CTOTF tackles user issues on a wide range of aero, frame machines

The Combustion Turbine Operations Task Force, which will celebrate its 30th anniversary next year, has the richest history of the many gas-turbine (GT) user groups. Chairman John Lovelace (jlovelac@aspc.com), a consulting engineer at Arizona Public Service Co, Phoenix, said a distinguishing feature of CTOTF (pronounced cee-toff) is that it addresses user issues on virtually all models of gas turbines—aeroderivative and frame—produced by the major manufacturers. The group meets twice annually (fall and spring) and counts members from over 150 companies in eight countries. Wickey Elmo (wickelmo@ctotf.com, 704-753-5377) is both the group and conference coordinator.

Elmo announced these dates and locations for the CTOTF’s 2005 meetings: April 3-8, Annapolis, Md, and October (dates to be announced), Banff, Alta, Canada. Updates are posted regularly at www.ctotf.com.

The recent Fall Turbine Forum and Trade Show (September 26-30) in Portland, Ore, typifies the group’s meetings, which run five days (Sunday through Thursday) and include networking functions, presentations on technical and managerial topics of interest to all users, roundtables dedicated to specific GT models, and a vendor fair. A robust program for spouses and significant others is unique among user groups.

Monday’s general session for all users included an open user forum and prepared presentations on the following subjects:

  • Laser imaging for hydrogen leak detection, Don Sparrow, Equipment Imaging & Solutions Inc, Kaufman, Tex.
  • Renegotiating long-term service agreements, Jeff Fassett, IEM Energy Consultants Inc, Alexandria, Minn.
  • Developing an effective maintenance program for electric generators, Bill Moore, Braum van Herwaarden, and Jane Hutt, National Electric Coil, Columbus, Ohio.
  • Improving operational excellence via turbine oil selection and treatment, Vatsal Shah, Shell Global Solutions (US) Inc, Houston, Tex.

Tuesday was dedicated to the Siemens Westinghouse roundtable and companion users-only forum. Alstom, GE aeroderivative, FT-8, and legacy roundtables were conducted on Wednesday. GE and Pratt & Whitney roundtables completed the program on Thursday.

Finding generator hydrogen leaks

At best, a hydrogen coolant leak in a generator is a nuisance and an extra operating expense. At worst, leakage is sufficient enough to be a safety hazard. Don Sparrow, Equipment Imaging & Solutions Inc (EIS, www. sf6detection.com), Kaufman, Tex, filling in for colleague Mark Baird (eisir@aol.com, 972-979-2078), gave a practical presentation on a relatively new leak-detection method for generators (patent pending)—one using sulfur hexafluoride (SF6) as a tracer gas.

The technique, developed for the military to identify the presence of lethal gases, was first applied commercially to pinpoint leaks from SF6-insulated high-voltage breakers. Note that the Electric Power Research Institute (EPRI), Palo Alto, Calif, was involved in the early efforts to adapt the technology for commercial use. The leak detection method is based on backscatter/ absorption technology and relies on an active scanning laser to provide a directed energy source to irradiate a target area.

Sparrow explained that the laser beam is reflected back to a source camera tuned to a specific frequency band. SF6 has high affinity to absorb this frequency of energy and appear as a dark cloud on the camera’s monitor (Fig 1). The image on the monitor provides a direct indication of how serious the leaks are by the size and darkness of the tracer-gas cloud.

Equipment is portable and manageable by one service technician, he continued. It consists of the laser camera (Fig 2) and monitor/recorder, plus a power pack, bottle of SF6 gas with regulator, an industrial weight scale, and small fan.

Conventional generator leak detection methods involve purging the generator with air and bringing it up to normal operating pressure and monitoring pressure decay over a 24-hr period. If the calculated leakage rate based on test data is higher than recommended, a bubble test is conducted using soapy water or similar solution applied over all areas where leaks might occur.

The process is time-consuming because each time a leak is located— this assumes that the leak can be found, which is not always true, according to Sparrow—and repaired, another day-long air test is required to confirm that the hydrogen system is at an acceptable leakage rate.

Alternative methods have involved using helium tracer gas and sonic detectors, continued Sparrow, but they take considerable time to implement and identifying the exact location and size of the leak are challenging at best. Note that SF6 is an unregulated greenhouse gas; however, for the quantities used to conduct a test, it has virtually no impact on the environment.

