NIULPE Class 5 cheat sheet

Boiler fittings are the appurtenances required for safe operation: safety valve, pressure gauge, water column/level indicator, low-water fuel cutoff, and blowdown valves; accessories (feed pump, economizer, air preheater, superheater) improve efficiency but are not safety fittings.

A safety valve on a power boiler must be set at or below the maximum allowable working pressure (MAWP) and sized so total relieving capacity exceeds maximum steaming capacity; the boiler cannot be fired with the safety valve gagged or with the outlet blocked.

The water column must have a visible connection at least 1 in. (25 mm) diameter and be mounted so the normal water level is at its center; the gauge glass lowest visible reading must be above the highest fire line in the furnace.

A low-water fuel cutoff must be tested by slow drain-down (evaporation test) and by the quick-drain method; the burner must shut off before the water drops out of the visible glass.

Staybolts carry load between tube sheets and shells in firetube and locomotive-type boilers; telltale holes in hollow staybolts leak when a stay cracks, giving early warning.

Fusible plugs melt at roughly 450 F (232 C) to release water onto the crown sheet if water level is lost; they are a warning device, not a substitute for low-water protection.

Handhole and manhole openings use gaskets and yokes; a manhole is elliptical (typically 11 x 15 in. or larger) for personnel access, handholes are smaller for inspection and cleaning of watersides.

Refractory and insulation: castable refractory protects tube sheets and furnace floors; mineral wool or calcium silicate block insulation limits shell heat loss; expansion joints absorb differential thermal growth between shell and settings.

Normal startup sequence: purge furnace with air at 25-50% of full airflow for the required purge time, prove ignition, light off at low fire, then raise load gradually; a purge that does not meet airflow or time interlocks must block light-off.

Flame failure response time: on loss of flame the fuel valve must close within 4 seconds (or the code-required interval) and a post-purge must follow before any relight attempt.

Three-element feedwater control uses drum level, steam flow, and feedwater flow; it corrects level before the shrink/swell effect of steam flow changes causes false level readings.

Combustion controls follow a burner management interlock chain: pre-purge, ignition trial, main flame proven, low-water, high-pressure, low-pressure, and high-temperature limits wired in series so any open contact stops fuel.

Boiler efficiency rises roughly 1% for each 40 F drop in stack temperature, but stack temperature must stay above the acid dew point (about 250-300 F for natural gas, higher for oil/coal) to avoid corrosion.

Blowdown: bottom blowdown removes sludge and sediment, surface (continuous) blowdown controls dissolved solids; blowdown should be done at low fire with the water level above normal to avoid low-water trip.

Short cycling occurs when the boiler is oversized relative to demand; symptoms include frequent burner starts, wide pressure swings, and high stack losses from repeated purge cycles.

Safety valve pop test: raise pressure until valve lifts, record set pressure and reseat pressure; reseat should occur within 2-5% below set pressure, and the valve must be tested at the required interval with the boiler under the supervision of a qualified operator.

Gate valves are for isolation only (fully open or closed); globe valves provide throttling and are installed with flow under the seat; check valves permit one-direction flow and are placed downstream of pumps and at boiler outlets.

Steam trap types: thermostatic (responds to temperature), mechanical/float-and-thermostatic (responds to density), and thermodynamic/inverted bucket (responds to velocity and flash); a failed-open trap causes steam loss, failed-closed causes waterlogging.

Pipe expansion: carbon steel expands about 0.0000065 in./in.-F; an 80 ft run heated 300 F grows about 1.9 in., which must be absorbed by loops, offsets, or expansion joints.

Steam main warm-up and draining: open bypass and drain valves ahead of the main valve, warm slowly to avoid water hammer, and keep drains open until steam reaches the traps.

Water hammer causes: trapped condensate, sudden valve closure, flash steam collapsing in cold condensate; prevention uses proper drainage, slow valve operation, and adequate trapping at low points.

Hot water system pressure: a compression tank or expansion tank absorbs thermal expansion; the relief valve is set at or below the system component rating, and the fill valve maintains minimum static pressure at the highest point.

Safety valve piping: discharge must be piped to a safe point of discharge, drain freely, and not be restricted; the discharge pipe must not impose load on the valve body.

Steam quality and superheat: saturated steam at 100 psig is about 338 F; superheated steam temperature depends on the superheater, and piping must be designed for the higher temperature with proper support and insulation.

Centrifugal pump affinity laws: flow varies with speed (Q2/Q1 = N2/N1), head with the square (H2/H1 = (N2/N1)^2), and power with the cube (P2/P1 = (N2/N1)^3).

