Gregory R. Stockton is President
of Stockton Infrared Thermographic Services, Inc. Based
in Randleman, NC; the corporation operates six complete
infrared systems in four divisions. He has twenty-four
years experience in the construction industry, specializing
in facilities construction, maintenance and energy-related
technologies. Greg has been performing infrared (IR) surveys
since 1989. He has published ten technical papers and numerous
articles on infrared thermography in technical and trade
journals.
Introduction
Think of the world as one
gigantic radiator. The transfer of energy happens everywhere
around us. We can see it with eyes no one else has. To
the interested, inquisitive, infrared thermographer, getting
paid to walk around and look at things with an IR camera
is a dream come true. Those of you bitten by the IR bug
know what I mean. Applications for infrared thermography
seem endless.
Electrical P/PM
Checking switchgear for hot spots-no other application
for infrared thermography is so well proven, documented,
written and talked about, easier to sell to management,
or easier to perform. It is what the majority of all infrared
thermographers do for a living.
The maintenance world has come to terms with the fact
that:
electrical resistance equals heat,
excess electrical resistance equals excess heat,
excess heat is bad (because it indicates a potential failure),
excess heat can be seen with an infrared camera,
a useful IR report of a problem can be generated so that
repairs can be accomplished on an electrical component
prior to failure.
It has been extremely well documented that annual and/or
semi-annual IR inspections produce a large return on a
small investment. The insurance industry has discovered
this fact and of late is promoting, recommending, and in
some cases requiring that the insured perform infrared
surveys on a regular basis.
Mechanical P/PM
For every piece of electrical component, there are five
mechanical components that can be checked using IR. Instead
of resistance, heat is promulgated by friction. Just as
electrical resistance equals heat, mechanical friction
equals heat. However, IR/PM on mechanical equipment is
more difficult to perform, since there are so many more
variables with mechanical equipment producing friction
than with electrical switchgear producing resistance.
For example, let’s look at electric motors. Electric
motors are probably a maintenance engineer’s biggest
headache, since they have lots of breakable parts such
as electrical connections and windings, they operate at
variable speeds and loads, and they drive many different
pieces of equipment. Often the rewind shop neglects to
change the nameplate ratings, such as a change in insulation
class. The environment surrounding electric motors also
changes with respect to dirt, dust and ambient temperature.
My experience has also been that the manufacturers either
do not know, are not willing to share, or do not want to
assume liability for in situ temperature data on their
products. True, all the above factors make it difficult
to know how hot is too hot on an electric motor, unless
temperatures have been trended over time and all variables
considered. Most mechanical components do heat up due to
friction, so comparison of time vs. temperature or direct
comparison to like-loaded components works best. There
are many mechanical components in the industrial setting
waiting to be scanned.
Infrared predictive maintenance (IR/PM) has become a regular
part of the maintenance of industrial electrical and mechanical
equipment. Damage to the equipment itself has never been
the real issue. The main motivation for IR/PM programs
is reducing downtime that equipment failures cause.
Electrical and mechanical IR/PM
are the undisputed “low-hanging
fruit” of infrared thermography.
Process Improvement
The fact is that infrared process
improvement has many times the potential payback of any
IR/PM program. Savings
from downtime reduction and equipment costs are minuscule
when compared to savings from making a machine run even
10% faster with 10% less waste, 24/7. It does not take
a math whiz to understand that if you can fix a problem
at the beginning of the manufacturing process, you will
eliminate waste, eliminate returns and promote customer
goodwill. Infrared surveys are very inexpensive when compared
to throwing away products that you sent all the way to
the end of the line before discovering a flaw…or
worse, sent a defective product to your valued customer
only to have it returned at your expense.
Even if it is not possible to look
inside a machine, the effects of the machine on the product
can almost always
be seen using IR. The key to process improvement infrared
is to get the machine designers, operators, and industrial
engineers involved in the process. They usually know all
about the machine and the process. They just need to “see” in
the infrared.
Infrared on-line monitoring equipment
for manufacturing lines has a great potential, although
sales of this equipment
have not yet met IR equipment manufacturers’ expectations.
Surely sales of this type of equipment will improve as
detectors and software improve and as product manufactures
seek more efficient ways to producing goods in a more competitive
marketplace.
Non-Destructive Testing
In general, there are two ways to
get information about what is going on inside any object(s).
Simply:
Don’t do
anything. Watch the object radiate heat.
Create the conditions needed. Either;
Apply heat to the object and
monitor the results, or,
Apply heat to the object and monitor
what happens when then object cools (this
works with applying
cold also),
or,
Put a heat source behind the object
and watch what happens when the
heat comes through
it.
There are variations on these. What a great application
for IR.
Research & Development
If successful, many R&D applications
are literally worth millions of dollars. Only a small
percentage of these
techniques and applications are published in forums such
as IR/INFO, because they are tightly held and legally
protected secrets. Often it is not as simple looking
at something
and seeing a defect. Instead, these techniques have been
developed over the course of years and refined by scientific
scrutiny at a cost of hundreds of thousands of dollars.
