The Gas Turbine Association (GTA) salutes Congressmen Paul Tonko (D-NY) and David McKinley (R-WV), and Senators Lisa Murkowski (R-AK), Thom Tillis (R-NC), Richard Burr (R-NC), and Joe Manchin (D-WV), for the time and effort they and their respective staffs contributed to advancing the Energy Act of 2020.

GTA Chairman Jonathan Li noted, “GTA appreciates the significant efforts made by these legislators who recognize the importance that gas turbines make and will continue to contribute towards achieving lower emissions and reducing the carbon footprint.  We believe gas-turbine technology is integral in realizing decarbonization of our nation’s power generation portfolio, and we look forward to continuing to support these efforts.”

The Energy Act of 2020 includes important legislation that would support a multi-year, multi-phase program focused on research, development, and technology advances to improve the efficiency of gas turbines in power generation—ensuring that GTs continue to play an important role in the generation mix to support the US with sustainable, clean, efficient, and reliable electricity.

The program’s elements include support for engineering and gas-turbine design in the following areas:

• • High-temperature materials—superalloys, coatings, and ceramics.
  • Improved heat-transfer capability.
  • Manufacturing technology required to construct complex parts with improved aerodynamic capability. Combustion technology to allow higher firing temperatures while reducing NOx and CO emissions per unit of output.
  • Advanced controls and systems integration.
  • Advanced high-performance compressor technology.

Additionally, an area of focus will be to increase fuel flexibility by enabling gas turbines to operate with high proportions of hydrogen or other renewable-gas fuels, something many of GTA’s member companies are already working on.

Under this new legislation, GTA will work to pursue the research goal of increasing combined-cycle efficiency to 70% and simple-cycle efficiency to more than 50%.  To achieve these objectives, the GTA believes R&D efforts should focus on the following:

• • Combustion technology.
  • Additive manufacturing for gas turbines.
  • Thermal management and advanced cooling strategies.
  • High-fidelity integrated simulations and validation experiments.
  • Unconventional thermodynamic cycles.
  • Condition-based operations and maintenance.
  • Digital twins and their supporting infrastructure.
  • Gas turbines in pipeline applications.

About. GTA is a membership organization, established in 1995, that includes gas-turbine manufacturers, owner/operators, consultants, and third-party equipment and services providers. Its mission: Serve as a unified voice for the gas-turbine Industry. Today, GTs produce more than a third of our nation’s electricity. They are a cornerstone energy conversion technology, providing electricity and heat for industries and communities. Gas turbines will play an increasingly important role in the achievement of national objectives related to energy and the environment and will play a key role as part of the energy mix moving forward.

Regardless of where you fall on the 3Hs of the H2 economy—hype, hope, happening soon—everyone can appreciate a seminar which delivered information on actual experience. The webinar, “Hydrogen: Utilizing Combustion Turbines as a Solution to ‘Low to No-Carbon’ Initiatives,” was presented by PSM (Power Systems Mfg LLC).

After a quick review of global-climate headlines, Jeff Benoit and Katie Koch, PSM, noted that while “gas turbines are a core pillar of decarbonization,” the world is woefully behind in meeting 2030 and 2050 global carbon-reduction targets being emphasized by the climate-science community.

The good news, according to PSM, is that “gas turbines can be a long-term part of the eventual zero-carbon power grid, and can be ‘future-proofed’ sooner rather than later.” If batteries and other storage systems represent grid-scale, shorter run-time options, H2 represents a gigawatt-scale, long-term energy-storage option.

As one example, renewable energy that might otherwise be curtailed, or even excess nuclear power, can be used to power H2 production units with the fuel stored in the same underground formations used for natural gas, other hydrocarbon fuels, and compressed air. While long-range and large-scale transport and distribution of H2 in the existing natural gas network present challenges, such as piping embrittlement and sealing, the US and Europe have proven large-scale H2 distribution networks connecting industrial process facilities.

PSM’s sweet spot of experience, however, is at the combustor. At a 3 × 0 9E GT customer site in The Netherlands, being deployed specifically for H2 combustion-technology development, H2/natural-gas fractions from 9% to 25% (field demonstration of 35%) have been fired successfully for four years with no impact on turbine life, with NOx emissions held to 9 ppm or below, reports Benoit.

The GT is equipped with PSM’s LEC-III® combustion system with the company’s “fin mixer” secondary fuel nozzle. PSM’s AutoTune controller logic handles the varying amounts of H2 coming into the system.

PSM is also participating in a Dutch-government-subsidized program to develop its FlameSheet™ combustor as a “platform” for 0 to 100% H2 firing.

“In Stage One of the program, PSM and sister company Thomasson retrofitted an existing 1.8-MW OPRA OP-16 engine with a scaled version of FlameSheet and tested it for up to 100% H2 by volume. Stage Two will be scaling the FlameSheet to additional applications.” That will be followed by a demo project on additional frame units to achieve the project goal of up to 100% H2 on units varying between 1 and 500 MW, while keeping emissions in check.

