MD&A provided all project management, inspection and analysis, supervision, labor and tooling for the owner’s dual-unit work scope.

During disassembly of the first unit, MD&A Gas Turbine Services personnel first removed roof sections, recorded thrust and lift checks, removed all relevant casings, and labeled/removed relevant piping/hoses. Half shell readings were taken on the turbine and compressor by recording all rotor and stator tip clearances.

The service run 7FA.04 hot gas path components were inspected and analyzed onsite by specialists from MD&A’s San Antonio Service Center to determine the potential for future component repairs. Our team has extensive knowledge on a range of gas turbine component repairs, including weld repair, blending, dimensional restoration, and machining. They can extend the service life of gas turbine components whose OEM service limit has passed or whose configuration is no longer suitable to operate. These experts provided feedback on the component repairability.

For these outages, the turbines’ first, second, and third stage buckets were removed and replaced with Customer provided components.

Additionally, nozzles and shrouds were removed and exchanged. For the compressor, stage 14 through EGV’s stator vanes were removed; new vanes were drilled and pinned upon installation.

MD&A inspected T1 and T2 bearings and determined replacements were required, in addition to new thrust bearings.

All combustion components were removed and inspected. Transition pieces, liners, flow sleeves, outer bellows, inner crossfire tubes and fuel nozzles were exchanged during reassembly.

The GE® 7FH2 generator was disassembled, including coolers, oil deflectors, gas shields and bearings. Hydrogen casings and seals were removed and sent to MD&A’s Bearings, Seals and Hydraulics Division in Euclid, Ohio for refurbishment.

The generator field was then removed and transported to our Turbine-Generator Repair Facility in St. Louis, MO for a complete field rewind utilizing the existing copper. The rewind process was expedited to allow for the rewound field to be installed in the sister unit. A spare generator field from the Customer’s inventory was installed on the first unit, to support the expedited outage schedule.

MD&A experts inspected the generator stator and found areas of greasing indicated a loose wedge structure and necessitating a full stator rewedge. Core and bellyband tightening was also required.

Stator electrical testing was completed, and electromagnetic core imperfection detections (ELCID) tests were conducted before and after wedge replacement.

MD&A’s Generator Experts replaced the wedges, then completed bellyband and core tightening. With the stator repairs complete, the generator field from owner/operator’s inventory was able to be installed.

During component reassembly, new hydrogen seals and springs provided by MD&A’s Bearings, Seals and Hydraulics facility were utilized.

Following reassembly of the gas turbines and generators, coupling alignments were performed by MD&A technical experts in full collaboration with the Owner/Operator.

MD&A’s Turbine and Generator Controls Division performed a complete inspection of the exciter and inverter equipment, ensuring no issues on return to service. Startup was completed with no operational concerns and full compliance with emissions standards.

Following execution of the first outage, MD&A personnel shifted focus to the sister unit, to complete a nearly identical work scope.

For this unit, turbine first, second, and third stage buckets were replaced as were nozzles and shrouds.

A spare Customer provided Gas Turbine rotor was installed after conducting green rotor inspections and repairs. At startup the green rotor run-in was completed in compliance with industry standards.

As with other unit, all Technical Information Letters were listed as completed, as were all Extra Work Authorizations.

For this unit, the service run generator field was removed for transport to our Turbine-Generator Repair Facility for a complete field rewind utilizing the existing copper. This field would be rewound and returned to Customer after the outage to be held as inventory.

Conclusion

Throughout these major overhauls on two 7F.04 Gas Turbines and 7FH2 Generators, detailed daily written and visual (photographic) job reports and updates documented all current and planned activities, alerts, needs, schedules, recommendations, and resolutions.

For every repair job, large or small, the speed and effectiveness of our response team is matched only by the depth and breadth of our engineering expertise.

Successful completion of these back-to-back projects clearly exemplifies the multi-divisional breadth, versatility, and corporate commitment of MD&A as a premier non-OEM service provider to the global gas and steam turbine-generator market. Call us at (518) 399-3616 today or use our contact form.

The post Back-to-Back Major Overhauls on Two 7F.04 Gas Turbines and 7FH2 Generators appeared first on MDA Turbines.

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 was contracted to manage and apply their hands-on skills to disassemble, inspect, re-stake, and reassemble a 9FA gas turbine with DLN 2.6 Gas Only configuration in the United Kingdom, ultimately saving both time and project cost for the owner/operator.

