Mechanical Seals For High-Speed Boiler Feed Pumps In Ultra-Pure Water

Abstract

Since 2007, the hot-filament Chemical Vapor Deposition (CVD) technology for crystalline diamond thin-film coatings has found its way into the mechanical seal market to combat the problems of dry running, corrosion and abrasion. This new technology has proved successful in hundreds of pumping applications in a wide range of services and duties. The reliability and lifetime of mechanical seals are improved by using diamond-coated faces. One such application involved the sealing of large boiler feed and steam generator pumps in power plants. The duty conditions for the pump’s seals can be as high as pressures up to 580 psig (40 bar), shaft RPMs up to 6,500 and temperatures up to 400˚F (200˚C). Consequently, the mechanical seal faces are highly loaded in a fluid with far less than ideal lubricating qualities. It is evident, therefore, that these applications are technologically challenging for mechanical seal manufacturers not only from a tribological perspective, but also from a corrosion viewpoint when the feed water has a low electrical conductivity or is free of impurities. This paper discusses a new seal-face treatment using hotfilament CVD manufacturing technology tested in a lab for 16,000 hours and currently used in feed pump operations in several power stations in the USA and Europe.