About Failure Analysis for Paintings & Coatings
A failure analysis investigation is much like the work of a detective. Clues or relevant facts pertaining to the investigation must be gathered, analyzed, explored, and studied to make a knowledgeable determination. As in the case of a good detective, firsthand field experience is of the utmost important, yet academic studies are also essential.
Sequence of Events
1) Justification for conducting paint or coating failure analysis investigations. Corrosion protection, aesthetic, production, or litigation related purposes provide excellent examples for justification.
2) Gather relevant information and facts concerning the failure. When the information has been obtained it must be carefully organized, labeled, and documented in a logical format for future reference.
3) The failure analyst will question why failure occurred, how to get the building facility, or equipment repair coated quickly if necessary, how to prevent a recurrence of the problem, and if more information is needed, how can the information be readily obtained
4) A logical plan for the investigation to follow must be developed and implemented. Each investigation will be different from the last and many variables will make it necessary to make decisions based on the investigation at hand.
5) Collection of background data and sample removal. This step includes site inspection, information regarding the current history of the failure, all relevant record keeping, and records on past failures if applicable.
6) A preliminary examination of the failed coating and the substrate, as well as a non-destructive examination of the failure, with extensive photographic documentation, precedes any destructive laboratory evaluation and analysis. The preliminary examination does not change or damage the failed coating or substrate in any way.
7) Specimens should be selected and identified for further laboratory testing and analysis.
8) A close examination of failed paint and coating chips using a stereo microscope at magnification of 50x or less may reveal that one of the layers is brittle and full of cracks, or perhaps that an entire layer of paint is missing.
9) A microscope at magnifications ranging from 50x to 1000x magnification can be used to examine the cross section of failed paint and coating samples for voids or inclusion, as well as observation of underlying corrosion products on substrates.
Fourier transform infrared (FTIR) spectrometers
Records the interaction of infrared radiation (light) with experimental samples, measuring the frequencies at which the sample absorbs the radiation and the intensities of the absorptions. Determining these frequencies allows identification of the sample’s chemical makeup, since chemical functional groups are known to absorb infrared radiation at specific frequencies.
Scanning electron microscope (SEM)
Uses electrons rather than light to form an image. The SEM has a large depth of field, which allows a large amount of the sample to be in focus at one time. The SEM also produces images of high resolution, which means that closely spaced features can be examined at a high magnification. Preparation of the samples is relatively easy since most SEMs only require the sample to be electrically conductive.
Energy dispersive x-ray spectroscopy (EDS)
Used in the characterization of materials through the use of ionizing radiation to excite a sample. This excitation generates x-ray energies that identify the elemental composition of the sample. Using x-ray detection equipment to count the number of x-ray photons emitted by this technique, an EDS system is able to characterize and quantify in an approximate manner the elemental composition of the sample.
electrochemical impedance spectroscopy (EIS)
Accelerated environmental exposure tests, such as salt spray (fog) tests, humidity tests, and ultraviolet light (QUV) exposure tests can help to confirm the proposed failure mechanism of a painted or coated substrate sample. Accelerated exposure testing can be complemented with EIS. In the EIS technique capacitance and electrical properties of the coating are measured as a function of time. If the impedance ratio does not change as a function of time, then one can with high degree of confidence conclude that the coating is not altered and performs very well under actual service conditions. The advantage of this technique is that we will not accelerate the test such that conditions will result in the failure of coating system. The test will provide reliable data in a short time of exposure. The data from this test can also provide data for calculating permeation rate and minimum coating thickness and cure schedule requirements for adequate corrosion resistance.
Documentation & Reporting
All information is gathered and analyzed to form a determination on the mode and probable cause of the failure. Identification of the mode and cause of failure provide the source for recommendations for corrective action. A final report including all relevant data, analyses, and recommendations are compiled and presented to the client. In litigation investigations, the client may not be interested in the recommendations section of the report.
The decision to remove a sample specimen of a paint or coating, or of the underlying substrate, is a very important part of the failure analysis investigation. Sample selected should be characteristic of the coating and/or substrate and contain a representation of the failure or corrosion attack. For comparative purposes, a sample of the intact coating and/or substrate should be taken from a sound and normal section. In conjunction, for a complete microscopic and chemical evaluation and analysis, samples from the failure, adjacent to the failure, and away from the failure are necessary.
The sample must be removed without changing the surface conditions or characteristics of the sample, nor inflicting physical damage of any kind. The sample is the basis on which the investigation and analysis rely, and extreme care must taken not destroy any of the sample’s properties.
Upon removal of the sample, the exact location where it was obtained must be documented both in writing and by photography. Any corrosion product found on the coating or the substrate should also be collected and examined. If necessary, the corrosion product may be removed carefully from the substrate and sent with the removed sample. When the sample has been removed from the structure or the component, it should be carefully packaged in a water-tight container appropriate to the size on the sample, identified and labeled.
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We respond to all customers promptly by sending a technical proposal to address testing, investigation and the proposal costs. If we need more information, our engineers will contact you.We respond to all customers promptly by sending a technical proposal to address testing, investigation and the proposal costs. If we need more information, our engineers will contact you. Whether you are a large corporation or a small enterprise, we will provide you with the attention you need and deserve. In so doing, we hope to work with you for many years to come.
Please call Dr. Zee at 412-952-9441 or the office at 412-788-1263 and let us know how we can assist you in your investigation. Alternatively, you can send your request to email@example.com.
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