Throughout each stage of the project, comprehensive inspections were performed, assessed and verified by MD&A experts, drawing on our world-class experience and knowledge.

MD&A arrived and immediately set up the foreign material exclusion zone inside the turbine compartment, removed all piping and ducting, then addressed the forward can assemblies. We worked closely with the customer to help procure specialized ITH equipment specific for their gas turbine.

The upper half combustion system transition pieces were soon removed allowing compressor blade inspection. The rotor was pushed downstream to take as-found turbine clearance measurements.

Visual inspection of the Stage 17 rotor blades showed migration downstream. At this point in the project, flowpath staking work was performed and NDE-verified on all R-17 compressor blades.

With the gas turbine compressor rotor blade re-staking complete, reinstallations and close-out inspections began.

While reinstalling the transition pieces, MD&A detected misalignments from a previous major outage. An inner floating seal had not been properly engaged. A new seal was installed by MD&A and work continued.

Setback readings were then taken and reviewed by MD&A experts. Consensus was reached to continue buildout of the combustion system.

Next, the majority of the turbine and combustion piping was installed and a close-out inspection of the combustion system was performed with the owner/operator. The upper half turbine shell manway cover was installed and work began on the turbine compartment roof sections.

Ducting work soon followed, leading to pressure testing of the turbine compartment. Positive and negative ventilation were tested and passed.

The turbine compartment was then cleaned and the site team demobilized. On-site work was completed in 26 days.

Throughout the project, sequenced and unobstructed photographs were taken of all inspection findings and details. Communication & follow-through was key to this & all projects success.

Specific recommendations were prepared for the owner/operator that included well-defined borescope examination locations and intervals, monitoring locations, and precise rationale for each task.

Every MD&A project concludes with a comprehensive report featuring specific recommendations in addition to spare parts review.

Bringing such expertise onsite not only assures success, but also offers a learning process for all participants. During the critical lift meeting, MD&A professionals added an experience-based recommendation going forward, suggesting a jacking system upgrade that would further improve efficiency for the customer on future projects.

This project exemplified many of the knowledge-based benefits brought to a project by MD&A, including:

• Forward-looking analysis and communication with all project participants.
• Globally recognized attention to detail.
• Project management skills and coordination.
• Clear understanding of the owner/operator’s schedule and cost.
• A strong commitment to all rotating equipment as part of a complete gas turbine/steam turbine/generator portfolio.
• Specific commitment to long-term operation of large-frame gas turbines.

MD&A’s technical directors and service technicians bring decades of experience to each project regardless of OEM, a process now proven in more than 20 countries worldwide.

We invite you to discuss any global gas turbine issue with us today. Call us at (518) 399-3616 or use our Contact Form.

The post Gas Turbine Compressor Rotor Blade Re-staking in the UK appeared first on MDA Turbines.

Our experts have over 15 years of experience in repairing single crystal gas turbine blades. We have repaired over 4,000 blades made of materials equivalent to the 7FA.04 1st blade (Rene-N4).

7FA.04 components can be repaired using MD&A’s procedures which aim to extend their life while enhancing performance.

Repairing 7FA.04 Buckets:

MD&A has also developed a comprehensive repair process for 7FA.04 1^st stage buckets, addressing various issues commonly observed in the incoming condition. Problems such as tip cracks, tip cap oxidation, and wall thinning, as well as airfoil TBC coating missing with oxidation through the bond coat and into the parent material.

The 7FA.04 1st stage bucket tip restoration process includes the removal of all cracks and airfoil damage, single crystal proprietary weld processes using high-quality materials, and the installation of a new tip cap.

MD&A implemented CT Scanning (3D X-ray) and white light scanning to develop the optimal welding techniques to ensure a top-quality tip welding restoration structure.  Metallurgical testing was performed to ensure that the process produced buckets free of cracks and re-crystallization at the airfoil tip cap.  The weld material above the tip cap is a high oxidation and erosion resistant structure that is proven to perform well in single crystal blades at high firing temperatures experienced in AGP applications.

The final configuration of the blade tip is accomplished by using a multi-electrode configuration tool during the electrical discharge machine process (EDM).  After re-establishing the tip geometry, all new cooling holes are established to ensure proper tip cooling.  The tip restoration technique ensures no double or triple drilling cooling holes.  This provides the best airfoil tip cap integrity.  All components are then x-ray inspected and airflow tested.

