strategy for extennding gap between og overhaul

7/31/2019 Strategy for Extennding Gap Between Og Overhaul

1/27

Strategy to increase the gap

betweenOH of ST-I units

By Boiler Maint Dept


2/27

WATER WALL

LIMITING FACTORS

Erosion at S panel. Steam erosion due to

wall blower

Fatigue failure at

bottom end finsbetween panels

Weld joint


3/27

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


4/27

Radiant Super heater

LIMITING FACTORS

Steam erosion due towall blower

Weld joint

Mechanical rubbing of

clamps. Blockage of tube during

maint


5/27

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.



6/27

Platen Super heaters

LIMITING FACTORS

Mechanical rubbing dueto binders, connectorsand shop joints.

Weld joint

Long term overheating

Blockage of tube duringmaint


7/27

Strategy for Platen Super heater

Present practices Thorough inspection.

Tube rep after 20% erosion.

Insitu oxide scalemeasurement everyalternate year



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.


8/27

Reheaters-II & III

LIMITING FACTORS

Mechanical rubbing dueto T spacers.

Weld joint

Long term overheating

Maint induced defect


9/27

Strategy for Reheater II &III

Present practice Thorough inspection.


Insitu oxide scalemeasurement everyalternate year





every alternate year

Replacement of tubes havinghigher oxide scale.





10/27

Regulating Stage Reheater

LIMITING FACTORS

Long term overheating.

Random flue gaserosion.

Constraint forinspection

Weld joint



11/27

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.


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.


12/27

Economiser

LIMITING FACTORS

Constraint forinspection

Flue gas erosion.

Weld joint



13/27

Strategy for Economiser


approachable area.

Modular replacement


Inspection and repair of

lower bank coils No gas cutting at vertical.

plastic capping



Replacement of upper bankcoils in every 6 years in phasedmanner.

Inspection and repair of lowerbank coils





14/27

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



15/27

Strategy for SCW & Hangers


approachable area.


DPT of end fins betweenpanels

No gas cutting at vertical.

plastic capping


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.


16/27

vents and drains

LIMITING FACTORS

Corrosion.

Stub joint

Weld joint

Mechanical rubbing of

lines at pent houseentry.



17/27

Strategy for Vents and drains

Present practice Thorough inspection after

removal of insulation. DPT of stubs.


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.


18/27

Pent house

LIMITING FACTORS

Mechanical rubbing

Stub joint.

Weld joint

Spray line stubs



19/27

Strategy for Pent house

Present practice Thorough inspection by team. DPT of stubs.


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.


20/27

Coal burners

LIMITING FACTORS

Minor erosion of coalnozzle

Erosion in coal nozzletips is minimum.

Coal nozzle area oferosion can bestrengthened life canbe extended.


21/27

Milling system

LIMITING FACTORS

More than 50 percentbends are MSfabricated.

Coal pipe orifice.

MDVs, MPOs

RCfeeder chute

Mill inner cone


22/27

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


23/27

Airpreheaters

LIMITING FACTORS

CE baskets lattice andtheir support.

APH support bearing


24/27

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


25/27

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.


26/27

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.


27/27

strategy for extennding gap between og overhaul

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