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Strategy to increase the gap
betweenOH of ST-I units
By Boiler Maint Dept
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WATER WALL
LIMITING FACTORS
Erosion at S panel. Steam erosion due to
wall blower
Fatigue failure at
bottom end finsbetween panels
Weld joint
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Strategy for water wall
Present practices Tube rep after 20% erosion
Soot blower operated fromremote.
There is no interlock for wallblower opn from steamtemp.
Wall blower is beingoperated 6 times a day.
Radiography of all welded jts
Proposed Strategy Tube rep after 10% erosion
Welding of sacrificial bar Soot blower operation from
local.
Incorporation of interlock forWB opn drain temp.
Optimization and intelligentsoot blowing
Radiography of all welded jts
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Radiant Super heater
LIMITING FACTORS
Steam erosion due towall blower
Weld joint
Mechanical rubbing of
clamps. Blockage of tube during
maint
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Strategy for Radiant Super heater
Present practices
Tube rep after 20% erosion
Soot blower operated fromremote.
There is no interlock for wallblower opn from steam temp.
Wall blower is being operated 6times a day.
No gas cutting plastic capping
Radiography of all jts
Proposed Strategy
Tube rep after 10% erosion
Soot blower operation fromlocal.
Incorporation of interlock forWB opn drain temp.
Optimization and intelligent
soot blowing Cutting by tube cutting m/c
and using metal caps.
Radiography of all jts
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Platen Super heaters
LIMITING FACTORS
Mechanical rubbing dueto binders, connectorsand shop joints.
Weld joint
Long term overheating
Blockage of tube duringmaint
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Strategy for Platen Super heater
Present practices Thorough inspection.
Tube rep after 20% erosion.
Insitu oxide scalemeasurement everyalternate year
No gas cutting plastic capping
Radiography of all jts
Proposed Strategy Thorough inspection by team.
Tube rep after 10% erosion Insitu oxide scale measurement
every alternate year
Replacement of tubes havinghigher oxide scale.
Cutting by tube cutting m/c and
using metal caps. Radiography of all jts
Reinspection by team whereever maint work is done.
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Reheaters-II & III
LIMITING FACTORS
Mechanical rubbing dueto T spacers.
Weld joint
Long term overheating
Maint induced defect
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Strategy for Reheater II &III
Present practice Thorough inspection.
Tube rep after 20% erosion.
Insitu oxide scalemeasurement everyalternate year
No gas cutting plastic capping
Radiography of all jts
Proposed Strategy Thorough inspection by team.
Tube rep after 10% erosion Insitu oxide scale measurement
every alternate year
Replacement of tubes havinghigher oxide scale.
Cutting by tube cutting m/c and
using metal caps. Radiography of all jts
Reinspection by team whereever maint work is done.
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Regulating Stage Reheater
LIMITING FACTORS
Long term overheating.
Random flue gaserosion.
Constraint forinspection
Weld joint
Maint induced defect
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Strategy for Regulating Stage Reheater
Present practice Thorough inspection of
approachable area. Tube rep after 20% erosion. Insitu oxide scale measurement
every alternate year No gas cutting plastic capping Radiography of all jts 3 way valve optimisation to control
metal temp.
Proposed Strategy Thorough inspection of
approachable by team.
Tube rep after 10% erosion Insitu oxide scale measurement
every alternate year Replacement of tubes having
higher oxide scale. Cutting by tube cutting m/c and
using metal caps.
Radiography of all jts Reinspection by team where ever
maint work is done. Monitoring metal temp and alarm
provision in UCB.
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Economiser
LIMITING FACTORS
Constraint forinspection
Flue gas erosion.
Weld joint
Maint induced defect
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Strategy for Economiser
Present practice Thorough inspection of
approachable area.
Modular replacement
Tube rep after 20% erosion.
Inspection and repair of
lower bank coils No gas cutting at vertical.
plastic capping
Radiography of all jts
Proposed Strategy Thorough inspection by team.
Replacement of upper bankcoils in every 6 years in phasedmanner.