Once the repairs and pre-coat inspections are complete, MD&A experts apply a NiCoCrAlY HVOF bond coat.  This coating is derived from military gas turbine technology and contains additional elements such as Hafnium and yttrium that provides for a superior oxidation resistant bond coat.  MD&A offers a low conductivity (Low-K) Thermal Barrier Coating that helps reduce the bulk operating temperature of the 7FA.04 1st Stage bucket.  Lowering the operating temperature provides for the long-term preservation during the operational lifespan of the component.

The MD&A blade tip restoration technique has been fully demonstrated in directionally solidified (DS) and single crystal (SC) components.  Evaluation and measurements of blade tip repairs after operation have demonstrated improved optimization of the blade tip height.  Keeping most of the original tip height during operation provides the best turbine performance.

In one case study comparison versus the OEM, MD&A’s blade repair procedures have proven to be highly effective, resulting in several benefits for customers. These include minimal loss of blade tip height, which helps maintain turbine performance, as well as, low erosion and oxidation of the repaired blade tips. MD&A’s repairs also exhibit excellent abrasion resistance against the thermal barrier coating (TBC) of 1st shroud tiles.

MD&A has successfully repaired over 4,000 single crystal blades, resulting in approximately millions of dollars of savings for customers. These repairs have enabled blades to operate at higher firing temperatures, contributing to improved turbine efficiency.

Experts in AGP Gas Turbine Component Repairs

MD&A has also performed inspections on 7FA.04 (AGP) 2^nd Stage Blades & 3^rd Stage Blades.

Our facility has leading-edge equipment and repair techniques with proven expertise on multiple-frame gas turbine hot gas path and combustion components.

Our team has extensive knowledge on a range of gas turbine component repairs, including weld repair, blend repair, dimensional restoration, and machining.

Our expert technicians are well-trained, seasoned professionals with in-depth knowledge of the many strict tolerances, procedures, and specifications to complete each repair.

Repairing Nozzles & Shrouds:

MD&A experts have also repaired 7FA.04 1st shroud tiles. This repair involves implementing true abradable coatings in new and repaired tiles to minimize stress on the blade tip during rubbing incidents.

MD&A’s repair expertise extends to gas turbine nozzles, including the 1st and 2nd stages.

Similar repair experience are Nickel-based V94.3A2 2nd and 3rd vanes with our weld/braze repair method refined over 15 years. Our experts have successfully repaired 45 sets and returned them to service.

For 7FA.04 2nd stage nozzles, our experts have made an alloy change and combined weld repair with braze repair.

MD&A specializes in the repair of several key gas turbine components across different models, allowing our customers to extend the lifespan of their equipment and optimize operational efficiency.

1. 6FA/7FA/9FA Repairs: We offer comprehensive repairs for the 1st, 2nd, and 3rd buckets, nozzles, shroud blocks, liners, transition pieces (TP), flow sleeves, and caps in 6FA, 7FA, and 9FA gas turbines.
2. 7EA Repairs: Our expertise extends to repairing 1st, 2nd, and 3rd buckets, nozzles, shroud blocks, liners, transition pieces (TP), flow sleeves, and cowl caps in 7EA gas turbines.
3. V94.3A and V84.3A Repairs: We provide repairs for 1st, 2nd, 3rd, and 4th blades, 1st, 2nd, 3rd, and 4th vanes, as well as the 1st outer seal in V94.3A and V84.3A gas turbines.
4. GT24/GT26 Repairs: Our repair capabilities encompass HPT1 blades/vanes and LPT1, LPT2, LPT3, and LPT4 blades/vanes in GT24 and GT26 gas turbines, with ongoing development in the repair processes.

MD&A is an industry leader in AGP gas turbine component repairs and has earned customer trust across the globe. Our expertise in repairing various gas turbine models allows our experts to constantly sharpen their skill set and brings both depth and breadth of experience to your parts lifecycle. We believe our historical track record of success is an important fact that differentiates our service from those available elsewhere in the industry.

Through meticulous repair processes and commitment to continuous improvement, MD&A delivers cost-effective solutions, enhanced performance, and extends the lifespan of gas turbine components.

For more information about our AGP gas turbine component repairs and services, please visit our website or use our contact form.

The post 7FA.04 (AGP) Gas Turbine Component Repairs – Enhancing Performance and Cost Savings appeared first on MDA Turbines.

