Maintenance of Pocket type Journal bearing , measuring clearances eccentricity crush clearance ,Hydrodynamic lubrication, rotor position in bearing General overview of Hydrodynamic lubrication and bearing

1. MAINTENANCE OF POCKET
TYPE JOURNAL BEARING D500
TRIPLE PRESSURE STEAM
TURBINE 400MW
PREPARED BY FAISAL NADEEM

2. STEAM TURBINE DATA
• TYPE STF30C
• OEM ALSTOM GE
• TRIPLE PRESSURE , ONCE REHEAT, SIDE EXHAUST, CONDENSATE TURBINE
• RATED OUTPUT 380MW , RPM 3000,24 C ,HUMIDITY 70 %,
• HP PRESS 16.29MPA (A), 586C HP STEAM FLOW 735 T /HR
• HRH STEAM PRESSURE 3.455MPA A,584 C, STEAM FLOW 831 T/HR
• CRH DATA
• LP STEAM DATA

3. OUR PLANT STEAM TURBINE BEARINGS
DATA

4. BEARING DETAIL
• THE PERFORMANCE OF A TURBO-MACHINE DEPENDS NOT ONLY ON THE ROTOR OR
THE TYPE OF
BEARING BUT ALSO ON THE INTERPLAY BETWEEN THE SHAFT, THE BEARINGS AND
THE BEARING
SUPPORTS (FOUNDATIONS ETC.). NONETHELESS, BEARINGS ARE TRULY THE HEART
OF THE
MACHINE AND MUST BE CAREFULLY SELECTED. THE MAIN CRITERIA TO CONSIDER
WHEN
CHOOSING BEARINGS FOR MACHINES IN CONTINUOUS OPERATION ARE:
• SIMPLE BUT RUGGED DESIGN AND EASY REPLACEMENT TO ENSURE RELIABLE
OPERATION FOR
MANY YEARS.
• KNOWN RIGIDITY.
• ADEQUATE DAMPING.
• SUFFICIENT RESERVE AGAINST INSTABILITY.
• ACCURATE INFORMATION ON OPERATING CONDITIONS.
• NOT SUSCEPTIBLE TO EXTERNAL INFLUENCES

5. TYPES OF POCKET TYPE JOURNAL BEARING
• THERE ARE BASICALLY 3 TYPES OF JOURNAL BEARING :
1.DRY
2.HYDRODYNAMIC
3.HYDROSTATIC
TODAY I WILL DISCUSS HYDRODYNAMIC ONLY

6. HYDRODYNAMIC THEORY
• IT IS POSSIBLE TO ESTABLISH A HYDRODYNAMIC LIQUID FRICTION BETWEEN THE
ROTOR AND
BEARING SO THAT THEY ARE NOT IN DIRECT CONTACT, SIMILAR TO A CAR TIRE AND
THE ROAD
DURING AQUA PLANNING.
IN 1883 EXPERIMENTS ESTABLISHED THE CONDITIONS WHICH MUST BE FULFILLED TO
BUILD UP A
PRESSURE WEDGE, NAMELY:
• VISCOUS LUBRICANT
• WEDGE-SHAPED SURFACES IN THE LUBRICATION GAP
• MOTION
• LOAD
PRESSURE IS BUILT UP IN A NARROWING, WEDGE-SHAPED GAP DUE TO THE ADHESION
OF A
LIQUID TO THE SURFACE OF A ROTATING PART. SINCE THE FORCE OF THE BUILT-UP
PRESSURE
WEDGE IS HIGHER THAN THE FORCE OF THE WEIGHT, A FILM OF LIQUID IS
ESTABLISHED BETWEEN
THE STATIONARY AND ROTATING PARTS. THERE IS NO LONGER A DIRECT CONTACT,

7. PLAIN BEARING CONCEPT

8. OIL WEDGE SCIENCE
At zero speed, the shaft rests on the bearing at bottom dead center.
As soon as shaft rotation begins the shaft
“lifts off” on a layer of oil. In fluid film bearings, lubrication is
required between a pair of surfaces with relative motion
between them. There is always a convergent wedge developed that
is formed due to the relative surface speeds and the
lubricant viscosity to carry the applied load. An oil pressure film
develops with equal and opposite force vectors to the
applied load. One surface drags the lubricant, usually an oil, into a
converging gap. As the space available in this gap
decreases, the fluid develops a pressure gradient, or pressure hill. As
the fluid leaves the gap, the high pressure helps
expel it out the other side. A simple diagram of this is shown
in figure 3

