James R. Martin, James Martin; Arthur Webb, Naval Research Lab; Keith E. Lucas, Naval Research Laboratory
Current corrosion control coatings surface treatment removal processes are time consuming and generate significant volumes of hazardous waste. In addition the process generates a great deal of noise and large volumes of airborne dust and debris that can contaminate other corrosion control processes and maintenance activities. Conservatively the U.S. Navy performs corrosion control on more the 750,000 ft2 of steel for its ships tanks and voids, generating more than 9 million pounds of mixed abrasive and paint waste. This waste must be disposed of at a cost of nearly $2.7 million annually. These numbers however do not include the additional corrosion control and maintenance painting performed at the facilities level which could be estimated to be at least equal to that for ship maintenance. Chief among these is the removal of submarine Special Hull Treatment or SHT. Heat Induction technology is not new, but the application for coatings removal is a fairly recent innovation. Removal of surface treatments is accomplished by pushing a relatively high frequency alternating current through an induction coil that is held in close proximity to the surface to be heated. This generates a localized electromagnetic field that induces eddy current into the steel substrate. The resistance of the substrate causes these current to convert to heat. Steel surface temperatures can reach hundreds of degrees in seconds at the metal surface/coating interface, while the non-conductive bulk coating is much less affected. At ideal surface temperatures the coating is heated to the point where the coating adhesive feature is released and the bulk coating can be effectively scraped away with a hand scraper, leaving nearly a bare or pristine almost re-paint able surface.
