ABSTRACT
The practical use of infrared thermography is, in a
nutshell: looking at the thermal energy emitted from
an object, explaining normality, seeing abnormalities
and reporting them in a graphic, usable and
easy-to-understand fashion, so that someone who is not
familiar with the technology, can act to fix whatever
is wrong. This works on heat emissions from all types
of energy - not just electrical energy. There are many
uses for infrared thermography other than inspecting
electrical switchgear. In this paper I will discuss
two of those other uses for infrared thermography.
FORWARD
Stockton Infrared Thermographic Services, Inc. (SITS)
has been performing infrared surveys of electrical
switchgear for about 10 years. Due to the marketing
efforts of our company and many others, the word is
getting out. By now, almost everyone in electrical
maintenance has seen an article about how infrared
thermography (IR) has saved a piece of electrical
switchgear from an imminent explosion. In fact, on a
daily basis, most practicing infrared thermographers
find big problems on the electrical systems that they
are checking. At least weekly, IR contractors (because
they more often look at previously uninspected
switchgear) discover a problem that if left unattended
would cause a world-class failure, explosion and fire.
An example of one of these is shown in figures 1 & 2,
where the warmest bolt was 909 degrees F. This is the
very nature of electrical thermography. Albeit slower
than we in this industry wanted or expected, IR
predictive/preventive maintenance (P/PM) is becoming a
regular part of the maintenance of electrical
equipment.
Thermographers, who challenge themselves to explore
new markets, develop new techniques and improve the
body of infrared knowledge, reap the financial and
intellectual profits. The beauty of infrared is that
the opportunities seem to be limitless. Here are two
examples: Part I is about an improvement of technique
over the current on-roof method of finding water that
is entrained in the insulation of roofs. Part II is
about a new method for inspecting the concrete
reinforcing in CMU (block) walls.
(PART I) ROOF MOISTURE SURVEYS
ABOUT ROOFS AND ROOF MOISTURE SURVEYS
Everything wears out. Roofs are no exception. The
ravages of sun, wind, rain, snow, hail, ice,
chemicals, leakage and time will eventually cause
every roof to fail. Just like electrical switchgear,
it must be maintained. To the owner of a building, a
roof warranty might seem to be the answer, however
roof warranties are written by roof manufacturers.
They are designed not to protect the owner of the
roof, but instead to limit the liability of those
writing the warranty. Vaguely written roof warranties,
which do not define words like "regular" or "routine"
or "maintenance" will come back to haunt the owner.
Roof owners should have some kind of agreement with
their roofer or roofing consultant to inspect the roof
at least once a year.
Waterproofing problems manifest themselves in two
ways: leakage and entrained water contamination.
Leakage is pretty simple, although the leak inside the
building rarely directly relates to the exact spot on
the roof where there is a hole, which you already know
if you ever tried to track one down. Since most types
of insulation absorb a certain amount of water, it is
harder to find the contamination because the roof may
not develop a leak (in the building) until the
insulation has absorbed all the water that it can
hold. There are basically three tools that owners can
use to find the subsurface water. Nuclear gauges-which
count neutrons, capacitance meters-which measure
resistance, and infrared-which measures heat. Both
nuclear gauges and capacitance meters allow a
technician to take a (sample) reading on a 5' X 5' or
10' X 10' grid on the roof. When plotted on a roof
plan, these measurements are used to extrapolate where
the water is. They work well of roofs that do not gain
or lose much solar energy and therefore do not lend
themselves to infrared. Some roofs and insulation
types or combinations do not even absorb water.
For roofs
that do absorb water, infrared is the preferred
method. Here is how it works. During the day, the sun
radiates energy onto the roof of the building and into
the roof substrate, then at night, the roof radiates
the heat back into outer space. This is called
radiational cooling. Higher mass (wet) areas retain
heat longer than the lower mass (dry) areas and
therefore radiate heat for a longer period of time,
because it takes longer to cool. Infrared cameras can
detect the heat and "see" the higher mass (wet areas),
during this "window" of uneven heat dissipation.
ON-ROOF INFRARED SURVEYING
To perform an on-roof survey, you need a crew of three
to four people. You need one experienced thermographer,
one thermographer's helper and one building owners'
representative for access and security. Hopefully
he/she will know the history of the roof. Also, it is
a good idea to have a roofer or roof consultant there.
