Superintendents & Resident Managers Technical Association - Glossary of Terms For Boilers & Heating

ACID CLEANING The process of cleaning the interior surfaces of steam-generating units by filling the unit with a dilute acid accompanied by an inhibitor to prevent corrosion and by subsequently draining, washing, and neutralizing the acid by a further wash of alkaline water.

ACIDITY Represents the amount of free carbon dioxide, mineral acids, and salts (especially sulfates or iron and aluminum) which hydrolyze to give hydrogen ions in water is reported as mill equivalents per liter of acid, or ppm acidity as calcium carbonate, or pH, the measure of hydrogen ion concentration.

AGGLOMERATION Groups of fine dust particles clinging together to form a larger particle.

AIR-ATOMIZING OIL BURNER A burner for firing oil in which the oil is atomized by compressed air, which is forced into and through one or more streams of oil, breaking the oil into a fine spray.

AIR/FUEL RATIO The ratio of the weight, or volume, of air to fuel.

AIR HEATER OR AIR PREHEATER Heat-transfer apparatus through which air is passed and heated by a medium of higher temperature, such as the products of combustion or steam.

1. Regenerative air preheater. An air heater in which heat is first stored up in the structure itself by the passage of the products of combustion, and which then gives up the heat so stored to the subsequent passage of air.

2. Recuperative air heater. An air heater in which the heat from products of combustion passes through a partition, which separates the products from the air.

(a ) Tubular air heater. An air heater containing a group of tubular elements through the walls of which heat is transferred from a flowing heating medium to an airstream.

(b ) Plate air heater. An air heater containing passages formed by spaced plates through which heat is transferred from a flowing heating medium to an airstream.

AIR PURGE The removal of undesired matter by replacement with air

AIR-SWEPT PULVERIZERS A pulverizer through which air flows and from which pulverized fuel is removed by the stream of air.

AIR VENT A valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.

ALKALINITY The amount of carbonates, bicarbonates, hydroxides, and silicates or phosphates in the water; reported as grains per gallon, or parts per million as calcium carbonate.

ALLOWABLE WORKING PRESSURE The maximum pressure for which the boiler was designed and constructed; the maximum gauge pressure on a complete boiler; and the basis for the setting on the pressure-relieving devices protecting the boiler. Also known as Maximum Allowable Working Pressure

ANTHRACITE ASTM coal classification by rank: Dry fixed carbon 92 percent or more and less than 98 percent; and dry volatile matter 8 percent or less and more than 2 percent on a mineral-matter-free basis.

APPROVED The world approved as used in a Code means acceptable to the authority having jurisdiction.

ASH The incombustible inorganic matter in the fuel.

ASH SLUICE A trench or channel used for transporting refuse from ash pits to a disposal point by means of water.

ATOMIZING MEDIA A supplementary medium, such as steam or air, which assists in breaking the fuel oil into a fine spray.

ATTEMPERATOR Apparatus for reducing and controlling the temperature of a superheater vapor or of a fluid. See also desuperheater.

1. Shell-and tube type. An attemperator consisting of a pressure vessel containing tubular elements through the walls of which heat is transferred.

2. Spray type. An attemperator in which a lower-temperature fluid is injected at relatively high velocity in an atomized state into the superheater vapor to reduce its temperature by direct contact with the atomized fluid.

3. Submerged type. An attemperator consisting of tubular elements located in the boiler circulation blow the waterline.

AUTHORIZED INSPECTION AGENCY The inspection agency approved by the appropriate legal authority of a state or municipality of the United States or a province of Canada, which has adopted a section of the ASME Code.

AUTOMATIC LIGHTER OR IGNITER A means for starting ignition of fuel without manual intervention. Usually applied to liquid, gaseous, or pulverized fuel. See igniter.

AVAILABLE DRAFT The draft which may be utilized to cause the flow of air for combustion or the flow of products of combustion.

BACKING RING A strip of thin plate used on the inner surfaces of the abutting ends of pipe, tubes, or plates which are to be butt-welded. Its purpose is to prevent irregularities at the base of the weld and to permit penetration oat its root.

BAG A deep bulge in the bottom of the shell or furnace of a boiler

BAG FILTER A device containing one or more cloth bags for recovering particles from the dust-laden gas or air which is blown through it.

