Process for making a component of a turbomachine, a component obtainable thereby and turbomachine comprising the same

Abstract

Turbomachines, as well as their components, are disclosed being in the field of production and treatment of oil and gas containing e.g. hydrocarbon plus hydrogen sulfide, carbon dioxide, with or without other contaminants. The components are made of a high corrosion high temperature resistant alloy, capable of resisting to corrosion and/or stress at high temperature better than state of art martensitic stainless steels and behaving similarly to premium nickel base superalloys, and at the same time showing a very improved hardness value.

Claims

1. A process for making a component of a turbomachine, the process comprising the steps of: a) melting an alloy chemical composition consisting of: TABLE-US-00014 C 0.005-0.03 wt % Si 0.05-0.5 wt % Mn 0.1-1.0 wt % Cr 19.5-22.5 wt % Ni 34.0-38.0 wt % Mo 3.0-5.0 wt % Cu 1.0-2.0 wt % Co 0.0-1.0 wt % Al 0.01-0.5 wt % Ti 1.8-2.5 wt % Nb 0.2-1.0 wt % W 0.0-1.0 wt % based on the composition weight, the remaining being Fe and impurities, the impurities comprising S 0.0-0.01 wt % and P 0.0-0.025 wt %, through vacuum induction melting (VIM), or arc electric furnace, b) refining by Argon Oxygen Decarburization (A.O.D.), Vacuum Induction Degassing and Pouring (V.I.D.P), or Vacuum Oxygen Decarburization (V.O.D.), c) re-melting through electro-slag re-melting (E.S.R.), or vacuum arc re-melting (VAR), d) heat-treating the alloy resulting from step c) to induce solubilization through at least one heat cycle, at a temperature of 1020-1150° C., and followed by fast cooling in liquid or gas media, and e) ageing by heating to a temperature of 600-700° C. for 2-20 h, and f) immediately cooling the alloy resulting from step e) at room temperature.

2. The process of claim 1, further comprising, before the step d), a step d′) of homogenization of the alloy resulting from step c), at a temperature above 1100° C. for at least 6 hours.

3. The process of claim 2, further comprising, before the step d) and after the step d′), a step d″) of hot or cold plastic deforming through at least one plastic deformation cycle.

4. The process of claim 1, wherein the resulting alloy is further atomized to produce powder and then treated by a powder metallurgy process selected from Cold Isostatic Pressing (CIP), Metal Injection Molding (MIM), sintering, Hot Isostatic Pressing (HIP), or MIM and HIP process.

5. A process for making a component of a turbomachine, the process consisting of the steps of: a) melting an alloy chemical composition comprising: TABLE-US-00015 C 0.015 wt % Si 0.09 wt % Mn 0.3 wt % Cr 20.4 wt % Ni 36.2 wt % Mo 3.7 wt % Cu 1.41 wt % Co 0.03 wt % Al 0.25 wt % Ti 2.04 wt % Nb 0.27 wt % W 0.1 wt % Fe balance having the following impurities: TABLE-US-00016 P up to 0.013 wt % S up to 0.0002 wt % B up to 0.003 wt % Bi up to 0.3 ppm Ca up to 50 ppm Mg up to 30 ppm Ag up to 5 ppm Pb up to 5 ppm N up to 100 ppm Sn up to 50 ppm O up to 50 ppm based on the composition weight, through vacuum induction melting (VIM), or arc electric furnace, b) refining by Argon Oxygen Decarburization (A.O.D.), Vacuum Induction Degassing and Pouring (V.I.D.P), or Vacuum Oxygen Decarburization (V.O.D.), c) re-melting through electro-slag re-melting (E.S.R.), or vacuum arc re-melting (VAR), d) heat-treating the alloy resulting from step c) to induce solubilization through at least one heat cycle in a vacuum, at a temperature of 1020-1150° C., and followed by fast cooling in liquid or gas media, and e) ageing the alloy resulting from step d) by heating to a temperature of 750° C. for 6 h, and f) immediately cooling the alloy resulting from step e) at room temperature.

