About 25 years ago, EGC Enterprises engineered the first of many graphite pressure seals for nuclear service. The US Navy felt that the silver-coated metal seals they had been using were far too heavy. And, and the silver coating, which provided a secure seal on imperfect valve surfaces, was a little too pricey. So, they were looking for an alternative. The answer was EGC’s Thermafoil® flexible graphite.
Soft and resilient, flexible graphite can micro-seal a valve surface. Its compressed graphite flakes are small enough to fill imperfections and anomalies in the surface, an ability that neither metal or silver can fulfil. When the seal is built at the proper thickness, it will also adjust for out-of-flatness conditions. And because flexible graphite has no property loss in the presence of nuclear radiation, it was a natural fit for the Navy’s nuclear pressure valve application.
Stainless steel caps were designed and manufactured to contain the graphite and protect it from anti-extrusion. By doing this, the seal would have the proper amount of mass to reach density and still fit in the same location as the metal seal it replaces.
Accelerated testing was done at Arizona Public Service, a public electric power utility, and the US Navy’s Target Rock steam test facility. After a week of testing, the data was extrapolated and showed a life expectancy of 26 years, significantly better than the metal seal. Best of all, the graphite pressure seal performed without any leakage and hit the mark on compressibility.
To this day, EGC is the only graphite pressure seal tested and approved by the U.S. Navy for use in Standard Navy Control Valve designs. A superior technology to silver-coated metal, the Thermafoil high-density graphite pressure seal sails under the U.S. flag aboard nuclear-propulsion vessels.
EGC is a recognized world leader in the engineering and manufacturing of graphite composites for high-temperature applications in sealing or thermal systems management. The EGC website can be accessed at https://egcgraphite.com/.