CoatingsPro Magazine

JAN 2009

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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continued from page 89 Exterior: with a Carboline patching material which was essentially the same material as the original coating Before the interior coating was in place, and even before the change After change order issued, welder returned and welded stand-offs for order to refurbish the exterior was complete, Alpine prepared the exterior for refurbishing so that any exterior welding would not burn the new interior coating The crew installed a rigid Monarflex fire-resistant scaffold sheet on the exterior to NACE No. 3/SSPC-SP6 commercial blast The blasted areas were primed with M.A.B. Ply-Mastic 650 primer the communications antennas arrayed on the top of the tank as well as uprights for the roof railing system outside of the scaffold with overlapped seals to create a Class 2A con- tainment system with planking on every level and a full guard system Using 20-40 coal slag mixed with Pre-Tox, the crew sandblasted the The finish coat was M.A.B. Ply-thane 890HS for a total exterior coating with an intermediate coat of the same product, spray-applied using Graco King 68-1 airless sprayers thickness of 7-10 mils, as called for in the specifications from TIC Before bringing the tank back into service, the crew re-chlorinated the interior of the tank by spraying a chlorine solution on the interior surfaces with a 4,000 PSI power washer. The higher areas were accessed through the roof hatches and by the use of 16'-18' extension poles SAFETY CONSIDERATIONS: The Contractor was required to have documented Confined Space Crews had to sign in with an attendant when entering the tank The crews used Bullard blast hoods, with supplied-air breathing and fall protection Entry Procedures available at the tank site at all times as required by OSHA 29 CFR 1910.146 The interior work was completed with low-voltage explosion-proof light- ing and safe motors for confined spaces steel surface temperature during application of the coating. Scaturro further explains, "The dehumidifier was important to prevent flash rust on the bare blasted metal during coating and the heater was critical to maintain the minimum specified surface temperature of 40ºF. The ambient temperatures during the day were in the 30s, so the tank needed to be warmed to 40ºF 24 hours a day. We used thousands of dollars in diesel fuel to run the heater to keep the tank at the specified temperature since bare metal has a very low R value to maintain temperature. The heater is an indirect fired one million BTU heater, so there are no exhaust fumes to contend with." TIC's Snodgrass describes the coating material: "The elasto- meric polyurethane coating systems are relatively easy to apply and have a relatively short material pot life. However, they are more difficult than the standard epoxy systems to apply as the application requires special plural-component spray guns, heaters, and other equipment, as well as a deep anchor pattern. Specialized training and certification are required for the applicator. It is also recom- mended that the equipment operator be trained appropriately." Since the Polybrid cures in about three minutes once the two components are mixed, the crew used a Graco Hydra-Cat airless plural component spray rig with a 68:1 compression ratio to mix the coatings components about 12 feet from the gun. The spray gun was a Wiwa 500F with a Graco HD RAC625 tip. The crew, wearing half-face 3M 6500 Series respirators with organic vapor cartridges, utilized one spray rig that remained on the ground with one crew member at the mixing block to 90 CoatingsPro J January 2009 ABOVE Prior to application of the interior product, Alpine took steps to facilitate any exterior welding and to make sure that the exterior welding didn't burn the interior coating — a step not included in the original job spec. Scaturro explains: "In an effort to not damage the newly applied interior coating, we suggested to the water company that we could complete an exterior welding that would prepare for any future tank refurbish project — and we would do it prior to applying the interior lining system." shut the material flow when the sprayer stopped and to run the solvent, Methl-Ethyl Ketone (MEK), through a third line that is purged directly into a container next to the sprayer. The foreman maintained pressures and made sure that the rig was running properly. The rest of crew acted as support for the crew on the ground as well as the spray man in the tank. The material needed to be maintained at 110ºF to 120ºF for both parts A and B, so Alpine installed a standard 20 foot long insulated stage container to keep the 55 gallon drums of material at temperature and maintained individual Acra Electric, Wrap-It-Heat heaters on each drum. Scaturro describes the complex and thorough heating process, "The drum heaters are in use while the material is unmixed and when drawn into the machine. Then there are heaters on the machine and spray lines to maintain the correct tempera- ture throughout the entire process. We used the power available on site plus available power from the two generators to run the heat required to apply the interior coating." The specifications called for a coating thickness of 25 to 35 mils so the crew used a wet film gauge to confirm the thickness when spraying. Scaturro says, "Off-ratio material needs to be scraped off entirely. It's extraordinary difficult to recoat for low mils — the recoat window is 18 hours. New material doesn't stick well unless mechani- cally abraded first or scraped and solvent wiped. It's got to be perfect and right the first time, which is why highly-trained crews are used." Fortunately, given the tank's configuration, the crew could break the tank into precise segments. There was a counter on the pump that could tell them how much material passed through for that particular segment, so they could compare usage to area sprayed as a secondary method of confirming the coating thickness. Finally, a dry film gauge was utilized to reconfirm on the next day. The cured coating edges were mechanically abraded with Norton Radnor 36 grit flap discs on an angle grinder for six inches and solvent wiped to reactivate material on edge to start each day. "We are very careful how we move through the tank; it's all

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