Mechanical Dynamics & Analysis (MD&A) completed a GE® 7FA gas turbine major inspection on a dual-fuel 7FA.03 unit alongside a hydrogen-cooled 7FH2 generator, returning the turbine-generator to service on schedule. The combined outage included full disassembly, inspection, repairs, and precision alignment to restore reliability and performance.
In the power generation industry, reliability and efficiency are paramount. Gas turbines, such as the 7FA series, are critical assets for utilities, and their performance directly impacts grid stability and profitability. Periodic major inspections are essential to ensure these machines operate within OEM specifications and maintain compliance with environmental and safety standards.
For this combined project, MD&A provided all tooling, supervision and labor to perform the outage work scope.
- 7FA Gas Turbine Overhaul: Complete disassembly of the compressor, combustion, and turbine sections for inspection and refurbishment.
- 7FH2 Generator Inspection: Disassembly and electrical testing of the 7FH2 generator, including stator and field assessments.
- Technical Information Letters (TILs): All TILs were completed.
As part of the outage, the inlet filter house and ducting were visually inspected internally down to the inlet plenum and confirmed to be in sound operating condition.
A customer-supplied, refurbished gas turbine rotor would be installed after MD&A inspection.
Arrival
Once onsite, tooling preparation and disassembly began, working two shifts. All as-found clearances were measured, and initial alignment checks were completed.
Turbine compartment scaffolding and field stands were installed, and preparations were made for removal of both the gas turbine rotor and the generator field.
Throughout disassembly, all reusable materials were identified, stored, and prepared for reuse.
7FA Gas Turbine
Following turbine casing and bearing removal, compressor component inspection and repairs began. Inlet guide vanes (IGVs) were inspected and would be returned to service. IGV inner bushings and spring/thrust washers were replaced. Bearings were replaced as needed.
Oil deflectors and seals were prepared for shipping to MD&A Bearings, Seals and Hydraulics Division in Ohio for inspection and repair. New seals would be required.
Stator compressor blades S1-4 and S5-8 were worn and replaced. Several rows exhibited foreign object damage (FOD) and casing pinch marks, requiring precision blending and vane replacement.
For the combustion section, chamber components revealed wear and coating damage. MD&A experts replaced the following with either new or refurbished parts: liners, flow sleeves, crossfire tubes and retainers, liner caps, FWD cans, TP bull horns and transition pieces. Check valves were also replaced. Fuel nozzles were swapped and flow-tested to ensure proper atomization.
For the hot gas path, First-, second-, and third-stage buckets and nozzles were installed with concentricity and clearance checks verified against OEM tolerances. For the exhaust, flex seals were replaced with new pins installed, and the diffuser was weld-repaired.
A new Bearing T1 was replaced. T3 and T4 bearings were also transported to MD&A Bearings, Seals and Hydraulics division in Ohio, refurbished, returned, and reinstalled. The T1 thrust journal was also replaced.
Degraded gaskets were replaced in the discharge casing, and the casing received blend repairs.
7FH2 Generator
At project start, generator shaft jacking devices and eyebrows were installed. Our team constructed our generator field support platform to allow for easy removal of the field when performing this 7FH2 Generator Major Inspection.
This system addresses the unique challenges associated with the 7FA/7FH2 configuration:
- The shaft centerline height is 13 feet above machine baseline (grade)
- The gas turbine inlet ducting and filter house limit crane access.
MD&A’s team removed the turning gear and disassembled the journal bearings, and shipped them to MD&A Bearings, Seals and Hydraulics division in Ohio for refurbishment. Oil deflectors and hydrogen seals were also prepared for shipment.
After end shield and fan blade removal, MD&A experts removed the generator field for covered storage on the turbine deck. The field was inspected, and field windings were found to be clean.
The generator end shields and gas shields were inspected, cleaned, and returned to service.
MD&A performed high-resolution borescope visual inspection of normally inaccessible areas on the generator, outside of the bore region. These areas include under the collector and turbine end retaining rings and the stator end windings, field coil end turns, auxiliary components and stator terminal connections.
The generator stator received visual inspection, insulation resistance testing, winding resistance measurements, DC leakage and RTD tests, and wedge inspection. The field received visual inspection, insulation resistance testing, winding resistance and impedance tests, and turn-to-turn pole balance.
T3 and T4 H2 casings were removed, visually inspected and sent to MD&A Bearings, Seals and Hydraulics division for further inspection and repair. New seals would be installed with refurbished casings.
New T3 and T4 lift oil lines were installed.
Stator testing revealed that more than one-third of the wedges were loose and/or hollow. MD&A experts therefore performed a complete rewedge on the generator stator. A full stator wedge tightness survey map followed.
The new turning gear was installed and aligned, followed by the hydrogen leak check. The gas turbine/generator load coupling was aligned to OEM specifications.
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Startup
Precision alignment was critical to minimize vibration and extend component life. Rim/face checks were performed and coupling bolts were replaced.
The unit was started on schedule and tuned with no issues.
Long-term recommendations to increase owner/operator confidence in continued operation included monitoring of the T3 area, ongoing inspections of variable inlet guide vanes, filter house visual and mechanical checks (with specific details), water washing frequency, and monitoring CDC (compressor discharge casing) slip issues.
MD&A’s multi-divisional team of experienced technicians and product experts successfully completed the GE 7FA gas turbine major inspection and 7FH2 generator major inspection on schedule. The project demonstrated MD&A’s ability to coordinate cross-divisional resources and execute complex inspection and repair scopes. Detailed recommendations were also provided to support long-term reliability, giving the customer assurance of a well-executed outage and confidence in future full-service operations.
For service of any generator regardless of original design, contact the premier non-OEM service provider to the global turbine-generator market. Call us at (518) 399-3616 today or use our contact form.
