What is involved in acid cleaning ?

Chemical cleaning involves the circulation of acid at low concentration around the equipment to remove scale. The acid used will depend on the type of deposit and the equipment material that is being descaled and typically are hydrochloric, sulphamic, citric, formic, hydroflouric and phosphoric.

The procedure uses specialised equipment designed for chemical cleaning and the procedure will involve the following:

• 1. A sample of the deposit is analysed to establish the most suitable acid to be used.
• 2. The equipment to be cleaned is isolated to ensure that the cleaning solution cannot escape and contaminate other equipment, pipes or water courses.
• 3. Pumps are connected for recirculation.
• 4. The equipment is filled with acid to the required strength.
• 5. A corrosion inhibitor is added to prevent acid attack on any exposed metal.
• 6. The solution is monitored for acid strength and further acid added if required.
• 7. The procedure is stopped when the acid strength remains constant which indicates that no more scale removal is taking place or by visual examination if this is possible.
• 8. The acid cleaning solution is removed to drain and neutralised at the same time.
• 9. The equipment is refilled with water with a small amount of alkaline solution to neutralise any residual acid.

What can be done to prevent scale formation ?

Scale deposition can usually be prevented by a well designed and controlled water treatment programme.
Systems such as steam generation, cooling towers and evaporative condensers which are supplied with hard water generally have some form of external water treatment equipment such as a water softener or reverse osmosis system to remove the hardness from the water before it enters the equipment. This is the only long term satisfactory method of ensuring scale free conditions and will be successful as long as the equipment is maintained and monitored correctly. See our Plant & Equipment section for further information on this type of plant.