Method for reconditioning a hot gas path part of a gas turbine

Abstract

A method for reconditioning a hot gas path part of a gas turbine to flexibly adapt an operation regime of said gas turbine for subsequent operation intervals. The method includes providing a hot gas path part to be reconditioned; removing a predetermined area of the hot gas path part, resulting in a cutout at the hot gas path part; and manufacturing a coupon for insertion into the cutout to replace the removed area of the hot gas path part. The method further includes inserting the coupon into the cutout; and joining the hot gas path part with the coupon. The coupon is manufactured by a selective laser melting method resulting in a fine grain sized material with significantly improved low cycle fatigue lifetime. The hot gas path part is coated, at least in an area including the inserted coupon, with a metallic overlay with improved thermo-mechanical fatigue and oxidation lifetime.

Claims

1. A method for reconditioning a hot gas path part of a gas turbine in order to flexibly adapt an operation regime of said gas turbine for subsequent operation intervals, comprising: providing a hot gas path part to be reconditioned; removing a predetermined area of said hot gas path part, resulting in a cutout at said hot gas path part; manufacturing a coupon or section for being inserted into said cutout to replace said removed area of said hot gas path part; inserting said coupon or section into said cutout; and joining said hot gas path part with said inserted coupon or section, wherein said coupon or section is manufactured by a selective laser melting (SLM) method to obtain a fine grain sized material with improved low cycle fatigue (LCF) lifetime, wherein said hot gas path part is coated, at least in an area comprising said inserted coupon or section, with a metallic overlay with improved thermo-mechanical fatigue (TMF) and oxidation lifetime, wherein, in order to introduce a self-healing property, said metallic overlay comprises an additional active phase containing a melting point depressant and/or a substance with a softening point or melting point below an operation temperature or within an operation temperature range of said hot gas path part, and wherein said coupon or section is completely over-aluminized by chemical vapor deposition (CVD).

2. The method as claimed in claim 1, wherein said coupon or section is made of a higher oxidation resistant material than said hot gas path part.

3. The method as claimed in claim 2, wherein said coupon or section is made of a highly precipitation strengthened Ni base superalloy.

4. The method as claimed in claim 3, wherein said coupon or section is made of an MM247 alloy.

5. The method as claimed in claim 1, wherein said metallic overlay is applied by a) providing a powder material in which a portion of the powder material is sub-micron powder particles; and b) applying said powder material to the surface of said hot gas path part by means of a thermal spraying technique to build up a coating layer.

6. The method as claimed in claim 5, wherein said powder material is of the MCrAlY type with M=Fe, Ni, Co, or combinations thereof.

7. The method as claimed in claim 5, wherein said powder material contains powder particles of micron size and/or larger agglomerates, and that the sub-micron powder particles are in said coating layer distributed around the surface of said powder particles of micron size and/or said larger agglomerates.

8. The method as claimed in claim 1, wherein at least said area with said metallic overlay is additionally protected by applying a thermal barrier coating (TBC).

9. The method as claimed in claim 1, wherein said hot gas path part is a front stage vane of a gas turbine, said vane comprising an airfoil with a leading edge and a trailing edge, and that at least part of said trailing edge is replaced by said coupon.

10. The method as claimed in claim 1, wherein said hot gas path part is a front stage blade of a gas turbine, said blade comprising an airfoil with a leading edge and a trailing edge, and that at least part of said leading edge is replaced by said coupon.

11. The method as claimed in claim 1, wherein the softening point or melting point is less than 1000 degrees Celsius.

12. The method as claimed in claim 1, wherein the active phase has particles that are woven.

13. The method as claimed in claim 1, wherein substances of the active phase include Chromium, Nickel, Aluminum, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows a front stage turbine vane in a side view.

(3) FIG. 2A shows in a first step the vane with removing at least a part of the trailing edge, whereby a cutout remains.

(4) FIG. 2B shows the respective trailing edge coupon manufactured by SLM.

(5) FIG. 2C shows the vane with the coupon inserted into the cutout.

(6) FIG. 2D shows the final reconditioned vane with the metallic overlay as the last step of the method.

(7) FIG. 3 shows a front stage turbine blade in a perspective side view and

(8) FIG. 4A shows in a first step the blade with removing at least a part of the leading edge, whereby a cutout remains.

(9) FIG. 4B shows the respective leading edge coupon manufactured by SLM.

(10) FIG. 4C shows the blade with the coupon inserted into the cutout.

