2019 OUTAGE HANDBOOK

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7EA USERS GROUP
tomized aluminum castings top and
bottom make the insulator the exact
dimensions needed.
Hack tooted the Crown horn for a
moment saying his company’s insu-
lators are reliable and long-lived
because they are designed to handle
more than four times the typical nomi-
nal operating voltage of 15 kV under
extreme environmental conditions.
To prove this point he showed videos
of Crown’s porcelain and cycloali-
phatic insulators operating normally
at 70 kV while being sprayed with
water. Many insulators would short to
ground under similar circumstances,
he said.
Rotor life
The Rotor Life Roundtable, chaired
by Tracy Dreymala of EthosEnergy
Group, covered issues, procedures,
and capabilities of life-extension pro-
grams. The following seven vendors
participated with brief overviews of
their companies’ capabilities/activities,
before Chairman Dreymala opened
the discussion portion of the session:
n Scott Kennedy, Veracity Technology
Solutions.
n Doug Sewell, Sulzer Turbo Services
Houston Inc.
n Paul Tucker, FIRST/TBS.
n Hilary Magner, NRG Energy Ser-
vices.
n Richard Rucigay, MD&A.
n Pete Miranda, Nord-Lock Inc/
Superbolt Inc.
n Kale Dreymala, EthosEnergy
Group.
With more than 400 7EAs expected
to reach the end-of-life parameters
established in GER-3620N (October
2017), “Heavy-Duty Gas Turbine O&M
Considerations,” within 10 years, this
roundtable attracted a great deal of
interest.
Snippets of information gleaned
from both the company-capability
overviews made by each of the panel-
ists and the open-discussion segment
of the program are summarized in the
bullet points below.
n The opening remarks of Paul Tuck-
er, FIRST/TBS, was indicative of
the panelists’ experience and the
depth of knowledge accessible to
the user attendees. Tucker said
his company has been conducting
end-of-life (EOL) inspections on
gas-turbine rotors since 2007. The
list includes: 10 Frame 3s, 31 Frame
5s, eight Frame 6s, 20 Frame 7s, six
W251s, and four W501s. Roughly
half of the rotors inspected were
hours-based, half starts-based.
Regarding the value of EOL inspec-
tions to engine owners, Tucker said
20 FIRST/TBS’s program had, by the
time of the 2017 meeting, enabled the
rotors examined to operate 4.7-million
more hours and start nearly 200,000
more times.
Concerning inspection results,
Tucker reported that flaws were found
in 17 of the 563 wheels/discs checked;
13 wheels were replaced in the 11
rotors requiring follow-on work. One-
third of the 13 were compressor wheels.
n NRG reported having performed
five rotor life assessments since
2013, with the lives of those rotors
each extended by 100,000 hours.
n Veracity explained that current
inspection techniques—especially
phased-array ultrasonic, which pro-
vides 3D measurements of internal
discontinuities—were not available
when most engines in the 7B-EA
fleet were ordered and almost all
wheel forgings have discontinui-
ties that have been present since
manufacture. The new capabilities
for mapping internal flaws can pro-
vide engineers data to help calculate
remaining life going forward.
n There is no “industry standard”
available to vendors that perform
rotor life-extension programs. Each
establishes its own process, guide-
lines, and disposition documenta-
tion—typically based on an in-house
engineering evaluation and experi-
ence.
n A user asked, “How long can a
rotor’s life be extended?” The ven-
dors answered in many different
ways, perhaps best summarized as
“It depends.”
n Tucker shared his opinion that if
wheel inspections reveal proper
metallurgy and internal flaws are
“cleared,” a rotor likely is good to
run indefinitely, provided surface
creep is monitored. You are not
going to find a “birth defect” flaw
after a detailed inspection, he said.
Other vendors suggested 100,000
hours as the life-extension norm,
but again there is no industry
standard to validate this claim. A
user commented that a rotor with
a 200,000-hr extension had been
shipped from the OEM’s Greenville
shop after its EOL inspection.
n Vendors typically unstack the com-
pressor, remove the last four stages
of blades (usually damaged in the
process), and perform detailed
wheel inspections during their EOL
evaluations. Most panelists rec-
ommended a complete compressor
wheel inspection to get a 150,000-hr
life extension.
n A user asked the roundtable panel-
ists to address a comment attrib-
uted to the OEM earlier in the
day that the GE standard (in its
rotor life-extension program) was
a mandatory replacement of the aft
compressor stub shaft. One panel-
ist commented that he had seen a
rotor recently returned from a GE
inspection that did not have the
aft stub shaft replaced. All on the
roundtable panel did not believe
a mandatory replacement was
required.
n A user asked which turbine wheels
have defects. The roundtable ven-
dors said they have found defects
in all stages from time to time.
GE Day
To say that developing and organiz-
ing content of interest and value to
owner/operators of a gas-turbine fleet
as large and diverse as the 7B-EA
is challenging would be trite. It is a
Herculean task. Be mindful that the
1168 engines in this fleet (the OEM’s
number in fall 2017) serve in simple-
cycle, combined-cycle, and cogen-
eration systems, operate on multiple
fuels, may be anywhere from less than
one to nearly 50 years old, generate
from about 52 to 90 MW depending on
the model and year of manufacture,
and are fighting to remain relevant
and profitable in a variety of elec-
tricity markets in a rapidly evolving
industry.
Consider too that customers are
demanding more from their services
partners, and while the 2017 program
focused on the core engine, it included
total plant considerations (Fleet360*
in GE’s lexicon) involving the steam
turbine, generators, HRSGs, environ-
mental control, digital solutions, and
balance of plant. Additionally, cyber-
security and regulatory initiatives.
Tall order.
GE brought its A-team of subject
matter experts—at least 20 by the
editors’ count—to St. Augustine to
present, answer user questions, and
conduct roundtable discussions dur-
ing breakout sessions. It’s impossible
to do justice to the OEM’s contribu-
tion in a summary here of only 1500
words. The highlights, in the eyes of
the editors, are presented below. If you
want to dig deeper, the first place to
look is in the presentations section of
the 7EA Users Group website (ge7ea.
users-groups.com); be prepared to sign
up if you’re not already registered. For
COMBINED CYCLE JOURNAL, Number 57, Second Quarter 2018