Conducting the inspection on a generator that is off-line is relatively simple and only takes from four to six hours on average. First, hydrogen is bled from the cooling circuit. Next, the SF6 bottle is placed on the scale and connected to the hydrogen supply header and the regulator is set to 10 psi above operating pressure. Compressed air containing 5% SF6 is injected until the normal operating hydrogen pressure is reached. The generator then is scanned with the camera to identify leaks (Fig 3).

Sparrow added that it also is possible to inject small amounts of tracer gas into the hydrogen coolant while the generator is in operation. However, hydrogen purity must be maintained to OEM specifications.

Leak-checking using SF6 tracer gas has been accomplished successfully at several plants, according to Baird, in a telephone interview with the editors of the COMBINED CYCLE Journal. The editors followed up with Phil Poytress at the Calhoun peaking plant in Alabama, home to four Frame 7FAs manufactured by GE Energy, Atlanta. Poytress said they had a leak in one unit that was of concern because of the hydrogen replacement cost.

It couldn’t be located with a standard bubble test but the SF6 tracer found the leak quickly. Use of alternative test methods is mandatory at the plant prior to using SF6 because the environmentally conscious owner is concerned with adding even relatively small quantities of greenhouse gas to the environment. Worthy of mention is that the unit was still under warranty and GE both approved and paid for the test.

Jim Dixon, VP of gas generation/ generation support for TXU Power, said the Dallas-based utility has used the SF6 leak-detection method on selected occasions to locate leaks in generators at its steam plants. He said that the company learned about the technology through EPRI and worked with EIS to evaluate its potential for practical powerplant application.

TXU Power normally relies on conventional procedures (typically, an air leak-down and bubble test) for its “suitability for service” test, but will specify the SF6 tracer when a leak can’t be found. Dixon said that one leak stumped everyone until the SF6 tracer located it in the hydrogen supply piping. That first job convinced the utility that this is a viable technique.

How to evaluate your LTSA

Jeff Fassett (fassettj@concentric. net, 320-846-5255), president, IEM Energy Consultants Inc, Alexandria, Minn, is respected for his knowledge of plant operations and long-term service agreements (LTSAs). The former plant manager began by reviewing the reasons for the initial popularity of LTSAs and why you might want to challenge that reasoning today.

The portion of Fassett’s presentation that appeared to be of greatest interest to the CTOTF community were the questions you must ask and then answer to organize the information needed for a “continue or cancel” decision on an existing LTSA and/or to decide on the type of LTSA that best serves your facility’s needs.

In the early 1990s, Fassett began, the sophistication of GTs took a quantum leap forward with firing temperatures sufficiently high as to require exotic alloys, complex component designs, and dry combustion solutions to NOx control.

Infant mortality issues soon were evident with the new engine designs, he said, and many owners entered into LTSAs primarily as a risk-management strategy. Keep in mind that dozen or so years ago few plant personnel had experience in the maintenance and repair of Fclass frame machines, and information on maintenance costs and the availability and cost of spare parts were relatively unknown. Others, continued Fassett, simply purchased LTSAs because the thought leaders in the industry had them; most of these buyers made decisions without careful analysis of LTSA provisions.

Rethinking of the value and provisions of LTSAs began perhaps in the late 1990s when watershed events— think California and Enron here— that would change the face of the industry first occurred. Plants originally projected to run 6000 hours and have 100 starts annually were operating in the neighborhood of 1000 hours with 250 starts. Pro formas fell far short and plants were put on the auction block or returned to lenders and new owners carefully re-evaluated LTSAs. Lines started forming, recalled Fassett, to renegotiate LTSAs or to cancel them outright.

Ears perked up in the audience when Fassett presented a chart that indicated 95% of the relative value in LTSAs (based on his involvement in such agreements with a total value of more than a quarter of a billion dollars) was connected to the GT. Also, that a typical cost breakdown for an LTSA shows 70% for parts, 20% for shop repairs, and 10% for field services. Thus one can infer that perhaps many conventional LTSAs are of greater value to the OEM than to the power producer they theoretically are designed to help.

As the experience base with advanced engines builds and parts become available from third-party providers, no wonder so many plant owners are reconsidering the value of and/or need for LTSAs. It’s somewhat analogous to auto insurance: As leases expire and vehicles age, it is common for owners to cancel the “big ticket” items in their policies— collision, for example.