Meanwhile, an F-class unit also has been retrofitted with FlameSheet and has been field-demonstrated with a fuel mixture containing up to 5% H2, the limit representing the amount of hydrogen available for this unit. The FlameSheet has been tested in the rig for F-class conditions at full pressure and full temperature for up to 80% H2 by volume without emissions excursions.

Seven 501F and 7F gas turbines (with an eighth being installed in December 2020) are currently operating commercially with a FlameSheet combustor, simply described as a burner (or inner combustor) with a conical flame sheet around it that promotes a trapped vortex mechanism which allows higher flame velocities to be maintained.

The flame is said to be “anchored” at the point of vortex (Fig 1) as defined by geometry and, therefore, less dependent on fuel constituents. Fig 2 shows a FlameSheet combustor being installed in an F-class gas turbine.

In addition to FlameSheet, PSM has demonstrated that its AutoTune controls will greatly contribute to successful H2 firing (Fig 3). At its base, AutoTune can continuously measure the constituents of the fuel mixture, then automatically adjust the combustor fuel/air mixtures to improve reliability and maintain stability. This functionality is already in practice today for a variety of shale gases with variable heating values. Even within the Marcellus and Permian regions, natural-gas heating value can vary significantly.

Differences in combustion properties with higher and higher H2 fractions are not trivial, stresses Benoit. Combustors are typically designed for a narrow range of natural-gas properties. H2 has higher reactivity, and “wants to oxidize quicker,” which can lead to high flame speeds, flames migrating into the metal, and flashback. In addition to ensuring stability of combustors firing these mixtures, AutoTune solves a variety of combustion challenges.

The GT-agnostic AutoTune product is already installed on more than 80 units (total anticipated by the end of 2020)—including 9FA, 7FA+e, W501F, M501F, 6B, 7E, GT26, and 9E engines.

GT owner/operators don’t want to lose their cycling and start/stop flexibility. While AutoTune has proven it can handle transient upsets, Benoit notes that “you don’t want to start up or stop the machine with high H2 fractions, so it’s best not to start on H2 from a safety standpoint, but instead transfer to an H2/gas blend at full premix mode. He also notes that many customers purchased FlameSheet specifically to improve load-following.

Finally, maintaining low NOx and CO emissions is a challenge with H2, but premix combustion is key here and even more critical. Although conventional premix combustors are limited in their ability to burn H2/gas mixtures, PSM sees AutoTune, combined with the aforementioned combustion technologies, as the key to successful firing in such GT-equipped machines.

For pragmatic entry into the H2-to-power market, Thomassen, in conjunction with OPRA Turbines of The Netherlands, can ready a “turnkey clean energy package” (Fig 4) that pairs a containerized 1.8-MW GT/generator with a skid-mounted, packaged proton PEM or atmospheric alkaline electrolyzer driven by low-cost or negatively priced electricity to produce and store H2 for scheduled firing in the GT. Fuel skids qualified for hydrogen are available as well through various supply-chain methods.

The Siemens session at the 2020 501F Users Group began with a high-level update on the Siemens Energy spinoff. Also highlighted was Siemens Energy’s roadmap to “Making Energy Greener.” A comprehensive gas-turbine update followed with technical updates on these topics:

• • 

    Hexavalent chromium residue.

  • Air-separator radial rubs and axial wear.
  • Exhaust manifold.
  • Advanced two-piece exhaust.
  • D5 turbine through-bolt fracture.
  • Bearing-bore drop-measurement tool.
  • New high-performance Row 4 turbine blade.
  • Peak firing and experience with ULN (ultra-low NOx).
  • Parts availability.
  • Torque-tube cracks.
  • Recent SGT6-5000F5 event.
  • Thermal-performance upgrade summary.

Next came a presentation on Brownfield Engine Exchange (BEX) which outlined the benefits and the process for a BEX and provided examples of several projects implemented by Siemens Energy. Following this was a generator update—including a fleet overview, discussion of generator findings observed during outages, and a review of various technologies to help reduce maintenance.

The session closed with a discussion of plant assessments (inclusive of operational assessment, performance/thermodynamic evaluation, availability, reliability, maintenance evaluation, and upgrade capability) and solutions to drive operational flexibility—including emissions reductions, adjusted maintenance intervals and faster cooldowns, enhanced-performance starts and stops, and alignment to grid requirements through load gradients. Operational enhancements for Siemens and Westinghouse steam turbines discussed were fast synchronization, fast speed and load ramps, fast close of bypass valves, fast shutdown, variable load-rate capabilities, variable speed rate potential capability, and considerations for speed roll times.

Most of the material presented is available on Siemens Energy’s Customer Extranet Portal. If you are an owner and/or operator of the company’s power generation equipment and do not have access to the portal, use this link to request it.