Cavitation occurs when local pressure drops below vapor pressure; symptoms are noise, vibration, and reduced head; prevention is adequate NPSH available, cool feedwater, and a properly sized suction line.

NPSH available = (pressure at suction source + static head - friction losses - vapor pressure) expressed in feet of head; NPSH required is a pump characteristic and must be less than available.

Positive displacement pumps deliver nearly constant flow against varying pressure and require a relief valve on the discharge; centrifugal pumps can run against a closed valve briefly but will overheat if left deadheaded.

Boiler feed pumps are sized for maximum steaming rate plus margin, with discharge pressure at least boiler pressure plus drum elevation plus piping losses; standby capacity is common on power boilers.

Air compressors: reciprocating units are positive displacement with pulsating flow and require receivers and aftercoolers; rotary screw units are continuous-duty; moisture is removed by separators and dryers.

Auxiliary equipment: economizers preheat feedwater using flue gas; air preheaters warm combustion air; deaerators remove oxygen and heat feedwater to saturation; sootblowers clean fireside surfaces with steam or air.

Pump alignment and lubrication: coupling alignment within manufacturer tolerance, proper lubricant level, and free rotation before start prevent bearing and seal failures; vibration monitoring detects early faults.

Stoichiometric air for natural gas is about 10:1 by volume (roughly 17 lb air per lb fuel); for fuel oil about 14.4 lb air per lb fuel; for coal about 10-12 lb air per lb fuel depending on analysis.

Excess air: natural gas typically 5-10%, oil 10-15%, coal 15-25%; too little excess air produces CO and smoke, too much lowers efficiency by carrying heat up the stack.

Combustion products: theoretical CO2 is about 11.8% for natural gas, 15.5% for oil, 18-19% for coal; measured CO2 lower than theoretical indicates excess air.

Draft systems: natural draft relies on stack height and temperature difference; forced draft uses a fan before the furnace; induced draft uses a fan after the boiler; balanced draft uses both and maintains furnace pressure slightly negative.

Flue gas dew point: water vapor dew point is about 130-140 F; sulfur in fuel raises the acid dew point above 250 F, so cold-end temperatures must stay above it.

Fuel oil properties: viscosity affects atomization and is controlled by heater temperature; API gravity, pour point, flash point, and sulfur content are key specification values; No. 2 oil is lighter than No. 6.

Coal characteristics: proximate analysis gives moisture, volatile matter, fixed carbon, and ash; ultimate analysis gives C, H, O, N, S; grind fineness affects combustion and unburned carbon loss.

Combustion safety: fuel/air mixture must be within flammability limits; gas leaks are detected before light-off; a combustible gas detector and proper ventilation are required in gas-fired boiler rooms.

Scale forms when hardness (calcium and magnesium) precipitates on hot surfaces; it insulates tubes and can cause overheating and tube failure; softening removes hardness by ion exchange.

Oxygen corrosion (pitting) is controlled by deaeration plus chemical oxygen scavengers such as sodium sulfite (for lower-pressure boilers) or hydrazine/carbohydrazide (for high-pressure systems).

pH control: boiler water typically 10.5-11.5 for carbon steel protection; low pH causes acidic corrosion, high pH promotes caustic embrittlement and foaming.

Alkalinity and TDS are controlled by blowdown; high dissolved solids cause carryover and foaming; silica limits are tighter at high pressure to prevent turbine deposits.

Phosphate treatment precipitates calcium as sludge for blowdown; chelant treatment keeps hardness in solution but can corrode if overdosed; polymer dispersants keep sludge fluid.

Conductivity is the usual field measure of dissolved solids; a conductivity meter reading is compared to the boiler water limit, and blowdown rate is adjusted to hold TDS within range.

Condensate return quality: iron and copper corrosion products indicate corrosion; condensate polishing or amine treatment protects the system; returning clean condensate saves energy and makeup water.

Water testing frequency: daily or shift tests for pH, conductivity, and hardness on operating boilers; records are required by many jurisdictions and support the logbook inspection.

ASME Boiler and Pressure Vessel Code Section I covers power boilers, Section IV covers heating boilers; the ASME Code is the construction standard adopted by most jurisdictions.

NBIC (National Board Inspection Code) governs repairs, alterations, and inspections of in-service boilers; a stamped repair nameplate and a certified welder are required for pressure-retaining repairs.

Jurisdictional inspection: most states require annual certificate inspections of power boilers with internal inspection at specified intervals; the certificate must be posted and the boiler must not be operated with an expired certificate.

Operator licensing: a Class 5 license typically requires documented experience and passing an examination; the license is issued by the jurisdiction and must be available at the plant.