BALANCED DRAFT The maintenance of a fixed value of draft in a furnace at all combustion rate by control of incoming air and outgoing products of combustion.

BANKING Burning solid fuels on a grate at rates sufficient to maintain ignition only.

BARREL The cylindrical portion of a fire-tube-boiler shell that surrounds the tubes.

BITUMINOUS COAL ASTM coal classification by rank on a mineral matter free basis and with bed moisture only.

1. Low volatile. Dry fixed carbon 78 percent or more and less than 89 percent; dry volatile matter 22 percent or less and more than 14 percent.

2. Medium volatile. Dry fixed carbon 69 percent or more and less than 78 percent. Dry volatile matter 22 percent or less and more than 31 percent.

3. High volatile (A). Dry fixed carbon less than 69 percent; dry volatile matter more than 31 percent. Btu value equal to or greater than 14,000 moist, mineral-matter-free basis.

4. High volatile (B). Btu value 13,000 or more and less than 14,000 moist, mineral-matter-free basis.

5. High volatile (C). Btu value 11,000 or more and less than 13,000 moist, mineral-free basis commonly agglomerating, or 8300 to 11,500 Btu agglomerating.

BLACK LIQUOR Liquid by-product fuel extracted from wood in the alkaline pulp-manufacturing process and containing the chemical used to accomplish the extraction.

BLOWBACK The number of pounds per square inch of pressure drop in a boiler from the point where the safety valve pops to the point where the safety valve reseats.

BLOWBACK RING An adjustable ring in a safety valve, used to control the amount of blowback.

BLOWDOWN The drain connection including the pipe and the valve at the lowest practical part of a boiler, or at the normal water level in the case of a surface blowdown. The amount of water that is blown down.

BOILER A closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, under pressure or vacuum by the application of heat from combustible fuels, electricity, or nuclear energy. The term does not include such facilities of an integral part of a continuous processing unit but does include fired units of heating or vaporizing liquids other than water where these units are separate from processing systems and are complete within themselves.

BOILER ASSEMBLER Means a corporation, company, partnership, or individual who assembles a boiler which has been delivered knocked down in multiple pieces by bolting, threading, welding, or other methods of fastening to produce a finished pressure vessel. A boiler assembler may also be a boiler installer.

BOILER, AUTOMATICALLY FIRED A boiler which cycles automatically in response to a control system

BOILER HEADER (BOX) A pressure part of a boiler consisting of a flat tube sheet into which the ends of the water tubs are rolled. In a parallel plane is a tube cap or handhole sheet. The tow sheets are spaced about 4 to 8 in. or more apart. The top and bottom and both ends are flanged together and riveted or may be closed by a narrow

flanged strip of plate riveted to each sheet. Circulating nipples connect the top of the header and drum, or the header may be flanged and riveted directly to the drum.

BOILER, HIGH-PRESSURE, STEAM OR VAPOR A boiler in which steam or vapor is generated at a pressure exceeding 15 psig.

BOILER, HOT-WATER-HEATING A boiler in which no steam is generated and from which hot water is circulated for heating purposes and then returned to the boiler.

BOILER, HOT-WATER-SUPPLY A boiler functioning as a water heater.

BOILER, LOW-PRESSURE, STEAM OR VAPOR A boiler in which steam or vapor is generated at a pressure not exceeding 15 psig.

BOILING OUT The boiling of a highly alkaline water in boiler pressure parts for the removal of oils, greases, etc. prior to normal operation or after major repairs.

BOURDON TUBE A hollow, metallic tube, bent semicircular, which forms the actuating medium of a pressure gauge.

BREECHING A duct for the transport of the products of combustion between parts of a steam-generating unit or the stack.

BRIDGEWALL A wall in a furnace over which the products of combustion pass

BRINELL TEST A hardness test performed by pressing a steel ball of standard hardness into a surface by a standard pressure

BRITISH THERMAL UNIT The mean British thermal unit (Btu) is ¹/₁₈₀ of the heat required to raise the temperature of 1 lb of water from 32 to 212ºF at a constant atmospheric pressure. It is about equal to the quantity of heat required to raise 1 lb of water 1ºF [251.9957 cal or 1054.35 joules (J)].

BUCKSTAY A structural member placed against a furnace or boiler wall to limit the motion of the wall against furnace pressure.

