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T Proion Guid
GAS DETECTION
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Content page1. Infrared Visualizes Gas Leaks 4
2. The Mid Wave Gas Detection Camera 6
3. The Long Wave Gas Detection Camera 12
4. Application Stories 18
5. The Gas Detection Camera Why It Is Different? 24
6. Techniques to Maximise Gas Detection 34
7. Safety 38
This booklet is produced in close cooperation with the Infrared Training Centre (ITC).
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE
Copyright 2009, FLIR Systems AB. All other brand and product names are trademarks of their respective owners.
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INTRODUCTION
Over the decades inrared cameras have revolutionized
maintenance in many industries, proving to be the most superior
technology or nding electrical and mechanical hidden aults
even beore they occur. The clear benet has been substantial
cost savings, increased worker saety and enhanced product/
process quality.
Inrared cameras can also play a major role in helping to decreaseenvironmental damage. They are successully used or detecting
insucient insulation in buildings, identied as one o the highest
opportunity areas or decreasing the greenhouse eect, as well
as detecting environmentally dangerous gas leaks.
Not only do some o the gases harm the environment but the
leaks also cost companies substantial amounts o money. Against
this background FLIR has introduced a range o gas detection
cameras capable o detecting many gases including SF6 - a gas
24,000 times more environmentally dangerous than CO2.
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1. INfRaReD VIsUalIzes Gas leaks
Many chemical compounds and gases are invisible to the
naked eye. Yet many companies work intensively with these
substances beore, during and ater their production processes.Strict regulations govern how companies are to trace, document,
rectiy and report any leaks o volatile gaseous compounds, and
how oten these procedures are to be carried out.
Earlier methods o gas detection required close or near contact
using snier technology and probes. The limitations o these
methods are that they are time consuming and run a risk o
missing gas leaks. They may expose inspectors to invisible and
potentially harmul chemicals, and do not allow or wind and
weather actors that can produce inaccurate measurements. In
addition, they can only tell us something about the test points
that have been identied beorehand and only give readings
within the immediate vicinity o the inspector.
The FLIR Gas Detection cameras are inrared cameras which are
able to visualize gas by utilising the physics o ugitive gas leaks.
The camera produces a ull picture o the scanned area and leaksappear as smoke on the cameras viewnder or LCD, allowing the
user to see ugitive gas emissions. The image is viewed in real
time and can be recorded in the camera or easy archiving.
The key success actors or businesses today are saety,
eciency and protability. When carrying out maintenance, it is
o vital importance that maintenance engineers are able to obtain
as complete a picture as possible o the condition o the plant.An inrared camera is an extremely important tool or tracing
potential aults.
The examples below demonstrate a wide range o applications
that can be served with IR cameras. Potential applications are
limited only by the imagination o the system designer.
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Greatly Improved Eciency
Experience shows that up to 84 percent o leaks occur in less
than 1 percent o the plant. This means that 99 percent o whatare expensive, time-consuming inspection tools are being used to
scan sae, leak-ree components.
Using a Gas Detection camera you get a complete picture and
can immediately exclude areas that do not need any action. This
means you can achieve enormous savings in terms o time and
personnel.
Another advantage is that systems do not have to be shut downduring the inspection, measurements can be carried out remotely
and rapidly and most important o all problems can be
identied at an early stage. An inspector using an inrared camera
system can get through an inspection regime o more than one
hundred objects an hour.
Sae Scanning
A Gas Detection camera is a quick, non-contact measuringinstrument that can also be used in hard-to-access locations. It
can detect small leaks rom several meters away and big leaks
rom hundreds o metres away. It can even show leaks on moving
transport vehicles, greatly improving the saety o both the
inspector and the plant.
Preserving the Environment
Fugitive gas emissions contribute to globalwarming, cost industry billions o dollars
in regulatory nes and damages, and pose
deadly risks to both workers and people living
close to these acilities. FLIR Gas Detection
cameras detects dozens o volatile organic
compounds, including the greenhouse gas
Sulur Hexafuoride (SF6), eciently contributing to a better
environment.
