Final Report: Self-Healing Corrosion-Control Coatings: An Enabling Technology To Restore Aging Water Infrastructure and Permit Alternative Water Use for CoolingEPA Contract Number: EPD10038
Title: Self-Healing Corrosion-Control Coatings: An Enabling Technology To Restore Aging Water Infrastructure and Permit Alternative Water Use for Cooling
Investigators: Liu, Jiong
Small Business: NEI Corporation
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $69,996
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Water and Wastewater
Description:Presently, there is a rapidly growing need to use alternate water sources for non-potable applications. The projected population growth and limited availability of fresh water sources have forced utility companies and industries to evaluate the use of alternate water (e.g., recycled water, produced water, and other impaired water sources) for non-potable water applications such as industrial and commercial cooling.
A key limitation in the use of such alternate water sources, however, is the corrosion of pipe materials, such as copper alloys, due to the presence of high levels of dissolved salts (1,000 to 400,000 mg/L sodium chloride in produced waters). The presence of dissolved salts causes the water to be ionic conductive and facilitates electrochemical corrosion pathways. In addition to dissolved salts, some reclaimed and produced water also contains highly oxidative metal ions and ammonia (1 to 30 mg/L). The dissolved oxidative metal ions promote corrosion of many metals. The presence of ammonia aids the corrosion of copper alloys in particular. Frequent replacement of corroded tubes and associated facility shutdown make it very expensive to use alternate water sources. Hence, successful use of these non-traditional water sources for cooling applications will require either (i) a treatment process for sodium chloride, oxidative metal ions, and ammonia removal; or (ii) an anti-corrosion metal surface treatment.
Most of the feasibility and pilot studies performed to date to use alternate water sources have evaluated either treating the water or adding corrosion control chemicals to meet the water quality requirements of the piping materials for corrosion control. Upon evaluation, these studies deemed this approach to be not viable due to either (i) high cost of treatment required to remove dissolved salts (~ $3000/AF), or (ii) the environmental implications of discharging a large quantity of corrosion inhibitors, such as 2-mercaptobenzimidazole and benzotriazole, in blowdown streams into a large water body.
NEI Corporation's solution to the problem is a sub-micron, thick, chemical conversion coating that adheres firmly to the internal surface of the heat exchanger tube. In the Phase I project, NEI has developed a new and novel conversion coating on copper alloys and other alloys. Laboratory corrosion testing in static conditions has demonstrated the high corrosion resistance of the coating formed on copper alloys. In addition, the unique microstructure of the coatings allows corrosion inhibitors to be incorporated and released in a controllable way. As a result, clear evidence of damage-responsive corrosion protection of the coating was demonstrated for copper alloys.
The main merits of the new coating system are as follows: 1) the formulation is water-borne, containing no toxic chemicals, and thus is environmentally benign; 2) the coating is highly stable and is a good barrier layer for corrosion protection of coated substrates; 3) the coatings showed damage-responsive characteristics, i.e., self-healing; 4) the coating layer is thin and does not affect the heat transfer efficiency of the tubes; 5) the formulation is universal, i.e., coatings can be formed on a variety of alloy substrates, including copper alloys, aluminum alloys, steel, and magnesium alloys; and 6) the coating is electrochemically active, akin to conducting polymer coatings.
In summary, the research has demonstrated the capability of a technology to provide corrosion protection of copper alloys in recycled water. As a result, the technology showed promise in enabling alternate water sources for cooling applications where heat exchanging tubes are made of copper alloys. In addition, a variety of engineering alloys can be coated with the new technology. Hence, the new technology developed in this research also may be capable of protecting other alloys from corrosion. Finally, the unique electrochemical characteristics of the coatings may enable the new technology to find wide application in a variety of industries.