A large mill anticipated its current General Electric® Frame 5 gas turbine’s rotor would reach the end of its life cycle in 2024. A replacement would be needed. The responsible, forward-looking solution was to locate a spare rotor and have it immediately available for the upcoming outage. Having reliable spare equipment on site would lessen the disruption.

Research led the owners to a used GE® Frame 5 gas turbine rotor which had the potential to be refurbished and its lifespan extended, then held in controlled storage until the changeout.

The mill owners also knew who to call for the reconditioning and rotor life assessment – the turbine-generator experts at Mechanical Dynamics & Analysis.

The spare was obtained and shipped to MD&A’s full-service turbine-generator repair facility in St. Louis, Missouri to institute their proven gas turbine rotor life assessment program and recondition this critical piece of equipment.

Traditional rotor evaluations at MD&A feature advanced NDE results and metallurgical evaluations, engineering analyses, and any required stress and thermal modeling.

Upon arrival, the asset was immediately inspected and analyzed based on its past operations, as-found status, and forecasted activity and service life requirements.

Exacting measurements were taken of all journal diameters and internal axial distances. Complete incoming runouts were performed, as well as compressor blade drops.

Individual section runout measurements and balance data were taken for all stages. Bore hole and rabbet details were included, all to be checked again after the final assembly.

Dummy journal, distance piece, and turbine wheel runouts were also performed, and compressor wheel interference fits were analyzed.

Blade inspection and replacement blade installation on the compressor followed, featuring proprietary coatings.

Re-stacking  

The rotor was then prepared for the MD&A Gas Turbine rotor stacking elevator in St. Louis, carefully aligned and verified according to the MD&A stacking program.

Stack processes and procedures were carefully monitored and controlled.

Each step included a stone face procedure to remove any high metal after cleaning, followed by compressor assembly coupling bolt stretch and thermal gap analysis.

Finishing journal diameters were taken, followed by thrust runner and coupling face measurements.

Additionally approved by the customer in the compressor section, MD&A experts performed concluding and comprehensive runouts, then recorded and evaluated.

Experts also machined the R0 journal and thrust faces after assembly, and machined selected forward fits. For the turbine section, they also machined the T2 journal after assembly, selected fits and radii to corporate specifications, and interference corrections.

Balance and delivery

Final balance was performed at MD&A’s state-of-the-art high speed balance facility also in St. Louis.

MD&A’s comprehensive finishing inspections included but were not limited to the following:

• All blades free of marks and all blade damage properly addressed.
• Optimum condition of all journals.
• Speed gear properly installed.
• Balance weights staked and properly stamped.
• Verified completion of all non-conformance reports.

The Frame 5 rotor was then protected and prepared for transport.

Additionally, the remaining scope will be carried out during the outage:

• Tip grinding of the new compressor blades for optimum clearance and performance.
• Final machining of the turbine rotor rabbet fit to mate up the generator.

MD&A’s Gas Turbine Reconditioning and Rotor Life Assessment & Extension program is the ideal solution for any aging component. The focus on analysis, precision and perfection ensures the customer of reliable and predictable long-term operation.

MD&A can provide new, replacement wheels & discs for GE® 7FA and 7EA gas turbines.

Rely on the talented and experienced team at MD&A, backed by its world-class organization.

Talk to MD&A today to verify, recondition, and extend the life of all critical life-limiting assets.  Call (518) 399-3616 or use our Contact Form.

The post Frame 5 Rotor Reconditioning and Rotor Life Assessment appeared first on MDA Turbines.

For Hermiston Generating Plant in Oregon, Mechanical Dynamics & Analysis (MD&A) completed a complex, multiple-component combined-cycle major inspection and overhaul project that successfully brought both turbines and both generators back to full and reliable operations.

The 474 MW combined-cycle plant was depending on the complete and efficient renewal of its Unit 2 system.

This major project demonstrates the full capabilities and product knowledge of MD&A personnel, and the organization’s commitment as a premier, fully integrated non-OEM supplier to the turbine/generator community.

It began with a full major inspection of a late 1990s vintage 170 MW GE® 7FA gas turbine and included the 7FH2 generator robotic inspection work. The GE® A-10 steam turbine and 7A6 generator would also be fully inspected and refurbished by MD&A in the same outage.

