The AOG, born of necessity to help owner/operators of Alstom gas and steam turbine/generators navigate the O&M challenges arising from GE’s purchase of that company in November 2015, looks ahead to its sixth annual meeting, March 20-23, at EPRI’s corporate offices and training facility in Charlotte, NC. This will be the organization’s first in-person conference since 2020.
AOG has grown dramatically since its founding in 2018. There were 41 members representing eight countries the first year. By the 2022 meeting, those numbers had increased to 193 members in 33 countries. Arnold Group, Pioneer Motor Bearing, Hughes Technical Services (HTS), and Liburdi Turbine Services have supported the organization since its beginning, sponsoring each of the first five meetings.
AOG is a private user organization that enables owner/operators of Alstom equipment to communicate directly with each other, and with third-party services providers, in a secure setting. Membership is limited to individuals directly involved in the construction, operation, and/or maintenance of Alstom gas and steam turbines and who are employed by companies with ownership and/or operational interest in those turbines.
Content for, and conduct of, AOG conferences is organized by a steering committee, with the following members for 2023:
- Brian Vokal, VP operations and engineering for Midland Cogeneration Venture.
- Pierre Ansmann, global head of marketing for Arnold Group.
- Robert Bell, plant manager of Tenaska Berkshire Power.
- Jeff Chapin, AOG founder, Liburdi Turbine Services.
- Ross Goessl, PE, senior engineer for We Energies.
Note that Goessl replaces Southern Company’s Chris Hutson, a founding board member and major contributor to the group’s success. Hutson resigned in early November, having transferred from the user community to K Machine Industrial Services.
AOG 2022, Day One
The fifth annual (2022) meeting, conducted virtually, was presented over five nominal four-hour days, February 7-11. Training sessions were conducted on two days the following week. Recordings and/or slide decks of all presentations made available to the steering committee can be accessed through the group’s website by registered users.
The conference opened with a keynote presentation, “Leading Change and Innovation at your Powerplant,” by Wade Younger, CEO, The Value Wave. The motivational speaker/author’s professional activities focus on technology implementation and organizational transformation.
A structured user-only, two-hour user discussion session followed Younger’s keynote. It was divided into the following sections: inlet and filtration, compressor, combustor, rotor and casing, hot-gas section, exhaust systems, generator and electrical, controls/BOP/auxiliaries, and safety/compliance/outages. The steering committee’s Robert Bell moderated the discussion session.
One of the combustor topics brought to the floor by users concerned unit pulsation, as well as high NOx during the shoulder months and winter. Tuning interval was discussed. Conclusion: Pulsation monitoring is important. One user disconnected his instrumentation with casing cracking the result. Another said he had no problem with the silo combustor. A GT26 user reported tuning after a major, adding that it took about 30k EOH to go out of tune.
During the combustor discussion the group was asked, “How often do you validate TIT formulas?” A GT11 owner recommended adjusting the C constant after a major inspection and also having a discussion with GE about this. The need for an energy balance around the GT was mentioned as was the need for top-grade instrumentation. HTS, recently acquired by AP4 Group, was recommended for an independent verification check.
Experience with the fuel water drain valve was next. Question: Have any users simplified or replaced this three-position valve (wash mode, drain, run)? Air leakage through the valve was mentioned as a potential issue. Suggestion by an attendee: Replace the valve with a simpler one.
Rotor and casing. The first question concerned the 5000-start inspection recommended in TIL-2040 Rev2. If you have done this, did you do it with the OEM or with a third party, after how many starts? Were there any findings? The message regarding inspection interval: You want to keep the rotor operating as long as possible, but safety should be your primary goal.
One user said his plant did the 5000-start inspection with the OEM plus two third parties—M&M Engineering and Doosan Turbomachinery Services. Recommendation: Use operating data to help decide what to look for—for example, creep.
Question to the group: Has any user encountered combustion casing cracks? If so, what remedial/temporary action is suggested for keeping the asset in operation? Stop/drill and/or weld repairs may be solutions—depending on the specific issue. Coatings and pulsation management also might help in at least some cases. One participant said control of pulsation mitigated cracking.
Hot-gas section. Have users experienced feather-seal wear on stator heat shields (SHS) severe enough to result in fallout after one cycle? Recall that feather seals are located in grooves between stator heat shield. The user soliciting help said his plant had almost a full set of SHS classified as fallout because of wall loss attributed to seals.
