Water control and hydro power facilities are a vital part of the infrastructure in most any region. Carbon steel corrosion of these assets has historically been addressed with the use of vinyl coatings. As volatile organic compound (VOC) regulations have tightened and vinyl resin availability has diminished, alternative systems are now in demand. Epoxy systems have been used with success, as they are readily available and meet VOC needs but have limited performance in intermittent immersion. These facts have left owners in search of a better alternative to the fading vinyl availability.
Vinyl technology has been the leading application on steel structures in the hydro industry for decades. Many structures coated with vinyl, particularly with lead as a base coat, are still in service from decades ago. Some of the system longevity can be attributed to vinyl performance, while reluctance to remove lead due to expense is a factor. Still, before regulation changes, vinyl proved a very lucrative investment for hydro owners. Issues of concern for vinyl technology are VOC content, manufacturing and supply. A typical vinyl will have a VOC content of 5.5-6.8 pounds per gallon. Since most state regulations will not allow applications beyond 2.5 pounds, getting approval to apply vinyl can be a challenge. While impacted immersion coatings exemptions and "fixedsite" permits help with a portion of the VOC burden, many organizations are conscious of the environmental impact and reluctant to use vinyl. Vinyl resin has become less available in the U.S. consistently over the past 20 years. Actual manufacturing of these materials also has its risks. The average vinyl volume solids level is well below 40 percent, with some being below 20 percent. Manufacturing material such as these increases the risk of employee safety and production incidents. The EHS issues along with the environmental impact are major concerns for manufacturers. These factors have impacted availability and have created an industry need for an alternative.
Epoxies have been used as an alternative. These systems provide barrier corrosion protection and are effective in immersion. Epoxies are plentiful in design and availability and have significantly less impact on the environment. Epoxy technology in broad and immersion grades can be delivered with attributes for abrasion resistance and underwater cure. Epoxies can achieve immersion service in one, two or three coats. Although recoat and return to service of some epoxies are slower than vinyl, availability and/or environmental impact have made them suitable alternatives. One property of hydro exposures is the intermittent immersion required. As water levels vary, portions of the structure are exposed to UV at different levels. In some cases, the structure is in the water less than 2 percent of its life, so an alternative coating need is most certainly versatility. An inherent property of an epoxy is its vulnerability to UV. An epoxy resin will break down with exposure to UV. As long as there is film coverage, the epoxy is providing a barrier, but the film begins to erode with exposure. Epoxies have shown the ability to provide good immersion service below the water line but have disadvantages when it comes to UV; owners have a need for a more versatile solution.
Siloxane technology such as PPG PSX 700 is a unique technology that provides the barrier protection of an epoxy and the UV resistance of a urethane. PSX 700 has been commercialized in the industry for over 20 years. Since this technology has been introduced to the market, various exposures and uses have emerged. With unique qualities of combined barrier and UV protection, it has had success in a wide range of industries. Other attributes such as ultra-low VOC, debris and ice release, graffiti resistance and unlimited recoats make it attractive for owners and applicators. It should be noted that not all siloxane-labeled products are true engineered siloxanes. There are many hybrid or modified siloxane offerings in the industry that do not meet the criteria discussed here. The ability to go in and out of immersion and resist UV damage makes PSX 700 unique and a good investment to owners.
With the evolution of coatings technology, the use of PSX 700 for hydro assets for immersion, intermittent immersion and atmospheric exposures is proving to be an alternative to vinyl technology. With the excellent UV resistance of a urethane and the barrier resistance of an epoxy, siloxanes are a unique solution for hydro exposures. The reduced environmental impact due to far lower VOC levels and 50-percent reduction in the number of coats makes the siloxane system attractive to both owners and contractors for these assets.
For more information, visit www. ppgpmc.com, call (888) 9PPGPMC [977- 4762] or email jwsmith@ppg.com.
