An interesting series of recommendations to carry out an accurate analysis of failures in coatings.
By José Manuel Guizado Solis*
In coatings, many times we talk about what we must do to avoid failing, there are reference standards, expert opinion and recommendations from the same manufacturers, who are always ready to warn us about what we must do so that their product does not fail due to inadequate labor, because of course, the product is not bad as long as it is used properly. But what if someone forgets to take into account some conditions of service of the product or surface that we want to protect? Then we could be on the verge of a fault or defect.
NACE and SSPC recommend us to always have details of the work that has been done, keep a record of every minute of the work (to then analyze what happened, in case of failures), the truth is that many times this is not done or is carried out in the wrong way, and it is precisely in these cases in which most problems occur prematurely.
We agree with the manufacturers that more than 80% of the time, the fault is alien to the product, but something that we often leave aside is that their recommendation of products, systems, thicknesses, are also out of the can and should be put in the dock of suspects.
To perform an adequate failure analysis, we must take into account some aspects that influence the performance of the coating. In this investigation we must act as detectives.
Gather in a written report, all the details of the service conditions to which the coating was subjected, do not forget to mention temperature, mechanical stresses and chemical exposure. It would be great to be able to see everything in normal operation.
Evidence collection
- Take panoramic and detailed photographs of the observed area.
- Collect a sample of the detached paint/system.
- Performs adhesion tests by cutting.
- Perform thickness measurement, either with an electromagnetic meter or with a tooke gage.
- Pass a cloth with solvent to verify the curing of the coating.
- Identify which of the layers of the system has failed.
- It is always good to carry a magnifying glass or portable microscope (minimum 60X)
Look for fault patterns
Most importantly, with all this information gathered: look for patterns!! Generally, when you review the complete information, it is easier to identify in which areas the coating has failed and how this relates to the operation of the substrate on the environment in which it is located, that is, we review the service conditions again. For example, we can obtain the following observations: "failed in the edges", "on the heavy traffic zones", "in the splash zone", "in the areas of higher temperature", "only on the east face of the tank", etc.
Interpretation of results
As long as you have collected and organized the information properly, you can stop seeing the tree and start visualizing the entire forest, it is convenient to have a list of possible causes of the problem and then discard, never forget that the suspects will be between:
- Product in poor condition.- Poorly stored, poorly formulated batch, expired product, contaminated product.
- Error in specification.- Product incompatible with the substrate, inadequate thicknesses for the product, under-dimensioned system, poor resistance to the medium.
- Change of service conditions.- Actual temperature, higher or lower than the design, change of liquid in immersion or splash, increase of load on floor covering.
- Insufficient surface preparation.- Presence of contamination between layers, surface without roughness.
- Poor product preparation (in the field).- Erroneous proportion of mixture, product contamination (water, oil, etc.), inadequate diluent, induction time was not respected or overpass pot life time.
- Finally, identify the type of fault or defect present, for this, it could be helpful to use photographic visuals with defects, this will shorten the path of research, even to the untrained eye; obviously the practice leads to a faster identification of the type of fault. It will finally be this observation that helps us to conclude that it could have caused the problem and how to correct it.
Best of all, each of the causes mentioned in the previous paragraph offers us a particular footprint when the failure occurs.
Never forget that the most important tool for identifying defects and faults is common sense.
* José Manuel Guizado Solis - Nace Coating Inspector - Level 3 (Lima Peru). Expertis Engineering and Application SAC. Email: [email protected] - Cel: +51 983503727
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