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 1^st, 2^nd and 3^rd stage were all removed and inspected. The 1^st stage buckets showed discoloration and TBC loss. MD&A replaced the buckets, pins, and D-keys. The 2^nd stage buckets also some discoloration and normal wear. The 2^nd stage buckets and pins were replaced.  The 3^rd 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 1^st 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 3^rd 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 7EA Turbine Major 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 or use our contact form.

The post 7EA Turbine Major & 7A6 Generator Minor Inspection appeared first on MDA Turbines.

MD&A provided all tooling, supervision, and labor to perform the planned generator major inspection outage scope.

This generator life extension project exemplifies MD&A’s position as a preferred non-OEM one-stop organization throughout the turbine-generator industry.

Generator enclosure

After removal of all attachments, MD&A experts held the critical lift meeting and removed the 24,000 lb generator enclosure and installed all FME covers, removed upper half T4 and T5 bearings, and prepared the base for generator field removal.

The field would be prepared and transported to MD&A’s Turbine-Generator Repair facility in St. Louis, MO. The T4 and T5 bearings and inner and outer oil deflectors would be transported to MD&A’s Bearings, Seals and Hydraulics division in Euclid, OH for inspection and repair.

Scaffolding was then installed for the generator rewind activities.

Coolers were removed from the TEWAC assembly and cooler heads were disassembled. New isomode pads were prepared for the reinstall.

Stator

This was a planned stator rewind, scheduled as preventive maintenance due to significant observed partial discharge. Over time, this could lead to a ground fault condition and forced outage.

A baseline electromagnetic core imperfection detection (ELCID) was performed on the stator core iron to determine the integrity of the as-found laminations.

The existing flat wedge system was removed by traditional methodology and MD&A procedure.

Top bars were then removed without issue, using come-alongs to remove the bars out of individual slots. Bottom bar removal was completed in the same manner. Significant levels of partial discharge were found on several bars.

Following full visual inspection, all connection ring blocking and ties were removed and replaced with new conforming material. A post-disassembly ELCID was performed to ensure no damage to the core iron. Each of the 72 core slots were cleaned of all contaminants and thoroughly inspected.

A core knife test determined the need for complete stator core tightening, completed by MD&A procedure. At the completion of torque activities, an additional ELCID was completed with satisfactory results.

Once received, binding bands were aligned axially and made concentric to the stator core. Three bottom bars were then fit into slots 120 degrees apart to ensure proper alignment. Two top bars were also aligned with the pitch of the bars to ensure the top and bottom bar series plates were properly aligned.

A thin layer of insulation was installed in each slot, and bottom bars were then installed and bottom-bar testing was performed.

A total of six dual-element RTDs were removed during disassembly and were replaced with twelve new dual-element RTDs and operation was verified.

All top bars were then installed, blocked and tied, with no issues.

A tapered wedge and slider design with a top ripple spring was selected to provide sufficient radial pressing forces. Following all winding activities, a final ELCID was performed to ensure no damage to the core iron.

After brazing, a winding resistance test was performed to ensure each of the three phases produced similar resistance values, and all other electrical testing was completed with good results.

Field

Following removal of the generator field the customer opted for a generator field exchange. We sent a refurbished field to site that had been completely rewound with the latest in rewind technology. The field forging had undergone NDE and inspections to ensure long term viability, along with it being high speed balanced with a full heat run to ensure no shorted turns. The exchange of the generator field produced a shorter outage duration which allowed for the customer to be back online sooner.

The original generator field was transported for complete inspection and rewind. On arrival in St. Louis, the field received in-depth visual and mechanical inspection. Three-dimensional scanning and hand mechanical dimensions were obtained.

During disassembly, indications were found on a few field body wedges, and some material damage was found on both retaining rings. All field coils were removed and sent for cleaning.

The cleaned coils were determined fit for service and reinstallation began.

Each installed coil was HI-POT and turn-to-turn tested. A baker surge test was also completed on each coil. During the rewind process, the MD&A standard strap and design blocking was installed. Turn insulation was coated, requiring a rotor bake cycle. After the bake cycle, a full set of electrical tests was completed.

The field was then moved from the clean room to the shop floor to install retaining rings and complete the electrical testing. It was then moved to the high-speed balance facility. After balance, it was staked and painted and prepared for exchange sale.

Isomode Pad 

During this project, the TEWAC assembly was removed. Mating surfaces with the generator enclosure were cleaned and weatherstrips were installed. Generator cooler heads and all piping were cleaned of corrosion and buildups, and new gaskets were installed.

The generator stator was raised to remove the old isomode pads and shims. The MD&A team cleaned the area and installed new isomode pads with pre-existing shims.

The TEWAC assembly was then reinstalled.

Summary

All MD&A inter-divisional work was performed on schedule without any injuries or accidents.

There were no issues with turbine-generator synchronization during startup.

Once again, the MD&A organization drew on its experience and multi-divisional expertise to complete a major inspection and repair project and ensure owner/operation confidence in continued unit operation.

MD&A is truly a one-stop shop! Call MD&A about your next outage today at (518) 399-3616.

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