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Improved durability and extended outage and
inspection intervals for combustion turbines
P
ower generation plants
need to operate as
efficiently as possible in
order to keep up with
the growing demand
for electricity. In order to maintain high
reliability rates, it is necessary to perform
periodic inspections and maintenance
as specified by the original equipment
manufacturer (OEM). However, thanks to a
series of modifications and enhancements
from Sulzer, one power plant in Missouri
is hoping to increase significantly its
maintenance interval for its turbines and
therefore reduce its maintenance costs.
The Holden Power Plant in Missouri,
which is owned by Associated Electric
Cooperative Inc. (AECI), operates three
Siemens V84.2 simple-cycle dual fuel
combustion turbines that have a
combined output of 321 MW. Designed
as a peaking plant, they are used to meet
peak power demands that are over and
above the base load demand on the local
electricity grid.
Due to the fluctuating demand for power
the amount of time each gas turbine
operates can vary greatly; this means
that maintenance schedules are defined
both in terms of equivalent operating
hours (EOH) and calendar years. Units that
operate infrequently will therefore reach
the calendar based intervals first.
Such units are unlikely to exhibit any great
amounts of wear, but oxidation of the
compressor is a much more likely issue
and so it is important to enforce regular
inspections, even on equipment that is
used infrequently.
The Siemens V84.2 requires a hot gas
path (HGP) inspection every 25,000 EOH
or every six years and a major inspection
every 50,000 EOH or every 12 years. The
units at the Holden plant had accumulated
around 10,000 EOH during 12 years of
service. As such, the owner wanted to
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PECM Issue 26
investigate the
possibility of
extending the
calendar based
inspection intervals
without affecting
the performance
or reliability of the
turbines.
As a leading
independent
service specialist,
Sulzer has
considerable
expertise in
delivering
maintenance
and performance
improvements
for both Siemens
SGT and V-Series
gas turbines. The
experienced design
team at Sulzer
proposed a range
of modifications
and enhancements
to both the rotating
and the stationary
sections of the
turbines.
Work was carried
out on the entire
compressor with
both the rotating
and stationary sections, as well as the
inlet guide vanes, being coated with
Anti-Fouling / Anti-Corrosion coatings
in order to prevent oxidation. The new
coating has greatly improved the corrosion
resistance and enabled the plant not
to be dependent solely on the inlet
dehumidification equipment.
In a standard V-series turbine, the flame
tube F-ring has a tendency to oxidize
and produce scale which can be ingested
by the turbine during normal operating
conditions. To improve this situation,
the component was carefully machined
to expose fresh material and allow an
Inconel overlay to be welded to the fresh
surface before being machined back to the
required diameter. Inconel 82 is a nickel
chromium alloy with high strength
and an outstanding corrosion
resistance that will improve the
durability of the component.
The combustion section of the
turbine was also protected
with a full thermal barrier