Mechanical Dynamics & Analysis (MD&A) performed a GE® Frame 7EA Gas Turbine Major inspection and a 7A6 air cooled Generator Minor inspection including planned maintenance for a peaking unit in the Midwest.
The planned scope of work included replacement of combustion and hot gas path (HGP) hardware and components, IGV gears, ring gear, and bushings. Additional replacements included the torque converter, flow divider, and liquid fuel stop valve. The fuel gas stop valve was also to be removed and replaced. Once completed, the team conducted generator testing. Recommendations for future repairs and considerations were provided as part of the inspections.
Compressor – MD&A’s experts inspected several compressor components. These include the bellmouth casing and inlet guide vanes which were cleaned, inspected and returned to service. The IGV inner and outer bushings as well as the spring/thrust washers were found to have light wear and replaced with new parts. The team mapped and buffed the compressor casing. They also mapped and blended the compressor’s rotor blades. The stator vanes were also removed, cleaned and inspected, demonstrating heavy rubbing with rolled material on the tips. MD&A’s experts blended, performed NDE and reinstalled the vanes.
Combustion Section – Several components in the combustion chambers were found to have various degrees of wear, and other deficiencies. The fuel nozzle tip assembly demonstrated heavy wear. MD&A’s experts replaced the fuel nozzles, combustion liners and caps, crossfire tubes/retainers, combustion cans and transition pieces. The piping components, igniters and flame scanners were found to be in acceptable condition and were cleaned and reused.
Compressor Discharge Casing (CDC) – The team found the first stage wheelspace thermocouple guide tubes and clips to be worn/broken. All were replaced. Additional CDC components were inspected including the inner barrel, clearance plugs, bolting and S1N support ring. All were found to be in acceptable condition and therefore cleaned and reused.
Turbine Section – MD&A’s team performed major repairs and replacement within the turbine’s hot gas path. Buckets for the 1st, 2nd and 3rd stage were all removed and inspected. The 1st stage buckets showed discoloration and TBC loss. MD&A replaced the buckets, pins, and D-keys. The 2nd stage buckets also some discoloration and normal wear. The 2nd stage buckets and pins were replaced. The 3rd stage buckets showed normal wear and missing material. They were replaced along with the pins.
The shroud blocks for each of these stages were also removed and inspected. The 1st stage blocks were discolored along with TBC loss. Normal wear was noted on the other two as well. MD&A’s experts replaced the shroud blocks, pins and seals for all three stages.
The 2nd stage buckets were removed and inspected. Slight discoloration and normal wear were noticed during this visual inspection. New 2nd stage buckets and pins were provided by and installed by MD&A.
The 3rd stage buckets were removed and inspected. Normal wear as well as missing material was noted during this inspection. New buckets and pins were supplied by and installed by MD&A.
The nozzle assemblies were also inspected on all three stages. Slight discoloration and deterioration were noted on all three, while the 2nd and 3rd stage nozzle segments also had small cracks. MD&A’s experts replaced nozzle segments and hardware for all three assemblies.
Other turbine section repairs in included tapping the casing’s plug threads and cleaning the bolting and replacing the discourager seal.
Exhaust Section – MD&A’s team inspected the exhaust section. The frame was found to be in good condition, while several seals were replaced. The diffuser, frame bolting, cowl and exhaust duct were cleaned and reused.
Bearings – The T1, T2 and T3 bearings were all removed, cleaned and inspected. Each showed heavy wear, were sent out for refurbishment, then inspected and installed. Other related components such as the thrusts, shims, thermocouples and wires were found to be in fair condition. MD&A’s experts cleaned and inspected the thrust runner, as well as the T1, T2 and T3 journals.
MD&A Bearings, Seals & Hydraulics Division also offers Rapid-Spares bearing exchange program. We maintain a new, identical turbine bearing in our inventory for our customers, eliminating uncertainty and excess costs. This program removes uncertainty from the bearing refurbishment process during critical outage intervals by giving customers the assurance that their bearings are ready to ship, in many instances, even before an outage begins.
Generator Inspection – MD&A’s experts also conducted a minor inspection of the generator field and stator. The scope of the inspection included visual inspection, borescope inspection and electrical testing. The field was found to be in good condition overall, except for some minor contamination which was removed. Other observations were noted, such as additional contamination and insulation migration, but not actionable at the time of inspection.
Electrical testing was conducted on the generator field including 500VDC IR with PI, DLRO and AC impedance testing. All results were satisfactory.
MD&A’s experts also performed a visual and mechanical inspection of the TG1 stator. The axial support hardware was found to be loose and was tightened and secured with epoxy. Other observations were made including oil contamination throughout the machine, minor greasing in end winding areas and partial discharge at phase breaks on the stator end arms. The team also completed visual inspection of the neutral enclosure, which revealed typical oil and dust contamination.
Stator electrical testing was performed as well. This included RTD element resistance and 500VDC IR test, DLRO, 5kVDC IR with PI and CD leakage testing. All results were satisfactory.
Alignments – MD&A’s experts realigned several coupling sections to OEM specifications as needed. These included cranking motor to torque convertor, torque convertor to accessory gearbox, accessory skit to turbine, and generator to turbine. They also aligned the bearing houses as required.
In addition to turbine major inspection and the generator minor inspection, MD&A’s team addressed:
Dovetail Material Abrasion
Upgrades to Fuel Controls
Spacer Seal Replacements
Replacement of Compressor Blades
Maintenance And Inspection Requirements for Gas Turbine Air Inlet System
Shim Inspections
Inspection Procedures for Variable Guide Vanes
Handling and Maintenance of Flexible Metal Hoses
Turbine Shell Inspections
Rub Prevention
Startup/Testing
Upon completion of the work, MD&A’s experts were onsite for startup assistance. Some minor issues were noted and immediately addressed, leaving the system up and running later that day.
Conclusion
The scope of this engagement was vast and demonstrates our depth of experience and capabilities, with the ability to conduct inspection and repairs across the entire power plant system. It’s another testament to MD&A being the reliable and dependable one-stop partner of choice for turbine-generator repair worldwide. Call us at (518) 399-3616 today.
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