Tackling Emerging Issues with 7FA Compressor Blade & Vane Replacement

Mechanical Dynamics & Analysis (HGTP) completed compressor blade replacement work on two 7FA units, including full inspections, and ongoing operational recommendations. We were responsive to emerging issues, scope change and flexible in supporting the customer’s needs.

HGTP was mobilized to address suspected fuel nozzle leaks on the customer’s unit 1 gas turbine. The unit had been shut down to replace the reported fuel nozzle-to-forward can gaskets on three combustion chambers. Our experts also inspected the combustion liners, transition pieces, and stage one nozzle in these locations.

While at the site, during a borescope inspection of unit 3, the customer discovered that one forward compressor R0 blade had migrated forward and was in contact with the rub ring. The customer then requested the site team to immediately relocate to the unit 3 gas turbine to address the migrated R0 issue, temporarily pausing work on unit 1.

HGTP relocated to the unit 3 gas turbine to replace the migrated compressor R0 blade and inspect all other R0 blade stakes on the forward compressor wheel. The team removed the #10 blade, cleaned and inspected the wheel slot, and re-staked a new R0 blade into position. As the unit was inspected, HGTP experts noted inadequate stakes in wheel position #7 and the blade was re-staked in place.  Inspections were then performed on the bellmouth casing, forward cone, inlet guide vanes, the plenum assembly, expansion joints, vertical floor bolts, piping flanges/fittings, and the wheel balance weight stakes. The unit was released on schedule following an off-line water wash.

After subsequent review of the borescope report for the unit 1 gas turbine, the customer requested the MD&A site team to then redeploy back to the unit 1 gas turbine to address issues with the aft compressor S17 segmented stator Vanes. The inspection revealed migration and moderate damage to the aft compressor S17 segments, therefore, indicating the need for an aft compressor S17 segment replacement.

The entire combustion system was disassembled to allow for turbine shell and compressor discharge casing removal. Once the casings were removed, foreign object damage was identified on several exit guide vanes. Moderate fretting between the S17 shrouded compressor vane segments and the inner barrel was also noted. Fragments of the S17 V-seal had caused damage to the exit guide vanes and were also located in the cooling air side of the stage 1 nozzle.

HGTP removed the damaged S17 segmented stator vane and V-seal. The customer supplied the new S17 segmented stator vanes.

The site team addressed inner barrel fretting damage and removed areas of high metal. In addition, the exit guide vanes with foreign object damage were precision blended and thoroughly NDE inspected.

HGTP also installed Spiral Wound Metal Gaskets and installed new aft compressor borescope plugs. Additionally, we inspected the customer’s DLN 2.6 Combustion Forward Casings.

The work scope was performed at the customer’s direction, including any Technical Information Letters (TIL), if applicable.

The unit was returned to service on schedule. As for longer-term professional guidance to the owner/operator, several recommendations were advised in a full written report.

HGTP’s specialized services range from Combustion, Hot Gas Path, and Major Inspections to Compressor and Turbine Rotor Repairs to Rotor Life Extension/ Assessment. HGTP offers a complete suite of parts, repairs, and services solutions for the Frame 7EA & 7FA heavy-duty gas turbine fleet.