This paper analyzes hydro turbine rehabilitation in regard to the field machining of embedded components. Field machining of hydro turbine embedded components such as stay rings is often required if the location and condition of the embedded components are not within design operational specifications. The alignment and condition of hydro turbine components are effected by powerhouse settling, concrete growth, seismic activity, maintenance practices, and unnatural circumstances. These factors can cause discharge rings to not be eccentric with stator cores limiting generation capacity, upper stay ring flanges to be out of level effecting shaft bearing performance, and wicket gate stem bores to not be plumb or eccentric increasing the chance of failure. These alignment problems can be remedied by means of field machining. Embedded components can easily be corrected or modified to improve and increase unit longevity. Hydro turbine perpendicularity and parallel conditions can be reestablished. Damaged critical surfaces can be overlaid with cavitation resistant materials. Modernization features such as o-ring grooves or wicket gate end seals can be added. Field machining is a custom process that can be preformed to any hydro turbine configuration. The correction of a hydro turbine unit's alignment is one of the central goals of a rehabilitation project. The process of field machining can be integrated into any rehabilitation schedule with minimal impact to the total duration of the project. If field machining is approached with the goal to optimize the balance between cost, risk, and schedule, the final outcome ensures a successful unit reassembly. This paper will present a detailed overview of a typical rehabilitation field machining scoping process, machining life cycle, and their results.
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