Boiler Operations
25%of exam
Safety + Emergency
25%of exam
Maintenance + Inspections
20%of exam
Inspection BasicsLayup ModesFouling SignsRepair Limits
Water + Combustion
15%of exam
MN Licensing
15%of exam
Quick Facts
- Agency
- MN DLI
- Pass
- 70%
- Time
- 2.5 hours
- Exam fee
- $50
- Retake wait
- 30 days
- Renewal
- 2 years
- Entry class
- Special
- High pressure
- >15 psig steam
Fire-Tube vs Water-Tube
Fire-tube
- Gases in tubes
- Simpler design
- Lower pressure typical
Water-tube
- Water in tubes
- Higher pressure
- Faster load response
What flows in tubes
Boiler Types
- Fire-tube
- Gases inside tubes
- Water-tube
- Water inside tubes
- Steam drum
- Steam-water separation
- Mud drum
- Sludge collection
- Economizer
- Flue heat to feedwater
- Superheater
- Steam above saturation
- MAWP
- Nameplate max pressure
- NB number
- National Board ID
Swell vs Shrink
Swell
- Load rises
- More bubbles
- Level looks high
Shrink
- Load falls
- Bubbles collapse
- Level looks low
Bubble volume illusion
Level Controls
- Gauge glass
- Visible water level
- Try cocks
- Manual level check
- Water column
- Glass + try-cock header
- Feed regulator
- Auto level control
- Feed pump
- Pressure above boiler
- Check valve
- Stops feed backflow
- Swell
- Level rises on load
- Shrink
- Level falls on unload
Light-Off Order
Level -> Purge -> Pilot -> Main
Verify water4 air changesProve pilotThen main fuel
Safety vs Relief Valve
Safety valve
- Steam service
- Pops full open
- Compressible fluid
Safety relief
- Hot-water service
- Opens proportionally
- Liquid/gas capable
Steam pops; water modulates
Emergency Picker
- LWCO trips→Secure burner(No cold water)
- Level disappears→Kill fire(Cool first)
- Smell gas→Evacuate(No switches)
- Flame failure→Fuel valves close(FFRT ≤4 s)
- Before light-off→Pre-purge(4 air changes)
- After shutdown→Post-purge(Clear vapors)
- Leaking safety valve→Report + remove(VR shop)
- Tube leak found→Document + plan outage(Monitor level)
Safety Devices
- Safety valve
- Pops for steamASME
- Safety relief
- Proportional for liquid
- LWCO
- Burner off on low water
- High-limit
- Manual-reset overpressure
- Operating control
- Cut-in / cut-out
- Flame scanner
- Proves flame present
- Fusible plug
- Melts on dry fire
- >500 sq ft HS
- Two safety valves min
Low-Water Rule
Fire off first; never add blind
Secure burnerNo cold waterCool metalFind cause
Operating vs High-Limit
Operating control
- Normal cut-in/out
- Auto restart
- Holds band
High-limit
- Safety overpressure
- Manual reset
- Investigate first
Run vs lockout
Emergency Actions
- LWCO trip
- Secure fire; no water
- Level out of sight
- Kill fire; cool first
- Gas odor
- Evacuate; no switches
- Furnace explosion
- Fuel off; evacuate
- Pre-purge
- Four air changes min
- Post-purge
- Clear after shutdown
- FFRT
- Fuel off ≤4 seconds
- Water hammer
- Condensate slug surge
Wet vs Dry Layup
Wet layup
- Short idle
- Full treated water
- Exclude air
Dry layup
- Long idle
- Drain + desiccant
- Seal openings
Idle duration chooses method
Inspection + Layup
- Internal inspection
- Typically annual DLI
- Nameplate
- MAWP + stamps
- Hydro test
- Water pressure integrity
- Wet layup
- Treated full for short idle
- Dry layup
- Desiccant for long idle
- Soot blower
- Clean fireside deposits
- Refractory
- Furnace heat shield
- Leaking SV
- VR shop repair only
Bottom vs Surface Blowdown
Bottom
- Sludge/sediment
- Short full opens
- Lowest point
Surface
- Dissolved solids
- Continuous skim
- Near waterline
Solids settle vs dissolve
Chemistry Picker
- Hardness present→Softener(Zero hardness out)
- Dissolved oxygen→Deaerator + sulfite(Stop pitting)
- High TDS→Surface blowdown(Cut carryover)
- Settled sludge→Bottom blowdown(Short bursts)
- Foaming/carryover→Chemistry + level(Not more fire)
- Low condensate pH→Amines(CO2 acid)