9. BEARING NOMENCLATURE
• RJ = RADIUS OF JOURNAL
RB = RADIUS OF THE BEARING
CB = RADIAL CLEARANCE OF THE BEARING = RB-RJ
H = RADIAL CLEARANCE AS A FUNCTION OF THE ANGULAR POSITION WHERE THE
CLEARANCE IS MEASURED
HMIN = MINIMUM OIL FILM CLEARANCE
E = ECCENTRICITY - THE DISTANCE BETWEEN THE CENTER OF THE BEARING AND
THE CENTER OF THE SHAFT
ECB = E/CB = ECCENTRICITY RATIO - IF ZERO, SHAFT IS CENTERED; IF 1 THEN
SHAFT TOUCHES BEARING
LINE OF CENTERS = LINE CONNECTING THE CENTER OF THE BEARING AND THE
CENTER OF THE SHAFT
Ö = ATTITUDE ANGLE = ANGLE FROM -Y AXIS TO LINE OF CENTERS
Ù OR Ù = ROTATION DIRECTION AND SPEED IN RAD/SEC
W = GRAVITY LOAD

10. PRESSURE PROFILE IN JOURNAL BEARING

11. VARIOUS
BEARING USED
IN TURBO
MACHINERIES

12. OUR PLANT STEAM TURBINE D500
BEARING CONFIGURATION
• THERE ARE 5 POCKET TYPE JOURNAL BEARINGS AND 1 COMBINED THRUST AND JOURNAL BEARING AT OUR STEAM
TURBINE
• I WILL DISCUSS D500 TYPICAL WHO DIMENSIONS ARE 500MM WHICH IS LOCATED BETWEEN IP STEAM TURBINE AND LP
STEAM TURBINE SECTIONS. PICTURE IS SHOWN BELOW

13. POCKET TYPE JOURNAL BEARING PEDESTAL
• HYDRODYNAMIC DESIGN PRINCIPLE ENSURES THAT THE SLIDING MACHINE PARTS DO NOT
COME INTO CONTACT.
• THE FULLY ENCLOSED BEARING CONSISTS OF TWO BEARING SHELLS, LINED WITH WHITE
METAL, CENTERED WITH CYLINDRICAL PINS AND HELD TOGETHER BY SOCKET HEAD SCREWS.
• THE BEARING IS SLIGHTLY CLAMPED IN THE BEARING CASING BY FITTED PLATES. SHIMS
UNDER THE FITTED PLATES PERMIT ADJUSTMENT OF THE BEARING. A CYLINDRICAL PIN IS
INSERTED IN THE UPPER FITTED PLATE TO PREVENT THE BEARING FROM TURNING.
• THE LUBE OIL FOR THE BEARING IS SUPPLIED THROUGH A BORE IN THE BEARING CASING
AND THE LATERAL OIL INLET AT THE BEARING FROM WHERE THE OIL PASSES TO THE INLET
POCKET OF THE BEARING SHELLS. THE OIL LEAVES THE BEARING AT BOTH FACE SIDES
ALONG THE ENTIRE SHAFT CIRCUMFERENCE.
• THE HIGHER-LOADED JOURNAL BEARINGS HAVE A JACKING OIL CONNECTION THAT
PREVENTS METALLIC CONTACT OF BEARING METAL AND BEARING JOURNAL

14. BEARING METAL
• THE LIFE SPAN OF A TURBO-MACHINE BEARING DEPENDS TO A LARGE EXTENT ON
THE BOND BETWEEN THE BEARING METAL, WHICH BUILDS THE RUNNING SURFACE
AND ITS SUPPORT-SHELL.
• ONLY WHITE METALS, WHICH HAVE A SOFT BASE METAL CONTAINING HARD, WEAR-
RESISTANT ADDITIVES, ENTIRELY MEET BEARING METAL REQUIREMENTS.
• WHITE METALS CAN BE BASED ON TIN, LEAD OR CADMIUM. FOR VARIOUS REASONS,
TIN-BASED METALS HAVE ESTABLISHED THEMSELVES FOR USE IN TURBINE BEARINGS.
THE BASIC COMPOSITION IS 80-90% TIN AND ANTIMONY WITH A COPPER ALLOY,
WHICH HARDENS THE SOFT BEARING METAL BY FORMING MIXED CRYSTALS
• FOR TECHNICAL REASONS SUCH AS STURDINESS, STRENGTH, EXCHANGEABILITY, AND
MANUFACTURE AS WELL AS FOR ECONOMY, WHITE METAL IS USED ONLY AS A SHELL
LINER

