POWER November 2020 - 34

GAS TURBINE
Safer and More Efficient Gas
Turbine Coupling Maintenance
In the past, routine maintenance on the General Electric (GE) 7FA-class gas turbine
coupling was time-consuming, costly, and presented unnecessary safety risks for
service technicians and plant maintenance crews. Now, there's an alternative that
improves the disassembly and reassembly process during planned outage maintenance
and when unplanned repairs are required.
Jim McTaggart
C
hris Stocker boarded a plane in early
March. The destination: Dallas,
Texas. His mission: To test a new
tool at a 300-MW combined cycle power
plant. The goal: To prove that the device
could reduce the time it takes to disassemble
and reassemble a turbine coupling
from a total of as long as 20 hours
to just 4 hours-an 80% time-savings
per turbine.
Stocker is a product account manager
for Power Generation with Enerpac. For
the past two years, Enerpac engineers
Robert Karol and Jon Slocum have been
working in close collaboration with power
plant service organizations to develop
the tool, which is designed to make it
safer and easier to perform routine
maintenance or unplanned repairs on
GE 7FA-class gas turbines. The project
began when the team recognized that
the current method for performing this
task was overly laborious and fraught
with risk.
Existing Maintenance Process and
Problems
When gas turbines reach certain milestones
based
on
runtimes
or
coupling
bolts that connect the main
turbine shaft to the generator. Each bolt
is made of high-grade alloy steel, which
is very expensive to replace. In fact, if
any one bolt is damaged during maintenance,
a matched replacement set must
be ordered from the OEM.
The reason something might go wrong
is because the current tool available on
the market to perform this job weighs
more than 110 pounds. The heavy weight
often causes fatigue and increases the
likelihood of trouble. The tool also requires
a lot of manual input and manipulation.
Having a tool that is very hands-on
and difficult to use brings added risk to a
job that is already inherently dangerous.
The level of confidence technicians have
when using the tooling is typically quite
low, and it makes for a time-consuming
job. Both the de-tensioning and tensioning
processes can take eight to 10 hours
each. After hearing gripes from users in
the field, Enerpac knew there had to be
a better way.
A New Alternative
The new tool, called the Enerpac Enhanced
Turbine Coupling Tool (or ETCT)
passed its trial test in the spring with flying
colors. It reduced the manpower to
de-tension a unit down to less than two
hours, a job that would have normally
taken a full 8- to 10-hour shift. Plus, the
tool allows the technicians to remain
hands off and safely away from any danger
during the process. Furthermore, the
built-in braking system keeps safety at
the forefront should any unforeseen instances
occur during operation. Customers
have been asking Enerpac to create
a tool that is safer and easier to use, and
now it's here.
Safety. The design of the tensioner that
Karol and Slocum developed is built from
decades of experience in hydraulic tooling
design and manufacturing. The engineers
knew how to select the right material and
design a suitable seal that would work
well for regular scheduled maintenance.
With proper training, technicians can have
startups,
original equipment manufacturers
(OEMs) recommend they be taken offline
for maintenance. During these maintenance
outages, a turbine can be out of
service for a month or more in some cases.
That's because not only is there a long
list of time-consuming tasks, there are
also some critical-path steps that cannot
be changed. This means that not all work
can happen simultaneously. Maintenance
goes smoother when there is more predictability
on the length of time criticalpath
jobs will take so that technicians
know when other tasks can commence.
There are several problems with the
current tooling method for coupling bolt
tensioning. Imagine this: Your job is to
carefully de-tension and then tension
34
1. The Enhanced Turbine Coupling Tool (ETCT) has been designed and tested to specifically
address the tensioning challenges that many power plants struggle with during gas turbine
coupling maintenance. Courtesy: Enerpac
www.powermag.com
POWER | November 2020
http://www.powermag.com
POWER November 2020

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