NIULPE Class 3 cheat sheet

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

A safety valve on a power boiler must relieve all steam the boiler can generate without allowing pressure to rise more than 6% above set pressure (ASME Section I).

Minimum required safety valve relieving capacity is based on the boiler's maximum evaporating rate, not on normal operating load.

Water column connections must be at least 1 in. (25 mm) NPS, and the lower connection must be in the water space with blowdown valves on both the water column and the gauge glass.

A try cock or gauge glass lowest visible reading must be at least 3 in. (75 mm) above the highest heating surface or the fire line.

Fusible plugs are installed in the crown sheet or upper firebox of fire-tube boilers and melt at approximately 445 °F (229 °C) to warn of low water.

Staybolts are designed for bending, not tension; crown stays, girder stays, and diagonal stays each carry loads by different stress paths.

Refractory and insulation selection is driven by hot-face temperature and flue gas velocity; a 1 in. thick castable refractory is not a substitute for a 4 in. insulating firebrick course.

Theoretical (stoichiometric) air for natural gas is about 17.3 lb air/lb fuel; for No. 6 oil it is about 14.4 lb air/lb fuel; excess air is added on top of these figures.

Combustion efficiency rises with lower stack temperature and lower excess O2, but CO and unburned hydrocarbons set the practical lower limit for excess air.

A 10% excess air setting typically corresponds to about 2.5–3% O2 in the flue gas for natural gas; 15% excess air is about 3.5–4% O2.

Dew point of flue gas rises with sulfur and moisture content; condensing below about 250 °F (121 °C) in a sulfur-bearing fuel risks cold-end corrosion.

A low-water fuel cutoff must be tested by blowing down the float chamber while the burner is firing; the burner must trip before the water level leaves the gauge glass.

A flame scanner must prove flame within the trial-for-ignition period (typically 10 s for gas, 15 s for oil) or the fuel valve must close.

Purge air volume before light-off is normally four to five air changes of the furnace and flue; a shorter purge is not permitted by NFPA 85 practice.

Drum level control uses three-element control (steam flow, feedwater flow, and drum level) to decouple the shrink/swell effect during load changes.

Hydrostatic test pressure is 1.5 times the MAWP for new construction and 1.25 times for in-service repairs, held long enough to inspect all joints.

A hydrostatic test is not a substitute for internal inspection; the boiler must be opened, cleaned, and visually examined on the waterside and fireside.

Ultrasonic thickness readings are compared to the original nominal thickness; a 12.5% loss of nominal wall is a common retirement or repair trigger.

Weld repairs on pressure parts require qualified procedures (WPS/PQR) and qualified welders under ASME Section IX.

Post-weld heat treatment is required for thick-section welds (typically over 1.5 in. for carbon steel) to relieve residual stress and avoid hydrogen cracking.

Crown sheet and tube sheet cracks are inspected by magnetic particle or dye penetrant methods; visual inspection alone misses tight cracks.

Refractory dry-out must follow a controlled heat-up curve to avoid spalling; a rapid heat-up can crack castable linings.

Blowdown valve seats are lapped or replaced when leakage is observed; a leaking blowdown valve is a safety hazard and must be corrected before returning to service.

ASME Section VIII Division 1 uses a joint efficiency E in the shell thickness formula t = P·R/(S·E − 0.6P) + corrosion allowance.

A pressure vessel must have a relief device sized for the worst credible overpressure scenario, including fire exposure and blocked outlet.

Piping systems are classified by ASME B31.1 (power piping) and B31.3 (process piping); each has different stress and flexibility rules.

Pipe support spacing and flexibility analysis prevent excessive nozzle loads on vessels and pumps; thermal expansion must be accommodated by loops or expansion joints.

Hydrotest of a pressure vessel is 1.3 times MAWP times the ratio of allowable stress at test to design temperature (ASME VIII-1).

Corrosion allowance is added to the calculated minimum thickness; it is not a margin for design error.

Flange rating (e.g., Class 150, 300) is based on material group and temperature; the same class number gives different pressure limits at different temperatures.

A rupture disc in series with a relief valve protects the valve from corrosive or fouling service; the burst pressure must account for the valve's back pressure.

Rankine cycle efficiency improves with higher steam pressure and temperature and with lower condenser pressure; the condenser vacuum is a major efficiency lever.

Turbine heat rate is the Btu of heat input per kWh generated; lower heat rate means higher efficiency.

A steam turbine must never be overspeeded; the overspeed trip is set at 110% of rated speed and must be tested before every start.

Throttle and governor valves must be closed before rolling; steam admission is controlled by the governor valve after the turbine is on turning gear.

Gas turbine output falls with rising ambient temperature because mass flow through the compressor decreases; inlet cooling recovers capacity.

Gas turbine exhaust temperature and NOx are controlled by the combustor and by water/steam injection or dry low-NOx combustors.

