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11 NACE INTERNATIONAL: VOL. 55, NO. 12 MATERIALS PERFORMANCE DECEMBER 2016 Continued on page 12 Adhesion Testing Q: I am looking for your considered opinion on the following: Is fair adhesion for the knife/tape tests accept- able for a newly applied inorganic zinc (IOZ)/epoxy/urethane coating system in terms of expected service life or perfor- mance? A: e problem with the knife test is in the skill and experience of the person conducting the test. It is highly subjective and you can get various degrees of results. e tape test is a little more objective, but it is still not a good tool for predicting service life of a newly applied IOZ/epoxy/urethane coating system. Several other factors have to be considered such as the plane of detach- ment within the coating system, the ty pe of detachment (flakes or peels), etc. A: My only comment would be is if you get a number less than a three you probably have a problem. If you get a four or five you probably do not have an adhesion problem but that does not necessarily correlate to the coating life cycle. A value less than three would certainly warrant concern and further evaluation of the coating system. Likewise with tensile adhesion. A low number might indicate a problem but a high number does not necessarily mean the coating system will achieve its full life cycle. In general, lower than expected numbers with either test indicate "possi- ble" problems. High numbers don't tell you as much. A: An evaluation of the system that you outlined resulting in any thing less than "very good " would seem to indicate that a more sophisti- cated evaluation should be performed. e time to deal with any skepticism is prior to warranty expiration, while the information on the project is still somewhat fresh. A: I would suggest asking the coating manufacturer if it will warrant its product with those test results and maybe also what that warranty would include. Old Lining Evaluation Q: We need to evaluate a two-coat, 30- to 35-mil (0.8- to 0.9-mm) glass f lake-f illed vinyl ester tank lining with close to 17 years of service. Visually, the lining appears to be intact. Several pull tests resulted in a combination of adhesive and cohesive failures between coats and in the topcoat. We discovered that a hold primer was used after the f irst coat of vinyl ester. None of the pull tests separated below this hold primer layer. The tank has held a variety of chemicals, oils, sludge, and solids (simultaneously).