If questionable areas are found, he can first use his
(non-destructive) nuclear or capacitance meter to test
them, and if needed, take core samples and competently
repair them. You need access to the roof and plenty of
time to collect data. Depending on how many problems
are found (very dependent), a crew can survey ~200,000
square feet of building roof each night. Usually,
areas that contain subsurface moisture are outlined
with marking paint directly on the roof and marked on
a drawing. Infrared images are stored on videotape
and/or on-board flashcards. The next day, after
thermograms are printed, at least one of the crew goes
back on the roof to take visual photographs of the
areas that are considered to contain subsurface
moisture. The report includes infrared and visual
imagery (example shown in figures 3 & 4), the roof
plan marked with areas of suspect moisture
contamination and a videotape of the entire survey.
That would characterize an on-roof survey correctly
performed.
HOW
MOST ON-ROOF INFRARED THERMOGRAPHY IS DONE TODAY
Most roofs never see an infrared survey. The ones that
do by and large are done by roofers or roof
consultants not infrared thermographers. I recently
presented a short course on infrared thermography at a
large plant maintenance and engineering show. On my
way to work the booth with our salesmen, I made it a
point to go to all the roofing companies' booths and
talk with the reps. Not to my surprise - every roofing
company, every roof consultant and every roof
manufacturer offered infrared thermography as a
service of their company. A full 85% of these
companies have their own infrared cameras. The other
15% have a contractor of some type to perform surveys.
The
quality of infrared surveys & reports that are
currently being performed on roofs is seriously
sub-standard due to the fact that infrared
thermographers, who are trained and paid to perform
surveys and make reports, in most cases, do not do the
work. Instead, the vast majority of roof surveys are
performed by roofers who do infrared as a sideline.
The
reasons that the quality is low is that:
Some
roofer-thermographers frankly, do not know how or when
to perform a proper roof moisture survey. They are
never trained.
- Often,
the large roofing (and engineering) companies have
one camera in the company or region, and it is
shipped to whatever office might need it, with
written 'instructions' on its operation!
- Some
use IR cameras that were never designed to produce
soft or hard copy of the images.
- Some
use IR cameras that are not capable of measuring
slight enough differences in temperature so that
discernible hard copy can be printed of the areas of
suspect contamination.
- Many
think that since IR "pictures" won't turn out
anyway, that instead painted marks on the roof or
photographs will suffice.
- Many
do not even think that a "thermographic" report is
necessary, because it is really not the end product
which is to fix the roof.
WHAT IS WRONG WITH THE TYPICAL NIGHT UP ON THE ROOF
Let's go scanning:
First we
need an IR camera - any kind will do - because no one
will ever see the images anyway.
Now we
need a guy who knows the roof - this is really
important! When we see that bright spot out there - he
can save us a lot of time by telling us that it is an
uninsulated patch that was applied two years ago or
confirm our suspicion that an area has "had problems"
or "has leaks".
We need
some meters lots of them.
We need
something to dig a hole in the roof to verify what we
are seeing - because many of the warm areas are going
to be either reflections, heavy flood coat, heavy
ballast, the effects of heat-producing equipment on
the underside of the roof, or old patches under the
latest roof. We could even have water
trapped/sandwiched between two good roofs.
We need a
photocopied fire plan of the plant, which is the best
that the owner can supply, as our roof plan. Somebody
is going to have to draw in those forty-two air
conditioning units on this thing.
We will
find some warm blobs. If our building owner's rep
cannot explain why they should be there and after
metering it and punching a hole and finding water we
got ourselves a finding. Tomorrow we will climb back
on the roof if its not raining and take a photo. Hey
let's take a photo of the core sample!
The
problem with the typical roof survey is that it is
performed by people, which have something other than
infrared that they are really selling. They do not do
infrared surveys for a living; they are not performing
the survey for the sake of the report, so they do not
see the necessity of keeping up with the latest
equipment or techniques. The thermographic end product
is not their end product. As a result, the quality of
the work is sub-standard and of course, the reaction
to the report is displeasure. The true agenda is to
sell roofing, consulting services and/or roof repairs.
Infrared thermography is a means-to-an-end and not an
end in and of itself. Because of this fact, IR is
sometimes given away as a loss leader, which are
seldom great products.
WHY
DON'T THERMOGRAPHERS DO ROOFS?
There are several reasons that IR thermographers have
failed to take advantage of this tremendous potential
market.
It is
difficult to schedule, perform and write a report for
a Roof Moisture Survey. Even if a company is getting
good money for a survey, roof surveys are often
difficult jobs, even for a professional thermographer.
Even with the image quality, portability, handy image
storage capabilities, improved software and
computerized reporting systems of the latest IR
cameras, the logistical considerations of the job and
thermal dynamics of a roof structure make it a tough
job to perform well. Also, there are many different
types of roofs, membranes, fastening systems,
substrates and insulations that are used to construct
the roof system, which have to be considered.