Fassett suggested that you consider the following questions to assist in evaluating your plant’s LTSA:

  • What is the cost of selfperformance? Benchmark to learn just how “good” your LTSA “deal” is. A life-cycle cost analysis is necessary.
  • What skills are available inhouse? Do you have millwrights, for example? Can your personnel work for the OEM to cut costs?
  • What skills are you willing to pay others for?
  • Are there other options available?
  • Do you have adequate resources, both in terms of man-hours and experience, in-house to assist with negotiating the contract?
  • Are there sufficient resources available in-house to cover the “owner’s responsibilities”?
  • How long is long enough? Can you exit a non-performing contract? What off-ramps do you have?
  • How will the plant be operated and what if the operating profile changes?
  • Are there any fleet issues that must be addressed through the LTSA?
  • Who covers “extra work”?
  • What about warranty provisions?
  • Who covers “fall-out” risk? For example, if you send parts to a shop for repair and only half pass inspection for repairability, who’s responsible?
  • What about consequential or collateral damage?
  • Do you want or need performance guarantees such as availability, reliability?
  • Do you want to commit to upgrades during the life of the contract? You probably want to think long and hard about allowing the OEM to insert beta-test parts in your machine. If they’re not “commercially available” your insurance coverage may not be valid.
  • What will the market for parts and services look like in the future? If your third-party supplier can’t provide the parts needed, expect to pay inflated amounts for what you must order from the OEM.

In wrapping-up, Fassett suggested that you pay particular attention to incentive and bonus clauses in the LTSA, keeping these guidelines in mind:

  • Offer bonuses only for exceptional performance.
  • Incentivize direct performance.
  • Be wary of incentives that might provide improper motivation.

Finally, he reminded all that the goal of LTSA providers is to “get a slice of your pie.” This is fine, he said, provided you derive commensurate value from the service. Be sure, Fassett concluded, to structure payments to fit your project. Options include up-front fee, pre-outage, power by the hour, levelized, periodic, bonus. Examples: If you run base-load, a monthly payment may make the most sense for you; intermittently, only make LTSA payments when you run.

Generator maintenance

Generators are commanding significant attention at GT user group meetings these days because of recurring problems—sometimes caused by inattention to a machine “taken for granted.” Bill Moore, PE, engineering manager at National Electric Coil, Columbus, Ohio, conducted a back-tobasics lecture at CTOTF that outlined the goals and key elements of an effective generator maintenance program. He then illustrated by way of photographs what happens when machine components are not properly cared for.

Moore began by mentioning some of the reasons many PM programs are not up to par:

  • Inspection and repair records lost, misplaced, misfiled as a result of a change in plant ownership.
  • Experience gap caused by the loss of key people through workforce reductions.
  • Less money allocated for equipment diagnostics, maintenance, and upgrades.

Not your fault, Moore continued. But you still are responsible for the equipment in the plant you manage and maybe there is good reason to review the key elements of a generator PM program as a benchmark against what you are now doing.

An effective PM program for generators includes three key elements: (1) inspection, (2) data collection and recordkeeping, and (3) testing. The information compiled is then used to initiate corrective action before failure.

To accomplish these goals effectively, said Moore, requires the following:

  • Clearly defined responsibilities.
  • Sufficient time for inspections.
  • Well-defined schedules for testing and maintenance based on equipment age, service demands, operating conditions, and safety requirements.
  • Established procedures.
  • On-going data trending and recordkeeping.

The last item is not a rote exercise. The person you assign to this task must have at least passing knowledge of generator failure modes and how to acquire more quickly when needed. Reason for this is obvious: Your trend-spotter must be able to identify data that correlate to failures. Also, once a trend indicates impending failure, they must determine the steps necessary to correct the problem and when this must be done.

To help you objectively evaluate your facility’s generator PM program, Moore offered these guidelines:

Standard equipment monitoring

  • Temperature: Monitor continuously, to ensure it is within manufacturer’s limits.
  • Grounds: Continuously, to guard against insulation failure.
  • Vibration: Continuously, to identify bearing problems, loose components, possibility of imminent failure.
  • Lube oil analysis: Semi-annually, or more often, to check for contamination and indications of bearing babbitt deterioration.

