7FUG 2020: Special Technical Presentations

One of the unique aspects of the 7F Users Group’s 2020 Digital Conference was the opportunity to interact online with nearly 50 third-party solutions providers. Ten of these companies were selected by the steering committee to conduct live Special Technical Presentations of one to two hours during Weeks Two, Three, and Four of the five-week program ending July 16. The remaining solutions providers participated in the conference with virtual booths in the Vendor Fair, conducted Tuesday and Wednesday of Week One. They connected directly with users via video (or audio) links.

In case you missed the opportunity to visit with one or more of these companies, the editors provide below summaries of the products/services they promoted at the meeting. The names of experts to contact for details are included.

More importantly, all supplier presentations are available to owner/operators in the Power Users Presentations Library. However, you must be registered on the website to gain access. This is a simple process.

As generators age and unit cycling increases bad things can happen

AGT Services’ Jamie Clark has been on a mission for the last couple of years presenting at the annual meetings of all major users groups to alert owner/operators about the significant increase in generator failures his company and other service firms are seeing. These failures are related in large part to unit cycling and age, with lapses in attention to detail during inspection and maintenance contributing. Recall that most generators at 7F combined-cycle plants were designed for baseload, not cycling, service.

Clark’s presentation at the 7F Users Group’s 2020 Digital Conference, “Five Minor Generator Inspections Turn Into Three Majors for Repairs,” illustrated the dramatic increase in the amount of emergent work some users are experiencing and its costly impact on both maintenance budgets and schedule.

His 7F presentation was similar to one he gave in June 2019 to the Frame 6 Users Group, attesting to the existence of an industry-wide problem, not one affecting a given frame.

Clark began his 7F presentation with a chart illustrating the dramatic increase in the number of starts experienced by a combined-cycle plant in Maine in the last decade compared to the start stats for the facility’s first eight years of service. He then polled attendees, asking how the number of starts in the last 10 years compared to years earlier at their plants. Nearly one-third of the users reported up to a 50% increase in the number of starts; 11% said their starts had doubled; 3% said starts had more than doubled.

Next, he asked the users to share their most common “unplanned” stator repair/upgrade finding during an outage. If you think it is endwinding dusting/greasing or resonance repair, you’re correct. Well over half the respondents said “yes” to that. Other choices were belly-band tightening or new install, stator re-wedging (full or partial), and stator core looseness.

Clark then highlighted the primary areas of the stator affected by cycling, including the following:

  • Endwinding vibration/loosening, noting the higher risk for strand-to-strand series connections.
  • Core looseness impacts, such as keybar rattle/belly bands and loss of core compression.
  • Slot support system—including wedge system and side packing/ripple springs.

The speaker stressed that all stator parts are designed to work together as a system. Example: Bellybands restrain keybars and when loose allow keybars to “rattle” producing iron oxide particles. Add in some oil and you have greasing that lubricates the connections, further compromising tightness.

Later Clark would address the many areas of concern cycling poses for fields—including slot component migration, turn insulation migration, copper distortion, braze failures, issues with collector systems, and brushless exciters.

There’s much you can learn from industry generator O&M experience to improve the reliability and availability of your plant. If you were unable to participate in the AGT Services session, access the recording on the Power Users website. How much you learn in only one hour might be surprising.

Come up to speed on today’s turbine tooling

Plant personnel are always challenged to perform outages faster, safer, better than previously; improved tooling might be one way to help you achieve those goals. But it’s difficult to keep up with new developments in a demanding plant environment. A virtual conference benefits in this regard, facilitating learning via field videos of actual work and simulations.

Enerpac had three experts—Mike Beres, Chris Stocker, and Phil Giagnacova—presenting on tooling solutions during its 1-hr session at the 7F 2020 Digital Conference last week. “Optimize maintenance: From turbine decoupling to rotor removal and alignment” was illuminating. It covered turbine-case removal, a safe and efficient coupling-bolt solution, turbine rotor removal, generator rotor removal, journal turning (field machining), etc.

The format was to review the “current state” of each of these applications and then demonstrate the “future state.” To illustrate: The current state of turbine-case removal relies on fixed slings and mechanical turnbuckles. The risks posed by these methods include working from height, ergonomic issues, large heavy components, insufficient adjustability. The future state using the equipment demonstrated focused on hydraulic turnbuckles and adjustable rigging beams. They permit precision adjustment and from a hanging load, allow control away from the lift, and have ergonomic benefit.

The company’s space-efficient ETCT (Enhanced Turbine Coupling Tool) solution was said to save more than six hours in tensioning a 7F coupling than the same job would take with a tool commonly used today. The time to tension joints on four 7FAs at one plant with current-state tooling was estimated at 32 hours. Enerpac tensioned the four units in just over nine hours. This is particularly impressive performance given 60% of users said coupling was on the critical path for their outage.