Lockout/tagout (LOTO) is required before maintenance on electrical, steam, or fuel systems; verify zero energy and apply locks and tags to each energy isolation point.

Confined space entry into a boiler requires atmospheric testing (oxygen, combustibles, toxics), ventilation, an attendant, and a permit; the boiler must be isolated from steam, water, and fuel.

Accident reporting: serious injuries and boiler failures must be reported to the jurisdiction within the required time; a logbook records daily operation, tests, and any abnormal conditions.

Relief valve and gauge requirements: each boiler has at least one safety valve, a pressure gauge with a siphon and shutoff valve, and a water level indicator; testing and calibration records must be retained.

Annual internal inspection: fireside and waterside surfaces are examined for scale, corrosion, cracks, and bulging; tube sheets, staybolts, and ligament areas are checked with visual and nondestructive methods.

Hydrostatic test: fill with water, vent air, pressurize to 1.5 times MAWP for new construction or as the jurisdiction requires for repairs; hold and inspect for leaks and permanent deformation.

Safety valve testing: verify set pressure and reseat, check for leakage and chatter; record results; valves are tested at intervals set by the jurisdiction and after any repair.

Low-water cutoff and flame safeguard tests are performed at the required frequency (often daily or weekly for operating boilers) and documented; a failed test requires the boiler to be shut down.

Non-destructive examination: ultrasonic thickness measures wall loss, magnetic particle and dye penetrant find surface cracks, radiography finds internal weld defects; a qualified examiner interprets results.

Preventive maintenance schedule: lubricate bearings, check fan belts, clean burners, inspect refractory, test controls, and record all work; vibration and temperature trending predict failures.

Layup protection: dry layup uses desiccant and sealed openings; wet layup uses nitrogen blanket or oxygen scavenger at proper pH; improper layup causes pitting and corrosion.

Tube failure causes: overheating from scale or low water, corrosion from oxygen or acid, and mechanical damage from expansion or sootblower erosion; failure analysis determines the corrective action.

Ohm's law: V = I x R; power P = V x I = I^2 R = V^2 / R; for three-phase power P = 1.732 x V x I x power factor.

Motor current and protection: overload heaters are sized to motor full-load amps; a motor draws high inrush current at start, and a running overload trip indicates mechanical or electrical trouble.

Instrument signals: 4-20 mA current loop is standard for process transmitters; 4 mA represents zero and 20 mA full scale, and a broken wire reads below 4 mA, signaling a fault.

Thermocouples produce a small millivolt signal from the Seebeck effect; RTDs change resistance with temperature (about 0.385 ohm/ohm per degree C for platinum); both require proper lead compensation.

Pressure and level transmitters convert process pressure to a signal; a differential pressure (DP) transmitter measures level by the head of water above a tap, using the relationship P = h x density.

Control loops: a PID controller uses proportional, integral, and derivative action; proportional-only control leaves offset, integral eliminates offset, derivative anticipates change but amplifies noise.

Interlocks and permissives: safety circuits are hardwired or safety-rated, not software-only; the burner management system must be independent of the modulating control.

Electrical safety: verify de-energized with a meter rated for the voltage, use lockout/tagout, and treat capacitors and VFDs as stored-energy hazards; arc flash boundaries apply.

Temperature conversion: F = (C x 9/5) + 32; C = (F - 32) x 5/9; absolute scales: R = F + 460, K = C + 273.

Sensible heat: Q = m x cp x delta-T; for water cp is about 1 Btu/lb-F; latent heat of vaporization at atmospheric pressure is about 970 Btu/lb.

Steam tables: saturated steam properties depend on pressure or temperature; superheated steam requires both pressure and temperature; enthalpy of saturated liquid at 0 psig is about 180 Btu/lb.

Heat transfer: conduction Q = kA(delta-T)/L; convection depends on fluid velocity and film coefficient; radiation varies with the fourth power of absolute temperature.

Pressure conversions: 1 psi = 2.31 ft of water = 2.04 in. of mercury; 1 atmosphere = 14.7 psia = 0 psig; absolute pressure = gauge pressure + atmospheric.

Boiler efficiency: efficiency = heat output / heat input; input from fuel flow and heating value; output from steam flow times enthalpy rise; use consistent units.

Combustion air math: air required = fuel flow x stoichiometric air/fuel ratio x (1 + excess air fraction); flue gas volume follows from the products of combustion plus excess air.

Fluid flow: flow rate Q = velocity x area; head loss in piping rises with the square of flow; pump power = (flow x head x specific gravity) / (3960 x efficiency) in customary units.