POWER April 2017 - 16

Using Rotor-In Major Inspections
to Shorten Outages
and Drive Safety
Today, some F-class operators continue to
opt for rotor-out major inspections, which
are cumbersome and inefficient. They involve
complex lifts and moves of the rotor,
as well as the need for substantial space
to store the rotor and other complications.
These inspections are typically the longest
portion of an outage, with risks to both
employees and equipment. However, there
is an alternative that can increase safety
and productivity while reducing downtime
and lowering the cost of a major inspection
of an F-class unit. It's called the rotor-in
major inspection (RIMI).
What Is a Rotor-In Major Inspection?
The RIMI is a process developed at GE's
full-size 7FA gas turbine mock-up facility,
part of its Global Repair Development
Center in Greenville, South Carolina, using
GE's unique experience, tooling, and
personnel. The process is built on years
of experience conducting rotor-in majors
for B and E fleets, and it accomplishes the
major inspection while leaving the rotor
in place, rather than removing it and laying
it down on the plant floor. Although
GE has become proficient at executing
rotor-out major inspections over many
years, problems still arise and damage can
occur from this single event.
GE has engineered a way to perform
the major inspection and complete all
required tasks while leaving the rotor in
place, thus increasing safety and reducing
downtime by an average of 15% to 20%.
Developing the RIMI process started in cooperation
with several GE customers, and
it began conducting RIMIs for our F-class
fleet on a limited basis in 2011.
How Rotor-In Major Inspections
Work
The only additional tooling needed is GE's
proprietary 7FA Rotor Jacking system.
These jacks allow crews to raise the shaft
and remove the lower half liner (Figure
1), at which time the bearing area and
cavities get cleaned and the liners are replaced.
Before
a RIMI can occur, each unit goes
through a technical review by GE's engineering
experts. This team helps ensure
that the integrity of the compressor is
capable of the rotor-in major. They scour
16
historical data, support cases, sister data,
borescope reports, and other data to identify
any possible issues with the lower half
stators that may be of concern. Only the
units that pass this engineering review are
eligible for a RIMI. GE has completed over
50 RIMIs across the globe, and to date
none have had an issue that resulted in
the removal of the rotor.
While the overall major inspection process
has not changed, numerous steps
were modified with the RIMI to represent
the proper order of the outage. The
bearing inspection and replacement were
moved to the beginning of inspection,
and the casing removal and installation
steps were reordered.
Leaving the rotor in place allows for previous
critical path items to be done in parallel
to shorten outage duration. While the
rotor is in place, foreign materials exclusion
(FME) Zone 1 controls are maintained
for the compressor section. All items get
logged in and out of the compartment
until completing the compressor section,
and the danger of foreign material entry is
mitigated. No inspections were modified or
omitted to allow the rotor to stay in place.
In fact, proprietary tooling was developed
to help facilitate this process.
Beneits vs. Rotor-Out
The benefits of a RIMI over a traditional
rotor-out inspection are many and include
faster turn-around, better safety, and fewer
demands on plant staff.
Improved Safety. One of the clearest
advantages of the RIMI is increased safety.
Since the rotor is not removed, there
www.powermag.com
is no need for heavy-duty lifting equipment
on-site, which reduces unnecessary
equipment movement and opportunities
for personnel injury or damage.
No Reduction in Quality. One of the
primary benefits for the RIMI is that there
is no gap in the scope from a rotor-out
inspection. The scope includes evaluating
the compressor and turbine sections,
cleaning the lower half stator vanes (Figure
2), and other traditional services. In
addition, the rotor can be rotated 360
degrees for maintenance without significant
complications. This process ensures a
thorough inspection with no performance
degradation when compared to rotor-out
major inspections.
Estimated Schedule Reduction. The
process of physically moving the rotor out
of the turbine and onto the plant floor takes
a lot of time during a rotor-out inspection,
during which few other services can be
conducted. The RIMI, by contrast, allows
simultaneous operations to take place. For
instance, while crews are still working on
the hot gas path area, the compressor section,
inlet bellmouth, and exhaust frames
can be reinstalled. This concurrent work is
impossible while the rotor is outside the
machine. Additionally, there is no downtime
during the rotation of cranes, allowing
generator alignment to begin sooner.
All together, there is a 15% to 20% cycle
time reduction with the RIMI compared to
rotor-out major inspections.
Less Laydown Area Needed. Since
the rotor is not removed from the machine,
the personnel can set other casings
on the ground without reserving space for
POWER | April 2017
1. In place. The rotor-in major inspection (RIMI) allows crews to perform all required tasks included
in a rotor-out major with less cost and time requirements. Courtesy: GE Power Services

http://www.powermag.com

POWER April 2017

Table of Contents for the Digital Edition of POWER April 2017