Coating Inspection

T.N. Bortak, Guide to Protective Coatings Inspection and Maintenance, United States Department of the Interior Bureau of Reclamation Technical Service Center, Washington DC, 2002. 

The war itself also drove the development of improved and miniaturised electronic components for creating oscillators and amplifiers and, ultimately, semiconductors, which made practical the electronic systems needed in portable eddy current test instruments. The refinement of those systems continues to the present day and advances continue to be triggered by performance improvements of components and systems. In the same way that today s pocket calculator outperforms the large, hot room full of intercormected thermionic valves that I first saw in the 50 s, so it is with eddy current instrumentation. Today s handheld eddy current inspection instrument is a powerful tool which has the capability needed in a crack detector, corrosion detector, metal sorter, conductivity meter, coating thickness meter and so on. 

The inspection possibility of welds and rough surfaces also under the coating of various foulings, oils, scale, rust etc. without the preliminary preparation. 

Photomechanical stencils are of two types direct coatings and transfer films. Direct coatings are either bichromated gelatin or bichromated poly(vinyl alcohol) (PVA). The coated screens are exposed through a positive, washed, and inspected. These screens are used for printing electronic components. They are not practical for commercial work because of the difficulty of reclaiming the screen after use. 

To add surface area, the supports are uniformly coated with a slurry of gamma-alumina and recalcined under moderate conditions. The wash coat acts to accept the active metals, typically low levels of platinum and palladium, in a conventional impregnation process. In the United States in passenger car apphcations the spherical catalyst is used almost exclusively, and methods have been developed to replace the catalyst without removing the converter shell when vehicle inspection reveals that emission standards are not met. 

After commissioning the protection installation, an on potential of = -0.82 V was imposed. In the course of a few years of operation, the protection current rose from 100 to 130 mA. The mean values were = -0.63 V and the values were t/ = -0.50 V. An inspection carried out after 5 years showed that cathodic blisters, whose contents were alkaline, had developed in the coating. The steel surface at these places was rust free and not attacked. Uncoated steel at the pores was covered with CaC03 deposits as a result of cathodic polarization. 

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