TUNGSTEN CARBIDE INSERTS AND METHOD
TECHNICAL FIELD
The embodiments of the subject matter disclosed herein generally relate to
wear protection and more particularly to adding inserts to combustion
hardware in gas turbine systems.
BACKGROUND
Combustors are used in a gas turbine to deliver hot combustion gases to a first
stage of a turbine. Each combustor used in the system typically includes a
fuel injection system with one or more fuel nozzles and a combustion
chamber. A typical combustion chamber may include a combustion liner, a
transition piece which is connected to and extends between the combustion
chamber and the first stage of the turbine, and a flow sleeve. A passage is
created between the combustion liner and the flow sleeve which allows at
least a portion of the compressor discharge air to be introduced into the
combustion liner for mixing with the fuel injected into the system through the
fuel nozzles and for cooling purposes. Additionally, the transition piece
directs and delivers the hot combustion gases to the first stage of the turbine
for power generation and expansion.
More specifically, a combustor and its associated transition piece are
described with respect to Figure . A combustor 2 for use in a gas turbine has
a combustion chamber 4, which is inside of a combustion liner 6 which may
be cylindrical in shape. Fuel enters the combustion chamber 4 via a nozzle(s)
12. The combustion liner 6 is surrounded by a substantially cylindrical flow
sleeve 8. However, a radial gap exists between the combustion liner 6 and the
cylindrical flow sleeve 8 which acts as an air flow passage to introduce air
into the combustion chamber 4 to be mixed with the fuel delivered through
the fuel nozzle 12. A transition piece 10 connects the combustion liner 6 with
a first stage of a turbine (not shown). More information regarding a
combustor for use in a gas turbine can be found in U.S. Patent Number
5,749,218, entitled "Wear Reduction Kit for Gas Turbine Combustors", the
entire context of which is included herein by reference.
During operation, some combustion parts are affected by wear induced by, for
example, hardware vibrations. This wear generates maintenance and expense
costs related to downtime and replacement parts. One method for reducing
wear of combustion parts in a gas turbine is spray coating. For example, high
velocity oxygen fuel (HVOF) coatings have been used to improve the wear
characteristics on parts which have been found to have wear damage. These
spray coatings, while improving wear characteristics, are not able to provide,
or cost effectively provide, a thick coating and instead are typically used in
applications of coatings of approximately 0.5 mm or less in thickness.
Additionally, these spray coating mechanisms are performed at approximately
a 90° angle to the desired coating surface. Some part geometries that it is
desirable to coat, e.g., corners and various curves, do not allow for the
required inclination (between the coating spray nozzle and the part surface) to
be achieved which results in either a thin coating or possibly no coating at all.
Accordingly, systems and methods for reducing wear and increasing the
lifetime of parts associated with the gas turbine combustor and reducing costs
are desirable.
SUMMARY
According to an exemplary embodiment there is a system for wear reduction
in a combustion system of a gas turbine. The system includes: at least one
substantially H-shaped block, the substantially H-shaped block being
configured to secure a transition piece of a gas turbine combustor to a support
piece; a first insert including a first tungsten carbide in a first metal matrix,
where the first metal matrix is selected from a group including cobalt and
nickel; and a first brazing material between the at least one substantially Hshaped
block and the first insert. The first brazing material is used in brazing
the first insert to the at least one substantially H-shaped block in at least one
location on an interior wear surface of the at least one substantially H-shaped
block, the interior surface of the at least one substantially H-shaped block
includes a first surface substantially perpendicular to a second surface which
is substantially perpendicular to a third surface, the third surface being
substantially parallel to and having a substantially same surface area as the
first surface.
According to another exemplary embodiment there is a method for reducing
wear in a combustion system of a gas turbine. The method includes:
providing an insert that includes tungsten carbide in a metal matrix, where the
metal matrix is selected from a group including cobalt and nickel; covering at
least one known wear area of at least one substantially H-shaped block with
the insert; and brazing the insert to the substantially H-shaped block. The at
least one known wear area of the at least one substantially H-shaped block is
located on an interior surface of the at least one substantially H-shaped block
which includes a first surface substantially perpendicular to a second surface
which is substantially perpendicular to a third surface, the third surface being
substantially parallel to and having a substantially same surface area as the
first surface.
According to another exemplary embodiment there is a wear resistant solid
material. The solid material includes: a substrate; an insert including either a
cobalt matrix with tungsten carbide or a nickel matrix with tungsten carbide,
the tungsten carbide comprises between 10 and 20 percent by weight of the
insert; and a brazing material between the substrate and the insert, the brazing
being configured to attach the insert to the substrate.
