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Additional water

- water after chemical and thermal processing meant to make up water losses after boiler blowing-down and leakages of water and steam in a steam-condensate duct.

Assembly unit

- unit which constituent elements are attached to each other by welding, screwing, beading and other assembly operations.

Autonomous economizer

- economizer integrated either in a boiler or in a flue-gas duct. Water heated in this economizer is in whole or in part used outside this boiler. It also can be a separate economizer with water at its outlet used (fully or partly) in a steam boiler.

Autonomous superheater

- superheater integrated either in a boiler or in a flue-gas duct. It also can be a separate superheater outside the boiler with an external supply of steam.


- sharply bent section of bent elbow.

Bent elbow

- elbow bent in a special machine or by special device


- process of releasing ample quantity of energy in a limited space for a short period of time followed by a blast wave. In a wave front pressure is over a design value that gives an impulse for blast pressure safety valves to respond. It causes residual deformation and (or) destruction of boiler elements.

Boiler burner (burner)

- device supplying fuel and air for its burning to the boiler furnace. Burner also maintains sustainable combustion of fuel.

Boiler dimensions

- the height, width and depth of the boiler with insulation, lining, supporting and stiffening elements (stiffening girders and mounting frames) excluding protruding instruments, sampling pipes, pulse tubes and others. Measurements of height, width and depth are taken from the top of the longitudinal rod. If there is no rod – from the top height mark of the boiler.

Boiler element

- assembly unit of the boiler designed to perform one of its basic functions (for instance, header, drum, steam superheater, heating surface, etc).

Boiler furnace (furnace)

- device designed for burning fossil fuel, partial cooling of combustion products and ash removal.

Boiler limits of water-steam circuit

- shut-off devices of feeding, drain and other piping, as well as safety valves, all other types of valves and valve gates constraining inner surfaces of boiler elements and connected piping. If there are no shut-off devices, delivery limits are considered the limits of the boiler.

Boiler water

- water circulating in the boiler.

Boiler working pressure

- Maximum excessive pressure behind the boiler (superheater) at normal operating conditions.

Burner device

- burner coupled with a fuel injector, shut-off fuel valves, inspection hole and automatic instrumentation (if provided in a design project).

Butt-welded joint

- joint where welded elements adjoin each other with butt ends. Butt-welded joint includes a weld and heat-affected zone.

Design pressure

- maximum excessive pressure in the part, for which strength calculation is performed to determine its basic dimensions providing reliable operation within a design service life.

Design service life

- service life calculated in calendar years. After its expiration basic elements of the boiler operated under pressure have to be inspected to determine whether the boiler can be further operated (parameters and conditions of such operation) or it is to be dismantled. Service life is to be calculated from the day when the boiler was put on line.

Design service life of the boiler (boiler element)

- duration of boiler’s service life within which OEM can guarantee reliability of its operation provided all operational conditions specified in OEM’s instructions are met as well as design number of hot and cold startups was not exceeded. 

Design temperature of ambient air

- average temperature of ambient air during the coldest week of the year.

Direct system water

- water with design parameters (temperature, pressure and chemistry) in a pressure pipeline of heat system from the source of heat to its consumer.


- device heated with combustion products and designed for warming-up and partial evaporation of water supplied to the boiler.

Expert technical diagnostics

- technical diagnostics of the boiler after expiration of its design service life or design time of its safe operation, after breakdowns or detection of failed elements under pressure to determine possibility of further operation and if so, its conditions and parameters.

Fabrication item

- industrial product counted in pieces or items

Feed water

- water with design parameters (temperature, pressure and chemistry) at boiler inlet.

Fuel injector

- device delivering, spraying and distributing liquid fuel supplied to the furnace in air flow.

Gap in a corner joint

- gap between a connecting pipe and a part itself which remains (fully or partly) after welding is completed.

Heat-Recovery Steam or Hot-water Generator

- steam or hot-water boiler without a furnace or with one for gas afterburning. Boiler fires hot flue gas of technological or metallurgical processing plants or other technological flows of products of combustion.


- profiled part of piping designed to change direction of handled medium flow at 15˚-180˚ angle.

Major element

- assembly unit made of parts under intrinsic pressure which perform certain functions of the boiler (for instance recovery of steam-water mixture and its separation, steam superheating, etc).

Makeup water

- Water after specified in the project chemical and thermal processing designed to recover water losses after boiler blowing-down and water leakages in heat-consuming devices and heat systems.

Maximum allowable boiler pressure (element)

- maximum allowable excessive boiler pressure determined on results of technical inspection or control strength calculations.

Maximum temperature of the wall

- maximum temperature of boiler part or piping from the side of medium with maximum temperature. Maximum temperature of the wall is determined on the basis of thermal and hydraulic calculations or on the results of testing without taking into account temporary increase of heating (not more than 5% of a design service life).

Normal operating conditions

- group of operational modes specified in scheduled regulations of work: stationary mode, startup, changes of capacity, shutdown and hot standby.

Normative documents (ND)

- technical specifications, industrial and national standards.


- item fabricated of one grade of metal without assembly operations

Piping element

- assembly unit of steam or hot water pipeline designed to perform one of its basic functions (for instance, straight-line section, knee, T-joint, cone reducer and others).


- taken into account in strength calculation short-time pressure boost in boiler furnace or flue-gas duct which doesn’t cause any permanent residual deformations and destruction of boiler elements.

Return system water

- water of design parameters (temperature and chemistry) in heat system from consumer to system pump.

Service properties of metal

- complex of mechanical and physical properties taken into account in strength and thermal calculations of power equipment.

Specialized project (design) organization

- project organization, research center (or research and development company) or manufacturer if one of its functions is design of boilers and boiler elements.

Stationary boiler

– boiler installed on immovable foundation.

Steam boiler

- unit with a furnace heated with combustion products of fuel burnt in it. The unit is designed to generate steam with superatmospheric pressure used outside the boiler.

Steam boiler with water-heater

- boiler with a device in its drum for heating water, with heated water used outside the boiler. Steam boiler with a separate water-heating plant included in its natural circulation.

Steam or liquid boiler with high removal fluid

- boiler where handled medium is high removal fluid in liquid-vapor or liquid state.

Steam superheater (superheater)

- device meant to increase steam temperature over the saturation point which corresponds with pressure in the boiler.

Technical documents

- technological instructions and flow-process charts designed by original equipment manufacturer.

Technical inspection

- examination of unit technical.

Test pressure

- excessive pressure necessary to perform strength and leak hydraulic testing of boiler or its elements.

Water heater

- heater of system water, steam or water heat exchanger, where heat of steam or boiler water is used to generate hot water and other parameters. Water heater can be either integrated in a boiler or a separate one.

Welded details not working under pressure

- details welded to inner or outer surfaces of boiler elements (drum, header, etc) not taken into account in stress calculations for this el
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