- Short idle→Wet layup(Treated full)
- Long idle→Dry layup(Desiccant)
Water Chemistry
- TDS
- Dissolved solids load
- Hardness
- Ca/Mg scale risk
- Softener
- Removes hardness ions
- Deaerator
- Strips dissolved O2
- Sodium sulfite
- Oxygen scavenger
- Boiler pH
- About 10.5–11.5
- Oxygen pitting
- Deep localized corrosion
- Scale
- Insulates heating surface
Draft Picker
- Push air in→Forced draft(Positive tendency)
- Pull gases out→Induced draft(Stack fan)
- Near atmospheric→Balanced draft(FD + ID)
- Trim excess air→Flue O2(Avoid CO)
- Recover stack heat→Economizer(Feedwater)
- Preheat combustion air→Air preheater(Efficiency)
- Rising stack temp→Clean fouling(Soot/scale)
- Match load smoothly→Modulating burner(Not on/off)
Blowdown
- Bottom blowdown
- Remove sludge briefly
- Surface blowdown
- Control TDS continuously
- Blowdown tank
- Cool before sewer
- Carryover
- Water leaves with steam
- Foaming
- Stable surface bubbles
- Priming
- Violent water surge
- Excess blowdown
- Wastes heat + water
- Column blowdown
- Clear false level
Combustion + Draft
- Excess air
- Air beyond stoichiometric
- Flue O2
- Excess-air indicator
- Incomplete burn
- CO + soot risk
- Forced draft
- Fan pushes furnace air
- Induced draft
- Fan pulls stack gases
- Balanced draft
- FD + ID near neutral
- Air preheater
- Flue heat to combustion air
- High stack temp
- Fouling or excess air
Letter Grades
C=low | B=high+low | A=turbines
C: low onlyB: high+lowA: engines/turbinesA includes B
Grade C vs Grade B
Grade C
- Low pressure only
- ≤15 psig steam
- Narrower scope
Grade B
- High + low
- >15 psig allowed
- No turbines
Pressure scope
Class Picker
- No experience yet→Special(50 Q)
- Low pressure only→C grade(≤15 psig)
- High + low boilers→B grade(No turbines)
- Need turbines too→A grade(Includes B)
- ≤100 HP charge→2nd Class(500 shift)
- ≤500 HP charge→1st Class(Unlimited shift)
- Unlimited plant→Chief(1st for 1 year)
- Document hours→Notarized affidavit(Rule 5225.0550)
License Classes
- Special
- Entry; no experience50 Q
- 2nd Class
- Limited HP plant
- 1st Class
- Higher HP plant
- Chief
- Unlimited HPTop
- 2-C / 1-C / Ch-C
- Low pressure only
- 2-B / 1-B / Ch-B
- High + low pressure
- 2-A / 1-A / Ch-A
- Boilers + turbines
Class Ladder
Special -> 2nd -> 1st -> Chief
Special: 50/100 HP2nd: 100/5001st: 500/unlimChief: unlimited
Letter Grades + HP
- Grade C
- Low-pressure boilers
- Grade B
- High + low boilers
- Grade A
- Boilers + engines
- Special HP
- 50 charge / 100 shift
- 2nd Class HP
- 100 charge / 500 shift
- 1st Class HP
- 500 charge / unlimited
- Chief HP
- Unlimited charge + shift
- High-pressure steam
- >15 psigASME
Exam + Affidavit
- Pass mark
- 70% minimum
- Time limit
- 2.5 hours all exams
- Application fee
- $50 includes exam
- Fail wait
- 30 days + reapply
- Affidavit
- Notarized experience proof
- Rule 5225.0550
- Who may sign affidavit
- License term
- 2 years; end of month
- Expired >2 years
- Retest usually required
Common Traps
Fifth-class myth
MN uses Special–Chief ≠ Not 5th–1st numbering
Must hold Special first
Special needs no experience ≠ Higher classes need affidavit
Add water on LWCO
Secure fire first ≠ Cold water can explode
Safety vs relief
Steam valves pop ≠ Hot-water valves modulate
Swell as true high
Bubbles raise level ≠ Do not cut feed rashly
Skip pre-purge
Four air changes required ≠ Bypass risks furnace blast
Gag leaking SV
Never gag in service ≠ VR-certified repair only
Last Minute
- 1.Pass 70%; 2.5 hr; $50 fee
- 2.Special = entry; Chief = unlimited
- 3.C low; B high; A turbines
- 4.High-pressure steam = >15 psig
- 5.LWCO trip: fire off; no water
- 6.Pre-purge: four air changes
- 7.Safety pops steam; relief for water
- 8.Bottom=sludge; surface=TDS
- 9.Swell rises; shrink falls
- 10.Affidavit notarized; 30-day retake
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