6. The process of claim 5, further comprising deforming the alloy resulting from step c) via two hot plastic deformation cycles.

7. The process of claim 5, wherein the alloy resulting from step f) has a critical pitting temperature between 30° C. and 40° C.

8. The process of claim 5, wherein the alloy resulting from step f) has a sulfide stress corrosion threshold between 750 Mpa and 800 Mpa.

9. The process of claim 5, wherein the alloy resulting from step f) has a tensile strength at 600° C. of 550 Mpa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will become more apparent from the following description of exemplary embodiments to be considered in conjunction with accompanying drawings wherein:

(2) FIG. 1 shows a three dimensional space governed by partial pressure of H.sub.2S (p(H.sub.2S)), pH (mainly function of CO.sub.2), and chlorides (and/or other halides) content;

(3) FIG. 2 shows a typical cross section of centrifugal compressor;

(4) FIG. 3 shows a typical cross section of centrifugal pump;

(5) FIG. 4 shows a typical cross section of a steam turbine;

(6) FIG. 5 shows a typical cross section of a gas turbine;

(7) FIG. 6A shows the phase equilibrium vs temperature of the alloy of Example 1 and FIG. 6B shows the phase equilibrium vs temperature of the comparative UNS N07718;

(8) FIG. 7A shows the Time Temperature Transformation curves for the alloy of Example 1 and FIG. 7B shows the Time Temperature Transformation curves for the comparative UNS N07718; and

(9) FIG. 8 shows the hardness process capability for the alloy of Example 1, wherein ‘ST’ means short-term standard deviation, ‘LT’ means long-term standard deviation, and ‘USL’ means upper specification limit.

DETAILED DESCRIPTION

(10) The following description of exemplary embodiments refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit embodiments of the invention. Instead, the scope of embodiments of the invention is defined by the appended claims.

(11) 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.

(12) The term “room temperature” as used herein has its ordinary meaning as known to those skilled in the art and may include temperatures within the range of about 16° C. (60° F.) to about 32° C. (90° F.).

(13) Regarding the alloy composition, the term “mandatory element” refers to an element that is present in the alloy and that, in combination with the other mandatory elements, allows to achieve the above objects. The mandatory elements in the alloy are Iron (Fe), Carbon (C), Silicon (Si), Manganese (Mn), Chromium (Cr), Nickel (Ni), Molybdenum (Mo), Copper (Cu), Aluminium (Al), Titanium (Ti), and Niobium (Nb).

(14) The term “optional element” refers to an element that is possibly present in addition to the mandatory elements defining the essential chemical composition of the alloy. The optional elements in the alloy are: Cobalt (Co), and Tungsten (W).

(15) The term “impurity” or “impurity element”, instead, refers to an element not provided in the design of the alloy composition in order to reach the aforesaid objects. However, said element may be present because, depending on the manufacturing process, its presence may be unavoidable. Impurities in the alloy comprise phosphorous (P), Sulphur (S), Boron (B), Bismuth (Bi), Calcium (Ca), Magnesium (Mg), Silver (Ag), Lead (Pb), Nitrogen (N), Tin (Sn), and Oxygen (O).

(16) In first embodiments, a process for making a component of a turbomachine comprises the steps of:

(17) melting an alloy chemical composition consisting of:

(18) TABLE-US-00003 C 0.005-0.03 wt % Si 0.05-0.5 wt % Mn 0.1-1.0 wt % Cr 19.5-22.5 wt % Ni 34.0-38.0 wt % Mo 3.0-5.0 wt % Cu 1.0-2.0 wt % Co 0.0-1.0 wt % Al 0.01-0.5 wt % Ti 1.8-2.5 wt % Nb 0.2-1.0 wt % W 0.0-1.0 wt %
based on the composition weight, the remaining being Fe and impurities, said impurities comprising S 0.0-0.01 wt % and P 0.0-0.025 wt %,
through vacuum induction melting (VIM), or arc electric furnace,
refining by Argon Oxygen Decarburization (A.O.D.), Vacuum Induction Degassing and Pouring (V.I.D.P), or Vacuum Oxygen Decarburization (V.O.D.),
re-melting through electro-slag re-melting (E.S.R.), or vacuum arc re-melting (VAR),
heat-treating the alloy resulting from step c) to induce solubilization through at least one heat cycle, at a temperature of 1020-1150° C., and followed by fast cooling in liquid or gas media, and
ageing by heating to a temperature of 600-770° C. for 2-20 h, and cooling at room temperature.

