KTA-TATOR,
INC.
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Pittsburgh, PA 15275
Phone: 412.788.1300
Fax: 412.788.1306
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Managing
Coating Failures
By
Rick A. Huntley
KTA-Tator, Inc.
Frustration!! That is the word that best describes the feeling that you can get when thousands or tens of thousands of dollars have been poured into a coating project, only to have it fail prematurely. The feeling then often turns into apprehension when you realize that making a wrong decision on how to repair the failed coating could lead to further coating failure and more costly repair work. Although the "frustration" may be unavoidable, a thorough analysis of the failure can go a long way to reduce the "apprehension." By determining what caused the coating failure, an effective repair procedure can be developed to help avoid the reoccurrence of previous problems.
In order to perform a thorough investigation of a coating failure, a logically sequenced, five-step approach is suggested:
1. What was supposed to be done?
2. Does it make sense?
3. What was done?
4. What caused the coating system to fail?
5. How should the failure be repaired?
Step 1:
What was Supposed to be Done?
The first step in determining what caused a coating failure is to find
out what was supposed to have happened during surface preparation and
coating application operations. This can be found in the coating specification
or on the manufacturer's product data sheets. One of the documents should
contain clear instructions on how to properly prepare the substrate for
coating. Once this has been determined, the next step is to find out what
actually did happen. Unfortunately, during a failure investigation, it
is often found that what happened does not match or sometimes even resemble
what was supposed to have happened. The applicator may not have understood
the surface preparation or application instructions or may have taken
shortcuts to save time and money. Information regarding the actual surface
preparation and coating application procedures employed can sometimes
be uncovered by interviewing those involved in the project, by reviewing
quality assurance or inspection documents, or by taking a first hand look
at the problem.
Step 2:
Does it Make Sense
Once you determine what was supposed to happen, the second is step is
to ask whether what was done makes sense. That is, could the specification
and/or the product data sheets be faulty. For the given service environment,
was the required level of surface preparation adequate? Was the correct
generic coating system selected and were the thicknesses adequate for
the intended use? If the system was doomed from the beginning, then the
failure investigation will take on a whole new light.
Step 3:
What was Done?
The third and most important step in determining the cause of a coating
failure is conducting a thorough and detailed visual examination of the
failure. Depending on the size and the nature of the failure, it is often
a good idea to spend the first hour or two of the examination just looking
at the entire coating project to determine whether the coating failure
occurs in any noticeable pattern. For example, is the failure widespread
or confined to just one or more areas? Does the failure occur mostly on
surfaces that get direct sunlight or mostly in shady areas? Is the shop-applied
coating all that is affected or is field-applied coating the problem?
These types of questions should be answered during the visual examination.
Next, a close examination of the coating should be conducted, both in failed areas and in areas that are not experiencing failure. Sometimes the key to determining the cause of a failure is found by comparing the two areas. The coating should be tested in both areas. There are a great number of field tests that provide data that may be useful in determining the cause of the failure. For example, coating thickness measurements can give valuable clues to the cause of a failure. And adhesion testing of a coating may provide information necessary to solve a peeling failure. There are numerous additional tests that can be conducted depending on the type of coating used, the substrate to which the coating has been applied, and the type of failure (blistering, peeling, rusting, etc.). The key is to determine which tests are applicable to the particular failure, and to perform the tests in both failing areas and non-failing areas.
To preserve the characteristics of the failure, it is a good idea to thoroughly photograph the area. The photographs will not only serve as a reminder of the project, but they will also make it easier to describe the failure to others. Remember that a picture is worth a thousand words.
If possible, samples should be removed from the field and brought to a reputable coatings forensic laboratory for analysis. Often the cause of a failure can only be positively determined by performing a microscopic examination, a chemical analysis, or by performing laboratory physical tests. During the field visit, samples should be removed from many of the areas of failure as well as from non-failing areas. The locations of all samples should be thoroughly documented so that the areas could be relocated, if necessary.
A forensic coatings laboratory will typically perform a series of tests on the samples collected from the field depending on the nature of the failure. A detailed microscopic examination of the samples can yield information critical to solving the failure that cannot easily be discovered during the field examination. For instance, the presence of microscopic voids or foreign material in the coating can sometimes only be detected using a high quality microscope under good lighting conditions. The laboratory can also detect problems with the resin using infrared spectroscopy, solvent problems using gas chromatography/mass spectroscopy or curing problems using differential scanning calorimetry, to name just a few. In order maximize the effectiveness of the laboratory investigation, you should provide the laboratory with as much information as possible regarding the failure, including any and all field observations.
Step 4:
What Caused the Coating System to Fail?
Once the laboratory investigation is completed, it is time to start analyzing
the data from both the field visit and the laboratory investigation. This
is where experience is critical. Often the data contains a little wheat
and a lot of chaff. To be able to separate the two requires a thorough
knowledge of the way coatings work, and some experience in evaluating
coating failures. An experienced coatings expert is able to take that
information and use it to pinpoint the most likely cause of the coating
failure.
Step 5:
How Should the Failure be Repaired?
It is only after the cause of the failure is known that a plan should
be worked out to repair the defective coatings. Repairing the failed coating
BEFORE determining the cause carries a huge risk of further failure and
costly repair, whereas proper management of a coating failure from start
to finish can result in an invaluable learning experience that will help
to preserve your most valuable resources: TIME AND MONEY!
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