Vocational Training Report

Turbine Blade Shop-Block 3

Bharat Heavy Electricals Limited

Ranipur,Haridwar (Uttrakhand)

Submitted By: Submitted To:

Yuganter Rawat Mr. Hitendra Bankoti

B-Tech 3rd year

Amrapali Institute of technology and science,Haldwani

1

2

ACKNOWLEDGEMENT “An engineer with only theoretical knowledge is not a complete engineer. Practical knowledge is very important to develop and apply engineering skills”. It gives me a great pleasure to have an opportunity to acknowledge and to express gratitude to those who were associated with me during my training at BHEL.

I am very great-full to Mr. R.M. Meena for providing me with an opportunity to undergo training under his able guidance. Furthermore, special thanks to Mr. Pradeep Pandey for his help and support in haridwar. Last, but not the least, I would also like to acknowledge the immense pleasure, brought about by my friends Adhar,Ashis,Rohit as they pursued their training along with me. We shared some unforgettable moments together. I express my sincere thanks and gratitude to BHEL authorities for allowing me to undergo the training in this prestigious organization. I will always remain indebted to them for their constant interest and excellent guidance in my training work, moreover for providing me with an opportunity to work and gain experience.

THANK YOU

3

B.H.E.L- An Overview BHEL or the Bharat Heavy Engineering Limited is one of the largest engineering and manufacturing organizations in the country and the BHEL, Haridwar is their gift to Uttaranchal. With two large manufacturing plants, BHEL in Haridwar is among the leading industrial organizations in the state. It has established a Heavy Electrical Equipment Plant or HEEP and a Central Foundry Forge Plant or CFFP in Haridwar.

The Heavy Electrical Equipment Plant in Haridwar designs and manufactures turbo generators, AC and DC motors, gas turbines and huge steams. The Central Foundry Forge Plant in Haridwar deals with steel castings and manufacturing of steel forgings.

The BHEL plants in Haridwar have earned the ISO - 9001 and 9002 certificates for its high quality and maintenance. These two units have also earned the ISO - 14001 certificates. Situate in Ranipur near Haridwar, the Bharat Heavy Engineering Limited employs over 8,000 people.

BHEL is an integrated power plant equipment manufacturer and one of the largest engineering and manufacturing companies in India in terms of turnover. BHEL was established in 1964, ushering in the indigenous Heavy Electrical Equipment industry in India - a dream that has been more than realized with a well-recognized track record of performance. The company has been earning profits continuously since 1971-72 and paying dividends since 1976-77  .BHEL is engaged in the design, engineering, manufacture, construction, testing, commissioning and servicing of a wide range of products and services for the core sectors of the

4

economy, viz. Power, Transmission, Industry, Transportation, Renewable Energy, Oil & Gas and Defence.BHEL has 15 manufacturing divisions, two repair units, four regional offices, eight service centres, eight overseas offices and 15 regional centres and currently operate at more than 150 project sites across India and abroad. BHEL places strong emphasis on innovation and creative development of new technologies. Our research and development (R&D) efforts are aimed not only at improving the performance and efficiency of our existing products, but also at using state-of-the-art technologies and processes to develop new products. This enables us to have a strong customer orientation, to be sensitive to their needs and respond quickly to the changes in the market.The high level of quality & reliability of our products is due to adherence to international standards by acquiring and adapting some of the best technologies from leading companies in the world including General Electric Company, Alstom SA, Siemens AG and Mitsubishi Heavy Industries Ltd., together with technologies developed in our own R&D centres. Most of our manufacturing units and other entities have been accredited to Quality Management Systems (ISO 9001:2008), Environmental Management Systems (ISO 14001:2004) and Occupational Health & Safety Management Systems (OHSAS 18001:2007).