MD&A focuses on Mark VI/VIe controls, HGP parts, fuel nozzles, generators

MD&A divided its two-hour session last Wednesday into four parts so crammed with information of value to O&M personnel that having recordings of each segment available on the Power Users website benefits both those who missed the presentations and those who didn’t but want to clarify some points. The video format used is convenient, enabling you to identify the information you want quickly.

What follows is a TV Guide-type summary of the material presented:

  • A Mark VI/VIe presentation by Senior Controls Engineer Joe Clappis focuses on the Toolbox/ToolboxST trend recorder a/k/a trender. It is used for capturing and analyzing data and for troubleshooting—more specifically, for analyzing trip history data (hourly data between
  • trips/stops, trip display data, and information captured by the dynamic data recorder. If you’re unfamiliar with this tool, listen to the half-hour video. Clappis is a knowledgeable controls engineer, excellent presenter, experienced teacher, and patient. You might just be introduced to an element of the Mark VI/VIe that can save you considerable analytical time.
  • Lifetime extension of 7FA HGP components was covered by Engineering Manager Jose Quinones, PE. Life-limiting factors of HGP parts, lifetime extension steps, implementation of repairs, and upgrades/modifications/improvements are included in the presentation. Quinones moves quickly through this material and you may have to listen to him a second time to confirm specific points. Perhaps the most valuable portion of the presentation is case histories that begin with evaluation of field condition, repair options, possible improvements for life extension, and results.
  • Fuel-nozzle end-cover-insert life extension was discussed by GM Joe Palmer of MD&A’s Fuel Nozzle Services Div. He covered system and product lifecycle analysis, technical advancements and life extension, and testing and validation. The graphics used to explain the cracking issue, design enhancements, and repairs are of great value to the unfamiliar user.
  • 7FH2 field-winding shorted turns and groundwall failure by James Joyce, a generator specialist at MD&A essentially is a short course the explains what shorted turns are, what causes them, and how to test for shorted turns online and offline. The hot spots and thermal vibration that result from shorted turns are explained. Explanation of rewind and patch-repair options for dealing with shorted turns follows.
  • Groundwall insulation failure is explained in the second part of the presentation. Damage and causes are described along with the recommended repair.

There were two special live technical presentations during Week Three of the 7F Users Group’s 2020 Digital Conference—one by PSM, the other by Shell/Advanced Chemical Technologies—and one extended live technical presentation from Doosan Turbomachinery Services. The video recordings on the Power Users website (owner/operators only) bring you up to date on the products and services offered by these companies to help keep your plant safe, efficient, and reliable.

PSM presentation covers all

“What Else Do you Need from your 7F Power Plants,” was divided among Marc Paskin, senior technical lead, combustion and digital; Dr Alex Torkaman, manager, airfoils, upgrades, and rotors; Josh McNally, technical lead, combustion and digital; Tim Hui, manager, combustion and digital; Brian Loucks, technical lead, airfoils, upgrades, and rotors; Dr Greg Vogel, manager, technology programs; Dr Scott Keller, manager, airfoils, upgrades, and rotors; and Ian Summerside, global product manager for F-class and digital.

Technical topics covered during the one-hour seminar were:

  • FlexSuite and FlexRamp upgrades.
  • Gas Turbine Optimization Packages (GTOP™).
  • FlameSheet™ install successes.
  • Total flexibility with FlameTOP™.
  • Proven rotor management solutions.
  • Manufacturing for the future with additive manufacturing.

Shell/ACT knows varnish

“Varnish Mitigation—Not a One Size Fits All,” is a collaboration between Chelsea Bukowski (Kovanda), well known to F-class users, and Dr Robert Profilet. Recall that American Chemical Technologies Inc was purchased by Shell in December 2019. ACT and its team continues to operate the ACT business on behalf of Shell for a transitional period.

The video recording covers the following:

  • Introduction to Shell/ACT.
  • Lubricant selection/base stock evolution.
  • Mitigation methods for varnish.
  • Top-off fluids.
  • Fluid solutions.
  • Maintenance of turbine oils.

Doosan Turbomachinery Services

The company overview/capabilities presentation by Glenn Turner, VP engineering, will be of particular value to users who have not yet visited the company’s new Houston-area facilities and are not familiar with the company’s products and services for the 7F, including its DART (Doosan Advanced Re-engineered Turbine) program. Also see the AOG (Alstom Owners Group) section in this issue.

Turner opens with an overview of Doosan’s extensive facilities and engineering and manufacturing capabilities worldwide. He moves quickly through Houston’s shop capabilities— including a 7FA major rotor overhaul. The DART program’s technology upgrades for the 7FA.03 (compressor, combustor, turbine) will be of special interest to owner/operators.