Reciprocating engine detonation is detected by knock sensors; detonation raises cylinder pressure and can crack pistons and heads.

Lube oil temperature and pressure are the primary protection signals for turbine and engine bearings; low oil pressure trips the machine.

Centrifugal pump head varies with flow; the operating point is where the pump curve intersects the system curve.

NPSH available must exceed NPSH required by a margin (typically 1–3 ft) to avoid cavitation.

Affinity laws: flow varies with speed, head with speed squared, and power with speed cubed for a fixed impeller diameter.

A centrifugal pump run at shutoff (zero flow) overheats because the fluid recirculates and no cooling occurs; a minimum flow bypass is used.

Positive displacement pumps must have a relief valve on the discharge; they can build pressure until something fails.

Gate valves are for isolation, globe valves for throttling, and check valves for preventing backflow; using a gate valve for throttling causes seat erosion.

Compressor surge occurs when flow falls below the surge line; anti-surge valves recycle flow to keep the compressor out of surge.

Compressor polytropic efficiency accounts for intercooling; isentropic efficiency is used for a single stage without cooling.

A 4–20 mA current loop uses 4 mA as the live zero and 20 mA as full scale; a 0 mA reading indicates a broken wire.

A thermocouple produces a millivolt signal proportional to the temperature difference between hot and cold junctions; cold-junction compensation is required.

A resistance temperature detector (RTD) changes resistance with temperature; a Pt100 has 100 ohms at 0 °C and about 0.385 ohms per °C.

A PID controller has proportional, integral, and derivative terms; integral eliminates offset, derivative resists rapid change and amplifies noise.

A safety instrumented function has a safety integrity level (SIL) determined by the required risk reduction factor; SIL 3 is roughly 1,000–10,000 RRF.

A flame scanner must discriminate between the burner flame and background radiation; UV scanners are blind to hot refractory, IR scanners are not.

A pressure switch and a pressure transmitter serve different purposes; the switch trips at a set point and the transmitter provides a continuous signal.

Loop calibration checks the transmitter, wiring, and final element as a whole, not just the transmitter output.

pH control is the first line of corrosion defense; carbon steel is protected at pH 9–11 in boiler water, and copper alloys need lower pH.

Oxygen pitting is prevented by mechanical deaeration plus a chemical oxygen scavenger such as sodium sulfite or hydrazine.

Scale forms when calcium and magnesium salts exceed solubility; softening and internal treatment keep hardness low.

Conductivity is used to control blowdown; high dissolved solids cause carryover and foaming.

Caustic embrittlement (stress corrosion cracking) occurs in riveted or high-stress areas at high caustic concentration; coordinated phosphate control avoids it.

Silica carryover causes turbine blade deposits; silica limits depend on boiler pressure and are tighter at higher pressure.

Condensate corrosion from carbonic acid is controlled by neutralizing amines or filming amines.

Corrosion coupons and corrosion product monitoring show whether treatment is working; a rising iron level in boiler water signals active corrosion.

Ohm's law: V = I·R; power in a single-phase circuit is P = V·I·PF; three-phase power is P = √3·V·I·PF.

A motor's full-load current is found on the nameplate; the overload heater or electronic overload is set at 115–125% of FLA for a service-factor-1 motor.

Motor starting current for a squirrel-cage induction motor is typically 5–7 times full-load current; reduced-voltage or soft starters limit the inrush.

A motor must be protected against overload, short circuit, and ground fault; the branch-circuit protection and the overload protection are separate devices.

Locked-rotor current flows until the motor accelerates; a motor that fails to accelerate overheats and trips its overload.

The National Electrical Code classifies hazardous locations by Class, Division, and Group; equipment must be listed for the specific location.

Grounding and bonding protect personnel and equipment; a missing ground can energize the frame and create a shock hazard.

Vibration and bearing temperature are the best early indicators of motor mechanical failure; electrical faults show as insulation resistance drops.

ASME Section I covers power boilers; Section IV covers heating boilers; Section VIII covers pressure vessels; Section IX covers welding qualifications.

The ASME Code Symbol Stamp and the manufacturer's data report are required for a new boiler or pressure vessel before it can be placed in service.

Jurisdictional inspection intervals vary; a common rule is annual internal inspection for power boilers and biennial for some heating boilers, but the authority having jurisdiction sets the actual interval.

NFPA 85 covers boiler and combustion system hazards; NFPA 654 covers combustible dust; NFPA 70 is the National Electrical Code.

OSHA 29 CFR 1910.217 and 1910.147 cover machine guarding and lockout/tagout; lockout/tagout is required before maintenance on energy-isolated equipment.

The ASME Boiler and Pressure Vessel Code is not law by itself; it becomes enforceable when adopted by a state or local jurisdiction.

A repair organization must hold a valid ASME Certificate of Authorization (R stamp) to repair pressure-retaining items.

Recordkeeping is part of compliance; inspection reports, hydrotest records, and relief valve test records must be retained and available to the inspector.