BHEL has a share of around 59% in India's total installed generating capacity contributing 69% (approx.) to the total power generated from utility sets (excluding non-conventional capacity) as of March 31, 2012. We have been exporting our power and industry segment products and services for approximately 40 years. We have exported our products and services to more than 70 countries. We had cumulatively installed capacity of over 8,500 MW outside of

5

India in 21 countries, including Malaysia, Iraq, the UAE, Egypt and New Zealand. Our physical exports range from turnkey projects to after sales services. BHEL work with a vision of becoming a world-class engineering enterprise, committed to enhancing stakeholder value.Our greatest strength is our highly skilled and committed workforce of over 49,000 employees. Every employee is given an equal opportunity to develop himself and grow in his career. Continuous training and retraining, career planning, a positive work culture and participative style of management - all these have engendered development of a committed and motivated workforce setting new benchmarks in terms of productivity, quality and responsiveness.

STEAM TURBINE

6

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884. It has almost completely replaced the reciprocating piston steam engine (invented by Thomas Newcomen and greatly improved by James Watt) primarily because of its greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 80% of all electricity generation in the world is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible process.

Types

7

These arrangements include single casing, tandem compound and cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound Steam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.

Steam Supply and Exhaust Conditions

These types include condensing, non-condensing, reheat, extraction and induction.

Non-condensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are available.

Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.

Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.

Casing or Shaft Arrangements

Turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.

8

Principle of Operation and Design

An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies ranging from 20%-90% based on the application of the turbine. The interior of a turbine comprises several sets of blades, or “buckets” as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.

Turbine Efficiency

To maximize turbine efficiency, the steam is expanded, generating work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as impulse or reaction turbines. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

Impulse Turbines

An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage.

Reaction Turbines

In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net

9

change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

SPECIFICATIONS OF MACHINES AVAILABLE IN BLOCK-III:

Vertical Boring Machine :

Max diameter of work piece accommodated :10000mm to 12500mm

Max height of work piece :5000mm

Diameter of table :8750mm

Max travel of vertical tool head RAM slides :3200mm

Max travel of vertical tool heads from centre of

Table :5250mm

Max weight of work piece :200 T

For N<=6rpm;100T for any speed

Diameter of boring spindle of combined head :160mm Travel of boring spindle :1250mm

Taper hole of boring spindle :100metric

Centre Lathe :(Biggest of all BHEL)

Max diameter over bed :3200mm Max diameter over saddle :250mm

Length between centers :16m

Max weight of work piece :100 T

Spindle bore :96mm

CNC Lathe :

10

Manufacturer: Safop, Italy

Swing over carriage :3500mm Centre distance :9000mm

Weight capacity :120 T

Spindle power :196KW

External chucking range :250-2000mm

Hydrostat steady range :200-1250mm

Max spindle rpm :200

CNC system :SINUMERIK 840D

CNC Indicating stand :

Manufacturer : Heinrich Georg, Germany

Turning diameter :5.3m Turning length :15m

Weight capacity :160 T

CNC Vertical Borer :

Manufacturer : M/S Pietro Carnaghi, Italy

Machine model :AP 80TM-6500

Table diameter :6500mm

Max turning diameter :8000mm

Min boring diameter :660mm

Max height for turning and milling :7000mm

Table Speed :0.2-50 rpm

11

Table load capacity :200 T

Milling spindle speed :3.4-3000 rpm

Spindle taper :BT 50

CNC system :SINUMERIK 840D

CNC Facing Lathe : KH-200-CNC Swing over bed :2300mm Swing over carriage :1800mm Max distance between faced plate and carriage :2000mm Max weight of job held in chuck :6000kg Face plate diameter :1800mm Spindle speed :1.4-400rpm Main spindle drive :95.5KW

Step boring Machine : Max boring diameter :2500mm Min boring diameter :625mm Table :4000mmx4000mm Max weight of job :100 T

Headstock travel :4000mm

Double Column Vertical Borer : Table diameter :4000mm Max travese of cross rail :4250mm Max weight of work piece :4200mm Max weight of job :50 T