Combustion hardware improvements include fuel nozzles and the combustion assembly; plus, the company’s auto-tuning solution. Upgraded designs of buckets, nozzles, and shroud blocks are part of the DART promise to deliver power and efficiency equal to or better than 7FA.04 AGP turbine components.

APG empowering solutions for years to come

The nondescript title of this presentation does no justice to its compelling content. A simple “Aaron Frost” would have told you much more. Yes, Frost was back in front of the 7F group sharing his encyclopedic knowledge of metallurgy, repair experiences on selected hot-section components, and views on the promise of additive manufacturing for new parts and for the rehabilitation of old.

Frost was the second of APG’s (Allied Power Group) three participants in the company’s hour- long sessionspeaking for three-quarters of that time. If you missed the presentation and have responsibility for the repair of hot parts for 7F engines, or simply want to add to your knowledge, access the video on the Power Users website; you’ll be glad you did.

Jeremy Clifton, VP sales and marketing, introduces APG and its recent acquisitions to attendees. Marty Magby, VP business development, follows Frost with an outline of how the company implements engine and plant overhauls to meet customer expectations.

Frost begins with a review of APG’s experience in repairing more than 100 sets of first-stage shroud blocks for the 7FA.03, illustrating some of the enhancements the company has made to extend parts lifetime and improve performance. One example he gave is to add full NiCrAlY side-face coatings on shroud blocks to prevent the oxidation uncoated tiles often experienced after only one service interval. Such oxidation was known to create gaps between adjacent tiles and provide a pathway for seals to go downstream and do damage.

Another enhancement is forward outer block shroud hook recovery which involves machining off the crack-prone original Type 310 stainless steel material and restoring the hook with Hastelloy S weld material followed by finish machining.

Final steps in the restoration of shroud blocks included dimensional checks, finish grinding, and application of a bond coat and a high-density thermal barrier coating on the tile face.

In concluding this portion of his presentation, Frost provides details on the repair of first-stage shroud blocks for the 7FA.04, illustrating how the company’s experience described above for the 7FA.03 qualified it to make Dot 04 repairs as well.

Frost links the shroud-block repair and additive manufacturing (AM) segments of his presentation, announcing that APG had successfully developed and printed a 3D 7FA.03 first- stage shroud tile. He is bullish on the future of AM for making critical gas-turbine parts but believes it will be years before it can be applied to mainstream production. An example he gave was that a single 3D tile for a 7FA.03 today takes about a day to make. Also, that commercial AM production equipment is incapable of making large parts—transition pieces, for example.

The big near-term advantage of 3D printing, Frost continues, is that single parts—such as shroud-block tiles—can be made and replaced, avoiding the need to purchase an entire row. Another advantage is that it’s possible to “print” the damaged section of a given part—second- stage nozzle, for example—and weld it into the original. Plus, the portion being replaced can be made with an improved combination of material, design, and coating changes such that the repair is better than a traditional weld or braze repair.

The final segment of Frost’s presentation discusses what he believes are design improvements to the OEM’s third-stage bucket which can extend the lifetime of these parts. He says that AGP has repaired 30 sets of third-stage buckets without a post-repair issue. Attendees were referred to GE Technical Information Letters 2006-R1 (for the 7FA.03) and 2045 (for the 7FA.04) issued relative to third-stage bucket failure potential.

One of AGP’s improvements is replacing the double-rail on original third-stage buckets with a single rail to reduce weight. Experience has shown this change can extend bucket lifetime from one HGP cycle to two. Also important to extending bucket life is AGP’s tight temperature control during heat treatment and a special fixture that allows vertical orientation of the buckets in the oven to maintain bucket integrity.

Learn about bolting and specialty tooling for large fasteners

Mike Dolan, Hytorc’s chief engineer for fasteners, had only a dozen slides and told the 7F audience at the outset that he probably would finish up in 45 minutes. Not! He barely got done in the hour maximum for his session. And it was all “good stuff,” including lessons learned and best practices of particular value to O&M technicians—an ideal presentation for a lunch-and- learn at the plant.

Proper tooling for bolting, he stresses, can make maintenance safer, faster, and more efficient than it is with the tools you might now be using. While acknowledging that most bolting work can be done with simple hand wrenches, Dolan continues, large fasteners require power tools to load and unload them. Gas turbines can be a particular challenge: They have large bolts, and long-term operation at high temperatures and loads exacerbates bolting challenges. He calls gas turbines “galling incubators.”

Dolan discusses torque control offered by powered wrenches and their safety attributes, and reviews hydraulic, bolt-heating, and mechanical tensioning. Galling gets deserved attention as does the company’s tension nut system which eliminates that condition.

Access this recorded presentation today; you won’t be disappointed.