BULGE A local distortion or swelling outward caused by internal pressure on a tube wall or boiler shell due to overheating. Also applied to similar distortion of a cylindrical furnace due to external pressure when overheated provided the distortion is of a degree that can be driven back.

BUNKER C OIL Residual fuel oil (no. 6 fuel oil) of high viscosity commonly used in marine and stationary steam power plants.

BURNER A device for the introduction of fuel and air properly mixed in correct proportions to the combustion zone.

BURNER ASSEMBLY A burner that is factory-built as a single assembly or as two or more subassemblies which include all parts necessary for its normal function when installed as intended.

BURNER, ATMOSHERIC A gas burner in which all air for combustion is supplied by natural draft, the inspiriting force being created by gas velocity.

BURNER, AUTOMATICALLY LIGHTED A burner in which fuel to the main burner is normally turned on and ignited automatically.

BURNER, NATURAL-DRAFT TYPE A burner which depends primarily on the natural draft created in the flue to induce the air required for combustion into the burner.

BURNER, POWER A burner in which all air for combustion is supplied by a power driver fan that overcomes the resistance through the burner to deliver the quantity of air required for combustion.

BURNER WIND BOX A plenum chamber around a burner in which an air pressure is maintained to ensure proper distribution and discharge of secondary air.

BYPASS TEMPERATURE CONTROL Control of vapor or air temperature by diverting part of or all the heating medium from passing over the heat-absorbing surfaces, usually by means of a bypass damper.

CAKING Property of certain coals to become plastic when heated and form large masses of coke.

CALCIUM A scale-forming element found in some boiler feedwaters.

CALORIE The mean calorie is ¹/₁₀₀ of the heat required to raise the temperature of 1 g of water from 0 to 100ºC at a constant atmospheric pressure. It is about equal to the quantity of heat required to raise 1 g of water 1ºC (4.184 J).

CARRYOVER The moisture and entrained solids forming the film of stream bubbles; a result of foaming in a boiler. Carryover is caused by a faulty boiler-water condition. See also foaming. Carry over usually results in the boiler sending water {wet Steam} up with the steam into the pipes.

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.

CAULK To make the contacting surfaces of a seam tight against leakage by a upsetting or forcing (by distortion) the edge or abutment of the plate into the surface of the adjoining plate. Also, to close any pinhole or fissure in a metal plate, by virtue of the ductility of boiler plate, bye distorting its surface to close a slight opening. A blunt tool is used in caulking.

CHECKER WORK An arrangement of alternately spaced brick in a furnace with openings through which air or gas flows.

CHECK VALVE. A valve designed to prevent reversal of flow. Flow in one direction only is permitted.

CINDER Particles of partially burned fuel from which volatile gases have been driven off, which are carried from the furnace by the products of combustion.

CIRCULATING TUBE A boiler tube used to connect the water spaces of tow 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 form contacting the boiler above the lowest safe 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 form the boiler.

COMBINED FEEDER CUTOFF A device that regulates makeup water to a boiler in combination with a low-water fuel cutoff.

COMBUSTION Chemical combination of the combustible that part which will burn) in a fuel with oxygen in the air supplied for the process. Temperatures may range form 1850 to over 3000ºF.

COMBUSTION (FLAME) SAFEGARD A system for sensing the presence or absence of flame and indicating, or initiating control action.

CONDENSATE Condensed water resulting from the removal of latent heat from steam.

CONDUCTION The transmission of heat through and by means of matter unaccompanied by any obvious motion of the matter.

CONDUCTIVITY The amount of heat (Btu) transmitted in 1 hr through 1 ft²of a homogeneous material 1 in, thick for a difference in temperature of 1ºF between the two surfaces of the material.

CONTROL A device designed to regulate the fuel, air, water, steam, or electrical supply to the controlled equipment. It may be automatic, semiautomatic, or manual.

CONTROL, LIMIT An automatic safety control responsive to changes in liquid lev3el, pressure, or temperature, normally set beyond the operating range for limiting the operation of the controlled equipment.

CONTROL MUNUFACTURER A corporation or company which manufactures operating and safety controls for use ion boiler and furnace units.

CONTROL, OPERATING, A control, other than a safety control or interlock, to star or regulate input according to demand and the stop 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 event of ignition failure or unintentional flame extinguishment, 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.

