This abstract comes from an article by Günter Binder, Federal Waterways Engineering and Research Institute, Karlsruhe, Germany. The complete 11- page article is here: https://corrosion-offshore.iqpc.de/mediacenter
What is the best method for finding out appropriate corrosion protection systems for steel structures?
Coated hydraulic structures for example undergo stresses from impacts, abrasion provoked by transport, erection and use as well UV-aeration, osmoses, and cathodic protection current.
The selection criteria generally are reduced to check the coatings by defined laboratory test procedures especially by measuring the rusting of the substrate at an artificial scribe after a certain time of corrosion loads in cabins. The advantage is obvious: short time of testing and getting a definite value of rusting for comparing it with the threshold value or forming ranking.
From that a further question arises: Which real stresses for coated steel structures are there and how they may be reproduced in laboratory test procedures? With the help of a variation diagram the rusting measurements of diverse coating systems may be checked for the correlation between field and laboratory results.
A first step for that is to compare rusting at a scribe and by that it is necessary to get rusting values from different protection systems from both the test procedures mentioned above (salt spray or cycle test procedures e.g. and long term trials in nature i.e. field tests). It is advantageous to subdivide the field test trials in immersion, water changing, and splash water zone.
The research carried out by BAW sometimes shows significant positive correlations with a certain statistic security. The results also show, that field test results are more reliable than laboratory tests and that protection systems work at best with special formulated primers.
This benefit also can be observed when protective coatings are tested to the resistance to electric protection currents: Systems with special primers generally show better results, which can be measured by the uptake of protection current and the grade of blistering. It should be mentioned that cathodic corrosion plants work especially in the immersion zone, where otherwise the corrosion stresses are low as shown.
Hydraulic and offshore steel structures often suffer by mechanical stress reasoned by transport and erection of the buildings. This kind of damages can be imitated by impacts to the coated panels. To make the damages by resulting micro fissures visible the panels in addition to the falling weight test where loaded by the salt spray test. The first results shows the positive effects of zinc-dust primer systems in combination with elastic binders, mainly single pack polyurethanes.
The rest of the 11-page article is available at the url above.
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