A Novel Adaptation of 1950 Vintage Technology to Prevent Pitting of Copper Heat Exchanger Tubes in a Hydronic System Infected by Corrosive Bacteria

After more than 20 years of less than ideal water treatment practices, a major southwest industrial park began experiencing frequent water leaks from copper heat exchanger coils served by semi-closed chilled water and warm water piping networks at the site.  Even new replacement coils began leaking in as little as 60 days after installation.  The immediate cause of the problem was diagnosed as microbiologically influenced corrosion but the extensive piping networks were designed and operated in a manner that made it nearly impossible to eradicate the offensive bacteria. 

This paper describes the development and implementation of an innovative offline passivation process that prevents pitting in the presence of corrosive micro-organisms.  The passivation process establishes a thin, yet robust film of lepidocrocite (FeOOH) on the surface of yellow metals and is based on technology that was first used 60 years ago.

Over the past six years, numerous coils have been passivated and installed in the bacteria-infested water systems with no failures of treated coils to date, whereas untreated coils have continued to fail.