industrial turbines, power cylinders, pipes, tubing,
boilers, and heat exchangers, within numerous
industrial applications.
Aerospace and power-generation gas turbine
operators benefit from RVI procedures, commonly
referred to as “borescope inspections.” In fact,
gas turbines in aerospace and industrial applica-
tions are among the largest industry segments that
use borescopes. Small port plugs can be quickly
removed from the external casing, and a borescope
inserted by a technician allows for the inspection
of internal stages or areas of the fan, compressor,
combustor, power turbine, and related accessories.
Borescopes for turbine inspections come in two
basic configurations: one with a flexible insertion
shaft and one with a rigid insertion shaft. Both types
can be configured with or without video capabil-
ity. This article focuses primarily on flexible video
borescopes.
In some cases, industrial turbines were initially
developed as aviation turbines. For instance, Pratt
&Whitney’s FT4000 is the aeroderivative industrial
variant of the PW4000, and Rolls-Royce’s RB211 is
used in both aviation and industrial applications.
Similarly, the GE Vernova LM6000 (LM is a
Land Marine designation) aeroderivative turbine
shown in Figure 3 was developed from the
CF6-80C2 aviation turbine platform. The CF6 has
been in use for over 50 years on long-haul flights
by Boeing and Airbus. A cut-away of the CF6 as
shown in Figure 4 depicts the major section of a gas
turbine.
In power generation, there are also much larger
and heavier frame turbines that have higher power
output. However, both turbine types operate funda-
mentally the same, in that ambient air is compressed,
mixed with fuel and heat in the combustion section,
and then passes through a power turbine section
where the energy is extracted. Notice the scale differ-
ence of the aeroderivative LM6000 in Figure 3 and
the large frame 7HA.03 in Figure 5.
Therefore, it makes sense that RVI inspections
on aeroderivative and large frame turbines would
be comparable to those conducted on aviation
turbines, and indeed they are. A significant dif-
ference is that aviation turbines are inspected on
Figure 3. GE Vernova
readies an LM6000
aeroderivative
turbine for service.
High-pressure
compressor
Low-pressure
compressor
Low-pressure
shaft Low-pressure
turbine Combustion
chamber
Nozzle
Fan
High-pressure
turbine High-pressure
shaft
Figure 4. Cut-away view of the major section of a CF6 gas
turbine used in aviation.
J U L Y 2 0 2 4 • M A T E R I A L S E V A L U A T I O N 43
CREDIT:
GE
VERNOVA

a more frequent schedule to ensure flight safety.
Another critical aspect of RVI for both aviation and
industrial turbines is determining whether a turbine
can operate safely and efficiently until the next
scheduled inspection, thereby ensuring maximum
uptime and profitability. This often involves needing
to make precise and accurate measurements of
various types of surface indications. A thorough
understanding of RVI techniques, and the equip-
ment being used, is critical for collecting accurate
image data to make these assessments.
Background
It is crucial to have RVI equipment that meets
examination requirements, can accurately measure
indications and anomalies on demand when
needed, and is standardized to provide indication
size analysis traceable to precision measurement
standards like those at the National Institute of
Standards and Technology (NIST). This ensures
accurate decision-making data can be obtained.
Even with the best equipment in the world,
training—or lack of training—of RVI technicians sig-
nificantly impacts the quality of the inspection data
obtained. Training for RVI technicians is no less critical
than it is for technicians in other NDT disciplines such
as ultrasonics, radiography, and electromagnetics.
When preparing for a borescope inspection,
some critical factors must be considered to help
ensure success. Ask yourself:
Ñ Is the camera and entire video borescope system
serviceable and standardized to provide indica-
tion size analysis traceable to precision measure-
ment standards like those at the National Institute
of Standards and Technology (NIST)?
Ñ Does the RVI technician know how to inspect the
cleanliness of the camera and optical tip adapters,
with both fixed and removable optical lenses?
Ñ Is the technician trained and qualified to use the
equipment, and do they understand the inspec-
tion requirements?
Ñ Is their training complete on both the RVI system
and the asset to be inspected?
Ñ Has the performance of the technician and RVI
equipment been evaluated with a Probability of
Detection study, or has a Gage Repeatability and
Reproducibility (Gage R&R) [3] been completed
on assets requiring accurate detection and
measurement analysis?
Ñ Does the technician know the necessary diameter
and length of the flexible camera shaft to ensure
access through all borescope ports and to reach
the farthest inspection points?
Ñ What is the required travel path of the camera
to the inspection area? Are guide tubes, push
poles, or other accessories required to deliver the
camera to the inspection site?
Ñ Does the technician know what to do and what
not to do if the camera becomes stuck in a
turbine?
Ñ What is the internal environment in the inspec-
tion area? Is it hot, cold, toxic, explosive, or
corrosive?
Each of these are key factors to be aware of
when performing an RVI task, and they should
all be addressed in a training program. One must
understand the benefits—and risks—of performing
RVI with the proper equipment and trained tech-
nicians versus best-in-class equipment and inade-
quately trained technicians.
RVI Data Collection and Analysis
In these examples, you will see where RVI measure-
ments were taken, and that the measurement data
obtained was accurate. However, the measurement
data was also very wrong. How can measurement
data in the same image obtained with best-in-class
RVI equipment be both accurate and wrong at the
same time?
FEATURE
|
REMOTEVT
Figure 5. Large
frame 7HA.03
GE Vernova gas
turbine.
44
M A T E R I A L S E V A L U A T I O N • J U L Y 2 0 2 4
CREDIT:
GE
VERNOVA