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Issue link: http://coatingspromag.epubxp.com/i/72303
were to call what happened a "fail" and I was the applicator, there would be quite some discussion between us. Then again, 300 psi really is not that much at all. By leaving your adhesion tester on there for 10 s, you probably are pulling and extra 50 to 100 psi just by its weight hanging there. What you could do is make the test destructive and see what value the dolly is pulled off. You should be able to reach values up to 600 psi easily; otherwise something may indeed be wrong with your curing. Perhaps you can check with the coating manufacturer. A: My opinion is that the coating failed the test. The fact that the test pull strength reached its maximum value and then "hung" at that value for 10 seconds before failing does not alter the fact that it failed. The test's valid- every mission a SPYfor Inspect Any Metal Surface Coating For pipes, tanks or any coated contoured surface in the field or inside your manufacturing facility, we simplify coating integrity testing with our full line of SPY® portable and permanent Holiday Detectors. SPY® Model 780, 785 and 790 Portable Holiday Detectors New ergonomic design Pipe coating inspections up to 60" Extremely durable Infinite voltage setting on the fly SPY® Wet Sponge Portable Holiday Detectors Compact, lightweight wet sponge holiday detectors No belts, lightweight, fast set up Sponge roller speeds large flat surface area inspections Interchangeable flat or roller sponge SPY® In-Plant Holiday Detector Systems Custom designed to streamline manufacturing Reliable continuous inspections on the assembly line For more details on SPY® From pipecoating inspections to large flat surfaces products and our complete line of SPY® PIPELINE INSPECTION COMPANY, LTD. PH: (713) 681-5837 • FAX: (713) 681-4838 Write in Reader Inquiry #119 22 CoatingsPro J July 2012 Holiday Detection Equipment visit our website @ www.picltd.com. ity is another question. I also wonder whether the zinc was fully cured at the time of the test. A: I have never heard that a coating can be tested to see if it complies with a certain adhesion value by leaving the pulling force on the dolly for a certain period of time. If you do this, you are exerting a supplementary force that you should not. If you were to apply this thesis to any other adhesion test, how are we going to define before what interval the dolly cannot come off? Ten seconds, 60 seconds? Or should you be able to leave your adhesion tester on there the whole day—and would you want to? If you have a standard three-coat epoxy/ polyurethane system that you know has an adhesion failure of say 1,000 psi, I bet that, if you pull it up to 800 psi and leave the load on long enough, your dolly eventually will pop off at that given load of 800 psi. At an adhesion of 300 psi, if this is at a vertical surface and your dolly comes loose after 10 seconds, I should expect the adhesion tester to supply some additional pulling force just be hanging onto that dolly. I don't think this was meant to be incorporated into the standardized test method. A: This is an interesting situa- tion. I agree that the adhesion results are sorry, but I don't agree that the coating failed the test. I think that one should either test to failure or test to the requirements of the specification and promptly remove the load. I would not load the dolly to the minimum stress required by the specification and then stand around filing my fingernails and whistling while waiting to see if adhesion failure might eventually occur. A: Ideally, the coating specification would tell us precisely how to perform the test. A further thought on the issue of leaving pressure on the dolly for a while: Is this not similar to pressure testing a vessel? The vessel is filled with water, pumped up to test pressure, then left at test pressure for how long—30 minutes? An hour? Six hours? I don't think the vessel would be taken up to test pressure and then immediately relieved of pressure, would it? CP