MD&A completes inspection and repair of four turbine-generator systems

Mechanical Dynamics & Analysis (MD&A) completed a wide-ranging technical intervention on two steam turbine systems and two generators associated with gas turbines. The work integrated inspection, repair, machining, electrical testing, non-destructive evaluations, and balancing of critical components.

In addition, execution required coordinating multiple company divisions to address rotors, diaphragms, generator fields, valves, actuators, and spare parts within a single outage schedule.

MD&A centralizes repairs at its St. Louis facility

MD&A’s turbine and generator repair center in St. Louis, Missouri, handled a significant share of the work. The Generators, Steam Circuitry, and Machining Services teams participated, along with the Bearings, Seals and Hydraulics division based in Ohio.

Likewise, joint planning made it possible to move each component between the different service areas depending on the type of inspection or repair required.

The scope included two generator fields, two high-pressure rotors, high- and intermediate-pressure diaphragms, spill containment strips, two valve sets, two actuator sets, and several parts considered critical to the outage.

Turbine inspection detects deformation in slip rings

During the review of the steam turbine generator fields, electrical tests produced results that required expanding the intervention. The mechanical inspection also detected deformation in the slip rings.

As a result, MD&A performed grinding and polishing work on these surfaces. It also identified thermal damage and axial cracks in existing dampers that had to be replaced.

Previously installed blocks were replaced with a belt-and-tie-rod system developed by the company. This design uses elastic forces in opposite directions to create interference and limit axial or radial movement after assembly.

Subsequently, the repaired fields underwent thermal and electrical testing at the high-speed balancing facility. After passing these evaluations, they were sent to machining to complete the work on the slip rings.

MD&A also recommended considering a full rewind during a future disassembly opportunity.

Gas turbine generators undergo comprehensive repair

The two fields corresponding to gas turbine generators also underwent mechanical inspection and repair.

On this equipment, deformation was observed in the slip rings and misalignment in the slot springs. The review also found partially blocked ventilation holes in the coils.

This condition can limit hydrogen cooling flow and promote thermal instabilities in the rotor. Possible consequences include elevated vibration levels 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.

Likewise, the slip rings were ground and polished to correct the detected deformation.

The retaining rings, clamping rings, and field wedges also underwent non-destructive testing. Due to the hydrogen cooling system, a pressure drop test was performed before proceeding with final component preparation.

Steam turbine rotors undergo NDT and balancing

The steam turbine rotors received visual and dimensional inspections, along with non-destructive evaluations and metallurgical analyses.

During these tests, minor indications were detected and reviewed and corrected before return to service.

In addition, eccentricity measurements and dimensional checks were performed to verify rotor condition. The process concluded with low-speed balancing and a quality inspection prior to release.

This type of evaluation is part of industrial maintenance applied to rotating equipment, where the rotor’s mechanical condition directly affects vibration, stability, and operational availability.

Valves and actuators complete the maintenance scope

MD&A’s Bearings, Seals and Hydraulics division in Ohio worked on two sets of steam turbine valve actuators.

The refurbishment included disassembly, cleaning, and component inspection, as well as replacement of soft parts and seals. Some critical components were also replaced or restored to recover operating dimensions.

Once repairs were completed, the actuators were assembled, cleaned by fluid circulation, and tested at a pressure equivalent to 110% of their operating condition.

These tests are intended to verify system performance and reduce the need for adjustments during plant start-up.

Technical coordination to reduce risks during the outage

Executing four major inspections within a single project required MD&A to maintain a consolidated schedule across its divisions.

The sequence combined inspection, NDT, machining, repair, balancing, and functional testing before the components were returned to the customer.

With this intervention, the company consolidated work on steam turbines, generators, rotors, valves, and actuators into a single program. The technical objective was to restore operating conditions and provide recommendations for the long-term operation of the equipment.

Source and photo: MD&A