Claims:WE CLAIM:

1. A method of welding for bi-metallic forgings of turbine rotor in three parts, wherein the three parts include one part of Alloy 617M forging between two parts of 10Cr Steel forging, in which the method comprising steps of:
- machining of Weld edge and cavity on both the matching surfaces of 10Cr steel forging and alloy 617M forging;
- placement of generator Side Rotor [1] Forging part of 10 Cr steel and Middle Rotor Forging part [2] of Alloy 617M on roller support system of “Hot Wire narrow Gap TIG Welding Machine” having inching movement in the three axis in loaded condition so as to align both the rotor parts before welding;
- Pre-purging with inert gas in-side the cavity through holes before & during welding to ensure proper purging & shielding from back side of the weld joint & to avoid oxidation of the welding;
- Root run welding with optimum parameter including current, voltage, welding speed, wire diameter, gas flow rate so as to avoid puncture of thin land of weld joint;
- Filling pass welding, which is the welding of part of weld groove joint except last 25-30 MM welding where extra shielding gas is required to protect weld pool from weld contamination from open cavity of weld joint from top side;
- Capping pass welding for last 25-30 MM of welding by providing shielding gas.

2. The method as claimed in claim 1, wherein the inert gas includes Argon Grade-1, in which the Argon Grade-1 shielding gas is supplied through the Narrow Gap TIG welding torch (NG Torch), wherein Initially tack weld at three locations is carried out by tilting the NG Torch by 90° in both the directions at two locations and from the top at third location.

3. The method as claimed in claim 1 or 2, wherein the holes are preferably square holes made at the lip of joining faces of both rotor forging parts.

4. The method as claimed in claims 1-3, wherein the root run welding is carried out continuously for 360°.

5. The method as claimed in claims 1-4, wherein Filler pass welding is carried out with high current & matching high wire feed speed to get high deposition rate.

6. The method as claimed in claims 1-5, wherein the shielding gas is provided though trailing shield inbuilt with NG Torch.

7. The method as claimed in claims 1-6, wherein after completion of first weld joint, weld edge & cavity are machined on other side of the middle part of Alloy 617M, in which Turbine Side Rotor [3] Forging part of 10 Cr steel & welded parts of rotor forgings are placed on roller support system and Alignment is done before tack weld & complete weld process is repeated for 2nd joint.

8. The method as claimed in claims 1-7, wherein Length of each part is 2.5-3 M and joining diameters is 0.9-1.1 M, in which Weight of each part of forgings is 15-20 TON with total weight of the rotor after welding is 45-60 TON and length is approx. 9M.

9. The method as claimed in the claims 1-8, wherein the method meets the below challenges:
- welding of dis-similar materials of rotor parts requires Pre-heating & Post Weld Heat Treatment (PWHT) for 10Cr steel whereas alloy-617 prohibits Pre-heating before welding;
- as per design, there is a cavity behind the narrow gap weld joints of 270 mm depth which needs to purged with Argon Gr-1 gas before start of welding, the cavity is closed from all sides, and Purging of this cavity and shielding of last 30 mm of the weld joints to avoid the oxidation of the weld metal;
- alignment of three parts of rotor and its distortion control while welding of 270 mm depth weld joint of approximate nine-meter-long rotor.

10. The method as claimed in the claims 1-9, wherein the depth of weld joint for rotor forging is 270 mm with a groove width of 15 mm at the bottom of the weld joint, in which welding of dissimilar materials of joint thickness is up to 270 MM.
, Description:A METHOD OF WELDING FOR BI-METALLIC FORGINGS OF TURBINE ROTOR IN THREE PARTS

FIELD OF INVENTION:
[001] The present invention relates to a technology for welding of Turbine Rotor in three parts under Advance Ultra Super Critical (AUSC) project. In Particular, the invention is directed to a method of welding for bi-metallic forgings of turbine rotor in three parts. Here, extreme two parts are made of forging X12CrMoWVNbN 10 1 1 (10 Cr steel) material while middle part is made of forging of Alloy 617M material.

BACKGROUND OF THE INVENTION:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] Turbine Rotor was available in one piece made of forging X12CrMoWVNbN 10 1 1 (10 Cr steel), which is associated with the following disadvantages:
[004] It can’t sustain AUSC parameter resulting in less power efficiency & high carbon emission to the environment as compared to proposed AUSC parameter.