The 2020 conference of the 501F Users Group marked GE’s fourth year of participation in this event, coordinated by Said El-Nahas, 501F product manager, and Ben Myers, service engineering manager. The program began with an introduction to GE Gas Power, a new organizational structure combining the company’s new-unit and services operations under a single business entity focused on advancing sustainable gas-plant technology.

The steering committee requested presentations from the OEM on its exhaust frame and HRSG cleaning solutions, plus an update on hex-chrome findings. The session concluded with a refresher on GE technology adoption for 501F engines—including cooling/seals, coatings, materials technology, (such as dense vertically cracked TBC), and patterned abradable ring segments to extend the repair interval.

GE reported on the success of its performance upgrades at the 2 × 1 Tuxpan and Norte-Durango combined cycles, owned by Naturgy Mexico SA de CV. The former is powered by Mitsubishi 501F3s, the latter by Siemens 501FD3s. Both plants are covered by GE performance LTSAs and include planned and unplanned maintenance for gas and steam turbines and auxiliaries, generators and auxiliaries, main-steam valves and actuators, and control systems. Here’s what the speakers said:

• • Maintenance intervals were extended to 32k hours/1250 starts.
  • Output was increased by up to 9.2%.
  • Heat rate was reduced by as much as 2.9%.

Regarding the exhaust frame, the speakers reported the following findings:

• • Severe liner cracking.
  • Strut creep affecting rotor position.
  • Bearing damage.
  • Baffle seal plate cracking.

GE’s objective was to mitigate these issues by developing repair solutions that could be implemented during a major inspection without schedule impact. Engineers developed an upgraded two-piece exhaust cylinder, made improvements to the saddle and strut shield, and upgraded baffle seals (new material and replaceable during an outage). Specialized repair processes also were developed for field implementation.

HRSG cleaning technology was covered next—specifically GE’s PressureWave Plus system. It was said to be superior to standard dry-ice cleaning, deep-clean dry-ice cleaning, and water washing regarding the following: no scaffolding required, reduced risk of fugitive emissions during startup after cleaning, reduction in cleaning time, depth of cleaning of at least 3 ft, and of no risk to pressure parts.

Hex-chrome concerns, probable causes, and containment/corrective actions were equal or similar to those presented at other user meetings in the last couple of years. Attendees were referred to GE’s PSSB 20180709A/B document and any subsequent update.

Mitsubishi Power spent a productive four hours with users on the third day of the meeting, discussing and answering questions on a wide range of topics. Presentation segments selected by the editors for coverage here, given their high interest to owner/operators, are the following:

• • Safety culture and initiatives to help protect plant and contractor personnel.
  • Lifecycle experience with critical turbine components.
  • Comprehensive rotor inspections and upgrades—for the air separator and torque tube, in particular—to address fleet issues.
  • Exhaust-system solutions.

Safety. The Mitsubishi Power program began with a field-service safety review demonstrating the company’s “safety first” attitude and approach to work. Continuous improvement is the goal of its behavioral-based safety programs.

Similar messages open presentations by virtually all OEMs and contractors these days, but many do not dig into the details like Mitsubishi Power did. The company uses OSHA metrics to benchmark its EHS performance against other manufacturers and service providers serving the electric-power and comparable industries. Example: From 2015 to 2019, its field-service effort grew from 1.1- to 1.7-million man-hours—or by about 50% in just five years.

Over the same period, Mitsubishi Power’s EMR score was stable at 0.6, in round numbers. Not familiar with the acronym EMR? Experience Modification Rates are provided by insurance companies—in Mitsubishi Power’s case, the National Council on Compensation Insurance (NCCI)—and used by OSHA to evaluate safety standards in the workplace.

The Safety Management Group, which promotes itself as a “nationally recognized” service organization providing workplace safety consulting, training, staffing, and program planning and implementation, says most companies have an EMR of 1.0. Generally speaking, the higher the EMR score, the higher the insurance premium.

Another measure of occupational safety is the Total Recordable Incident Rate (TRIR). It is derived by combining the number of safety incidents and total work hours of all employees in a “standard” employee group—typically 100 employees working 40 hours a week for 50 weeks of the year. Thus, it offers a company the means to benchmark itself against others in its industry, as well as to evaluate its own performance over time.

Mitsubishi Power’s average TRIR for the 2015-2019 period studied was 0.84, well below the benchmark figure of 1.1 reported by a reputable source for the electricity, gas, water, and waste services industry. Manufacturing, by contrast, had a 2.8 incident rate per 100 workers; construction, 2.6.

A goal of continuous improvement means there’s no time off for a good report. Mitsubishi Power continues to drive its EHS initiatives forward. In 2019, for example, the company was approved for ISO 45001 certification. No findings, major or minor, were revealed during a detailed review of its EHS documentation or during a three-day external audit of its field service safety program. Recall that 45001 is the ISO standard for management systems of occupation health and safety. Its goal is the reduction of occupational injuries—including the promotion and protection of physical and mental health.

