The use of electrochemical noise methods (ENM) to study thick, high impedance coatings

• Published in: Progress in organic coatings 1995-07, Vol.29 (1-4), p.21-29
• Main Authors: Bierwagen, G P, Jeffcoate, C S, Li, J, Balbyshev, S, Tallman, D E, Mills, D J
• Format: Article
• Language: English
• ISSN: 0300-9440

Thick, high impedance organic coatings are the class of coatings used to provide corrosion protection to naval vessels, pipelines, gasoline storage tanks, and other large structures such as bridges and plant structures. These coatings, especially the newest generations now being used in practice, can provide exceptional protection and a lifetime of performance such that properly and accurately assessing and differentiating among competing coatings is a very difficult task. The standard protocol of salt fog testing (ASTM B117), immersion testing, and outdoor exposure in a corrosive environment with subjective evaluation of a coating's performance during and after testing does not adequately rank and predict coating lifetimes for new coating systems, especially for the environmentally compliant coating system such as powder coatings (especially the thick, fusion bonded epoxy (FBE) coatings used for pipelines), two component epoxy and urethane coatings and waterborne coatings. New objective test methods are desperately needed by users and manufacturers of coatings. A relatively new electrochemical test procedure, electrochemical noise methods (ENM) developed by Skerry and Eden, has been shown in the laboratory to be very successful in the ranking and prediction of relative coating performance. The method has been used successfully on naval ship coatings, several pipeline coatings, and other related systems, and Skerry has used them successfully on industrial maintenance coatings. These methods have been used in conjunction with electrochemical impendance spectroscopy, dc resistance measurements and cyclic salt fog testing of the Prohesion type. In the studies of pipeline coatings, thermal effects were investigated because of their extended range of use temperature. In these studies, it was discovered that electrochemical methods can be used for an in situ measurement of the T sub g of coatings in electrolyte immersion. Further, the "plasticizing" effect of aqueous electrolyte absorption and its relative irreversibility has been shown. For all coatings studied, ENM provided useful, objective, numerical data that rapidly ranks coatings and provides useful information on the relative lifetime prediction of coatings, which may provide up to 30 years of service.