KR100686792B1 - Dry cleaning method of Ni-based superalloy components for a gas turbine - Google Patents

Abstract

The present invention is part of the regeneration process of nickel-based superalloy parts, which are parts of gas turbines used in combined cycle power plants, aircraft, etc. The present invention relates to a dry cleaning method of nickel-based superalloy parts, and more particularly, by mixing a polytetrafluoroethylene (PTFE or Teflon) powder with a volatile fluid and applying it to a crack surface, thereby allowing the PTFE powder to be inserted into the microcracks. The present invention relates to a dry cleaning method of nickel-based superalloy parts that can use HF gas generated by the reaction of C ₂ F ₄ and hydrogen generated by pyrolysis of PTFE powder in the deep part of microcracks.

Description

Dry cleaning method of Ni-based superalloy components for a gas turbine

FIG. 1A is an electrophotograph showing cracks generated in a first stage blade of a nickel-based superalloy GTD-111 discarded after being used as a gas turbine part. FIG.

FIG. 1B is an enlarged view of the square of FIG. 1A and a component distribution diagram present in a crack;

2A to 2F are the shape and component distribution diagrams of oxides formed on artificial cracks having a depth of 1 mm and a width of 100 μm after the high temperature oxidation test of Example 1,

3 is a Dayton fluorine ion device used in the present invention,

4A to 4F are oxide shape and component distribution diagrams of artificial cracks after dry cleaning according to Example 2,

5a to 5f are oxide shape and component distribution diagrams of artificial cracks after dry cleaning according to Comparative Example 1;

Figure 6 is a comparison graph of the oxygen maximum concentration of the residual oxide present in the microcracks according to the amount of PTFE during dry cleaning according to the present invention and the conventional method.

<Description of the code | symbol about the principal part of drawings>

1b, 2a, 2c, 2e, 4a, 4c, 4e, 5a, 5c, 5e

Red line: O Lime green line: Ni

Pink line: Ti Blue line: Cr

Sky Blue Line: Co Yellow Line: Al

2b, 2d, 2f, 4b, 4d, 4f, 5b, 5d, 5f

Red line: O Blue line: Ni

Lime green line: Ti Orange line: Cr

Black line: Co Light blue line: Al

The present invention is part of a nickel-based superalloy regeneration process for gas turbine components used in a combined cycle power plant, aircraft, etc., and uses a HF gas to remove oxides present on the surface or microcracks of a regenerated product. The present invention relates to a dry cleaning method of a system superalloy component, and more particularly, by mixing a polytetrafluoroethylene (PTFE) powder with a volatile fluid and applying it to a crack surface, thereby allowing the PTFE powder to be inserted into the microcracks. It is a dry cleaning method of nickel-based superalloy parts that can use HF gas generated by the reaction of C ₂ F ₄ and hydrogen caused by pyrolysis of PTFE powder in the deep crack.

Hot gas components, which are used in gas turbines operated directly from the combustion gas of fossil fuels, generate microcracks on the surface when used to some extent, through which the base material or MCrAlY (M = Ni or Co) layer is formed. The surface of the crack rapidly oxidizes when exposed to this direct oxidizing atmosphere. When oxides are formed in the microcracks, stresses are generated due to volume expansion, and thermal stresses and structural stresses of the gas turbine components are combined to continuously grow cracks. If the crack is over a certain size, discard it. FIG. 1A is an electrophotograph showing cracks formed on the first stage blade of the nickel-based superalloy GTD-111 discarded after being used as a gas turbine component, and FIG. 1B is an enlarged view of the square of FIG. 1A and components present in the cracks. It is a distribution chart. As can be seen here, it can be seen that the parts used for the gas turbine operated at high temperature generate fine cracks when used for a certain period of time. Parts that are not severely damaged or that have elapsed a certain operating time may be rebuilt or repaired. In order to restore the damaged parts during regeneration, it is necessary to remove the oxides formed on the surface by pretreatment process by using welding welding or joining with a material (powder or wire) similar to the base material.

