The objectives of this demonstration were to (1) provide a full-scale validation of the low volatile organic compound (VOC) barrier coating (LVBC) for use as an architectural and industrial maintenance (AIM) coating, (2) assist in the transition of a nonaircraft topcoating using the zero-VOC topcoat (ZVT) (MIL-PRF-85285D, Type III, Class W), and (3) enable the transition of this very low VOC AIM coating system directly into the hands of U.S. Department of Defense (DoD) end users who require aboveground storage tank (AST) maintenance painting.
Corrosion of AST steel exterior surfaces is a perennial and costly problem. To protect against corrosion, AST exterior surfaces typically receive a three-coat system consisting of the following:
- A zinc-rich epoxy primer (MIL-DTL-24441, Formula 159, Type III)
- An epoxy intermediate (MIL-DTL-24441, Formula 152, Type IV)
- A polyurethane topcoat (MIL-PRF-85285D, Type II).
These coats are commonly formulated with about 304 grams per liter (g/l) (2.5 pounds per gallon [lbs/gal]), 340 g/l (2.8 lbs/gal), and 340 g/l (2.8 lbs/gal) of VOCs, respectively. Exterior AST maintenance painting is often required at around 8 to 10 years of service. However, the original three-coat system described above is not appropriate for use over aged and weathered coatings. When the original system has been used as an overcoat system, it has contributed to costly premature coating failures. These overcoat failures typically occur as a result of high levels of residual cure stress (curing of the overcoat system) combined with the daily thermal cycling (daily temperature extremes). Therefore, typical maintenance consists of making spot repairs to visibly corroded areas or waiting until the existing coating is fully removed and a reapplication is necessary.
In effect since August 2006, California’s South Coast Air Quality Management District requires all AIM coatings to contain no more than 100 g/l of VOCs. A solution to the environmental problem of using a high VOC AIM coating system is to employ a system consisting of LVBC, developed by Small Business Innovative Research (SBIR), for use as both the spot primer and intermediate coat, followed by the ESTCP validated ZVT.
The demonstration was conducted in Southern California at the Defense Energy Support Center, San Pedro, California. Two ASTs, originally coated in 1987 and located on the waterfront, were recoated with the LVBC/ZVT system. One AST was completely recoated on the top and sides for a total of about 10,500 square feet (SF) of exterior surface area. The other AST was coated on the roof only (2,850 SF).
The demonstration consisted of the following:
- A determination of coating assessment parameters
- Examination of the selected tank’s exterior coating system to ensure it meets overcoat requirements
- Surface preparation
- Application of the LVBC followed by the ZVT
- Documentation of established coating application parameters.
The resulting demonstration coating was monitored after 1 year of service in accordance with coating assessment parameters. To date there have been no breaks or bubbling of the overcoats. All coats withstood their respective corrosion, peeling, blistering, tape adhesion, pull-off adhesion, film thickness, and LVBC/ZVT patch test adhesion testing in an acceptable or better manner. Additional coating assessments after 4 and 8 years of service are required for an adequate assessment of the technology.
Demonstration results have been used to develop a nongovernment product standard: Master Painters Institute (MPI) #213. Results will also be used to develop a new Unified Facilities Guide Specification (UFGS) entitled “Maintenance Painting of Aboveground Storage Tank (AST) Exterior Surfaces.” UFGS will be available at http://www.wbdg.org/ccb/browse_cat.php?c=3. These documents will support Tri-Service activities with ASTs in need of maintenance painting. In addition, results will be posted at the Joint Service Pollution Prevention Library and presented at the Tri-Service Environmental Centers Coordinating Committee meeting, if applicable.
The ZVT technology contains less than 5 g/l of VOC and the resulting cured paint contains no hazardous materials. Furthermore, the ZVT was developed from novel resin chemistry to be applied using conventional or high volume, low pressure application equipment.
Both the Army and Air Force exclusively employ a Navy-developed UFGS entitled UFGS 09 97 13.27 “Exterior Coating of Steel Structures” for coating the exterior surfaces of either new ASTs or complete removal or reapplication of previously coated ASTs. The Army and Air Force rely heavily on Navy-developed criteria for use in all AST coating applications. A successful AST demonstration and validation of an AIM coating system based on LVBC/ZVT followed by the availability of new UFGS and MPI guidance documents will lay the groundwork for wide acceptance of this technology.
The LVBC system was applied to the exterior of some small tanks at one project site in accordance with a draft UFGS. The cost associated with this application was approximately 80% of what it would have cost to remove and replace the existing system. On the basis of cost alone, it would have been more effective to remove and replace the existing coating system on the tanks; however, adjustments and lessons learned during the initial implementation of the LVBC system had a significant impact on the cost, and these added costs would not be expected in subsequent implementation. The end results have been favorably received by installation personnel. A finalized version of the maintenance UFGS that can be used by all military services is forthcoming.