The “splash zone” is defined as the area between the year’s lowest tidal mark and up to 10 feet above the year’s highest tidal mark. It is extremely difficult to protect steel structures against corrosion in this zone where corrosion rates have been documented to exceed 30 mm per year on unprotected steel. This is more than six times the corrosion rate typically found on steel under constant water immersion.
Specific guidance for coating the Navy’s steel sheet piling employs two coating system options for the initial painting of steel placed in seawater immersion/splash zones: 1) three coats of epoxy-polyamide or 2) two coats of coal tar pitch epoxy-polyamide. In theory, the three-coat epoxy system should provide better in-place service than the two-coat coal tar epoxy system. In practice, the coal tar system is used almost exclusively due to the lower material cost. The coal tar system provides approximately five years of splash zone service before maintenance is required which can include complete removal and reapplication. However, maintenance is rarely performed due to the high cost and environmental issues that need to be addressed.
The environmental issues associated with the two coating system options include high volatile organic compounds (VOC) content, hazardous air pollutants (HAP), and may also include hazardous pigment content. The coal tar epoxy also contains coal tar pitch which is regulated by the Occupational Safety and Health Administration (OSHA) due to known human carcinogen content. The product developed under this effort is 100% solids and therefore has no VOC content, has no coal tar pitch, and exceeds the field performance of the two current coating system options.
The first liquid polysulfide polymer became commercially available in 1943. Today, there are several liquid polysulfide polymers, each with distinctly different properties but similar in chemical structure. The liquid polysulfides have the advantage of being room-temperature vulcanized, meaning they can be cured at ambient temperatures after the addition of an oxygen-donating curing agent.
Epoxy resins date back to approximately 1949. Their many excellent properties include rapid during at normal temperatures, good adhesion to most surfaces, toughness, and chemical resistance. Today, versatile epoxy resin compounds and systems are customized to meet the different physical properties required by various markets. None of the commercially tested coatings met the desired Navy performance requirements. The two most significant limitations were the inability of the commercial coatings to adequately bond to clean, semi-damp steel and insufficient curing under immersion. To make a flexible epoxy that could potentially meet the requirements of the splash zone coatings (SZC), a liquid polysulfide polymer was used. The polysulfide addition improves certain physical properties without adversely affecting the existing performance capabilities of the epoxy resin.
Naval Facilities Engineering Command’s (NAVFAC) Small Business Innovative Research (SBIR) program solicited the topic entitled “Polysulfide Modified Epoxy Novolac Cladding for Steel Immersion/Splash Zone Service.” Naval Facilities Engineering Service Center (NFESC) subsequently awarded Phase I and Phase II work to PolySpec Corporation and Polymeright, Incorporated. Phase I results were promising whereas preliminary Phase II results were exceptional. The tests included small-scale application trials under actual field conditions.
Early SBIR-funded studies of the SBIR-developed polysulfide modified novolac epoxy formulation (renamed Zero VOC, Coal Tar Free Splash Zone Coating) indicated that the SZC will provide at least twice the performance compared to the currently specified coating systems. This demonstration provided a full-scale validation of the SZC for use as an in-service waterfront maintenance system and enables the transition of this coal tar free coating directly into the hands of Department of Defense (DoD) end-users who require waterfront metal (e.g., sea walls, sheet pile) maintenance painting.
This project addresses Air Force, Army, and Navy performance and environmental requirements for sustainability and reduction of VOC and HAP emissions in the use of such SZCs. Federal, state, and local environmental agencies such as the Environmental Protection Agency (EPA) and Air Quality Management Districts (AQMD) across the country classify many VOCs as hazardous and restrict their emissions through regulations such as the Clean Air Act and local EPA and AQMD rules. Chief of Naval Operations (CNO) directives require significant reductions in the amount of hazardous waste generated by the Navy. This technology will satisfy all of these requirements due to the SZC being free of toxic metals, hazardous air pollutants, coal tar pitch, and VOCs.