Metals, corrosion biocidal effect

Removing suspended solids, decreasing cycles of concentration, and clarification all may be beneficial in reducing deposits. Biodispersants and biocides should be used in biofouled systems. Simple pH adjustment may lessen precipitation of certain chemical species. The judicious use of chemical corrosion inhibitors has reduced virtually all forms of aqueous corrosion, including underdeposit corrosion. Of course, the cleaner the metal surface, the more effective most chemical inhibition will be. Process leaks must be identified and eliminated. 

The pH of a metalworking fluid must be kept above neutrality in order to prevent acid corrosion of the metal In vitro, acid catalyzed nitrosation is optimized at pH 3.5 (4 0) however, it has been shown that In the presence of other catalysts, aqueous solutions of amines and nitrite leads to significant yields of nitrosamines at room temperature over the pH range of 6.4 to 11.0 (41). Furthermore, C-nitro-containing, formaldehyde-releasing biocides, such as bronopol or tris nitro, exert their potential catalytic effect in alkaline solution. It would thus be desirable to determine the optimum pH for a metalworking fluid that would lead to the lowest concentration of nitrosamine possible. 

An example of such a product is ioBio , marketed by Baltimore Aircoil Co. (BAC). It is proposed for small cooling systems. This system is, in effect, an in-line dispenser of prilled elemental iodine (U), with replaceable iodine canisters available. The equipment is placed in the makeup waterline to the tower, and in-line options include filters, water meters, and back-flow prevention devices. Claims made are that the biocidal action of the elemental iodine is not affected by changes in temperature, system load, or water chemistry. Also, the system is compatible with virtually all scale and corrosion inhibitors and does not contribute to the corrosion of metal surfaces. 

Chlorine (usually as NaOCl) is an excellent universal biocide. Problems Chlorine compounds are corrosive to metals (only slightly with stainless steels). Chlorine is neutralized by organic matter (but a more concentrated solution, e.g., 1% NaOCl, will probably overcome the problem). Many of the chlorine household bleaches make effective and economical biocides. NaOCl (10%) stored in brown plastic bottles was stable for two years at 4°C and 1% solution for 20 weeks at 24 °C. Addition of 0.1% anionic detergent increases the power of hypochlorite (a useful anionic agent is sodium lauryl sulfate, 496). CAUTION A few anionic and some nonionic detergents will reduce active chlorine compounds. 

---