Because
it is sometimes used as a loss leader, the prices for
IR on roofs are held artificially low, making roof
jobs unattractive to infrared companies. No one can
blame an engineer for buying roof infrared from a
roofer when:
He does
not know the quality difference between products.
He cannot
find an IR company to bid on the survey.
He has
some level of trust in his roofer to start with. They
may really be an excellent roofing company.
It is
easier for an infrared thermographer to make a living
doing electrical IR. This is the case. Electrical IR
is proven, accepted, graphic and fairly well
understood by the engineering community as important
in the short term. It is much easier to sell an
electrical survey.
Roof
problems are not emergencies, therefore roof surveys
are not deemed as important. Unless water drips onto
the final product line or into the switchgear panels,
it is not an emergency. Buckets can be placed under
the leaking area for a quick fix. Roofers are
painfully aware of this fact, and roof P/PM programs
often suffer as a result of inadequate funding.
WHAT TO DO ABOUT IMPROVING THE QUALITY?
In order to perform a really good infrared survey, you
need to have a good working knowledge and experience
about roofs and about infrared thermography. While
there may be a couple of infrared companies that have
well trained roof consultants working for them, and
there may be a couple of roofing companies with really
well-trained infrared thermographers, they are few and
far between. Even if there are a few they can't
possibly perform IR on 1/1000th of all the roofs.
We are
doing a lot of aerial roof work for roofing companies
and roof consultants. They let us know what they want
in an infrared report. They want high quality infrared
thermograms and visual photographs that their
customers can understand. They want scaled, accurate
drawings of the heat they can figure out what is
causing it. The answer for roofers is to hire
excellent thermographers. The answer for infrared
thermographers is to perform excellent surveys, make
excellent reports and let the roof experts work over
the data. Many of these guys are actually very good at
roofing.
Infrared
thermographers are not (and should not profess to be)
experts on every single thing that they inspect, but
there is always someone out there that can get to the
true problem, if given a well prepared thermographic
report. The same holds true for roof surveys. WE
ARE NOT A ROOFING COMPANIES; WE ARE INFRARED
COMPANIES!
HOW
AND WHAT HAPPENED WHEN WE WENT TO THE AERIAL PLATFORM
We have been performing infrared roof moisture surveys
for eight years and for the past three years, we have
been using aerial infrared almost exclusively for our
roof clients. Aerial IR started for SITS, when I
attended IR/INFO in January, 1996 and saw the
presentation "Aerial Infrared Remote Sensing -
Selected Applications", by Lawrence R. Davis, Davis
Aviation. After the presentation, I found the author
and told him that I was interested in hiring his
company to do all of our roof moisture surveys. I told
him then; that I thought his market was working for
infrared thermographers that were having the same
problems I was, surveying roofs. After seeing his
paper, I knew that hiring a company that could do the
roof a lot better than we could, was the right thing
for our clients and our company.
Literally
overnight, we started producing Qualitative Aerial
Infrared Roof Moisture Surveys that were far, far
superior to our previous reports.
To get
this new service 'off the ground', I went first to all
my roof clients who, to my surprise resisted, sighting
every conceivable reason not to do aerial IR. They
were happy with my on-roof method it had worked
before and they were quite creative with reasons why
not to change. I answered all their objections with
the exception of painting the roof. I showed them
scaled AutoCAD drawings, and explained that this way
was superior. But, they liked being able to climb up
on the roof, walk the repairman up to a marked area,
step down firmly and hear the unmistakable squishy
sounds that are moisture contamination. The only valid
reason that they could come up with for staying with
the old method was the marking. So, I told the hard
liners that after we flew the roof, I would take the
AutoCADs and my trusty marking device up on the roof
and mark the wet areas. Problem solved. It was great
flying over jobs that we had done previously, which
had not yet been repaired. I could see all those warm
blobs - in seconds - that we had struggled for nights
and days to document.
Next, I
went to all my electrical clients, sat down with them
and played an aerial video. Many of these people did
the surveys because they trusted me when I told them
this was the proper way to maintain the roof. Some of
them, I had never approached because I did not want to
do their roof. Some had roofs that were heavily
ballasted, had multiple levels, many patches, and some
so dangerous looking, that we hated to go on them to
check the air conditioning and dust handling
equipment.
Then I
started calling on companies that we had never done
business with. I found that sometimes they were more
interested in our other services, so not only did we
get aerial work, we also picked up some electrical and
other contracts as a direct result of marketing aerial
infrared.
