INDUSTRIAL WATER to use phosphorus. Initially used over 30 years ago, zinc is a well-known and commonly used corrosion inhibitor. Unfortunately, zinc can also cause deposition issues and is a priority pollutant that is deemed harmful to the environment. Overall, this approach works well but has significant environmental drawbacks. In the last few years, it has become common for many companies to utilize stannous chloride (tin) in combination with a polyaspartic, glucaric or saccharic type acid. Typically fed at 2 – 3 times the levels required for zinc, at significantly higher cost, tin can provide an improvement in corrosion control versus an untreated system, but only in waters that do not have an oxidizer like hypochlorite or bromine present. These oxidizers are commonly fed continuously to cooling water systems to control biological growth. Tin materials have multiple oxidation states and in a cooling water system where oxidizers are present, the tin is quickly oxidized to an insoluble form and proceeds to precipitate in the bulk water, rendering it useless for corrosion control. In addition, tin has a solubility product constant similar to that of calcium phosphate salts, meaning it can cause deposition and failures, just like a phosphate-based material. The final issue for tin materials is that they can cause direct, galvanic corrosion to occur in production assets like heat exchangers. Many companies have attempted to use carboxylic acids to sequester the tin and keep it soluble, which works well in a neat, formulated chemical product. Still, upon introducing the product to the cooling water system, the carboxylic acid releases the tin, where it is affected by oxidizers and system metals. So how can companies meet their sustainability and environmental goals with a cost-effective solution? By using new technologies based on engineered films. Instead of trying to develop anodic or cathodic corrosion inhibitors to control a corrosion cell effectively, a team at SUEZ redefined the known mechanisms for corrosion control. By leveraging a series of techniques to understand every layer of a corrosion-inhibiting passivation film (<150 nm thick) on a metal 24 | June/July 2020
Tin vs E.C.O. Film performance.
surface, the team spent 15 years developing methods and chemistries to engineer a robust, protective film in an aqueous solution, that doesn’t inhibit heat transfer, and is thinner than previous phosphate-based technology. SUEZ’s E.C.O. (engineered carboxylate oxide) Film technology allows customers to meet or exceed changing environmental regulations and take significant steps towards reaching their sustainability goals. While it may contain trace amounts, this non-phosphorus technology helps to reduce toxicity to aquatic life, minimize harmful algae growth and algae blooms and increase water reuse. It also delivers the same performance and protection standards that cooling water system operators have come to expect from traditional chemistries. E.C.O. Film uses polymeric technology based solely on carbon, hydrogen and oxygen (CHO) containing polymers. In a cooling water system, the CHO technology primes the metal surface and aids in promoting a passivated metal oxide layer before helping to protect the metal oxide with a protective, dynamic, heterogeneous capping matrix layer. The film formation takes minutes to hours, not days or weeks, and is self-limiting in thickness. This means that the protective film will never grow to a point where deposition could cause production problems. Instead, it stays 20 – 50 nm thick. In some applications, a patented
surface film formation catalyst (SFFC) is used to enhance corrosion protection. This catalyst targets only the metal surface (it’s not found in the capping matrix) and helps to develop a stronger passivated metal-oxide layer in corrosive water conditions. Typically fed at 92% lower levels than zinc, and 96% lower levels than tin, the SFFC is an excellent choice for a non-phosphorus, environmentally conscious approach to treatment. In some applications, it has been documented that asset life (time to failure) can be 10 – 20 times longer due to the improved corrosion protection of E.C.O. Film. Unlike tin technology, it is 100% halogen/oxidizer stable, so regardless of how much hypochlorite or oxidizer is fed to control biological growth, it will continue to work and provide protection against harmful corrosion and deposition. This technology allows production facilities to minimize phosphorus contributions to outfalls, which, in turn, prevents harmful algae growth and detrimental eutrophication of freshwater resources. It can help facilities meet or exceed new and changing phosphorus discharge regulations and can prevent costly deposition associated with phosphate-based materials. James Green is with SUEZ – Water Technologies & Solutions. Email: j.green@suez.com
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