CNC Skoda Horizontal Borer : Spindle diameter :200mm Taper spindle :BT 50 RAM size :450x450mm RAM length :1600mm Spindle length :2000mm Headstock :5000mm Table :4000x3500mm CNC system :SIMENS 850mm

12

Job : I.P. Outer

Horizontal Borer : LSTG 8006 Spindle diameter :250mm Height of machining bed :600mm Max boring depth with spindle :2000mm Max extension of RAM :1600mm Width of bed guide ways :2500mm Actual length of headstock with vertical lift :2150mm Actual length of column horizontal feed :15000mm Lowest position of spindle axis upon bed guideways :1475mm Machine weight with electrical equipments :140 T Height of machine :10.3m

CNC Lathe : 1-120 Manufacturer : Ravensburg

Main spindle bore :150mm Distance between centers :12m Turning diameter over bed cover :1400mm Turning diameter over carriage :1100mm Workpiece weight unsupported :4000kg Workpiece weight between centers :20 T

Centre Lathe : 1-23 Manufacturer : K3TC, USSR

Max diameter over bed :1250mm Max diameter over saddle :900mm Length between centers :6300mm Max weight of work piece :25 T Spindle bore :80mm Machine wattage :55KW

Horizontal Boring Machine : 1-28 Diameter of spindle :150mm Working surface of table :2250x1250mm Max travel of table :1200mm Max vertical travel of headstock :2000mm

13

Horizontal Boring Machine : Boring spindle taper :BT50 Boring spindle diameter :160mm Headstock vertical travel :3000mm Longitudinal RAM travel :700mm Longitudinal spindle travel :1000mm Column cross travel :10m Rotary table travel :3000mm Table load :40 T

Horizontal Boring Machine : 1-11 Boring spindle internal taper material :200 Boring spindle diameter :320mm Max spindle travel :2500mm Vertical head travel :6000mm Transverse column travel :6000mm Max longitudinal column travel :800mm Machine wattage :90KW

Double Column Rotary Table Vertical Borer : Max diameter of work piece accommodated :10m Max height of work piece accommodated :5m Diameter of table :8.75m Max travel of vertical tool head RAM slides :3.2m Max travel of vertical tool head from centre of table :5.25m Max weight of work piece :200T for N<=8rpm;100T for any speed Diameter of boring spindle of combined head :160mm Travel of boring spindle :1250mm Taper hole of boring spindle :100mm

Horizontal borer : 1-2 Spindle diameter :220mm Working surface :8100 x 5000mm Max vertical travel :3mm Max transverse travel of column :6m Max longitudinal travel of column :6m Max longitudinal travel of spindle :1.8m

CNC Lathe : 2-36014

Manufacturer : Hoesch Max load :320 T Max length between centers :18m Swing over bed :3.2m

Horizontal Borer : 2-198 Spindle diameter :220mm Max vertical travel :3m Max transverse travel of column :6m Max longitudinal travel of column :6m Max longitudinal travel of spindle :1.8m Working surface :1800x500mm

Creep Feed Grinding Machine : Diameter of job :2m Job height :2.4m Table rpm :10rpm(max) Table diameter :2050mm Swing diameter :2500mm CNC control :SIEMENS-3GG

Broaching Machine : Broaching capacity :32 T Broaching stroke :10.3m Broaching slide width 1500mm Broaching specific cutting stroke :1.25m/min Broaching specific return stroke :60m/min Max diameter of disc :2300mm Max move of table :600mm Helix angle/skew angle setting :+45/-45 Cone angle :0-20

CNC Lathe :Manufacturer : Innse Berardi, Italy

Swing over carriage :1500mm Swing over bed :2000mm Capacity :30 T Cost :16 crore CNC system :SINUMERIK 840D

15

Over Speed Balancing of Turbines : Main features :

