Post on 24-Jan-2021
Routine Boiler Maintenance & Inspection5th Class Power Engineering Book 1, Unit 3 Chapter 12
Learning Outcome
Describe the service and maintenance required for boilers. Discuss the procedure for preparing a boiler for inspection and cleaning, and describe mechanical boiler cleaning methods
Glossary
• Combustion gases
• Rattler
• Soot blower
• Tags
Objective 1Describe the general servicing and routine maintenance of packaged firetube and cast-iron sectional boilers
Packaged Firetube Boiler Maintenance
• General maintenance• Watch for leaks in steam, water, fuel connections
• Tension on front and rear door closing bolts
• Feedwater pump packing glands
Door Bolts
Packaged Firetube Boiler Maintenance
• Lubrication• Blower motors
• Large valves have grease nipples to keep stems lubricated
• Gas valves
Packaged Firetube Boiler Maintenance
• Cleaning a new boiler• Take offline, shut down, drain, open, flush
• After first three months of operation
• Then annually unless more often warranted
Packaged Firetube Boiler Maintenance
• Cleaning the fireside• Open front and rear doors according to manufacturers instructions
• Remove flame retarders from tubes if used
• Brush soot, combustion debris
• Reinstall flame retarders if used
• Close doors according to manufacturers instructions
https://www.youtube.com/watch?v=bwuFEZBsxSA
https://www.youtube.com/watch?v=bwuFEZBsxSA
Packaged Firetube Boiler Refractory Maintenance
Packaged Firetube Boiler Maintenance
• Burner Maintenance • Observe flame in operation
• Remove burner for inspection, clean of soot/build-up
• Gas/oil fitter to set up annually using combustion analyser
Cast-iron Sectional Maintenance—Steam
• Steam boilers waterside drained, opened, cleaned• Gauge glass, piping, washout plugs, low water cut-off bodies
• Clean fireside• Soot, carbon is corrosive over the summer
• Re-assemble and leave full of water or in dry condition• Add corrosion treatment chemical
Cast-iron Sectional Maintenance—Hot Water
• Hot water boilers—do not open waterside• Isolate, dismantle, clean low water cut off body
• Clean fireside
Objective 2Explain the importance of lay-ups and state the procedures to be followed for wet and dry boiler lay-ups
Dry Lay-up
• Boiler out of service for a prolonged period
https://www.suezwatertechnologies.com/handbook/handbook-industrial-water-treatment
https://www.suezwatertechnologies.com/handbook/handbook-industrial-water-treatment
Dry Lay-up
• Clean waterside and fireside
• Inspect boiler, make necessary repairs
• Dry boiler completely—absorbing material (slack lime, silica gel, activated alumina), or blower
• Close manhole and handholes
• Protect fireside from corrosion by coating with mineral oil; close dampers to keep fireside dry
• Keep boiler and surrounding tidy
Wet Method
• Boiler on standby, ready for service• Clean boiler
• Fill and fire to drive oxygen from water
• Add chemicals to adjust alkalinity and oxygen scavenger
• Once boiler cooled, fill completely and connect drum to vent line; half fill drum with treated water
• Coat fireside with mineral oil
• Check boiler water chemical at least monthly
Objective 3 Describe symptoms of a leaking firetube
Boiler Repairs
• Consult with Office of the Fire Commissioner
• http://www.firecomm.gov.mb.ca/itsm_steam_pressure.html
http://www.firecomm.gov.mb.ca/itsm_steam_pressure.html
Defective Firetubes
• Tube failure• Overheating
• Caused by excessive firing rate
• poor water circulation
• heavy scale on the tubes (poor heat transfer)
• a low water condition
• Corrosion
• Cracked tube ends
Defective Firetubes
• Indicated by leakage• Minor leaks cause staining on tubesheet
• Major leaks cause water dripping from front or rear door
• Hissing sound at front or rear door
• Steam in the chimney (billowy white/black smoke)
Tube Attachment
Cracks in tube ends/tube sheet
• Develop over time