15. JOURNAL BEARING PEDESTAL
• DURING TURNING GEAR OPERATION, STARTUP AND RUNDOWN WHEN A HYDRODYNAMIC FILM IS NOT
YET AVAILABLE. THE FRICTION COEFFICIENT IN THE BEARINGS AND THE TORQUE TO BE PRODUCED BY
THE TURNING GEAR ARE THUS REDUCED SIGNIFICANTLY

16. POCKET
TYPE
JOURNAL
BEARING
D500
INSIDE
VIEW

17. OIL SUPPLY TO
JOURNAL BEARING
AND TEMP
MONITORING

18. DISMANTLING THE BEARING COUPLING AND INSERT
RING UPPER HALF

19. OIL DEFLECTOR LP
AND IP SIDE
CLEARANCES

20. REMOVING
UPPER
RING
INSERT
HALF

21. DISMANTLING / ASSEMBLING THE BEARING LOWER HALF
Auxiliary
bearings are
erection devices which
perform two
functions:
• They are used as
rotor lifting devices
during erection and
dismantling work on
journal bearings.
• They are used as
auxiliary bearings
during coupling and
uncoupling of the
rotors as well as
during erection.
Max rotor lift don't
exceed 0.2 to 0.3mm
Use 100 ton Jack

22. • REMOVING LOWER
HALF BEARING

23. INSPECTION OF LOWER HALF BEARING
• IF THERE ARE CRACKS IN OR POOR ADHESION OF THE WHITE METAL LAYER, EXCHANGE THE
INNER SHELL.
• IF THERE ARE SMALL SCRATCHES AND RUBS, SMOOTH THEM CAREFULLY OR EXCHANGE THE
INNER SHELL.
• IF THERE ARE TRACES OF SHAFT CURRENT, CHECK THE GROUND BRUSHES.
• CHECK FOR SMOOTH SURFACES. ROUGHNESS MUST CORRESPOND TO < ISO-N6. RA (CLA)
= 0.8ΜM (32 ΜINCH). OIL INLET EDGES SHOULD BE CLEANLY RADIUSED.
• IF A JACKING OIL POCKET IS PROVIDED IT MUST NOT SHOW ANY SCRATCHES DEEP ENOUGH
TO PREVENT THE BUILD-UP OF OIL PRESSURE. USE A DIAL GAUGE TO CHECK PROPER LIFTING
OF THE SHAFT. COMPARE IT WITH THE VALUE RECORDED ON THE TEST CERTIFICATE.
• POLISHED SPOTS IN THE AREA OF THE SHAFT SUPPORTING POINTS SOMETIMES DEVELOP
BASED ON OPERATING EXPERIENCE; THEY ARE NO CAUSE FOR ALARM.
• IF THERE IS DISCOLORATION OF THE INNER SHELL, VERIFY THAT THE OIL SUPPLY IS FUNCTIONING
PROPERLY. THERE SHOULD BE SUFFICIENT HEAT DISSIPATION AND NO CARBONIZING CAUSED
BY OIL, WHICH IS TOO HOT OR TOO COLD.
• IF THE WHITE METAL SURFACE SHOWS DULL SPOTS, WHICH CANNOT BE ATTRIBUTED TO
INSUFFICIENT OIL SUPPLY, CHECK THE BONDING OF THE WHITE METAL ON THE STEEL SURFACE
BY THE ULTRASONIC TEST PROCESS. (SEE SPECIAL INSTRUCTIONS FOR THE TEST PROCEDURE).