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2. The mID waVe GasDeTeCTION CameRa
Applicable Industries
The mid wave gas detection camera is particularly suited to theollowing industries:
Oil Refning The typical renery consists o two
types o process, separation and conversion. The
separation processes split crude oil into useul
ractions to be sold as uel or used as eed orurther processing. The conversion processes
modiy molecules to provide products with suitable
characteristics or blending into nished uels. The
camera has an excellent response to most o the
light end products and intermediates ound in uels
processing reneries. The general rule o thumb is
that the camera can detect crude oil ractions rom
gas down to the kerosine part o the barrel.
Petrochemical The industries that make
hydrocarbon substances using base eedstocks
rom the oil rening processes either by conversion
processes or urther separation that is not normally
carried out at an oil renery. Most o the chemicals
used or made in these industries have good visibility
using the mid wave gas detection camera.
Chemical The production o non-hydrocarbon
or inorganic chemicals rom base eed stocks.
These are oten a mixture o batch and continuous
processes that yield very high purity products.
The mid wave gas detection camera has a good
response to some chemicals ound in this sector o
industry.
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Power Generation The production and
distribution o electric power. Gas red power
stations oten use natural gas as uel. The mid
wave camera is thereore very suitable or leak
detection in this industry.
Natural Gas The production, storage,
transportation and distribution o natural gas.
Natural gas consists mainly o methane and
ethane, both o which are clearly detectable with
the mid wave camera. The camera can be used
or leak detection in all parts o this industry
rom the gas production eld right through thedistribution network to the end consumer.
Service Providers Increasingly companies are
contracting out services or leak detection and
repair (LDAR). LDAR service providers currently
using non-imaging gas detection methods will
see a dramatic improvement in productivity andgas detection capability using a gas detection
camera.
Regulators Enorcement o statutory
regulation by government agencies rather than
industry is common in many countries. The gas
detection camera enables these agencies to
monitor industry ensuring their compliance with
regulations and auditing their perormance in
emission reduction.
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aPPlICaTIONs
Leak Location
The camera can be used to detect gas rom many dierent
sources in the petrochemical industry but some o the mostcommon leak paths are rom:
Flanges Valvestems
PlugsandCaps Machinery
Couplings Pumpseals
Holes Passingvalves
Draincovers InstrumentConnections
In a complex petrochemical acility there may be many thousandso potential leaks paths. Some may be leaking but most will not.
Using the Gas Detection camera allows the user to examine
many potential leaks sources in a short time and rom a distance.
ConventionalleakdetectionmethodssuchasaVolatileOrganic
Compound meter (or snier) mean that the operator must visit
and test each potential leak site. Each item must thereore be
accessible or made accessible to be tested. A ull survey by this
method would clearly be signicant longer and more expensive
than with the gas detection camera.
Level oat switch
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Corrosion Under Insulation (CUI)
Occasionally leaks are ound in unexpected locations. Equipment
that is thermally insulated is susceptible to water penetration
into the insulation i the sealing o the outer cladding is poor. I
the equipment temperature is suitable, the water heats up and
can create a region o very high corrosion out o sight under the
insulation. The shell o the equipment can rapidly corrode to such
an extent that it starts to leak and this leakage can be detected
by the camera at considerable distance, sometimes several
hundred metres away rom the leak source.
Improving Plant Start-Up Saety
The reasons or conducting a survey may vary rom site to site
but also rom time to time. Most petrochemical acilities are nowrequired to examine their process plant or leaks to reduce the
emissionofvolatilecompounds(VOCs)totheatmosphere.This
orms the bulk o the use o the mid wave camera in this industry
but there are other advantages that are not so readily apparent.
The camera has had proven success in leak detection surveys
during the start up o process plants ollowing both planned
and unplanned shut-downs. The thermal cycles associated with
shut-down and start-up can initiate leaks in equipment that waspreviously leak ree and components that have been disturbed
due to maintenance activity may also leak. Perorming a leak
detection survey using a gas detection camera during this critical
phase in the operating cycle o a process plant can help to
achieve every owners aim o a sae, leak ree start up.
Lost Product Opportunities
Leaks rom process equipment, no matter how small, not
only constitute a potential damage to the environment, they
also represent lost product that could otherwise be sold to
customers. There may be many very small leaks that have been
in existence or many years in locations that are dicult to access
or test that all add up to considerable lost prot. Frequently
surveying the process plant can help to eliminate these leaks and
maximise the owners prot.
