Descaling
Deep cleaning of highly encrusted systems and equipment
Descalers are usually products of a highly acidic nature suitable for descaling systems, washing tunnels, nozzles, pipes, heat exchangers, tanks. They are used above all to clean the phosphodegreasing tunnels during periodic bath changes, but also in all those systems where mineralized deposits and/or sludge of various kinds form. They are therefore "programmed" cleaning products that are used and thrown away after the purpose. Usually the descaler bath is neutralized after use with a strong base in order to be disposed of correctly. Being very acidic, these products must be used carefully and with the right percentages (from 5 to 15%) to avoid corroding the system itself or the more delicate components. The chemistry of these products is quite simple and similar to pickling products, since their primary purpose is only to remove encrustations in a short time. We therefore find formulations based on strong acids such as phosphoric, hydrochloric, nitric, sulfuric acid or mixtures of them. The addition of corrosion inhibitors and a minimal surfactant part is always recommended, in order to speed up and mitigate the aggressive action of the acid towards the surfaces to be cleaned.
Depending on the type of materials to be treated, different acid mixtures will be recommended, for example hydrochloric acid is not recommended for steels as it causes strong corrosion. If it is used (to remove strong encrustations that would otherwise not be removable) it must be buffered or assisted with other acids or inhibitors.
For phosphodegreasing tanks, descalers based on phosphoric acid alone can be used, this allows neutralization to be avoided at the end of the wash since the subsequent filling of the tanks will not be contaminated by acids not consistent with phosphating.
The acids used in traditional formulations are dangerous for humans, they develop toxic and corrosive gases, especially if heated, and they are also expensive to dispose of. For this reason there is an increasing tendency to use organic acids; although they have a lower pickling strength, if used at higher percentages or at higher temperatures, they can replace the mineral acids of old descalers. Worthy of note in this area is sulfamic acid, often combined with other organic acids (citric, glycolic, sulfonic) and with the synergistic action of strong sequestrants and surfactants. As with picklers, if it is necessary to operate on encrustations that are not too developed, neutral descalers can be used, based on metallic sequestrants, inhibitors and surfactants (the cost is higher but in favor of a very low risk for health and lower maintenance costs wastewater management).
Old generation formulation example:
- Demi water: 30-40%
- Nitric acid 52%: 13-16%
- Phosphoric acid 75%: 20-30%
- Hydrochloric acid 30%: 10-15%