(11) FIG. 4D shows the final reconditioned blade with the metallic overlay as the last step of the method.

DETAILED DESCRIPTION

(12) The new, herewith described method to reconditioning IGT hot gas path parts allows power plant owners to flexibly adapt their operation regime for subsequent operation interval(s), without the need to exchange the expensive turbine hardware by installing new designed spare parts.

(13) Furthermore, parts with already consumed cyclic design lifetime (by previous accomplished operation intervals) can still be reconditioned by locally replacing consumed areas with inserts and/or by application of tailored coating systems, allowing additional subsequent operation (base load and/or cyclic, fuel flexibility) or significant operational changes (to high cyclic load or peaker operation).

(14) With the herein described new Reconditioning technology concept (RECONCEPT) parts can be repaired and also significantly changed in their conceptual design intent.

(15) This new approach combines different key technologies: (a) SLM (selective laser melting) manufactured part sections (also made of difficult to weld materials, such as highly precipitation strengthened Ni base super alloys, using specifically adapted metal powder mixture(s)) to replace local areas; (b) (optional) locally changed design features/materials; and (c) the local/overall application of a new metallic and ceramic coating system, specifically tailored for the expected main distress modes (LCF, creep, oxidation, corrosion, erosion).

(16) The new Reconditioning concept (RECONCEPT) is based on four key technology fields: 1) CERCOTEC (advanced ceramic coating technology); 2) AMCOTEC (advanced metallic coating technology); and 3) MODALTEC (Modular/hybrid design concept based on advanced SLM and joining technologies).

(17) With the herein described technology it is also possible to manufacture new IGT parts in a modular design, allowing to always using a determined core element, which can be supplemented with variable inserts. This gives the basis to specifically tailor the final IGT part for a peaker, cyclic or rather base load operation regime. It is also possible to adapt IGT parts of a gas turbine, in the case that customers need to comply with new market boundary conditions, without having to exchange IGT parts against new parts with different design.

Example 1

(18) Problem:

(19) Front stage turbine vane with trailing edge (TE) limited in TMF and base material oxidation lifetime. An example of such a vane is shown in FIG. 1 in a side view. The vane 10 of FIG. 1 comprises an airfoil 11 extending between an inner platform 12 and an outer platform 13 with hooks 17 and 18, and havingwith respect to the hot gas flow 16 in the hot gas patha leading edge 14 and a trailing edge 15.

(20) Solution:

(21) Reconditioning of the vane 10 starts with removing at least part of the trailing edge 15 (FIG. 2A), whereby a cutout 19 remains. Then, a respective trailing edge (TE) coupon 20 is manufactured by selective laser melting (SLM) in order to get a fine grain sized material with significantly improved LCF lifetime and (with appropriate heat treatment) local/overall optimum grain size (FIG. 2B). The coupon 20 is made of higher oxidation resistant material MM247 (instead of IN738) and may be optionally completely over-aluminized by CVD. The coupon 20 is then inserted into the cutout 19 of the vane 10 (FIG. 2C).

(22) Finally, the standard MCrAlY coating is replaced by using a metallic overlay 21 (FIG. 2D) with improved oxidation and TMF lifetime, which may optionally additionally protected by a thermal barrier coating (TBC). These measures will not only give an additional lifetime benefit to the coupon 20 itself, but also to the joint area between vane 10 and coupon 20 with its welding or high temperature brazing in the split line.

(23) For this reconditioning, processes may be used, which are disclosed in document US 2012/0251777 A1.

(24) There, it is described to use at least one base material together with an active phase and optionally with a reservoir phase. The base material is around the active (and the reservoir) phase. The material can be used for a coating, a coupon, a braze joint or part of a vane, blade or liner.

(25) The self healing system comprises an active phase. In particular, this active phase has particles with potentially different shapes and/or fibers, which are optionally woven. The particles or fibers preferably have a core/shell structure. The core and shell can be made of chemical substances like non oxide or oxide ceramics, metals or combinations thereof.

(26) Preferably, the chemical substances of the core have preferably the following characteristics: a) decrease the melting point of the base material so that softening occurs at operating temperature or have a low (<1000 [deg.] C.) softening or melting temperature; b) diffuse into the base material and/or optionally into the cracks; c) do not strongly oxidize when present at the surface in contact with oxygen; d) are able to chemically dissolve the metal oxides; e) have a limited reactivity with Cr in order to avoid a decrease of the corrosion resistance; and f) do not react with the shell substance.

