crack generated in a target part and the opening of the crack is sealed. This third method is similar to the second method, but seals the opening of the crack with a weld metal by welding a welding material to the opening of the crack. In this case, similarly to the second method, the crack remaining in the target part can be shielded from the oxidizing environment, and the heat input to the base material, which is the target part, can be selected by appropriately selecting a welding material. The effect that it is possible to reduce is acquired.

  In addition, regarding the general repair technique of the components used under high temperature and high pressure, there is a technique disclosed in Patent Document 1, for example. Patent Document 1 is a method of repairing a through-damage portion of a high-temperature part, and grinding shaping and groove formation of the through-damage portion, nickel foil arrangement on the formed groove portion, and inside the groove from the top of the nickel foil The process includes filling the nickel-base alloy brazing material and heating and melting it, and heating and melting at least part of the nickel foil and the base material so as to be integrated with the nickel-base alloy brazing material. The technique of Patent Document 1 is considered to be similar to the first method.

JP 2003-176727 A

  The above repair method has the following problems. First, in the first method, since it is necessary to perform groove processing after grinding and removing the crack portion of the target part, the repair work takes time, the work efficiency is low, and the repair cost is high. Further, when repair work is performed at the site where the target part is assembled in the apparatus, there is a problem that heat treatment for removing residual stress cannot be performed at the site.

  In addition, the second method has a problem in that the base material, which is the melted target part, is rapidly cooled thereafter, so that the base material structure becomes martensite and hardens. There is also a problem that cracks may occur afterwards due to the residual stress of the base material that has been melt-cured.

  In the third method, since the weld metal is raised in the crack opening of the target part, the raised weld metal projection becomes a resistance against the high-temperature and high-pressure steam flow, and the projection becomes the steam flow. When it is peeled off, there is a problem that other parts in the apparatus may be damaged.

  The present invention has been made to solve the above-mentioned and other problems, and repairs of metal parts that make it possible to easily repair damage caused to cast steel metal parts used in high-temperature and high-pressure environments. It aims to provide a method.

  In order to achieve the above object, according to one embodiment of the present invention, a damaged part of a metal part is mechanically removed, and the part from which the damaged part is removed has a lower melting point than the metal material forming the metal part. A method for repairing a metal part comprising filling with a brazing material and polishing the surface of the portion filled with the brazing material so as to be smooth.

  The damaged part is, for example, a crack. The metal parts include, for example, cast steel parts used for a casing of a steam turbine device or a valve mechanism.

  The brazing filler metal can be filled by melting the brazing filler metal using an arc as a heat source. At that time, the arc can be generated by an arc welding machine capable of automatically feeding a wire-like brazing material. As the arc welding machine, the arc current generated between the molten brazing material and the wire-shaped brazing material before melting is monitored, and the feeding amount of the wire-shaped brazing material is determined according to the measured arc current value. What to control can be used.

  According to the method for repairing a metal part according to one aspect of the present invention, it is possible to easily repair damage caused to a cast steel metal part used in a high temperature and high pressure environment.

It is a schematic diagram which shows the state of the crack which arose in the metal component. It is a schematic diagram which shows the crack removal operation | work of the repair method of the metal components by one Embodiment of this invention. It is a schematic diagram which shows the welding material welding operation | work of the repair method of the metal components by one Embodiment of this invention. It is a schematic diagram which shows the state after implementation of the welding material welding operation | work of FIG. It is a schematic diagram which shows the state after the surface finishing operation | work of the repair method of the metal component by one Embodiment of this invention.

  Hereinafter, the present invention will be described in accordance with an embodiment thereof with reference to the accompanying drawings.

  FIG. 1 schematically shows a state in which a crack has occurred in an application target of the metal part repair method of the present embodiment. FIG. 1 is a cross-sectional view showing a part of a metal part 10 with a crack 20 generated from the surface to the inside of the metal part 10, and an opening 22 is formed on the surface of the metal part 10. ing.

  The metal parts 10 are parts such as a casing part that constitutes a casing of the steam turbine apparatus, a valve body that constitutes a valve apparatus for controlling the flow rate, flow path, and the like of the steam flow in the steam turbine apparatus. The present invention includes, but is not limited to, metal parts installed in a high temperature and high pressure environment, in particular, cast steel parts in general. A typical material for the metal part 10 is, for example, chromium-molybdenum steel, but includes other materials suitable for use in a high temperature and high pressure environment.

  The crack 20 generated in the metal part 10 can be found by visual inspection, inspection such as ultrasonic flaw detection, etc., at the time of periodic inspection of equipment such as a steam turbine device in which the metal part 10 is used. Further, the depth of the crack 20 inside the metal part 10 can be measured by an inspection such as ultrasonic flaw detection.

  Next, the removal operation of the crack 20 will be described with reference to FIG. FIG. 2 is a partially broken cross-sectional view of the crack 20 generation portion of the metal part 10, as in FIG. 1. First, as a first step of the repair method of this embodiment, the crack 20 generated in the metal part 10 is removed. This removal operation is performed using a metal grinding tool such as a grinder so that the crack removing portion 30 becomes deeper than the deepest portion of the crack 20, that is, the crack 20 generated in the metal part 10 is removed. Shave like so.

