There were eight V94.3A user presentations at last year’s meeting, half based on experience in Europe, half in Asia. The European speakers focused on the following: gas-turbine O&M history covering nearly 10 years, generator major, expansion-joint failure analysis and repair/replacement, and combustion tuning to allow an increase in fuel temperature. Presenters from Dubai Electricity & Water Authority discussed GT inspection findings, what is believed to be the world’s fastest major for this frame (11 days), and the underlying cause of fuel-oil flex-hose damage.

Here are thumbnail sketches of the assets upon which the presentations were based:

• • Two single-shaft combined cycles with a total full-load output of 870 MW, designed for a nominal 300 starts annually, hot starts (less than 8-hr shutdown) in 15 minutes, warm starts in 50 minutes.
  • Two single-shaft combined cycles built in the mid-2000s with a total full-load output of 850 MW.
  • Early 2000s repowered oil-fired steam station (2 × 125 MW) burning gas with heavy-oil backup. Current configuration is two 363-MW 1 × 1 × 1 combined cycles.
  • Standard 2 × 1 combined cycle rated 850 MW.
  • Plant built in stages with 400-MW single-shaft combined cycles installed nearly a decade apart.
  • A 590-MW 2 × 0 addition to power and desalination plant.
  • Two 375-MW 2 × 1 combined cycles with flash distillers.

Perhaps there’s no better way to learn about plant operations than to listen to a user colleague give an objective review of his plant’s history and be able to ask questions. This speaker’s review covered eight years from commercial start to an extended HGP more than 34,000 EOH and nearly 400 starts later.

He talked about the plant’s experience with hexavalent chrome—sampling and measurement, and dealing with contaminated insulation mattresses. Conclusion: Further investigation is required to assure a safe working environment on the steam turbine.

Another safety topic discussed was working at height, including the use of davits to tie off worker harnesses when climbing on the turbine.

Moving to the compressor, the speaker discussed IGV actuator ring axial wear and repair, plus replacement of rollers, bushings, and pins. A diaphragm exchange made necessary because of wear at vane hooks was another talking point. Exchange of the compressor bearing shell because of damage, the need for new shaft coupling bolts, repair of the coating on the leading edges of airfoils, and other compressor topics kept attendees in their seats.

Mention of a trip caused by the unexpected closing of IGVs during baseload operation was a surprise highlight of the presentation. Analysis revealed the cause was servomotor internal leakage, considered an isolated incident.

In the combustion chamber, minor repairs were required. In the turbine, all vanes were disassembled and reassembled; a few were replaced. Plus, blades in Rows 1, 2, and 3 were renewed.

Recommissioning revealed engine work during the outage enabled a power boost of more than 2%; heat rate also was better.

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The original metal-bellows expansion joint installed between the gas turbine and exhaust duct had 125,000 EOH and more than 1200 starts at the time of failure. Material was described as heat-resistant austenitic stainless steel. The expansion joint was designed for 12,000 cold starts, 620C operating temperature, ±50 mm elongation, and ±1 mm movement in the vertical direction.

Plant personnel knew they had a problem because both the temperature and the concentration of carbon monoxide inside the package had increased significantly. Plant operations were modified to avoid unit trips. Inspection revealed the joint had failed in two locations—at the 12 and 6 o’clock positions—and insulation was damaged. Temporary metal shields mitigated damage to affected components.

Temporary repairs were made about six months after the failure was identified, but the protective pillows and belting holding the pillows became ineffective over time and the replacement of the expansion joint became necessary. The new joint was installed during a steam-turbine outage.

There were difficulties with the installation, which should not be surprising. Examples: misalignment between the exhaust section and the gas turbine as well as cracking and deformation of the transition cone. Leak testing was the final step in the replacement project.

A finding during the root-cause analysis (RCA) investigation was that sliding feet on the exhaust cone were not performing as intended and hang-ups impeded expansion of the joint during turbine starts, causing stresses that contributed to cracking. At user meeting after user meeting the editors hear of problems with sliding feet on heat-recovery steam generators, rotor air coolers, shell-and-tube heat exchangers, etc. They should be inspected and lubricated annually.

The failure of flexible hoses for fuel oil can be avoided in many cases. The speaker describing her experience said that before the unit’s minor inspection, the operator received a fire-detector alarm, and personnel found the flex hose between one burner and the manifold ring completely torn apart. It was replaced. Flex-hose damage also was found on at least one other machine.

Like the condition of sliding feet in the previous experience, the condition of flexible hoses must be monitored. Subject matter expert Brian Hulse, a frequent contributor to CCJ ONsite, acknowledges that hoses are expensive and that users always try to extract maximum value from them before they’re replaced. Replace decisions are not easy because the hoses used on most gas turbines are manufactured with no published shelf-life or working-life limitation.

Hulse says plant O&M personnel should be aware that the following conditions impact hose life and to be on the lookout for them during inspections: chaffing, kinking, prolonged exposure to UV, mechanical abrasion, lying in fluids (water, fuel, oil, etc).

A simple database can help you avoid surprises. Include any recommendations on the care of hoses offered by the gas-turbine manufacturer in the O&M instructions for your machine, note the type of service for each hose cataloged, enter findings of routine inspections, inspection interval, inspection procedure, etc.

Also, bear in mind that some hoses are equipped with an exterior protective sleeve—designed to protect against the hazards of high heat and occasional flame. If this cover is torn, chaffed, or oil-soaked, the hose should be removed from service—especially if it too shows signs of distress.

A generator major was scheduled early based on the OEM’s recommendation to replace all hydrogen seals after about 64k EOH and 1700 starts. Wedge tightness was an initial concern when the unit was removed from service, but the inspection team ruled it “acceptable” based on results of a test method provided by Siemens USA.