Type of pedestials :DH 90/DH 12 Rotor weight :Min 4 MT, Max 320 MT Rotor diameter :Max 6900mm Rotor journal diameter :Min 250mm,Max 950mm Bearing centre distance :Min 3000mm,Max 15700mm Balancing speed :180-3600rpm Min vibration limit :1 micron Max vacuum :1 torr

Tunnel Features : Tunnel length :19000mm Tunnel diameter :6900mm Max thickness of tunnel :2500mm Steel plate thickness :32mm Cost of balancing equipment(FE) :444 lakhs Total cost of balancing tunnel :770 lakhs

Main Features of Drive : Drive motors (2 no.) :950V DC, 500rpm,3.5

MW each Total drive power :7 MW(2x3.5)

MG set of Drive : Synchronous motors :11 KV,9MW,50Hz,500rpm DC Generator (2 no.) :950V,500rpm,3.8MW each

3d coordinate measuring machine in new blade shop: Model refrence: 22129 LIETZ Germany Plan no 3-068 Measuring range: X axis 2200mm Y axis 1200mm Z axis 900 mm Volumetric error: (max) 1.5 micron Resolution: 0.05 micron Max weight of job: 2250 kg Accuracy: 1.5+L/350 micron

16

Application: dimensional and profile management of turbine moving and guide blades

HOW IT WORKS

17

18

19

LP rotor with moving blades various blade profiles

20

STEAM FLOW THROUGH STEAM TURBINE

21

22

23

24

Modernization of Facilities:

CNC Lathe for LP Rotor from SAFOP, ITALY

CNC Horizontal Boring machine for machining of casing from PAMA, ITALY

CNC Indicating Stand for LP Rotor Blade machining from GEORG, GERMANY

CNC Fir Tree Root Milling machine

CNC Gantry Milling machine

Major Facilities for New Turbine Shop:

CNC V Borer-Table diameter-7500mm

CNC V Borer-Table diameter-4000mm

CNC H Borer Spindle Diameter-200mm,160mm

CNC Lathe capacity-120 T,80T

CNC Fir Tree Root Milling machine

CNC Gantry Milling machine

Highlights:

Imported Substitutions :

Hybrid burner for gas turbine

E ring for gas turbine

25

Deep hole drilling in HP outer casing supplied by Machine Shop, CFFP

Process Improvement :

Slitting of casing, thrust rings, GT rings on Band Saw milling machine, thus saving the time on critical machines such as Ram Borers

Using KOMET drilling systems, the productivity in joint plane drilling of casing and LP Rotors has increased

Seeing the congestion on KOOP milling machine, a new work center machine called RAMBHOR machine(No. 2473

Tool Brands: Widia Sandwick Seco Isear Addisson Guhring Indian tools Mitutoyo

Tool Instruments: Die ring spanner Hack saw frame Burr cutter Solid tap (carbide) Hand tap

Grinding Cutters: Combination cutter-140x40mm Fillet cutter-160x32mm Hand mill cutter

26

End mill cutter Internal profile cutter Shell end mill cutter-63x80mm Ball nose Slab mill

500 MW Steam Turbine: HP Turbine: Module :H30-100-2 Steam Pressure :170Kg/sq.cm Steam temperature :537 deg.cel Reheating temperature :537 deg.cel Weight :86400 Kg Length of Rotor :4.61m Height :2.15m

LP Turbine: Module :N30-2x10sq.m Weight :3.5 T Length of Rotor :8.7m Width :10.7m Height :4.6m

IP Turbine: Length :4.425m Width :5m Height :4.8m Steam pressure :41Kg/sq.cm Steam temperature :537 deg.cel

Milling Cutters:1) Side end face milling cutter2) Interlocking side and face milling cutter3) Shell end mill cutter4) Metal slitting saw5) Single angle milling cutter6) Double unequal angle milling cutter7) Double equal angle milling cutter8) Keyway milling cutter