(19) In this way, the presence of impurities, segregation thereof and in-homogeneities is significantly reduced and at the same time improved mechanical characteristics and corrosion resistance of the alloy are achieved.

(20) Particularly, the selected ageing conditions as set in step e) allow to achieve very significant improvements in terms of hardness, while keeping very good the other characteristics, such as corrosion resistance and stress corrosion cracking resistance. In fact, as shown below, the resulting component of a turbomachine achieved a hardness value of 29-33HRC.

(21) These hardness values lead to a very tough material with improved performance in particular in terms of sulphide Stress Corrosion Cracking resistance. Indeed the SSC resistance of CRAs increases lowering the hardness of the alloy. The ageing treatment described assures a high process capability in treating even high dimension forging products, targeting the hardness requirements detailed in NACE MR0175/ISO15156-3.

(22) In preferred embodiments, the step e) of ageing is performed by heating to a temperature of 720-760° C. for 5-10 h, and cooling at room temperature.

(23) In some embodiments, the process further comprises, before the step d), a step d′) of homogenization of the alloy resulting from step c), at a temperature above 1100° C. for at least 6 hours.

(24) In other embodiments, the process further comprises, before the step d) and after the step d′), a step d″) of hot or cold plastic deformation through at least one plastic deformation cycle, in order to attain a minimum total reduction ratio of 2:1. Such plastic deformation cycles include forging (open or close die), rolling, extrusion, cold expansion, to produce a raw component shape or more generally a raw shape to be further machined to produce centrifugal compressor, pump, gas and steam turbine, as well as components thereof.

(25) In other embodiments, the step d) of heat-treating to induce solubilization through at least one heat cycle, at a temperature of 1020-1150° C., can be carried out inside furnaces, under air, controlled atmosphere or vacuum, and followed by fast cooling in liquid or gas media, in order to put and keep in solution the alloying elements (i.e. copper, titanium, aluminium, niobium, etc. . . . ) for the subsequent heat treatment step.

(26) In other embodiments, the alloy is further atomized to produce powder and then treated by powder metallurgy. In an embodiment, with the term “powder metallurgy” it is meant that said powder is consolidated by Cold Isostatic Pressing (CIP), by Metal Injection Moulding (MIM), Sintering, Hot Isostatic Pressing (HIP), or fabricated by MIM and exposed to a HIP process. Basically, powders are fed into a die, compacted to a desired shape. The pressed powder is then sintered or hipped in a controlled atmosphere furnace at room or high pressure to produce metallurgical bonds among powder particles. Optional post-sintering operations, such as isothermal forging, infiltration, finish machining or surface treatment, may then be applied to complete the component.

(27) In second embodiments, a component of a turbomachine is obtainable by the process as above described, the component being made of an alloy having a chemical composition consisting of:

(28) TABLE-US-00004 C 0.005-0.03 wt % Si 0.05-0.5 wt % Mn 0.1-1.0 wt % Cr 19.5-22.5 wt % Ni 34.0-38.0 wt % Mo 3.0-5.0 wt % Cu 1.0-2.0 wt % Co 0.0-1.0 wt % Al 0.01-0.5 wt % Ti 1.8-2.5 wt % Nb 0.2-1.0 wt % W 0.0-1.0 wt %
based on the alloy weight, the remaining being Fe and impurities, said impurities comprising S 0.0-0.01 wt % and P 0.0-0.025 wt %, and having a hardness value of 29-33HRC. Owing to its high resistance to corrosion (even at high temperature) and/or to its high resistance to fatigue and/or creep, the component is very useful, in particular it is very useful for components that get in touch with the working fluid of the turbomachine, while showing at the same time a very advantageous hardness value.