According to still another exemplary embodiment, there is a system for wear
reduction in a combustion system of a gas turbine. The system includes at
least one substantially H-shaped block, the substantially H-shaped block
being configured to secure a transition piece of a gas turbine combustor to a
support piece; and an insert configured to cover a wear area on an interior
surface of the H-shaped block. The insert includes a tungsten carbide and a
brazing material in a metal matrix, the metal matrix is selected from a group
including cobalt and nickel. The interior surface of the at least one
substantially H-shaped block includes a first surface substantially
perpendicular to a second surface which is substantially perpendicular to a
third surface, the third surface being substantially parallel to and having a
substantially same surface area as the first surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate exemplary embodiments, wherein:
Figure 1 depicts a traditional combustor and a transition piece;
Figure 2 illustrates an H-block attached to a flange according to exemplary
embodiments;
Figure 3 shows a support piece and fingers according to exemplary
embodiments;
Figure 4 illustrates a combustor liner and a combustor liner stop according to
exemplary embodiments;
Figure 5 shows a combustor liner stop and its mating piece according to
exemplary embodiments;
Figure 6 shows an H-block with inserts according to an exemplary
embodiment;
Figure 7 illustrates a combustor liner stop with an insert according to
exemplary embodiments;
Figure 8 shows an H-block with a tape-like substance covering a wear area
according to exemplary embodiments; and
Figure 9 is a flowchart illustrating a method for reducing wear according to
exemplary embodiments.
DETAILED DESCRIPTION
The following detailed description of the exemplary embodiments refers to
the accompanying drawings. The same reference numbers in different
drawings identify the same or similar elements. Additionally, the drawings
are not necessarily drawn to scale. Also, the following detailed description
does not limit the invention. Instead, the scope of the invention is defined by
the appended claims.
Reference throughout the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure, or characteristic
described in connection with an embodiment is included in at least one
embodiment of the subject matter disclosed. Thus, the appearance of the
phrases "in one embodiment" or "in an embodiment" in various places
throughout the specification is not necessarily referring to the same
embodiment. Further, the particular features, structures or characteristics
may be combined in any suitable manner in one or more embodiments.
As previously described, various parts of the combustor can experience wear
over time caused by, for example, vibration, when the gas turbine is in use.
Examples of wear locations include, but are not limited to, various
connectors, connection points and stops (see Figure 1) associated with the
components of the combustion liner 6 and the transition piece 10, which are
used in attaching the two components, as well as the mating points between
the combustion liner 6 and the flow sleeve 8. More specifically, stops can be
used to position, secure and ensure the desired radial spacing between the
combustion liner 6 and the flow sleeve 8 at one end of the combustion liner 6.
An H-block connected to fingers is used at the other end of the combustion
liner 6 to connect the combustion liner 6 with the transition piece 10. The Hblock
is also referred to herein as a "substantially H-shaped block" and an
"H-shaped block". Additionally, methods and systems for connecting these
parts are generally known in the art, see, e.g., U.S. Patent Number 5,749,218
(the entire content of which is incorporated herein by reference), and as such
only an overview of the connection points is described to present context for
the exemplary embodiments described herein.
According to exemplary embodiments, the wear characteristics of these
contact points can be modified such that their useful lifetime is extended.
Prior to discussing these exemplary embodiments, Figures 2-5 will be
described to provide context with respect to the components which tend to
wear in a gas turbine combustion system. Initially, as seen in Figure 2, the
transition piece 10 can have a flanged section 208 which has an opening 210.
Within the opening 210 and attached to the flanged section 208 is an Hshaped
block 202. The H-shaped block 202 can be attached to the flanged
section 208 in various ways, such as, welding. While Figure 2 shows only a
single H-shaped block 202 and a single flanged section 208, there may be two
of these pieces/sections attached to the transition piece 10. Fingers 204 and
206 are slidably received within the H-shaped block 202 such that the
opposed facing surfaces of the finger elements can engage opposite sides of
the cross piece 212 of the H-shaped block 202. As shown in Figure 3, fingers
204 and 206 are attached to a structural member 214 which is attached to a
casing (not shown) which holds the combustor liner 6. Wear can occur on the
interior surfaces of the H-shaped block 202 where the fingers 204 and 206
could rub or vibrate. Wear can also occur on the facing surfaces of the
fingers 204 and 206 that contact the interior surfaces of the H-shaped block.
