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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Page 18 of 92

16 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIAL MATTERS Enhanced plastisol coating can be cured in situ to protect highway structures in coastal environments A product development team with Ovante, LLC (Tallahassee, Florida) has formulated an enhanced plastisol (plasticized poly vinyl chloride [PVC]) coating (EPC) that withstands exposure to chlorides, acids, ultraviolet (U V) light, sand, seawater, and other corrosive elements. When cured, the EPC forms an nonporous, inert, corrosion-resistant covering that can protect metal substrates in atmospheric, transitional, and immersed environments (soil and water). Because the EPC must be heat- cured, the team also has developed and demonstrated a portable infrared curing system that can cure f ield-applied EPC. Both the coating and curing technologies are patent-pending. An independent laboratory tested various properties of EPC-coated coupons, and signposts coated with the EPC were exposure tested by the A labama Department of Transpor- tation (A LDOT). According to NACE International member Jon Brasher, president and chief technolog y off icer of Ovante, plastisol coatings have been used for decades to protect metals against corrosion. They provide a durable, protective coating for items such as racks, handle grips, clips, clamps, electrical connectors, etc. These anticorrosion coatings are comprised of PVC resins suspended in a liquid plasti- cizer. Ty pically, components to be coated are preheated, dipped into the liquid plas- tisol, and then cured in an oven at tem- peratures ranging from 350 to 400 °F (177 to 204 °C). During the heating process, and it was selected by the development team as a starting point because it f lows over the entire surface of the substrate and does not leave voids in crevices or corners, says Brasher. The team changed the formulation's component ratios to better control the f low rate during appli- cation and added U V inhibitors. The resulting EPC was put through a series of tests to determine the scope of its corrosion-resistant properties. Labo- ratory tests included a salt fog test ac- cording to ASTM B117-11, 1 an X-cut pull- off test according to ASTM D6677-07, 2 and U V tests according to ASTM G154- 12A 3 and ASTM G151-10. 4 For the salt fog test, EPC-coated and uncoated galva- nized steel hurricane ties were tested. The EPC-coated tie was not primed prior to being coated so the coating could be peeled off to expose the substrate at the end of the test. A hanging ring pierced the coating and allowed salt water to accu- mulate within the coating over the dura- tion of the test. The coated tie was tested for 3,072 h and the un coated tie was tested for 1,008 h. When removed from the chamber, the EPC coating on the hur- ricane tie was intact. When the EPC coat- ing was removed, the substrate of the coated tie showed less corrosion than the uncoated tie. For the pull-off test, an X-cut was made in the coating with the blade angled at 45 degrees to undercut the coating, and then tape was placed over the intersect- ing cuts and quick ly removed. The coat- ing performance was graded by the amount of coating material removed by the tape. The adhesion rating for three samples tested was 10, indicating the coating was extremely diff icult to remove and fragments were no larger than ~0.8 by 0.8 mm. The cyclic U V test, performed prior to the addition of U V inhibitors, exposed one side of a double-sided coated galva- nized steel coupon to 8 h of U V light at An EPC-coated signpost installed next to an uncoated galvanized signpost on the side of an Alabama coastal highway for an ALDOT exposure test. Photo courtesy of Ovante. the PVC resins expand and absorb the plasticizers and the liquid plastisol coating gels and fuses into a solid, homogeneous plasticized coating that forms a mechanical bond with the steel substrate as it cools. Around eight years ago, the team began studying the liquid plastisol coating historically used in hot-dip applications as the founda- tion for a plastisol coating that could be spray-applied during manufacturing or in situ on construction com- ponents and structures that corrode and deteriorate when exposed to harsh coastal and marine envi- ronments. A liquid plastisol coating is known to be abrasion resistant, it doesn't expand or contract in extreme heat or cold, and it is non-conductive, so it resists galvanic corrosion and cathodic disbondment; 16 NOVEMBER 2014 MATERIALS PERFORMANCE

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