The problem was found during a C-inspection but it was not immediately obvious why feather seals would rub against SHS. The condition was said to be “uncommon.” In the opinion of the user, the OEM didn’t provide information of value as to why the wear occurred.
Other. An attendee mentioned that he had two units in an outage showing bent pedestal rods. He thought the plant should be able to straighten the rods but he wanted colleagues to share any knowledge they might have on the topic believing two instances as “suspicious.” One thought was to check the spring cans under the stilts for freeze-up. Another reported a similar finding of bending and decided to take no immediate action to avoid the possibility of creating another issue.
A question on remote operation of GT11Ns received some good discussion. No one said they were operating remotely but the question transitioned to “What would you have to do to replace the operator who was walking down the unit to enable remote operation?” Example: Plume. Would you have a camera watching the stack? What other instruments would you need for detecting noise, leaks, wherever and whenever they occur? What risks do you have without having a person onsite with the senses one associates with finding a problem: sight, hearing, feel, smell?
There was a concern brought to the group regarding the hardwired pressure switch for starting the emergency dc lube-oil pump. According to the OEM and a third party, operators are able to valve open this switch using the black knob, thereby allowing oil to drain through the manifold. This is supposed to create sufficient pressure drop to activate the pump. But it doesn’t.
The user said plant’s goal is to check this function weekly or monthly but not possible as configured; an additional orifice or isolation valve would be required, he said. Someone offered that you still would not be fooling the pressure switch with the mod proposed. A question from another attendee: How often do you have to run the test?
Nothing was resolved; perhaps the same question might be posed at an in-person meeting where concerned parties could meet after the session.
What follows are abstracts of the three user presentations made at the meeting and what the OEM had to share on GE Day. Thumbnails of presentations by vendors important to the fleet will appear in the next issue of CCJ ONsite.
Challenges and surprises from recent GT11NM C-inspections
This presentation on Day Three is of particular value to owner/operators of GT11N gas turbines with the M upgrade because it shares the findings of C-inspections on eight peaking units—six in the last couple of years. Coverage includes the following:
Compressor diffuser bolt failure. Turbine rotor axial position and bearing vibration alarms of concern on one of the units were first received in mid-2018. That fall, numerous rotor-seal-air low-DP alarms were received, causing runbacks. By year-end, the plant had revised its alarms based on guidance from the OEM. This scenario was repeated in 2019, 2020, and 2021—reaching the point where the unit could not run reliably because of the runbacks. A forced outage was taken.
Broken vertical split-line and radial bolts were found in the lower casing during the ensuing inspection. The bolting loss had allowed the casing to move about ⅜ in., resulting in significant casing-to-rotor rubs, Labby seal wear to below that allowed by the spec, and the loss of axial lock tabs on a rotor heat shield.
The bolts, which failed where their shafts and heads meet, have been redesigned to reduce stress in that critical area. The speaker suggested that his colleagues with engines equipped with the original bolts replace them during their next C-inspection, adding that the part numbers of the bolts have not changed.
Row 5 turbine-blade Z-notch fretting was found on six of the eight N1 units upgraded to NM that had completed their first C-inspections. The speaker stressed the need for a good Z-notch fit to mitigate vibration capable of damaging the base material. He characterized the wear as consistently inconsistent—the wear at all notches not being the same. As to cause, an RCA (root cause analysis) had not been completed prior to the 2022 conference.
Blowoff-valve internal corrosion. A significant amount of rust has been found on the control-air side of these valves. When the valves were opened for inspection, standing water was in evidence. The culprit: Plugging of the small drains in the water traps with gunk and other debris. Action taken: Close, regular inspection to ensure the drain holes remain open.
Fuel-oil block-valve leak through. Fuel-oil nozzle coking was the resulting issue. Plus, there was the odor of gas from a leak in the centrifugal extractor. When the valve was opened, significant pitting was in evidence along with accumulated corrosion products and gunk. Re-machining of valve seat was necessary. The valve has worked well since taking the corrective action and the odor of gas essentially has disappeared.
A valve rebuild kit (FSI 223271) is available and that task is now incorporated into C-inspection activities.
QA/QC issues with OEM parts. Complaints always are a hot topic at user-group meetings. One of the problems raised was the varying degree of Teflon thickness on new seals for blowoff valves. The tolerance is only 1 mm, so this is a significant concern. A fuel-nozzle machining issue also was identified.
