Patent Description:
In a turbomachine, air is passed into an inlet of a compressor. The air is passed through various stages of the compressor to form a compressed airflow. A portion of the compressed airflow is passed to a combustion assembly and another portion of the compressed airflow is passed to a turbine portion and used for cooling. In the combustion assembly, the compressed airflow is mixed with fuel and combusted to form a high temperature gas stream and exhaust gases. The high temperature gas stream is channeled to the turbine portion via a transition piece. The transition piece guides the high temperature gas stream toward a hot gas path of the turbine portion. The high temperature gas stream expands through various stages of the turbine portion converting thermal energy to mechanical energy that rotates a turbine shaft. The turbine portion may be used in a variety of applications including providing power to a pump, an electrical generator, a vehicle, or the like.

From <CIT> a method for repairing a turbomachine diaphragm is known. It includes removing a worn area from a diaphragm rail member by machining and forming a repair coupon mounting element in the diaphragm rail member. Further a repair coupon is machined and bonded to the machined surface at the repair coupon mounting element.

In <CIT>, which forms the basis for the preamble of claim <NUM>, a technique for refurbishing nozzle diaphragm sections of a gas turbine is described. This technique replaces an eroded or worn section of the nozzle diaphragm with a replacement part designed to be positively locked in a slot machined in the nozzle diaphragm. The replacement part is formed of a material having a similar coefficient of expansion as the material used for manufacturing the original nozzle diaphragm. The combination of the nozzle diaphragm and the replacement part conform to the original manufacturer's dimensional specifications for the nozzle diaphragm.

It is an object of the invention to further improve and enhance the possibilities of repairing a turbomachine diaphragm. Further it is an object of the invention that the repaired diaphragm has improved abilities and extended service life compared to a new diaphragm.

These objects are achieved using a method of repairing a turbomachine diaphragm according to claim <NUM>.

The claimed method is rather efficient since it comprises only three steps. The first and second step consist of machining the worn or eroded coupon of the diaphragm rail such that a clean, not corroded and geometrically exact machined surface is generated. Of course, the machined surface has reduced dimensions compared to the nominal dimensions of the diaphragm rail member. The difference in size between the machined surface and the nominal dimensions of a new diaphragm are filled by a filler material, which forms the claimed cladding (third step).

The claimed method has been successfully executed repairing diaphragm cast of a nickel iron alloy, so-called Ni-resist, and a cladding consisting of a filler material from austenitic stainless steel, such as LS 309LSI, <NUM> series fillers and <NUM>. The claimed method is flexible since only the worn parts of the diaphragm rail member are machined and cladded. Those parts of the rail member that are not worn or eroded, need not be cladded. This means that solely the worn parts of the diaphragm are repaired, reducing costs for machining and cladding of the diaphragm.

In case the distance between the machined surfaces and the nominal dimensions of the diaphragm are greater than the thickness of one layer of the cladding, several layers up to ten or even more layers can be welded to the machined surface of the diaphragm such that the whole affected feature or coupon is being restored. At the end of the welding process the surface of the cladding overtops the nominal dimensions of a new diaphragm. The last step of the claimed method consists of machining the cladding to the nominal dimensions of a new diaphragm according to the manufacturer's specification. Machining may be a milling process or any other suitable process.

According to the invention, at least one welding layer includes several weld passes welded in close proximity to each other such that a compact cladding is achieved.

The claimed method may be further improved if the main welding parameters, such as weld speed, current and voltage, wire speed, and other parameters, well-known to the man skilled in the art, are adapted accordingly. It is possible to adapt these parameters for each pass of a layer, each layer or only once for welding a complete cladding.

To avoid or at least reduce mechanical stress due to the welding process and according to the invention, the machined surfaces have a symmetric cross-sectional area and the passes are welded alternating on each side of the axis of symmetry.

It has been proven advantageous if the welding process is a MIG/MAG-process. Further, it has been proven advantageous if the welding process is supported by an inert gas, wherein the inert gas preferably consists of more than <NUM>% argon and the rest CO2. A TIG process may also be used for the repair process however different parameters are used in this case.

After the welding process is finished, the claimed method comprises the step of machining the cladding until it has the nominal dimensions of a new diaphragm according to the manufacturer's specification.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:.

Referring to <FIG>, a turbomachine, in accordance with an exemplary embodiment, is indicated generally at <NUM>. Turbomachine <NUM> includes a turbine portion <NUM> having a housing <NUM> that defines, at least in part, a hot gas path <NUM>. Turbine portion <NUM> includes a first stage <NUM>, having a plurality of first stage vanes or nozzles <NUM>, and first stage buckets or blades <NUM>; a second stage <NUM> having a plurality of second stage vanes or nozzles <NUM> and second stage buckets or blades <NUM>; and a third stage <NUM> having a plurality of third stage vanes or nozzles <NUM> and third stage buckets or blades <NUM>. Of course it should be understood that turbine portion <NUM> could also include additional stages (not shown).

