2002 R&D 100 Award Winner
Smart, High-Performance Polyphenylenesulfide (PPS) Coating System
Developers: Dr. Keith Gawlik, National Renewable Energy Laboratory; Dr. Toshifumi Sugama, Brookhaven National Laboratory; Edward Curran, Bob Curran & Sons Corporation; Edward Hallahan, Ticona Corporation.
The PPS coating system is a giant step forward in the technology of coating carbon-steel surfaces for use in hostile, corrosive environments. It is a smart coating system that repairs itself. It has a high thermal conductivity. It protects surfaces from corrosion, oxidation, cracking, flaking, and fouling. And its use not only extends the life of carbon-steel tubing by 4 to 5 fold, but also cuts capital and maintenance costs for these tubes by as much as two orders of magnitude.
The key to these characteristics lies in the PPS coatings' unique three-layer approach. The first layer, a zinc phosphate ceramic primer is applied to the steel surface to provide cathodic protection against corrosion and to supply a strong bond between the steel and the coating. The second layer, a carbon-fiber/PPS matrix provides toughness, corrosion protection, and high thermal conductivity. The final layer, a calcium bialuminate (CBA)-filled PPS/polytetrafluoroethylene (PTFE, or Teflon) blend polymer alloy that contains carbon fibers, gives the coating system a self-healing mechanism — repairing damage to the lining of the coating system by filling in small cracks generated by physical wear and impacts — that makes it highly resistant to wear and abrasion.
Although it was primarily developed to coat carbon-steel heat-exchanger tubes used in geothermal power plants, the PPS coating system is ideal for a wide range of harsh-environment applications, including chemical and petrochemical plants, sea-water desalination, water treatment facilities, air-conditioning facilities, and rail-road tank cars.
Compared to other coatings for carbon-steel tubes, the PPS coating system represents major improvements in almost every important category. Even when compared to stainless steel or titanium tubes, PPS-coated carbon steel tubes represent life-cycle cost savings of up to 82%. The PPS-coated tubes save this amount for two basic reasons: they represent a much smaller capital investment than their competitors, and they are far less expensive to clean and maintain.