Other 2019 highlights of the Mitsubishi Power safety program included these:

• • OSHA safety training—a 30-hr program for site leadership, 10 hours for non-supervisory employees.
  • Confined-space, LOTO, fall-protection, scaffold, and hex-chrome courses for all field-service personnel.
  • An increase in full-time safety staffing by 20%.

Highlights of 2020 initiatives are the following:

• • Review of recent EHS performance and actions taken, including analysis of behavioral trends to identify deficiencies. One example: Inconsistent PSA (Planning and Safety Assistant) quality was identified as an issue. Deficiencies were addressed in a training program.
  • Pre-outage safety training, one day. Some of the topics reviewed include site safety plan, proper tool usage, and incident reporting.
  • Measurement of training effectiveness and procedure compliance. Service and operations managers perform joint site EHS audits—at least one per outage—and share results with executives and staff.
  • Improve vendor management through an EHS review and evaluation of key craft vendors, including a follow-on plan for training, safety, etc, to correct deficiencies.
  • Increase training in the use of support devices for knees, wrists, elbows, and back, and make more devices available in site safety kits.

Critical turbine parts. Scott Cloyd, chief engineer, Gas-Turbine Service Engineering, and his team reviewed product improvements and upgrades for the compressor, turbine, DLN combustion products, liquid-fuel system, and combustion system. In opening remarks, the Mitsubishi Power engineering team stressed its focus on best-in-class reliability, availability, and lifecycle maintenance cost, suggesting their products are leading the market in these three performance indicators.

To prove the point, inspection results were presented for Rows 1 and 2 turbine vanes and blades—specifically:

• • R1 vanes. An R1 vane with a service history of 40,020 hours/290 starts (baseload unit) is shown in the left two frames of Fig 1, R1 vane with 14,499 hours/1010 starts (peaking unit) in the two photos to the right. Condition of all airfoils was excellent with TBC intact, no detectable cracks, and no wall thinning attributed to oxidation. Such positive results contributed to Mitsubishi Power’s decision to validate its R1 vanes in the W501F fleet for intervals of 32,000 hours/1200 starts.
  • R1 blades in Fig 2 showed similar results with the blade at the left having a service history of 34,676 hours/10 starts and the one in the two images to the right with 6496 hours/1001 starts. TBC also was intact here. Plus, there was no detectable cracking, or wall thinning attributable to oxidation. Result: R1 blades in the W501F fleet were validated for a service life of 32,000 hours/1200 starts.
  • R2 vanes. Experience similar to that for R1 vanes—TBC intact, visible cooling traces, no oxidation-caused wall thinning, no fillet cracking, and only minor cracking on the platform (within the limits of a light-repair scope). Validated in the W501F fleet for 32,000 hours/1200 starts.
  • R2 blades also showed TBC intact, no detectable cracks, and no oxidation-caused wall thinning in both baseload and peaking service. Validated in the W501F fleet for 32,000 hours/1200 starts.

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Rotor inspection, upgrades. Mitsubishi Power recommends what it calls a “comprehensive rotor inspection,” or CRI, after 12 years or 100,000 hours of service, whichever comes first. It requires a shop visit and involves complete disassembly of the rotor. All components undergo detailed nondestructive examination; repairs, replacements, and mods/upgrades are performed as necessary to assure performance and reliability goals are achieved.

The Mitsubishi Power speakers touted the experience of the company’s engineers and shop personnel at its Savannah Machinery Works (SMW). They also discussed the facility’s state-of-the-art equipment and capability to make complex rotor components, plus the depth of SMW’s material stocking program. Together, the foregoing attributes enable the OEM to provide the flexible solutions to meet customer needs.

While a full CRI is required to qualify a rotor for an additional 12 years or 100,000 hours, Mitsubishi often inspects rotors onsite during the turbine inspection (TI) ahead of the CRI to determine its general condition and to develop a risk assessment to guide planning. Mitsubishi Power calls this a pre-CRI. It reduces the likelihood of emergent work during the CRI by trending data to anticipate refurbishment scope, thereby allowing the owner/operator to source long-lead-time items in advance.

A pre-CRI conducted as part of a TI (so-called Level 1) has no impact on the scheduled outage and includes a disc creep assessment and turbine-blade groove wear and corrosion evaluation.

If the engine owner finds it necessary to postpone a full CRI, Mitsubishi Power recommends a more detailed review of the machine at the major inspection following the TI, one that includes removal of all compressor blades.  This Level 2 pre-CRI adds to the Level 1 menu an evaluation of compressor-blade groove wear and corrosion. It also has no impact on outage schedule.

A Level 3 pre-CRI adds cleaning and NDE of all exposed rotor surfaces to the outage scope. Depending on the effort required, this could add to the outage schedule—possibly up to 10 days.