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Incorrect Fault Location
Items o machinery may sometimes be shut-down or
maintenance unnecessarily. It has been known or leaks to
bedetectedwithVOCmetersonlytondthatsubsequent
examination with a camera proves that the source o the leak is in
a dierent location that does not require an expensive shut-down
to rectiy. The camera shows in real time the leak plume and
allows it to be traced back to its true origin.
Regulation
Statutory regulation, laws and external audits are all driving
owners o petrochemical plants to monitor, report and reduce
theiremissionsofVolatileOrganicCompounds(VOCs).Some
countries rely on the company to reduce their emissions byrepairing the leaks o their own ree will; others use nes or the
threat o nes as an incentive.
In the USA the Environmental Protection Agency requires
companies to ollow the Method 21 process or their LDAR
(Leak Detection And Repair) programmes. This method is less
common outside the
US but there is still arequirement to carry
out leak detection
surveys by a method
that is acceptable to
the regulator. The use
o the gas detection
camera is permitted
as an Alternate Work
Practice under Method
21 and is becoming
accepted as a suitable
method in the EU. In
the EU, industry bodies
such as CONCAWE
have reviewed the perormance o the gas detection camera
method and have ound that it is an acceptable alternative to
theconventionalVOCmeterorsniffermethodforpointsourceemissions.
Inrared image o a process urnace
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Spectral Response and Detectable Gases
The mid wave gas detection camera has a detector response o
3-5 m which is urther spectrally adapted to approximately 3.3
m by use o a cooled lter. This makes this particular model o
camera most responsive to the gases commonly ound in the
petrochemical industries. The camera can detect many gases but
it has been laboratory tested against 19 which are:
Benzene
Butane
Ethane
Ethylbenzene
Ethylene
Heptane
Hexane
Isoprene
MEK
Methane
Methanol
MIBK
Octane
Pentane
1-Pentane Propane
Propylene
Toluene
Xylene
Conclusions
The gas detection camera technique has a wide range opotential uses in the petrochemical industry, all o which have
positive benets or the owner o the plant. It is an accepted
Alternate Work Practice in the Method 21 leak detection
procedure and has clear time and cost benets over the
conventionalVOCmeterorsniffermethod.Althoughlimited
to a certain extent by environmental conditions, the camera
has proven many times that it can identiy leaks at some
distance thereby reducing the cost o surveys by removing the
requirement to provide access to every potential leak path.
A leaking pressure gauge
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3. The lONG waVe GasDeTeCTION CameRa
Applicable Industries
The long wave gas detection camera is particularly suited to theollowing industries:
Electrical Utility A large amount o the
equipment used in the distribution o high voltage
electrical power uses Sulphur Hexafuoride (SF6)
as an insulating gas. This allows the equipment
to be more compact and protected rom the
elements inside substations. The long wave gasdetection camera is extremely sensitive to SF6.
Petrochemical The industries that make
hydrocarbon substances using base eedstocks
rom the oil rening processes either by
conversion processes or urther separation that is
not normally carried out at an oil renery. Some
o the chemicals used or made in these industrieshave good visibility using the long wave gas
detection camera.
Chemical The production o non-hydrocarbon
or inorganic chemicals rom base eed stocks.
These are oten a mixture o batch and continuous
processes that yield very high purity products.
The long wave gas detection camera has a good
response to some chemicals ound in this sectoro industry.
Service Providers Increasingly companies are
contracting out services or leak detection and
repair (LDAR). LDAR service providers currently
using non-imaging gas detection methods will
see a dramatic improvement in productivity and
gas detection capability using a gas detectioncamera.
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aPPlICaTIONs
SF6 Detection
The primary market or the long wave gas detection camera to
date is the electrical distribution industry and specically thedetection o Sulphur Hexafuoride (SF6). SF6 is used extensively
in the electrical distribution industry as an insulating gas in high
voltage switchgear and transormers. It is a potent greenhouse
gas with a global warming potential (GWP) o 23,900 and an
atmospheric lietime o 3,200 years. The GWP means that a
release o 1kg o SF6 into the atmosphere has the same impact
as a release o 23,900 kg or 23.9 tonnes o CO2. To put this in
perspective a company
that purchases 1 tonne per
year o SF6 as top-up gas is
releasing 1 tonne per year
through leaks. This is the
equivalent o 23,900 tonnes
o CO2. To produce this
amount o CO2 you would
have to drive an average
sized car just over 149million miles (239 million
km). Thats the equivalent
o driving 311 times to the
moon and back or 5964
times round the equator!