Inspection and repair of lowerbank coils
Cutting by tube cutting m/c and
using metal caps. Radiography of all jts
Reinspection by team whereever maint work is done.
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Steam cooled wall & hanger tubes
LIMITING FACTORS
Fatigue failure at
bottom end finsbetween panels atsecond pass and gooseneck side walls.
Flue gas erosion. Weld joint
Maint induced defect
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Strategy for SCW & Hangers
Present practice Thorough inspection of
approachable area.
Tube rep after 20% erosion.
DPT of end fins betweenpanels
No gas cutting at vertical.
plastic capping
Radiography of all jts
Proposed Strategy Thorough inspection by team. Tube replacement after 10%
erosion and shielding. DPT of end fins between panels Ensuring through ness of panel
drains before unit shut down. Checking for free expansion of
panels. Cutting by tube using tube cutting
m/c and using metal caps. Radiography of all jts Reinspection by team where ever
maint work is done.
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vents and drains
LIMITING FACTORS
Corrosion.
Stub joint
Weld joint
Mechanical rubbing of
lines at pent houseentry.
Maint induced defect
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Strategy for Vents and drains
Present practice Thorough inspection after
removal of insulation. DPT of stubs.
Radiography of all jts
Proposed Strategy Thorough inspection after removal
of insulation for corrosion and
mechanical rubbing. Replacement of all vents and drains
after one lakh running hours.
Replacement of corroded tubes. DPT of stubs. Radiography of all jts
Reinspection by team where evermaint work is done.
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Pent house
LIMITING FACTORS
Mechanical rubbing
Stub joint.
Weld joint
Spray line stubs
Maint induced defect
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Strategy for Pent house
Present practice Thorough inspection by team. DPT of stubs.
Radiography of all jts
Proposed Strategy Thorough inspection for corrosion
and mechanical rubbing of lines.
DPT of stubs. Inspection adjustment o hangers. Replacement of all vents and drains
after one lakh running hours. Replacement of corroded tubes. DPT of stubs. Radiography of all jts
Reinspection by team where evermaint work is done.
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Coal burners
LIMITING FACTORS
Minor erosion of coalnozzle
Erosion in coal nozzletips is minimum.
Coal nozzle area oferosion can bestrengthened life canbe extended.
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Milling system
LIMITING FACTORS
More than 50 percentbends are MSfabricated.
Coal pipe orifice.
MDVs, MPOs
RCfeeder chute
Mill inner cone
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Strategy for Milling system
Present practice
Replacement of eroded coal
pipe bends (35-40 nos)every year
Replacement of50 percentMPOs.
Replacement of30 percentMDVs
Replacement of30 percentMDVs
Replacement all orifices
Proposed Strategy
Provision electrical operated
gate at burner inlet to isolatemilling system.
Replacement of all MSbends with ceramic linedbends
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Airpreheaters
LIMITING FACTORS
CE baskets lattice andtheir support.
APH support bearing
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Strategy for Airpreheaters
Present practice
Replacement of erodedlattice.
Replacement of erodedlattice supports.
Wear debris analysis ofAPH bearing and gearbox lub oil once in 3months
Proposed Strategy
Replacement of all lattice
Replacement of all latticesupports
Withdrawal and inspection ofAPH support bearing duringcapital OH.
Wear debris analysis of APHbearing and gear box lub oilonce in 3 months
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Conclusion
Following action can increase OH Gap Replacing eroded tubes below 10%.
Extensive DPT as identified locations. Replacement of ECO upper bank coils once in six
years. Optimization and careful operation of wall blowers. Insitu oxide scale measurement once in two years and
replacing higher oxide scale tubes. Installation of gate for isolating milling system near
burner.
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Conclusion
Educating the maintenance contract personnel aboutpossible maintenance induced defect.
Radiography of all welded joints.
Replacing vents and drains periodically.
Heating and cooling boiler in normal way.
Wear debris analysis of APH lub oil. Withdrawal of APH bearing for inspection during
capital OH.
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