7FA Gas Turbine

MD&A mobilized and completed the disassembly process utilizing a two-shift operation. Detailed visual inspections began, coupled with detailed NDE, followed by the recommended refurbishments.

In the turbine section, first-, second-, and third-stage buckets were replaced due to rubbing wear and thermal barrier coating (TBC) loss.

First-, second-, and third-stage nozzles were also replaced due to foreign object damage, evidence of cracking, and coating loss. Inspections and similar indications revealed the need to also replace the shrouds.

In the combustion section, liners and transition pieces were replaced with refurbished sets due to TBC loss. New inner crossfire tubes and retainers were installed due to wear and outer crossfire tube packing was replaced at reinstallation.

Although no abnormal visible wear was found, forward combustion cans and fuel nozzles were replaced with customer-provided refurbished sets. Flow sleeves also showed no wear, but the flow sleeve piston rings were replaced.

Liner caps were replaced with refurbished, and transition piece bullhorn brackets were found worn and replaced with new.

For the compressor section inlet guide vanes, MD&A replaced gears, rack, inner and outer bushings, and spacers. Inlet guide vane blades themselves will need to be replaced at the next major inspection.

Rotating and stationary blades showed no damage. R-0 inlet compressor blades were replaced with a refurbished set and shims were added to stages 14, 15, and 16. The casing and rotor showed no need for immediate action, but the discharge casing retention bars were replaced.

The inactive thrust bearing showed heavy scoring and the T-1 & T-2 bearings revealed pitting and scoring, which were subsequently replaced with refurbished bearings. The active thrust bearing was cleared for service.

7FH2 Generator

For the generator, the initial scope of work was visual inspection, robotic wedge map analysis, electromagnetic core imperfection detection (ELCID), and a full battery of electrical testing.

The borescope inspection showed substantial widespread greasing and several areas that had loose hardware. The field was recommended to be removed for a more comprehensive stator investigation. After field removal, a core wedge map was performed that showed approximately 90% of the wedge system was loose and/or hollow, not meeting MD&A criteria. A full stator re-wedge, replacement of greasing blocking/ties, and axial support tightening was recommended and performed.

MD&A also provided and installed an improved the wedge design.

Prior to re-wedging, a significant amount of time was expended cleaning the core. All slots were cleaned including dovetails.

New filler material and top ripple springs were installed during the re-wedge. A modification was made to the end wedges to improve mechanical strength. The original flux probe was installed without issue, and a final ELCID was performed with acceptable values.

Based on modal bump testing, MD&A recommended that the entire collector and turbine ends have series blocking installed to reduce resonant frequency response. Saturated felt and ties were added to dampen the response.

New axial support hardware was installed, replacing the loose axial supports and hardware found during initial inspections. Locking epoxy was applied on all hardware to ensure no complications during operation.

H2 seals were replaced with new, and field collector rings were ground.

Successful electrical testing was performed at the completion of all work performed.

A-10 Steam Turbine

MD&A performed a major inspection and overhaul of the 81MW GE® A-10 steam turbine, generator stator, and field installed in 1996.

The main steam valves were also removed by MD&A and sent to MD&A’s St. Louis Repairs Facility for inspection and repairs.

MD&A specialists performed a complete steam path structural audit of the A10 steam turbine.

Although many minor diaphragm indications could be repaired by MD&A onsite, ILP diaphragms 9, 10, 11, and 13 were shipped to MD&A’s repair facility for major repairs. Stages 10 and 11 would also have inserts installed on the steam seal face due to dishing.

HP and ILP rotors remained coupled and were removed for sand blasting and NDE. Minor bucket repairs were performed on site to correct impact damage and moderate solid particle erosion.

On reassembly, MD&A performed a Topless Alignment®, and MD&A On-Site Seal Services fit and installed new diaphragm and gland steam packing.

7A6 Generator

The 7A6 air-cooled generator was disassembled and the field removed. The generator field was shipped to MD&A’s St. Louis Facility for a full rewind. In addition, MD&A’s Generator Division mobilized onsite to perform a full stator rewind.

The combined HP stop and control valve was disassembled and the cores were shipped to MD&A’s St. Louis Repair Facility for inspection and repairs. The Steam Turbine Repairs Division also received two reheat stop valve and two intercept valve cores for inspection and repair.

Stator

Concurrent with the major steam turbine inspection, an elevated workspace onsite was constructed to support the generator division for stator disassembly and reassembly work. A baseline ELCID was performed to determine integrity of the current stator core iron. No shorted laminations were noted.