? In order to address the aforesaid shortcomings, under the aegis of Principal Scientific Advisor to the Govt. of India, Indigenous development of a power plant operating at Advance Ultra Super Critical (AUSC) Parameters has been initiated.
? The primary objective is to successfully install and operate a reliable 800 MW demonstration AUSC power plant operating at 310 kg/cm2 / 710 degree C / 720 degree C.
? With this AUSC parameter, power plant efficiency will increase up to 46 % and carbon emission will reduce up to 17 %.
? As a consortium partner of national mission project for the development of AUSC Technology, BHEL is developing HP and IP steam turbine modules.
? Under this project, welded rotor made of dissimilar materials have been provided in high pressure (HP) and intermediate pressure (IP) module of Turbine. Since conventional Ferritic steels used in Super Critical Turbines can’t sustain temperatures beyond 600°C, for AUSC temperature of range 700°C, Nickel based alloys are chosen for middle part of rotor.
? To optimize the use of costly Nickel based alloys, dissimilar metal weld joint (DMWJ) is made between Nickel alloys and Ferritic steel at the location of temperatures of around 550 degree C.
? Material selected for welded rotor is forged Alloy 617M and 10%Cr martensitic steel. As such, there is dissimilar metal welding (DMW) between 10% Cr steel to alloy 617M for welded rotor /casing.
? 10% Cr steel is used for section of the rotor subjected to maximum temperature up to 600?C. While, Alloy 617M is considered for high temperature section of the rotor above 600?C and maximum up to 720?C. Hence, there is a dissimilar metal welding (DMW) between 10% Cr steel rotor parts and Alloy 617M rotor parts.
? This dissimilar metal welding (DMW) has been executed by specialized Hot Wire Narrow-gap TIG (NG-TIG) welding process.

[005] However, welding of dis-similar material of rotors meeting the required mechanical properties and joint integrity was a technologically challenging task. Hence, the present invention has been devised, which can overcome the challenges and serve the purpose efficiently.

OBJECTS OF THE INVENTION:

[006] Primary object of the invention is to provide a method of welding for bi-metallic forgings of turbine rotor in three parts by Hot wire Narrow Gap TIG Welding Process.
[007] Another object of the invention is to provide a method of welding for bi-metallic forgings of turbine rotor in three parts by Hot wire Narrow Gap TIG Welding Process, which works efficiently.

[008] Still another object of the invention is to provide a method of welding for bi-metallic forgings of turbine rotor in three parts by Hot wire Narrow Gap TIG Welding Process, which results in increase in power plant efficiency up to 46 % and reduction in carbon emission up to 17 %.

[009] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0010] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0011] Alloy 617M and 10%Cr ferrite-martensitic steel are preferred rotor materials under consideration for steam turbine of Indian Advanced Ultra super Critical (AUSC) coal fired power plants. 10% Cr steel is used for section of the rotor subjected to maximum temperature up to 580°C, while alloy 617M is considered for high temperature section of the rotor above 580°C and maximum up to 720°C.

[0012] Hence, there is a dissimilar metal welding (DMW) between 10%Cr steel rotor parts to alloy 617M rotor parts. This narrow gap dissimilar material welding is done by Hot Wire Narrow Gap TIG welding process by using alloy matching filler wire. The depth of weld joint for rotor forging is 270 mm with a groove width of 15 mm at the bottom of the weld joint.

[0013] Prototype Rotor has been welded on horizontal welding station of Hot Wire NG TIG Welding Machine in down hand (1G) welding position.

[0014] The technology is established for welding of dissimilar materials of joint thickness up to 270 MM, for back purging of weld joint in case of welding of solid turbine rotor forgings by making a cavity at the center of joining face and to weld the joint of groove width of 15 mm at a depth of 270 MM.

[0015] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0016] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0017] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTON OF THE ACCOMPAYING DRAWINGS:
[0018] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-

Figure 1: Welded Turbine Rotor indicates the following:
J- Weld Joint
1-Generator Side Rotor
2-Middle Part Rotor
3-Turbine Side Rotor

Figure 2: Narrow Gap weld joint details of joint thickness of 270 MM. indicates the following:
Y-Weld Groove Thickness
Z-Buttering
X-Weld Root Side

Figure 3: Cavity at the centre of joining face of rotor forging parts indicates the following:
W-Weld Edge
Z-Buttering

[0019] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS:

[0020] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0021] The present invention makes a disclosure regarding a technology pertaining to an invention for a method of welding for bi-metallic forgings of turbine rotor in three parts by Hot wire Narrow Gap TIG Welding Process.

