EP3472472B1

EP3472472B1 - Layer system, impeller, method to produce

Info

Publication number: EP3472472B1
Application number: EP17739949.0A
Authority: EP
Inventors: Peter MARTINIUS
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens Energy BV
Priority date: 2016-08-10
Filing date: 2017-07-10
Publication date: 2020-04-22
Anticipated expiration: 2037-07-10
Also published as: WO2018028908A1; RU2708187C1; EP3282130A1; EP3472472A1; CN109642583A

Description

The invention relates to an impeller of a turbo-machine, in particular a turbo-compressor, in particular a centrifugal turbo-compressor, wherein said impeller comprises a base element of a base material comprising blades being arranged along a circumferential direction of a rotational axis, wherein said blades comprise a leading edge and a trailing edge. Said impeller comprising a layer system applied on said base element, wherein said layer system extends in a border area of said base element up to an outer surface, wherein said layer system comprises at least one layer of cladding material provided onto the base material. Further the invention relates to a method to produce an impeller respectively according to the before mentioned type.
EP 2 135 698 A1 , EP 2 789 713 A1 , DE 10 2009 043097 relate to free standing blades being partly coated. These blades are generally used in steam turbines to withstand e.g. droplet erosion.
US 2011/229338 A1 discloses an impeller according to the preamble of claim 1.
The specific focus of the invention is the avoidance of erosion in turbo-compressors. The rotating parts, especially the impellers of the turbo machine may suffer from a dramatic decrease in lifetime due to severe erosion wear. Dust particles carries by a process fluid through the machine, for example so called 'black dust', may have hardnesses between 230 up to 600HV 0.01 (Vickers hardness test). In combination with the high velocities of the rotating equipment especially the rotating parts of pipeline compressors are quickly damaged in particular at the leading edge and the trailing edge of impeller blades.
It is one object of the invention to reduce the erosion phenomenon in particular to rotating parts of turbo-machines.
In order to solve the problems outlined above the invention proposes a layer system, an impeller and a method to produce such a layer system or an impeller as according to the respective independent claims. The respective dependent claims refer to beneficial embodiments of the invention.
The layer system according to the invention comprises said base material and one or several of cladding material layers provided onto the base material. Further said layer system comprises a compressive residual stress layer extending from said outer surface into at least the outermost layer of cladding material. In case of several cladding material layers provided on a base material as part of the layer system said compressive residual stress layer may extend through several layers of cladding material from said outer surface and even extend into the base material as well. Preferably said compressive residual stress layer extends only in the outermost layer of cladding material.
A preferred embodiment of the invention is provided by generating said layer or layers of cladding material by gas tungsten arc welding (GTAW).

Preferably a base material is X3CrNiMo13-4 (martensitic alloy). In detail the composition of X3CrNiMo13-4 (material number: 1.4313 according to EN10250) in weight percent (wt%)is:

Element	Minimum	Maximum
Carbon (C)	0	0.05
Silicon (Si)	0	0.7
Mangan (Mn)	0,5	1.5
Chromium (Cr)	12.0	14.0
Molybdenum (Mo)	0.3	0.7
Nickel (Ni)	3,5	4.5
Sulfur (S)	0	0.015
Phosphor (P)	0	0.04
Nitrogen (N)	0	0.02
Iron	base

Another preferred embodiment of the layer system provides that the material of at least one layer of cladding material is Stellite 21 (Stellite 21=commercial name (UNS=W73041, ASME/AWS=(SF)A5.21, ERCCoCr-E), HRC=28-40)). In detail the composition of Stellite 21 in weight percent (wt%) is

Element	Minimum	Maximum
Carbon (C)	0.15	0.40
Mangan (Mn)	0	1.0
Chromium (Cr)	25	30
Silicon (Si)	0	1.5
Molybdenum (Mo)	4.5	7.0
Nickel (Ni)	1.5	3
Iron (Fe)	0	5.0
Tungsten (W)	0	0.5
Cobald (Co)	base
others
	0	1.0

One preferred embodiment provides that at least two layers of cladding material are provided to the base material and most preferably three layers of cladding material are provided. Preferably all three layers are of the same chemical composition and most preferably all three layers are of Stellite 21.
Another preferred embodiment of the layer system is provided by giving a heat treatment of up to three hours at 570°C to the base element for at least one time to eliminate residual welding stresses. Surprisingly it was found that the subsequent heat treatment as proposed does not impair the desirable high hardness of the cladding.
The most preferred application of the invention is the production of an impeller of a turbo-machine, in particular a turbo-compressor, in particular a centrifugal turbo-compressor, wherein said impeller comprises a base element of a base material comprising blades being arranged along a circumferential direction of a rotational axis, wherein said blades comprise a leading edge and a trailing edge, wherein said leading edge and said trailing edge belong to a surface treatment zone, wherein at least part of said surface treatment zone is a layer system as described and defined in several embodiments above. Preferably these impeller blades are attached to a hub section of said base element and are extending radially and/or axially from said hub section. Said impeller can be designed as a so called open type or closed type. In case of the closed type impeller flow channels are circumferentially delimited by said blades, a hub section and a shroud section being attached to the blades tips respectively defining the flow channels in axial-radial direction. In case of the open type impeller only the hub section defines the flow channels in axial-radial direction (see also figure 1, 2 regarding the difference).
Preferably the layer system in particular the layer system of the impeller is produced applying the following steps:

1) machining a base element of a base material
2) defining a surface treatment zone,
3) transforming at least a part of said surface treatment zone into a layer system by the substeps of:
1. a) cladding at least one layer of cladding material to said base material of said surface treatment zone,
2. b) shot peening at least the area of said surface treatment zone in the area of said layer system.

It was found that the hardness of the Stellite cladding hugely increases after shot peening.
Preferably a further substep is conducted by:
c) heat treatment of said base element. The heat treatment of said base element after the shot peening improves the residual stress in the base element down to an acceptable minimum of the one hand and on the other hand it does not impair the desired high hardness of the Stellite cladding. Since the heat treatment and the shot peening change the geometry of the base element a final machining of the base element is preferably performed as a substep d).
Subsequently to step 3) a further forth step can be conducted as:
4) mounting a shroud section to said base element. The shroud section is preferably welded to said base element, in particular to the blade tips of said base element. To further improve mechanical properties of the combination of the base element with the shroud section a heat treatment may be performed afterwards. Due to the changes in geometry expected from welding and heat treatment a final machining may preferably be done afterwards. In case of the base element being an impeller of a turbo-machine preferably balancing of the impeller and overspeeding may be performed to improve operational behavior and minimize risk of any damage.
A preferred embodiment of the impeller is provided by machining the base element with additional grooves respectively recesses compared to the ordinary impeller in the area of the surface treatment zone where the layer system according to the invention is provided. Theses recesses may be provided cumulatively or alternatively like the following:

In particular the respective leading edges of the blades should be provided with recesses in the area, where the layer system is to be provided and the layer system should be provide there.
In particular, in the area of the trailing edges, the trailing edge should be provided at least partly with a recess to fit in the layer system and the layer system should be provide there.
In particular, in a transition area between the blade and said hub section in proximity to the blade's trailing edge a recess to fit in the layer system should be provided to also improve the hub section erosion resistance and the layer system should be provide there.

The above mentioned attributes and other features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood with reference to the following description of the currently best mode of carrying out the invention taken in conjunction with the accompanying drawings, wherein:

Figure 1: shows a schematic depiction of a longitudinal section through an impeller according to the invention including a shroud section,
Figure 2: shows a schematic depiction of a longitudinal section of an impeller as according to the invention without a shroud section,
Figure 3: shows a schematic flow diagram to illustrate the method according to the invention,
Figure 4: shows a longitudinal section through a layer system according to the invention.