27

9) Milling cutter for chain wheels10) Single corner rounding milling cutter11) Convex milling cutter12) Concave milling cutter13) T slot milling cutter with plane parallel shank14) T slot milling cutter with Morse taper shank having tapered end15) Cylindrical milling cutter16) Slot milling cutter with parallel shank17) End mill with parallel shank18) Ball nosed end mill with parallel shank19) Flat end tapered die sinking cutter with plane parallel shank20) Ball nosed taper die sinking cutter with plane parallel shank21) Slot milling cutter with morse tapered shank having tanged end22) End mill with morse tapered shank having tanged end23) Ball nosed end mill with morse tapered shank having tanged end24) Flat end tapered die sinking cutter with morse tapered shank having tapped end25) Ball nosed tapered die sinking cutter with morse tapered shank having tapped end26) Slot milling cutter with morse tapered shank having tapped end27) End mill morse tapered shank having tapped end28) Ball nosed mill morse tapered shank having tapped end29) Roughing end mill with parallel shank finishing type 30) Roughing end mill with parallel shank roughing type 31) Slot milling cutter with 7/24 taper shank 32) End mill with 7/24 taper shank33) Ball nosed end mill with 7/24 taper shank34) Woodruff key slot milling cutter with parallel shank 35) Screwed shank slot drill

28

Major Components of Steam Turbine:

LP Rotor LP Inner Casing Upper Half LP Inner Casing Lower Half LP Outer Casing Upper Half LP Outer Casing Lower Half IP Rotor IP Inner Casing Upper Half IP Inner Casing Lower Half IP Outer Casing Upper Half IP Outer Casing Lower Half HP Rotor HP Inner Casing Upper Half HP Inner Casing Lower Half HP Outer Casing Upper Half HP Outer Casing Lower Half Diffuser GBC (Guide Blade Carrier) IVCV (Intercept Valve Control Valve) ESVCV (Emergency Stop Valve Control Valve)

Auxiliary Parts of Steam Turbine:1) Valve Seal2) U-Ring3) Piston Rod4) Base Plate5) Sealing Ring6) Liner7) Guide Ring8) Valve Cover9) Guide Blades :

Fixed Blades Moving Blades

10) Support11) Bearing12) Bearing Shell13) Angle Ring14) Sleeve15) Pin Taper (25x140)16) Journal Bearing Shell

29

17) Casing18) Guide bush19) Piston (500MW)20) Valve Cone21) Yoke22) Mandrel 23) Support Ring24) Thrust Ring25) Adjusting Ring26) Shaft Sealing Cover

Types of Blades: T2 blades T4 blades TX blades 3DS blades F- blades GT-Compress blades Brazed blades Russian design blades Z-Shroud blades Compressor blades (Sermental coated)

LP Moving blade 500MW

New Blade Shop:

First Generation Blades : T2 Profile Blades Cylindrical Profile Blades (1970)

Second Generation Blades : T4 Profile Blades Cylindrical Profile Blades ( late 1980)

1% Gain in Stage Efficiency over T2 Profile Blades TX Profile Blades

Cylindrical Profile Blades ( late 1990)

Gains : Reduces Profile Losses

30

0.2% Gain in Stage Efficiency over T4 Profile Blades

Applications : Middle Stage Of H.P. and I.P Turbine Initial Stage of L.P. Turbine

3DS Blades :

Gains : Reduces Secondary Flow Losses 0.5 – 1.0% Gain in Stage Efficiency over TX Profile Blades

Application : Initial Stage of H.P. and I.P Turbine

F- Blades

Gains : Reduces Indirect Flow Losses 0.5 – 1.0% Gain in Stage Efficiency over TX Profile Blades

Applications : Rear Stage of H.P. and I.P Turbine Middle Stage of L.P. Turbine

Sequential operation for machining of TX blades:

Operation Machine

1) Blanking2) Rhomboid machining

Band sawCNC rhomboid machine cell

3) Removal of tech allowance/parting off band saw

31

4) Root machining CNC high speed root machining5) Profile and expansion angle(internal and

external)CNC heavy/light duty machine or CNC profile and fillet machining center

6) Shroud copying CNC heavy/light duty machine7) Taper grinding CNC creep feed grinding machine8) Grinding and polishing Polishing machine9) Final fitting of blades -10) Vibro finishing of blades Vibro finishing equipment11) Final inspection -