Visual inspection

  • Stator winding: Look for dust, grease, oily surfaces, broken ties, discoloration, and foreign object damage before every outage to help determine scope.
  • Stator core: Inspect for damaged iron, loose iron, discoloration, and foreign objects during every major outage with the rotor out.
  • Rotor: Look for discoloration from overheating, loose or shifted blocks, and arcing during every outage with the rotor out.

Stator electrical tests

  • Insulation resistance or “Megger” with PI (Polarization Index, to determine presence of contamination, every outage.
  • Winding resistance, to verify integrity of brazed connections and find broken conductors, every outage.
  • Hi-pot, to “stress” insulation to prove its integrity, every major outage.
  • DC ramp, to determine insulation strength, every major outage.

Rotor electrical tests

  • Insulation resistance or “Megger” with PI, to determine presence of contamination, every outage.
  • Winding resistance, to verify integrity of brazed connections, every outage.
  • Flux probe, to identify shorted turns when the unit is in operation, annually.
  • Pole balance, to identify shorted turns when the unit is stationary, every major outage.

Specialty tests

  • ELCID (Electromagnetic Core Imperfection Detection), to identify shorted laminations, every major outage.
  • Core loop, to detect shorted laminations, after rewinds or core repair.
  • Wedge tightness, to locate loose wedges, every major outage.
  • Partial discharge, to identify insulation deterioration and verify coil tightness in slot, yearly.
  • Bump, to detect end-winding resonant frequencies, every major outage.

NDE tests

  • Magnetic particle, to locate surface cracks in magnetic steel components, fans, rings, wedges, shaft, coupling, and hubs, every major outage.
  • Dye penetrant, to find surface cracks in nonmagnetic parts, fans, rings, and wedges, every major outage.
  • Ultrasonic, to pinpoint interior cracks in metal components, rings, and shaft, every major outage.

Turbine oil selection

Vatsal Shah, a technical services team leader at Shell Global Solutions (US) Inc, Houston, spoke about improving the availability of rotating equipment by doing a better job managing lube-oil quality. This is to help avoid such nagging problems as varnish and deposit formation.

Shah captured the audience’s attention by noting that over the last several years there have been significant changes in turbine oil formulations offered by the major suppliers. He suggested that careful evaluation and screening of additives are necessary to ensure proper oil performance. In any system, Shah continued, turbine oils will degrade over time and understanding the degradation process and ways to predict problems before they occur are important for any plant with a goal of maximizing operating time.

Periodic testing of lube oil is, perhaps, the best way to monitor its quality. A rundown on the various tests you should conduct, and when, is presented in “Maintain lube oil within spec to ensure high reliability,” COMBINED CYCLE Journal, Summer 2004, available at www.psimedia.info/ccj.htm.

SWPC has biggest OEM presence

Siemens Westinghouse Power Corp, Orlando, was a principal in the vendor participation at the CTOTF meeting. Its full-day roundtable, the only conference session scheduled for September 28, included presentations by senior managers such as Phil Karwowski, director of GT service engineering, who addressed W501F topics; Gary Hensley, manager of field NDE development, who covered new diagnostic tools; and Project Manager Dr Volker Thien, who flew in from Germany to update participants on VX4.3A engine upgrades.

W501F topics. First item on Karwowski’s agenda was W501FD modifications to remove hot-restart limitations . Karwowski ( phil.karwowski@siemens.com, 407-736- 5630) explained that this machine was originally designed (circa 1990) for base-load service and that cycling duty was not anticipated. Karwowski discussed the effects of hot restart or spin cooling observed on some of the units as originally designed—including some control-system limitations.

Karwowski indicated that SWPC has removed limitations on hot restarts for some units that have increased clearances and added abradable coatings (Fig 4) and honeycomb seals (Fig 5). He added that the performance impact of any potential rubbing of these abradable coatings during hot restarts is likely to be minimal.

DLN pilot. Karwowski next updated the group on the company’s DLN gas-only pilot nozzle, now in service on six W501Fs and running as well at full-scale on the Siemens test rig in Berlin. This fully instrumented engine continues to verify Siemens’ expectations for the technology, the group was told. For more information, see COMBINED CYCLE Journal, Summer 2004, p 83, available at www. psimedia . info/ccj.htm (click on 501D5/ D5A Users).

The effects of high-frequency dynamics were discussed, along with the reasons for HFD and measures that can be taken to help mitigate the phenomenon. These have included bringing the unit up to full load as quickly as the manufacturer’s guidelines allow and, in some cases, the use of resonators to dampen the offending frequencies.