Several small cracks were found on the generator’s PPS (hydrogen Performance Plus Seal™) segments. The bumper ring also was damaged. No obvious root cause was identified. The speaker advised that segments can be replaced onsite, but bumper-ring replacement requires a factory visit. Important: Damaged segments cannot be replaced individually; the entire ring must be replaced. Attendees also were made aware of the OEM’s development of a special tool for installing new PPS segments.

Several wrinkles were found in stator top bars. “Advanced” wrinkles could be seen by the naked eye; several other bars sounded hollow on one side when tapped in the same area. Insulation was cracked in areas revealing advanced wrinkles and it was repaired. Engineers determined that wrinkles and delamination were caused by thermal expansion/contraction of the bars during starts and shutdowns, which had increased in recent years. The repairs contributed to a significant reduction in partial discharge, which had been increasing over time.

Generator bushings were changed to ones with cast rather than welded supports to mitigate damage caused by vibration. However, the new design also showed signs of vibration damage on all three phases, as indicated by green dust. Engineers could not determine the cause of vibration. The three bushings had capacitance deviations, likely caused by bad connections between clamp and the inner electrical-field control layer. One bushing was replaced. The other two were relocated to new positions at “star” points, where there is no voltage stress.

An upgraded bearing (MKD11) was installed on the gas-turbine side of the generator because of tilting and problems during turning-gear start. The new bearing has improved lift-oil grooves and coated bearing saddles, but its normal temperature runs about 6 deg C higher. Monitoring of the new bearing is ongoing.

Combustion tuning was discussed by an engineer associated with a practical research project for a large generation company. The goal of the program was to minimize cost of power production while maximizing efficiency and output. Results enable the company to tune its engines at less cost than would be charged by the OEM.

The sticking point described was that while the gas turbine met performance guarantees, it was not possible to operate at the maximum fuel temperature (200C) at low ambient temperatures. The power generator wanted 200C fuel at all times to increase efficiency.

A solution was found whereby fuel temperature was raised and efficiency increased. The annual saving in fuel and carbon costs amounted to more than $US100,000. Plus, NOx emissions were reduced. Work on the project continues with the goal of fine-tuning combustion and saving still more fuel.

Outage time reduction is the goal of virtually all power producers when they are “in the money.” Speaker described how his company was able to reduce the time for major inspections on two gas turbines from 51 days in 2013 to 11 days in 2018 and 2019. Likely you find this hard to believe. Learn what’s truly possible by attending user-group meetings for your engine.

For this case history, be aware that plant personnel were motivated to set a world record for the major inspection of a SGT5-4000F. And they were empowered to do so. There was plenty of relevant in-company experience to draw upon: It owned and operated two-dozen V94.3As.

The first engine to complete its 11-day major (2018) required more than 12,000 man-hours of effort from a field staff of 115 working 11-hr shifts; the second engine’s 11-day major in 2019 took just north of 9400 hours with 95 field staff working 10-hr shifts.

Critical to the achievement were the following:

• • Detailed planning and prioritization of work permits to minimize the time needed to isolate various systems.
  • Created a fast-track entry process for staff and logistics at the security gate.
  • Maximized onsite logistics—such as meals, laundry, transportation, etc—to minimize lost time.
  • Conducted a kickoff meeting of all field staff prior to the outage to build a sense of ownership in the project.
  • Shifted critical risky activities to outside the overhaul period. The thinking: The shorter the outage the lower the technical risk and the fewer the number of human errors.

Project planning was especially critical to success, the speaker said. Here were some of the key steps taken:

• • Activities thoroughly planned in advance with resources mapped to overcome foreseen challenges.
  • Staff qualifications were scrutinized and the best team selected.
  • Optimized the work-shift model to permit round-the-clock activity.
  • Organized and managed spare parts and tools to minimize time constraints.
  • Conducted daily project review meetings to identify and eliminate schedule sticking points and to measure progress.

The speaker closed by identifying some considerations to shave days from the outage schedule, including these:

• • Consider a rotor swap rather than a shop visit.
  • Provide onsite capability for coating compressor blades.
  • Review lessons learned and implement optimized findings into your plans.
  • Swap out burners, valves, etc.
  • Focus on enhanced project management techniques.

Inspection findings were reviewed by an engineer from a major generator. A summary follows:

• • Minor inspection revealed TBC loss and some oxidation of the protective layer on the pressure side of two first-stage turbine blades, which were replaced.
  • Linear crack indication on the platform of one second-stage blade, also replaced.
  • Bearing balls found missing on one side of the turning-gear pinion. It was replaced.
  • Lift-oil pump failure was characterized by black-colored oil, metallic chips in the filter, and coupling damage. After failed parts were replaced, oil was run through the filter until clean.

Extended HGP inspections on the gas turbines for one 2 × 1 combined-cycle block (nearly 68k EOH/314 starts) at a two-block plant revealed the following:

• • Compressor bearing reverse thrust pads were found scored to a depth of 0.4 mm; coking was in evidence.
  • All vanes were removed for NDE, two were replaced because of excessive caulking clearances, IGVs and first- and second-stage vanes were recoated, compressor blades in Rows 1-4 were recoated on the leading edges of the airfoils, some new tiles were required.

During recommissioning, new KV curve settings were required for gas control valves, newly implemented logic called for in product bulletins presented problems, compressor bearing temperature came in higher than expected, the baseload power output was lower than expected, a unit trip was experienced during a switch-over from diffusion oil mode to fuel gas.

The second combined cycle at the plant went through its extended HGP inspection the following year with some of the same findings identified with the first block—such as replacement of a few blades and vanes in the compressor, coating fix on compressor blades. Recommissioning of Block 2 also was similar to that of Block 1.

GTUsers.com, a web portal designed and maintained by Gasre Oy (www.gasre.com) to facilitate communication among owner/operators of gas turbines, transitioned from a “hobby” to a professional service in 2014. Coincidentally, the independent Finnish firm, launched in that year the development of its TMMonitor™ product for gas-turbine maintenance management and parts tracking. This software is represented in the US by Lodestar™ and TTS Energy Services.

