METHOD FOR THE THERMOCHEMICAL CLEANING AND/OR STRIPPING OF TURBINE COMPONENTS

PROCEDE POUR LE NETTOYAGE ET/OU LE DECAPAGE THERMOCHIMIQUE D'ELEMENTS DE TURBINES

English Abstract

The invention relates to a process for the thermochemical cleaning and/or
stripping of turbine components, in particular engine components, with the
steps: Production
of a first gaseous mixture containing HF and H2 in which the part by volume of
HF in the
mixture of HF and H2 is in the range of 2.5 to 45% by volume, and application
of the first
gaseous mixture containing HF and H2 on and/or in a turbine component for
cleaning and/or
stripping this turbine component.

French Abstract

L'invention concerne un procédé pour le nettoyage et/ou le décapage thermochimique d'éléments de turbines, en particulier d'éléments de propulseurs. Le procédé selon l'invention comprend les étapes suivantes : production d'un premier mélange gazeux contenant HF et H2 dans lequel la part volumique de HF est comprise entre 2,5 et 45 % en volume; application du premier mélange gazeux contenant HF et H2 sur et/ou dans un élément de turbine afin de nettoyer et/ou de décaper cet élément de turbine.

Claims

6
Claims
1. A process for the thermochemical cleaning and/or stripping of turbine
components, in
particular of engine components, with the steps:
- Production of a first gaseous mixture containing HF and H2 in which the part
by volume of
HF in the mixture of HF and H2 is in the range of 2.5 to 45% by volume; and
- Application of the first gaseous mixture containing HF and H2 on and/or in a
turbine
component for cleaning and/or stripping this turbine component.
2. The process according to Claim 1, characterized in that the part by volume
of HF in the
mixture of HF and H2 is in the range of 5 to 25% by volume.
3. The process according to one of the previous claims, characterized in that
after the
production and application of the first gaseous mixture on the turbine
component this turbine
component is washed.
4. The process according to Claim 3, characterized in that the washing of the
turbine
component takes place by a second gaseous mixture or substance.
5. The process according to Claim 4, characterized in that the second gaseous
mixture
contains HF and H2 and that the amount of HF in the mixture of HF and H2
measured in % by
volume is less than in the first gaseous mixture.
6. The process according to Claim 5, characterized in that the second gaseous
mixture
contains HF and H2 and that the amount of HF in the mixture of HF and H2 is in
the range of
0.5 to 5% by volume.
7. The process according to one of Claims 4 to 6, characterized in that in
order to clean
and/or strip the turbine component the first and the second gaseous mixture or
substance are
applied on and/or in this turbine component in a multiply alternating manner.

7
8. The process according to one of the previous claims, characterized in that
the pressure of
the first and/or of the second gaseous mixture or substance is varied over
time, in particular
for the washing.
9. The process according to one of the previous claims, characterized in that
this process is
carried out in a container or in a closed system.
10. The process according to one of the previous claims, characterized in that
the first and/or
the second gaseous mixture or substance is/are supplied to the container and
that a chemical
reaction is brought about by this first and/or second gaseous mixture in the
container that
brings about a cleaning and/or stripping of the turbine component, and that
the reaction
products are subsequently removed partially or completely from the container.

Description

CA 02714778 2010-08-10
1
WO 2009/106044 PCT/DE2009/000228
Method for the Thermochemical Cleaning and/or Stripping of Turbine Components
Specification
The invention relates to a process for the thermochemical cleaning and/or
stripping of turbine
components, in particular of engine components.
US 5,898,994 teaches using a mixture of HF gas and hydrogen in which the HF
gas is in the
range of 10 - 15% by weight, in particular in the range of 13% by weight and
the remainder
is hydrogen, in particular 87% by weight hydrogen for the removal of products
produced by
hot gas corrosion, such as metallic sulfides.
US 5,728, 227 teaches a process for stripping gas turbine components in which
a section of
the gas turbine component is exposed to a reduction gas containing more that
6% by weight
halogen gas at a temperature above 1600 F.
US 5,373,986 teaches a process for cleaning fissures in turbine components in
which a tape
is adhered over the fissure.
It is the purpose of the invention to make a process available by means of
which turbine
components can be cleaned and/or stripped in a simple manner.
According to the invention a process according to Claim 1 is suggested in
particular.
Preferred further developments are subject matter of the subclaims.
The process in accordance with the invention provides for the thermochemical
cleaning
and/or stripping of turbine components, in particular engine components, that
at first a first
gaseous mixture is produced containing HF and H2. It can be provided that this
first gaseous
mixture consists of HF and H2. The first gaseous mixture is such that the part
by volume in
the mixture of HF and H2 is in the range of 2.5 to 45% by volume.
Subsequently, the first

CA 02714778 2010-08-10
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gaseous mixture, that comprises HF and H2, is applied on and/or in a turbine
component for
cleaning or stripping this turbine component. In an advantageous embodiment
the part by
volume of HF in the mixture of HF and H2 is in the range of 5 to 25% by
volume, preferably
between 10 and 20% by volume. In an advantageous embodiment the turbine
component is
washed after the production and application of the first gaseous mixture on
this turbine
component. Such a washing can take place, e.g., by a second gaseous mixture or
by a second
gaseous substance.
For the sake of simplification the term second gaseous mixture is used but it
should be noted
that a second gaseous substance can also be used instead of it. The second
gaseous mixture
can be, for example, H2. It can also be provided that the second gaseous
mixture is a mixture
of HF and H2 in which the part by volume of HF in the mixture of HF and H2 is
in the range
of 0.5 to 5% by volume, preferably in the range of 0.5 to 4% by volume,
preferably in the
range of 1 to 3% by volume. The second gaseous mixture is preferably produced
and applied
on the turbine component. It can be provided that a first gaseous mixture is
repeatedly
produced and applied on the turbine component and then a second gaseous
mixture is
subsequently produced and applied on the turbine component. This producing and
applying
of a first and the second gaseous mixture can be multiply repeated in an
alternating manner
for cleaning and/or stripping the turbine component. It can be provided that
the pressure of
the first gaseous mixture is varied over time. It can also be provided that
the pressure of the
second gaseous mixture is varied over time.
Furthermore, it can be provided that the first gaseous mixture is applied with
a different
pressure than the second gaseous mixture. The pressure of the second gaseous
mixture can
be lower than that of the first gaseous mixture. It can also be provided that
the pressure of
the second gaseous mixture is greater than that of the first gaseous mixture.
An advantageous embodiment provides that the pressure is varied in such a
manner that it is
present partially in the range of a subpressure and partially in the range of
an overpressure.
It can be provided that pressure changes take place in steps or that pressure
changes take
place continuously. It can also be provided that pressure changes take place
solely in the
overpressure range or that pressure changes take place solely in the
subpressure range.

