Defect Area Determination of Organic Coated Steels in Seawater Using the Breakpoint Frequency Method
Abstract
Coating breakdown is a major maintenance cost on ships. It is therefore desirable to have a rapid technique for predicting or evaluating coating performance nondestructively. A method for simply determining the extent of coating breakdown would therefore be of great use to the Navy. The breakpoint frequency method is described which allows determination of the electrochemically active area of a coated metal seawater. A computer model is used to explain the basis of the breakpoint method, and the model is compared to impedance and visual data from epoxy coated steel panels in ASTM (American Society for Testing and Materials) artificial seawater with and without an intentional defect of known area. The breakpoint frequency method was found to be extremely useful in determining the electrochemically active area of coated steel in seawater. The equivalent circuit model used in this analysis was found capable of fitting actual data in coated steel panels with and without an intentional defect. A correlation was obtained between the breakpoint frequency and visually estimated electrochemically active area on epoxy coatings of a variety of thicknesses. This method offers a simple alternative to determination of defect areas via the use of the pseudocapacitance from difficult-to-analyze low frequency impedance data. This approach also can detect the beginnings of coating breakdown long before visual indications are present. Keywords: Organic coatings, Naval vessels, Steel, Ships, Sea water corrosion, Deterioration, Breakpoint frequency method.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1990
- Accession Number
- ADA221066
Entities
People
- HP Hack
- John R. Scully