Low CO. SWPC also is working on strategies for reducing CO emissions during startup and low-load operation in response to customer requests. Tests of a new support housing have indicated CO reductions of up to 50% at loads to 30% of the full-load rating. Karwowski also said that new fuel nozzles and changing the position of inlet guide vanes can contribute to lower emissions. Work on recirculation of compressor air also may yield a benefit, he added. Changes to achieve lower CO emissions can be implemented during any combustor inspection, Karwowski continued.

SWPC’s combustion dynamic monitoring system is designed to actively control fuel flow to the pilot to maintain the lowest NOx level possible when fuel composition changes. Also, to back down the machine if combustion dynamics are abnormal, with a potential positive effect on parts life and life-cycle cost. For more information, see sidebar in the “Notes from the exhibit hall” segment of the 7EA Users meeting report elsewhere in this issue.

Wet compression is gaining real-world operating experience on a W501F machine in South America. The power increase for that unit has been measured as high as 20 MW at 90 gpm. For more information on wet compression see COMBINED CYCLE Journal, Spring 2004, p 47, available at www.psimedia.info/ ccjarchives.htm.

Repair technology. Karwowski also covered repair upgrades and enhancements for W501F components. This presentation included discussion of transition repair enhancements, row 1 vane repair and upgrades, and rows 1 and 2 blade repair and upgrades.

After a review of SWPC’s repair facilities and their capabilities, Karwowski dug into the subject of transition repair to help extend component life. Transitions typically are removed after 8000 operating hours, stripped, and recoated and new exit nozzles installed. SWPC has developed new transitions that are intended to last longer between overhauls— perhaps up to 12,000 hours.

Karwowski gave some examples of distress that limit transition life and cited repair developments that can help address the life limiters. These include:

  • Oxidation, cracking, and wall thinning of uncoated areas caused by strip-masking of cooling holes: Laser cleaning and pin-masking of effusion cooling holes, and polymer masking of cooling-channel holes.
  • Thermal distortion and loss of material strength properties caused by high operating temperatures over time: Use Trans- Coat™, TransCool™, and Trans- Shield™ treatments.
  • Wall thinning caused by using the grit-blast stripping method: Change to chemical stripping.
  • Fretting wear on exit face caused by contact with floating seals: Apply hardface coating to exit face.
  • Slot-cracking of inner-seal rail seal: Implementation of innerseal slot design change.

Karwowski suggested that users interested in extending row 1 vane life consider Siemens’ SICOAT 2464. He said that this bond coat is specified to tolerate temperatures 90 deg F higher than the bond coating formerly used. The durability enhancement, he said, can help virtually eliminate shroud burning. It can be used with either Siemens or other commercially available thermal barrier coatings.

NDE tools. Gary Hensley (gary. hensley@siemens.com, 724-387- 7235) manager of field NDE development, discussed methods and tools for nondestructive examination of GTs that are available for use now as well as some under development. These tools are not for sale. Rather, they are used by SWPC field service personnel under contract to users.

Hensley said that SWPC developed advanced diagnostics to reduce outage duration and cost and to increase unit availability. His message was simple: “Lift the cover only after you try the latest diagnostic tools and find that they can’t provide the information you need.”

Two tools that have proved their value in two years of commercial service inspecting both gas and steam turbines are a high-temperature borescope and EddyVision™. Former permits visual inspection shortly after shutdown. Its video system delivers high-quality images that specialists can evaluate immediately to recommend appropriate service measures.

Specifically, the borescope is designed for use when turbine internal temperatures drop below 1000F, thereby eliminating up to eight hours of cool-down necessary to accommodate standard instruments of this type. For a quick verification, the high-temperature borescope can survive at 2100F for 15 seconds. The rigid instrument comes in lengths up to 10 ft, permitting inspection of transition pieces, combustor baskets, and first-stage blades to proceed while the machine is on turning gear.

EddyVision is a remote eddy current/optically enhanced inspection system that allows a qualified specialist to examine, analyze, and validate the existence of indications detected by visual inspection methods. Keep in mind that what you see in a pure visual inspection may not be what you think.

