NIULPE 2nd Class cheat sheet

MAWP is set by the weakest pressure-containing component; the safety valve set pressure may not exceed the MAWP stamped on the boiler nameplate.

Safety valve relieving capacity must equal or exceed the boiler's maximum steaming rate; the valve is sized in lb/hr of saturated steam at set pressure.

Each boiler requires at least one safety valve; boilers with more than 500 sq ft of heating surface require two or more, and the total capacity must be adequate with the largest valve out of service where codes require it.

A try lever test confirms valve freedom of movement at no less than 75% of set pressure; a pop test verifies actual set pressure and requires the boiler at normal operating pressure with a qualified witness.

Fusible plugs melt at approximately 445 °F (229 °C); they protect against low water by releasing steam into the furnace when uncovered.

Water column and gauge glass connections must be at least 1 inch NPS, and the gauge glass lowest visible reading must be at the lowest permissible water level.

Blowdown of the water column and gauge glass proves both high and low connections are clear; a slow-returning glass indicates a partially plugged lower connection.

Staybolt spacing and diameter are governed by the flat-plate stayed-surface rules; staybolt pitch is reduced as plate thickness and pressure increase.

Theoretical (stoichiometric) air for natural gas is about 17.2 lb air per lb fuel; for No. 2 oil about 14.4 lb/lb; for coal roughly 11–12 lb/lb depending on analysis.

Excess air targets: natural gas 5–10%, oil 10–15%, coal 15–25%; O2 trim typically holds 3% O2 (gas) or 3–4% O2 (oil) at high fire.

Flue gas CO2 falls and O2 rises as excess air increases; a rising stack temperature with constant O2 signals fouling or poor heat transfer.

Combustion efficiency ≈ 100 − (dry flue gas loss + radiation + unburned losses); dry gas loss rises roughly 1% per 40 °F of stack temperature above ambient at fixed excess air.

Pre-purge must be completed before light-off - typically 4 to 8 air changes of the furnace and gas passages - and the trial-for-ignition period is limited to a few seconds.

Flame scanners must prove main flame within the trial-for-ignition time; loss of flame signal closes the main fuel valve within 4 seconds on most burner management systems.

Low-fire hold, firing rate control, and high/low or modulating firing are interlocked with the drum level and fuel pressure switches.

A furnace implosion results from a sudden loss of flame or fan trip; the draft control must close the ID fan damper and trip fuel immediately on master fuel trip.

Feedwater flow must equal steam flow plus blowdown; blowdown percentage = (blowdown flow / feedwater flow) × 100.

Deaerator removes dissolved O2 by heating to saturation at the deaerator pressure; 5 °F approach to saturation is typical, and O2 residual is held below 7 ppb with scavenger.

Economizer raises feedwater temperature using flue gas; inlet water temperature must stay above the acid dew point (roughly 250–300 °F for oil, lower for gas) to avoid cold-end corrosion.

Steam header and main steam line are protected by a warm-up drain and a safety valve; thermal expansion is absorbed by loops and anchors, not by rigid restraints.

Boiler feed pumps are sized for maximum steaming rate plus margin, with discharge head equal to drum pressure plus line losses and the feedwater regulator drop.

Steam traps: thermostatic traps discharge subcooled condensate, float-and-thermostatic traps discharge continuously, inverted bucket traps cycle; a failed-open trap wastes steam.

Air preheaters recover heat from flue gas to combustion air; a regenerative (Ljungström) unit has leakage from air side to gas side of a few percent.

Soot blowers use steam or air to remove ash deposits; blowing frequency is set by gas-side differential pressure and stack temperature rise.

Rankine cycle efficiency = (h1 − h2) / (h1 − hf2); turbine work is the enthalpy drop across the stages, and condenser loss is the largest single rejection.

Turbine stage efficiency = actual enthalpy drop / isentropic enthalpy drop; a rise in exhaust pressure with fixed throttle flow signals fouling or condenser trouble.

Impulse stages convert pressure to velocity in nozzles; reaction stages convert pressure to velocity in both fixed and moving blades.

Critical speed is the rotor speed where operating speed equals natural frequency; turbines pass through criticals quickly and never dwell at them.

Overspeed trip setting is typically 110% of rated speed; the trip must be tested before each startup and after any governor work.

A steam turbine gland seal uses low-pressure steam to prevent air in-leakage on a condensing unit; excessive seal steam shows as high condenser air ejector load.

Reciprocating engine indicator diagrams show mean effective pressure; MEP × piston area × stroke × strokes per cycle gives work per cycle.

Governor droop = (no-load speed − full-load speed) / full-load speed × 100; isochronous governors have zero droop and are used on isolated loads.

Centrifugal pump affinity laws: flow varies with speed, head with speed squared, power with speed cubed; the same relations apply to impeller diameter.

NPSH available = (pressure at suction surface + static head − vapor pressure) / specific weight − suction friction loss; NPSHa must exceed NPSHr to avoid cavitation.

Best efficiency point (BEP) is where hydraulic efficiency peaks; operating far left of BEP causes recirculation and vibration, far right causes cavitation and overload.

Pump power = (flow in gpm × head in ft × specific gravity) / (3960 × efficiency); a motor driving a pump should be sized above this value with margin.

Reciprocating compressors are positive displacement and need a discharge relief valve and unloaders; centrifugal compressors surge when flow falls below the surge line.

Compressor volumetric efficiency falls as clearance volume and pressure ratio rise; multi-staging with intercooling reduces power and discharge temperature.