The wedge system was removed, then the flex probe was carefully set aside for reassembly.

With wedges and series loop connections removed, bar removal began. Inner axial supports were left in place and prepared for the reassembly. Connection pieces were cleaned for reuse.

The stator was thoroughly cleaned to remove any contaminants from the wedge/bar removal process. A post wedge/bar removal ELCID indicated no core iron damage during wedge and bar removal.

Each core slot was cleaned, and a detailed inspection of any abnormalities was conducted. The core compression flange and all exposed areas where the end windings sit were painted with an epoxy paint for a uniform color on the compression flange.

After a thorough cleaning, the rewind began.

Bar boxes were moved to the scaffolding deck with an innovative safety-conscious method of disassembling the scaffolding roof and flying the boxes to the deck with a crane following completion of a detailed lift plan.

Each of the six circuit rings were acceptance tested, and the outside binding bands were installed.

A tapered gauge from the bar manufacturer was used to ensure concentricity was achieved on the four binding bands. Concentricity of each band is a vital step that will properly align each bar and subsequentially the end winding basket once the rewind is completed.

Two top and two bottom bars were installed to ensure alignment. Bars were fit into a shoe on the collector end and carefully transferred through the bore to the turbine end. All 72 bottom bars were installed, blocked, and tied. All 72 top bars were then installed, blocked, and tied, along with 12 new resistance temperature detectors (RTD’s).

After all bottom bars were installed, a Hipot test was performed using a high potential voltage to ensure no bar armor insulation damage. Another Hipot was performed on all top & bottom bars at the completion of top bar installation.

Wedges were then installed, and filler was adjusted at each wedge for proper radial compressive force. Axial locking pins were installed, followed by a final ELCID and brazing. The existing circuit ring copper connection pieces were re-used and brazed to respective top and bottom phase connections.

Upon completion of all rewind activities, final electrical testing consisted of winding copper resistance, insulation resistance, and a final Hipot of each respective phase. Each phase produced satisfactory resistance values.

The stator rewind activities progressed as expected throughout this project. The consistent bar shapes and robust bar design aided in completing the project without incident.

Field

The 7A6 generator field was sent to MD&A in St. Louis for testing, disassembly, coil removal, cleaning, further testing, re-assembly, and high-speed balance.

During initial electrical testing of the heavily dished collector rings, collector studs, and bore copper, the collector studs failed high potential testing. This resulted in the replacement of the collector rings which included removing the old collector rings, manufacturing new collector rings, new collector ring insulation, and reinsulating of the collector studs.

Coils were removed and sent off-site for cleaning. They were then returned and checked by MD&A.

After reinstallation, each coil received AC Hi-Pot and turn-to-turn testing.

Also, during the rewind process, the blocking was upgraded to the MD&A standard block and tie design. Turn insulation was coated, requiring a rotor bake cycle.

Electrical testing, high-speed balance, acceptance testing, and shipping followed.

Post-Outage GT Performance Analysis

MD&A issued a report that calculates the relative change in output and heat rate after the gas turbine outage. Operating data from pre and post-outage was used for the analysis.

Full-Scope MD&A

MD&A provided startup and balance support of the unit.

Our team provided full recommendations of what to look for or replace at the next outage.

This combined-cycle inspection and overhaul clearly reveal MD&A’s total service capability and non-OEM commitment with deep and focused product knowledge and experience. The precision of all MD&A divisions in support of a common goal merged into a powerful, comprehensive response, returning the facility to full and long-term operations.

With this project, MD&A has added to its impressive project resume as a holistic provider of services to all makes and models of turbines and generators, returning them to and above their original standards.

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

The post MD&A Completes Significant Combined-Cycle Inspection and Overhaul appeared first on MDA Turbines.

A braze-cracking issue can occur with F-Class DLN 2.0 and 2.6 end cover designs. Turbines at the greatest risk are those burning unheated fuel.

Low-cycle fatigue is the primary cause of braze-joint fracture at the 4 possible braze locations on each insert location. Thermal stresses are a contributor because temperatures in the susceptible locations can cycle from 100°F to 700°F.

For fuel nozzles of OEM design, insert braze cracking creates the opportunity for gas to leak into neighboring circuits and contaminate burner-tip cooling air. This scenario can create emissions and tuning challenges, not to mention the possibility of increased flash-back potential. Flashbacks can result in nozzle damage which can lead to catastrophic failure.