A full CRI in the SMW rotor facility typically takes 30 days for the base scope, with time added as necessary to accommodate repairs and or upgrades specified by the owner. A rotor exchange is the preferred option for those requiring a faster turnaround.

Here are some of the important rotor-component inspections conducted during a CRI:

• • Spindle bolts, for fatigue or fretting associated with high turning-gear hours and low-speed operation.
  • Torque tube, for cracking.
  • Turbine-disc cooling-air passages, for clogging attributed to corrosion of the rotor and cooling-air piping and/or foreign material.
  • Turbine-disc blade serrations, for wear and fatigue caused by blade rock, pitting corrosion, etc.
  • Curvic clutch, for wear from high hours on turning gear and/or through-bolt relaxation contributing to relative motion between adjacent discs.
  • Compressor and turbine discs, for corrosion, cracking, pitting, creep, and/or hardness changes attributed to high operating hours or starts, prolonged exposure to corrosive elements, and abnormal operating conditions.
  • Shaft journals, for wear, scoring, and/or cracking attributed to high operating hours, insufficient oil filtration, loss of lube oil, and/or electrolysis.

A focal point of the CRI for most 501Fs is the torque tube, which joins the compressor and turbine sections of the rotor, and its companion air separator. A long-term fleet issue on gas turbines of Westinghouse design (up to and including the Model FD3) has been cracking of torque tubes configured for gooseneck-type air separators, a problem concealed by the air separator.

An indicator of torque-tube cracking is a vibration event, one that can’t otherwise be explained. Although visual confirmation of a crack at this location is not possible, it can be confirmed with an ultrasound scan. If a crack is present, it’s important to implement a solution quickly. Experts say that once initiated, a crack capable of introducing a vibration event will rapidly propagate by fatigue.

Mitsubishi Power solutions for a failed W501F torque tube and air separator are rotor replacement (exchanging with a new or refurbished rotor), in-kind torque-tube replacement, and an upgrade option. The last includes a replacement torque tube of additional thickness where cracks have occurred and a bolted air separator (elimination of the gooseneck design). The design of the upgraded components offered by Mitsubishi Power have operated failure-free for about 3-million hours and 30,000 starts (round numbers) on its M501F engines.

The first Mitsubishi Power torque tube/bolted air separator was retrofitted on a W501F peaker more than two years ago and reportedly is meeting expectations. Several retrofits have been completed in the interim, with others in the pipeline. Mitsubishi Power recommends replacement of the torque tubes and air separators on all W501F rotors going through its Savannah shop as a risk-mitigation measure.

Exhaust solutions. Mitsubishi Power’s solutions for the W501F exhaust cylinder and manifold address that model’s recurring durability issues—such as cracking of the diffuser and strut shields. They have been adopted from the successful exhaust systems installed on the OEM’s M501G and J units (with more than 5.3-million hours and 53k starts) which operate at higher temperatures than F engines.

The Mitsubishi Power two-piece exhaust cylinder is a drop-in replacement for the W501F; no changes to auxiliary piping and foundation are necessary, and no special tooling is required for installation. Additional features: The design incorporates improved material, a floating diffuser system to allow for thermal expansion, a passive tangential strut cooling system, and the ability to remove the journal bearing with the upper exhaust cylinder casing in place. To date, five W501F exhaust systems have been retrofitted with Mitsubishi Power’s upgraded design, with additional orders in the pipeline to fulfill; they have been operating defect-free as expected.

Doosan Turbomachinery Services’ (DTS) presentation to the 501F Users Group at the 2020 conference featured a company/facility profile followed by details on how it conducts major maintenance on rotors, exhaust sections, and blade rings. The company’s relatively new shop in La Porte (Houston), Tex, has the capability for F-class inspection, overhaul, repairs, and new-parts manufacturing.

Doosan has earned respect among 501F owner/operators for its work in this fleet. To illustrate, the company’s repair/upgrade solution developed for the 501F two-piece exhaust system six years ago has been adopted by several plants.

More recently, it completed the in-kind replacement of the torque tube and air separator for a W501FC during a major maintenance interval. Reverse engineering for that project began immediately after de-stack at the La Porte shop. White-light 3D scanning and metallurgical analysis of the existing torque tube and air separator started the process. Note that neither component had failed but the owner decided to replace both given fleet history and unit age.

Doosan Heavy Industries, the parent of DTS, had a turbine forging in Korea that matched the material composition required; the forging properties were confirmed and rough machining commenced shortly after receipt of the rotor. A team of DHI engineers was dispatched to Houston to help complete the reverse engineering and characterization.

In the final stages of the project, DTS send the 16th-stage compressor disk and curvic adapter to DHI in Korea. The disk was properly matched to the torque-tube pins, the curvic adapter was mated, and components were returned to La Porte for reassembly. The project was completed on schedule. The original torque tube and air separator were refurbished and returned to the customer as emergency spares for its fleet.

