Power Eng 5th Class flashcards
Power Eng 5th Class · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- MAWP
- Maximum allowable working pressure: the highest pressure at which a boiler or pressure vessel may operate under design conditions, based on wall thickness, material strength, and joint efficiency.
- Boiler horsepower
- A measure of boiler capacity equal to 33,475 BTU/h, equivalent to evaporating 34.5 lb of water per hour at 212°F and atmospheric pressure.
- Joint efficiency
- A factor (E) applied in pressure vessel design to account for the strength of welded seams relative to seamless plate; ranges from 0.6 to 1.0 depending on radiography.
- Hydrostatic test
- A pressure test using water to verify vessel integrity, typically at 1.5 times MAWP for new boilers; water is used because it stores little energy if rupture occurs.
- Safety valve
- A spring-loaded pressure relief device that opens automatically at set pressure to discharge steam and protect the boiler from overpressure; must be set at or below MAWP.
- Stoichiometric combustion
- The ideal air-fuel ratio where all fuel is burned with exactly the theoretical amount of oxygen, producing only CO2, H2O, and N2; excess air is added in practice.
- Pre-purge
- A forced-air period before ignition that removes combustible gases from the furnace and breeching, typically at least five air changes or 30–60 seconds.
- Flame failure response
- The safety action that shuts off fuel within a specified time (often 4 seconds for main flame) when the flame scanner loses the flame signal.
- Low-water cutoff
- A safety device that trips the burner when boiler water level falls below a safe point, preventing overheating and explosion; must be tested regularly.
- Swell and shrink
- Transient false level readings caused by steam bubble expansion (swell) on load increase or contraction (shrink) on load decrease, affecting drum level indication.
- Excess air
- Air supplied beyond the theoretical stoichiometric amount, typically 5–15% for gas and 10–20% for oil, to ensure complete combustion and reduce CO and smoke.
- Balanced draft
- A boiler arrangement where forced draft and induced draft fans maintain a slight negative pressure (about −0.05 to −0.1 in. w.c.) at the furnace outlet.
- Boiler explosion
- A catastrophic failure releasing stored energy from pressurized hot water flashing to steam, often caused by low water, overpressure, or scale-induced overheating.
- Lockout/tagout
- A safety procedure isolating all energy sources (fuel, steam, electrical, pneumatic) with locks and tags to prevent accidental startup during maintenance.
- Confined space entry
- Entry into a boiler or vessel requiring atmospheric testing (O2 19.5–23.5%, LEL <10%), a permit, an attendant, and a rescue plan.
- Emergency shutdown
- A procedure that trips fuel, closes the main fuel valve, keeps the forced draft fan running to purge unburned gases, then stops the fan.
- Jurisdictional inspection
- A legally required examination of a boiler by an authorized inspector, typically annual internal and periodic external, with a certificate posted in the boiler room.
- Centrifugal pump affinity laws
- Relationships stating flow varies with speed, head with speed squared, and power with speed cubed; also apply to impeller diameter changes.
- NPSH
- Net positive suction head: the margin between absolute suction pressure and vapor pressure, available at the pump inlet; must exceed the pump's required NPSH to avoid cavitation.
- Cavitation
- Formation and collapse of vapor bubbles in a pump due to low suction pressure, causing noise, vibration, and impeller pitting; prevented by increasing NPSH available.
- Deaerator
- A vessel that heats feedwater to saturation and vents dissolved oxygen and carbon dioxide, typically operating at 5–15 psig and 227–250°F.
- Positive displacement pump
- A pump that moves a fixed volume of fluid per cycle (gear, piston, diaphragm), delivering constant flow regardless of pressure and requiring a discharge relief valve.
- Fan laws
- Relationships for fans: airflow varies with speed, static pressure with speed squared, and horsepower with speed cubed.
- Scale
- Deposits of calcium and magnesium salts on boiler surfaces that reduce heat transfer, cause overheating, and are measured as hardness in ppm or grains per gallon.
- Softener regeneration
- The process of restoring a water softener resin by passing brine (NaCl) through it, exchanging sodium ions for accumulated calcium and magnesium ions.
- Oxygen scavenger
- A chemical such as sodium sulfite or hydrazine added to boiler water to remove residual dissolved oxygen and prevent pitting corrosion.
- Blowdown
- The removal of boiler water to control dissolved solids and sludge; continuous surface blowdown controls conductivity, while bottom blowdown removes sludge.
- Caustic embrittlement
- A cracking failure of boiler metal caused by high caustic alkalinity concentrating in seams and crevices, mitigated by pH and alkalinity control.
- 4–20 mA loop
- An analog instrumentation standard where 4 mA represents zero and 20 mA full scale; the live zero allows detection of broken wires.
- PID control
- A control algorithm using proportional (gain), integral (reset), and derivative (rate) actions to minimize error and stabilize a process such as boiler steam pressure.
- Thermocouple
- A temperature sensor made of two dissimilar metals that generates a voltage proportional to temperature difference; common types are J, K, and T.
- Refrigeration cycle
- A sequence where refrigerant is compressed, condensed (rejecting heat), expanded (dropping pressure), and evaporated (absorbing heat) to provide cooling.