CoatingsPro Magazine Supplements

STEEL 2019

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24 STEEL SURFACES 2019 COATINGSPROMAG.COM To Stripe or Not To Stripe By BJon R. Cavallo, PE, FASTM, Consultant for Jon R. Cavallo PE LLC Photos Courtesy of Jon R. Cavallo PE LLC O ne of the worst disappointments in the painting of steel structures is when the owner carefully plans a painting/coating/lining project to include a well-written specification, careful material evaluation and selection, a qualified contractor, and thorough inspection of the work — but something goes wrong. e project is executed on time, within budget, and with no claims for extra work, but two years later, visual inspection reveals that 99 percent of the painting/coating/ lining work exhibits no signs of failure, yet essentially every edge, bolt, and weld shows rusting of the substrate. How can this happen? e simple fact is that the project specification probably did not require "striping" or "stripe coating" of all edges and welds during the painting/coating/ lining work. But it should have. What Is Stripe Coating? e Society for Protective Coatings' (SSPC) "Protective Coating Glossary – Acronyms and Terms Related to Coating Industrial Steel and Concrete Structures as Well as Failure Analysis and Regulations" (2012) contains the following definitions: Stripe Coat – A coat of paint applied only to edges or to welds on steel structures before or after a full coat is applied to the entire surface. The stripe coat is intended to give those areas sufficient film build to resist corrosion. Striping – (1) Painting the edges of a surface or welds to give them extra protection. Striping is done before priming or before the application of a full coat of paint. Is Stripe Coating Necessary? Stripe coating in structural steel painting/coating/lining work is intended to provide a satisfactory final amount of liquid-applied material on edges, including member edges, nuts, bolts, and washers. ese areas are common on steel assets, such as tanks, bridges, and ship hulls, because of the nature of steel needing to be tied together. Unlike concrete substrates, steel is not often poured into the shape of the finished product; sheets must be connected. Liquid paints may tend to flow away from edges due to surface tension. In most cases, a paint/coating/lining applied by brush, roller, or sprayer to an edge may flow away from the edge due to a combination of surface tension in the paint film and shrinkage of the paint film during curing. If this phenomenon occurs, the paint film at and near the edge will be thinner than at the remainder of the painted surface and subject to premature failure. Often, visible rusting of the substrate will evidence the premature failure. Higher-solid paints/coatings/linings and solvent-borne inorganic zinc will be less prone to edge failure phenomenon than lower-solid paints. e reason for this difference is the combination of faster setting time and/or higher viscosity and/or lower surface tension of the paint film. erefore, stripe coating can help mitigate these failure-prone areas. Stripe Coating Techniques Today, very little other formal written guidance for use by the painting/coating/lining specifier or applicator concerning Edge failure evident on yellow angle. Onset of coating failures at bolt and washer edges. Steel Surfaces

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