Alignment of a motor to a driven machine uses dial indicators or laser alignment; soft foot must be corrected before alignment is recorded.

Vibration severity is judged by velocity (in/s or mm/s) over a frequency band; a 2× running speed peak often indicates misalignment, 1× indicates unbalance.

Sensible heat Q = m × cp × ΔT; latent heat of vaporization of water at atmospheric pressure is about 970 Btu/lb.

One boiler horsepower = 33,475 Btu/hr = 34.5 lb steam/hr from and at 212 °F; 1 kW = 3,412 Btu/hr.

Steam tables: enthalpy of saturated liquid hf, latent heat hfg, and saturated vapor hg; hg = hf + hfg.

Heat transfer by conduction: Q = kAΔT/L; convection follows Q = hAΔT; radiation follows Q = εσA(T1⁴ − T2⁴).

Overall heat exchanger coefficient U combines conduction and convection resistances; Q = U × A × LMTD, with LMTD = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2).

First law for a steady-flow device: q − w = Δh + ΔKE + ΔPE; for a nozzle or turbine with negligible heat loss, work equals the enthalpy drop.

Thermal efficiency of a cycle = net work out / heat in; Carnot efficiency = 1 − Tc/Th with absolute temperatures.

Absolute temperature conversions: °R = °F + 460; K = °C + 273; specific gravity of a gas = molecular weight / 29.

Three-phase power = √3 × V × I × power factor; single-phase power = V × I × power factor.

Motor full-load current is read from the nameplate; conductors and overloads are sized from the applicable code tables, not from the nameplate alone.

Motor slip = (synchronous speed − actual speed) / synchronous speed; synchronous speed = 120 × frequency / number of poles.

A motor starter's overload relay protects the motor from sustained overcurrent; the short-circuit protective device protects the circuit, and the two functions are not interchangeable.

A 4–20 mA loop reads 4 mA at zero and 20 mA at full span; a live zero distinguishes a failed signal (below 4 mA) from a true zero reading.

RTDs change resistance with temperature (platinum 100 Ω at 0 °C); thermocouples produce a millivolt signal and require cold-junction compensation.

Control valves fail-safe position (air-to-open or air-to-close) is chosen so loss of air or power drives the process to a safe state.

Grounding and bonding limit fault voltage; a ground fault on a control circuit trips the circuit rather than leaving exposed metal energized.

Refrigeration capacity: 1 ton = 12,000 Btu/hr = 200 Btu/min; coefficient of performance = refrigeration effect / work input.

The vapor-compression cycle has four steps: compression, condensation, expansion, and evaporation; the expansion valve maintains superheat at the evaporator outlet.

Superheat at the evaporator outlet protects the compressor from liquid slugging; subcooling at the condenser outlet improves capacity and is limited by charge and ambient.

Low suction pressure with high superheat indicates a restricted expansion valve or low charge; high suction with low superheat indicates an overfeeding valve.

Condenser approach temperature is the difference between condensing temperature and entering air or water temperature; a rising approach signals fouling or non-condensables.

Refrigerant safety classification: A1 low toxicity, no flame propagation; B2 and A3 refrigerants require ventilation and ignition-source control.

Psychrometrics: dry-bulb, wet-bulb, dew point, and relative humidity; cooling coil apparatus dew point sets the leaving air condition.

Chilled water flow and temperature difference: capacity = 500 × gpm × ΔT (°F) in Btu/hr for water.

Lockout/tagout requires isolation of all energy sources, verification of zero energy, and a personal lock for each worker; the lock is removed only by the person who applied it.

Confined space entry requires atmospheric testing for oxygen (19.5–23.5%), flammables, and toxics before entry and continuous monitoring during occupancy.

Hot work permits require a fire watch, removal of combustibles, and a check for combustible gas before welding or cutting.

Boiler and pressure vessel rules are enforced by the jurisdiction; the inspector's certificate must be posted, and the boiler may not be operated without a current certificate.

Steam and hot-water piping must be insulated and labeled; safety valves must be piped to a safe discharge point and never plugged or valved off.

Air permits set emission limits for NOx, CO, SO2, and particulates; continuous emission monitors (CEMS) must be calibrated and data retained per the permit.

Wastewater discharge limits apply to boiler blowdown and cooling tower blowdown; pH, temperature, and total dissolved solids are commonly regulated.

OSHA hearing conservation applies at 85 dBA TWA; an 8-hour exposure limit of 90 dBA applies, and noise controls follow the hierarchy of elimination, engineering, and PPE.

Preventive maintenance is scheduled by time or run hours; predictive maintenance triggers work from condition data such as vibration, oil analysis, and thermography.

Overall equipment effectiveness (OEE) = availability × performance × quality; each factor is measured against planned production time.

Mean time between failures (MTBF) = total operating time / number of failures; mean time to repair (MTTR) = total repair time / number of repairs.

A work order system tracks labor, parts, and downtime; backlog is measured in crew-weeks and is typically held between 2 and 4 weeks.

Root cause analysis tools include the 5-Whys, fishbone diagram, and fault tree; corrective action is verified by recurrence data, not by the report alone.

Critical spares are identified by failure consequence and lead time; a part with long lead time and high downtime cost is stocked regardless of price.

Shift turnover must document boiler status, abnormal conditions, open permits, and equipment out of service; verbal-only handoff is not acceptable.

Training records, licenses, and confined-space and hot-work authorizations are auditable documents and are retained per the jurisdiction's schedule.