The same reference signs are used in different embodiments of the invention in the detailed description to identify elements of identical function. Terms like axial, radial, circumferential or tangential always refer to a central rotational axis X if not indicated otherwise.
Figure 1 and figure 2 respectively show a 2-dimensional longitudinal section through an impeller according to the invention along a rotational axis X. The impeller IMP rotates during operation in a turbo-machine, in particular in a turbo-compressor TC around the rotational axis X. Said impeller IMP comprises a based element BE of a base material BM comprising blades BLA being arranged along a circumferential direction CDR of said rotational axis X. These blades BLA comprise a leading edge LE and a trailing edge TE. The terms 'leading edge LE' and 'trailing edge TE' refer to a process fluid flow direction during operation for which the impeller IPM is fluid dynamically designed. Said leading edge LE and said trailing edge TE belong to a surface treatment zone STZ. A layer system LSY is provided to said surface treatment zone STZ. This layer system LSY is shown in figure 4 schematically in a longitudinal section in detail in a border area (shown as a detail in Figure 4) of said base element BE. Said layer system LSY comprises said base material BM of said base element BE and extends in said border area of said base element BE up to an outer surface OSF. In the preferred embodiment shown in figure 4 said layer system LSY comprises three layers of cladding material, a first layer LCM1, a second layer LCM2 and a third layer LCM3. This number of layers is an example which what was found to be advantageous.
Figure 3 shows schematically the steps of the method according to the invention to produce a layer system LSY as part of a base element BE here an impeller IMP. In particular this example of figure 3 refers to the impeller IMP but basically includes the generation of a layer system according to the invention to other parts as well preferably rotating parts of turbo-machines.
In step 0) a raw part is provided, which is subsequently machined into the basic shape of an impeller IMP during steps 1), 2). In step 2) a surface treatment zone STZ is defined. The impeller IMP is machined with additional grooves in the area of the leading edge LE and the trailing edge TE belonging to the surface treatment zone STZ of the base element BE. These additional grooves respectively recesses RE are provided to avoid any protrusion due to the provision of the layer system LSY in this areas. The final impeller IMP is meant to have the same fluid dynamic properties as any conventional impeller IMP.
In step 3) a) the surface treatment zone STZ defined during step 2) is transformed at least partly into said layer system LSY by the substeps of:
3)a) cladding at least one layer of cladding material LCM1-LCMn to said base material BM of said surface treatment zone STZ.
In subsequent step 3)a)a) a heat treatment is performed at 570°C for 2 hours to reduce stresses caused by the welding procedure of the cladding.
Any deformations are eliminated during machining in step 3) a) b).
During subsequent step 3) b) shot peening in the area of said layer system LSY is performed to improve surface hardness. In case of producing a closed impeller configuration including a shroud section SRS said shroud section SRS is mounted to the blade's tips of the base element BE preferably by welding. Subsequently a heat treatment and final machining is performed during step 4) a).
After not illustrated optional steps of balancing and overspeeding the impeller IMP is mounted during assembly in a turbo-compressor TC in step 5).
Between all these steps of the method several examinations may be performed to detect any material defects like cracks, in particular magnetic particle examinations can be done as non-destructive examination procedures.
The resulting impeller IMP including the layer system LSY applied by gas tungsten arc welding cladding of Stellite 21 powder onto the base element BE or base material X3CrNiMo13-4 results in an erosion resistant rotating part having partly a high hardness of approximately 690HV0.01 after heat treatment. In these critical areas of the surface treatment zones STZ the impeller surface is therefore harder than the maximum particle hardness of approximately 600hv0.01.

Claims

Impeller (IMP) of a centrifugal turbo-compressor(TC), wherein said impeller (IMP) comprises a base element (BE) of a base material (BM) comprising blades (BLA) being arranged along a circumferential direction (CDR) of a rotational axis (X), wherein said blades (BLA) comprise a leading edge (LE) and a trailing edge (TE), wherein said leading edge (LE) and said trailing edge (TE) belong to a surface treatment zone (STZ), wherein at least part of said surface treatment zone (STZ) is a layer system (LSY) comprising a base material (BM) of a base element (BE), wherein said layer system (LSY) extends in a border area of said base element up to an outer surface (OSF), wherein said layer system (LSY) comprises at least one layer of cladding material (LCM1-LCMn) provided onto the base material (BM),
characterized in that at least the outermost layer of cladding material (LCMn) at least partly belongs to a compressive residual stress layer (CRSL),
wherein said compressive residual stress layer (CRSL) extends from said outer surface (OSF) at least into the outermost layer of cladding material (LCMn).
Impeller (IMP) according to claim 1,
wherein said layer(s) of cladding material (LCM1-LCMn) is(are) provided by gas tungsten arc welding (GTAW).
Impeller (IMP) according to claim 1 or 2,
wherein said base material (BM) is X3CrNiMo13-4 (1.4313).
Impeller (IMP) according to claims 1, 2 or 3,
wherein the material of at least one layer of cladding material (LCM1-LCMn) is Stellite 21.
Impeller (IMP) according to claim 1,
wherein said base element (BE) comprises a hub section (HSC) and impeller blades (BLA) extending radially and/or axially from said hub section (HSC).
Method to produce an impeller (IMP) with a layer system (LSY) according to one of the claims 1-5 comprising the following steps:
1) machining a base element (BE) of a base material (BM)

2) defining a surface treatment zone (STZ),

3) transforming at least a part of said surface treatment zone (STZ) into a layer system (LSY) by the substeps of:
a)cladding at least one layer of cladding material (LCM1-LCMn) to said base material (BM) of said surface treatment zone (STZ),

b) shot peening at least the area of said surface treatment zone (STZ) in the area of said layer system (LSY).
Method according to claim 6,
wherein a further sub-step is conducted:
c) heat treatment of said base element (BE).
Method according to claim 7,
wherein a further sub-step is conducted:
d) final machining of base element (BE).
Method according to at least one of the preceding claims 6 to 8, wherein a further step is conducted:
4) mounting a shroud section (SRS) to said base element (BE).
Method according to claims 6, 7, 8 or 9, wherein said layer cladding material (LCM1-LCMn) is/are provided by gas tungsten arc welding (GTAW).
Method according to claims 6, 7, 8, 9 or 10, wherein said base material (BM) is X3CrNiMo13-4 (1.4313).
Method according to claims 6, 7, 8, 9, 10 or 11, wherein said layer of cladding material (LCM1-LCMn) is Stellite 21.