Might be a good time to consider which meetings you want to attend in the first quarter of next year. Summer is over, fall outages will take center stage for the next couple of months, and then there are the holidays. This means 2018 is peering over the horizon, especially if corporate approvals are required. A possible benefit of submitting paperwork early is use of 2017 budget surplus to pay for a future activity.

The first user group meeting in the coming year, based on information made available to the editors, will be the 501F Users Group conference at the Hyatt Regency Grand Cypress (Orlando, Fla), February 25 to March 2. CCJ ONsite considers this is a must-attend event for owner/operators of 501F engines.

The all-volunteer organization’s steering committee (sidebar) is honing the 2018 agenda; it will be posted on the group’s website when complete. Next year’s program is sure to have some of the same elements as the information-rich 2017 conference, which ran four and a half days and included the following:

• • • User-only roundtables promoting open discussions and short presentations by owner/operators on safety, combustion section, hot-gas section, inlet and exhaust, compressor, rotor, generator, auxiliaries, and outage management. The roundtables typically ran from 60 to 120 minutes each. They are considered by many users as the “heart of the meeting.”

    • Seminars by major products/services providers—Mitsubishi, PSM (Ansaldo Energia SpA), Siemens, Sulzer, and GE—ranging from two to four hours each.

    • Vendorama program. This year, 38 companies made 41 technical presentations ranging from 30 to 50 minutes each to bring users up to date on products/services of interest to the 501F community. The program matrix—seven time slots in each of six rooms, running from 9:30 a.m. to 4:00 p.m.—allowed each attendee to participate in up to seven presentations. Note that Vendorama presentations are vetted by the steering committee to ensure a technology focus and to eliminate blatant sales messages.

    • Vendor fair, following the Vendorama program on the first day of the meeting, provided users the opportunity to peruse the offerings of 89 vendors.

If you have never attended a 501F Users Group meeting, make the 2018 conference your first. The following case history presented by a user at the 2017 meeting offers a glimpse at the level of detail you will gain access to by participating. Material like this, possibly vital to your plant’s future success, is not available anywhere else. Watch for detailed coverage of the last conference in CCJ ONsite in the coming weeks.

Important note for shy O&M personnel: The 501F users is a brotherhood and first timers (about half of the 125 to 150 attendees typically expected at an annual meeting) are accorded the same respect given to more experienced participants.

Steering committee

Officers

Russ Snyder, Cleco Power LLC, President and Chairman
Paul Tegen, Cogentrix Energy Power Management LLC, Vice Chairman
Carey Frost, Duke Energy, Secretary
Dave Gundry, Xcel Energy Inc, IT Officer

Board members

John Burke, NAES Corp/LSP-Cottage Grove LP
Blaine Gartner, Xcel Energy Inc
David Lucas, PacifiCorp
Arlen Morris, NextEra Energy Inc/FPL
Jeff Parker, SRP
Ramon Gonzalez Recio, Falcon Group/Comego

Case history: Turbine blade ring burn-through

Vital stats: 2 × 1 combined cycle powered by 501FD2 gas turbines commissioned in 2001 with an average of nearly 60,000 equivalent operating hours per engine and nearly 3200 equivalent starts.

Incident profile: One engine tripped on blade-path spread; a high-temperature alarm was received for disc-cavity (DC) 2 prior to the trip.

Initial findings:

• • • Event lasted three minutes.

    • Combustion seemed stable.

    • Inlet-bearing vibration increased slightly during the event.

    • Blade-path thermocouples (TCs) 1 and 16 increased to 1185F and then dropped to less than 1000F, causing the trip.

    • Coast down took 23 minutes, only slightly longer than normal.

    • Turning-gear amps were normal after coast-down.

Operators decided to spin-cool the unit. After the gas turbine was off turning gear, inlet guide vanes were inspected for looseness, TC2 was found melted, and debris was in evidence when the exhaust door was opened. A borescope inspection revealed significant turbine damage. A crawl-through of the combustor case confirmed burn-through of two blade rings (photo); the unit was disassembled.

Damage assessment:

• • • Combustion hardware was fine.

    • R1 vanes had minor impact damage at the trailing edge.

    • Tips of R1 blades were worn off and there was evidence of trailing-edge impact damage.

    • Two segments of the R1 ring segment were missing.

    • The breech in the R1 blade ring was about 10 in. in diameter.

    • R2 vanes revealed local melting.

    • R2 blades suffered impact damage.

    • There was no damage to the R2 ring segment.

    • Downstream impact damage.

Root-cause analysis incorporated hardware inspection, metallurgical analysis, and review of operating data and of inspection reports. Investigations revealed the following:

• • • Metallurgical analysis showed nothing out of the ordinary.

    • R1 vanes had been repaired previously and areas of erosion had been repaired during the last outage.

    • R1 ring segments were installed new, not refurbished.

    • Assembled blade-tip readings were within spec for non-VGP (Value Generation Program) components.

    • Hardware has 569 equivalent stars and 12,700 equivalent operating hours at the time of failure.

    • Previous borescope inspections identified a rub in the area where the ring segments were missing. The rub had removed the thermal barrier coating and smeared base metal; however, the OEM considered the damage low risk and approved a return to service.

An operational review identified the following changes in the engine:

• • • One week prior to the event, a step change occurred on the blade-path TC—7-deg-F warmer on BP TC1. The monitoring center was asked to watch for a worsening condition. No vibration change was noted.

    • Baseload output dropped by 1 to 2 MW over the week prior to the event. But operators would not have detected this on a cycling unit with varying loads.

    • While the temperature in DC2 remained stable, the cooling valve opened gradually throughout the week leading up to the failure.

So, what happened?

No single root cause was in evidence and the findings were relatively inconclusive. A timeline of events during the week leading up to and including the trip was difficult to compile based on operating data.

Investigators believed that the combination of blade-tip rubbing on the ring segment which removed TBC and potentially reduced cooling, and vane shroud erosion which reduced ring-segment leading-edge cooling, likely caused erosion of the ring segment and isolation segments—thereby allowing liberation of the ring segments. After the ring segments liberated there was no protection for the blade ring from hot gas.