turbine overhauls

8/4/2019 Turbine Overhauls

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TURBINE OVERHAULS

A.R.SAOJI, SE, NTC


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IMPORTANCE OF O/H PLANNING

A detailed planning for Capital overhaul of turbine not

only helps in timely completion of overhaul but alsoimproves the quality of maintenance activities and thusensures better performance of set.

Pre Outage Survey Measurement of bearing vibrations

Performance of Governing system/ CVs

Measurement of steam parameters/ Lub Oil temperatures

Thermal expansions, differential expansions and axial shift etc

Leakages of steams, water and oil

Abnormal noises, vibrations of components specially nearcouplings and bearing pedstals.


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IMPORTANCE OF O/H PLANNING

JOB PLANNING

SCOP OF WORKS DURATION OF CAPITAL MAINTENANCE

MATERIAL MANAGEMENT

T&P

SPECIAL T&P CONSUMABLES

INFRASTRUCTURE PLANNING

EOT CRANE

SITE STORES

SAND & ASH BLASTING ARRANGEMENTS

QUALITY CONTROL AND DOCUMENTATION

CHECK LIST AND DOCUMENTATION

SAFETY ARRANGEMENTS

OTHER FACILITIES


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OBSERVATIONS BEFORE SHUT DOWN

Defects of temporary & permanent nature

Behaviour of machine at various loads Important parameters & vibration levels

Coasting down period

Governor characteristics

Above records will be given to maintenanceengineer, who in turn has to pay special

attention towards those problems & ensurethe improvement of the machine afteroverhauls


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DESCRIPTION OF ACTIVITIES

1-2 COOLING/ PREPARATION OF BOLY HEATING

2-3 REMOVAL OF TURBINE GEAR & BARRING COVER3-4 CHECK RUN OUT AND LEVEL

4-5 CHECK BEARING CLEARANCES & INTERFERENCE

5-6 DECOUPLE TG TO CHECK ALIGNMENT

6-7 DECOUPLE IP-LP & CHECK ALIGNMENT

7-8 SLING CHECK

8-9 REMOVE HP-IP & LP UPPER CASING

9-10 REMOVE TOP LINERS AND SEAL HOUSINGS

10-11 CHECK THRUST FLOAT & BEARING

11-12 CHECK STEAM PATH CLEARANCES12-13 REMOVE ROTORS

13-14 BOTTOM LINERS AND DIPHRAGMS

14-15 REMOVE HP STUDS OF HP-IP-LP CASING


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DESCRIPTION OF ACTIVITIES- CONTINUED-1

15-16 CHEK HP CAPS OF HP-IP CASING

16-17 ALIGNMENT, BEARING MATCHING & SLINGCHECKING

17-18 CENTERING OF DIPRAGMS

18-19 CHECK THERMAL CLEARANCES

19-20 ASSEMBLE THRUST BEARING AND CHECK FLOAT

20-21 CHECK STEAM FLOW PATH & DO SEAL CUTTING21-22 BOX UP HP-IP & LP CYLINDERS

22-23 FINAL ALIGNMENT, OIL CLEARANCES &INTERFERENCES

23-24 SETTING OF BEARING FOR OIL FLUSHING

24-25 OIL FLUSHING

25-26 FINAL BOXING UP OF BEARINGS

26-27 CHECK INTERLOCKS & PROTECTIONS

27-28 TURNING GEAR OPERATION AND GOVERNING

SETTINGS


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02-29 DRAIN OIL

29-30 CLEAN TANKS, FILTERS, OIL INJECTORS30-24 FILL UP OIL

31-08 UNBOLT PARTING PLANE

09-32 OVERTURNING OF CASINGS

32-17 CLEANING OF CASINGS & P.P. MATCHING

10-33 BOX UP HP-IP & LP CYLINDERS

33-17 OVERTURNING OF TOP LINERS & DIPHRAGMS

14-34 SAND BLASTING OF BOTTOM DIAPHRAGMS

35-36 CHECKING BEARING CLEARANCES/LEVELS

36-37 ROCKER & HYDROGEN SEAL REMOVAL37-38 REMOVAL OF END SHIELDS

38-39 CHECK AIR GAP

39-40 CHECK RUNOUT OF SEAL COLLAR

40-41 AIR TIGHTNESS TEST OF GENERATOR ROTOR


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41-42 PREPARATION OF THREADING OUT ROTOR

