COATING ENGINEERING EXPERT
Coating are applied as a liquid film and after the solvent evaporation and / or chemical conversion forms a continuous protective film. Under ideal conditions a properly applied barrier coating will resist penetration of the chemical to the substrate, thus eliminating corrosion. In order to do this, a coating must have the following characteristics:
A.- Be completely unaffected by chemicals;
B – Have zero water permeability (also not penetrated by oxygen and ions);
C – Have excellent adhesion to the surface so that corrosion will not be occurring under the film even if mechanically damaged.
These requirements are so extreme that no protective coating has yet been found to satisfy all the above requirements. But several types of coatings approach these requirements to a certain degree. A proper selection is, therefore, very important, if corrosion is to be eliminated or at least controlled at a low level.
The application of a coating is critical to the long term success of any coating system. Most coating system failures are direct result of not following manufacturer’s recommended application procedures. ES has extensive coating inspection experience and have performed many coating failure analysis.
One of the most unusual coating failures was the curious result of decarbization of the surface of pipe, that was not previously identified and result in an unusually soft surface that prevent an adequate profile (anchor pattern). As seen in the following: Micrograph of Decarburization
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