Figure 4 shows the combustor liner 6 with an attached combustor liner stop
402. Numerous combustor liner stops 402 can be attached to the combustor
liner 6 to position the combustor liner as desired. Figure 5 shows the
combustor liner stop 402 and a male mating piece 404. The male mating
piece is attached to the inside of the flow sleeve 8. Where these two pieces
mate are also locations where wear can occur during operation of the
combustor 2. Additionally, the H-shaped blocks 202, the combustor liner
stops 402 and their respective mating pieces can be made from a Cobalt based
super alloy, e.g., L-605 or Hynes 25.
When in operation some of the various wear components in a combustor 2 can
have a relatively short life time which results in a higher than desired
frequency of inspection and replacement. According to exemplary
embodiments, the application of tungsten carbide in a metal matrix, e.g., cobalt
or nickel, can increase the wear resistance of the various wear components,
thus reducing the frequency of inspection and replacement of various wear
components in a gas turbine combustor 2.
The tungsten carbide in a metal matrix is formed into a desired shape for
increasing the usable life of the part by, for example, creating a wear surface
with a high hardness. For example, appropriate amounts of tungsten carbide
in either cobalt or nickel still allow the part to have the desired strength and
other material properties while operating at the high temperatures of the
combustor. The tungsten carbide in the metal matrix, which is also referred
to as a "tungsten carbide insert" or "insert" herein, may be formed through a
sintering process. The tungsten carbide inserts start as tungsten carbide
powders embedded in the metal matrix. The powder is placed into a die, for
shaping the insert as desired. A pressure, e.g., 1000 bar, is applied to the
powder and then, while in the die, the pressurized powder undergoes sintering
in a furnace at approximately 1200° C. After sintering, the insert can be
further modified to achieve the desired shape if needed through various
processes, e.g., grinding for shape, size and surface finish. The insert may be
then attached to the desired location on the part, e.g., the wear surfaces,
through a brazing process using an appropriate brazing material, e.g., a low
melting point brazing alloy such as a silver brazing powder, for the tungsten
carbide insert and the part. According to other exemplary embodiments, the
insert may be mechanically joined to the base piece, e.g., the insert can be
bolted to the part.
According to another exemplary embodiment, the entire piece that
experiences wear can be made using tungsten carbide in a metal matrix. n
this case, a die which is shaped to the part, as compared to being shaped for
an insert, is filled with the tungsten carbide powder in the cobalt or nickel
matrix and undergoes the sintering process. The part can then, if needed, be
processed to conform to the desired part shape prior to being placed in a
combustor system. The part formed can include, but is not limited to any of
an H-shaped block 202, a combustion liner stop 402, the male mating piece
404 and the fingers 202 and 204.
According to exemplary embodiments, a range of tungsten carbide in the
metal matrix can be approximately between 10-20 percent by weight.
Considerations for the amount of tungsten carbide to be used in the metal
matrix include, but are not limited to, brittleness, ductility and hardness.
Additionally, in another exemplary embodiment, the amount of tungsten
carbide in the metal matrix is approximately 12 percent by weight.
According to exemplary embodiments as described above, a die can be used
to shape the insert or multiple dies may be used to shape multiple, possibly
different, inserts. These inserts can be a single piece or a combination of
pieces as desired. Additionally, sintering the tungsten carbide in a metal
matrix allows the creation of inserts which are relatively thick, e.g., 1 mm or
thicker, as compared to the thickness of the spray coatings, e.g., less than 1
mm but typically less than 0.5 mm, which have been traditionally used.
According to another exemplary embodiment, the thickness of the inserts are
in a range of 2-4 mm. Also, inserts of various shapes and geometries can be
created to cover surfaces in a uniform thickness of the insert, e.g., interior
corners of the H-shaped block 202. The H-shaped block 202 is often of the
size having a length of about 5.08 cm and a width of about 2.54 cm.
According to an exemplary embodiment, an insert can be attached on the
known wear areas of the H-shaped block 202 as shown in Figure 6. The wear
surfaces associated with the H-shaped block 202 are the interfaces 604
between the H-shaped block 202 and the insert(s) 602. This wear is caused by
the contact and movement between the H-shaped block 202 and the fingers
204, 206 (shown in Figures 2 and 3). Each insert 602 can be placed either as
a single roughly U-shaped piece or, for example, as three separate pieces, one
per surface. The wear surfaces are the interior surfaces to the H-shaped block
202 and can be described as a first surface 606 substantially perpendicular to
a second surface 608 which is substantially perpendicular to a third surface
610, the third surface 610 being substantially parallel to and having a
substantially same surface area as the first surface 606. Similar inserts can be
placed on the wear surfaces of the fingers 204 and 206.