42-43 THREADING OUT OF ROTOR43-44 INSPECT STATOR WDG & TIGHTNESS OF WEDGES

44-45 CLEAN, WARNISH & HEAT STATOR WINDING

45-46 CHECK I.R. VALUES

46-47 THREADING IN OF ROTOR

48-23 FINAL ASSEMBLY

36-49 DISMENTLING OF COOLERS

49-50 CLEANING & HYDRAULIC TEST OF COOLERS

50-51 ASSEMBLY OF COOLERS & PIPING

52-53 REMOVAL OF CROSS OVER PIPES53-54 REMOVAL OF INSULATION

52-55 REMOVAL OF LINKAGES

55-56 REMOVAL OF RACK & CAM ARRANGEMENTS

56-57 DISMANTLING/REVISIONING OF GOV.SYSTEM


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57-24 ASSEMBLY OF GOVERNING SYSTEM

56-58 DISMANTLING & OVERHAULING OF E.S.V.

58-24 ASSEMBLY OF E.S.V.

56-59 DISMANTLING & OVERHAULING OF C.V.s

59-26 ASSEMBLY OF C.V.s

54-08 OPENING PIPE JOINT CONNECTED TO TOP CASING

22-60 HEAT TIGHTENING OF HP-IP

23-61 PICK UP SETTING


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LMW (LENINGRAD M WORKS)

&KWU (KRAFTWERKUNION)

TURBINES


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WORKING PRINCIPLE

When steam is allowed to expand through a narrow orifice, itabsorbs the kinetic energy at the cost of enthalpy (heat energy).

This kinetic energy of steam is changed into mechanical energywhen steam moves over the turbine blades.

Motive force to the turbine is not produced due to static pressureof the steam or from any impact of the steam jet. The blades areso designed that the steam will glide on and off the blade without

any tendency to strike it. When steam moves over the Rotorblades its direction is continuously changing and centrifugalpressure is exerted on the blade, normal to the blade surface atall the points. The total motive force acting on the blades is thusthe resultant of all the centrifugal force plus the change ofmomentum. This causes the rotational motion of the blades.


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TYPES OF TURBINE

According to the principle of action of the steam, turbine can be

classified as:

a) Impulse Turbine b) Reaction Turbine

a) Impulse Turbine :

The steam is expanded in the fixed nozzles.

Thus the velocity of steam is increased at thecost of reduction in pressure. This high velocitysteam moves over the rotor blade and imparts itskinetic energy to the rotor blade.

No pressure drop takes place when steam glidesover the blade.


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TYPES OF TURBINE

b) Reaction Turbine :

In this type pressure drops both in fixed as well asmoving blades.

In other words steam expands on both, fixed andmoving blades. Fixed blades work as nozzleswhere as steam expansion on moving bladeproduces reaction.

The expansion on moving and fixed blade is theresult of the design of blade profile.


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DEGREEOF REACTION

I0 - enthalpy of the steam at the entrance to the fixed blade.

I1 - at the outlet of fixed blade which enters on the moving blade with the sameenthalpy.

I2 - is the enthalpy at the outlet of the moving blade.

Then the factor A is known as degree of Reaction.

I1 - I2

A =

I0 - I2

If A < 0.5 then the turbine is known as Impulse turbine.

If A > 0.5 then the turbine is a reaction Turbine.


