Every Industry has its own unique terminology. Sometimes these terms can be confusing so we thought a boiler dictionary would be helpful. The following definitions can be found in a number of texts.
Glossary of Boiler Terms and Definitions
Calorie – The amount of energy required to raise the temperature of 1 gram of water by 1 degree C. The kilocalorie (kcal) is a typical unit of measure in the process industry, 1 kcal = 1000 calories.
Carryover – The moisture and entrained solids forming the film of steam bubbles; a result of foaming in the boiler. Carryover is caused by a poor water condition within the boiler.
Casing – A covering of sheets of metal or other material such as fire resistant composition board used to enclose all or a portion of a steam-generating unit.
Caustic cracking – Also called caustic embrittlement cracking, usually occurring in carbon steels or iron-chromium nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 400 to 480 deg. F.
Check valve – A valve designed to prevent reversal of flow. Flow in one direction only is permitted.
Circulating tube – A boiler tube used to connect the water spaces of two drums or the pressure parts of a boiler.
Closed feedwater heater – An indirect -contact feedwater heater; that is, one in which the steam and water are separated by tubes or coils.
Closing-in-line – The sealing by plastic refractory between a boiler shell or head and the firebrick wall; used to prevent hot gases from contacting the boiler above the lowest waterline.
Colloid – A finely divided organic substance which tends to inhibit the formation of dense scale and results in the deposition of sludge, or causes it to remain in suspension, so that it may be blown from the boiler.
Combined feeder cutoff – A device that regulates makeup water to a boiler in combination with a low water fuel cut off.
Combustible – The heat-producing constituents of a fuel.
Combustible loss – The loss representing the unliberated thermal energy occasioned by failure to oxide completely some of the combustible matter in the fuel.
Combustion – The rapid reaction of fuel and oxidant (usually oxygen in air) to produce light, heat and noise. Major products of combustion for hydrocarbon fuels (e.g., natural gas, refinery gas, fuel oils) are carbon dioxide and water vapor. Trace products include carbon monoxide and nitrogen oxides, which are pollutants.
Combustion chamber – See furnace
Combustion efficiency – The fraction of carbon in the fuel that is converted into CO2 in the flue gas, customarily expressed as a percent.
Combustion rate – The quantity of fuel fired per unit of time, as pounds of coal; per hour or cubic feet of gas per hour.
Combustion (flame) safeguard – A system for sensing the pressure or absence of flame and indicating, alarming or initiating control action.
Condensate – Condensed water resulting from the removal of latent heat from steam.
Conduction – The transfer of heat by molecular collision. This process is more efficient in metals and other thermal conductors and poorer in fluids and insulators such as refractory.
Conductivity – The amount of heat (Btu) transmitted in 1 hour through 1 sq. ft. of a homogenous material 1 in. thick for a difference in temperature of 1o F. between two surfaces of the material.
Continuous blowdown – The uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.
Control – A device designed to regulate the fuel, air, water, steam, or electrical supply to the controlled equipment. It may be automatic, semi-automatic or manual.
Control, limit – An automatic safety control responsive to changes in liquid level, pressure, or temperature; normally set beyond the operating range for limiting the operation of controlled equipment.
Control, operating – A control, other than s safety control or interlock, to start or regulate input according to demand and to stop or regulate input on satisfaction of demand. Operating controls may also actuate auxiliary equipment.
Control, primary safety – A control responsive directly to flame properties, sensing the presence of flame and, in the event of ignition failure or unintentional flame extinguishments, causing safety shutdown.
Control, safety – Automatic controls and interlocks (including relays, switches, and other auxiliary equipment used in conjunction to form a safety control system) which are intended to prevent unsafe operation of the controlled equipment.
Convection – The transfer of heat or mass by large-scale fluid movements. When the process occurs, due to density and temperature differences, it is termed natural convection. When the process occurs due to external devices (such as fans), it is termed forced convection.
Convection section – The part of a furnace between the radiant section and the stack. The area is filled with tubes or pipes which carry process steam and which absorb heat via convection heat transfer from the hot gases passing through the area on their way out of the stack. The convection section forms an obstacle to the combustion gas flow and can greatly affect furnace draft in the radiant section of the furnace.
Corrosion – The wasting away of metals as a result of chemical action. In a boiler, usually caused by the presence of O2, CO2, or an acid.
Corrosion fatigue – Cracks produced by the combined action of repeated or fluctuating stress and a corrosive environment, which produces the cracking at lower stress levels or fewer cycles of stress than would be the case if no corrosive environment were present.
Course – A circumferential section of a boiler shell or drum. With usual diameters, the number of courses will equal the number of plates forming the shell or drum.
Creep – The time-dependent stretching or strain, heavily influenced by temperature, of a material under stress.
Crimping tool – A tool used to reduce the diameter of the end of a boiler tube preparatory to its removal from a boiler.
Critical pressure and critical temperature – That point at which the difference between the liquid and vapor states for water completely disappears.
Cross-box – A boxlike structure to the longitudinal drum of a sectional header boiler forconnecting circulating tubes.
Crown sheet – The plate forming the roof of an internally fired furnace or a combustion chamber.
C-scan – In ultrasonic testing a means of data presentation to show a plan view of the material, and of any discontinuities therein.Sources:
Sources for this listing were found in the ASME Boiler Codes, American Society of Mechanical Engineers, New York; ABMA; Metals Handbook, American Society for Metals; ASHRAE Handbooks; and Boiler Operator’s Guide by Anthony L. Kohan, The John Zink Combustion Handbook, Charles E. Baukal, Jr., editor.