24. INSPECTION OF LOWER HALF BEARING
• IF A JACKING OIL NOZZLE IS PROVIDED, CHECK ITS TIGHTNESS BY PERFORMING A PRESSURE
TEST WITH 500 BAR (7250 PSIG).
• CHECK BEARING CLEARANCES USING INSIDE AND OUTSIDE MICROMETERS. BE SURE THE
INSIDE MICROMETER IS APPLIED TO THE CYLINDRICAL SECTION OF THE INNER SHELL SIDES AND
NOT TO THE AREA OF THE OIL POCKETS. BECAUSE TURNING GEAR PARTS RESTING ON
THE BEARING BODY TEND TO TILT THE INNER SHELL AND MAKE IT IMPOSSIBLE TO MEASURE
CORRECTLY, THE CHECK SHOULD NOT BE CARRIED OUT WITH THE BEARING SHELL MOUNTED ON
THE SHAFT.
CHECK BEARING CLAMPING.
• CHECK THE CONDITION OF THE ADJUSTING PLATES AND SHIMS. THEY COULD BE PITTED DUE
TO AN UNBALANCE IN THE ROTOR. IF SO, BALANCE THE ROTOR AND EXCHANGE THE
ADJUSTING PLATES AND SHIMS.
• IF THE ADJUSTING PLATES OR SHIMS ARE EXCHANGED, CHECK AND READJUST THE CLEARANCE
AT THE HORIZONTAL JOINT. REMOVE ~ 0.50 MM (0.20”) TOTAL SHIM THICKNESS TO GAIN
ENOUGH CLEARANCE FOR THE LEAD WIRE.
• DURING REASSEMBLY, ENSURE CLEANLINESS

25. MAIN JOURNAL INSPECTION
• HIGH SPOTS
• SCORING
• DISCOLORATION DUE TO
OVERHEATING
• CRACKING
• PITTING
• ANY KIND WEAR
• ONLY IN CASE OF DEEP SCORING
SHAFT SHOULD BE RE MACHINED

26. POCKET TYPE BEARING CLEARANCE

27. STANDARD BEARING PRESSURE AND TEMP

28. ROTOR POSITION IN POCKET TYPE BEARING

29. HIGH WHITE METAL TEMPERATURE AND ACTIONS
• INSUFFICIENT OIL SUPPLY.
• INLET OIL TEMPERATURE TOO HIGH.
• AIR CONTENT IN OIL IS TOO HIGH.
• FAULTY THERMOCOUPLE.
• EXCESSIVE LOADING OF THE BEARING.
• DISTURBANCE OF BEARING CLEARANCE
RECOMMENDED ACTION(S):
TO DETERMINE WHETHER THE OIL SUPPLY IS INSUFFICIENT, MAKE THE FOLLOWING
CHECKS:
• CHECK PRESSURE BEFORE AND AFTER ORIFICE.
• CHECK FOR OBSTRUCTION IN THE SUPPLY LINE.
• CHECK FUNCTION AND SETTING OF CONSTANT PRESSURE VALVE.
• CHECK FOR EROSION ON OIL BAFFLES DUE TO SHAFT CURRENTS

30. ECCENTRICITY
• THE DIFFERENCE BETWEEN THE
MAXIMAL AND MINIMAL WALL
THICKNESS IS CALLED
ECCENTRICITY:
• ECCENTRICITY = T - TE
• ECCENTRICITY PRODUCED BY THE
VARYING WALL THICKNESS IS ADDED
TO THE ECCENTRICITY “E” CAUSED
BY THE DISPLACEMENT OF THE
JOURNAL FROM THE CONCENTRIC
POSITION. SUCH INCREASED TOTAL
ECCENTRICITY ALLOWS TO
ESTABLISH A MORE STABLE REGIME
OF HYDRODYNAMIC LUBRICATION.

31. BEARING PERFORMANCE
• BEARING PERFORMANCE
WHILE THE STIFFNESS AND DAMPING PROVIDED BY A JOURNAL BEARING ARE
CRUCIAL, THERE ARE OTHER DESIGN FACTORS THAT MUST BE
CONSIDERED IN ORDER TO UNDERSTAND HOW BEARINGS WORK. FOR EXAMPLE,
IF THE ECCENTRICITY IS TOO HIGH THERE IS A RISK OF METALTO-METAL
CONTACT AND HIGHER DYNAMIC LOADS BEING IMPARTED TO THE BABBITT
CAUSING PREMATURE FATIGUE. IF THE ECCENTRICITY
IS TOO LOW (JOURNAL IS NEARLY CENTERED) THEN THE MACHINE COULD MORE
EASILY BECOME UNSTABLE. ECCENTRICITY IS A FUNCTION
OF BOTH SPEED AND LOAD. FIGURE 8 INDICATES THAT, WITH A CONSTANT
LOAD, AS SPEED INCREASES, THE ECCENTRICITY DECREASES

