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re was no real time measurement to monitor the MOP Year MOP Thrust Bearing Condition
thrust bearing health. During annual overhauling the FY 2017-18 No Inspection
Thrust bearing of BBGS unit 3 would be inspected and FY 2017-18 Ok but high axial float.
the findings would result in very high ‘thrust float’ and FY 2018-19 White metal surface totally damaged.
damage of the bearing white metal surface. FY 2019-20 No Inspection
FY 2020-21 Shaft damaged.
CONSTRUCTION & LAYOUT OF MOP FY 2021-22 Ok but high axial float
BBGS #3 TG unit Main Oil Pump is a centrifugal pump PROPOSED SOLUTION &
responsible for lube oil supply into the TG bearings. It is FEASIBILITY STUDY
housed at No. 1 Bearing pedestal. MOP shaft is placed in a
volute casing and rested on to 2 nos. radial journal bearings. Considering the repeatability of failure ascertained
It has a Thrust bearing to cater to the axial loading on the during inspections, it became imminent to adopt
pump. The MOP shaft is connected to the HP rotor via one some methodology to monitor the health of BBGS#3
extended shaft & flexible coupling at one end & other end MOP Thrust Bearing. A feasibility study was carried
is connected to the Turning gear assembly of the TG unit. on introduction of a new set of Axial shift probe with
holder arrangement inside No. 1 Bearing pedestal from
which we could measure the axial float of MOP thrust
bearing during machine running condition so that any
gradual increase in the axial thrust float will be available
immediately for future course of action both in terms of
spare procurement and outage planning.
Figure 1: Construction of BBGS Unit#3 Main Oil Pump AXIAL SHIFT PROBE HOLDER –
assembly. EXPLORED DESIGN & SELECTION
OBSERVATIONS DURING ANNUAL The designing phase was very critical for successful
OVERHAULING completion of the project. The probe was facing towards
the shaft collar which was low in diameter thus presenting
Following are the inspection reports of MOP thrust a very low surface area. Due to space constraint an 8 mm
bearing of BBGS#3 during unit overhauling. diameter axial shift probe was chosen for fitment and a
probe holder was designed (Figure 3 and 5) accordingly
Table 1: MOP Thrust Bearing Condition to match with the MOP Casing profile. There were two
Found Ok options - either to weld the probe holder with the MOP
Year No Inspection casing or to fit the holder by Allen head bolts. Now as
FY 2010-11 White metal surface totally damaged. welding in casting body of MOP casing could create
FY 2011-12 No Inspection or lead to a crack in future, hence the first option was
FY 2012-13 White metal surface totally damaged. abandoned. The second option of fixing the probe holder
FY 2013-14 No Inspection with Allen head bolts was chosen which required critical
FY 2014-15 drilling & tapping operation on the MOP casing. However,
FY 2015-16 the concern was that improper drilling might puncture
the MOP casing parting plane bolt holding threads. The
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thrust bearing health. During annual overhauling the FY 2017-18 No Inspection
Thrust bearing of BBGS unit 3 would be inspected and FY 2017-18 Ok but high axial float.
the findings would result in very high ‘thrust float’ and FY 2018-19 White metal surface totally damaged.
damage of the bearing white metal surface. FY 2019-20 No Inspection
FY 2020-21 Shaft damaged.
CONSTRUCTION & LAYOUT OF MOP FY 2021-22 Ok but high axial float
BBGS #3 TG unit Main Oil Pump is a centrifugal pump PROPOSED SOLUTION &
responsible for lube oil supply into the TG bearings. It is FEASIBILITY STUDY
housed at No. 1 Bearing pedestal. MOP shaft is placed in a
volute casing and rested on to 2 nos. radial journal bearings. Considering the repeatability of failure ascertained
It has a Thrust bearing to cater to the axial loading on the during inspections, it became imminent to adopt
pump. The MOP shaft is connected to the HP rotor via one some methodology to monitor the health of BBGS#3
extended shaft & flexible coupling at one end & other end MOP Thrust Bearing. A feasibility study was carried
is connected to the Turning gear assembly of the TG unit. on introduction of a new set of Axial shift probe with
holder arrangement inside No. 1 Bearing pedestal from
which we could measure the axial float of MOP thrust
bearing during machine running condition so that any
gradual increase in the axial thrust float will be available
immediately for future course of action both in terms of
spare procurement and outage planning.
Figure 1: Construction of BBGS Unit#3 Main Oil Pump AXIAL SHIFT PROBE HOLDER –
assembly. EXPLORED DESIGN & SELECTION
OBSERVATIONS DURING ANNUAL The designing phase was very critical for successful
OVERHAULING completion of the project. The probe was facing towards
the shaft collar which was low in diameter thus presenting
Following are the inspection reports of MOP thrust a very low surface area. Due to space constraint an 8 mm
bearing of BBGS#3 during unit overhauling. diameter axial shift probe was chosen for fitment and a
probe holder was designed (Figure 3 and 5) accordingly
Table 1: MOP Thrust Bearing Condition to match with the MOP Casing profile. There were two
Found Ok options - either to weld the probe holder with the MOP
Year No Inspection casing or to fit the holder by Allen head bolts. Now as
FY 2010-11 White metal surface totally damaged. welding in casting body of MOP casing could create
FY 2011-12 No Inspection or lead to a crack in future, hence the first option was
FY 2012-13 White metal surface totally damaged. abandoned. The second option of fixing the probe holder
FY 2013-14 No Inspection with Allen head bolts was chosen which required critical
FY 2014-15 drilling & tapping operation on the MOP casing. However,
FY 2015-16 the concern was that improper drilling might puncture
the MOP casing parting plane bolt holding threads. The
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