(29) In fact, said alloy is high corrosion and high temperature resistant, thus capable of resisting to corrosion and/or stress at high temperature better than state of art martensitic stainless steels and behaving similarly to premium nickel base superalloys like those complying the requirements of UNS N07718 e UNS N00625, but at the same time the process for making the component as above described allowed the alloy to achieved a desirable hardness value of 29-33HRC.

(30) In preferred embodiments, the alloy has a high resistance to corrosion at a high temperature, in particular in the range of 200-250° C.

(31) In other preferred embodiments, the alloy has a high resistance to fatigue and/or creep at a high temperature, in particular in the range of 400-700° C.

(32) In an embodiment, the alloy has a chemical composition consisting of:

(33) TABLE-US-00005 C 0.005-0.02 wt % Si 0.05-0.2 wt % Mn 0.1-0.6 wt % Cr 20.0-21.5 wt % Ni 35.0-37.0 wt % Mo 3.5-4.0 wt % Cu 1.2-2.0 wt % Co 0.0-0.2 wt % Al 0.05-0.4 wt % Ti 1.9-2.3 wt % Nb 0.2-0.5 wt % W 0.0-0.6 wt % Fe at least 30 wt %
based on the alloy weight, the remaining being impurities, said impurities comprising S 0.0-0.001 wt % and P 0.0-0.02 wt %.

(34) More particularly, the alloy has a chemical composition consisting of:

(35) TABLE-US-00006 C 0.005-0.02 wt % Si 0.06-0.15 wt % Mn 0.2-0.4 wt % Cr 20.2-21.0 wt % Ni 36.0-36.5 wt % Mo 3.6-3.8 wt % Cu 1.3-1.7 wt % Co 0.0-0.1 wt % Al 0.1-0.3 wt % Ti 2.0-2.2 wt % Nb 0.25-0.4 wt % W 0.01-0.4 wt % Fe at least 30 wt %
based on the alloy weight, the remaining being impurities, said impurities comprising S 0.0-0.001 wt % and P 0.0-0.015 wt %.

(36) The above alloy is a cost effective alloy, which at the same time surprisingly encompasses a reduced amount of expensive alloying elements, such as mainly nickel, but also chromium, molybdenum and titanium, without negatively affecting the mechanical and anticorrosion properties. Said alloy also shows a great resistance to high temperatures and pressures, so that the components made of the same result to be suitable for turbomachines, particularly centrifugal compressors.

(37) Said impurities are P, S, B, Bi, Ca, Mg, Ag, Pb, N, Sn, O or a combination thereof.

(38) In an embodiment, said impurities are less than 0.5 wt %; more particularly, less than 0.2 wt %.

(39) In preferred embodiments, said impurities are P up to 0.025 wt %, S up to 0.01 wt %, B, Bi, Ca, Mg, Ag, Pb, N, Sn, and O.

(40) In particularly preferred embodiments, the alloy has a chemical composition consisting of:

(41) TABLE-US-00007 C 0.015 wt % Si 0.09 wt % Mn 0.3 wt % Cr 20.4 wt % Ni 36.2 wt % Mo 3.7 wt % Cu 1.41 wt % Co 0.03 wt % Al 0.25 wt % Ti 2.04 wt % Nb 0.27 wt % W 0.1 wt % Fe balance
having the following impurities:

(42) TABLE-US-00008 P up to 0.013 wt % S up to 0.0002 wt % B up to 0.003 wt % Bi up to 0.3 ppm Ca up to 50 ppm Mg up to 30 ppm Ag up to 5 ppm Pb up to 5 ppm N up to 100 ppm Sn up to 50 ppm O up to 50 ppm

(43) In some embodiments, the alloy has a grain size finer than plate 3 as per ASTM E112.

