High Risk Work Licence - Standard Boiler (BS) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Fire-tube boiler

A boiler in which hot combustion gases pass through tubes surrounded by water. It is limited to lower pressures and smaller capacities than a water-tube boiler.

Water-tube boiler

A boiler where water circulates inside tubes that are heated externally by combustion gases. It suits high pressure and large steam output because small tubes withstand pressure well.

Boiler heating surface

The gas-side area of the boiler exposed to products of combustion, measured in square metres. It largely determines the evaporative capacity of the boiler.

Equivalent evaporation

The steam output expressed as evaporation of feedwater from and at 100 degrees Celsius. It allows boilers of different operating conditions to be compared fairly.

Low-water fuel cutout

A safety device that shuts off fuel to the burner when the water level falls below a safe limit. It must be tested regularly by evaporation or drain test.

Safety valve accumulation test

A test confirming that with the safety valve fully open, boiler pressure does not rise more than ten percent above the valve set pressure at maximum firing.

Gauge glass blowdown

Opening the gauge glass drain and connections to clear sludge and confirm that the indicated water level is true. It is done at least once per shift.

Non-return feed valve

A check valve between the feed pump and the boiler that allows feedwater in but prevents boiler water and steam from flowing back into the feed line.

Injector principle

Steam expands through a nozzle and condenses in the feedwater, transferring momentum and creating a pressure high enough to force water into the boiler.

Normal water level

The water level at the centre of the gauge glass during normal operation, with the lowest visible level safely above the highest heated surface.

Modulating level control

A control system that continuously adjusts the feedwater valve to hold water level within a narrow band as steam demand changes, avoiding cycling.

Excess air

Air supplied above the theoretical amount needed for complete combustion. Too little produces carbon monoxide and smoke; too much wastes heat up the stack.

Balanced draft

A combination of forced-draft and induced-draft fans that keeps the furnace slightly negative, preventing flame escape while drawing gases through the boiler.

Furnace pre-purge

Passing air through the furnace before ignition to clear any accumulated combustible gases, typically at least four furnace volume changes, preventing explosion.

Flame failure protection

A system that proves the flame with a scanner and shuts off fuel within seconds if the flame is lost, preventing unburnt fuel from accumulating.

Scale formation

Deposits of calcium and magnesium salts on heating surfaces. Scale insulates the metal, raises metal temperature and can cause tube overheating and failure.

Dissolved oxygen corrosion

Pitting of boiler metal caused by oxygen in the feedwater. It is controlled by deaeration and by chemical oxygen scavengers such as sodium sulphite.

Total dissolved solids

The concentration of dissolved salts in boiler water. It is controlled by blowdown to prevent foaming, priming and carryover into the steam system.

Bottom blowdown

Opening the valve at the lowest point of the boiler to remove sludge and sediment from the mud drum. It is done with the boiler at the correct water level.

Surface blowdown

A continuous or intermittent draw-off from the water surface that removes dissolved solids and scum, helping to control total dissolved solids and foaming.

Cold start warming

Bringing a cold boiler up to pressure slowly, with air vents open, to limit thermal stress on the shell, tubes and seams and avoid differential expansion damage.

Paralleling a boiler

Bringing a boiler on line by raising its pressure slightly above header pressure, draining the connecting line, then opening the stop valve slowly.

Low-water emergency action

If water is not visible in the gauge glass, shut off fuel immediately and do not feed water. Allow the boiler to cool before inspection to avoid a violent failure.

Foaming and priming

Foaming is a frothy water surface; priming is carryover of water droplets into the steam line. Causes include high dissolved solids, alkalinity, oil and overloading.

Water hammer

A sharp pressure shock caused by condensate slugs or trapped steam in a line. It is prevented by warming and draining lines before admitting steam.

Furnace explosion

Ignition of accumulated combustible gases in the furnace or flue. Prevention relies on pre-purge, proven flame scanner, correct fuel-air ratio and interlocked fuel valves.

Hydraulic test

A pressure test, usually at 1.25 to 1.5 times maximum allowable working pressure, with the boiler isolated and safety valves removed or gagged, to prove strength.

Internal inspection

An examination of the boiler interior, including shell, tubes, tubesheets, crown sheet, stays and mud drum, carried out at statutory intervals and recorded.

Boiler log book

A record of water level, steam pressure, feedwater temperature, blowdown, chemical tests and abnormal conditions, signed by the operator on each shift.

High-risk work licence

A statutory licence authorising the holder to operate a boiler of a specified class. Operating outside the scope of the licence is an offence.

Primary duty of care

The duty on a person conducting a business or undertaking to ensure health and safety so far as reasonably practicable, including safe plant and systems of work.

Hierarchy of risk control

The order of controls: eliminate the hazard, substitute, isolate, engineer, then administrative controls, with personal protective equipment as the last line.