MT Boiler Operator flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- MAWP
- Maximum allowable working pressure is the highest pressure at which a boiler may be operated; it is stamped on the nameplate and set by the thinnest pressure part at design temperature.
- Joint efficiency
- A factor in shell thickness formulas that accounts for the strength of welded seams; it is 1.0 for seamless or fully radiographed seams and lower for partially inspected welds.
- Lowest permissible water level
- The lowest water level at which a boiler may be safely operated; the gauge glass and low-water cutoff must be arranged so this level is visible and protected.
- Staybolt
- A threaded rod connecting opposite flat plates of a boiler to resist pressure loads; its diameter and pitch are sized so the load per bolt stays within allowable stress.
- Fusible plug
- A plug with a low-melting alloy core installed in a firetube boiler; it melts when the tube is uncovered, releasing steam as a warning of low water.
- Safety valve
- A pressure-relief device that opens at set pressure and reseats after blowdown; its capacity must equal or exceed the boiler's maximum evaporating capacity.
- Low-water fuel cutoff
- A safety control that shuts off the burner before the water level drops below the lowest permissible level; it is not an operating control and must be tested regularly.
- Water column
- A chamber connected to the boiler that supports the gauge glass and low-water cutoff; its connections must be at least 1 inch and must be blown down to prevent plugging.
- Flame scanner
- A UV or IR sensor that proves main flame within the trial-for-ignition period; loss of signal closes the fuel valve within 4 seconds or less on small burners.
- High-pressure limit switch
- A safety control that shuts down the burner at a pressure below the safety valve set pressure, preventing the valve from lifting during normal operation.
- Economizer
- A heat recovery device that preheats feedwater using flue gas; it improves efficiency and must have a bypass for startup and low-flow protection.
- Excess air
- Air supplied above the theoretical amount needed for complete combustion; typical values are 15-20 percent for gas and 20-30 percent for oil firing.
- Stoichiometric combustion
- Combustion with exactly the theoretical air required; for methane it is CH4 + 2O2 producing CO2 and water, with no excess oxygen remaining.
- Trial for ignition
- The timed period during which the burner may attempt to establish flame; if the flame scanner does not prove flame, the fuel valve closes and a lockout occurs.
- Purge
- A flow of air through the furnace and flue before ignition to remove unburned fuel; typically four to five air changes are required to prevent explosive accumulation.
- Turndown ratio
- The maximum firing rate divided by the minimum stable firing rate of a burner; a high turndown reduces cycling and improves efficiency at part load.
- LEL
- The lower explosive limit is the minimum fuel concentration in air that will ignite; methane's LEL is about 5 percent by volume, and meters read in percent LEL.
- Deaerator
- A device that heats feedwater to saturation temperature at its pressure and vents released gases, removing oxygen and carbon dioxide that cause corrosion.
- Oxygen scavenger
- A chemical such as sulfite added to feedwater to remove residual dissolved oxygen; a residual of about 20-40 ppm is maintained in the boiler water.
- Blowdown
- The controlled removal of boiler water to limit dissolved solids and sludge; the rate is set by the allowable TDS and the feedwater TDS.
- Scale
- A hard deposit of calcium and magnesium salts on heat transfer surfaces; it insulates the surface, raises fuel consumption, and can cause overheating.
- Water softener
- An ion exchange unit that replaces calcium and magnesium with sodium; it is regenerated with salt brine, and hardness leakage indicates resin exhaustion.
- Hydrostatic test
- A pressure test with water at typically 1.25 to 1.5 times MAWP for in-service boilers; the boiler is held at test pressure and inspected for leaks.
- Ultrasonic thickness testing
- A non-destructive method that measures wall loss from corrosion and erosion; readings are compared to the minimum required thickness for the pressure part.
- Magnetic particle testing
- A non-destructive method that detects surface and near-surface cracks in ferromagnetic materials by attracting magnetic particles to flux leakage at defects.
- ASME Section I
- The section of the ASME Boiler and Pressure Vessel Code that governs power boilers, including design, materials, and required safety valves.
- ASME Section IV
- The section of the ASME Boiler and Pressure Vessel Code that governs heating boilers; it covers construction and required safety devices for low-pressure heating units.
- NBIC
- The National Board Inspection Code governs in-service inspection, repairs, and alterations of boilers and pressure vessels; it is often adopted by the authority having jurisdiction.
- Authority having jurisdiction
- The regulatory body that enforces boiler codes, sets inspection intervals, and issues operating permits and operator certifications.
- Lockout/tagout
- A procedure that isolates and locks energy sources before maintenance; stored steam and water energy must be released and verified before work begins.
- Confined space entry
- Entry into a boiler or vessel requires atmospheric testing for oxygen and combustibles, ventilation, and an attendant stationed outside the space.
- Fired-dry boiler
- A boiler that has lost water while firing; water must never be added until it has cooled, because sudden water contact can cause a violent steam explosion.