These failing conditions are identified if insert replacements requirements are met and reported on at incoming inspection (pressure test). At this point, under these conditions, the industry standards are to perform a full insert replacement of each failed cover assembly.

Additionally, the currently understood industry standard for brazed insert replacements (as set forth and published by the OEM) is a maximum of 3 insert replacements per cover before the cover is deemed scrap. Each time an insert replacement occurs, .030” of material is removed from the bore to establish clean parent metal for the new braze joint.

Our team has performed extensive research and development found that the “3-and-out” strategy was only true for the original 7FA DLN 2.0 cover design and not the others.

Using the original 7FA gas turbine DLN 2.0 combustion end cover as a baseline for our assessment, which used the as-designed 5/8-11 threaded wire inserts in order to secure the outer fuel nozzles to the end cover. A minimum wall thickness, at pressure vessel requirements, had been calculated to be .078”.

It was confirmed that the 7FA DLN 2.0’s 3^rd repair cycle, the minimum wall thickness is optimally .081”. Therefore the 3 insert maximum was met.

We modeled and destructively tested the 6FA DLN 2.0 end cover which had also been assessed by the OEM to only permit 3 insert replacements.

However, we had also discovered through destructive testing and 3-D modeling of the “6FA” 2.0 cover’s internal passages, that while maintaining minimum wall thicknesses insert replacements can double over the OEM recommendations of “no more than 3 replacements allowed”.

Solution & Life Extension:

MD&A Fuel Nozzle Services found that insert replacements up to 7 repair cycles, had a minimum wall thickness at .093”.  The same is true for the 7FA DLN 2.6 since the 6FA DLN 2.0 and 7FA DLN 2.6 designs use ½-13 threaded wire inserts rather than the 5/8-11 of the 7FA 2.0 to secure the nozzles to the end cover.

Our team can extend the life of the end cover on the 6FA DLN 2.0 and 7FA DLN 2.6 past the currently understood industry standard by continuing the repair cycles until the minimum wall thickness is obtained. We have also incorporated additional machining of the cover to address the warping issue that is associated with the end covers throughout their lifetime, especially with those that are utilized in an unheated application.

Conclusions & Results:

With a new maximum of up to a final 7^th insert replacements per cover, the life expectancy of an end cover increases from the OEM claim of 48,000 hrs. to over 125,000 hrs. At an average estimated rate of repairing 4 covers every 3 years, you would not need to replace a cover for 75 years!

MD&A is a worldwide leader in the repair and refurbishment of gas turbine fuel nozzles.  Our advanced engineering expertise combined with leading-edge equipment delivers reliable, extended life for new or refurbished fuel nozzle products.

Call MD&A today for Fuel Nozzle End Cover Insert Life Extension at +1 (864) 721-4200 or use our Contact form.

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An exhaust temperature spread refers to a high differential in readings between the thermocouples placed radially around the exhaust of a gas turbine. The worst exhaust temperature spreads occur when the hottest- and coldest exhaust thermocouple readings are grouped very closely (adjacent). Most exhaust temperature spreads are the result of combustion section problems that can lead (very quickly in some cases) to premature turbine blade (“bucket”) failures. In other words, exhaust temperature spreads are indicative of combustion troubles that can lead to catastrophic failure.

Most heavy duty gas turbines employ multiple combustors, called ‘can annular combustors,’ each of which produce high temperature gases that are “funneled” to the first stage nozzles of the turbine section where they are expanded to produce torque. Ideally, each one of these combustors should be receiving equal amounts of fuel and air which should result in relatively uniform hot combustion gas temperatures from each of the combustors entering the first stage turbine nozzles.

The turbine buckets rotate past each combustor at very high rates—from 50 times per second for a 3000 RPM machine, to as many as 85 times per second for a 5100 RPM machine.

It surprises most people to learn that there are no temperature sensors monitoring the hot combustion gas temperatures as they leave the combustors and enter the first stage turbine nozzles. There are many reasons for this, but the four most important ones are:

1. the currently available sensors are very expensive;
2. the currently available sensors are prone to fail quickly requiring frequent replacement;
3. a failed sensor could result in pieces entering the turbine section and causing catastrophic damage;
4. there is too much stratification of the gases flowing into first stage turbine nozzle making it impossible for one sensor to adequately sense the temperatures under all conditions.

