Maintenance Technology August 2014 - (Page 27)
FUNDAMENTALS
3. Regular comparison of the operating temperature of a single unit to previous images of the
same unit
Since the thermographer guides the infrared
inspection process, his/her knowledge is of the
utmost importance. Thermal imaging can be used
to identify several conditions such as inadequate
airflow, unbalanced voltage, impending bearing
failure and insulation degradation in a motor's rotor
or stator. It can also identify heat produced by shaft
misalignment.
Regardless of the application, however, the final
results of a thermographic inspection depend upon
understanding the task to be performed, selection
of equipment, operator skills, inspection techniques
and documentation of findings. Before embarking
on an inspection, a thermographer needs to consider
and understand how these factors will influence
final results. The following steps outline the basic
elements a thermographer needs to consider for a
successful inspection in any environment.
Define the task
Perhaps the most important-and often most overlooked-part of thermography is the need to define
the project. Before any successful task can begin, the
thermographer must determine exactly what is to
be done and what is expected of the final results. In
the case of routine inspections of industrial equipment, this will typically be understood. Infrared
can and should be included in normal maintenance
"rounds" to establish benchmark results for ongoing
comparison.
In non-routine situations, however, specific
details are needed to ensure a useful inspection.
For example, a thermographer may be asked to
"conduct an infrared scan to locate wet areas" on
a facility's roof, a request that does not adequately
define the task. It is unclear when the work is to be
performed, what type of imager is be used and what
type of documentation may be required. But regardless of inspection type, it is always desirable for the
thermographer to fully comprehend all aspects of
what is expected. If the inspection requires skills
beyond thermography, the thermographer, if qualified, may elect to perform these tasks or work with
others who are qualified. Once the exact nature of
the task has been determined, a scope of work can
be developed.
Thermographer qualifications
The operator may be the greatest limiting factor
in thermography. Although thermal imagers have
AUGUST 2014
IR Imaging Gives Fast Results
on Gearbox Health
The ability to determine lubrication health is another key IR
capability, and should be included in any PdM program. The
lifeblood of any gearbox is the oil that lubricates its gears. If oil
loses its ability to lubricate-or the level of oil gets too low-
the gearbox will overheat and eventually fail.
Traditional preventive maintenance for gearboxes has
consisted of regular oil-level checks and replenishments as
needed. Some maintenance departments add a predictive
element to gearbox maintenance in the form of oil sampling
and analysis. Oil analysis, usually performed by an outside
laboratory, reveals if the oil in a gearbox has lost its ability to
lubricate. It will also detect any metal particles in the oil, a sign
of gear wear that foreshadows possible failure.
While effective, oil sampling is relatively time-consuming,
and can be costly. It can also require equipment shutdown.
Moreover, gearboxes often are inaccessible or in unsafe locations, which can make oil-level checking and oil sampling
difficult. For these reasons, thermal imaging is a good alternative PdM approach. Since gearboxes generally overheat
before they fail, an infrared (IR) camera can detect when a
unit is running hotter than normal and/or hotter than similar
gearboxes performing similar work in similar environments.
Because thermography is a non-contact, non-destructive
technology, even inaccessible gearboxes in dangerous locations can be scanned while running. The IR camara can be
used to capture all thermal images as well as visible-light
digital images of all units that are running hotter than normal.
These processes can also reveal leaking seals where hot oil is
running down the sides of gearbox cases.
Be aware that any excessive heat generated in mechanical
gearboxes is the result of friction, and that inadequate lubrication is not always the source. The cause could also be faulty
bearings, misalignment, imbalance, misuse or just normal
wear. Still, thermography is a good first step toward a complete
analysis of the condition of any gearbox.
Source: Fluke Corporation
their limitations, thermographers can overcome this
by selecting the proper equipment (discussed later).
Since the thermographer is the most important
factor in thermography, knowledge is of the utmost
importance. Unless otherwise specified, it is usually
not enough for a thermographer to understand
only how to operate a thermal imager to produce
thermograms. At a minimum, the thermographer
should have completed a Level I thermography
training course. Thermographers who perform
inspections involving temperature measurement
should be trained to at least Level II.
The professional thermographer needs a thorough understanding of infrared theory and heatMAINTENANCETECHNOLOGY.COM | 27
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