Traditional tank lining coatings are costly, have high VOC content and generally require a high film thickness of multiple coats. This paper presents the results of testing a new type of coating system applied to the inside of tanks, exposed to corrosive environments. This new coating system has been extensively tested in the laboratory and field applications. The field applications include several holding tanks, where the products for storage vary from hydrocarbon to high salinity solutions. The coating system consists of a low VOC rust converting water based primer and a high solids moisture cure urethane coating which are applied at a much lower film thickness then the traditional tank lining coating systems, yet provides the same or better corrosion protection.
Currently the tank lining industry has been using high build tank lining systems made of heavy layers, consisting of several 8-10 mil coats of coal tar epoxies which do not contain corrosion inhibitors. These current systems require sand blasting of the metal to SPCC SP-10 near white metal blast before placing the spray in-liner of the coal tar epoxy at mil thicknesses up to 30 mils. Using the low VOC rust-converting water-based primer and a high solids moisture-cure urethane coating results in a lower film thickness, a total of 5-7 dry mils (125-175 microns), saving time and money. The VOC of the low VOC rust-converting water-based primer is 0.3- 0.4 pounds per gallon (35.9-47.9 g/l) and the VOC of the high solids moisture-cure urethane coating is 3.1-3.2 pounds per gallon (371.5-383.5 g/l). One comparative epoxy paint system would put out an estimated 44.9 tons per year of VOC compared to the system of a low VOC rust-converting water-based primer and a high solids moisture-cure urethane coating which only puts out an estimated 1.86 tons per year of VOC. This calculation was made by calculating the amount of product used per tank, based on 2 tanks coated per day. To prove the coating system could withstand the harsh environments, it underwent various accelerated weathering exposure tests in the laboratory and field applications as will be discussed in this paper.
Test Criteria The goal of the experimental effort was to replace the existing tank lining systems that are currently used to hold hydrocarbon and/or high salinity solutions with better performing and environmentally sound coating system of the low VOC rust-converting water-based primer and a high solids moisture-cure urethane. 1. Visual Inspection 2. ASTM B117 Salt Spray Testing Coating Procedures. 1. The corroded panels had the low VOC rust-converting water-based primer applied to the pre-rusted panel by brush at a wet film thickness of 3-5 mils (75-125 microns). 2. The panels with the low VOC rust-converting water-based primer were air dried in ambient conditions for 24 hours. 3. Next the panels were coated with the high solids moisture-cure urethane coating at a wet film thickness of 3-4 wet mils (75-100 microns). 4. The wet film thickness was checked by using a wet film gauge.