[0022] The instant invention involves two parts of 10Cr steel forging and one part of Alloy 617M forging. Length of each part is 2.5 to 3 M and joining diameters is 0.9 to 1.1 M. Weight of each part of forgings is 15 to 20 TON and total weight of the rotor after welding is 45 to 60 TON and length is approx. 9M.
[0023] There are following challenges in welding of such large sizes of turbine rotor of dis-similar material:
- First, welding of dis-similar materials of rotor parts requires Pre-heating & Post Weld Heat Treatment (PWHT) for 10Cr steel whereas alloy-617 prohibits Pre-heating before welding.
- Secondly, as per design, there is a cavity behind the narrow gap weld joints of 270 mm depth which needs to purged with Argon Gr-1 gas before start of welding. The cavity is closed from all sides. Purging of this cavity and shielding of last 30 mm of the weld joints to avoid the oxidation of the weld metal is a challenge.
- Thirdly, alignment of three parts of rotor and its distortion control while welding of 270 mm depth weld joint of approximate nine-meter-long rotor.
The present invention meets all the aforesaid challenges.

[0024] According to the invention, weld buttering on both the Rotor Forging parts of 10 Cr steel (1 & 2) is done with matching welding wire followed by stress relieving. Pre-heat and inter-pass temperature is maintained throughout the weld buttering process. Buttered layer is examined by Ultrasonic Testing (for volumetric examination) & Die Penetrate Testing (for surface examination).

[0025] Weld edge & cavity were machined on both the matching surfaces of 10Cr steel forging & alloy 617M forging.

[0026] Generator Side Rotor [1] Forging part of 10 Cr steel & Middle Rotor [2] Forging part of Alloy 617M are placed on roller support system of “Hot Wire narrow Gap TIG Welding Machine” having inching movement facility in all the three axis in loaded condition to get both the rotor parts aligned before welding. There are preferably square holes made at the lip of joining faces of both rotor forging parts. Pre-purging with inert gas including Argon Grade-1 gas is done in-side the cavity through these square holes before & during welding to ensure proper purging & shielding from back side of the weld joint & to avoid oxidation of the welding. This Argon Grade-1 shielding gas is supplied through the Narrow Gap TIG welding torch (NG Torch) itself. Initially tack weld at three locations is done by tilting the NG Torch by 90° in both the directions at two locations & from the top at third location.

[0027] Root run welding is carried out with optimum parameter including current, voltage, welding speed, wire diameter, gas flow rate etc so as to avoid puncture of thin land of weld joint. Welding is carried out continuously for 360°.

[0028] Filling pass welding is the welding of major part of weld groove joint except last 25-30 MM welding where extra shielding gas is required to protect weld pool from weld contamination from open cavity of weld joint from top side. Filler pass welding is conducted with high current & matching high wire feed speed to get high deposition rate.

[0029] Capping pass welding is done for last 25-30 MM of welding by giving extra quantity of shielding gas though special device called trailing shield inbuilt with NG Torch.

[0030] After completion of 1st weld joint, weld edge & cavity are machined on other side of the middle part of Alloy 617M. Turbine Side Rotor [3] Forging part of 10 Cr steel & welded parts of rotor forgings are placed on roller support system. Alignment is done before tack weld & complete weld process is repeated for 2nd joint.

[0031] After completion of welding, both the weld joints are examined by Ultrasonic Testing (for volumetric examination) & Die Penetrate Testing (for surface examination).

ADVANTAGEOUS FEATURES
- Increase in power plant efficiency up to 46 %
- Reduction in carbon emission up to 17 %
- Reduction in environment pollution;
- Works efficiently.

WORKING OF THE INVENTION
[0032] This invention will work in coal based power plant with AUSC parameter for increased efficiency & reduced carbon emission to the environment.

TEST RESULT
[0033] IP Rotor was successfully welded with help of this innovation. Total three parts of Rotor have been kept on Roller support system & alignment for all the three parts was done. Welding was done by Hot Wire Narrow Gap TIG welding process and weld quality was acceptable in Ultrasonic Testing (UT).

[0034] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0035] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0036] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogue to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0037] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0039] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0040] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.