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COMPOUNDING

Steam velocity becomes very high if steam isallowed to expand in a single stage (single row ofnozzle and blade). Hence the rotational speed of

the turbine becomes very high and impracticable. So energy conversion of steam is done in number

of steps to achieve the practicable desired speed ofthe turbine.

This is known as compounding.


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TYPESOFCOMPOUNDING

a) Velocity Compounding :

In this type of compounding entire steam pressuredrop takes place in one set of nozzle.

The kinetic energy so converted in nozzle is utilised innumber of row moving and guide blades.

The role of guide blade is just to change the directionof steam jet and guide it to next row of moving blades.

This types of turbine is also called curtis turbine.


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B) PRESSURE COMPOUNDING :

In place of single nozzle ring, numbers of nozzle ring arrangedalternatively after moving in blade wheels. Thus instead ofallowing the pressure drop in one step, It is done in no of steps.

Steam is passed through one nozzle ring in which it is partiallyexpanded. It then passes over the first moving blade wheel, wheremost of its velocity is absorbed. Then this steam passes throughsecond nozzle ring. The velocity so obtained, is again absorbed bythe second moving wheel and so on, the process is repeated tillwhole of the pressure is absorbed.

This type of turbine is also called Rateors turbine after its Inventor.


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C) PRESSURE VELOCITY COMPOUNDING

This is the combination of both previous methods

It has the advantage of allowing a higher pressure dropin each stage and so less stages are necessary. Hence

for a given pressure drop the turbine will be shorter. But the diameter of Turbine is increased at each stage

to allow for the increasing volume of steam. This typewas very popular.

But it is rarely used now as efficiency is quite low.


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TURBINE TURBINE SUPPORTS & CYLINDER

EXPANSION

TURBINE CASINGS

DIAPHRAGMS AND LINERS

ROTORS

TURBINE BEARINGS

SEALING GLANDS

BARRING GEAR


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TURBINE SUPPORTS & CYLINDER EXPANSION

TURBINE SUPPORT: Complete turbine assembly ismounted on foundation frames, pedestals and sole platesso designed that the components are free to expand orcontract.

FRONT BEARING PEDSTAL SUPPORT: It houses a journalbearing, main oil pump and most of governing systemelements. It is held transversely in sole plate by axialguide key. Pedstal is prevented from getting lifted by fourinverted L-shaped clamps.


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MIDDLE BEARING PEDESTAL SUPPORT

Rests on sole plate secured to foundation block.

Pedestal is free to move in axial direction.

Traverse movement is restricted by axial key.

Any tendency for pedestal to lift is prevented by L-shaped clamps.


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HIGH PRESSURE CYLINDER SUPPORT

Outlet end of HPC is supported on FBP and inletend is supported on MBP.

Four lugs (2 at inlet end & 2 at outlet end) arecast integral with bottom half cylinder flange athorizontal joint.

To maintain correct alignment and guiding forvertical expansion, vertical keys are providedbetween cylinder & pedestal.


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INTERMEDIATE PRESSURE CYLINDERSUPPORT

Four lugs (2 at inlet end & 2 at outlet end) are castintegral with bottom half cylinder flange athorizontal joint.

Inlet end of IPC rests on the transverse keyssecured on the pads machined on the rear end ofthe MBP.

Exhaust end of IPC is supported on the transversekeys secured to the LPC bottom half.


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LP CYLINDER SUPPORT

LPC is supported on foundation framespositioned around bottom halves of exhaustcasing.

These are joined by special bolts with sphericalwashers and clearances between the bolt headand spherical washers allows for free expansionof LPC.

The anchor point of the turbine is located at therear end of front exhaust part of LPC.


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HP CASING

HPC is made of Creep Resisting Chromium-Molybdenum -Vanadium steel casting.

Top & bottom halves of casing are secured together at theflange joint by heat tightened studs.

Four steam chests, two on top and two on sides are weldedto the nozzle boxes which in turn are welded to casing atMBP end.

The steam chests accommodate four control valves toregulate flow of steam to the turbine according to loadrequirement.