According to another exemplary embodiment, an insert can be attached on the
known wear areas of the combustor liner stop 402 as shown in Figure 7. Each
insert 702 can be placed either as a single substantially U-shaped piece or, for
example, as three separate pieces, one per surface. The wear surfaces are the
interior surfaces to the liner stop 402 and can be described as a first surface
704 which is substantially perpendicular to a second surface 706 which is
substantially perpendicular to a third surface 708, the third surface 708 being
substantially parallel to and having a substantially same surface area as the
first surface 704. Similar inserts can be attached to the mating wear surfaces
of the male mating piece 404.
Exemplary embodiments described herein can provide an increased wear
resistance to the combustion parts without the geometrical limitations
associated with spray coating processes. Using sintered carbide, inserts can
have a hardness of greater than 1500 HV (Vickers pyramid number) on the
various mating surfaces, which lowers the material loss due to the wear
phenomena. Regarding various material properties of the inserts, the hardness
is mainly driven by the presence of carbides, while the oxidation protection
and the cohesion of the insert are provided by the metal matrix. Ductility of
the inserts can be modified by changing the chemical composition of the
matrix. According to exemplary embodiments, hardness values for the inserts
may be in a range from 1000 Vickers to 1800 Vickers, or even more in some
cases. A fracture toughness, or ductility, can range from a K c of 5 to a ic
of 30. According to another exemplary embodiment, the hardness can be
approximately 1250 Vickers with a K c of approximately 20.
Using a low melting point brazing alloy 7 10, e.g., a silver brazing powder,
allows penetration by the brazing alloy 710 into the insert structure, which
when the brazing alloy 710 diffuses in the base material 402, creates a
metallurgical joining with minimal (or no) porosity and good adhesion
between the base material 402 and the inserts 702. Additionally, according to
exemplary embodiments, these inserts can be applied to other flat or curved
surfaces in a gas turbine or other device, providing that the coefficient of
thermal expansion mismatch between the insert and the base material of the
part to be protected is within acceptable design limits, e.g., the higher the
adhesion achieved, the higher mismatch can be allowed. For example, the
coefficient of thermal expansion (CTE) of a base metal is about 14 °C while
the CTE for tungsten carbide is around 6 °C 1, however thermal cycling tests
have shown that the adhesion is maintained at 400-500 °C which is acceptable
according to exemplary embodiments.
According to exemplary embodiments, in one application, different
composition inserts may be applied to a same part, e.g. the H-shaped block,
with corresponding different brazing materials. In another application, a first
insert material and a first brazing material may be used on the H-shaped block
and second insert material, different from the first insert material, and a
second brazing material, different from the first brazing material, may be used
on a combustor liner stop.
According to another exemplary embodiment, the inserts can be formed with
the brazing powder mixed into the tungsten carbide powder. This combined
powder is then exposed to pressure for compaction creating a tape-like
substance, i.e., the combined powder is flexible yet has enough integrity to
stick together while being applied to a wear surface. This tape-like substance
is then applied to the desired wear surface and heat treated. During heat treat,
the brazing powder in the combined powder diffuses into the base metal to
fuse the tape-like substance to the base metal. At the same time, the tungsten
carbide powder is sintered. Thus, according to this exemplary embodiment,
the step of brazing and the step of sintering are performed simultaneously.
An example of the tape-like substance 802 covering a wear section 804 of an
H-shaped block 202 is shown in Figure 8. According to an alternative
exemplary embodiment, a polymer may be added to the mixed brazing powder
and tungsten carbide powder, in low concentrations, to increase the flexibility
of the tape-like substance. Additionally, the volatile organic compounds in
the low concentration polymer generally burns off during the heat treating
process.
Utilizing the above-described exemplary systems according to exemplary
embodiments, a method for reducing wear is shown in the flowchart of Figure
9. A method for reducing wear in a combustion system of a gas turbine
includes: a step 902 of providing an insert that includes tungsten carbide in a
metal matrix, where the metal matrix is selected from a group including
cobalt and nickel; a step 904 of covering at least one known wear area of at
least one substantially H-shaped block with the insert, where the at least one
known wear area of the at least one substantially H-shaped block is located on
an interior surface of the at least one substantially H-shaped block which
includes a first surface substantially perpendicular to a second surface which
is substantially perpendicular to a third surface, the third surface being
substantially parallel to and having a substantially same surface area as the
first surface; and a step 906 of brazing the insert to the substantially H-shaped
block.
