Chemical cleaning, considered one of the most effective methods of cleaning, is essentially a process to cleanse internal surfaces and walls of equipment, pipelines, vessels, kettles and heat exchangers of deposits or unwanted contaminants accumulated over a period of time.
Newly built systems require chemical cleaning to ensure that excess deposition such as grease, slag and residual contamination do not damage machinery or contaminate the product. Piping systems already in service also need to undergo chemical cleaning to remove scaling and contaminants deposited on the inner surface and walls which affect the flow of water or heat.
The hard dense scales are generally the result of deposit of calcium, magnesium or silicon, which act as insulators to elevate the temperature of the equipment beyond the design permit limit leading to operational failure due to overheating. Soft porous deposits on the other hand concentrate solids dissolved in water to an excessive level leading to internal corrosion of the equipment.
Chemical cleaning is required as part of preventive maintenance to avoid failures and breakdown in equipment and machinery due to deposits built over time. Several factors need to be considered before deciding on the chemical cleaning method to be used.
Chemical cleaning of pre commissioned systems refers to removal of contaminated deposits like miliscale and construction debris from new pipe work installations in heating as well as cooling water systems. It is now a mandated requirement in new plant installations for chemical cleaning to be undertaken before commissioning to achieve maximum efficiency.
Chemical cleaning for existing installations however needs to be customized and undertaken as per specific client needs. It might be necessary in such cases to keep undertaking cleaning in parts while ensuring existing heating and cooling systems are operational so that normal business is not interrupted. Conducting chemical cleaning in parts while keeping systems operational generally requires a higher level of expertise.
Chemical cleaning methods can be of the following kinds
- Inhibited Acid Cleaning is the use of acidic solution of low concentration to remove scales and oxides from the insides of pipe surfaces of systems like boilers, cooling towers and condensers. Inhibited hydrochloric acid as well as ammoniated citric acid is mostly used as they contain chemicals that form a protective film over the pipe work preventing further corrosion.
- Polymer Cleaning is the breaking down of deposits on pipe work into smaller particles which can then be flushed down into the drain by chemicals.
- Biocide Wash is essentially preventive chemical cleaning to control the spread of bacteria and biofilms both in new and existing pipe work. Chlorine dioxide, for instance is particularly effective in treating Pseudamonas and Legionella.