(44) Owing to the above described chemical composition, level of impurities, grain size resulting from the process conditions, the alloy shows the following properties:

(45) superior hardness properties,

(46) superior anticorrosion characteristics in terms of general and localized corrosion, threshold stress in solution A method A as per NACE MR0175, higher Stress Corrosion Cracking (SCC) resistance, higher Chloride Stress Corrosion Cracking (CSCC), Sulphide Stress Cracking (SSC), Galvanically-induced Hydrogen Stress Cracking (GHSC);
higher tensile properties at room and high temperature;
suitable toughness properties;
higher high and low cycle fatigue properties;
higher creep strength;
higher oxidation and hot corrosion resistance;
with respect to stainless steels (martensitic, ferritic, austenitic and austenitic-ferritic) and comparable to premium nickel base superalloys.

(47) In thirds embodiments, a turbomachine comprises at least one component as defined in general above.

(48) In preferred embodiments, the turbomachine is a centrifugal compressor or a centrifugal pump.

(49) In other preferred embodiments, the turbomachine is a gas turbine or a steam turbine.

(50) FIGS. 2, 3, 4 and 5 show different turbomachines where one or more components as set out above may be used. FIG. 2 shows a typical cross section of centrifugal compressor, FIG. 3 shows a typical cross section of centrifugal pump, FIG. 4 shows a typical cross section of a steam turbine, and FIG. 5 shows a typical cross section of a gas turbine.

(51) It should be understood that all aspects identified as preferred and advantageous for the alloy component are to be deemed as similarly preferred and advantageous also for the process for making thereof as well as for the turbomachine comprising the same.

(52) It should be also understood that all the combinations of preferred aspects of the alloy component, and process for making thereof, as well as their uses in gas turbine applications, as above reported, are to be deemed as hereby disclosed.

EXAMPLES

Example 1

(53) An alloy has been prepared having the following composition:

(54) TABLE-US-00009 C 0.015 wt % Si 0.09 wt % Mn 0.3 wt % Cr 20.4 wt % Ni 36.2 wt % Mo 3.7 wt % Cu 1.41 wt % Co 0.03 wt % Al 0.25 wt % Ti 2.04 wt % Nb 0.27 wt % W 0.1 wt % Fe balance
having the following impurities:

(55) TABLE-US-00010 P up to 0.013 wt % S up to 0.0002 wt % B up to 0.003 wt % Bi up to 0.3 ppm Ca up to 50 ppm Mg up to 30 ppm Ag up to 5 ppm Pb up to 5 ppm N up to 100 ppm Sn up to 50 ppm O up to 50 ppm

(56) The above chemical composition was melted through vacuum induction melting (VIM), refined by Argon Oxygen Decarburization (A.O.D.), and re-melted re-melting through electro-slag re-melting (E.S.R.).

(57) The resulting alloy was homogenized at a temperature above 1100° C. for at least 6 hours.

(58) The alloy was then subjected to two cycles of hot plastic deformation.

(59) Subsequently, the alloy was subjected to a heat treatment to induce solubilization at a temperature of 1020-1150° C., followed by fast cooling in liquid or gas media.

(60) Finally, the alloy has been subjected to an ageing treatment by heating to a temperature of about 750° C. for 6 h, and cooling at room temperature.

(61) The resulting alloy has been tested to assess mechanical and anticorrosion properties. The results have been compared to a known Martensitic Stainless Steel (shortly ‘Martensitic SS’) in the following Table 1. Martensitic stainless steels are a class of stainless steels characterized by Chromium content between 12-18 wt %, low Nickel and a crystalline structure defined as Martensite. This class of alloys has medium-high mechanical properties and a fair corrosion resistance.

(62) TABLE-US-00011 TABLE 1 Typical Corrosion Characteristic Martensitic SS Alloy of Example 1 Critical Pitting Temperature 0 ÷ 5° C. 30 ÷ 40° C. (CPT)AST G48 method C [° C.] Sulphide Stress Corrosion (SSC) 250 ÷ 300 MPa 750 ÷ 800 Mpa Threshold in NACE TM0177 (<50% AYS) (>95% AYS) Solution A method A [MPa] Chloride Stress Corrosion Cracking Failure <300 h Passed ≥1000 h ASTM G123

(63) Additional verified SSC properties are reported in Table 2 and Table 3.