THE
DIFFERENCES BETWEEN ON-ROOF AND AERIAL INFRARED
The cameras that we use to use for on-roof surveys
were not of sufficient thermal or spatial resolution
to obtain good imagery from our minimum flight
altitudes of 1000 feet AGL (above ground level). Most
modern infrared cameras have 256 X 256 pixels, a total
of 65,536 pixels. The infrared cameras that we use for
Aerial IR have 512 X 512 pixels, which total 262,144
pixels. We use a specially modified Cessna 182 to
perform the surveys. A helicopter will work, however
high operating costs, vibrations, and slow ferrying
speeds make a fixed-wing the best option for us.
Very
little time is required to obtain the infrared data,
once the aircraft is over the building. Usually, a
200,000 square foot building is imaged in less than 5
minutes. This will include multiple passes over the
building from varying altitudes, attitudes, speeds and
angles. This spring we surveyed a two million square
foot tire manufacturing plant in less than 20 minutes
over the building! The imagery is recorded on digital
videotape and/or captured directly onto a computer.
The visual photographs are taken earlier in the day or
the next day.
When the
thermographer returns to the office, the image
processing begins. The visual photographs are
developed and the thermograms are saved on the
computer. The infrared images and digital or
"scanned-in" photographic images are used to make an
edited videotape of the passes over the building. Both
visual and infrared images are used to do the analysis
by overlaying the infrared images "over" the AutoCAD,
to draw in the areas of suspected moisture
contamination. The result is a report where visual,
infrared and AutoCAD components (printed and video)
are well matched and lined-up.
The same
laws of physics apply to both aerial IR and on-roof
IR. We need a dry roof surface, low winds, no rain and
few clouds on the night of the survey. Of course the
"window" when the roof is radiating heat differently
from wet and dry areas, has to be longer in order to
do an on-roof survey. One very big advantage to aerial
is angle of view. We used to climb up rickety ladders
with $80K cameras to get as high above and as close as
possible, to a 90 degree angle over a particular area,
to avoid reflections and image a larger area. Aerial
has the advantage of looking straight down over the
target, and access to multiple levels is never a
problem. The drawing dimensions are close to perfect,
which is a big problem with on-roof.
There are
three distinct advantages that on-roof surveys have
over aerial.
- If you
are on the roof, you can look underneath rooftop
equipment with marginal results.
- If you
take along a roofer or roof consultant, he can
verify wetness (or lack of wetness) before the
report is prepared.
- You
can mark suspect areas of the roof with paint, then
and there.
Aerial
infrared has every other advantage over on-roof.
QUALITY
There is no comparison. Image quality* is superior by
every standard (examples shown, figures 5-8).
*By image
quality I am referring to the overall usable quality
of the imagery. Last summer, we were performing some
on the ground infrared wall work in Florida. We found
ourselves within 100 miles or so of a roof job which
needed to be done right away. The airplane was 800
miles away. Since we were doing on-ground work, we had
the cart and decided to try the Mitsubishi 600 up on
the roof. Of course, the resolution on the 5' X 5' wet
sections that we were imaging was better, due to the
fact that we were only a few feet from the roof.
However, the quality of the imagery (to see an outline
of heat from the moisture contamination) was inferior
to what an aerial shot of the same sections would have
been.
Angle of
view allows for accurate marking of areas of suspect
roof moisture contamination on AutoCAD drawings and
later, if needed, directly on the roof.
Visual
images, infrared images and AutoCAD drawings are
lined-up.
Improved
reporting allows the end user to understand the report
much easier.
LOGISTICS
We can wait for the PERFECT NIGHT and survey lots of
roofs under ideal conditions.
Instead
of tying up four people for a night to perform a
survey, we can use an airplane crew of two, and do 50
times as much data collection. Then, while it rains or
snows, we can process the data not in a hurry on a
freezing cold night but at our own pace in the
office.
If we do
not like the image we are getting from a roof, we can
come back at different times of the night in order to
catch the "window" at just the right time.
SPEED OF DATA COLLECTION
Instead of 200,000 square feet in a night, as much as
ten million square feet can be imaged in a night.
Since
there are a limited number of perfect nights in a
year, a company needs to survey as many square feet of
roofing as possible on these perfect nights.
SAFE AND NON-DESTRUCTIVE
Unless something falls off the plane nobody will
ever get hurt, and a hole will not be cut in a roof
while performing an aerial survey.