Surface oxides are removed by mechanical or chemical methods. When using chemical methods, thermodynamically very stable high temperature oxides such as alumina on the surface of part cracks during gas turbine operation are difficult to remove or clean by conventional methods.

In order to efficiently remove such thermodynamically stable alumina, a dry cleaning process using fluorine ions, that is, a fluoride ion cleaning (FIC) process has been adopted for cleaning gas turbine components of 1300 ° C or higher. Fluoride ions are supplied in the form of HF gas, and there is a method of directly supplying HF and an indirect supply of HF gas generated by reacting hydrogen with C ₂ F ₄ gas generated by pyrolysis of PTFE. The HF indirect supply method is more stable (higher safety) than the HF direct supply method, and the configuration of the system is simpler, and the cost of the device is low. The disadvantage is that it can't be.

Therefore, a method of directly introducing HF gas under sub-pressure below atmospheric pressure for the cleaning of narrow and long cracks has been proposed. However, unlike conventional methods of using solid precursors such as chromium fluoride or PTFE as the raw material for HF, the operating pressure can be easily and easily adjusted, but more complicated control and safety systems are required due to the direct manipulation of highly toxic gases. As a result, the entire system is much more expensive than the conventional one.

Therefore, the present invention is to solve the conventional technical problem, the first object of the present invention is to dry and clean the nickel-based superalloy for gas turbine, which is economical because it is possible to use the conventional device, while removing the oxide deep in the cracking stably and effectively To provide a way.

A second object of the present invention is to provide a gas turbine component in which oxides formed deep in cracks are effectively removed by a dry cleaning method.

In order to achieve the first object, the present invention

Dry cleaning method of nickel-based superalloy parts for gas turbines that removes oxides on the surface or microcracks of regenerated products by using HF gas during the regeneration process of nickel-based superalloy parts, which are parts of gas turbines operated at high temperatures. In

Applying a mixture of PTFE powder and volatile fluid to the microcrack surface, vacuuming for a period of time to infiltrate the microcrack, and

It provides a dry cleaning method of nickel-based superalloy parts for gas turbines comprising the step of treating at a high temperature.

The mixture of the PTFE powder and the volatile fluid is preferably mixed by mixing the PTFE powder so that the content of the PTFE powder is 30 to 70% by weight.

It is preferable that the said high temperature processing temperature is 800 degreeC-1000 degreeC. Oxide removal is most effective at this temperature.

It is preferable that the said PTFE powder has a particle size of 10 micrometers or less. This is because it is not easy to penetrate the fine crack when the particle size of PTFE is 10㎛ or more.

The mixture of the PTFE powder and the volatile fluid is prepared by mixing the PTFE powder and the oil of the mineral oil system, and the oil of the mineral oil system is not limited. The oil of the mineral oil-based oil is a volatilized mineral oil and its composite that can be completely volatilized at 300 ° C. or lower at 300 ° C. or lower, and can be easily handled at room temperature when mixed with grease.

The nickel-based superalloy is 10% to 20% Cr, 5% to 15% Co, 1% to 6% Al, 1% to 6% Ti, 0.001% to 5% W, 0.001% to 4% Ta, 0.001% to 3% Mo, Preference is given to other minor amounts of C, Fe, B and residual nickel.

In order to achieve the second object, the present invention,

Provided are parts for a gas turbine cleaned according to a dry cleaning method of a nickel-based superalloy according to the present invention.

Hereinafter, the present invention will be described in more detail.

The present invention is a dry process of nickel-based superalloy parts for gas turbines that removes oxides present on the surface or microcracks of regenerated products by using HF gas during the regeneration process of nickel-based superalloy parts that are gas turbine component materials operated at high temperatures. In the cleaning method, dry cleaning of a nickel-based superalloy component for a gas turbine, comprising applying a mixture of PTFE powder and a volatile fluid to a microcrack surface and vacuuming for a predetermined period of time so as to penetrate into the microcrack and at a high temperature. Provide a method.