(64) TABLE-US-00012 TABLE 2 Method pH.sub.2S pH Chlorides Stress Temperature Result Alloy of NACE TM0177 10 bar 3 25% NaCl 750 MPa  25° C. Passed (>720 h) Example 1 Method A 10 bar 3 25% NaCl 750 MPa 150° C. Passed (>720 h) Solution C

(65) TABLE-US-00013 TABLE 3 High Temperature Characteristics Martensitic SS Alloy of Example 1 Stress Rupture 600° C., 240 Mpa, 140 hrs 600° C., 690 Mpa, 140 hrs Tensile 430 MPa 550 Mpa @600° C. Impact 27J @−15° C. 27J @−101° C. Charpy - V notch

(66) The alloying elements' weight percent is tailored to avoid or minimizing topologically closed packed phases (TCP). Excessive quantities of Cr, Mo, W would promote the precipitation of intermetallic phases which are rich in these elements. Generally speaking, the TCP phases have chemical formulae A.sub.xB.sub.y. For example, the μ phase is based on the ideal stoichiometry A.sub.6B.sub.7 and has a rhombohedral cell containing 13 atoms, such as W.sub.6Co.sub.7 and Mo.sub.6Co.sub.7.

(67) The σ phase is based upon the stoichiometry A.sub.2B and has a tetragonal cell containing 30 atoms, such as Cr.sub.2Ru, Cr.sub.61Co.sub.39 and Re.sub.67Mo.sub.33.

(68) The P phase, for example, Cr.sub.18Mo.sub.42Ni.sub.40 is primitive orthorhombic, containing 56 atoms per cell.

(69) As it is shown in FIGS. 6A (thermodynamic equilibrium) and 7A (kinetics estimation), only σ phase is thermodynamically possible and precipitation kinetics is so slow that neither during solution annealing, nor during ageing can happen.

(70) The chemical composition of this alloy is optimized to enlarge the hot workability window. This is accomplished by a low nickel content and reducing the temperature of precipitation of hardening secondary phases (gamma prime). As it can be seen in FIG. 6, the theoretic workability range at equilibrium is quite large and is between 1020° C. and 1280° C. This interval is larger than those provided by UNS N07718 (FIGS. 6B and 7B).

(71) Equilibrium intervals do not take into account kinetics and visco-plastic phenomena, but can give an idea of how much better this alloy behaves in comparison with other well known commercial premium nickel base alloys.

(72) Practically, this alloy has a hot forming range between 900°-1200° C., thus reducing the risk of failure during production and cycle time.

(73) The alloy has a combination of chemical elements so as to provide secondary phases hardening such as to provide a minimum yield strength of 750 Mpa with a hardness value of 29-33HRC thus enhancing stress corrosion properties.

(74) In fact, with reference to FIG. 8, the hardness process capability for the alloy of Example 1 is shown, as having tested 30 samples of the alloy above at 750° C. for 6 h. The diagram of FIG. 8 shows that the mean of hardness value obtained in 30.86HRC.

(75) The reduced hardness level results in a better machining if compared with premium nickel based alloys like UNS N07718. This level of hardness allows the turbomachinery components to be machined in aged conditions resulting in an optimization of manufacturing cycle if compared with premium nickel based alloys like UNS N07718. FIG. 7A shows the Time Temperature Transformation curves for the alloy of Example 1 and FIG. 7B shows the Time Temperature Transformation curves for the comparative UNS N07718. It is clear to see how the precipitation of deleterious phases (i.e. delta phase and sigma phase) are slower in the presented alloy with respect to UNS N07718. This allows to have a wide area of heat treatment and a cleaner microstructure, less sensitive to embrittlement and low toughness properties.

(76) This alloy is designed to be easy welded by common arc welding processes (SMAW and GTAW) with homologous or different nickel base filler materials like UNS N06625, UNS N07725, or UNS N09925.

(77) This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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 if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.