Hensley said that EddyVision has saved users from “lifting the lid” at least a couple of times because it simultaneously displays both the borescope visual signal and the eddycurrent test results. It allows the specialist to examine and develop a complete condition assessment with minimal tear-down. For special situations, in-situ black light/dye penetrant capability also can be linked into EddyVision.

Work in progress includes the so-called Global Inspection Systems (GIS), eddy current inspection of turbine disks, and conductivity testing of compressor blades. The GIS is an enhanced NDE vision system with flexible borescopes that permit inspection—when the unit is cool and off turning gear—of all exposed surface areas in the compressor inlet, compressor proper, combustor, and turbine vanes and blades.

It can be used in conjunction with a rigid borescope when the unit is on turning gear to inspect all exposed surface areas of the rotating blades—provided the machine ambient is 350F or less. Benefit of the system is that its high-quality electronic images can be transmitted instantly for analysis by experts in remote locations.

A new eddy current device specifically designed to inspect rows 1 and 2 turbine disks is in trial use on W701DA and W501D machines (Fig 6). It eliminates the need for magnetic particle inspection in critical areas, ensuring more complete and accurate inspections without disassembling the machine.

Conductivity testing of compressor blades facilitates inspection of custom blades and can verify the extent of damage to blade tips that have been rubbed. A further goal being pursued is to allow verification of cracking and/or pre-crack initiation (Fig 7).

VX4.3-A upgrades. SWPC presented the details on a compressor upgrade for the V94.3A designed to increase mass flow and the potential for an increase in power output of up to 3%, as well as a slight increase in efficiency. Dr Volker Thien (volker. thien@siemens.com, +49 (208) 456- 2800) said the upgrade has been successfully implemented and operated for more than a year on 50- Hz engines. The same upgrade is now available for the 60-Hz frame (V84.3A) as a scaled version. The upgrade includes the exchange of inlet guide vanes (IGVs) and the first four rows in the compressor.

In combination with the compressor upgrade, Thien continued, a retrofit package designed to allow turndown to less than 50% of rated load in the dry low-NOx mode also is available. With this turndown package, also derived from the 50-Hz frame unit, compressor mass flow is reduced by closing the IGVs below the current setpoint.

A third upgrade available is the socalled hydraulic optimization package, which Thien said is designed to increase both power output and efficiency. With this upgrade, the compressor bearing is modified and retrofitted with additional pistons that enable a shift in rotor position during steady-state operation—even at base load. By shifting the rotor in the direction of the compressor, clearances in the turbine section can be optimized and losses reduced.

Thien stressed that all the mods present often can be accomplished during a major outage.

Other OEM roundtables

Legacy Roundtable

The legacy roundtable at CTOTF, which was called to order by Vice Chairman Steve Hedge of Texas Genco Holdings Inc, featured a workshop conducted by Charlie Pond and Dave Lucier (dave@pondlucier.com, 518-330-4801), two former GE field engineers, who are the principals at the firm that bears their names. Pond and Lucier LLC (PAL), Clifton Park, NY, specializes in improving the value of aging GT assets, offering fuel conversions, modifications and upgrades, reconditioning of hydraulic and fuel system components, and a host of other field engineering services.

The PAL workshop specifically addressed (1) troubleshooting GTs with fuel regulator controls, (2) controls upgrade for the MS5001L, and (3) troubleshooting Speedtronic ™ Mark I control systems for the MS5001N and MS7001B-C.

Troubleshooting GTs with fuel regulator controls focused on MS3001, MS5001D-LA, and MS3002B-F machines manufactured from 1949-1969. Lucier stressed the value of “cranking tests”—unfired tests that allow you to check the fuel regulator, fuel pump stroke, and gas control-valve stroke. He reviewed how this is done and what data should be recorded. Expected values were stated to provide a benchmark for all users in attendance.

Next, he covered the auxiliaries that are checked during cranking tests—diesel engine, hydraulic ratchet, jaw clutch engagement, torque converter, and dc starting auxiliaries—and what to look for/ listen for during the test. Examples: Check that the diesel actually starts after a 30-sec warmup delay, verify that the jaw clutch engages, etc.

Pond and Lucier’s PAL5000™ is an alternative to a complete control system upgrade. The package includes a PLC (programmable logic controller) by Horner Electric, the OCS-200 from GE Fanuc’s product line, PAL’s application software, and programming language by Cscape. A primary feature of the retrofit product is that the fuel regulator, said Lucier, remains “in charge,” taking signals—such as fire, accelerate, etc—from input signals from turbine exhaust thermocouples, compressor inlet/outlet pressure, turbine speed, etc.

