Compressor Stator Vane Pinning

Gas turbine axial-flow multi-stage compressor integrity and efficiency are critical to the thermodynamic performance of the entire power generation system. Mechanical Dynamics & Analysis (MD&A) recently completed a General Electric® 9FA.03 compressor stator vane pinning after a vane analysis revealed issues.

Common issues to investigate are stator vane rocking tilt, fretting wear in the T-slot groove, shim protrusions or migration, and possible airfoil clocking. The potential for foreign material damage should always be considered when reviewing stator vane conditions.

Loose pin found during removal.

Loose shim found during removal.

These issues can lead to performance efficiency loss, damage to both compressor and turbine sections, and potentially a forced outage event. At risk are both Frame 9FA and 7FA machines, as well as many others.

For this project, Our Gas Turbine Parts Service Facility (San Antonio Service Center) was contracted to manage and perform casing preparation, stator vane removal, vane repair, or replacement as needed, pinning, shims, reinstallation, and final horizontal joint drop dimension adjustment and verification.

The Process

The upper half compressor mid and discharge casings were removed and placed vertically on cribbing for vane access. With the rotor out, all upper and lower stator vanes were then removed in rows S5 through S16 for vane and casing inspection.

Several vanes had the OEM shim TIL pinning solution installed by others in a previous outage. Most shims showed considerable looseness around the countersunk pin head and many were not well retained, falling loose during removal. Continued operation could have led to shim ingestion, downstream blade damage and forced outage.

During the inspection by MD&A field service personnel, most stator vanes were deemed acceptable for reuse. Galling and fretting were minor, and most hook fits were in good condition.

Some stator vanes exhibited damage on various locations on the airfoil and base and required replacement, most of these replacements were on Stage 16 (38 upper, 7 lower).

The required vane replacements (provided by the customer) were drilled as required for pinning along with the rest of the non-replaced stator vanes to ensure proper alignment upon re-installation. For those stator vanes being reused that contained old broken pins, these pins were either drilled out or secured to ensure no future movement. Stator vanes that contained the TIL pinning condition were either used as a single centerline pin in Stages 5 through 12, or drilled and pinned on the side not affected by the TIL, then placed at the ends of vane groupings during reinstallation.

MD&A directed and oversaw all stator vane drilling and pre-installation inspection and provided the machining fixtures needed to hold individual vanes at the correct drilling orientation. Rows S5 through S12 were pinned in either a single configuration, except those closest to the horizontal joint were pinned in a double pin configuration to provide increased robustness. Rows S13 through S16 received all double pins both upper and lower.

Stator vane drilling fixture

All casing grooves were inspected and cleaned. Vanes were then reinstalled in both upper and lower casings in the planned 4- to 6-vane sectors.

Final shims were installed as needed to achieve OEM guidelines for joint drop dimensions. A total of 67 shims were installed along with the 1,332 vanes.

The unit returned to service with MD&A’s recommendation for periodic borescope inspections in line with OEM guidelines.

Example of a S5 pair double pinned near the half joint during assembly and after joining

Example of a S5 pair double pinned near the half joint during assembly and after joining

The Experience

The stator vane and shim pinning process reduces wear during both start/stop and long-term operation. More than 200 gas turbines are operating with vanes pinned by the MD&A process. These units are successfully operating in Frame 7EA, 9E, 7FA and 9FA turbines.

MD&A’s San Antonio Service Center provides proven expertise on multiple frame gas turbine combustion and hot gas path components and is an F-Class Repair Center of Excellence.

The dedicated professionals throughout MD&A excel in site-based and condition-specific analysis and repair. Maintaining site schedules is always a priority.

Call MD&A today for your Compressor Stator Vane Pinning at +1 (210) 256-5000 or use our Contact form.

Completed view of the mid compressor case after re-installation of pinned rows S5 through S12