Conversely, a company that
reduces its emission o SF6
to the atmosphere by usinga gas detection camera
to locate and x leaks is
improving the environment by the same amount as taking 11,950
average cars o the road.
Leak paths ound on electrical distribution equipment are ewer
than in the process industries. The most common are fanges,
bushings, bursting discs and valve stems. Leaks may be due
to poor installation, disturbance during planned maintenance or
ailure o the sealing parts due to age.
Typical SF6
Filled Substation
Equipment
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The long wave gas detection camera has proved to be highly
eective at detecting very small leaks. The pressures used in
switchgear and transormers are relatively low which results in
very small leak rates. In addition, the operating temperature o
the equipment is generally close to ambient. The result is a low
thermal contrast between the leak and the background. Despite
this, the camera is capable o detecting leaks as small as 0.25 kg/
year and has had success in both indoor and outdoor substations.
As with the mid wave camera, the long wave camera is eective
at some distance which not only removes the requirement to
provide access to all potential leak paths it also permits leak
surveys to be completed when the equipment is energised.
Chemical IndustriesThe applications or the long wave gas detection camera in
these industries are very similar to the applications or the mid
wave gas detection camera in the petrochemical industries but
the reasons or the surveys may be slightly dierent. In the
petrochemical industry the main drivers or leak detection surveys
are the protection o the environment, reduction in lost product
and the elimination o potentially fammable leaks. These priorities
also apply in the chemical industries but the chemical compoundsvisible with the long wave gas detection camera are generally
more toxic. Protection o personnel may thereore become an
additional reason or perorming leak detection surveys.
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Rerigerant Gases
The long wave camera is also ideal or detecting several
rerigerant gases. These include gases that are used or domestic
and commercial rerigeration and automotive air conditioning. The
gas camera is most eective when used at the manuacturing
stage or these items rather than the maintenance stage. New
product design testing and production sample testing can lead to
reduced ailure rates improving reliability o the nished product
and reducing the emission o potentially harmul gases to the
atmosphere.
Regulation
Governments are becoming more aware o the risk posed to
the environment by release o SF6. There is a general increase
worldwide in the use o gas lled substation equipment and no
alternative substance is currently known or used. Consequently
they are providing a combination o reward and punishment or
the reduction o losses and the release o gas respectively. Some
governments are enorcing reduction in SF6 release by means o
nes; some are advocating encouraging the reduction o leaks by
giving nancial incentives such as tax breaks or demonstrated
reduction in consumption. The cost o SF6 is also increasing whichurther increases the nancial motivation to eliminate leaks.
Co-workers identiy the location o a gas leak
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Spectral Response and Detectable Gases
The long wave gas detection camera has a detector response
o 10-11 m which is urther spectrally adapted to approximately
10.5 m by use o a cooled lter. This makes this particular model
o camera most responsive to Sulphur Hexafuoride (SF6) as
well as many gases used in the chemical industry and severalcommon rerigerant gases. The camera can detect many gases
but it has been laboratory tested against 8 which are:
SulphurHexauoride
AnhydrousAmmonia
EthylCyanoacrylate(Superglue)
ChlorineDioxide
AceticAcid FREON-12
Ethylene
MethylEthylKetone(MEK)
SF6 leak rom a high voltage insulator
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In addition to the laboratory tested gases there are 18 additional
gases that the camera is known to detect. These are:
AcetylChloride
AllylBromide
AllylChloride AllylFluoride
Bromomethane
FREON-11
Furan
Hydrazine
Methylsilane
MethylVinylKetone
Propenal Propene
Tetrahydrofuran
Trichloroethylene
UranylFluoride
VinylChloride
VinylCyanide
VinylEther
Conclusions
The gas detection camera technique has a wide range o
potential uses in the electrical distribution and chemical
industries, all o which have positive benets or the owner
o the plant. It is an accepted Alternate Work Practice in the
Method 21 leak detection procedure and has clear time, saety
andcostbenetsovertheconventionalVOCmeterorsniffermethod. Although limited to a certain extent by environmental
conditions, the camera has proven many times that it can
identiy leaks at some distance thereby reducing the cost
o surveys by removing the requirement to provide access
to every potential leak path and permitting surveys to be
completed on energised electrical equipment.