So, how are these combustion problems detected by the exhaust thermocouples? It also surprises most people to learn that as hot combustion gases flow through the turbine stages there is very little mixing. Hot combustion gases from a combustor don’t travel axially straight through the turbine section (a phenomenon known as “swirl”), but they mix very little with the gases from adjacent combustors before they enter the gas turbine exhaust. It’s this fact (that very little mixing occurs as the hot gases pass through the turbine section) that allows the exhaust temperature thermocouples to be used to sense cold or hot spots in the gas turbine exhaust which are indicative of unequal fuel- and or air flows into individual combustors.

So, what causes most exhaust temperature spreads? Far and away, most exhaust temperature spreads are the result of mechanical issues. Plugged fuel nozzle orifices, enlarged fuel nozzle orifices and fuel nozzle assembly problems (loose components; worn components) are the most common causes of unequal fuel flow-rates. MD&A has In-Situ Air Flow Test stand capabilities that allow for immediate and conclusive data on gas turbine nozzle performance.

On liquid fuel-fired machines, liquid fuel flow divider issues can cause unequal fuel flow-rates, as can leaking liquid fuel purge air check valves. Failed liquid fuel check valves can also cause incomplete combustion and high exhaust temperature spreads. Severe problems can even result in loss of flame in one or more combustors (combustors with or without flame detectors) which can cause very high exhaust temperature spreads/trips. Low, high or uneven atomizing air flows can result in incomplete combustion and even loss of flame. Primary zone re-ignition or flashbacks in DLN combustors can cause high exhaust temperature spreads. Cracked or broken combustion liners or transition pieces, hula seal problems, and leaking transition piece side seals can result in high exhaust temperature spreads.

Some exhaust temperature spreads have been caused by insulation found to be blocking the air flow across the thermocouple. Improperly inserted- or terminated exhaust thermocouples can cause high exhaust temperature spreads immediately after a maintenance outage.

Finally, failed, failing or intermittent exhaust thermocouples can cause false exhaust temperature spreads and even trips. While commonly suspected at the first hint of exhaust temperature spread problems on running units, instrumentation problems are not usually to blame for exhaust temperature spreads unless wiring is damaged by heat or other causes. One way to quickly eliminate instrumentation issues is to change load appreciably. If the highest and/or lowest exhaust thermocouple readings do not move with load changes—meaning the position of the coldest (or hottest) exhaust thermocouple will change (“move”)—the cause may be attributed to failed or intermittent instrumentation. As was mentioned before, due to the swirl phenomenon a true exhaust temperature spread will appear to move (rotate; change position) as load changes; if the problem is one or two failed or failing exhaust thermocouples the position of the hottest/coldest thermocouple will not change with load.

MD&A Turbine and Generator Controls Division maintains a staff of OEM experienced field engineers who provide installation, technical support, advanced troubleshooting, training, and consulting services for gas turbine controls, generator excitation, and turbine auxiliary systems.

Call our MD&A Turbine and Generator Controls Division today at +1 (970) 224-2223 or use our Contact form.

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View our video to see the process and then call MD&A today at (518) 399-3616 or use our Contact form.

MD&A’s Gas Turbine Rotor Life Extension Program provides solutions for your aging fleet.

Our goal is to meet your operating strategy for remaining life through validation, repair, or replacement of life limiting components.

MD&A will evaluate your specific needs with input from you, including Operating History & Forecast to provide the best solution.

Our experts will assess your rotor with specialized inspections including Metallurgical Evaluation and perform a Complete Engineering Analysis with modeling.

Next, we will discuss our recommendations and your options, ranging from specific component repairs or replacement, A Rotor Exchange Program or Full Rotor Replacement.

Our Turbine-Generator Repair facility in St. Louis, MO is fully equipped, featuring a Rotor Stacking Elevator with support equipment, Overhead Cranes, Blast Cleaning Facilities, Advanced Rotor Welding, Reverse Engineering Lab and a State-Of-The-Art High Speed Balance Facility.

MD&A is a premier worldwide manufacturer of heavy-frame gas turbine rotor components from replacement turbine wheels & disks to spacers.

Our components are Based on a reverse engineered – never fired – OEM design. Our solutions provide more robust, superior re-engineered components.

MD&A provides power generators around the globe with a full-service, OEM-alternative for your gas turbine. Together, we power through experience!

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