Chemical flushing is the removal of deposits with chemical solutions that dissolve or loosen them. The solution circulates in a closed loop through the internal cavities of the equipment, so the method can be used where tools and nozzles cannot reach: channels of plate heat exchangers, boiler heating surface tubes, long pipelines with complex routing. For such equipment it is often the only way to remove deposits.
Chemicals
Deposits are usually a mixture of substances, so a single chemical is rarely enough. Alkaline solutions are used — sodium hydroxide, soda ash, trisodium phosphate (alkaline treatment) — to remove oily contamination and loosen deposits containing silicon compounds and sulphates, as well as acid solutions and complexones (Trilon B / EDTA) in compositions with organic acids. Corrosion inhibitors are added to acid solutions to protect the equipment metal during treatment. After acid treatment, chemical residues are neutralised and the metal surface is passivated against corrosion with special oxidiser-based compositions — sodium nitrite, hydrogen peroxide, etc.
The formulation and mode — concentration, temperature, duration — are selected according to the composition and amount of deposits and the equipment material; if necessary, the mode is tested in the laboratory on samples with deposits. Chemicals for flushing and protecting equipment can be purchased separately — see the Cleaning chemicals section.
Stages
- Preparation. Assembling the flushing circuit: connecting the flushing unit, pressure-testing the circuit with water, checking circulation.
- Water flushing. Removal of loose deposits and sludge.
- Alkaline treatment — if oily contamination, silicon compounds and sulphates are present.
- Acid treatment. Circulation of an inhibited solution with control of acid concentration or pH, temperature and iron content in the solution; with large amounts of deposits — in several stages.
- Neutralisation and water flushing. Displacement of the solution, neutralisation of chemical residues, flushing until the water is clear.
- Passivation. Treatment of the cleaned surfaces to form a protective film that protects the metal against corrosion.
Limitations
- circulation is required: it must be possible to connect a flushing unit to the equipment;
- the formulation is selected for the material — copper, aluminium and stainless steel have their own restrictions;
- spent solutions are neutralised and rendered harmless before discharge or handed over for disposal.
Other methods
- 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.
Frequently asked questions
Will the acid damage the equipment?
Corrosion inhibitors are added to the solution, and the process is controlled by pH, temperature and concentration. After cleaning — neutralisation and passivation of the metal.
Does the equipment need to be disassembled?
As a rule, no: the solution circulates through the internal channels. Connection points for the flushing unit are needed.
How is the chemical selected?
Based on the composition of the deposits and the equipment material. This requires an inspection and, if necessary, deposit analysis.
How do you know the cleaning is complete?
By the solution parameters — the end of the reaction, stabilisation of pH and iron content — and by the result: inspection of surfaces, opening up the unit or restoration of its operating parameters.
What do you do with spent solutions?
We neutralise them and render them harmless before discharge, or hand them over for disposal.