• Can seal under heat, open when boiler cools
• Hot/cool cycle speeds crack growth
Leak
• Shut down boiler firing immediately
• Close steam stop valve
• Close hot water stop and return valves
• Maintain normal water level/pressure
• Open front/rear doors and look
Cracks in tube ends/tube sheet
• Non-destructive testing (NDE)• Dye-penetrant
• Developer highlights crack
• Black Light• Penetrant under UV lights
Objective 4 List the steps and precautions to be taken to prepare a boiler for inspection
Annual certification inspection—OFC
• Steam boilers—internal
• Hot water boilers—operational/external
Internal Inspection
• Take boiler off line, cool, open vent
• Drain, flush
• Lockout-tagout (tagged valves) all sources of energy• Steam
• Water
• Electrical
• Take pumps/auxiliaries offline
• Open boiler waterside
• Open boiler fireside
• 12 V lighting; grounded & waterproof fixtures, ground extension cords, grounded
• PPE, confined space procedures
Internal Inspection
Open manholes
Internal Inspection
Internal Inspection
Flush tubes
Objective 5 Describe the inspection of a boiler
Inspections
• External (Operational)• Hot water boilers
• Internal• Waterside
• Fireside
Internal Fireside Inspection
• Cracking, corrosion, erosion, leakage• Tubesheet
• Fireside of tubes
• Furnace tube/firebox
• Refractory
• Indications of combustion performance
Internal Waterside Inspection
• Boiler drums
• Drum internals
• Tubes/tube connections
• Fittings (LWCO, connecting piping)
• Stays
• Manhole/handhole flange condition
• Scale, corrosion, pitting, cracking, indications of chemical treatment
Furnace Stays
Through or longitudinal
Diagonal
Staybolts
Firetubes
Firebox Boiler/Firetube Boiler Stays
Objective 6
• Describe methods and tools used for mechanical and chemical cleaning of a boiler
Boiler Cleaning
• Mechanical• “rattler”—air-driven hammer put through firetube boiler tubes to hammer
scale off the waterside
• Air or water driven brushes & cutting heads for waterside of watertubeboilers
• Wire brush for fireside of firetube “punch” tubes
Chemical Cleaning
• Alkaline boil out of new boiler to eliminate grease/oil• Caustic soda (sodium hydroxide/NaOH)
• Soda ash (Sodium Carbonate/Na2CO3)
• Sodium phosphate (Na2PO4)
• Sodium nitrite (NaNO2)
• Sodium sulphite (Na2So3)
• Raise and maintain pressure for 48 hours
• Inhibited Acid Cleaning• 5% hydrochloric acid
• 65C/150F
• Circulation Method
• Soak method
Boiler Cleaning
• Inhibited Acid• Dilute (5%), inhibited HCl or other acid/chealants
• Depending on constituents in deposit
• Non-ferrous parts protected
• Proper venting—H2 gas formed
• PPE, WHMIS, disposal
• Proper neutralization afterward cleaning
Inhibited Acid Cleaning
• Circulating Method• 65C (150F)
• Soak Method• 65C (150F)
Objective 7
• Discuss the standard procedure for a hydrostatic test and the reasons for doing the test
Hydrostatic Test
• Check for tightness of the pressure vessel• Always after weld repair
• Confirm suspected leak
Why “hydro”
• Water is non compressible
• If the pressure vessel fails during test, water will leak out at same volume at atmospheric pressure as it is at test pressure
• If a compressible gas (air, nitrogen) were to be used, and the pressure vessel fails, the gas volume would increase quickly (explosively) as it dropped from test pressure to atmospheric pressure
Hydrostatic test pressure
• 1.5 x MAWP as stamped on boiler
Procedure
• Close boiler except for vent and feedwater
• Isolate/remove gauge glass and controls that cannot withstand 1.5 x MAWP
• Remove safety valves (or gag)
• Fill completely with ambient temperature water (overflow the vent, then close vent)
• Use pump to raise to test pressure
• Hold test for 24 hours
• Bleed pressure slowly after test
Hydrostatic Pump
Sootblower
• An in-boiler device used to blow accumulated soot or ash off tubes and heating surfaces