BELIEVE IN WHAT YOU DO
The only reason an infrared thermographer ever has to
lay down a meter or cut a hole in a roof is if he does
not trust the infrared. At that moment, he stops being
an infrared thermographer, and starts being a roof
consultant. OUR JOB is to excellent at what WE do.
Leave the touching to others! Do you wiggle that high
voltage wire to make sure it is loose? Of course not.
You have learned to trust IR, make reports and let
somebody else take the connection apart.
Since
roofs cost several dollars per square foot to repair,
knowing where the water is (it got there through a
hole, tear, or leak around a penetration), is a very
cost-effective means of planning the extent of
repairs. Building owners have tremendous investments
over their heads. Extending the life of the roof will
save them a lot of money. Also, their motivation may
be, for example, to use this information to plan
budgets, look at a building before they buy it, or to
put some teeth into a new roof warranty. That's right,
a lot of our work is on new roofs. They get baseline
information to compare at any time in the future, and
catch any installation problems. This is real roof
asset management!
(PART II) CHECKING THE PLACEMENT OF GROUTED CELLS IN
SINGLE-WYTHE CMU WALLS
OVERVIEW
Another virtually unexplored application for infrared
thermography is its use as a quality assurance tool
for Concrete Masonry Unit (CMU) building walls. It is
not hard to find these buildings. Your local schools,
malls, strip shopping centers and retail buildings
were probably built using this type of construction.
CMU walls are erected fairly quickly. Due to their
load bearing capabilities, relative low cost, fire
ratings, versatility and a wide selection of
decorative outer faces, they are popular as inside and
outside walls in these types of buildings.
Heretofore, determining the placement of reinforcing
grout in single-wythe (contiguous) CMU walls has been
a painstaking and destructive undertaking. Usually, a
test is performed because, by accident, missing cells
are discovered when a wall penetration is retrofitted
or change order is executed, requiring the wall to be
opened. Often, a hammer or hammer drill is used to
punch holes where the grouting is supposed to be. The
test results are used to extrapolate to the extent of
the problem. This method falls short, since the sample
is so small (1/10,000th of the wall), that only
outright fraud can be found, and excess grouting
cannot be determined. This is where IR can help. It is
quick, non-destructive and accurate.
HERE IS HOW IT IS DONE
As with roof IR, the sun does the energy loading.
After sunset, wall areas that contain concrete are
warmer (higher mass) because the heat from daylight
sunshine radiates from these areas longer than areas
with empty or insulated cells (lower mass). As the
building structure cools down, we go to each wall
section (buildings use a grid line system based
usually on structural column lines) and stand far
enough back to get a column on the left, and a column
on the right in the image, for reference purposes. Of
course, you want to catch the building when it is
radiating the largest delta-T between the pilasters
(concrete filled cells) and the rest of the wall.
The trick
is timing.
The
building goes through a heating and cooling cycle over
the course of 24 hours. At dawn, the outside
temperatures rise; the sun warms the air and more
importantly shines directly on the walls. At this
point the pilasters are cooler. At sunset, the outside
temperatures fall and the pilasters are warmer
(example shown in figure 9 & 10). Under ideal
conditions, this lag time between the two different
masses, allow us to see (depending on many factors) as
much as a five Fahrenheit degree delta-T. Now, to an
IR thermographer that is a significant delta-T. Just
about any IR camera can detect where the concrete is.
I can see it easily with my Hughes Probeye, however,
that is the best case scenario. Many factors affect
the absorption of energy into the wall and radiational
cooling out of the wall. Lee R. Allen (AAIT
Corporation) and I have been working on a methodology
for years and we still have not figured out exactly
when to look at a wall. The delta-T is usually no more
than a degree or so and the window does not always
last very long.
There are
lots of other factors that affect the cooling and
heating cycles:
- wind,
- the
weather (as nearly as we can figure for about the 60
hours prior),
-
moisture content in the wall itself,
- the
orientation of the building to the path of the sun
during different seasons of the year,
- what's
going on thermally inside the building,
-
emissivity of the paint on the wall (and how dry the
paint is).
- and
more
(PART III) CONCLUSIONS
To an
infrared thermographer, the world is one big radiator.
Energy and the transfer of energy is happening
everywhere around you. We can explore the world with
eyes that nobody else has. With our modern infrared
cameras, software and computers, we are almost never
limited by the camera's ability to measure
temperatures or discern differences in temperature.
Rather, we are limited by our knowledge of how hot the
object that we are looking at should be. It is our
industry's challenge to figure how to improve what we
are doing, come up with new uses and techniques for
gathering and disseminating infrared data effectively
and efficiently.
