OH Boiler Operator key terms

A boiler in which hot combustion gases pass through tubes that are surrounded by water, so the water sits on the outside of the tubes. Common in small, lower-pressure heating and process plants.

A boiler in which water flows inside tubes that are heated on the outside by combustion gases. It can produce high pressure and large steam flows and responds quickly to load changes.

The upper cylindrical pressure vessel of a water-tube boiler where steam separates from water and collects for delivery to the superheater or steam header. It holds the normal water level.

The lower cylindrical vessel of a water-tube boiler that distributes feedwater to the tubes and collects sludge and sediment, which are removed by bottom blowdown.

The top sheet of a firebox in a fire-tube boiler, directly exposed to flame and supporting the water above it. It must stay covered by water to avoid overheating and failure.

A rod or brace that ties two pressure-retaining surfaces together so they can resist the force of internal pressure. Stays are commonly used on flat surfaces such as firebox sheets.

The flat plate at the end of a boiler shell or drum into which tube ends are rolled or welded. It separates the water space from the fire or gas space.

A bank of tubes that adds heat to steam after it leaves the boiler drum, raising its temperature above saturation. This improves efficiency and reduces condensation in steam piping.

A heat exchanger that uses hot flue gas to preheat boiler feedwater before it enters the drum, recovering heat that would otherwise be lost up the stack.

A spring-loaded valve that opens automatically at a set pressure to release steam or vapor and keep the boiler from exceeding its maximum allowable working pressure. It is the final overpressure protection.

A plug with a low-melting-point core installed in the crown sheet or a similar hot location. If the metal overheats because of low water, the core melts and releases steam as a warning.

A control that senses water level and shuts off the burner or fuel supply when water falls below a safe level, preventing overheating of heated surfaces and possible explosion.

A transparent tube or assembly connected to the boiler at two points so the operator can see the actual water level inside the drum at all times.

A fitting connected to the boiler that steadies the water level shown in the gauge glass and provides mounting points for level controls and try cocks.

Small manually operated valves mounted at known levels on the boiler or water column. They are used to confirm water level when the gauge glass is suspected of being clogged or inaccurate.

The operating water level marked on the gauge glass at which the boiler has adequate steam space and remains safely above the lowest permissible level.

The carryover of boiler water, rather than dry steam, into the steam line. It is usually caused by high water level, a sudden load change, or foaming, and can damage downstream equipment.

The formation of a stable layer of bubbles on the water surface inside the boiler, often caused by dissolved solids or organic contamination. It can lead to priming and carryover.

Boiler water and the dissolved solids in it leaving the drum with the steam. Carryover causes scale and deposits in superheaters, turbines, and steam-using equipment.

A sharp banging or shock in piping caused by rapid steam condensation or sudden changes in flow. It can damage valves, fittings, and pipe supports.

The removal of water and settled sludge from the lowest part of the boiler through a blowdown valve, usually done in short, controlled bursts.

The continuous or periodic removal of water from the surface of the drum to control the concentration of dissolved solids and sludge. Also called continuous blowdown.

A hard crust of mineral deposits that forms on heated surfaces when impurities in the water precipitate out. It reduces heat transfer and can cause overheating and tube failure.

Water supplied to the boiler to replace steam that has been used. It is usually a mixture of returned condensate and treated makeup water.

The exact quantity of air theoretically needed to burn a given amount of fuel completely, leaving no oxygen and no unburned fuel. Also called theoretical air.

Air supplied to the burner beyond the theoretical amount, used to ensure complete combustion. Too much excess air wastes heat; too little produces smoke and carbon monoxide.

The difference in pressure that moves air into the furnace and flue gases out of the stack. It may be natural from a chimney, forced by a fan before the furnace, or induced by a fan after it.

The lowest temperature at which a fuel gives off enough vapor to form a momentary flash when an ignition source is applied. It is a key indicator of fire hazard.

The range of fuel-vapor concentration in air that will ignite. Below the lower limit the mixture is too lean to burn; above the upper limit it is too rich.

Breaking liquid fuel into fine droplets so it can mix with air and burn efficiently. Poor atomization causes smoke, carbon buildup, and an unstable flame.

A sensor that verifies a flame is present in the furnace and signals the flame safeguard system to shut off fuel if the flame is lost.

A forced flow of air through the furnace and flues before lightoff that clears any accumulated combustible gases, preventing a furnace explosion on ignition.

A pressure test in which the boiler is filled with water and pressurized, usually above its normal operating pressure, to check for leaks and structural weakness before returning it to service.

Inspection methods such as ultrasonic thickness measurement, radiography, and magnetic particle testing that reveal defects in boiler material without cutting or damaging it.

Sealing off a leaking or failed tube by driving a plug into each end so the boiler can keep operating at reduced capacity until a proper repair is made.

The highest pressure at which a boiler or pressure vessel may legally be operated, based on its design, material thickness, and code calculations.

The recognized set of design, fabrication, and inspection rules for boilers and pressure vessels in the United States. Compliance is generally required by state law.

A code that sets rules for the repair, alteration, and inservice inspection of boilers and pressure vessels, and for qualifying organizations that perform those repairs.

A document issued by the jurisdiction after a boiler passes the required inspections, permitting operation for a stated period and at a stated pressure.

A record kept by the operator of readings such as pressure, water level, temperature, and blowdowns, used to spot trends and show that required checks were performed.