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.

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.

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.

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.

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.

Sign Up for MD&A’s Insight Newsletter: Get quarterly our turbine-generator expert’s case studies and tips!

The post Combined Cycle Overhaul with our One-Stop Shop appeared first on MDA Turbines.

The customer was able to locate a gray market Gas turbine and Heat Recovery Steam Generator (HRSG). Our team modeled how each component would interact with one another, and were able to calculate output, heat rate, as well as determine if other existing equipment could be utilized in the conversion.

The existing steam turbine is a 150 MW non-reheat, condensing unit with 11 stages. The gas turbine is a GE® 7FA.05 with a simple cycle rating of 211 MW.

The client requested MD&A to perform an analysis and create heat balances for four operating points, as well as two additional cases to determine how the plant would operate at different ambient conditions.

The analysis process began with creating a model of the steam turbine using the computer software ThermoFlex®. No recent performance reports were available for the analysis, therefore, steam turbine efficiency degradation was estimated at slightly below the new and clean condition illustrated on the OEM’s heat balances.

A model of the gas turbine was developed in ThermoFlex®, independent of the steam turbine model. The performance of the compressor, turbine, turbine inlet temperature, and IGV controls were tuned to match performance correction curves provided by the OEM.  The model was also adjusted to account for site specific conditions including elevation, ambient temperature, relative humidity, fuel composition, inlet and exhaust pressure drops.

A third independent ThermoFlex® model was created with just the Heat Recovery Steam Generator (HRSG). A hot gas source with the same constituents as the gas turbine exhaust and a steam sink with the same pressure as the main steam line in the provided combined cycle heat balance was used to control conditions at both ends of the HRSG. Steam drums, evaporators, superheaters, reheaters, etc. were built so that the steam and exhaust conditions between each component matched the conditions listed on the heat balance.

Lastly, all three models were combined into a single model to create the combined cycle. The extraction lines used for feed water heaters were eliminated with the exception of the auxiliary steam line used for station heating.  At the customer’s request, the gas turbine was throttled back to a position where the sum of the gas turbine generator and steam turbine generator minus auxiliary loading equaled transmission constraints at the generating station.

With the gas turbine exhaust providing the thermal energy to the HRSG, which in turn provided steam to the steam turbine, all component interactions could then be evaluated. The results were validated to assure output and heat rate were appropriate for a combined cycle of this size and configuration, and that steam flow through the steam turbine was still within the range of the original OEM heat balances.

Components such as water pumps, a condenser, drains, and a steam seal regulating system were also added.

MD&A also provided recommendations on how to improve the overall performance of the cycle.

MD&A provides clients with the engineering and technical expertise to perform complex thermodynamic analysis including analyzing cycle efficiency and providing recommendations for correcting thermal problems. We offer pre and post-outage testing, uprate analysis and heat balance modeling.

Call MD&A today for performance services at +1 (518) 399-3616 or use our Contact form.

The post Thermodynamic Analysis on a Steam to Combined Cycle Plant Conversion appeared first on MDA Turbines.

At our 100,000-square-foot facility in Euclid, Ohio, we stock a large number of components, everything from MHC governor stands to Rexroth® actuators to servos and solenoid valves.

We also take a lot of pride in our repair documentation. In addition to recording the model and serial number, we note any auxiliary equipment like a servo solenoid, which most of the actuators have, before we start the disassembly process.

GE® and Toshiba® both use Rexroth® actuators on their combined cycle units. Toshiba® mounts their actuators in a horizontal position, while, GE® mounts them vertically. That difference can cause a maintenance problem.

Mounting the actuator in a horizontal position causes a lot of stress on the shaft. As the actuator control valve strokes back and forth, it puts a tremendous amount of weight on the seal. All that weight sits on the down side of the spring can retainer. So as the actuator strokes to regulate the speed of the turbine, it causes a lot of stress.

One customer has a large Toshiba® steam turbine that uses these valves and gets about two years out of them before the stress wears away the seal. Then metal-to-metal contact occurs between the ID of the spring can and the OD of the spring can retainer. That causes drag and friction and also lowers the shaft.

As the shaft lowers and the friction increases, the forces put more stress on the guide bushing that’s closest to the spring can. Those seals start to wear away and the equipment may leak fluid into the spring can.

Our technicians have worked on different actuators for different Toshiba® units from large steam turbines to combined cycle units. All examples had the same scoring and the same wear on the lower side of the spring can where the spring can retainer and the spring can meet.

MD&A experts created an actuator upgrade for horizontal mounted actuators where we coat the inside of the spring can, upgrade the seal, and redesign the HP bushing & the LP bushing.

With those modifications, we expect to extend the life of the Rexroth® actuator on the Toshiba® units so that they need service no more than once every four years, roughly doubling the current outage interval.

MD&A Bearings, Seals & Hydraulics division, since 1984, has refurbished and upgraded hydraulic control components, such as actuators.  We can offer a short cycle turnaround because of our inventory of components, along with our team’s knowledge.

Call our MD&A Bearings, Seals & Hydraulics division today at (800) 446-4776 or use our Contact form.

The post Horizontal Mounted Actuator Upgrade for Toshiba® Units appeared first on MDA Turbines.