The activities of GTUsers.com are coordinated by Yrjo Komokallio, a turbine specialist, who is CEO of Gasre. The web portal is segmented by engine type (currently 11 machines are represented), and access to the discussions, databases, etc, associated with each is restricted to the members of that group. You can be a member of a group only if you own and operate such a unit. The individual groups are controlled by their own end-user steering committees. In sum, more than 5000 users, representing over 1500 gas turbines, participate in GTUsers.com.

Pertinent to this report, GTUsers.com has hosted web meetings for owner/operators of V94.3A (SGT5-4000F, AE94.3A) engines since 2009 and for V94.2 (SGT5-2000E, AE94.2) machines since 2012. Annual conferences were added in 2014 and 2015, respectively. Last year (2019), the 94.3A group met in Istanbul in October, the 94.2 users in Berlin in November.

Sponsors of GTUsers.com activities familiar to US readers include ARNOLD Group, Sulzer, APG, MD&A, Freudenberg, Liburdi, Dekomte, Trinity Turbine Technology, and Gas Turbine Controls.

The first gas-turbine user group known to the editors got its start in the US in the mid-1970s. It provided valuable experience on the operation and maintenance of these relatively new prime movers, which were ordered by electric utilities in large numbers following the Northeast Blackout of 1965. Back then the dominant engines for power production were Pratt & Whitney’s FT4 and General Electric’s Frame 5.

With world leaders in the development of industrial GTs—GE and Westinghouse Electric Corp—headquartered here, where natural-gas transmission lines moved fuel over long distances relatively inexpensively and additional capacity always was needed, larger and more efficient engines debuted regularly, promoting a need for user groups to facilitate technical communication among the owner/operators. Meetings of these organizations attracted 60-Hz users from around the world.

But what about 50-Hz users? Until recently, there was no efficient way for CCJ ONsite to follow the frame-specific experience of these owner/operators, most meetings being small and geographically dispersed. However, over the last several years, the Finnish organization GTUsers.com has built a loyal following among European, Asian, and Middle Eastern owner/operators who regularly participate in its online and face-to-face conferences. CCJ ONsite and GTUsers.com are working collaboratively to help users share experiences globally.

Here are some facts about the V fleet to keep in mind as you read through the first part of this report (Part II, focusing on 60-Hz engines, will appear in our next edition):

• • There are about 1000 V engines operating worldwide. This total includes both E- and F-class models operating at 50 and 60 Hz, providing plenty of experiences to share across national borders.
  • Two OEMs manufacture 50-Hz V engines, Siemens and Ansaldo Energia. The engine designations for Siemens machines are V94.2 (SGT5-2000E) and V94.3A (SGT5-4000F); for Ansaldo engines, AE94.2 and AE94.3A. Roughly 80% of all V machines in service were made by Siemens, most of the remainder by Ansaldo under a Siemens license.
  • com has hosted web meetings for 50-Hz V users since 2009, face-to-face meetings since 2014. The 2020 conference of the V94.3A users is scheduled for Prague, Czechia, October 12-15; the V94.2 meeting, Prague, Czechia, November 9-12.

What follows are summary notes from the 2019 V user conferences in Europe, a plant best practice from the V94.2-powered Amman East combined cycle, and a technology update from ARNOLD Group, one of the leading third-party service providers for the V fleet. Use the links below to quickly locate content of greatest interest.

• • Who is GTUsers.com? 
  • V94.3A meeting highlights from Istanbul
  • V94.2 meeting highlights from Berlin
  • ARNOLD insulation helps V engines maintain top performance
  • Best practice: Custom ear plugs protect hearing

ARNOLD Group is well known worldwide for its gas- and steam-turbine insulation solutions; in Europe and Asia also for its powerplant rotating-equipment and valve field-services capabilities. The company’s history in gas-turbine insulation, the focus of this report, goes back nearly a quarter of a century to the installation of the first Arnold 3D single-layer system on a V64.3A (SGT-1000F) machine at EnBW Energie Baden-Wuerttemberg AG’s 1200-MW Altbach/Deizisau combined heat and power plant (Fig 1).

Since then, more than 300 V-type engines—most V94/84.2s and .3As—in Europe, Asia, Africa, the Middle East, and the Americas have been insulated by Arnold. These units were manufactured by Siemens or its licensees—including Ansaldo Energia (Europe and Asia), Shanghai Turbine (China), and LMZ (Russia). Many other models of gas turbines also wear Arnold.

Revisiting Altbach, in more than two decades of service only 14 blankets have required replacement on that unit. Having an Arnold technical field advisor onsite during outages is said to have contributed significantly to this excellent service history: The TFAs made certain that the hundreds of numbered insulation blankets required for a typical E- or F-class gas turbine to assure easy access to critical instrumentation, borescope holes, etc, were removed, handled, stored (temporarily), and replaced correctly.

To date, Arnold has replaced the insulation on seven SGT6-2000E gas turbines in the US (Fig 2), with a few more projects in the pipeline for 2021. No SGT6-4000F machines have been refurbished in North America yet, but several SGT5/6-4000Fs in South America have been.

Key steps in insulation replacement

The success of any engineering project depends on rigorous planning. Pierre Annsman, a member of ARNOLD Group’s management team, told the editors at a recent user conference that a good first step in an insulation replacement project is a photo session with the candidate turbine.

A laser scan allows the company’s design and manufacturing personnel to adjust existing shop patterns for a particular engine model to the unit being reinsulated. Bear in mind that in-package piping and equipment arrangements vary.

Adjustments to the manufactured blankets may be required in the field to accommodate such things as flange positions, thermocouples, borescope inspection ports, etc. This work is done by experienced technicians—think of them as tailors—equipped with the proper sewing hardware.

