Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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41 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 tion change, this epoxy had the ability to be applied at 100 to 150 µm (4 to 6 mils) by either spray or roller, and f lowed and lev- eled nicely when applied by a reasonably competent painter. The finish coat in these tank exterior coating systems is typically aliphatic polyurethane; therefore, a smooth intermediate coat is desirable. After the solvent change, complaints immediately began coming in that the epoxy coating looked horrible on applica- tion. If sprayed, the coating would start to ball up and look like cottage cheese. If applied by brush or roller, it would look ropey and would not f low to form a uni- form film. When confronted with these problems, the manufacturer's solution was to mix additional VOC-exempt solvent into th e p aint in th e h op e s th at it w o ul d improve the film properties. This did not work. It seems as though the epoxy resins and other raw materials in the formula had a compatibility issue with the solvent. Therefore, this product as manufactured was unsuitable for use and the manufac- turer was forced to pull it from the market. It took several months of trial-and-error reformulation in the lab before a new ver- sion of the product could be reintroduced to the market. What Is This Crud in My Epoxy? Ever y once in a w hile, a complaint comes in from the field that just does not make any sense—at least on first report. While working as a sales manager for a small regional coatings company in the 1980s, I received one of these complaints from an applicator in Wyoming. He was working on a tank lining project at a refin- ery and was using one of this manufactur- er's more popular epoxy phenolic coatings, which was specified for the work. The con- tractor reported that when he opened the c a n a n d m i xe d t h e tw o c o m p o n e n t s together, he noticed "big chunks of crud" in the bucket. Knowing how the products are manufactured, filtered, and canned, the plant quality control (QC) manager was stumped and had no explanation for this complaint of "crud." Since this project was located at a far distance from the manufacturing plant and the project was on a tight schedule, it was decided that the painter should buy some filter bags and strain the material on site into new clean buckets before use. A week or so later, we received a plastic sandwich bag in the mail that contained a few of these epoxy-coated "chunks of crud." The QC manager took some of these chunks into the lab for analysis and quickly real- ized that they were not chunks of epoxy or FIGURE 1 Poor epoxy intermediate coat caused the poor fnish because of solvent incompatibility. Photo courtesy of CSI Services, Santa Clarita, California.

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