Power Eng 5th Class cheat sheet

ASME Section I covers power boilers; Section IV covers heating boilers; Section VIII covers unfired pressure vessels.

MAWP is the maximum allowable working pressure calculated from wall thickness, material allowable stress, and joint efficiency.

Boiler horsepower: 1 BHP = 33,475 BTU/h = 9.81 kW = 34.5 lb steam/h at 212°F.

Factor of safety on ultimate tensile strength is typically 3.5 to 4 for boiler plate; design uses allowable stress, not yield alone.

Shell thickness formula (ASME): t = P·R / (S·E − 0.6P) + corrosion allowance, where P = design pressure, R = inside radius, S = allowable stress, E = joint efficiency.

Safety valve set pressure must not exceed MAWP; for power boilers the valve must be set at or below MAWP and capacity must handle maximum steaming rate.

Hydrostatic test pressure for new boilers is typically 1.5 times MAWP; for existing vessels it may be reduced per code.

Stay bolts and ligaments: stayed surfaces require staybolt pitch and diameter to satisfy bending stress limits in ASME Section I.

Fusion-welded joints have joint efficiency E = 1.0 (full radiography), 0.85–0.95 (spot), or lower for non-radiographed seams.

Stoichiometric air for natural gas ≈ 10:1 by volume; for fuel oil ≈ 14.5:1 by mass; excess air 5–15% for gas, 10–20% for oil.

Three T's of combustion: Time, Temperature, Turbulence - all must be sufficient for complete combustion.

Flame failure response: pilot and main flame scanners must prove flame within 10 seconds (pilot) and 4 seconds (main) per NFPA 85 timing.

Pre-purge: at least 5 air changes of the furnace and breeching before light-off; typical duration 30–60 s for small boilers.

Low-water fuel cutoff must be tested daily (or per jurisdiction) by blowing down the float chamber; burner must trip on low water.

Drum level should be maintained at normal water level (NWL); swell and shrink cause false level readings during load changes.

Combustion efficiency: dry flue gas loss = (stack temp − ambient temp) × (A1 / %CO2 + B) for natural gas; typical A1 ≈ 0.38, B ≈ 0.5.

Furnace draft: balanced draft boilers maintain −0.05 to −0.1 in. w.c. at furnace outlet; positive pressure boilers run +0.5 to +2 in. w.c.

Safety interlock sequence: purge → pilot ignition → pilot proven → main flame → main proven → modulation enabled.

Boiler explosion vs. pressure vessel rupture: boiler explosions release stored energy of hot water flashing to steam - energy ≈ 1 BTU per lb per °F above saturation.

Immediate actions on low water: shut off fuel, do not add water to a hot empty boiler, allow to cool slowly, notify supervisor.

ASME Code and jurisdictional boiler acts require annual internal inspection and periodic external inspection; certificate of inspection must be posted.

Confined space entry requires atmospheric testing (O2 19.5–23.5%, LEL <10%, H2S <10 ppm, CO <35 ppm), permit, attendant, and rescue plan.

Lockout/tagout: isolate all energy sources (fuel, steam, electrical, pneumatic), verify zero energy, apply personal lock and tag.

Emergency shutdown: trip fuel, close main fuel valve, keep FD fan running to purge unburned gases, then stop fan.

OSHA 1910.261 covers pulp/paper and 1910.263 bakery equipment, but general boiler safety falls under 1910.147 (LOTO) and 1910.119 (PSM for >100 psig steam).

Reportable incidents: any boiler accident causing injury or property damage must be reported to the jurisdictional authority within 24 hours (typical).

PPE for boiler room: safety glasses, hearing protection >85 dBA, gloves, and face shield for blowdown.

Centrifugal pump affinity laws: Q ∝ N, H ∝ N², P ∝ N³; also Q ∝ D, H ∝ D², P ∝ D³ for impeller diameter change.

NPSH available = (P_atm + P_static − P_vapor)/ρg − h_friction; NPSH required must be less than available to avoid cavitation.