The most economic scheduling for insulation replacement is about 20 single-shift weekdays with two TFAs and six local insulators. Calendar time can be reduced, of course, by working weekends, increasing the number of TFAs, and running double shifts. Turbines typically are reinsulated during major or hot-gas-path inspections in parallel with mechanical work. Insulation is not on the outage critical path.

Work begins when the turbine is cold and proper scaffolding is installed, if necessary. Insulation is removed by a local contractor, typically in a day and a half, and plant I&E technicians remove all instrumentation. About another two days is required to cut off all pins installed to accommodate the original insulation system, grind the pin stubs smooth with the casing, and brush/vacuum the unit and package clean.

Respiratory protection is highly recommended during this work. It’s also a good idea to have a health and safety engineer to measure the concentration of dust in the package to assure safe working conditions.

Installing the retention brackets and studs (photo) required to position and attach the new insulation is the next step. If the casing is forged steel, these components can be welded to the casing; if cast, drilling and tapping are required. Both procedures are done in accordance with the OEM’s recommendations. At this point, may be a good idea to laser scan the unit again to pin-point the location of all attachments, just in case.

Final steps: Install the new insulation system, have I&E techs replace the instrumentation removed previously, and dismantle temporary scaffolding.

Why replace insulation? Pierre Ansmann, global head of marketing for ARNOLD, says it’s only a matter of time before the economics of electric power generation suggests US owner/operators consider seriously replacement of the original insulation on their SGT6-4000Fs and other SGT6-2000Es.

Loss of earnings results from poor design/installation of turbine insulation and/or premature wear and tear of blankets. A plant’s balance sheet can be impacted negatively by reduced power production, contractual penalties, damage to mechanical and electrical equipment and instrumentation, and shorter outage intervals.

Insulation can wear out faster than you think, he says, particularly that installed on gas turbines with issues dictating frequent removal of their upper casings. If your unit was purchased during the “bubble” of 1999 to 2004 and still has its original insulation, Ansmann recommends conducting a thermal survey (Fig 3) to evaluate its effectiveness, keeping personnel safety in mind.

Benefits of replacement typically include less heat loss, less noise in the enclosure, a reduction in insulation removal/replacement time during outages, greater flexibility in maintenance scheduling, and longer lifetimes for in-package equipment—especially heat-sensitive motors, wiring, and instrumentation sometimes associated with unit trips.

Note that all the V engines in the US that have upgraded their machines with Arnold insulation began commercial operation during the bubble. They reported having done extensive repairs to the original blankets, or replacing them, during every outage. As-built performance remained elusive, however. In these cases, marginal materials of construction, and the use of blankets well beyond their design durability limits, made the decision to replace a relatively easy one.

As a rule of thumb, Ansmann figures standard insulation systems typically perform as-designed for three to five off/on cycles, not close to Arnold’s guarantee of 15 cycles when removal and reinstallation are done correctly. After about five outages, he says, users with insulation made by others often find blankets difficult to reinstall properly—especially where they overlap.

This is particularly true when blankets must be held in place by pins welded to the casing. Pins are not used in the Arnold insulation system: Rather, interlocking high-temperature-resistant blankets, cut to conform to the turbine surface (Fig 4), are held in place by industrial Velcro® and a unique support system that is secured by studs welded to the casing. You may recall that pins sometimes are removed during maintenance for safety concerns, or otherwise; if not replaced, there’s little chance of getting blankets tight.

Other concerns of plant personnel regarding marginally designed and ageing insulation systems, in Ansmann’s experience, include these:

• • Insufficient protection for thermocouples, borescope inspection ports, and instrumentation (Fig 5).
  • Activities that require walking on insulation can move blankets out of position and/or release fibers—a possible health threat. Arnold’s aluminum deck-plates-style step protection system reduces the possibility of insulation damage during maintenance (Fig 6).
  • Sagging of insulation can cause uneven thermal expansion of the casing.

Comprehensive training transforms coal-plant personnel into multi-skilled CC operators

Powerplant technical training has evolved from learning on the job to VHS tapes to DVDs to eLearning with hands-on laboratory modules. As the power-generation business strategy changed to include the Riverton Power Station’s conversion from coal to combined cycle, steps were put in place to re-tool operations personnel. Led by Plant Manager Ed Easson, efforts to research and establish an operator training process got underway. Initially, what was to be an application for one plant site was expanded to include additional sites.

Plant management looked for resources that would take operations training to a new level and provide a more systematic, comprehensive approach to building a multi-skilled workforce. But, what do you do when you don’t find what you’re looking for? You build your own. That’s exactly what Liberty Utilities’ plant managers did.

The Energy Supply Operator Training System was launched in 2016. Comprised of three key learning and development strategies, the system reflects a focus on plant performance indicators, operator competencies, and continuous improvement.

The learning and development strategies are the following:

• • eLearning courses including electrical, mechanical, I&C, power generation, industrial math, leadership, and communications. The 24/7 access provides plant operators the flexibility needed to complete courses in shift-work environments. The curriculum currently includes 126 courses over multiple development levels with annual reviews and enhancements.
  • Performance laboratories that build on the associated eLearning courses are designed and delivered by in-house subject matter experts. Labs for each development level provide hands-on, experiential learning. Currently, there are 21 labs in the training system with annual reviews and enhancements.
  • On-the-job training (OJT) always has been a mainstay of learning and typically very informal. The training system recognizes OJT as a critical component deserving of acknowledgement and documentation of operators’ progress. A more formal process that defines the scope of OJT is in practice with refinements in development.

The company’s Learning Management System provides eLearning course access, and training system records tracking and reporting.

Results achieved by the fourth year of implementation (2019): Four operators had completed training system requirements with six more working through their programs. Plus, operators continue to expand knowledge and skills to build on their multi-skill capabilities.

