Winning ways

20 March 2008

Nuclear vessels

The job for Barnhart Crane ' Rigging for Detroit Edison Co. was to replace two moisture separator reheaters at the Fermi Nuclear Power plant. The vessels were 113 feet long (34 m) and each weighed 300 US tons (272 tonnes).

The existing vessel locations and the location for the new vessels are deep within the structures and piping of the power plant. Traditional methods for extraction and installation would have meant extensive removal of plant equipment and structures, and an extended plant outage to accomplish the work.

A standard approach, and the one used during the plant construction, was to install each of the vessels in two half sections and to join them by welding and then install piping to fit. In this case, however, it was time and cost prohibitive to remove the previously installed piping, and the vessels were housed inside reinforced concrete structures.

The project was further complicated by the fact that the components were in a radiological controlled part of the plant and inaccessible while the plant is operating due to a high radiation environment. The new vessel, therefore, needed to be made and moved to fit the existing plant within a very tight tolerance.

To accomplish the work the project team, which included Barnhart Crane ' Rigging, developed a one piece installation approach. This unique method provided the shortest plant outage with all outage activity completed in a 35-day window.

This saved more than $10 million in replacement power cost.

It was a formidable challenge to move such large components from the fabrication facility in Oklahoma to the plant site in Michigan, and then to move them inside the plant with clearances of less than two inches (50 mm) and to a final fit-up position within 1/8 inch (3.3 mm) tolerance. During initial planning for the project, the one-piece option was determined to be impossible. This was unacceptable to the team so they went back to the drawing board, this time coming up with a unique plan to implement the one-piece approach.

First, the existing plant equipment was meticulously mapped using laser surveying technology. This information was translated to a 3-D design tool from which the team designed and planned to the necessary tolerances. A virtual construction plan was developed with 3-D animation, simulating the heavy rigging path and proving that a one-piece approach was actually possible. The design data and the laser surveying tool were then used to design the exact dimensions for the new vessels, including nozzle locations, for piping up to 48 inch (1.2 m) diameter, and then to confirm through exacting measurement that the vessels were a fit for the plant equipment.

The unique construction approach included application of a full array of specialized equipment. A special rail car was adapted to move the new vessels from Oklahoma to Michigan, US. Barnhart's modular lift tower and integrated slide system was designed and erected at the site to move the new vessels from the rail car up to and inside the power plant. A unique cantilever lifting beam was used to remove large concrete wall sections to give access for the new vessels.

Once inside the plant, an hydraulic slide system was used to maintain positive control and to ease the vessels into their cubicles to the exact location required. The seamless hand off of the MSR from the module lift tower to the plant overhead turbine bay cranes further enhanced the overall project safety.

The project met all of its objectives, with more than 300 building trades’employees participating. The project was completed with no lost time and no OSHA recordable injuries. The vessels matched the plant piping and the 800 required pipe welds were completed within the planned 35 day window.

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