In the dry cleaning method in which HF gas is indirectly supplied to the microcracks by using the existing PTFE, the HF gas that removes the oxides by the reaction between C ₂ F ₄ and hydrogen due to the thermal decomposition of PTFE powder from the cracks is generated. It has been difficult to supply HF gas deeply, and it has been difficult to control the feed rate and amount.

However, in the dry cleaning method according to the present invention, by applying a crack surface of a nickel-based superalloy to a mixture made by mixing PTFE powder with a volatile fluid and inserting the PTFE mixture into the microcracks, the volatile fluid is volatilized at a predetermined temperature or more. Only the PTFE powder remains on the crack surface and inside the crack. Therefore, the PTFE powder can penetrate deep into the crack, and it is easy to control the amount of the penetrating powder. In this case, however, the particle size of the powder is preferably 10 μm or less. This is because it is not easy to infiltrate the microcracks with the PTFE powder mixed in the volatile fluid when the size of the particle size exceeds the above range. Here, the volatile fluid is not limited so long as it is a volatile oil of mineral oil system. The oil of the mineral oil-based oil is preferably a mineral oil and a compound thereof, which volatilizes at 50 ° C. or higher and completely volatilized at 300 ° C. or lower, and is preferable because grease is easy to handle at room temperature.

In addition, in the dry cleaning method according to the present invention, while the conventional dry cleaning method using PTFE generates HF gas only from the outside of the crack, the dry cleaning method may generate HF gas from which the oxide is removed from the outside and the inside of the crack. More effective in removal.

Looking at the reaction scheme of the dry cleaning method according to the invention schematically, it occurs in three steps, the first step is converted to monomer C ₂ F ₄ when PTFE is heated as shown in the following equation I, this monomer is reacted with hydrogen again HF Generate gas. It is preferable that the said high temperature processing temperature is 800 degreeC-1000 degreeC. This is because oxide removal is most effective at this temperature.

PTFE-△ ---> C ₂ F _4- (a)

C ₂ F ₄ + 6H _2- > 4HF + 2CH _4- (b) (I)

Surface oxides and oxides in cracks become fluorides respectively by the reaction of the following formula II.

Al ₂ O ₃ + 6 HF-> 2AlF ₃ + 3H ₂ O (II)

That is, when hydrogen is supplied, the C ₂ F ₄ gas cleans the cracks by the reaction of the following equation III.

2Al ₂ O ₃ + 3C ₂ F _4- > 4AlF ₃ + 6CO (III)

Except for CrF ₃ , most fluorides are volatile and volatilized in the gas stream. With continued heating, Al and Ti in the vicinity of the surface move to the surface by diffusion and are converted into volatile fluorides as shown in Equation IV. At the end of this reaction, these elements are depleted at the surface and form a surface depleted layer in which only solid CrF ₃ is concentrated.

Al + 3HF-> AlF ₃ + 3 / 2H ₂ (IV)

As the process temperature reaches its peak and the hydrogen flow rate increases, the conversion of solid CrF ₃ (formula V) occurs on the chromium surface.

CrF ₃ + 3 / 2H _2- > Cr + 3HF (V)

Here, the cleaning is completed.

Nickel-based superalloys for gas turbines using the dry cleaning method according to the present invention are 10% by weight, 10% to 20% Co, 5% to 15% Co, 1% to 6% Ti, 1% to 6% W, 5% to 5% W, It is preferably composed of Ta 0-4%, Mo 0-3%, other minor amounts of C, Fe, B and residual nickel.

The present invention also provides a gas turbine component which is effectively cleaned by the dry cleaning method according to the present invention.

The parts for gas turbines of the nickel-based superalloy material cleaned by the dry cleaning method of the present invention are cleaned more cleanly than the parts cleaned by the conventional method, so that brazing or welding, which is a subsequent process of regeneration maintenance, is performed. It can be done more easily and effectively.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, an Example is for illustrating this invention and does not limit the scope of the present invention only by these.