As with any new process, training or otherwise, experiences along the way point to new possibilities for continuous improvement of the system. Content and process reviews/updates are natural steps within the training system and continued visionary leadership will ensure an effective and successful operator training system for years to come.

Riverton Power Station, owned and operated by Liberty Utilities, is a 285-MW, gas-fired, 1 × 1 combined cycle powered by a V84.3A(2) gas turbine, located in Riverton, Kans.

Sulzer’s Rotating Equipment Services unit—formerly Sulzer Turbo Services—offers a wide range of inspection, shop, repair, and manufacturing services for gas and steam turbines, generators, pumps, compressors, and other power and process equipment. The company actively supports the V94/84.2 and V94/84.3A fleets through its participation in user meetings here and internationally. It has major shop facilities worldwide to serve powerplant owner/operators.

Not familiar with Sulzer? Tour the company’s website at www.sulzer.com for an overview of shop capabilities pertinent to your equipment—including physical and metallurgical inspections, welding, heat treatment, machining, turbine and compressor coatings, rotor disassembly/reassembly, etc. Sulzer offers field-service (Fig 1) and new-parts manufacturing to complement its repair offerings.

Most of Sulzer’s efforts with regard to V engines focus on the Siemens SGT5/6-2000E and Ansaldo AE94.2 machines. Aftermarket services for about two-thirds of this market segment are “competitive”—that is, not influenced by an OEM’s long-term services agreement. By contrast, Siemens says 80% of the SGT5/6-4000F engines it has supplied are governed by an LTSA.

While Sulzer, like ARNOLD Group and APG, does perform repairs and field services for some 94/84.3A owner/operators, the manufacture of major new parts is not included among its current offerings.

New parts. The company makes the following parts for legacy 94/84.2 engines: compressors; inner casings, mixing chambers, and flame tubes for the combustion section (Fig 2); and Row 3 turbine blades. Plus, for the 94.2 only: combustion-section heat shields and fuel nozzles, as well as turbine blades for Rows 1 and 2 and vanes for Rows 1, 2, and 3.

For 94/84.2 models through Version 7: Combustion-section inner casings, mixing chambers, and flame tubes; turbine vanes for Rows 1 and 2. Additionally, new fuel nozzles are available for 94.2 models through Version 7.

New parts are said to be “ready to drop in,” having the same form, fit, and function as those supplied by the OEMs.

Mods and upgrades for critical 94/84.2 parts are a significant part of Sulzer’s value-add offerings. Some examples follow:

• • Relocation of the F-ring to mitigate burnout of tile clips by moving the holders to a region of lower temperature, in addition providing easier access to tiles for replacement.
  • Coating upgrades for flame tubes (Fig 3). This includes adding thermal barrier coating (TBC) to burner plates, bezel rings, and F-row tile clips; plus, depositing chrome carbide (CrC) on bezel rings and burner plates.
  • Flame-tube upgrades include an Inconel overlay for F-rings and Hastelloy-X tile support rings.
  • Improved cooling-hole pattern for flame-tube burner plates. Also available are larger plates and a material upgrade to Haynes 230.
  • Inner-case upgrades include TBC coating of the hot-gas-path surface and CrC coating of inlet collars.

Burners, etc. Sulzer recommends swapping out legacy H burners with the HR3 low-emission design (Fig 4), which is said to offer the following benefits:

• • More stable combustion, primarily because of better mixing of the fuel gas with combustion air.
  • Increased resistance to flame flashback. One reason: The higher velocity of the fuel/air mixture through the HR3’s optimized flow channel reduces the probability of the flame traveling upstream.
  • Corrosion-resistant gas supply piping minimizes leakage risk and reduces maintenance.
  • Reduced NOx emissions. The better mixing of fuel and air inherent in the HR3 design eliminates flame hot spots (emissions spikes) associated with the H burner.

Sulzer also actively promotes its E-UP program for the 94/84.2 fleet, which promises users a 5-MW increase in power output and a 0.8% efficiency improvement for retrofitting turbine Rows 1 and 2 blades and vanes with airfoils of its design. All incorporate what the company believes is an improved nickel-base superalloy (Rene 80), TBC coating system, and more efficient airfoil design.

The specific coating system selected depends on an engine’s operating conditions. Generally speaking, MCrAlY is used on the external surfaces of Row 1 and 2 airfoils because of its superior oxidation and corrosion resistance in both base- and peak-load applications. Use of TBC is optional where necessary to reduce metal temperatures and thermal gradients for improved protection against creep and fatigue. Internal surfaces have an aluminum diffusion coating to help prevent intergranular attack.

In addition, R1 vanes feature internal impingement cooling, re-staggered and optimized airfoil design, integrated cover plate with impingement cooling, and cut-back trailing edge. Highlights of the R2 vane design include tilted and optimized airfoil design, serpentine internal cooling geometry, and throttle sleeve to control the mass flow of cooling air.

For R1 turbine blades, enhancements include: cut-back trailing-edge design adopted from the 94/84.3A blade, serpentine internal cooling geometry, and squeeler tip.

The enhancements cited above are said to allow Sulzer’s Row 1 and 2 turbine blades and vanes to operate reliably in engines with turbine inlet temperatures of up to 1080C (1976F).

Eta Technologies LLC, believed by many to be the nation’s leading independent provider of new and aftermarket parts and maintenance solutions for Siemens V series industrial gas turbines, was purchased by Allied Power Group (APG) in mid-2018. Principals Rich Curtis and John Kearney, who launched Eta Tech in 2004 and were well known to V users, joined APG as part of the acquisition.

Eta Tech’s expertise fit seamlessly with APG’s strategy of providing full-service solutions to the power industry—including turbine component repair, rotor repair, new-parts manufacturing, and field service—thereby creating a highly capable aftermarket resource for owner/operators of V engines worldwide. To date, APG has focused its attention on the E-class V84.2 engine.