(27) The chemical substances from the core may be solid or liquid at the operating temperature. They may react with the base material, or not.

(28) The chemical substances of the shell, on the other hand, have the following characteristics: a) diffuse slowly in order to liberate the core substances or break and liberate the core substances; b) do not react with the core substances; and c) have a limited reactivity with Cr in order to avoid a decrease of the corrosion resistance.

(29) An additional reservoir phase, which may also have a core/shell structure, might be needed in order to balance the composition and achieve a constant optimal concentration of chemical substances (in particular the concentration of Chromium is important for the corrosion protection).

(30) For the active phase with its core/shell structure, the core substances can be so-called melting point depressants (MDP) like Boron, Carbon, Phosphorous, Silicon, Nickel or a combination thereof. On the other hand, the core may be of a material with a softening or melting temperature below or in the range of the operating temperature according to the invention.

(31) The MDPs preferably react with the base material in order to reduce the melting temperature. Materials with a softening or melting temperature below or in the range of the operating temperature preferably do not react with the base material. The shell substances of the active phase can be Chromium or Nickel or Aluminum or a combination thereof. For the above-mentioned reservoir phase the core substances can be Chromium or Nickel or Aluminum or a combination thereof. The shell substances of the reservoir phase can also be Chromium or Nickel or Aluminum or a combination thereof.

(32) For the processing of the base material with the self healing system, different methods are applicable: For a coating with a self healing system the active phase and the bond coat particles, for example MCrAlY particles, are dispersed (mixture of both powders or suspension of both powders) and then sprayed with High Velocity Oxy Fuel (HVOF), a standard process to apply a bond coat, or Air Plasma Spray (APS), or Suspension Plasma Spray (SPS), or slurry coating or another process to apply a coating. For a coupon with a self healing system the active phase and the base material particles, for example superalloy particles, are dispersed (mixture of both powders or suspension of both powders) and processed by means of casting, Selective Laser Melting (SLM) or Selective Laser Sintering (SLS), or any other laser technique, or any additive manufacturing technique. For a brazed joint with a self healing system a braze sheet or tape or paste with self healing particles or fibers is used.

(33) A method for applying said metallic overlay 21 may comprise the steps of: a) providing a metallic powder material containing at least a fraction of sub-micron powder particles; and b) applying said powder material to the surface to be coated by means of a spraying technique to build up a coating layer.

(34) Said powder material is applied to the surface of the component by means of a thermal spraying technique, especially one of High Velocity Oxygen Fuel Spraying (HVOF), Low Pressure Plasma Spraying (LPPS), Air Plasma Spraying (APS) or Suspension Plasma Spraying (SPS). The powder material has preferably the form of agglomerates or of a suspension.

(35) The powder material preferably contains powder particles of micron size and/or larger agglomerates, and the sub-micron particles powder particles are in said coating layer distributed around the surface of said powder particles of micron size and/or said larger agglomerates. The sub-micron powder particles may be pre-oxidized, especially in-flight during spraying or by an oxidative pre heat treatment of the powder material before being incorporated into said coating layer.

Example 2

(36) Problem:

(37) Front stage turbine blade with leading edge (LE) incl. transition radius to platform, limited in base material and coating TMF lifetime after reaching the end of the original maximum cyclic lifetime targets. FIG. 3 shows in a perspective side view an example of a turbine blade 22 with an airfoil 23 with leading edge 26 and trailing edge 27, a tip 25 and a platform 24. A transition region 28 between airfoil 23 and platform 24 has a specific transition radius.

(38) Solution:

(39) Reconditioning of the blade 22 starts with removing at least part of the leading edge 26 (FIG. 4A), whereby a cutout 29 remains. Then, a respective leading edge (LE) coupon 30 is manufactured by selective laser melting (SLM) in order to get a fine grain sized material with significantly improved LCF lifetime and (with appropriate heat treatment) local/overall optimum grain size (FIG. 4B). The coupon 30 is made of higher oxidation resistant material MM247 (instead of IN738) and may be optionally completely over-aluminized by CVD. The coupon 30 is then inserted into the cutout 29 of the blade 22 (FIG. 4C). Finally, the standard MCrAlY coating is replaced by using a metallic overlay 31 (FIG. 4D) with improved oxidation and TMF lifetime.

(40) The processes involved may be the same as for example 1.