Specimen Preparation and High Temperature Oxidation Test

Example 1

The plate-shaped casting of GTD-111 material, which is the composition of Table 1, was prepared by cutting 100 mm wide, 50 mm long, and 3 mm thick. . The specimen prepared as described above was heated to 1000 ° C. at a rate of 100 ° C./h using a box-type electric furnace in order to perform an oxidation test, and maintained at that temperature for 48 hours and then cooled to room temperature. The shape and distribution of the oxides formed on the surface of the GTD-111 material after the high temperature oxidation test are shown in FIGS. 2A to 2F.

Table 1 (wt%)

Ni Cr Co Ti W Al Ta Mo Fe C B Bal. 13.5 9.5 4.76 3.84 3.6 2.7 1.53 0.23 0.09 0.01

Looking at the distribution of oxygen, it can be seen that the surface is distributed relatively much up to about 13 μm. Compared with other components, it can be seen that the Ti-based oxide is distributed from the surface to 3 µm and the Cr-based oxide is distributed from 3 to 13 µm. It can be seen that aluminum oxide is formed discontinuously in the middle of the surface from 13 to 30㎛. Comparing with Figures 1 and 2 it can be seen that the shape and distribution of the oxide is similar, and aluminum can be seen that the internal oxidation occurred like the actual gas turbine blade.

Fluoride ion dry cleaning

Example 2

On the artificial crack of the specimen prepared according to Example 1, after applying a fluid mixture (trade name: Ultra Slick ^™ from Permatex INC.) Of PTFE powder having a PTFE powder content of 30% by weight to grease onto the surface, The grease mixed with PTFE powder was penetrated deeply into the crack in a low vacuum oven maintained at 150 ° C. The specimen was placed in a reactor of Dayton's fluorine ion cleaning equipment as shown in FIG. 3, charged with 60 g of PTFE powder at the bottom, and cleaned according to the DCC (Deep Clean Cycle) work schedule of Table 2. The shape and distribution of oxides of artificial cracks after dry cleaning are shown in FIGS. 4A to 4F.

TABLE 2

step Temperature rise (Ramp-up: ℃) Ramp-up Rate (℃ / h) Hydrogen flow rate (Lpm) Time Interval: min One 25-400 600 5 37.5 2 400-450 150 5 20 3 450-550 150 35 40 4 550-750 300 0 40 5 750-780 300 5 6 6 780-950 300 0 34 7 950-950 0 0 20 8 950-950 0 5 20 9 950-950 0 35 30 10 950-950 0 75 30 11 950-200 -600 35 -

Comparative Example 1

The cracks of the specimens prepared according to Example 1 were dry-cleaned in the same manner as the dry cleaning method of Example 2, except that the step of infiltrating the ultra slick grease into the microcracks during dry cleaning was not performed. Oxide shape and distribution of artificial cracks after dry cleaning are shown in FIGS. 5A to 5F.

Comparison of Residual Oxides with Changes in PTFE Powder Content

In order to confirm the oxide removal efficiency of the dry cleaning method of the present invention, twelve specimens were prepared by cutting microcracked portions in the waste gas turbine single stage blades at 10 mm intervals laterally. Six specimens were subjected to dry cleaning in the same manner as in Example 2. However, the amount of PTFE powder charged to the bottom of the reactor of the dry cleaning equipment of Figure 3 was changed step by step to 60g, 200g and 600g. The other six specimens were dry-cleaned by changing the content of PTFE powder in steps of 60g, 200g and 600g according to the method of Comparative Example 1. Residual oxide concentration after dry cleaning is measured and compared at the leading edge (thick edge at the cross section of the gas turbine blade) and at the pressure side (the pressure side of the gas turbine blade cross section). The results are shown in FIG. 6. The TG, which employs the dry cleaning method according to the present invention, and the dry cleaning using only the conventional method are denoted by UTG.

Analysis of the results

Referring to FIG. 5 showing the result of dry cleaning according to the conventional method, it can be confirmed that the surface is slightly roughened due to the oxide removal of the surface, and the distribution of oxygen shows that the oxides of Ti and Cr series are removed from the surface. Able to know. It can be seen that the aluminum oxide, which is discontinuously produced in the middle of the surface between 13 and 30 μm, is also partially removed.