Hot combustion gases flow axially along hot gas path <NUM> through nozzles <NUM>, <NUM>, and <NUM>, impact and rotate blades <NUM>, <NUM>, and <NUM>. In addition, a cooling airflow is guided into a wheelspace (not separately labeled) of turbine portion <NUM>. The cooling airflow, typically from a compressor portion (not shown) is directed through various components of turbine portion <NUM> to reduce localized hot spots, improve wear, and increase an overall component life. Each nozzle <NUM>, <NUM>, and <NUM> includes a corresponding diaphragm, one of which is shown at <NUM>, that provides a seal which prevents hot gases from passing from hot gas path <NUM> into the wheelspace. Diaphragm <NUM> cooperates with additional structure, (not shown), to limit ingestion of hot gases into the wheelspace. Loss of hot gases from hot gas path <NUM> into the wheelspace reduces operational efficiency of turbine portion <NUM>. Over time, portions of diaphragm <NUM> may become worn and require localized repair as will be discussed more fully below.

Reference will now follow to <FIG> in describing a new, not worn diaphragm <NUM>. Diaphragm <NUM> is often cast from nickel-iron alloy and includes a body <NUM> having a sealing section <NUM>, a first rail member <NUM> and a second rail member <NUM>. Sealing section <NUM> includes a first end portion <NUM> that extends to a second end portion <NUM> through an intermediate portion <NUM> that defines an outer surface portion <NUM> and an inner surface portion <NUM>. Outer surface portion <NUM> is provided with a plurality of seal elements <NUM> that cooperate with additional structure (not shown) arranged in the wheel space of turbine portion <NUM>. First rail member <NUM> extends from first end portion <NUM> and second rail member <NUM> extends from second end portion <NUM>. First rail member <NUM> includes a first end section <NUM> that extends to a second end section <NUM> through an intermediate section <NUM> that defines an inner surface section <NUM> and an outer surface section <NUM>. Outer surface section <NUM> includes a discourager seal mounting section <NUM> that supports a discourager seal (not separately labeled). Second end section <NUM> supports a coupon <NUM> being an integral part of the first rail member <NUM>.

Similarly, second rail member <NUM> includes a first end section <NUM> that extends to a second end section <NUM> through an intermediate section <NUM> that defines an inner surface section <NUM> and an outer surface section <NUM>. Outer surface section <NUM> includes a discourager seal mounting section <NUM> that supports a discourager seal (not separately labeled). Second end section <NUM> supports a coupon <NUM> being an integral part of the second rail member <NUM>. Over time the original coupons <NUM>, <NUM> wear. Worn coupons <NUM>, <NUM> may allow hot gasses to flow from hot gas path <NUM> into the wheel space or other regions of the turbomachine. The loss of gases from the hot gas path <NUM> reduces turbine efficiency. Accordingly, diaphragms <NUM> are either repaired or replaced during a maintenance interval. In accordance with the exemplary embodiment, instead of a labor intensive repair of the original coupon, the exemplary embodiment discloses various techniques for replacing the original coupon with a repair coupon.

Reference will now be made to <FIG> illustrating in more detail the contour of the coupon <NUM> with an understanding that coupon <NUM> has a rather similar contour.

Second end section <NUM> includes a surface <NUM> and the coupon <NUM>. The surface <NUM>, the coupon <NUM> and a discourager seal mounting section <NUM> among others constitute the main dimensions of the second rail member <NUM>.

More specifically, coupon <NUM> includes an end <NUM> joined by first and second opposing sides <NUM> and <NUM> forming a substantially rectangular cross-sectional area defined by <NUM>, <NUM> and <NUM>. This cross-sectional area complies with the nominal dimensions of a new diaphragm <NUM> according to the manufacturer's specification.

A hatched line <NUM> illustrates an exemplary contour of a worn diaphragm <NUM>. By comparing the cross-sectional area and the cross-sectional area <NUM> of a worn diaphragm <NUM>, it becomes apparent that due to the reduced contour <NUM> of a worn diaphragm <NUM> the loss of hot gases increases significantly and repair of the diaphragm <NUM> is required.

Before cladding the worn part(s) of the diaphragm <NUM> the worn part(s) have to be removed in part such that the claimed welding process start on a clean machined surface of the diaphragm <NUM>. The at least on machined surface can be manufactured for example by milling or the like.

In the embodiment illustrated in <FIG> there are five (<NUM>) machined surfaces <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. As can be seen by the comparison of the machined surfaces <NUM> to <NUM> and the cross-sectional area of a new diaphragm <NUM> according to manufacturer's specification (c. the reference numerals <NUM>, <NUM>, <NUM> and <NUM>) it can be seen that the contour of the machined surfaces <NUM> to <NUM> is smaller than the contour of a new diaphragm. The volume between the machined surfaces <NUM> to <NUM> and nominal dimensions (c. <NUM>, <NUM>, <NUM> and <NUM>) are filled by a filler material.

