Installation of 250 ton turbine overhead crane for nuclear power plant

A nuclear generation station in Michigan, États-unis, produces enough power for a city that 1.25 million people call home. So when a complex retrofit was required, Whiting Corporation was commissioned to install a new 250-ton turbine bridge crane.

The station in Michigan produces 2.2 gigawatt of electricity, enough for the city that houses in excess of a million residents. Whiting Corporation was called upon to install and commission a 250-ton turbine bridge crane so adjacent turbine generators could run at full power with no downtime.

To prepare for the project, Whiting constructed a hydraulic heavy lifting and rotation test structure off-site ahead of the installation itself.

According to Whiting Corporation, installing the bridge crane while the station was operating saved millions of dollars as well a significant amount of time prior to an upcoming refuelling outage.

The manufacturer explains: The innovative installation saved $18 million that would have been absorbed into the community rate base. The savings achieved in time and money are applicable to other turbine, generator and heavy lift applications across a wide range of industries seeking to enhance safety and avoid downtime. It also cut the retrofit outage by a week."

Whiting Corporation employed multiple telescoping gantry systems and a hydraulic turntable to safely lift and rotate components for the 250-ton bridge crane with 60-ton auxiliary hoist.

Two 26.6m girders were lifted 60.28m above the turbine floor and placed between the two operating units. Workers configured the gantry system as an engineered temporary lift assembly that had never been used in such a manner during power operation. This design proved less invasive to the plant structure.

"Thanks to the project, the industry now has a proven method for the practical application of a telescoping gantry system and a turntable for component rotation," says Whiting.

According to the manufacturer, the second bridge crane used allows for a reduction in outage duration by as much as seven days in the upcoming turbine retrofit outage alone. In addition, all future outages are expected to continue to realise additional costs savings, as a point of vulnerability has been eliminated through the addition of the second bridge crane. The entire hydraulic heavy lifting and rotation structure produced off-site in preparation for the installation exactly replicated actual lifting conditions. It was used to remotely load test the innovative telescoping gantry system and turntable technology to 125 percent of maximum load through the entire range of movements, while also maintaining levelling tolerances to 0.5 percent.

They explain: "The lifting team exceeded the provisions of Subpart 2.15 of ASME NQA 1-2008 quality assurance requirement, stipulating a dynamic load test equal to 110 percent of the rate load, instead choosing to proceed with a more conservative 125 percent rated load test. "The trial also exceed the new ASME P30.1.2014 "Planning for Load Handling Activities" code issued during the project's planning phase, which was exceeded despite not being part of the initial scope."

Test loads were taken beyond the operational limits so to ensure there was sufficient margin to encompass any of several failure modes that could have been encountered during installation.

In addition, controls were established to ensure assembly of the gantry system was identical to that used during the demonstration. This featured redundant level control, LED levels and 3D Laser Scanning Total Station guidance, time lapse and live video of the whole sequence.

"We learned from the mock-up that the system was rock solid even in 15-20 mph winds (approximately 32 kph). Fine control of the power towers easily kept the lift level, while the rotation motion was exceptionally smooth," explains Dave Weber, director of nuclear services at Whiting Corporation.

The company also employed an additional total station and operator to monitor the power towers in the reverse operating direction and a communication protocol was established. This system was reviewed for compliance with the new ASME P30.1 and as a result, found to be in alignment with this latest code.

Weber adds: "The installation method require collaborative efforts between ourselves as the crane vendor, the utility and the installation contractor to manage the risk by performing a robust demonstration of lifting operations, in addition to independent review of analytical calculations for the temporary engineering lift system.

"The results allowed the owner to avoid opening the turbine building envelope during installation and to complete the work without impacting outage duration.

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