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4. aPPlICaTION sTORIes
Read how our customers are using FLIR Gas Detection cameras.
Tracing gas leaks: maintenance and saety
problems highlighted
With more than 160,000 kilometres o piping o every
imaginable kind, Shell Nederland Rainaderij in Pernis
(Rotterdam) is the largest oil reinery in Europe. Saety
and environmental considerations are irmly embedded
throughout the company, its quality systems and its
production management processes. Shell has also adopted
a stringent saety policy in which preventive maintenance is
uppermost.
Many chemical compounds and gases are invisible to the
naked eye. Yet many companies work intensively with these
substances beore, during and ater their production processes.
Strict regulations govern how companies
are to trace, document, rectiy and report
any leaks o volatile gaseous compounds,
and how oten these procedures are to
be carried out. The most commonly used
technologyistheToxicVaporAnalyzer(TVA)
or snier technology. When searching or
potential gas leaks, we check all systems
at points that may or may not have beenidentied beorehand. These checks are
carried out regularly, and are particularly
important ollowing a shutdown. At a
renery like the one we have here, this
means carrying out tens o thousands tests
on piping, stopcocks, seals, valves, torches,
etc.BeforewehadtheFLIRGasFindIR,
aninspectorusingtheTVAcouldcarryoutaround ve hundred inspections per day.
Rutger Zoutewelle,
research analyst at ShellPernis.
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An inspector using this inrared camera system can, on the
other hand, get through an inspection regime o more than one
hundred objects an hour. The most important reason or using the
system is to minimise discharges o gas and other volatile organic
substances rom our pipework, particularly (potential) leaks
around fanges and other gaskets, explains Rutger Zoutewelle,
research analyst at Shell Pernis.
Sae scanning
The key success actors or businesses today are saety,
eciency and protability. When carrying out maintenance, it is
o vital importance that maintenance engineers are able to obtain
as complete a picture as possible o the condition o the plant.
A thermal imaging system is an extremely important tool ortracing potential aults. Experience shows that up to 84 percent
o leaks occur in less than 1 percent o the plant. This means that
99 percent o what are expensive, time-consuming inspection
tools are being used to scan sae, leak-ree components. Using
the FLIR GasFindIR in this sector allows us to achieve enormous
savings in terms o time and personnel.
The technologies currently in use may expose inspectors toinvisible and potentially harmul chemicals, and do not allow
or wind and weather actors that can produce inaccurate
measurements. In addition, they can only tell us something
about the test points that have been identied beorehand and
only give readings within the immediate vicinity o the inspector.
The inrared technology used by the FLIR GasFindIR shows
gas emissions as a plume o smoke. When a leak has been
identiedfromasafedistanceusingthedevice,theToxicVapor
Analyzer can be used to determine the concentration percentage
o the substance. Rutger Zoutewelle: We heard about FLIR
GasFindIR through our colleagues in Houston. Compared to how
we did things beore, using the camera or testing oers many
advantages over more conventional technologies. The camera is a
quick, non-contact measuring instrument that can also be used in
hard-to-access locations. It also oers benets in terms o saety
and the environment.
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BeneftsThe core o the FLIR GasFindIR is a cooled Indium Antimonide
(InSb) detector. This detector produces clear images with a high
level o detail. The camera, which weighs only 2.5 kg, has been
designed or use in harsh industrial environments and operates
within a wide temperature range o -15 C to +50 C. It produces
inrared images in real-time in the widely used PAL ormat. It has
an industrial shock rating o 40G. The camera can detect twenty
dierent types o gas in real time; these appear on the screen as
black smoke. These characteristics mean that miles o piping can
be scanned rom a sae distance. Rutger Zoutewelle: Most pipes,
fanges, valves and other connections in petrochemical operations
are ree o aults. However, certain actors that are beyond our
control could result in a small number o components not beinghundred percent. The positive experiences o our colleagues at
the plant in Houston in using the system to trace leaks resulted
in Shell Pernis deciding to introduce the technology here as well.