While using tungsten carbide for improved wear performance associated with
parts of a gas turbine has been described in some of the exemplary
embodiments described above, tungsten carbide in a metal matrix, e.g., cobalt
or nickel, can be used for its properties in other applications. For example,
using the tungsten carbide in a metal matrix, various shapes, sizes and
thicknesses of pieces can be created during the sintering process as desired,
potentially for use in other high temperature applications which could benefit
from the properties of tungsten carbide in a metal matrix.
The above-described exemplary embodiments are intended to be illustrative in
all respects, rather than restrictive, of the present invention. Thus the present
invention is capable of many variations in detailed implementation that can be
derived from the description contained herein by a person skilled in the art.
All such variations and modifications are considered to be within the scope
and spirit of the present invention as defined by the following claims. No
element, act, or instruction used in the description of the present application
should be construed as critical or essential to the invention unless explicitly
described as such. Also, as used herein, the article "a" is intended to include
one or more items.
This written description uses examples of the subject matter disclosed to
enable any person skilled in the art to practice the same, including making
and using any devices or systems and performing any incorporated methods.
The patentable scope of the subject matter is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims.

CLAIMS:
1. A system for wear reduction in a combustion system of a gas turbine,
said system comprising:
at least one substantially H-shaped block configured to secure a
transition piece of a gas turbine combustor to a support piece;
a first insert including a first tungsten carbide in a first metal matrix,
wherein said first metal matrix is selected from a group comprising cobalt and
nickel; and
a first brazing material between said at least one substantially Hshaped
block and said first insert, said first brazing material being configured
to braze said first insert to said at least one substantially H-shaped block in at
least one location on an interior wear surface of said at least one substantially
H-shaped block,
wherein said interior surface of said at least one substantially H-shaped
block includes a first surface substantially perpendicular to a second surface
which is substantially perpendicular to a third surface, said third surface
being substantially parallel to and having a substantially same surface area as
said first surface.
2. The system of claim 1, further comprising:
at least one combustor liner stop configured to attach to a combustor
liner of the gas turbine;
a second insert including a second tungsten carbide in a second metal
matrix, wherein said second metal matrix is selected from a group comprising
cobalt and nickel; and
a second brazing material between said at least one combustor liner
stop and said second insert, said second brazing material being configured to
braze said second insert to said at least one combustor liner stop in at least
one location on an substantially U-shaped wear surface of said at least one
combustor liner stop.
3. The system of claim 1 or claim 2, wherein a composition of said first
or second or both tungsten carbides in said first or second or both metal
matrices is in the range of 10 to 20 percent by weight.
4. The system of any preceding claim, wherein said first insert has a
thickness greater than or equal to 1.0 mm.
5. A method for reducing wear in a combustion system of a gas turbine,
said method comprising:
providing an insert that includes tungsten carbide in a metal matrix,
wherein said metal matrix is selected from a group comprising cobalt and
nickel;
covering at least one known wear area of at least one substantially Hshaped
block with said insert, wherein said at least one known wear area of
said at least one substantially H-shaped block is located on an interior surface
of said at least one substantially H-shaped block and includes a first surface
substantially perpendicular to a second surface which is substantially
perpendicular to a third surface, said third surface being substantially parallel
to and having a substantially same surface area as said first surface; and
brazing said insert to said substantially H-shaped block.
6. The method of claim 5, wherein a composition of said tungsten carbide
in said metal matrix is in the range of 10 to 20 percent by weight.
7. The method of claim 5 or claim 6, further comprising:
covering at least one known wear area of a combustor liner stop with said
insert; and
brazing said insert to said combustor liner stop.
8. The method of any of claims 5 to 7, further comprising:
forming said tungsten carbide in said metal matrix into said insert
through a sintering process in a die.
9. A wear resistant solid material, said solid material comprising:
a substrate;
an insert including either a cobalt matrix with tungsten carbide or a
nickel matrix with tungsten carbide wherein said tungsten carbide comprises
between 10 and 20 percent by weight of said insert; and
a brazing material between said substrate and said insert and
configured to attach said insert to said substrate.
10. A system for wear reduction in a combustion system of a gas turbine,
said system comprising:
at least one substantially H-shaped block configured to secure a
transition piece of a gas turbine combustor to a support piece; and
an insert configured to cover a wear area on an interior surface of said
at least one substantially H-shaped block, said insert including a mixture of a
tungsten carbide and a brazing material in a metal matrix, wherein said metal
matrix is selected from a group comprising cobalt and nickel,
wherein said interior surface of said at least one substantially H-shaped
block includes a first surface substantially perpendicular to a second surface
which is substantially perpendicular to a third surface, said third surface
being substantially parallel to and having a substantially same surface area as
said first surface.