Finally, the attendees were made aware of water intrusion into the blowoff-valve silencer and of chattering wear on the pulsation probe assembly.
EV burner front-segment issues
Thursday’s (Day Four) user presentation on two incidents of EV front-segment displacements was based on 11 years of experience at an electric-power and desalination plant in the Middle East with five GT26B gas turbines. Arrangement: Two 2 × 1 combined cycles and one backpressure cogeneration unit.
Three machines each had completed three C-inspections prior to the conference, the others, two C-inspections. The second inspections on all machines and the third on three were conducted by Ansaldo Energia—as required by a European Union directive put in place when GE purchased Alstom.
Equivalent operating hours (EOH) of the five gas turbines range from 81,000 to 98,000. The interval between C-inspections conducted by Ansaldo is 32k EOH, up from 28k with Alstom/GE.
The first incident in mid-2016 occurred when the EV pulsation-probe fixation front segment was found displaced during a borescope inspection following multiple trips on high pulsations. A broken “J” hook had allowed the front segment to move. An Alstom technician with special tools replaced the defective hook without opening the machine.
Plant personnel learned EV front-segment displacement had occurred at one other plant at least (see CIB 2012015_GT26) and that Alstom had a new fixation design. The recommendations of the Alstom directive were implemented in all five gas turbines during their second C-inspections.
The fix for the second incident at the Middle Eastern plant was far more complex. In this case, one of the gas turbines was challenged with high CO emissions in some load ranges. Ansaldo borescoped the unit as 2021 drew to a close, finding one EV-combustor front segment leaning because of suspected damage to two of its four “J” hooks.
Concerned that a unit restart at that time might cause the front segment to release and cause significant damage, a forced outage was taken. Rotor removal was required to replace the affected front segment. The outage ran four weeks, costing more than $1 million in parts and repairs, plus business interruption. At the time of the 2022 conference, a third-party consultant had been retained to assist Ansaldo in determining the root cause.
In the editors’ minds, this incident certainly warrants discussion at the upcoming meeting—particularly so if the affected front segment had been replaced, as believed, with the new design.
A highly experienced gas-turbine engineer/project leader at a UK combined cycle shared, on the last day of the conference, a couple of ideas developed at the facility to reduce outage time. Plant was built in two phases: The first, installed in 1996, is a 3 × 1 unit powered by 13E2 Alstom gas turbines. The second, a 2 × 1 with 13E2 gas turbines as well, went commercial in 1998.
Two of the three Phase I gas turbines were partially (60%) upgraded to Alstom’s new (at the time) MXL2 technology during a C-inspection in 2012—the first engines in the fleet so equipped. Full upgrades of the other units followed, including installation of AEV burners on all machines.
The innovations contributing to the plant’s “lean” outages are these:
Bolt beams and access platform. It allows rapid release and tightening of the split line using a high ITH tensioner without need for a crane. Plus, it eliminates the manual handling risks associated with moving the tensioner and heavy bolts during their removal. The process is illustrated in the presentation posted on the AOG website.
Other advantages of the bolt beam: (1) Support a platform (photo provided in presentation) to allow O&M personnel (and rescue team, if necessary) safe entry to and exit from the combustion chamber, (2) eliminates the need for scaffolding, and (3) provides a secure place to attach harnesses when working on casings.
Experience: At the time of the 2022 meeting, the plant had completed two outages—one with the beam, one without. A table compares the times to complete necessary tasks (such as loosening bolts on the split line) under each scenario. Using the new method, approximately 41 hours was saved in setting up and securing from a C-inspection—for each gas turbine. This paid for the bolt beams and access platform with first use.
Intelligent asset management. The second innovation is a graphical system that tracks gas-turbine components from cradle to grave, providing complete operating data along with all historical documentation (reports and photos)—all while eliminating Excel spreadsheets.
It can be used for multiple different gas turbines—even portfolios—within your fleet. Information available helps you carry out an efficient flow of parts through different GTs or migration to another plant.
Plant personnel developed this system for the 13E2, but it can be adapted for any gas turbine. Versions for the 9E and 9F were under development at the time of the 2022 conference.
The intelligent asset management system is comprised of eight modules—including scheduler, material inspection, plan execution, etc. But you really can’t grasp the value of this enhancement without perusing the slides and demo available on the AOG website.
Dig into the details of the user presentations by accessing the slide decks at www.aogusers.com.