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EFD Induction solves bolt heating challenges

Induction heating is rightly prized for its versatility. But bolt heating? Is induction really an effective alternativeto traditional gas and resistance heating methods? Here we report on how two customers fared when they turned to EFD Induction to solve their bolt heating challenges.



Bolt expansion

British Energy, the largest electricity producer in the UK, utilises induction heating for bolt expansion. Fred Hunter, Development Engineer at British Energy’s Turbine Support Group, comments: "We used to rely upon resistance heaters to release the studs on turbine control valves. But it was a far from efficient procedure. Such technology is inherently unreliable. The electrical elements are fragile, fuses are prone to blowing, and it is essential to have a huge spares inventoryon-site. Moreover, such heaters are not mobile. You can imagine the considerable prep-work that was needed before we could deploy the equipment."

The limitations of resistance heaters had serious implications for British Energy. Opening control valves for inspection is a statutory obligation. That is, it is a legally mandated maintenance action—it has to be done. Since the frequency of such mandatory outages cannot be changed, the only cost-cutting opportunity lies in reducing the duration—and the knock-on disruption—of each outage. Converting to EFD Induction’s mobile Minac converters let British Energy achieve reductions in the duration of these maintenance activities.

From days to hours

"That’s correct," agrees Richard Stewart, Engineering Group Head at the Turbine Support Group. "We were very impressed when we ran our first trials with Minac. Previously, bolt loosening at one of our power plants took up to two days. Minac slashed that time to a couple of hours." The main reason for the time saving is Minac’s extremely quick and precise heat delivery. With gas or resistance heaters, excessive heat is entered into the workpiece and heating times are slow. During re-assembly, lengthy periods are spent waiting for the assembly to cool down prior to measuring the bolt strains. "The EFD Induction method," adds Stewart, "lets us better deliver the right amount to just the right place, leading to considerably shorter cool-down times. Minac is now part of the standard maintenance kit used by our Group at three British Energy power stations." The conversion from resistance to induction was a relatively painless experience. "There were the inevitable teething hitches, one of which was a high starting current that caused tripping. But the EFD Induction guys worked with us and they fixed the problem by adding an additional transformer." Shorter outages are not the only benefits delivered by Minac.. Because the Minac equipment is mobile and so easy to use, British Energy’s own in-house maintenance staff—in this case its Turbine Support Group— can now perform the bolt loosening and tightening. The procedure was formerly outsourced to external subcontractors with Induction Heating expertise. "This," says Stewart, "of course means we have complete control. We can undertake our maintenance actions as needed during outages. This flexibility means that sub-contractors are not kept waiting on-site, thereby minimising costs."

75% faster

Obviously, Minac can be used outside of power stations for bolt loosening applications. One prime example of the versatility of Minac is the case of Sulzer Elbar B.V., part of Sulzer Turbo Services. Based in Lomm in The Netherlands, Sulzer Elbar specializes in gas and steam turbine refurbishment, component manufacture and field service and gas turbine relocation. The company also offers inventory management and maintenance service agreements. Previously, Sulzer Elbar used a gas bolt heater. But according to Rob Bormans, loosening one bolt took on average 12 minutes. So when Björn Rosvik, an EFD Induction application engineer, organized a demonstration of Minac, Bormans and his colleagues were "absolutely impressed" when "bolts were loosened in a record time of only three minutes per bolt." Rosvik is deservedly thrilled with the outcome of the work together with Sulzer Elbar: "This case really illustrates the potential of Minac for this demanding application. Thankfully, it seems more and more companies— especially those concerned about costs and quality—are realizing that they don’t have to continue with outmoded gas and inefficient resistance heaters. Induction is a viable, proven alternative." Rosvik first demonstrated Minac to Sulzer Elbar more than one year ago. Since then cooperation has developed, and the company has acquired two Minacs, a Minac 50–80, and a 25–40 model. Comments Bormans in conclusion: "I’m sure we will find new applications within our company for induction heating. I’m happy for Sulzer Elbar that we chose the right partner for solving our bolt heating problems!"