Owner/operators might consider reviewing Doosan’s presentation posted on the user group’s website for the detail it provides. Example: The Class III inspection for rotor lifetime determination begins with an incoming inspection that includes dimensional checks, runout measurements, balance checks, and a review of customer data and experiences (known issues, for example).

The slide on rotor unstack, the next step, highlights all the various actions involved—including the removal of the air separator and curvic adapter and unstacking of the torque tube and compressor. Unstack checks are next: dimensional checks, mag-particle inspections, fit-up checks, NDE of bolting, etc.

Phase 1 of the life-evaluation process is a thorough inspection after all airfoils and hardware are removed and the rotor is cleaned. Phased-array ultrasonic and eddy-current inspections of critical areas are conducted along with microstructural examinations. Phase 2 of the process focuses on engineering analysis (of flaws found, for example) and recommendations regarding continued service. New components installed may include torque tube, air separator, and upgraded bolting. Pictures of these parts are provided in the presentation.

The restacking procedure focuses on items users should be aware of, such as the following:

• • Accurate measurement of compressor torque pins to verify clearances and alignment, assuring proper bolt placement, etc.
  • On the turbine end, correct air-separator crush, disc-adapter stretch, proper bolt depth and stretch are important—among other things.
  • Balance and reassembly involves runout measurements (verify less than 2 mils at the rotor midpoint, for example), checking locking hardware, moment weigh of compressor and turbine blades for low balance corrections, etc.

The exhaust cylinder was discussed next (photo). This section offers a valuable review of nomenclature before reviewing typical as-found damage—such as strut-cover damage and cracking, and outer diffuser cracking and distortion. Most of the material presented thereafter focused on the company’s “zero-hour” program for inspection, baffle seal and strut shield improvements, alignment and atmospheric-vent mods, and manifold repairs.

Think of the content in this portion of the program—24 detailed/heavily illustrated slides—as a checklist of things you should be aware of before digging into an exhaust system project. You’ll also learn what work can be done in the field and what requires a shop visit.

Blade-ring disassembly and inspection was the last topic on the Doosan program. It covered the special fixturing and procedures believed necessary to assure proper repairs and provided a checklist of things to be aware of during shop work—including vane cam-fit, torque pin slot, seal engagement, joint gaps, etc.

At the upcoming virtual 501F Users Group conference, owner/operators will have the opportunity to hear the latest on solutions for leaky 4-way joints. Below is a primer and brief history of Nord-Lock’s experience in mitigating this common problem in the fleet. The latest information on their solution will be presented on Tuesday, February 23 from 2:10-2:40pm EST during one of the the 501FUG’s Vendorama sessions. View the full agenda and register here.

The editors can’t remember a meeting for Siemens 501F users that didn’t include at least a mention of leakage at the 4-way joint. A typical fleet-wide remedy was to weld on so-called leak boxes to prevent leakage from offending joints (Fig 1). These, of course, had to be removed during an outage and then reinstalled before resuming operation.

Nord-Lock Group VP Peter Miranda discussed his company’s engineered approach to preventing leakage at the 4-way joint in a Vendorama session at the 2020 501F Users Group meeting at the Hilton West Palm Beach, February 10, a month prior to the onset of Covid-19 restrictions. Nord-Lock has continued perfecting its solution since and a progress report on that work follows.

Miranda’s presentation can be reviewed by registered 501F owner/operators on the user group’s website. Non-members who meet the organization’s requirements can gain membership status by completing the online registration form.

Background. New turbine cylinders are perfectly aligned, faces flush, with no leaks at the joints. Over time, extreme thermal variations and startups lead to warping and distortion. Cylinder misalignments compound the problem because flange surfaces must maintain the maximum contact area needed to ensure a proper seal, allowing leaks to occur.

Another contributor to leakage is the lack of an upper-half spigot, which is removed after final assembly in most cylinders. The concept here is simple: Emulate the lower-half spigot (Fig 2) on the upper half since pressure inside the combustion chamber will affect these exposed areas and cause leakage through cylinder joints, bolts, or bolt holes.

The helicoil bolt-hole misalignment shown in Fig 3 is evidence of cylinder displacement of the flange face. To remedy leaks, the misalignment must be addressed. If holes can be forced into alignment and maintain concentricity during loading, the flanges likely will sit flush, preventing the leak. Proper tension of the joint is critical to success.

Leaks can cause significant damage to instrumentation and insulation, and also jeopardize operations and worker safety. Maintenance is required to weld-on leak boxes (refer back to Fig 1) to contain the leak and requires removal and reinstallation during an outage—adding time, resources, and cost to the outage schedule.