Sequential operation for machining of 3DS and F blades:

Operation Machine

1) Blanking Band saw

2) Preparation of technological ends for work piece holding

CNC machining center

3) Complete blade machining(with normal shroud/Z shroud)

CNC 5 axis machining centre

4) Inspection 3D CMM5) milling off technological ends at root and

shroud radius machiningCNC machining centre

6) Fitting -7) vibro finishing for surface finishing

improvementVibro finishing equipment

8) Inspection -

Number of advance design blades:

Blades 250MW 500MW TX Profile blade 10390 6820F and 3DS blade 3100 2852Free standing blade 224 252

32

NON- DESTRUCTIVE TESTING (Liquid penetration ,magnetic flaw&radiography)

Failure of the turbine blades was one of the challenges addressed with the help of BHEL by modifications of LP stage-5

blade, shroud modifications etc., and based on its success, the same technique was used for other plants to sort out

inherent problems. Grid-induced Outages Grid disturbance induced outages were overcome by house load schemes and

in one-month viz., May 1998, as many as 150 house load operations took place and units operated withstanding these

transients. Healthiness of the control system and other equipment to withstand external grid transients was remarkable.

The sharp corner in the root section of the blade causes the blade to crack. Failure of the turbine blades was one of the

challenges addressed with the help of BHEL by modifications of HP stage-5 blade, shroud modifications etc., and based

on its success, the same technique was used for other plants to sort out inherent problems. The material used was 12Cr-

Mo martensitic steel,which is a very high temperature resistant material. The microstructure was observed was

tempered martensitic structure. These turbine blades were collected from Madras Atomic Power Station (MAPS) for

analysis. These blades were found to be failed. These blades were used for the present investigation of defects using

ultrasonic phased array and X-ray radiography techniques. Turbine blades are known to fail due to tempered martensite

embrittlement, fatigue, fretting, high temperature creep age hardening, firtree design, high residual stresses etc.

Chemical compositions of the turbine blade:Element Weight %Sulphur 0.019 to 0.03Phosphorus 0.019 to 0.028Carbon 0.20 to 0.24Chromium 12.8 + 1.2Manganese 0.45 to 0.54Silicone 0.30 to 0.43Nickel 0.40 to 0.52Vanadium 0.05Molybdenum 0.1 to 0.13Iron Balance

TURBINE MATERIALS

33

In the case of turbine, the advancement in steam conditions mainly affects its high pressure (HP) and intermediate pressure (IP) sections.As a result, the associated rotations as well as stationary parts of these sections experience more severe service conditions than that of conventional sets. Since they operate well within the creep range, their design is based primarily on the long-term creep strength ofthe material, but the stress levels during steady and non-steady operating conditions, particularly during 593°C contemplate the use of 12Cr steel rotor with steam cooling to bring the rotor temperature downto 566°C, where its creep strength is adequate to meet the design pressure. However, presently several super 12Cr steels with much superior creep resistance are available and they should also be considered before a final decision is taken. Above 593°C steam temperature, X12CrMoWVNbN 10 11 and austenitic stainless steel must be considered. Amongst the austenitic steels, A286 and X8CrNiMoBNb 16 16 offer better creep strength for an HP rotor ofadvanced sets operating at 649°C. One of the rotor-related problems is the maximum size that can be produced from the 12Cr and austenitic steels. Due to severe segregation in conventional ingots, the size of the austenitic steel rotors used in earlier supercritical units was limitedto small size, as a result of which, it became necessary to divide the HP turbine into two stages. It is estimated that a large advanced plant would require a one-piece super-alloy HP rotor forgingweighing 11,300 kg with a barrel diameter of 890mm. Similarly, a double-flow reheat rotor made of 12Cr steel is expected to be about 1150mm in diameter and 31,750 kg in weight, which wouldrequire to start with an ingot size of 63,500 kg . Significant progress has been made, in recent years, in increasing the size as well as the quality of the forging by employing modern steel making techniquessuch as low sulfur silicon deoxidation (low S), vacuum oxygen decarburization (VOD), vacuum carbon deoxidation (VCD), central zone refining (CZR), electro slag hot topping (ESHT) and electroslag remelting (ESR). By employing these techniques, either individually or in combination, production experience with low-alloy ferritic [39], 12Cr as well as austenitic steels [4, 40] demonstrate that the rotors of the candidates materials can be made to the required size and quality without experiencing much