The PAL5000 can be fully tested and calibrated at cranking speed, added Lucier, and it permits retention of the existing fuel regulator, fuel pump, gas pressure ratio valve, gas stop/control valve, and flow divider. Antiquated components are eliminated or replaced—including thermocouple averaging cabinet, millivolt amplifier, electropneumatic transducer, speed relays, timers, undercurrent relay, auto-load controller, etc.

Troubleshooting Speedtronic Mark I control systems for MS5001N and MS7001B machines made from 1970 to 1973 was particularly valuable given the large number of these machines still in peaking service— such as those units installed on barges off Brooklyn, NY, in the East River.

Lucier’s comprehensive library of photographs showed equipment details and how to prepare and conduct troubleshooting tests. GE’s Speedtronic “calibrator” allows testing of the Mark I panel—including startup simulation, and monitoring and testing during actual startup and operation.

Lucier stressed that approximately 90% of the circuits can be tested and calibrated without running the turbine; only fuel system calibration requires cranking, and firing can be simulated without fuel flow. Simulation of startup and operation of the plant can be accomplished in about four hours, he said, adding that such simulation also allows observation of auxiliary relay actions.

Alstom Roundtable

Chairman Ed Sundheim (espower@att.net, 973-347-3633), chair of the Alstom roundtable and president, ES Power Support Services, Andover, NJ, reported that the CTOTF information exchange among users was directed primarily at the manufacturer’s GT11, N, N1, N2, and NM models.

Sundheim said the discussion in Portland focused on generators—two users presenting reports about recent failures. Last spring’s meeting, by contrast, concentrated on corrosionrelated compressor failures associated with the GT11N/N1 machines and the action required to prevent them—including non-Alstom options for replacement components with improved corrosion resistance.

Participants in the fall meeting were aware of several generators that failed similarly to the ones described in the case histories presented. Sundheim described the problem as one of in-service failures of the copper clamping lugs that connect the generator’s stator winding bars to their radial leads. To present a virtual image of the failure, Sundheim suggested imagining six large copper S-shaped lugs with one end connecting to the radial lead and the other end to the stator winding bar. The failures known to the CTOTF group all have occurred in the middle of the S curve—the point where flexing causes maximum fatigue.

The failures, Sundheim added, initially were attributed to the manufacturing process although subsequent user-driven investigations indicate that winding vibration and lax QC may have contributed to the problem. Replacement lugs were characterized by improved metallurgy and machining that did not create stress risers. This fix proved inadequate for at least some situations, continued Sundheim, and a lug design in the shape of a lower-case “b” (shaft connects to the radial lead and lower loop surrounds and clamps to the end of the winding bar) was offered as a substitute for the S bend. The jury is still out on this design.

Obvious from the foregoing is the considerable value offered by usergroup meetings. Unless you attend, you cannot network effectively to get the answers and experience that permit making the right fix the first time, thereby reducing O&M cost and maximizing availability.

FT-8 Roundtable

Roundtable Chairman Richard Evans, the plant manager at the 250- MW Wolf Hills Energy LLC facility, Bristol, Va, owned by Constellation Energy, couldn’t be more positive about the progress made by the CTOTF FT-8 group in “connecting” users with the OEM, Pratt & Whitney Power Systems.

Evans told the COMBINED CYCLE Journal that Constellation has a robust fleet of 22 FT-8 TwinPacs (including five at Evans’ Wolf Hills plant) and the company wanted to form a user group in 2001. “We believed that the simplest way to achieve this goal,” he continued, “was to organize the group within the CTOTF. It was clearly a win/win opportunity because the organization already had the administrative infrastructure in place and an excellent reputation in the industry.”

Evans said the group began with a half-day session but now, with the support of Pratt & Whitney, conducts two half-day sessions. One is a user-only session, the other a collaborative effort between the users and the OEM. Typically, Evans added, the users identify issues that require answers and forward a list of questions to Pratt & Whitney about one month in advance of the meeting. Pratt & Whitney then provides answers to the questions at the conference. Note that the Pratt & Whitney session will be expanded to a full day at the CTOTF spring meeting in Annapolis, Md.