Facilities
Building Heat Loss
Inspecting buildings for heat loss was one of the first
commercial uses for infrared thermography. As countries
decide to become less dependent on fossil fuels, IR
will again be used as it was in the 1980’s in
order to monitor the energy efficiency of buildings.
In very cold climates, poorly installed insulation
and vapor barriers can lead to condensation problems
and the degradation of the building itself. As more “fresh” outside
air is introduced into buildings, condensation and
its side effects, mold and mildew, are a real threat
(especially in the form of health-related lawsuits)
to the building owner/operator.
Building Quality Control
Infrared thermography can be used as a building quality
assurance tool. Almost all building materials will
retain heat energy and therefore can be checked for
quality of installation. Improper installation of insulation
and/or seals in buildings can be seen in the form of
heat loss and air leaks. Also, building components “inside” the
walls, ceilings and floors are recognizable because
of their differences in mass. For example, infrared
thermography can be used to determine the presence
and correct placement of grouted cells in concrete
block walls. If the owner of a new block building spends
a little money checking their (the low-bidder’s)
work with infrared thermography, the contractor will
be forced to build the building per specifications
or face the added direct cost of repairs and resulting
loss of schedule repercussions.
Roof Moisture Surveys
A well prepared, graphic and accurate map of the infrared
signatures of a roof can be of tremendous benefit to
a building roof owner at all stages of the roof’s
limited life. Knowing where the subsurface moisture
is located will help the roof owner manage his assets.
This form of predictive maintenance works well on many
types of flat and low-slope roofs. Here are the basics:
At night, areas of roof moisture are warmer, because
the accumulated heat (from daylight sunshine) in the
trapped water mass is greater than in the dry, functioning
insulation or roof substrate. After sunset, as the
roof’s structure cools down, the wet areas of
roof insulation and other materials maintain higher
temperatures because of their higher mass, allowing
infrared cameras to detect the sources of heat and
record them for later analysis.
There are two ways to perform IR roof moisture surveys:
on-roof and aerial. I first performed an on-roof infrared
survey as part of an overall building survey in 1989.
I do not like performing these surveys from the roof…here’s
why. When standing on the roof, eye-level is at best
six feet over the surface. If you are looking out over
a roof with large areas of moisture contamination (even
if you have a good camera) there is virtually no way,
without taking multiple shots, that you can get, say,
a 900-square foot amoeba-shaped blob, or an 80-foot long
striation of subsurface moisture resolved on the screen
in one infrared shot. If you take multiple shots, the
report becomes confusing, and the visual images that
you have to take the next day are hard to line up with
the infrared images. J. P. “Sonny” Ledoux,
an infrared thermographer with over twenty years of infrared
experience, describes the problem best in saying “When
performing on-roof surveys, many times, you can’t
see the forest for the trees.” It is difficult
to schedule, perform, document and produce high quality
reports. One can easily be fooled by heat due to other
factors such as water between multiple layers, old patches,
heavy flood coats, reflective coatings, heat-producing
equipment under the roof, heat blowing down onto the
roof surface, stains on the roof, heavy build-up of ballast
at parapet walls and along edges, etc. The best way to
obtain excellent imagery is to get high above the roof
and look down. This helps avoid reflections and one gets
a larger area in the picture.
We tried using helicopters. Ferry times were slow, costs
were high, and we had to deal with vibrations. We have
found that by using fixed-wing aircraft together with
high spatial resolution (512 x 512 focal plane array
cameras with 262,144 pixels) infrared cameras, we now
have the right platform. The disadvantage is that small
roofs, far away from the plane’s operational area,
become cost-prohibitive.
There are numerous advantages to performing the infrared
roof moisture surveys this way:
Costs are comparatively
low per square foot because we fly millions of square
feet per flight, with a crew
of two. We can wait for the right night for imaging, and
survey many roofs under good conditions.
Aerial imagery is better than on-roof imagery, but not
because we have four times the pixels. We use up
our pixels by flying typically 1,500-2,000 feet above the
building. The reason is that by getting a large
area of the roof in one view, we have more useful imagery.
One can see the beginning and end of a long striation
or large amoeba-shaped blob of heat on the roof.
This allows us to see lesser and more water, by mass, because
we are not standing on top of it.
High-angle, straight down infrared images lessen reflections,
eliminate the problem of rooftop equipment being
in the way of the image and eliminate the problem of access
to multiple levels of the roof.
Plan view imaging allows for the accurate marking of
areas of suspect roof moisture contamination onto AutoCAD
drawings. The drawings are made by laying the blank AutoCAD “over” the
captured visual and/or infrared image on the screen.
If dimensional information is available, this creates
a quantitative, scale-quality AutoCAD drawing of
the suspect moisture contamination on the roof.