CONSTANT IGNITION Usually a gas pilot that remains lighted at full volume whether the main burner is in operation or not.

CONVECTION The transmission of heat by the circulation of a liquid or a gas such as air. Convection may be natural or forced.

CORNER FIRING A method of firing liquid, gaseous, or pulverized fuel in which the burners are located in the corners of the furnace. Se also tangential firing.

CORROSION The wasting away of metals as a result of chemical action. In a boiler, usually cause by the presence of O₂, CO₂, or an acid.

COURSE A circumferential section of a boiler shell or drum. With usual diameters, the number of courses will equal the number of plate forming the shell or drum.

CRIMPING TOOL A tool used to reduce the diameter of the end of a boiler tube preparatory to tits 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 for connecting circulating tubes.

CROWFOOT The end of a brace in a boiler, split in two dir3ections for riveting to the plate.

CROWN SHEET The plate forming the roof of an internally fired furnace or a combustion chamber.

DAMPER A device for introducing a variable resistance of regulating the volumetric flow of gas or air.

1. Butterfly type. A single-blade damper pivoted about its center.

2. Curtain type. A damper consisting of one or more blades, each pivoted about one edge.

3. Flap type. A damper consisting of one or more blades, each pivoted about one edge.

4. Louvre type. A damper consisting of several blades, each pivoted about its center and linked together for simultaneous operation.

5. Slide type. A damper consisting of a single blade which moves substantially normal to the flow.

DEAERATING HEATER A type of feedwater heater operating with water and steam in direct contact. It s designed to heat the water and to drive off oxygen.

DESIGN PRESSURE the pressure used in the design of a boiler for the purpose of determining the minimum permissible thickness or physical characteristics of a the different parts of the boiler.

DESUPERHEATER Apparatus for reducing and controlling the temperature of a superheated vapor. See also attemperator.

1. Shell-and-tube type. A desuperheater consisting of a pressure vessel containing tubular elements through the walls of which heat is transferred.

2. Spray type. A desuperheater in which a lower-temperature fluid is injected at relatively high velocity in an atomized state in to the superheater vapor to reduce its temperature by direct contact with the atomized fluid.

3. Submerged type. A desuperheater consisting of tubular elements located in the boiler circulation below the waterline.

DIAGONAL STAY A brace used in fire-tube boilers between a flathead or tube sheet and the shell.

DISTILLATE OIL Light fraction of oil which has been separated form crude oil by fractional distillation. See fuel oil.

DOLLY A riveting tool.

DOWNCOMER A tube or pipe in a boiler or waterwall circulation system through which fluid flows downward between headers.

DOWTHERM An organic chemical with an exceedingly high boiling point, sometimes used in special types of boilers for high-temperature service. It is composed of diphenyl and diphenyloxide.

DRAFT the difference between atmospheric pressure and some lower pressure existing in the furnace or gas passages of the steam-generating unit.

DRAFT CONTROL, BAROMETRIC A device that controls draft by means of a balanced damper which bleeds air into the breeching on changes of pressure to maintain a steady draft.

DRAFT DIFFERNTIAL The difference in static pressure between two points in a system.

DRIFT PIN A tapered steel bar used to drive into and align rivet holes or bolt holes in plates or pipe flanges.

DRIP LEG The container placed at a low point in a system of piping to collect condensate and from which it may be removed.

DRUM A cylindrical shell closed at both ends, designed to withstand internal pressure.

DRYBOTTOM FURNACE A pulverized-fuel furnace in which the ash particles are deposited on the furnace bottom in a dry, nonadherent condition.

DRY PIPE A perforated or slotted pipe or box inside the drum and connected to the steam outlet.

DRY STEAM Steam containing no moisture. Commercially dry steam containing not more than 0.5 percent moisture.

DUCTILITY A plastic property of metal to withstand deformation without failure.

DUMP GRATE STOKER One equipped with movable ash trays, or grates, by means of which the ash can be discharged at any desirable interval.

DUTCHMAN A wedge or tapered plug used in butt-and-double-strap longitudinal seams of some boilers to fill the space between the abutting edges of the plate form the end of the inside butt strap to the edge of the adjoining course.

DUTCH OVEN An extended furnace, external to the main setting of a boiler, used to increase the volume of an existing furnace.