Update. Nord-Lock Group partnered with a Siemens 501F user on an R&D project to investigate 4-way-joint leak issues with the goal of finding a fleet-wide solution. The partners consider remedying leakage issues important for the protection of both personnel and critical equipment. A comprehensive testing program was identified, then validated on several units, as an effective solution—one that combined multiple Nord-Lock products and technologies.

Solution. Given the multiple contributing causes of 4-way joint leakage, the most effective solution identified combines a specific mix of products and technologies. The combination works in concert to address multiple potential failures and provides the following advantages:

• • To quickly assess and manipulate cylinder alignment, the solution includes a Boltight™ hydraulic closure system (HCS, Fig 4). This ensures the 4-way joint is tensioned, temporarily, to conduct a proper alignment check of the cylinder—one similar to the tops-on/tops-off alignment checks performed on steam turbines.
  • If the bolt hole or flange is misaligned, a proprietary CamAlign tensioner system is used to realign the cylinder. The system can close an internal gap of the cylinder by 10 to 15 mils after the cylinder has been “squeezed” by the HCS, to ensure the smallest possible gap is achieved.
  • The HCS is pressured up to simultaneously and uniformly squeeze the turbine cylinder around the 4-way joint—thereby isolating the area. Multiple hydraulic tensioners remain pressured up while internal and external gap readings are recorded, and cylinder alignment is checked.
  • Once adjustments are complete and the 4-way joint is aligned properly, the joint is squeezed again using the HCS, which allows load transfer to the Superbolt™ mechanical multi-jackbolt tensioners—to permanently tension the joint—without losing tension on the joint.
  • Rather than tensioning one bolt at a time, which can continually create movement of the load, the HCS immobilizes the entire joint.
  • An internal seal is installed to reduce leakage at the 4-way joint area where the cylinders for the combustion and turbine sections meet (Fig 5). The seal functions to eliminate any leakage paths that cannot be corrected by realigning the cylinders.
  • Aggressive operating requirements and maintenance schedules needed to keep pace with operating requirements contribute to misalignments that cannot be corrected completely with CamAlign. The seal provides an added layer of leak protection.

Over the course of several installations, variations were noted in spigot fit and seal shapes. Internal seal retainers were redesigned to allow for thermal growth and variations in the cylinders.

Editor’s note: This article illustrates some of the benefits that accrue from upgrading ageing control systems. Dig deeper into the topic by participating in the upcoming webinar, “GT Mods and Upgrades: Take advantage of high-value generating opportunities,” Wednesday, February 10 at 2 p.m. Eastern. Presenters are Pat Begley and Ricky Morgan of TTS Energy Services. 

The adage “age is only a number” pertains to equipment as well as to people, homes, and many other things. This article illustrates how gas turbines well cared for can provide good value far beyond their design lifetimes with modest investment.

Perhaps the best place to start this case history is with the Great Northeast Blackout of 1965. As the event title indicates, the Northeast went dark late in the afternoon of November 9 when a transmission line near Ontario, Canada, tripped, causing several other heavily loaded lines to fail—a domino effect.

Restoring power was a chore. As some involved in the process recall, the key to getting the New York metropolitan area up and running was a black-start Frame 5 on Long Island. Bootstrapping a grid start was the day’s challenge. The success of gas turbines in this endeavor made these machines the backstop of choice for grid support going forward.

Sales of simple-cycle gas turbines boomed in the late 1960s and early 1970s, with GE’s Frame 5 and Pratt & Whitney’s (P&W) FT4 leading the charge. Westinghouse Electric Corp (now Siemens Energy) had its W171, W191, and a few years later the W301, but those machines weren’t as popular in utility board rooms at that time.

The early gas turbines were conservatively designed and had “good bones,” assuring long life if properly operated and maintained (Fig 1). However, most have disappeared because larger and more-efficient machines make best sense in the majority of applications today. But some of these legacy units, uniquely positioned in the market, not only remain productive, but are worth investing in to extend their lifetimes beyond the half-century or so they have already served.

Kimura Power LLC, with generating plants in Ohio and Indiana, upgraded the control systems of its four- and five-decades-old gas turbines in 2016 primarily to improve their reliability in starting and in dual-fuel operation—an investment that continues to pay dividends. A bit of history: The Kimura Peaker Portfolio was a unit of AES Ohio Generation LLC, a wholly owned subsidiary of DPL Inc (Dayton Power & Light Co), until it was acquired by Rockland Capital LLC in spring 2018.

The upgrade projects described below involve Kimura’s Yankee FT4s and Frame 5s, and Hutchings W301—assets identified in the accompanying table. These peaking units serve the PJM capacity and black-start markets. They average about 70 starts annually, virtually all during June, July, August, and September. Typical summer-peak run time is 16 hours—early morning to about 9 p.m.