With few opportunities in the US for showcasing its products and services to the V user community, APG’s Curtis and Kearney caught up with the editors to review both the issues they are finding during visits to US plants powered by V84.2 engines and the successful corrective steps they have used to restore engine health. The many explanatory photos included here double as a valuable training aid for new hires and as a reminder for veterans who have not been involved in an overhaul recently.

1. Diffusion burners. Broken pilot tubes found during burner inspections must be repaired quickly to maintain outage schedule. Recall that four pilot tubes are installed in each burner (Figs A and B) to deliver pilot gas to the swirler (C) for stabilizing combustion while in premix operation. For the case illustrated, not all pilot-gas tubes were in evidence (D), some having fractured (E) just above the hole through the swirler casting (F).

Metallurgists, including Curtis, suspected stress corrosion cracking of the 300-series stainless steel tubes was the underlying cause of the pilot-tube failures and selected Inconel-600 as the replacement material (G).

The burners at this plant exhibited other damage as well—such as severe oxidation of carbon-steel oil-burner flanges, which were weld-repaired and finish-machined as part of the project. Also of note, the thermocouples provided by the OEM were not replaceable without disassembly. Eta Tech developed a replaceable T/C mod, now included among APG’s solutions.

Perhaps the biggest challenge on this project, Curtis said, was completing the repairs, installation, and final inspection within a 12-day window to avoid an outage extension. The plant had no spare burners so replacement of the pilot-tubes was the only viable option.

At other plants, swirler casting defects—including cracks and porosity (H and I)—have been found. No problem, generally speaking, according to Curtis, APG can now manufacture new and replace swirlers, as well as diffusion-burner assemblies (J and K).

2. Pre-mix gas distributors. Curtis next discussed repairs to the legacy H-style gas distributor. He seemed particularly proud of the procedure Eta developed to replace corroded “S” bends (Fig A), originally fabricated from 16Mo carbon steel, with P11 material of increased wall thickness.

The company’s fixture enables the making of precision repairs (B) as an alternative to purchasing a new distributor assembly from the OEM for significantly more money. A corrosion-resistant coating adds a measure of protection (C). Note the notches in the six distributors to accommodate the igniter tube visible in Fig B in Section 1 on diffusion burners.

Curtis mentioned seeing “S” tubes lose up to 40% of their wall thickness, much like HRSG tubes subjected to FAC. The weld process used, he continued, has been qualified with sample cut-ups and hardness traverses as-welded and after stress relief. Welds made in refurbishing gas distributors are stress-relieved, x-rayed, and liquid-penetrant inspected.

Over the last several years, most V84.2 units in the US fleet have upgraded to the so-named HR3 style of distributor, where pre-mix gas is delivered to each of the six “heads,” a/k/a diagonal swirlers. Fuel gas enters the air stream through holes in the airfoils in each head. Damage mechanisms associated with this design include fretting wear of the flange on each head (D) and corrosion of the airfoils (E). Should airfoil corrosion or other damage get too severe for repair, APG offers a new HR3 (F).

Kearney, a former plant manager, interjected that an additional “hot button” on this component today is the cleaning of internal passages. He said the OEM brings an ultrasonic cleaning bath to the plant for this purpose, but users have told him this method is ineffective and expensive. Plus, disposal of spent cleaning solution can be problematic in some locations. APG offers an offsite thermal cleaning alternative (takes about a week from removal to reinstallation).

3. Compressor diaphragms. Kearney said many V84.2s he’s familiar with have never had compressor diaphragms removed for inspection or repair. Simple erosion and corrosion over time is to be expected and not much of a concern beyond reducing compressor efficiency.

However, diaphragms are prone to developing airfoil cracks emanating from the inner tenon, where the vane attaches to the assembly’s inner ring (Figs A and B). Curtis concurred with what he believes is a general feeling among users that the OEM has overly conservative repairability criteria on the number/sequence of cracked vanes that allow or disallow full diaphragm repair. Eta Tech, and now APG, routinely extend these criteria if analysis confirms the decision.

In the event repairs are not practicable, APG has the engineering/manufacturing know-how to make all diaphragm stages (C). In fact, Curtis said, new coated diaphragms were delivered to customers last year.

4. Fuel-oil burners. According to Kearney, Siemens manufactures two different styles of fuel-oil burner lances: oil only and oil/water, the water circuit for NOx abatement and/or power augmentation. The OEM design relies on shrink fits to separate and seal the water and oil flow channels, Curtis added, connections that can fail in service and cause coking (Fig A), bellows damage (B, oil/water design only), unusual spray patterns, and flame-tube damage.

Burners that are repairable are completely disassembled by APG, cleaned, parts replaced as necessary, reassembled, and flow-tested. When repairs are not cost-effective APG offers new. It manufactures both styles of burners (C and D). Excellent performance in service is claimed.

5. Combustor flame tubes. The OEM’s design of combustor flame tubes has evolved over the years to address service-related material distress. The upper F-ring (Fig A) and the lower tile support ring (B) are made from carbon steel and are exposed to combustor temperature—thereby making them prone to severe oxidation damage.

Curtis recalled mechanical design changes made by the OEM to protect the F-ring—changes requiring the purchase of new-style combustor dome plates and relocation of combustor-brick “removable” rows. He said Eta Tech took a different approach: Make F-rings and tile support rings from an oxidation-resistant alloy that did not require flame-tube or dome-plate configuration changes, and add TBC to mounting hardware for combustor-brick “removable” rows. APG can supply all of the hardware used in the combustors, including the ceramic bricks.

Recently, APG has manufactured and delivered new flame tubes with rings of upgraded nickel-based alloy. Plus, it has repaired and upgraded used flame tubes with the upgraded rings (C).