  Next, with reference to FIG. 3, the process of welding a welding material to the crack removal part 30 is demonstrated. FIG. 3 is a partially broken cross-sectional view including the crack removing portion 30 of the metal part 10 as in FIG. 1. In the present embodiment, the portion from which the crack 20 has been removed from the metal part 10 is filled with the brazing material by welding the brazing material as the welding material to the crack removing portion 30. For the brazing material, a metal material having a melting point lower than the melting point of the base material of the metal component 10 and a melting point higher than the steam temperature used is selected when the repair target is a steam turbine device component. Such a brazing material may be appropriately selected based on the composition of the metal part 10 to be brazed, the use environment conditions of the metal part 10, and the like. Moreover, in order to improve the wettability of the base material with respect to the welding material, an appropriate flux can be applied to the surface of the crack removing portion 30 where the welding material is welded.

  In the case where chromium-molybdenum steel, which is a material generally used as a casing material of a steam turbine apparatus, is a base material, the applicant of the present application has determined a certain amount on the base material in order to select an appropriate material as a brazing material. Overlaying was performed under arc current conditions, and bead stability, penetration characteristics, and weld hardness were examined. The target brazing materials are the same wire for welding (chrome-molybdenum wire (Cr-Mo wire), copper brazing wire (Cu-Si wire), silver brazing wire (Ag-Cu wire, with flux), and silver brazing As a result, it was found that the best results were obtained when the silver brazing wire was used together with the flux among the four types of brazing materials investigated. When a silver brazing wire was used together with a flux, a stable bead was obtained, no unwelded portion was formed between the base material and the weld metal, and almost no change in the hardness of the weld was observed.

  In the example of FIG. 3, arc brazing is adopted as a brazing method, and the brazing material is supplied as the wire material 110 from the arc welding machine 100 and welded into the crack removing portion 30 to become the weld metal 40. . For example, a CMT (Cold Metal Transfer) welder can be adopted as the arc welder used for the welding operation in FIG. The CMT welder monitors the arc current generated between the molten brazing material and the wire material 110, and if the distance between the molten brazing material and the wire material 110 increases and the arc current decreases, the wire The wire material 110 is supplied so that the arc does not extend beyond a certain length. Conversely, when the wire material 110 comes into contact with the welded brazing material and the current becomes excessive, the supply of the wire material 110 is stopped and the wire material 110 is stopped. The front end of 110 is controlled to be separated from the welded brazing material. Thereby, in the CMT welding machine, it is possible to weld the brazing material while suppressing heat input to the base material, and to obtain an effect of suppressing the residual thermal stress in the base material. In addition, as a welding machine, it is not restricted to a CMT welding machine, A normal manual arc welding machine can be used.

  FIG. 4 shows a partially broken cross-sectional view in a state where the welding operation of the brazing material is completed. Due to the welding operation, the crack removing portion 30 is completely filled with the weld metal 40 and is raised from the surface of the metal component 10. The reason why the weld metal 40 is filled up from the surface of the metal part 10 as shown in FIG. 4 is to restore the surface of the metal part 10 to a state before the crack is generated.

  With respect to the metal part 10 in the state of FIG. 4, the weld metal 40 swelled from the surface of the metal part 10 is scraped off by a grinding tool such as a grinder to restore the surface shape and surface state of the original metal part 10. Thus, the repair by the repair method of the present embodiment is completed. In FIG. 5, the state after the surface finishing operation | work of the metal component 10 is shown typically.

  According to the repair method of the metal part 10 of the present embodiment described above, the crack 20 generated in the metal part 10 can be removed, and the surface of the removed part is covered with the brazing material. Isolated from oxidizing environment.

  Further, since a brazing material having a melting point lower than that of the base material is welded when the crack 20 is removed, preheating work for the base material is not required as compared with a welding process for melting a normal base material, and heat input to the base material is performed. Can be suppressed. Therefore, the hardening of the base material due to heat input is suppressed as much as possible, and it is not necessary to perform heat treatment such as residual stress removal on the metal part 10 after repairing to remove the crack 20. In addition, by selecting an appropriate brazing material excellent in properties such as high-temperature strength and oxidation resistance, the brazing material welded part is mechanically reinforced by the brazing material, and damage such as new cracks and cracks occurs. The effect to prevent can be expected. Furthermore, since the surface of the metal part 10 after repair is restored to the shape at the time of manufacture, there is little possibility of affecting the performance of the steam turbine apparatus or the like in which the metal part 10 is used.

  In addition, this invention is not limited to said embodiment, A various change is possible in the range which does not deviate from the summary.

10 metal parts, 20 cracks, 22 crack openings,
30 crack removal part, 40 weld metal,
100 arc welding machine, 110 wire material

Claims (6)

Mechanically remove damaged parts of metal parts,
The part from which the damaged part has been removed is filled with a brazing material having a melting point lower than that of the metal material forming the metal part,
Polishing the surface of the portion filled with the brazing material so as to be smooth,
A method for repairing metal parts. A method for repairing a metal part according to claim 1,
A method for repairing a metal part, wherein the damaged part is a crack. A method for repairing a metal part according to claim 1,
A method of repairing a metal part, wherein the metal part includes a cast steel part used in a casing of a steam turbine device or a valve mechanism. A method for repairing a metal part according to claim 1,
The filling of the brazing material is performed by melting the brazing material using an arc as a heat source, and repairing metal parts. A method for repairing a metal part according to claim 4,
The arc is a method for repairing metal parts, which is generated by an arc welder capable of automatically feeding a wire-like brazing material.   6. The method of repairing a metal part according to claim 5, wherein the arc welder monitors and measures an arc current generated between the molten brazing material and the wire-shaped brazing material before melting. A method for repairing a metal part, wherein the feeding amount of the wire-like brazing material is controlled according to the arc current value.

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