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Evaluating Corrosion Under Protective Coatings for Steel in Marine Environments

Destructive physical inspection for corrosion under protective coatings post-exposure suggests that significant metal loss may be occurring in the absence of a visual indication and that actual corrosion/material loss does not correlate with the visual inspection data.

Product Number: 51317--9005-SG
ISBN: 9005 2017 CP
Author: James Ellor
Publication Date: 2017
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Protective organic coatings are the primary form of corrosion control for steel structures exposed in a marine environment. For more than fifty years testing of coatings suitable for various service environments has relied substantially on exposure of coated steel panels of different configurations followed by evaluation via visual inspection. Exposure may include accelerated testing or natural environmental exposure in immersion or atmospheric conditions. Common visual inspection practices include semi-quantitative evaluation of the degree of rusting degree of blistering and extent of scribe creep (i.e. cutback). Coatings performing well in these evaluations versus specification standards are often deemed “acceptable.”Recent research suggests that common visual inspection protocols while useful for judging aesthetic concerns may not be sufficient in identifying the substrate corrosion control provided by a coating. Destructive physical inspection for corrosion under protective coatings post-exposure suggests that significant metal loss may be occurring in the absence of a visual indication and that actual corrosion/material loss does not correlate with the visual inspection data. With a broader dataset of similar results the data may suggest that the industry needs to reevaluate coating performance evaluation methods wherein the primary issue is substrate corrosion control as opposed to aesthetics.

Protective organic coatings are the primary form of corrosion control for steel structures exposed in a marine environment. For more than fifty years testing of coatings suitable for various service environments has relied substantially on exposure of coated steel panels of different configurations followed by evaluation via visual inspection. Exposure may include accelerated testing or natural environmental exposure in immersion or atmospheric conditions. Common visual inspection practices include semi-quantitative evaluation of the degree of rusting degree of blistering and extent of scribe creep (i.e. cutback). Coatings performing well in these evaluations versus specification standards are often deemed “acceptable.”Recent research suggests that common visual inspection protocols while useful for judging aesthetic concerns may not be sufficient in identifying the substrate corrosion control provided by a coating. Destructive physical inspection for corrosion under protective coatings post-exposure suggests that significant metal loss may be occurring in the absence of a visual indication and that actual corrosion/material loss does not correlate with the visual inspection data. With a broader dataset of similar results the data may suggest that the industry needs to reevaluate coating performance evaluation methods wherein the primary issue is substrate corrosion control as opposed to aesthetics.

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