6. Exhaust diffuser cladding. The exhaust diffuser, or frame, for the V84.2 has inner and outer cylindrical and conical sections and airfoil-shaped struts that support the turbine end-bearing compartment (Fig A). Replacement of the stainless-steel liner for the diffuser is necessary when embrittlement occurs and cracks occur, and poor weldability makes repair difficult. For users opting to replace damaged components, APG offers individual sections of cladding (B) or full-replacement cladding “kits.”

7. Rotor disks. Looking ahead, Curtis said that as V84.2s approach 200,000 equivalent operating hours, compressor (photo) and turbine rotor discs, and hollow shafts, become candidates for retirement. Anticipating the coming demand, APG has completed all necessary engineering work and supplier qualification for the supply of new rotor components. The company is expecting orders for delivery in late 2020 and beyond.

Perhaps the best way to begin this section on experiences shared by V84.2/V84.3A owner/operators during the annual conference of V users at the Pittsburgh Marriott City Center, September 2019, is to share the following passage from an announcement on the meeting from Scott Wright of PowerSouth Energy Co-op:

“Many of you know Olaf Barth, who has been the key contact for the users to Siemens for the last few years, is leaving the group. Dominion no longer owns Manchester Street, so Olaf is working on other topics. Many thanks to Olaf for his expertise and all his efforts.” The CCJ editors extend their thanks to Olaf as well. He continues to be a valuable resource for us when gas-turbine O&M questions arise on these and other frames.

Interaction among owner/operators at the annual V conference is robust, similar to that at other user group meetings. These are ideal venues for tapping into the industry’s knowledge on how to operate your plant more economically, reliably, and with less environmental impact.

Perhaps the best way to characterize the availability of OEM representatives, third-party suppliers, and plant personnel to address your concerns and answer your questions is free consulting—provided by experts. And this meeting is truly free, the OEM picking up all but your transportation and hotel room costs. It’s the optimal way for anyone with a V machine in his or her plant to learn.

Safety is a first-day topic sure to create discussion and get attendees engaged. At last year’s V meeting hexavalent chrome—a byproduct of welding chrome-containing alloys—was a topic of great interest, as expected. Siemens employees had expended great effort in the last year to mitigate the issue—finding the contaminant on combustion basket flanges, bolting, exhaust diffuser, exterior case of the IP turbine, etc.

The yellow residue identified with the problem, calcium chromate, is formed by the oxidation of a chrome-containing base metal in the presence of a calcium source—such as anti-seize compounds and high-temperature insulation pads. Anti-seize test results reported at the meeting indicated Molykote, Loctite, and Nominal Blue Grease tested positive for hex chrome, while Kluber, Tiodize, and Lube-O-Ring were negative. Kluber Paste HEL46-450 and Tiodize T8F-H were recommended.

Additionally, bolts that had tested positive and were bathed in a 10% citric-acid solution for 5 to 10 minutes, then rinsed with clean water, reduced chrome 6 to harmless chrome 3. However, no such easy cure for contaminated insulation; it must be disposed of in an environmentally responsible manner.

Doing business online. There are questions from the floor at virtually every user meeting concerning the OEM’s processes and procedures, and last year’s V meeting had its share—including snags in the ordering of parts (such as functionality issues encountered when using the online quoting/ordering system), delivery delays, response time on technical issues, etc.

Siemens representatives listened carefully and provided immediate assistance where possible. More thorough guidance was reserved for a web meeting in early March. The good news from that event: Enhanced e-commerce capabilities would be released this fall.

Plant specific questions and observations included the following:

• • The SPPA-E3000 Electrical Solutions Excitation and Startup Frequency Converter System was regarded problematic by several users who thought more specifics should be made available to owner/operators. One attendee suggested that the excitation system was a “black hole.”
  • A participant said his steam turbine experienced vibrations close to the trip limit when a restart was attempted less than two hours after shutdown.
  • Failure reported in a blowoff bypass line: Butterfly valve was installed backwards but never noticed until the third major.
  • Support for Teleperm and TXP parts, training, and service was called into question by one user with a legacy unit.
  • Gas-turbine output reported dropping a few months after a CMF (compressor mass flow) upgrade, and hadn’t recovered. No other user in attendance had experienced this and the OEM questioned whether the performance loss was a problem unrelated to CMF. Evaluation continues.
  • Exhaust transition liner with low EOH was said to have experienced excessive cracking. More information and analysis were required for a proper evaluation.
  • A user expressed interest in operating at a lower gas supply pressure and wanted to know if pressures lower than those stated in the O&M manual be allowed. Question was referred to the OEM.
  • Problems were reported with combustor thermocouples of a new designed released to the fleet.
  • Some discussion revolved around the compressor casing and when it was likely to need replacement.
  • Performance degradation over time was another topic of interest. Can the degradation be correlated to starts and EOH? What are the ranges for loss and recovery? What can users do to minimize losses?
  • Issues igniting in high humidity received mention. One specific question: Should there be any change to tuning or procedure to accommodate high humidity?
  • Wet compression versus power augmentation was discussed. With Caldwell Energy in the exhibition hall, attendees could get answers to their questions direct from the experts.
  • Actuators for inlet guide vanes were reported by one user as being upgraded to REXA Electraulic™ actuators which combine the simplicity of electric operation, the power of hydraulics, and flexibility. There was no manufacturer support available for the legacy actuators being replaced.
  • Paint specs for the filter housing were discussed with Taylors Industrial Coatings Inc recommended by one attendee (see recently published “Air inlet system maintenance critical to assure top gas-turbine performance).
  • Vane-carrier cracking was identified as a problem in the V84.3A fleet.
  • One user was upgrading his gas turbine’s evap-cooler framework from PVC to stainless steel to combat premature degradation. Schock Manufacturing was mentioned for its filter-house work, in addition to silencers and exhaust systems.