Boiler feed pump must overcome drum pressure plus economizer and piping losses; typically sized for 110% of maximum steaming rate.

Positive displacement pumps (gear, piston, diaphragm) deliver constant flow regardless of pressure; require relief valve on discharge.

Compressor types: reciprocating (high pressure, low flow), rotary screw (medium pressure, continuous), centrifugal (high flow, low pressure).

Air compressor intercooler reduces air temperature between stages, improving efficiency and condensing moisture.

Fan laws: CFM ∝ RPM, static pressure ∝ RPM², horsepower ∝ RPM³.

Pump cavitation symptoms: noise, vibration, reduced flow, pitting on impeller; cure by increasing NPSH available or reducing suction lift.

Deaerator removes dissolved O2 and CO2 by heating feedwater to saturation and venting; operates at 5–15 psig for 227–250°F.

Scale is primarily calcium and magnesium salts; hardness is measured as ppm or grains per gallon (1 gpg = 17.1 ppm as CaCO3).

Softener exchange: 2 Na+ exchanged for 1 Ca2+ or Mg2+; regenerate with brine (NaCl).

Alkalinity and pH control: boiler water pH 10.5–11.5 to prevent corrosion; caustic embrittlement risk if alkalinity too high in high-pressure boilers.

Dissolved oxygen causes pitting; remove with deaerator (mechanical) plus oxygen scavenger (sodium sulfite or hydrazine).

Blowdown controls dissolved solids: conductivity target typically 3,000–5,000 µS/cm for low-pressure boilers; continuous blowdown from surface, bottom blowdown for sludge.

Silica carryover: limit silica in boiler water to ~150 ppm for pressures <600 psig to prevent turbine deposits.

Phosphate treatment precipitates calcium as hydroxyapatite sludge; polymer dispersants keep sludge fluid for blowdown.

Condensate return: monitor for iron and copper corrosion products; pH 8.5–9.5 with amine filming.

Foaming and priming caused by high dissolved solids, organics, or oil; controlled by blowdown and antifoam.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Three-phase power: P = √3 × V_line × I_line × PF; single-phase P = V × I × PF.

Thermocouple types: J (iron-constantan, 0–750°C), K (chromel-alumel, 0–1250°C), T (copper-constantan, −200–350°C).

RTD (resistance temperature detector) uses platinum (Pt100) with positive temperature coefficient; more accurate than thermocouple at low temperatures.

4–20 mA current loop: 4 mA = zero, 20 mA = full scale; live zero allows broken wire detection.

PID control: proportional band = 100/%gain; integral (reset) eliminates offset; derivative (rate) anticipates error.

Boiler control types: on/off, high-low-fire, modulating; modulating uses PID to match steam demand.

Electrical hazards: 120 V across body can be lethal; use GFCI, lockout, and test before touch.

Flame safeguard: ultraviolet scanner responds to UV radiation; infrared scanner to IR; both must prove flame signal within trial-for-ignition time.

Refrigeration cycle: compressor → condenser (reject heat) → expansion valve (drop pressure) → evaporator (absorb heat) → compressor.

Refrigerant R-134a is HFC, R-410A is HFC blend, R-22 is HCFC (phase-out); ozone depletion potential (ODP) of HFCs is zero but GWP is high.

Superheat = actual vapor temperature − saturation temperature; subcooling = saturation temperature − liquid temperature.

Sensible heat changes temperature; latent heat changes state; total heat = sensible + latent.

Psychrometrics: dry-bulb (DB) temperature, wet-bulb (WB), relative humidity, dew point; comfort zone 68–75°F DB, 30–60% RH.

Air handling unit components: filter, heating coil, cooling coil, humidifier, fan, dampers.

Chiller types: reciprocating, scroll, screw, centrifugal; absorption chillers use heat instead of compressor work.

Cooling tower approach = leaving water temperature − wet-bulb temperature; range = entering − leaving water temperature.

Duct static pressure control: VAV systems modulate fan speed or inlet vanes to maintain static setpoint.