Safety-related FIELDVUE™ DVC6000 digital valve controllers are monitoring critical valves in nuclear plants in Sweden, China, and the USA
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Diagnostic technology helps Wolf Creek Generating Station extend life of critical control valves through normal refueling cycle
Marshalltown, Iowa (March 4, 2010) – The Wolf Creek Generating Station, Kansas' only nuclear power plant, recently used Emerson's Fisher® FIELDVUE™ digital valve controllers to extend the life of critical control valves. This action avoided a potential unplanned shutdown that in a plant this size could cost up to $1 million per day in lost revenue.
Operating since 1985, the Wolf Creek plant produces electricity for more than 800,000 homes near Burlington, Kansas. FIELDVUE DVC6000 Series instruments with Performance Diagnostic capabilities are used in combination with AMS™ ValveLink™ software to monitor critical valves in the plant’s feed water system. The instruments and software provide online, real-time data about the valves' position and condition, including variables such as valve packing friction. This performance data is easily documented and trended over time, enabling plant operators to diagnose problems and to plan and prioritize valve maintenance.
This capability proved its value after operators noticed an accumulation of graphite dust on the packing flange of a feed water regulator valve, which indicated a problem. Packing friction acts to stabilize the valve and keep its plug from vibrating or “chattering,” which can accelerate packing failure. Loss of friction on these critical service valves could lead to a plant trip or unscheduled shutdown at any time.
The maintenance crew discussed how to keep the valve operating until the plant’s next scheduled outage for refueling, almost 18 months later. The team decided to inject leak sealant into the packing while the valve remained in service. The sealant would extend the life of the packing and enable the valve to continue operating. The injection process would require careful monitoring, however, because the sealant might also affect packing friction. Too little friction and the valve would continue to leak and chatter. Too much friction and the valve could lock up.
Justin Keim, Supervisor of Engineering at Wolf Creek, said this on-line repair process would not have been possible without the FIELDVUE instruments. “The FIELDVUE DVC6000 positioner’s accurate measurement and monitoring capabilities enabled us to maintain system stability while packing friction dropped from 500 pounds to zero during the sealant injection,” he said. “The FIELDVUE instrument’s fast response kept up with the changing friction load, in spite of the valve’s heavy chatter.”
Keim said the team would not have attempted this project using the old pneumatic positioner that the digital valve controller replaced. “On-line valve diagnostics via FIELDVUE instruments enabled our personnel to document drive signal, valve position, and packing friction levels throughout the injection process,” he said. “The valve remained in service the entire time, and we avoided a potentially costly plant shutdown.”
He added that two other feed water regulating valves with the same problem were subsequently repaired using the same method and diagnostic tools. The work helped the plant avoided a costly unplanned shutdown.
Fisher valves are installed in over 90% of the world’s nuclear facilities. Emerson also makes Rosemount® measurement instruments and Ovation® control systems that are used in nuclear power plants.