Anyone using the system has to go on a short training course and
then needs a ew days o on-the-job amiliarisation to become ully
conversantwiththesystem.But,onceyouhavegotthehangof
it, the camera oers many benets. The camera is in constant use
at the renery and is always used ollowing a shutdown. Its aninvaluable tool and a great preventive solution.
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A Smart SolutionUsing thermal imaging techniques in the eld can place high
demands on the equipment and the user: oten a sae distance has
to be maintained rom the object being tested or, in other cases,
the problem might be how to get close enough. Then you have to
remember that the work may involve climbing, or hours at a time
spent inspecting a major plant. Thereore, the size and weight o
the equipment that inspectors have to carry around with them are
important actors. The FLIR GasFindIR contributes to the saety
and the eective operation o our plants. It provides direct, tangible
results and gives peace o mind, concludes Rutger Zoutewelle.
Its particularly useul when inspecting high pressure systems, as
these are at the greatest risk o developing leaks. Here, the camera
has become virtually indispensable.
The camera can be used in a number o dierent ways to inspect
plant saely. There are several major benets to using thermal
imaging techniques. These include the act that systems do not
have to be shut down during the inspection, measurements can be
carried out remotely, rapidly and at relatively low cost and most
important o all problems can be identied at an early stage.
Using the FLIR GasFindIR, an inspector can get through an
inspection regime o more than one hundred objects an hour.
The most important reason or using the system is to minimisedischarges o gas and other volatile organic substances rom our
pipework.
A modern complex petrochemical acility
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FLIR GasFindIR inrared camera spots
methane leaks, prevents uncontrolled gas
venting and keeps air clean at Norwegian
landllEconomic and environmental concerns push or an increasinglystreamlined waste disposal, treatment, neutralization andrecycling process. Waste treatment companies increasinglyturn into energy suppliers. The GasFindIR gas detectioninrared camera supports these trends by providing immediateand tangible results.
Lindum Ressurs og Gjenvinning AS, based in Norway, specializesin waste treatment solutions. Lindum ollows a consistent waste-to
energy conversion by composting, recycling, as well as extracting
landll gas or power production and residential heating. The
companys main site at Drammen, one hour drive rom Norways
capital Oslo, has a biogas production plant and a huge landll
consisting o selected solid waste covered with clay layers.
The methane gas produced by the landll is extracted and used orpower production and residential heating. Methane is an odourless,
environmental harmul gas which is created as a result o pressure
ormed in the landll. Moreover, the landll discharges hydrogen
sulphide (H2S) a malodorous gas that at times annoys surrounding
residential areas.
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To detect relevant leaks, Lindum
decided to procure a FLIR
GasFindIR, an inrared camera that
traces and visualizes about twenty
VolatileOrganicCompoundgases
including methane.
The landll, with a surace o approx
10 hectares, is inspected twice a
week at dawn or about one hour.
The GasFindIR instantly shows gas
leaks, visualized in black or white
smoke. Landll workers then cover
the leaks with clay and an ironedmass to neutralize the sulphide
odours.
The FLIR GasFindIR is also used or
inspection o the biogas production
piping on a weekly basis. And the
Lindum company, convinced o
the cameras benets is oeringinspections with its GasFindIR to
other landll companies, as imagery
can be easily recorded by a standard video recorder and stored.
The FLIR GasFindIRs eciency can be measured easily: we nd
some our to ve leaks per week and we have been able to reduce
the oul odour development considerably, says operations manager
Aud Helene Rosenvinge.
We consider the GasFindIR both a maintenance and a saety
instrument that has become indispensible, says Rosenvinge,
adding that she estimates cost savings at a minimum o EUR
12,000 per year.
To access more application stories, please visit
www.fir.com/thg/applicationstories
Gas leak on land fill surface
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5. The Gas DeTeCTION CameRa why IT Is DIffeReNT?