Referring to FIG. 4, the specimens dry-cleaned according to the present invention have a slightly roughened surface due to oxide removal as in the conventional method, and have Ti, Cr-based oxides present on the surface, and an Al series present between 13 to 30 μm. It can be seen that the oxide of. However, when looking at the oxygen distribution, it can be seen that oxygen is more effectively removed by infiltrating PTFE deeply into the crack, unlike the dry cleaning method according to the conventional method. The difference in oxygen intensity is prominent at the depth of the crack.

6 summarizes the effect of the dry cleaning method using the method of infiltrating the fluid mixture of PTFE and grease into the crack of the blade used. The graph of FIG. 6 plots the peak of oxygen concentration in the crack as a function of the reactor loaded PTFE powder. That is, the graph shows the relative content of oxygen in the cracks versus the content of PTFE powder. Here, when the dry cleaning method of the present invention is adopted (TG), it is uniform regardless of the change of the PTFE powder content, whereas when washing according to the conventional method (UTG), the relative content of oxygen as the content of PTFE powder increases Decreased. For all conditions, the relative content of oxygen was low when the present invention was adopted, and the penetration effect of PTFE grease was greater when the amount of PTFE powder used was small. In addition, when the dry cleaning method according to the present invention using 60 g of PTFE powder and filling the PTFE grease into cracks, the effect is the same as the effect of dry cleaning only by the conventional method without adopting the method according to the present invention with PTFE 600 g. Able to know.

As can be seen from the above results, the present invention is effective to remove oxides formed on the narrow and deep cracks generated after using the blades of a gas turbine, and is made by mixing PTFE powder with volatile fluid during the conventional dry cleaning process. The effect can be obtained by applying the PTFE fluid mixture to the crack and penetrating deep into the crack, so that it can be applied to a conventional system without complicated additional equipment, and thus it is a dry cleaning method of nickel-based superalloy with high cost saving effect.

In addition, the present invention provides a gas turbine component that is cleaned more cleanly than the prior art, thereby enabling a more effective regeneration process to be performed.

Claims (9)

Dry cleaning method of nickel-based superalloy parts for gas turbines that removes oxides on the surface or microcracks of regenerated products by using HF gas during the regeneration process of nickel-based superalloy parts, which are parts of gas turbines operated at high temperatures. In Applying a mixture of PTFE powder and volatile fluid to the microcrack surface, vacuuming for a period of time to infiltrate the microcrack, and Dry cleaning method of nickel-based superalloy parts for gas turbines comprising the step of treating at a high temperature. The method of claim 1, The dry cleaning method of the nickel-based superalloy parts for gas turbines, characterized in that the mixture of the PTFE powder and the volatile fluid is mixed so that the content of the PTFE powder is 30 to 70% by weight relative to the volatile fluid. The method of claim 1, Dry cleaning method for a nickel-based super alloy component for a gas turbine, characterized in that the high temperature treatment temperature is 800 ℃ ~ 1000 ℃. The method of claim 1, Drying method of nickel-based superalloy parts for gas turbines characterized in that the PTFE powder has a particle size of 10㎛ or less. The method of claim 1, The dry cleaning method of the nickel-based superalloy parts for gas turbines, characterized in that the mixture of PTFE and volatile fluid is prepared by mixing PTFE powder and oil of mineral oil system. The method of claim 5, wherein Drying method of the nickel-based superalloy parts for gas turbines, characterized in that the oil of the mineral oil system is volatilized at 50 ℃ or more and completely volatilized at 300 ℃ or less. The method of claim 5, wherein Dry cleaning method of nickel-based superalloy parts for gas turbines, characterized in that the oil of the mineral oil system is grease. The method of claim 1, The nickel-based super alloy is 10% to 20% Cr, 5% to 15% Co, 1% to 6% Al, 1% to 6% Ti, 0.001% to 5% W, 0.001% to 4% Ta, 0.001% to 3% Mo, Dry cleaning method for nickel-based superalloy parts for gas turbines, characterized in that it comprises a small amount of C, Fe, B and residual nickel. delete

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