A boiler is one of the main components of a boiler plant. In it, the heat of fuel combustion or of hot process gases (waste heat boilers) is used to produce hot water or steam for use outside the unit itself.
Boilers can be broadly divided into two large groups: fire-tube (smoke-tube) boilers, in which water (steam-water mixture) surrounds tubes carrying hot gases, and water-tube boilers, in which water flows inside the tubes.
An economiser is an auxiliary component of a boiler plant that preheats feed or network water using the heat of flue gases.
The heat of fuel combustion or hot process gases is transferred to water through the walls of the heating surfaces: furnace and smoke tubes, waterwall and convection tubes, and the water economiser.
Deposits and why they are dangerous
Deposits on the water (internal) side sharply reduce heat transfer, since the thermal conductivity of scale and iron oxide deposits is 3–4 orders of magnitude lower than that of steel. In practice this leads to:
- overheating of tube metal, bulging and pinhole leaks, up to tube rupture and emergency boiler shutdown;
- excessive fuel consumption and lower boiler efficiency;
- higher hydraulic resistance of the water circuit and higher load on the pumps.
The composition of water-side deposits is determined by the water chemistry regime. When the regime is strictly observed, deposits consist mainly of iron oxides; when it is violated or the boiler is fed with poor-quality water, they contain hardness salts (carbonates), silicon, copper and phosphate compounds. Steam boilers also accumulate sludge at the low points — drums and headers.
The need for operational chemical cleaning is determined by the specific contamination of the heating surfaces (g/m²), measured on tube samples cut from the most thermally loaded sections, and by the increase in hydraulic resistance of a hot-water boiler. For hot-water boilers, Russian regulatory guidelines (RD 34.37.402-96) recommend cleaning at a contamination level of 800–1000 g/m² or more, or when hydraulic resistance has increased 1.5 times compared with a clean boiler.
RD 34.37.408 requires mandatory pre-commissioning alkaline cleaning of steam boilers to remove oily, siliceous and other contaminants from the internal surfaces, as well as part of the loose rust and mill scale formed during manufacture, storage and installation.
Cleaning methods
- Chemical flushing — dissolving deposits with chemicals circulated through the internal cavities of the equipment, followed by neutralisation of the spent solutions and passivation of the metal; used where tools cannot reach.
- Alkaline cleaning — removal of loose rust, oils and other contaminants from the internal surfaces of the boiler with alkaline solutions, most often a 0.5–0.8% sodium hydroxide solution with 0.3–0.5% trisodium phosphate.
- Hydrodynamic cleaning — breaking up deposits with a high-pressure water jet using high-pressure units, channel-cleaning hoses and special nozzles; for tubes, channels and vessels accessible to the nozzle.
- Mechanical cleaning — removal of dense and fully blocking deposits with manual and power tools; as a rule, requires disassembly or opening of the equipment.
- Dry ice blasting (cryoblasting) — gentle cleaning of accessible surfaces with solid carbon dioxide pellets, without chemicals, water or abrasives.
- Laser cleaning — non-contact removal of rust, mill scale, carbon deposits and coatings from accessible metal surfaces.
The applicability of a method to specific equipment is determined after inspection and agreed with the customer; methods are often combined. The methods used for each type of equipment are listed in its description on this page.
How the work is carried out
- Inspection. Examination of the equipment and, if necessary, video inspection (endoscopy) of internal surfaces. We determine the composition and thickness of deposits.
- Method selection. The method and mode are agreed with the customer for the specific equipment, material and deposits.
- Preparation. Any assembly and disassembly work required by the selected cleaning method.
- Cleaning. Cleaning by the selected method with control of the result.
- Protection. After chemical flushing — neutralisation of chemical residues, water rinsing and passivation of the metal surface against corrosion.
We work on a one-off basis or under a scheduled maintenance contract, with periodic inspections and preventive cleaning.
What we need for a quote
- boiler type and model, year of manufacture, capacity;
- fuel type, water chemistry regime, source of make-up water;
- when and how the boiler was last cleaned; deposit analysis results — if available;
- photos and videos, equipment passport or diagram — if available;
- preferred timing: scheduled shutdown, off-season, urgent work.
Frequently asked questions
Why is scale in a boiler dangerous?
Scale is a poor heat conductor: fuel consumption rises, efficiency falls and the walls overheat, which shortens the service life of the boiler.
When is the best time to clean a boiler?
The most convenient time is a scheduled shutdown or the off-season. We also consider urgent cleaning — please state your timing in the request.
What is done after chemical flushing?
The system is rinsed with water, chemical residues are neutralised and the metal is passivated — this protects the surfaces against corrosion after cleaning and during downtime.
Do you clean chimneys?
Yes, chimneys and flue ducts are part of our boiler services.