HPC has 12 stages, 1st stage being governing stage. Eachturbine stage consists of a diaphragm and a set of movingblades mounted on a disc.


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INTERMEDIATE PRESSURE CASING

IPC of the turbine is made of two parts.

Front part is made of Creep resisting Cr-M-V steel casting andexhaust part is of steel fabricated structure. Two parts are connectedby a vertical joint. Each part consists of two halves having vertical

joint. Horizontal joint is secured by studs & nuts. Four Control valves are mounted on casing itself.

There are 11 stages in the IP turbine. Fist stage is of weldedconstruction and is directly mounted in casing. Next two stages arealso housed in casing while other 8 diaphragms are housed in threeliners which in turn are mounted on casing.

From IPC steam is carried by two Cross Over pipes to LPT. CrossOver pipes are provided with compensator for taking care of thermalexpansion.


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LOW PRESSURE CASING

LPC consists of three parts i.e. one middle partand two exhaust parts. These are fabricated fromwelded mild steel. Exhaust casings are bolted tomiddle part by vertical flange.

LPC has eight stages, 4 on either side. Last butone stage on each side are Baumanns stages.They expand a part of steam down to condenserpressure and allow rest of the steam to expandthrough the last stages.


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ATMOSPHERIC RELIEF VALVE

To protect LPC against excessive internalpressure, four relief valves are provided in theexhaust hood.

Each assembly has 1 mm thick gasket 525/755,clamped between valve seat and valve disc. Ifdue to some reason the pressure at exhaust hoodrises to 1.2 abs, then the valve disc tries to liftand thereby ruptures the gasket ring.


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DIAPHRAGMS AND LINERS

HP Diaphragms & Liners: HP diaphragms are housed inliners which are in turn located in HPC. All liners are in twohalves connected at horizontal joints by bolts. Alldiaphragms, designed for minimum deflection, are divided at

horizontal joint.

IP Diaphragms & Liners: First two diaphragms are directlyhoused in casing. The other 8 diaphragms are housed inthree liners which are in turn located in the grooves of thecasing. Diaphragms from 14th to 22nd Stages are of weldedconstruction. 23rd stage diaphragm is machined from Highgrade cast iron castings with cast in guide blades.


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LOW PRESSURE DIAPHRAGMS

These diaphragms are machined from high gradecast iron casting.

All diaphragms are divided on the horizontal jointfitted with keys to maintain accurate alignment.

On each side, the first three diaphragms are fittedthrough liners while last one is mounted directly inthe casing.


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ROTORS

HP ROTOR: It is machined from single Cr-Mo-V steel forging with integral

discs. The blades are attached to respective wheels by T:root fastening.

In all moving wheels, balancing holes are machined to reducethe pressure difference which results in reduction in axialthrust.

First stage has integral shrouds while other rows haveshrouding riveted to blade periphery.

The number of blades connected by single strip of shrouding

is called a blade packet and number of blades per packet isdecided from vibration point of view.


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ROTORS

IP ROTOR:

It has seven discs integrally forged with rotor while last fourdiscs are shrunk fit. The shaft is made of Cr-Mo-V steelforging while the shrunk fit discs are machined from high

strength nickel steel forgings. The blades on integral discs are secured by T root

fastenings while shrunk fit discs by fork root fastening.Except the last two wheels, all other wheels have shroudingsriveted at the tips of the blades.

To adjust the frequency of the moving blades, lashing wireshave been provided in some stages.


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ROTOR

LP ROTOR:

LP Rotor has shrunk fit discs on the shaft. The shaft is madeof Cr-Mo-V steel forging while the discs are machined fromhigh strength nickel steel forgings.

The blades are secured by forkroot fastening. To adjust the frequency of the moving blades, lashing wires

have been provided in all the stages.

In last two rows stellite strips are provided at the leadingedges of the blades to protect them against wet steam

erossion.

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