A paradigm shift in gas-turbine lubricant maintenance

Presentations on turbine lubricants and/or their maintenance are oft-discussed subjects at user- group meetings. Plus, you can expect to see a half-dozen or more companies in the exhibit hall offering fluids and varnish-removal systems—all competing for your business. Having so much information from disparate sources can make it difficult for a user to decide on the optimal lubrication and treatment options for his or her plant.

How about starting anew? Listen to EPT’s Matthew G Hobbs who recommends that you treat your turbine fluid as an asset, not a consumable. You’ll probably make better decisions if you do, he says. Hobbs “knows his stuff” and has the sheepskin and experience to support his research and findings. Plus, he speaks clearly and is an excellent “explainer” of things you probably should know. The presentation is only an hour.

Hobbs encourages you to understand and use the tools at your disposal to eliminate unpredictable oil-related failures, which can cause astronomical unbudgeted expenses. His best- practices recommendations include these:

  • Select high-quality lubricants from reputable manufactures/suppliers.
  • Exercise caution with aftermarket additives.
  • Demand reliable oil-analysis data.
  • Use a conditioning system to remove varnish-precursors as they form.
  • Clean your oil so it can clean your system.

Hobbs shows by way of a case study how to keep your lubricant costs affordable and predictable. Recall that most owner/operators generally decide on fluid replacement when the acid number increases by two- or three-fold and additives decrease by 75%. In round numbers, this means that a nominal 10% annual rate of additive consumption equates roughly to a 10-year lifetime for your oil—assuming conditions remain the same over time. A polling question during the presentation indicated about half of the respondents were getting 10 years or less from their lubricants.

The details of a 10-year case study conducted by EPT for a plant using its ICB™ ion-exchange technology since COD to maintain the fluid in top condition, revealed an additive level at the end of a decade of service of 91%; the acid number has never increased. The oil is expected to serve for another 10 years—at least.

The paradigm shift, Hobbs says, is that by annually adding 5% top up with the existing brand of new oil, in conjunction with ICB conditioning, provides a step change in how the oil ages.

7FA LCI digital-front-end case history

John Downing, Turbine Controls & Excitation Group (TC&E), celebrated his company’s 10th anniversary at the 7F Users Group’s 2020 Digital Conference. He reminded the 300 or so owner/operators attending his presentation that many gas turbines are starting and stopping far more frequently than originally designed for. At the same time, independent system operators (ISOs) are imposing stiff fines for failure to meet startup and performance obligations.

Most plants have adapted to these more aggressive operating tempos and performance challenges, but one component that may be getting overlooked is the starting subsystem, especially for older machines equipped with a load commutated inverter (LCI).

Downing says that the Innovation Series™ and LS2100 LCIs, introduced in the late 1990s and early 2000s, consist of three subsystems, or functions: control section, silicon-controlled-rectifier (SCR) bridge section, and cooling section. For units not originally designed for lots of starts, it was common to have one LCI for multiple GTs, often in a one-to-two ratio.

For nearly 25 years, the LCI has provided reliable service. However, with an expected life of 20 years, many have failed, and a substantial number are at, or past, end of life. Failures usually are experienced in the controls and/or the cooling system.

Last production of the Innovation Series and LS2100 LCI controls supplied with GE machines was in 2013. Today, replacement parts are difficult to locate; acquisition times of four to six weeks are common. Also, qualified service and field engineering personnel are becoming harder to find as they retire out of the workforce.

Options to address this risk include the following:

  • Complete replacement of the LCI.
  • Locate, purchase, and inventory critical spare parts, especially those relating to the control and cooling sections, and identify the engineers and technicians qualified to make the replacements when the time comes.
  • Install a “digital front end” (DFE) control section replacement. In this case, the controls are replaced with a modern alternative that extends LCI life by 20 years.

TC&E partners with TMEIC, one of the world’s largest manufacturers of LCIs and drives, to provide a turnkey DFE solution that Downing says is far less expensive than the other two options.

Guts of the partnership’s offering are as follows: The obsolete programmable logic controller (PLC), standard VME (Versa Module Europa) rack, power supplies, and input/output (I/O) boards are replaced with new processor-based control circuit cards and a new PLC. The new digital controls fit in the existing panels and reuse most of the existing fiber optic cables and connectors.

The upgrade includes a local color touch-screen control panel and HMI interface. In the control center, the associated software suite expands the programming, control, optimization, troubleshooting, and data logging of onsite operations, engineering, and maintenance personnel. The new LCI DFE utilizes appropriate communications protocol to talk directly to the GE Mark VI and Mark VIe control systems.

The typical upgrade project can be accomplished in about five days; a turbine shutdown is not necessarily required, although, of course, the LCI will be unavailable for that period.

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