US-based machining specialist Hydratight has become the first company to use electrical discharge machining (EDM) for maintenance work. The company said it had completed the “technically challenging campaign” for a major energy company at a US power station as part of post-Fukushima upgrades. According to Hydratight, the use of EDM avoided an expensive unplanned shutdown of the reactor for the operator and took 48 hours off the reactor outage schedule. The EDM process used a heated solid electrode to accurately cut a hole within the reactor feed water line then removed microscopic cuttings using back-flushing and vacuums. It prevented 99.5% of foreign material exclusion (FME) particles, such as drill cuttings and debris, from entering the reactor, which can cause contaminations and lead to unplanned outage.
Mike Riordan, Hydratight’s nuclear specialty services manager, said: “The work has created another way to feed water into the main line if there is ever a power loss to the reactor.” He added: “Tool pressure was also a concern on this particular project, so we were able to use a method which was completely contactless.” The line had water pressure of 120 PSI and electrical conductance exceeding 3,500 micro-siemens. Hydratight’s specialty services deployed customised tooling to negotiate a 15-inch-long, 1-inch wide pipe as an entry point to reach the spot where the ¾-inch EDM penetration was to take place.
EDM is typically deployed as an alternative to mechanical methods, such as drilling and hot-tapping, during planned outages. As well as preventing FME particles from entering process piping, the cutting is highly accurate and can maintain a tolerance of .002-inch when making the hole in the pipe, Hydratight said. Hydratight is wholly owned by Actuant Corporation, a diversified industrial company serving customers from operations in more than 30 countries and headquartered in Menomonee Falls, Wisconsin.