Combined Cycle Overhaul with our One-Stop Shop

Mechanical Dynamics & Analysis (MD&A) recently completed an overhaul at a combined cycle plant consisting of gas and steam turbine majors, a steam turbine generator minor inspection, and a gas turbine generator major inspection. The customer combined scope was the largest single project implemented at the site since the combined cycle plant was commissioned.

MD&A sent all 3 rotors from the steam turbine, gas turbine & gas generator to our one-stop shop, which was a huge selling point for the customer. MD&A was able to leverage the full capabilities of our state-of-the-art 250,000 square foot, Turbine-Generator Repair Facility in centrally located St. Louis, Missouri to inspect and repair the major components all under one roof.

Combined Cycle Overhaul

To ensure success with this large project, coordination between all MD&A divisions was critical, as well as, constant communication with the customer. MD&A assigned a dedicated project manager responsible for all on-site services, including subcontractors, parts supply & shop services.

MD&A’s scope included a 7EA gas turbine major with a gas turbine rotor inspection & assessment in our St. Louis Repair Facility. Upon incoming inspection, the aft coupling patch ring migrated, leading to galling on the aft flange coupling #12 bolt hole, galling in forward flange coupling #10 bolt hole, wear groove and scratches on #3 journal, and circumferential lines & scratches on #2 journal. Our experts removed the damaged patch ring, manufactured & installed a new ring, and machined the ring fit.

Incoming Runouts and low-speed balance checks were performed on the gas turbine rotor with no runout issues found.

Our team observed the coating peeling from S1 buckets. They measured dovetail wear and bucket rock and found them to be well within MD&A acceptable range, therefore dovetail coating was not recommended. Bucket rock is often caused by cycling power plants that spend a considerable amount of time on a slow roll or turning gear and the result is wear between the wheel and the buckets that often abrade the fir tree surfaces causing a loose fit.  We performed an S1-S3 Bucket replacement during the repair portion and confirmed the final assembly with a low-speed balance.

Combined Cycle Overhaul


Our Fuel Nozzle Services Division also performed a 7EA dual fuel Dry Low NOx System 1.0 (DLN1) Primary & Secondary Refurbishment.

The steam turbine major included removal of the rotor and shipping it to our steampath division at our St. Louis Repair Facility for L-0 and L-1 bucket replacements. During the incoming inspection, our experts found heavy damage to the Stage 2 buckets and it was determined that they needed to be replaced as well, which was agreed to by the end customer. Our team removed the buckets and performed a rotor blast cleaning to include the affected wheels. We reverse-engineered and manufactured the Stage 2 buckets and covers. We also installed L-0 buckets and reamed for new pins, machined to fit wheel, and installed L-1 buckets. Lastly, we performed the final NDE and a low-speed balance.

In addition, the scope included a full rewind on the 7A6 gas turbine generator field. After the field was removed from the stator, it was shipped to our St. Louis Repair Facility’s generator clean room. Upon incoming inspection, it was found to have Nomex® tab style end blocking with broken and torn tabs, damage to the original creepage blocking, and cracked & deformed main lead copper leaves. The field was rewound with new creepage blocking, main lead replacement, and our experts incorporated an end winding blocking modification to optimize the field’s future reliability.

After rewind, the field was balanced in our modern high-speed balance facility contained at our one-stop repair shop in St. Louis.  Capabilities of our high-speed balance bunker include the ability to excite the field while at speed in order to ensure no shorted turns when operating at load.

On-site, our Generator Specialist performed a test and inspection on the gas turbine’s generator stator, which included a visual inspection, end winding inspection, borescope inspection, bore crawl through, and inspection. The electrical testing consisted of winding insulation “megger” testing, polarization index (PI), winding resistance, DC leakage testing, and RTD testing. Our specialist additionally performed a wedge tap test to determine tight and loose wedges to produce a wedge tightness map, and lastly a thorough cleaning. A minor inspection was also performed on the steam turbine’s generator.

Lastly, our Alignment division performed a Topless Alignment® on the steam turbine which eliminates the reassembling of the turbine for “Tops-On” measurements, saving hundreds of man-hours and labor per turbine section. Our experts performed a traditional top on/tops off internal alignment on the gas turbine.

Combined Cycle Overhaul

Along with having access to MD&A’s St. Louis Turbine-Generator Repair Facility “One Stop Shop”, the customer additionally benefited from choosing MD&A to execute the outage by having a single point of contact for multiple services across the entire combined-cycle platform.

Single point Project Management allowed for coordinated scheduling of concurrent work on-site and in the shop, leading to an optimized execution that was achieved on schedule. The project manager had clear and responsive communication with the elimination of multiple vendor interfaces and provided daily divisional job activity reports directly to the end customer. With the elimination of multiple vendors, there is clear warranty responsibility which gives peace of mind to the customer.  Lastly, the customer was able to derive significant value from having one vendor supply services, parts & repairs due to the inherent efficiencies of this approach.

MD&A is your full-service combined cycle overhaul provider and OEM-alternative! Services, Repairs, and Parts for your gas or steam turbine or generator. For every job, large or small, the speed and effectiveness of our response team are matched only by the depth and breadth of our engineering expertise. Call MD&A today for your combined cycle outage at +1 (518) 399-3616 or use our Contact form.

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