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.

Several 7FH2 units have experienced failures of the core step iron, caused by inadequate compression of the core laminations.  This issue was first brought to light by GE® TIL 2260, which only covered certain units; however, this recent failure was outside the scope of this TIL, indicating that other units may be at risk of a similar failure.

MD&A recommends that all 7FH2 generators be subjected to core tightening, preferably during the rewind of the stator.  However, if no rewind is in scope, then the core tightening should be performed during the next planned outage. Many of the 7FH2 units are more than 25 years old and are approaching their intended design life.  This particular unit had the damaged core iron replaced and windings replaced.

The unit was last inspected during spring 2020 utilizing a generator robot and was classified as “good” with no issues noted, indicating that the issue can develop & present over a short period of time.

The outage started as a Gas Turbine Hot Gas Path with Generator Robotic In-Situ Inspection. The Generator scope included a full battery of electrical testing on the field & stator. The Robotic In-Situ Visual Inspection included a Wedge Map, & ELCID core iron assessment.

The Robot crawler traversed axially from CE (collector end) to TE (turbine end) utilizing both a straight facing camera and 360-degree rotating camera to assess wedges, core iron condition, field body, and to note any abnormalities. The initial inspection proved highly challenging due to the amount of oil/greasing present on the stator, particularly on TE – as the robot began slipping. At the 12 o’clock position, MD&A noted high amounts of contamination at TE step iron and body wedge system.

After discussing recommendations and repair options, the Customer opted for a partial re-stack of the core step iron and full stator rewind. Three full packs of iron and full set of 7FH2 windings were readily available as part of MD&A’s inventory. The generator field was shipped to MD&A’s Turbine-Generator Repair Facility where thorough inspection and testing of the field was performed. This allowed the field to be in a controlled climate to reduce the potential for moisture ingress during the stator repair activity duration.

The repair of this unit required that the generator be stripped of all stator windings, followed by a thorough cleaning of the stator to remove all core ferrous debris from the stator prior to performing the rewind.

The damaged iron was removed from the stator core in circumferential sections moving axially inboard from the TE step iron where the fretted iron was located. Core iron packs were removed just past the damaged section to ensure reliability for future operation of the unit.

Once the core iron was removed, new core iron was replaced in the reverse process, moving axially outboard in circumferential bands. With the new core iron in place, MD&A then axially compressed the core to the required values. A Core Loop test was performed at the completion of the partial re-stack to verify successful compression of the new core and to ensure no hotspots were present on the newly installed or original remaining core iron.

After the core iron was replaced, new 7FH2 generator stator windings were installed. All quality checks were performed according to MD&A procedures to ensure reliable future operation of the unit.

Stator Experts

MD&A has a long track record of successful generator stator inspections and rewinds on-site. You can count on MD&A’s attention to quality!

Additionally MD&A has Stator Rewind Kits available for immediate use along with new step iron laminations in stock for 7FH2 units. There are several options of on the shelf rewind kits including GE® 7FH2, 7A6, 9A4 and 324 units.

For any questions or concerns about operational issues with these large generators, or to arrange service or inspection, contact MD&A’s generator experts today at +1 (314) 880-3000 or use our Contact Form.

The post 7FH2 Partial Re-Stack of the Core Step Iron & Full Stator Rewind appeared first on MDA Turbines.

The customer contracted MD&A to perform the inspection and emergent repairs on a tight schedule. Our industry experts completed the work on time maintaining full customer communication throughout the outage utilizing our on-site project management.

For the gas turbine, all combustion and hot gas path components were removed, cleaned, and inspected. All required hardware was provided by MD&A. Our San Antonio Service Center, which is our Gas Turbine Parts Service Facility, refurbished all combustion parts of fuel nozzles, combustion system liners, liner caps, transition pieces, and flow sleeves.

The stage 1 nozzle was replaced with a new assembly. The site team replaced both the right and left stage 1 forward wheelspace thermocouple guide tube assemblies. The stage 2 and stage 3 nozzle segments were also replaced. New shroud blocks and new installation hardware were provided for all stages. Moderate fretting was observed that warranted the replacement of the exhaust frame flex seals.

Simultaneously, MD&A experts removed both turbine-end and collector-end upper half end shields to perform a generator minor inspection consisting of stator and field visual inspections, including in-situ robotic inspections, ELCID, and electrical testing.

The Generator Specialist immediately recognized that the stator had significant connection ring damage that could have led to catastrophic damage had it continued to operate.

The solution: MD&A expeditiously removed, reverse engineered, and replaced the damaged components with no impact on the overall outage schedule (5 days total repair time).

Scoring was identified on both the turbine-end and collector-end journals. The lower half bearings had moderate abrasion/scoring. Minor babbit damage was also noted. The turbine-end and collector-end hydrogen gas and air side seals were found in poor condition and replaced.

Winders were mobilized to perform numerous tie repairs on each end of the unit and connection ring replacement on the collector end with the rotor still in place.

As a result of MD&A’s impact testing and modal analysis, additional blocking and ties were made on the connection rings to ensure the unit will not see this type of problem again.

At project conclusion, comprehensive reports were provided listing each step of the process and its engineering rationale, along with detailed analysis and long-term predictions and recommendations.

MD&A site and shop repair teams worked closely together to deliver first-class service. MD&A provides a one-stop shop solution for turbine & generator services, parts, and repairs.