Kurt Lammrish and Mark Meade were among the decision-makers on the DPL team responsible for upgrading Kimura’s legacy peakers with 21st century controls. Design, installation, and commissioning of the new hardware and software, and training, were done by Orlando-based Turbine Technology Services Corp (TTS). Today, Lammrish is plant manager and Meade, who retired from DPL as peaker supervisor about when the Kimura assets were sold, serves the plants in a consulting capacity.

They told the editors the relay logic on the Frame 5s and the 301 had not been changed since those units were commissioned and that the Fives were equipped with Young & Franklin (Y&F) fuel regulators for engine control. Recall that the fuel regulator predated GE’s Speedtronic™ I, the OEM’s first electronic control and protection system for gas turbines. Think about the challenge associated with finding spare parts for those machines and then locating a technician to do the controls work needed.

The Kimura upgrade. The original control systems for the legacy peakers, tough to troubleshoot, were replaced with TTS’s TMS-1000S turbine management system, built on Allen Bradley’s widely used ControlLogix® distributed-control platform (Fig 2). Not having to rely on the OEM for service cuts both outage time and cost when repairs, logic changes, etc, are needed.

The TMS-1000S uses the Ethernet-based Device Level Ring (DLR) architecture for processor I/O connections, thereby meeting NERC cybersecurity requirements. The provided switch assures a secure access point to the NERC recommended security perimeter by networked devices—such as remote HMI or engineering laptop.

TMS-1000S also relies on dedicated DeviceNet Networks for communications with such upgrades as the vibration monitor, electronic overspeed detection system hardware, and the electronic valve-position controller for GT gas-fuel control (get the details by attending the TTS webinar on Feb 10). DeviceNet uses the Common Industrial Protocol (CIP) to provide the control, configure, and data-collection capabilities for industrial devices.

Modbus TCP/IP delivers additional information from the TMS-1000G (generator) system, which includes generator protection relays, auto sync, power and energy meters, etc. Finally, the Distributed Network Protocol (DNP3), together with the power-quality and revenue meter, allows for remote viewing of output parameters such as megawatts, megavars, and generator breaker status.

Here’s an overview of key actions undertaken by TTS to bring the Kimura assets up to current requirements:

• • Unit rewire. First, removed all existing wiring and terminals, cleaned all conduit, tray, and junction boxes, and replaced broken and damaged conduit fittings and terminal blocks. Next, installed new high-temperature cabling designed specifically for gas-turbine applications.
  • Fuel systems. Control valves are core to the fuel system, which has experienced significant technological advancement in the last two decades. Removed pneumatic and electrohydraulic systems and replaced them with modern Woodward and Y&F electronic fuel valves, both highly reliable based on industry experience.
  • On-base devices. Replaced transmitters and pressure switches and upgraded all instruments, thereby increasing reliability and making more information available to the control system and the operator. These upgrades allow the control system to generate more meaningful diagnostic alarms, thereby facilitating troubleshooting of problems.
  • Liquid fuel system. Modified fuel pumps, replaced flow dividers, and upgraded other components to increase system reliability during starting, load changes, and fuel transfers.
  • Multiple-unit HMI front end. TTS engineers believe upgrades to the human machine interface (HMI) offer huge benefits to users. Examples: Eliminates the need for an operator to enter pressures and temperatures in a log book, provides an indication as to why a unit tripped, etc.
  • The modern HMI with the proper mix of useful/usable/readable graphics, alarm messaging, and real-time and historical trending provides operators the tools to properly manage the machine, monitor the unit and react as necessary to changing conditions, respond appropriately to alarms, and provide actionable information to others. An example of the last: Give maintenance teams the tools needed to identify and resolve problems quickly, minimizing downtime.
  • Generator controls. The excitation-system upgrade involved removing the existing relay, potentiometer, static-based system and replacing it with a modern digital excitation control system. The protection-relay upgrade focused on the original electromagnetic relays. While reliable, they do not provide the historical information so valuable in troubleshooting. Modern digital protection relays provide the needed protection as well as actionable information. The excitation and protection systems are connected to the turbine control system, allowing key information to be displayed, trended, and logged by the HMI.

When all upgrades were completed—on time and within budget—the units were tested to base and peak loads on both fuels, and to maximum and minimum VArs. Plus, fuel transfers were executed successfully on load. Note that the controls for the Yankee and Hutchings peakers are local (at the individual units) with all remote-start capable and AGC (automatic generation control) operable. Control central is at the Tait facility, which has seven 7EAs and is manned 24 × 7.

The results. As to the all-important question, “How have the upgrades and the units performed over time,” Lammrish and Meade shared their experience thusly: Excellent! As of this writing, no outage or reliability issues have been attributed the TTS control system.  In fact, Kimura will be ordering control-system spares for the first time in 2021—nearly five years after commissioning. There is no retirement plan for these units.

In closing, Lammrish and Meade shared their thoughts on TTS: A highly reliable, very capable partner always willing to go the extra mile to do the job correctly. A case in point was recreating controls drawings for the units, which involved an unexpected engineering effort.