At the spring 2004 conference in Savannah, the user discussion focused on the lube oil system, including a generic pump failure issue. The FT-8 users, Pratt & Whitney, and the pump manufacturer were able to work closely together to identify the causal factors of the failures. To correct the problem, a thrust bearing was added and preliminary results indicate that the problem has been solved. The pump manufacturer has offered the upgrade at a modest cost to the user. The idea of having an additional backup pump in stock was discussed as part of an action plan until all pumps are upgraded with the new design.

Lube-oil quality also was part of the discussion and the need for a focused test plan supported by the group. (For more information on this vital subject, consult “Maintain lube oil within spec to ensure high reliability,” COMBINED CYCLE Journal, Summer 2004 Outage Handbook Supplement, available at www.psimedia. info/ccj.htm.)

The half-day segment with Pratt & Whitney participating included an update of open issues from the spring meeting, details on a new site audit plan from the OEM, identification of new issues, responses to submitted questions, and group discussion. Perhaps the most nagging user issue, said Evans, was concerned with power turbine vibration. The OEM is addressing this concern.

Jerry Mc Cormick ( jerry. mccormick@pw.utc.com, 860-565- 6935), Pratt & Whitney’s customer service manager, spoke for about 20 minutes about a new service offered by the company to maintain high availability and starting reliability: an annual site audit. It takes a service team about three days to conduct the needed inspections and run diagnostics.

The process begins with a review by a Pratt & Whitney engineer of operating data prior to the site visit to check GT performance. The information gleaned from that investigation aids in planning the site visit and identifying the test work required. On-site work typically includes the following:

  • Interview operating personnel regarding operational abnormalities, etc.
  • Inspect control enclosure.
  • Inspect GT enclosure.
  • Borescope both GTs.
  • Check calibration of critical sensors.
  • Conduct full-load test run on all fuels.
  • Test overspeed protection.
  • Debrief customer prior to exit.
  • A comprehensive audit report is compiled after the field work is complete. It includes test data, observations, and recommendations.

Aero Roundtable

The CTOTF aero roundtable is chaired by PSEG Fossil LLC’s Richard Rebori, a senior plant engineer with responsibilities at multiple peaking locations for FT4, LM6000, and Frame 7EA machines. Vice Chair Dave Murray, also from PSEG Fossil, is production manager for the company’s Linden combined cycle.

Rebori said that about two dozen users participated in the roundtable, which focused on the LM6000. GE Energy’s (Atlanta, Ga) Gerry Babic was in attendance to review recent product and service bulletins associated with this machine and to discuss upgrades—including the enhanced Sprint package for power augmentation— and uprate packages. Part of the discussion was on new software to reduce nuisance trips.

GE Roundtable

GE Roundtable Chairman Bob Kirn of Tennessee Valley Authority covers a lot of territory in his CTOTF meetings—all frame machines manufactured by GE Energy, including those not represented by model-specific user groups. Kirn’s group meets for a full day and his challenge is to balance the discussion to cover issues of importance to all participants as well as those specific to certain models.

At the fall meeting, attention focused on the 7EA—specifically row 1 compressor blade failures, exciter issues, and flame detector reliability. Generators remain a topic of concern across all GT models; technical presentations were made during other segments of the CTOTF forum. Technical issues concerning balanceof- plant equipment also generated considerable discussion.

Kirn said that a goal of every meeting is to help expand the knowledge base of the attendees. In Portland, he engaged Hans van Esch (hvanesch@teservices.us, 281-291- 0447), Turbine End-User Services Inc, Houston, to provide a presentation on GT metallurgy and key aspects of parts repair. Van Esch is an expert on the subject and periodically conducts a three-day seminar on metallurgical aspects of industrial GT component refurbishment. It includes materials fundamentals, superalloys, heat treatment, degradation mechanisms in hot-gas-path components, coatings, stripping and cleaning, welding, brazing, inspection/ NDE, and lots of case studies.

From this course, van Esch extracted material specific to strengthening (grain, solution, precipitation) of materials, use of iron, cobalt, and nickel in materials formulations to accommodate the GT’s demanding operating conditions, topologically close packed phases that weaken superalloys, the ins and outs of heat treatment, etc. Much ground was covered in very short time.

Kirn said the presentation was very well received and that he hoped to continue the program at future meetings with presentations on due diligence of repair vendors and repair processes, as well as on preparation of repair work scopes. CCJ