Call our MD&A Gas Turbine Services today at (518) 399-3616 or use our Contact form.

The post Coordinated 7FA Hot Gas Path and 7FH2 Generator Inspection and Repair appeared first on MDA Turbines.

GE^®  7FH2 and 324 type generators have a history of end-winding dusting as a result of materials used during manufacturing. A major contributor to this issue is the connection ring blocking.

On some affected generators, the utilization of consolidated dry ties for the connection ring and connection ring to axial support blocking causes the Textolite™ blocking wrap felt and the connection ring mica insulation to lose their bond. When this occurs the connection ring blocking material can abrade the mica insulation to the point where the copper is exposed.

If not addressed the dusting can lead to serious damage to the generator up to, and including, a ground fault.

MD&A has trained personnel who are qualified to inspect the stator end-winding and identify if the unit has consolidated dry ties being affected. Our experts can solve this problem by replacing both the connection ring and connection ring to axial support blocking and ties with new blocking and wet ties.

Have MD&A look at your stator today. Call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

Also, see MD&A’s Solution 7FH2 Spring Migration Repair

The post MD&A Solution for 7FH2 & 324 Stator End Winding Dusting Issues appeared first on MDA Turbines.

Rotor field inspections can either be performed on-site or in a shop environment.  Repairs generally require the rotor field to be transported to a qualified repair facility. 

MD&A has developed a field pulling & support system to address the unique challenges associated with the 7FA/7FH2 configuration: 1) the shaft centerline height is 13 feet above machine baseline (grade), and 2) the gas turbine inlet ducting and filter house limit crane access.

The MD&A system consists of a modular work platform using adjustable rotor field trolley carts to efficiently and safely extract the field from the stator core, providing a stable work platform for on-site inspections and sufficient length to enable crane access to lift the field for off-site repair transportation.

Key features of the system include:

• Modular design work platform for expedited setup/teardown and efficient transportation on standard trailers
• Overall platform length and height can be adjusted based on site and workscope requirements
• Tongue and groove work platform connections and integrated trolley cart rail system provide seamless transitions between platforms
• Wide walkway wings on left & right sides enable worker & equipment access
• Modular safety rail system allows flexible scaffold stair access based on site arrangement
• Adjustable trolley carts use low-friction, self-guided rollers for safe and fast positioning of the field on the platform
• The system is very stable and is rated for continuous use with steady wind speeds up to 30 mph (with minimum 3x factor of safety)

MD&A offers a complete suite of parts, repairs, and services solutions for gas turbine fleets. We focus on delivering consistent quality and value with fast response, superior communications, and innovative solutions.

Call our MD&A Gas Turbine Services today at +1 (518) 399-3616 or use our Contact form.

The post Generator Field Support Platform appeared first on MDA Turbines.

The blockage of the radial ventilation passages results in reduced hydrogen gas cooling flow, which can lead to thermal instabilities with the rotor leading to excessive rotor vibration and forced outages.

View the video to see how you can have our experts repair your 7FH2 Generator field. For additional information call MD&A’s Generator Division today at (314) 880-3000 or use our Contact form.

The springs migrate axially within the slot:

Also, see MD&A’s Solution for 7FH2 & 324 Stator End Winding Dusting Issues

See all our Gas Turbine Services offerings from major inspections to capital parts to control systems!

The post MD&A 7FH2 Spring Migration Repair appeared first on MDA Turbines.

Our reputation for accuracy and reliability in power plant services has spanned over 30 years. Our technical expertise and effective project management will get the job done on time and within budget.

MD&A provided our customer with a replacement 7FH2 generator field. MD&A’s gas turbine maintenance team removed the original generator field from the site and shipped it to our St. Louis turbine-generator repairs shop for refurbishment. As well as, we sent the new generator field to St. Louis for a complete test and inspection, and high-speed balance before being brought to site.

The scope of work also included:

• The replacement generator field was removed from a unit in storage, and sent to the St. Louis Repair facility, and subsequently installed at the customer site.
• The unit was re-assembled with a new 7FH2 field with the existing #4 bearing installed and a new #3 bearing. Both were cleaned and measured, before installation.
• All new oil deflectors were used on both ends, inner and outer.
• The coupling faces were cleaned, inspected, and found to be in good condition. MD&A performed a 16-point alignment.
• New hydrogen seals were lapped and installed with existing cases.
• The air shields were cleaned and reinstalled and torqued to OEM specifications.
• The generator air test was performed, and the results were within acceptable limits.

After MD&A performed its checks, the unit started up without issues.

The gas turbine maintenance team replaced the faulty field with the new one under very difficult circumstances during the peak of the outage season. MD&A made this project happen in a few weeks from start to finish.

MD&A also performed minor repairs on the customer’s steam turbines as well, including a turning gear replacement and thrust bearing adjustment.

MD&A’s specialized services range from Combustion, Hot Gas Path and Major Inspections, as well as, Compressor & Turbine Rotor Repairs to Plant Performance Testing and Analysis. We also provide turbine internal alignment to your gas turbine, along with vibration analysis and balance (low-speed & high-speed.)

Call our Gas Turbine Services today at (518) 399-3616 or use our Contact form.

The post 7FH2 Gas Turbine Generator Repair appeared first on MDA Turbines.