34

problems.

BladingConventional 12CrMoV steel blades are adequate to meet the steam temperature at 566°C. But a wide variety of high-temperature blade materials with proven service performance in large gas turbines areavailable, and they should be considered for more advanced steam conditions. These include super 12Cr steels, austenitic steels, Nimonic 80A, 90, 105, 115, In718 and precision casting alloys such as Udimet 500 and IN 738LC. LP RotorThe principal requirements of material for lowpressure (LP) rotor are high yield strength to withstand the high stress imposed on it by long blades and high fracture toughness to minimize subcritical flaw growth so as to avoid the possibility of fast fracture. 3.5NiCrMoV steel is widely used for LP rotor throughout the power industry. To avoid temper embrittlement, the maximum operating temperature of the LP rotor made of this steel is generally limited to about 350°C [9]. The inlet steam temperature to LP turbine of the supercriticalunits, on the other hand, is dictated by the exhaust steam from the second IP section. The IP-LP crossover temperature from advanced supercritical units at steam temperatures of 593°C and abovewould be 400-455°C [9]. To maintain the inlet steam temperature of LP turbine at its present maximum allowable limit, it would be necessary to cool the steam either through cooling of the rotoror by adding an additional stage of expansion to the IP turbine. The latter approach would be a difficult design task, as it requires usage of long blades at high temperature, whereas the former approach has tosacrifice a part of the thermal efficiency. Another approach to the problem would be to render LP rotor material more resistant to temper embrittlement [41]. Efforts are, therefore, being made to improve the fracture toughness of the IP rotor steel by improved steel making technology and closer control of chemical composition. The interaction between Mn, Si, P and Sn was shown to have promoted the degree of temper embrittlement. Resistance to temper embrittlement of 3.5NiCrMoV rotor steel with low Mn and low Si

35

contents was found to have greatly improved as compared to conventional steel [9]. By utilising the modern steel making technologies, it is now possible to decrease both Mn and Si contents to levels of- 0.002%.

ELEC

TRIC

AL

MAI

NTAI

NENC

E

MEC

HAN

ICAL

MAI

NTAI

NENC

E

STO

RES

TO

OL-

CRIB

TRO

LLEY

TRA

CK

STO

RES

C

NC

MAI

NTAI

NENC

E

TBM

B

LANK

ING

MAC

HIN

E

RAILWAY TROLLEY TRACK

HEA

VY M

ACH

INE

SH

OP

B

AY-1

HEA

VY M

ACH

INE

SH

OP

BAY

-2

TURN

ING

AN

D M

ILLI

NG

SECT

ION

BAY-

3

TB

M

B

AY-4

TROLLEY TRACK

36

RAILWAY TROLLEY TRACK

GO

VERN

ING

AND

MED

IUM

MAC

HIN

E SH

OP

T

BM

LP B

LAD

E S

ECTI

ON

BAY-

4

GO

VERN

ING

ASSE

MBL

Y

TEST

ING

(HYD

RO/ S

TEAM

)

TOO

L-RO

OM

BAY

-4

LIG

HT

MAC

HIN

E

SHO

P BA

Y-3

LAYOUT OF BLOCK-3 WAY FROM BLOCK-2

37

E

S

W

N