By capturing large areas at once, a high quality report
is easier and less expensive to produce. Infrared
thermographs, visual photographs and AutoCAD drawings can be made
of the roof. As a result, the report is clear, concise and
easy to understand. The report can also be purchased
as needed, with respect to level of detail. Here
are the different levels of reporting, in order of costs:
a) unedited videotape, b) edited videotape, c)
printed thermographs, d) aerial photographs, e) AutoCAD drawings,
f) digital and printed report. The buyer of this
service has the advantage of obtaining any one or all of these
report components, with the cost being proportional
to the level purchased. Also, since the digital videotape
(a record of the roof on that night) is archived,
he/she can use this information later, to compare proportional
images of that same roof to images from a later date.
Perhaps the biggest advantage of aerial infrared is
not its use on roofs that have well-defined areas of
moisture at all, but those roofs that are the most difficult
to image from any distance or angle. I am referring to
the roofs that, for instance, have a lot of ballast,
are covered with reflective coatings or ones that for
whatever reason are impossible to image from the roof.
With high-resolution aerial imagery, slight nuances of
temperature can be seen from far enough away to actually
see the pattern of heat.
Aerial Infrared Applications
When a liquid is introduced into a body of water (ocean,
river, stream, lake) the former can be differentiated through
the use of high-resolution thermal imaging because the
temperatures are almost always different. Often these liquids
can be followed back to their source. These environmental
impact infrared surveys can be used to detect illegal dumping
and/or discharge, track pollution such as waste spills
or oil spills, monitor effluents from storm drains and
sewage treatment plant discharge, monitor ground water
seepage into rivers, streams and lakes, manage heated water
from power plant cooling towers, or measure the amount
of fresh water from ground sources that is introduced into
an estuary.
Many warm-blooded animals can be found and counted from
the air. It is far more accurate than any other method
and is used primarily by government agencies. Animal counts,
such as deer population density information, is used to
monitor and control the population of deer on city, county,
state and federal lands.
When a road or building complex is planned, the site can
be flown to see if any geothermal activity is present at
the surface. The U.S. Forest Service uses aerial infrared
imaging to monitor forest fires. This information can be
sent immediately to those in charge of controlling fire
lines. Subsurface fires can also be monitored using aerial
infrared thermography. Landfill fires can be hazardous
to the surrounding environment. Knowing where, how many
and the extent of underground fires is useful to those
in charge of containing and/or extinguishing them. Peat,
coal and wood chip piles, which combust spontaneously,
can also be monitored. Aerial infrared can be helpful to
the firefighters of structural fires, especially on large,
single story buildings. Where ancient Indian trails cross
the desert, the land under the trails has been compacted.
By using nighttime aerial infrared imaging, the aerial
infrared thermographer can see this higher density differentiated
from the lower density adjacent to the trails.
Even from high altitudes, steam line inspections are one
of the easiest applications for aerial infrared thermographers.
Thermal contrast between active steam lines and the surrounding
ground are usually good. High voltage electrical transmission
lines can be imaged from the air. Even from shorter distances,
accurate temperatures of electrical faults are almost impossible
to measure due to the spot size to target distance ratio
problem. Detecting electrical faults is much easier and
can be accomplished. Specification writers have not yet
realized the simple physics of this problem and continue
to ask that quotations include providing quantitative data
on fault areas. Because they are smaller, lower to the
ground and run through populated areas, high voltage electrical
distribution lines are much more difficult to see against
all the thermal clutter on the ground such as trees, street
lights, people, animals, etc. They are best left to ground-based
thermographers. Pipelines are also difficult to survey.
Trees, shrubs, brush and water often cover the pipeline.
Search and rescue (SAR) operations
are often “rush” jobs
where conditions are less than ideal. Aerial infrared SAR
is better than ground-based SAR in most instances; however,
it is still overrated. People targets either do not want
to be seen, are disabled and unable to move to an area
where they can be seen, or are trying to keep the warmth
of their body close by insulating themselves, so they cannot
be seen.
Applications: Everywhere
So far, I have discussed electrical
and mechanical predictive maintenance, process improvements,
R&D, NDT, facilities
and miscellaneous aerial infrared applications. There are
many more that do not fall directly into a particular category.
And there are many more. The point of this paper is that
there are too many to list...
Conclusions
The infrared thermographer who performs only one or two
types of surveys is missing out on many rewarding applications.
Do you ever notice how you loathe writing the reports?
The reason is that you have already done the fun part-that
is, the discovery. It is great fun to discover, no fun
to disseminate information to others. It is our industry's
challenge to explore new markets, improve our methodology
for gathering and disseminating infrared data and find
new ways to use this fantastic technology.
Those who challenge themselves to
explore new markets, develop new techniques and improve
the body of infrared
knowledge will reap the financial and intellectual rewards.
With modern infrared cameras, software and computers, infrared
thermographers today are almost never limited by the infrared
equipment’s ability to measure temperatures or discern
differences in temperature. Rather, we are only limited
by our imagination.
Fig. 1-Loose lug connection on electrical circuit breaker