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It can be provided that the pressure permanently changes during the entire
process. However,
it can also be provided that the pressure is constant at least at times.
The process is carried out in an advantageous embodiment in a closed system or
in a closed
container.
An especially preferred embodiment provides that the first or the second
gaseous mixture is
supplied and that a chemical reaction is brought about by this first and/or
second gaseous
mixture in the container that brings about a cleaning and/or stripping of the
turbine
component, and that the reaction products are subsequently removed partially
or completely
from the container.
This can take place in such a manner that the cited chemical reaction is
brought about in
particular by the first gaseous mixture and that the reaction products are
subsequently
removed out of the container by the second gaseous mixture.
An especially preferred embodiment provides that the turbine component is a
hollow
component. It can be provided, for example, that the inside surface of such a
hollow
component is cleaned and/or stripped by the process of the invention. The
component can
be, for example, a blade, in particular a compressor blade or turbine blade.
The
component is preferably a hollow blade, in particular a hollow turbine blade.
It is provided in an especially preferred manner that the thermochemical
process in
accordance with the invention for cleaning inside surfaces of hollow turbine
components
or service-conditioned damage by hot gas corrosion is carried out by a
controlled
thermochemical gas phase process at high temperatures.
It can be provided that the process has different periods or time sections in
which time
sections or periods can be present with high parts by volume of hydrogen
fluoride (HF) of
2.5 to 45% in hydrogen-containing reaction atmosphere, followed by process
sections with
substantially hydrogen-containing reaction atmosphere.

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The process of the invention is used especially preferably to remove metal
oxides from the
casting- and production process of the components before the coating with Pt,
Pd, Zr, HF,
Y, Al, Cr, Si and to remove metal oxide compounds and/or metal sulfur
compounds and/or
cover layers, in particular ceramics/oxide cover layers, and/or thermal
insulation layers, in
particular Zr02 thermal insulation layers in the case of coated components.
It can be provided that the turbine components on which the process of the
invention is used
consist of nickel-based alloys and/or cobalt-based alloys that are used or can
be used, e.g., in
the hot areas of airplane turbines and gas turbines. Such components and
turbines often have
small wall thicknesses and have, especially when they are cooled with air
during use, inside
cooling surfaces and cooling fits.
The Ni/Co super alloys for gas turbines are frequently optimized for the best
possible
combination of temperature resistance, creeping strength and expansion change
capacitance.
Such a component can be used, for example, in the process of the invention.
This can take place, for example, by the selection of suitable alloy elements
or also by the use
of high-quality castings that are solidified in a directed manner or
solidified in a
monocrystalline manner.
Such measures for increasing the strength such as, e.g., Cr reduction in the
base material and
limitation of the Al- and/or Ti content can, however, result in a limited
service life as regards
oxidation and corrosion. In order to improve the resistance to oxidation and
corrosion, the
components can be diffusion-coated with Al, PtAl, Cr, or Si or be coated with
McCrAlY
support layers. This can take place, for example, in the framework of the
manufacturing of
new parts but also in the framework of the overhauling of already coated
parts.
In an advantageous embodiment inside surfaces and/or outside surfaces of
turbine
components, in particular turbine blades, can be cleaned with the process in
accordance with
the invention for being prepared for the coating in the thermochemical
process.

CA 02714778 2010-08-10
It is provided in an especially preferred manner that during the process in
accordance with
the invention a pressure fluctuation of Ap > 5 mbar and Ap < 200 mbar is
given. For
example, a pressure fluctuation can be present during the process that is in
the range
between 20 and 60 mbar. It can also be provided that a pressure fluctuation is
present that
corresponds substantially to 30 mbar.
The process can take pace with a high flow of > 5 volume elements exchange
rate per
hour.
This means in particular that per hour at least five times the container
volume is introduced
into the container and removed from it.
It can be provided that the HF components vary in time. This can be
controlled, for
example, by the addition of H2. It can also be provided in particular that
fissures are cleaned
by the process of the invention.
The container in which the process can be carried out can have a volume, for
example, that >
0.3 m3 and < 10 m3. For example, it can be provided that the container volume
is in the range
of 0.5 to 5 m3, preferably between 0.5 and 3 m3, especially preferably between
1 and 2 m3,
especially preferably substantially 1.5 m3. In an especially preferred
embodiment a thorough
washing always takes place during the process of the invention, i.e., a
gaseous mixture is
supplied and reaction points [sic - products?] are removed. For example, it
can be provided
that the following reaction is carried out during the process of the
invention:
6 x HF + A1203 2 AIF,+3 H20..
The cycle time AT can be, for example, in the range of 10 sec. to 10 min. It
can be provided
that the pressures and/or the mixing ratio of the gaseous mixture is/are
changed during the
process.