Welding this filler material to the machined surfaces <NUM> to <NUM> creates a compact cladding comprising one or more layers which fills the a. Of course, the cladding has to overtop the contour of a new diaphragm <NUM> since welding is a process that does not produce geometrically exact surfaces. This means that a part of the cladding has to be machined after the cladding process to bring the cladding in conformity with the nominal dimensions following the surface <NUM>, the sides <NUM> and <NUM> as well as the end <NUM> of a new diaphragm <NUM>.

<FIG>, wherein like reference numbers represent corresponding parts in the respective views, illustrates a perspective view of the second rail member <NUM>.

<FIG>, wherein like reference numbers represent corresponding parts in the respective views, illustrates a perspective view of the contour <NUM> of the second rail member <NUM> that is worn over an angle alpha in a tangential direction.

The angle alpha illustrates the length of the worn part of a diaphragm rail member <NUM>. Of course, only the worn parts of the diaphragm have to be repaired. It is in most cases not necessary to machine the diaphragm rail member <NUM> over its entire length. This reduces the machining time and further reduces the time and expenses for welding a cladding on the machined surfaces.

Of course, if necessary it is possible to machine the diaphragm over the entire length of its rail members <NUM>, <NUM> and weld a cladding over the entire length of the rail member <NUM>, <NUM>. This is necessary, if the whole rail member is worn or if the material of the diaphragm that is exposed to the hot gases should be replaced by a cladding material that better withstands the hot gases, such as austenitic stainless steel compared to cast nickel iron, which is in most cases the material of the diaphragm <NUM>.

The <FIG> and <FIG> illustrate the cross-sectional area of a worn diaphragm that has been machined according to <FIG>. As can be seen from <FIG> the machined surfaces <NUM> to <NUM> make a more or less symmetric cross-sectional area. To reduce the thermal tensions to the diaphragm it is preferred if the weld passes are alternatingly welded on both sides of the axis of symmetry.

In this particular case, a first weld pass <NUM> is welded on the machined surface <NUM>, which is the end of the machined contour. A second weld pass <NUM> is welded in the corner between the machined surfaces <NUM> and <NUM>. A third weld pass <NUM> is welded in the corner between the machined surfaces <NUM> and <NUM>. The sequence of the weld passes <NUM> to <NUM> can be seen from <FIG>. Each weld pass has a number and this number describes the sequence of the welding passes welded to the diaphragm.

The most important welding parameters have been listed in the subsequent tables that are linked to each of the figures.

Very good results have been achieved using these welding parameters if the diaphragm is cast of nickel iron and the filler-material for welding the passes is an austenitic stainless steel. Appropriate stainless steel alloys are known under the tradenames <NUM> series and <NUM>.

<FIG> and <FIG> illustrate the process of cladding a machined surface of a diaphragm rail member. In this case a weld robot or a weld automat is used. The welding method is MIG/MAG. A TIG process may also be used for the repair process however different parameters are used in this case.

Cladding is achieved by welding several passes side by side. If necessary several layers of passes are welded to achieve the desired contour of the cladding. Up to ten layers have been welded in several applications.

In the <FIG> and <FIG> the passes have been numbered and in the respective tables listed below the most important welding parameters (welding speed and welding angle) have been noted.

The weld passes <NUM> to <NUM> results in a compact first layer of the cladding.

The weld passes <NUM> to <NUM> results in a compact second layer of the cladding.

The weld passes <NUM> to <NUM> results in a compact second layer of the cladding. The entirety of welding passes <NUM> to <NUM> forms the cladding <NUM>.

<FIG> illustrate a further embodiment not falling under the scope of the claims. The cladding generated in this embodiment comprises ten (<NUM>) layers.

The entirety of weld passes <NUM> to <NUM> forms the cladding <NUM>.

Claim 1:
A method of repairing a turbomachine diaphragm (<NUM>) consisting of cast nickel-iron, in particular a Ni-resist alloy, the method comprising:
removing a worn coupon (<NUM>, <NUM>) from a diaphragm rail member (<NUM>, <NUM>).
forming at least one machined surface (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>); and
welding a cladding (<NUM>) on the at least one machined surface (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) using a weld robot or a welding machine, wherein welding a cladding (<NUM>) on the at least one machined surface (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) includes covering the at least one machined surface (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) with at least one welding layer such that surface of the cladding (<NUM>) overtops the nominal dimensions (<NUM>, <NUM>, <NUM>) of a new diaphragm (<NUM>);
characterised in that the cladding (<NUM>) consists of a stainless austenitic steel, and in that covering the at least one machined surface (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) with at least one welding layer includes welding several passes (<NUM>, <NUM>, ..., <NUM>) in close proximity to each other; wherein the machined surfaces (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) have a symmetric cross-sectional area and wherein the passes (<NUM>, <NUM>, .., <NUM>) are welded alternating on each side of an axis of symmetry.