Ingenuity Magazine Spring 2019

Pond Ingenuity Spring 2019 7 should be most concerned about? Whether the coating system is being applied on water tanks, offshore platforms, floating production storage and offloading (FPSO) units, bridges, refineries, or power plants, edge failure can be a major problem and can cause coatings to fail. The way that specifiers can start to combat this at the start of the project is to specify a stripe coat, which is to simply apply an additional coat of material (typically by brush) to edges/welds/bolts, etc., to build the film thickness. Stripe coating is expensive, but it is one item that can help to maximize coating life. But if stripe coating is expensive, and your inspection personnel can only show up at varied times, how can you be sure that the stripe coating actually happens and to the thickness that’s specified? The task is extremely difficult to verify after the fact, and it’s nearly impossible to do without damaging the coating. What’s an inspector to do? Hiding in Plain Sight Coating materials have an interesting property called opacity, or hiding. Defined as the ability of the coating material to obscure the surface color beneath it, opacity is different for each generic coating, each formulation of coating, and even each color of each formulation. By specifying color as a means to assist inspection, the specifying engineer and the facility owner can take a giant leap forward in assisting inspection personnel in verifying compliance with the specification. The contrast of the colors must be significant enough that the minimum dry film thickness of the next coat will hide the color of the coating below it. In other words, an off-white primer should not be specified with a white topcoat. Instead, a dark gray primer could be specified with a white topcoat, therefore assuring that a minimum amount of the white topcoat was applied in order to hide the primer below. What this allows is the inspection personnel in the field to immediately locate the random potential areas of non-conformance by visual examination alone, as these would be the areas that could have low material thickness with regard to conformance. In a similar way, a contrasting stripe coating color can help ensure compliance and ensure that the stripe coat is actually being applied. This may add a higher cost to the manufacturer and/or contractor, and it will certainly also create more onus for compliance, but it may be worth the discussion up front to ensure that the specified system is being delivered to the client. Caution: If you’re using color as an inspection tool, you will need to verify with the coating manufacturer that the colors specified do cover or hide at the minimum specified thickness. This can be done by the coating manufacturer using drawdown cards with the specified colors applied to them. Depending on product formulation, a specified color may not hide at the specified thickness. Yellows and reds, in particular, are notorious for this. If the engineer specifies, for example, a gray primer with a safety yellow topcoat at 2–3 mils (50.8–76.2 microns), the yellow topcoat may not hide the gray primer at 3 mils (76.2 microns), and the engineer may receive a change order by the contractor. Using Color With limited personnel on projects with multiple tasks and locations, inspection time is limited. The simple use of color can act as an inspection assistant to help determine that the correct coating thicknesses were applied in those random areas. This can be an option to help an owner get what was specified. It is not foolproof, nor is it by any means a substitution for a full-time coatings inspector, but it can assist a project in getting closer to the quality specified regarding dry film thickness.  David A. Hunter NACE Protective Coating Specialist Copyright 2019 • Reprinted with permission from CoatingsPro Magazine Coatings have opacity, which can assist the inspector in determining if the minimum film thickness has been achieved. 4 mils 6 mils 8 mils Painted on black background Painted on white background Most coatings, as they dry and cure, go from a liquid to a solid and shrink, pulling away from edges and discontinuities