Page 185 - An Introduction To Predictive Maintenance

Thermography 175

checks of process piping temperatures, and similar applications. It is limited in that the
temperature represents a single point on the machine or structure. When used in con-
junction with vibration data, however, point-of-use infrared data can be valuable.

8.2.2 Line Scanners
This type of infrared instrument provides a single-dimensional scan or line of compar-
ative radiation. Although this type of instrument provides a somewhat larger field of
view (i.e., area of machine surface), it is limited in predictive maintenance applications.

8.2.3 Infrared Imaging
Unlike other infrared techniques, thermal or infrared imaging provides the means to
scan the infrared emissions of complete machines, process, or equipment in a very
short time. Most of the imaging systems function much like a video camera. The user
can view the thermal emission profile of a wide area by simply looking through
the instrument’s optics. A variety of thermal imaging instruments are on the
market, ranging from relatively inexpensive, black-and-white scanners to full-color,
microprocessor-based systems. Many of the less expensive units are designed strictly
as scanners and cannot store and recall thermal images. The inability to store and recall
previous thermal data limits a long-term predictive maintenance program.

Point-of-use infrared thermometers are commercially available and relatively inex-
pensive. The typical cost for this type of infrared instrument is less than $1,000.
Infrared imaging systems have a price range from $8,000 for a black-and-white
scanner without storage capability to more than $60,000 for a microprocessor-based,
color imaging system.

8.3 TRAINING
Training is critical with any of the imaging systems. The variables that can destroy
the accuracy and repeatability of thermal data must be compensated for each time
infrared data are acquired. In addition, interpretation of infrared data requires exten-
sive training and experience.

Inclusion of thermography into a predictive maintenance program will enable you to
monitor the thermal efficiency of critical process systems that rely on heat transfer or
retention; electrical equipment; and other parameters that will improve both the reli-
ability and efficiency of plant systems. Infrared techniques can be used to detect prob-
lems in a variety of plant systems and equipment, including electrical switchgear,
gearboxes, electrical substations, transmissions, circuit breaker panels, motors, build-
ing envelopes, bearings, steam lines, and process systems that rely on heat retention
or transfer.