The V84.3A session began much like the E-class segment of the program, with a review of key facts about the frame: more than 370 engines of Siemens manufacture operating worldwide, 22-million EOH of fleet experience, and more than 99.3% overall fleet reliability. One big difference between the sister frames is that 80% of the F-class units operate under a long-term service agreement with the OEM, compared to about 35% for the E-class machines.

The theme of this session was “Future-proofing your plant: Ensuring commercial success through mods and upgrades.” Confirmation of the OEM’s commitment to continual performance improvement is that the fleet service factor (operating hours divided by period hours) increased from 57% to 62% in the last three years even as competition in the power generation sector of the industry intensified and renewables gained market share.

Reviewing the OEM’s development plan for future enhancements—some already in commercial service or beta testing—one comes away with the belief that this frame is destined to remain competitive for many more years. If any of the following products/services are new to you, access the 4000F Engineering Session slides on the CEP for more information, or contact the Siemens representative for your plant.

Maintenance:

• • Optimized maintenance intervals.
  • Increased outage flexibility.
  • Wider range of service concepts available—including the fast outage incorporating innovative field service solutions.

Performance:

• • Performance boost with Siemens’ Advanced Turbine Efficiency Package.
  • Upgrade with Service Packages 7 and 8—including cooling-air reduction, HGP improvements, compressor mass-flow increase.
  • GT Auto Tuner.
  • Low-NOx emission solutions.

Flexible operation:

• • Increased load gradients.
  • Fast start, turn up, extended turndown.
  • Optimized part-load capabilities.
  • Expanded Wobbe range and hydrogen capability.

Improved airfoils. One of the speakers explained why compressor blade and vane enhancements have contributed in a major way to gains in output and efficiency: Improved manufacturing processes and materials. For example, five-axis precision milling has replaced conventional manual finishing methods, improving the accuracy of the airfoil profile and leading and trailing edges. Working surfaces also are smoother, and improved materials mitigate corrosion and erosion.

33MAC. The 33,000 EOH interval, introduced in 2009, is the standard maintenance concept for the SGT5/6-4000F. The leap from 25MAC, when the engine was introduced in 1996, to 33MAC (some machines have had positive experience to 38,000 hours), was enabled primarily by improvements in coatings and airfoil geometry and cooling. Looking ahead, advanced turbine hardware, scheduled for 2022 commercial availability, with a new base material and geometry improvements to increase low-cycle-fatigue life, will allow up to 2000 starts—double that of today’s blades and vanes.

FODS Smart. The benefits of Siemens’ Foreign Object Detection System, installed on well over a hundred turbines worldwide, were examined. FODS provides continuous monitoring for potential loss of combustion-chamber parts by way of acceleration sensors and a data acquisition and evaluation unit. System warns if a minor issue is detected (one that might lead to a system fault in the future) and alarms on a fault.

Other topics addressed included improvements to inlet guide vanes for faster response and the RCIE process, similar to that described above for the E-class engines.

The mods and upgrades presentation for the V84.3A was introduced with a chart that said enhancements to assure rapid frequency response, fast starting, part-load optimization, combustion of synthetic liquid fuels, and lower emissions by use of a premix pilot burner were ready for validation on this engine. Operational experience was offered on the following products:

• • Service Package 6 (SP6). Implement during a major outage to increase efficiency and boost power output. SP6 includes the HR3 burner with reduced swirl (HR3 RS), combustion chamber requiring less cooling air (CAR), and improved turbine blades and vanes. Upgrade benefits depending on conditions are a gas-turbine power boost of up to 16 MW and an efficiency increase of up to 0.7% (for a 1 × 1 combined cycle, 21 MW and 0.4%).
  • Compressor Mass Flow Increase (CMF++). Implement during a major outage to increase power output by up to 13 MW from the gas turbine and up to 22 MW from a 1 × 1 combined cycle.
  • Part load optimization. Implement during an HGP inspection to reduce minimum load while maintaining CO within regulatory limits and to improve frequency response. Hardware mods include new seals in the compressor and modifications to the inlet guide vanes. Quantification of financial benefits requires a site evaluation.
  • NOx reduction. Reduce NOx emissions while increasing power output. Calculation of benefits depends on fuel, site conditions, and other considerations.
  • GT Auto Tuner (GTAT). Implement during a minor inspection to maximize efficiency and minimize emissions during normal operational changes. First use revealed a NOx emissions reduction of up to 10% by activating the GTAT and virtually no degradation in power output over time between major outages.

In round numbers, there are about five-dozen V84.2s operating in the US, three-dozen V84.3As. CCJ ONsite has covered the 60-Hz fleet since the mid-2000s. Siemens has hosted annual face-to-face user meetings over the last decade and invited the editors to participate.

HEADS UP. The 2020 conference planned for September 14 to 17 at the Hilton Niagara Falls/Fallsview Hotel & Suites in Niagara Falls, Ont, Canada, was canceled at the end of May. CCJ will be assisting the V users with digital, user-only presentation and discussion sessions to take place sometime in mid-late July. Stay tuned. Siemens will be hosting a variety of NetMeetings in September to bring customers up-to-speed on their offerings and to provide answers to user questions. Next meeting is planned for the week of August 16, 2021 at the same venue. Details are not yet available.

What follows are summary notes from the 2019 Americas V users conference, a plant best practice from the V84.2-powered Riverton combined cycle, and technology updates from Siemens and two third-party service providers. Use the links below to quickly locate content of greatest interest.

• • Siemens SGT6-2000E highlights from Pittsburgh
  • Siemens SGT6-4000F highlights from Pittsburgh
  • User presentations/discussion from Pittsburgh
  • APG aftermarket parts, maintenance solutions
  • Sulzer inspects, repairs V engines worldwide
  • Best practice: Training turns out multi-skilled operators

Part I of this special report focused on the 50-Hz V fleets. Important to note is that ARNOLD Group, the insulation experts and the featured third-party vendor in Part I also serves power producers in the Americas.