32. ECCENTRICITY VS SPEED AT CONSTANT LOAD

33. CRUSH HEIGHT
• BEARING CLEARANCE IS ONE OF THE MOST
IMPORTANT PARAMETERS IN THE
OPERATION OF A BEARING. THEREFORE, IT
IS IMPORTANT TO DETERMINE THE
INSTALLED CLEARANCE ALONG WITH THE
BORE CONTOUR AND CONCENTRICITY TO
THE OUTSIDE FIT DIAMETER. THE FINAL
BEARING CLEARANCE IS INFLUENCED BY
THE CONTOUR OF THE HOUSING INTO
WHICH IT IS INSTALLED, AND ALSO BY THE
AMOUNT OF INTERFERENCE OR CRUSH
BETWEEN THE BEARING SHELL AND THE
SUPPORT HOUSING. PROPER CRUSH IS
CRUCIAL IN THE OPERATION OF HIGH
SPEED AND CRITICAL MACHINERY.
IMPROPER CRUSH CAN LEAD TO EITHER A
HOT BEARING OR A LOOSE BEARING FIT.

34. CRUSH MEASURING METHOD
• PLACE SHIMS OF EQUAL THICKNESS (TS)
ALONG BOTH SIDES OF THE SPLIT LINES.
LAY A STRIP OF PLASTIGAGE OR LEAD WIRE
ON TOP OF THE BEARING SHELL ALONG
THE SHAFT AXIS. INSTALL THE BEARING
CAP OR STRAP AND TIGHTEN ALL SPLIT
LINE BOLTS. THE PLASTIGAGE OR LEAD
WIRE SHOULD INDICATE A THICKNESS (TF)
EQUAL TO OR LESS THAN THE SHIM
THICKNESS USED AT THE SPLIT LINE. THE
AMOUNT OF INTERFERENCE (CRUSH) IS
EQUAL TO THE DIFFERENCE BETWEEN THE
INDICATED CLEARANCE (TF) AND THE SHIM
THICKNESS (TS).
• A NEGATIVE VALUE FOR THE CRUSH
INDICATES A LOOSE BEARING AND THE
PROBLEM HAS TO BE RECTIFIED BY
REPLACING THE BEARING OR USING SHIMS
AROUND THE CIRCUMFERENCE TO
MAINTAIN AN INTERFERENCE FIT. ONCE
THE DESIRED CRUSH HAS BEEN OBTAINED,
THE BEARING CLEARANCE SHOULD BE
CHECKED AGAIN TO ENSURE THAT THE
CRUSH IS NOT EXCESSIVE TO THE POINT OF

35. BEARING CLEARANCE THUMB RULE
• FOR MOST APPLICATIONS .00075 TO .0010” (THREE QUARTERS TO ONE
THOUSANDTH OF AN INCH) OF CLEARANCE PER INCH OF SHAFT DIAMETER IS A
REASONABLE STARTING POINT.
• FOR EXAMPLE, A 2.000” SHAFT DIAMETER WOULD REQUIRE .0015 TO .0020”
BEARING CLEARANCE (.00075 X 2.000” = .0015” AND .0010 X 2.000” = .0020”).
USING THIS FORMULA WILL PROVIDE A SAFE STARTING POINT FOR MOST
APPLICATIONS. FOR HIGH PERFORMANCE MACHINES IT IS RECOMMENDED THAT
.0005” BE ADDED TO THE MAXIMUM VALUE DETERMINED BY THE ABOVE
CALCULATION. THE RECOMMENDATION FOR OUR 2.000” SHAFT WOULD BE
.0025” OF CLEARANCE. REMEMBER HOWEVER, THAT THE ABOVE ARE ONLY
RECOMMENDED STARTING POINTS.

36. ROTOR
POSITION
IN
BEARING
HOUSING

37. JOURNAL
BEARING
CLEARANCE

38. JOURNAL
BEARING
CLEARANCE

39. BEARING
CLEARANCE
USING DIAL
GAUGE

40. TEMPERATURE VS SPEED AT CONSTANT LOAD

41. THANKS YOU ALL
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