Mechanical Dynamics & Analysis (MD&A) has completed a major inspection and repair program covering two steam turbine systems and two gas turbine generators, integrating non-destructive testing (NDT), mechanical inspection, machining, electrical testing, repair and balancing of critical components.
The project brought together multiple MD&A divisions under a single outage schedule, with work spanning turbine rotors, diaphragms, generator fields, valves, actuators and critical spare parts. The company’s turbine and generator repair facility in St. Louis, Missouri, handled a significant portion of the work, involving its Generators, Steam Circuitry and Machining Services teams, along with the Bearings, Seals and Hydraulics division in Ohio.
The coordinated approach enabled components to move between specialized service areas according to the inspection, NDT and repair requirements.
NDT Identifies Deformation and Thermal Damage in Generator Field.
During inspection of the steam turbine generator fields, electrical testing produced results that required an expanded repair scope. Mechanical inspection also identified deformation in the slip rings, prompting grinding and polishing of the affected surfaces.
The inspection further identified thermal damage and axial cracks in existing dampers. These components were replaced with a belt-and-tie-rod system developed by MD&A. The system uses elastic forces in opposite directions to create interference and limit axial or radial movement after assembly.
Following repair, the generator fields underwent thermal and electrical testing at the high-speed balancing facility before being sent for machining to complete the slip-ring work. MD&A also recommended considering a full rewind during a future disassembly opportunity.
Gas Turbine Generator Fields Receive Inspection and Repair
The two generator fields associated with gas turbines also underwent mechanical inspection and repair.
The inspection identified deformation in the slip rings, misalignment in the slot springs and partially blocked ventilation holes in the coils. Restricted ventilation can limit hydrogen cooling flow and contribute to thermal instabilities in the rotor, with potential effects including increased vibration and unplanned shutdowns.
For one 7FH2 generator, specialists implemented a modification intended to prevent axial migration of the slotted leaf springs that were restricting airflow. The slip rings were also ground and polished to address the deformation identified during inspection.
Non-destructive testing was performed on the retaining rings, clamping rings and field wedges. A pressure-drop test was also conducted in connection with the hydrogen cooling system before final component preparation.
Steam Turbine Rotors Undergo NDT and Balancing
The steam turbine rotors were subjected to visual and dimensional inspections, non-destructive evaluations and metallurgical analyses.
Minor indications identified during testing were reviewed and corrected before the components were returned to service. Eccentricity measurements and dimensional checks were also performed to assess rotor condition.
The rotor work concluded with low-speed balancing and a quality inspection before release.
Valve Actuators Complete Repair Scope
MD&A’s Bearings, Seals and Hydraulics division in Ohio worked on two sets of steam turbine valve actuators.
The refurbishment involved disassembly, cleaning and component inspection, along with the replacement of soft parts and seals. Critical components were also replaced or restored where required to recover operating dimensions.
After repair, the actuators were assembled, cleaned through fluid circulation and pressure-tested at 110% of their operating condition. The testing was intended to verify performance and reduce the need for adjustments during plant start-up.
Integrated NDT and Repair Program Supports Outage Execution
The four major inspection and repair scopes required coordination across MD&A’s divisions, combining NDT, inspection, machining, repair, balancing and functional testing within a consolidated outage schedule.
The work covered steam turbine systems, gas turbine generators, rotors, generator fields, valves and actuators. The inspection findings enabled specific component repairs and modifications to be completed before the equipment was returned to service.
MD&A’s current capabilities include services, parts and repairs for gas turbines, steam turbines and generators, with its St. Louis facility supporting turbine repair, generator services, machining and high-speed balancing.
Reference: https://www.mdaturbines.com/resources/quadruple-steam-turbine-generator-majors/