ECONOMIZER A series of tubes located in the path of flue gases. Feedwater is pumped through these tubes on its way to the boiler in order to absorb waste heat from the flue gas.

EFFICIENCY Of boiler operation: Output in heat units divided by input in heat units. The number of Btu’s contained in all steam evaporated is the useful output. The number of Btu’s contained in all fuel supplied to the boiler is the input. Of a riveted seam: Ratio of the strength of a unit length of a riveted seam to the same unit length of the seamless plate.

EJECTOR A device which utilizes the kinetic energy in a jet of water or other fluid to remove a fluid or fluent material from tanks or hoppers.

ELASTIC LIMIT The maximum tensile load to which a metal may be subjected with out becoming permanently deformed upon cessation of the load.

ELECTRIC BOILER A boiler converting electric energy to heat energy.

ELECTRIC FURNACE A furnace used for the refinement of high-grade steel.

ELECTROSTATIC PRECIPITATOR A device for collecting dust, mist, or fume form a gas stream, by placing an electric charge on the particle and removing that particle onto a colleting electrode.

EMBRITTLEMENT An intercrystalline corrosion of boiler plate occurring in highly stressed zones. Cracking may result.

ENTHALPHY A thermal property of a fluid which is a function of state and is defined as the sum of stored mechanical potential energy and internal energy. It is generally expressed in Btu per pound of fluid (joules per kilogram).

ENTRAINMENT The conveying of particles of water or solids from the boiler water by the steam.

EQUALIZING TUBE A boiler tube used to connect the steam spaces of two steam drums, or pressure parts of a boiler.

EROSION The wearing away of refractory or of metal parts by the action of slag or fly ash.

EVAPORATION RATE The number of pounds of water evaporated in a unit of time.

EVAPORATOR A pressure vessel used to evaporate raw water by means of a steam coil. The steam is condensed by means of cooling water coils, and this distilled water is used as makeup boiler feed.

EVAPORATOR CONDENSER That section of an evaporator installation which condenses the vapor.

EXCESS AIR Air supplied for combustion in excess of that theoretically required for complete oxidation.

EXPANDED JOINT The pressure tight joint formed by enlarging a tube end in a tube seat.

EXPLOSION DOOR A door in a furnace or boiler setting designed to be opened by a predetermined gas pressure.

EXPLOSION FIRESIDE Combustion which proceeds so rapidly that a high pressure is generated suddenly.

EXTENDED SURFACE Heating surface in the form of fins, rings, or studs, added to heat-absorbing elements.

EXTERNAL CORROSION A chemical deterioration of the metal on the fireside of boiler heating surfaces.

EXTRACTION FEEDWATER HEATER A closed feedwater heater supplied with steam extracted or bled from a stage of a steam turbine. See also feedwater heater.

FACTOR OF SAFETY The ratio between that stress which will cause failure and the working stress. This ration often applies to pressures instead of stresses

FAN PERFORMANCE A measure of fan operation in terms of volume, total pressures, static pressures, speed, power input, and mechanical and static efficiency, at a stated air density.

FAN PERFORMANCE CURVES The graphical presentation of total pressure, static pressure, power input, and mechanical and static efficiency as ordinate and the range of volumes as abscissas, all at constant speed and air density.

FATIGUE LIMIT A measure of the ability of a material to withstand repeated stress reversals without fracture or damage to the crystalline structure. A piece of soft iron wire may be broken easily by hand when it is bent back and forth a few times. Its fatigue limit is low. Conversely, a piece of spring steel may be flexed many thousands of times without showing any indication of distress. In this case, the fatigue limit is high. This property is of special value in steam-boiler construction.

FEED THROUGH A trough or pan form which feedwater overflows in the drum.

FEEDWATER HEATER A device used to heat feedwater with stream. See also extraction feedwater heater.

FEEDWATER REGULATOR A device for admitting feedwater to a boiler automatically on demand. Practically a constant water level should result.

FERRULE A short, metallic ring rolled into a tube hole to decrease in diameter. Also a short, metallic ring rolled inside of a rolled tube end. Also, a short, metallic ring for making up handhole joints.

FIN Usually a strip of steel welded longitudinally or circumferentially to a tube.

FIN TUBE A tube with one or more fins.

FIRE CRACK A crack starting on the heated side of a tube, shell, or header resulting from excessive tempera