Detectors
The construction o a thermal imaging camera is similar to theconstruction o a digital video camera. There is a lens, a detector,
some electronics to process the signal rom the detector and a
viewnder or screen or the user to see the image produced by
the camera. The detectors used or the Gas Detection cameras are
quantum detectors that require cooling to cryogenic temperatures
(around70Kor-203C).TheMWcamerausesanInSbdetector
and the LW camera a QWIP detector.
In materials used or quantum detectors, at room temperature
there are electrons at dierent energy levels. Some electrons have
sucient thermal energy that they are in the conduction band,
meaning the electrons there are ree to move and the material can
conduct an electrical current. Most o the electrons, however, are
ound in the valence band, where they do not carry any current
because they cannot move reely. (See let-most views o Fig 1.)
When the material is cooled to a low enough temperature,
which varies with the chosen material, the thermal energy o the
electrons may be so low that there are none in the conductionband (upper centre view o Figure 1). Hence the material cannot
Figure 1. Operating principle o quantum
detectors
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carry any current. When these materials are exposed to incident
photons, and the photons have sucient energy, this energy can
stimulate an electron in the valence band, causing it to move
up into the conduction band (upper right view o Figure 1). Thus
the material (the detector) can carry a photocurrent, which is
proportional to the intensity o the incident radiation. There is a
very exact lowest energy o the incident photons that will allow
an electron to jump rom the valence band into the conduction
band. This energy is related to a certain wavelength, the cut-o
wavelength. Since photon energy is inversely proportional to its
wavelength, the energies are higher in the SW/MW band than
in the LW band. Thereore, as a rule, the operating temperatures
or LW detectors are lower than or SW/MW detectors. For an
InSb MW detector, the necessary temperature must be lessthan173K(-100C),althoughitmaybeoperatedatamuchlower
temperature. A QWIP detector typically needs to operate at about
70K(-203C)orlower.ThelowercentreandrightviewsofFigure
1 depict quantum detector wavelength dependence. The incident
photon wavelength and energy must be sucient to overcome the
band gap energy, E.
Cooling MethodThe Detectors in the Gas Detection cameras are cooled using
Stirling Coolers. The Stirling process removes heat rom the cold
nger (Figure 2) and dissipates it at the warm side. The eciency
o this type o cooler is relatively low, but good enough or
cooling an IR camera detector.
Figure 2. Integrated Stirling cooler,
working with helium gas, cooling
down to -196C or sometimes even
lower temperatures
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Image Normalization
Another complexity is the act that each individual detector
in the FPA has a slightly dierent gain and zero oset. To
create a useul thermographic image, the dierent gains and
osets must be corrected to a normalized value. This multi-
step calibration process is perormed by the camera sotware.
The nal step in the process is the Non-Uniormity Correction
(NUC). In measurement cameras, this calibration is perormed
automatically by the camera. In the Gas Detection camera, the
calibration is a manual process. This is because the camera does
not have an internal shutter to present a uniorm temperature
source to the detector.
The ultimate result is a thermographic image that accuratelyportrays relative temperatures across the target object or scene.
No compensation is made or emissivity or the radiation rom
other objects that is refected rom the target object back into
the camera (refected apparent temperature). The image is a
true image o radiation intensity regardless o the source o the
thermal radiation.
Real-time image o the gas cloud displayed on the built in LCD
screen
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Spectral Adaptation
The gas detection camera diers rom measurement cameras.
In addition to the lens, detector, cooler and image processing
electronics there is a lter mounted on the ront o the detector.
This lter is cooled with the detector to prevent any radiation
exchange between the lter and the detector. The lter restricts
the wavelengths o radiation allowed to pass through to the
detector to a very narrow band called the band pass. This
technique is called spectral adaptation. The lter band pass
wavelengths or the dierent gas detection cameras are shown in
Table 1.
Camera Model Detector Spectral Range Filter Waveband
Mid Wave 3-5 m approx. 3.3 m
Long Wave 10-11 m approx. 10.5 m
Table 1. Spectral Response or Gas Detection Cameras
Gas Inrared Absorption Spectra
For many gases, the ability to absorb inrared radiation depends
on the wavelength o the radiation. In other words, theirdegree o transparency varies with wavelength. There may
be IR wavelengths where they are essentially opaque due to
absorption. Physical property databanks exist containing inrared
absorption data or many substances. To determine the inrared
absorption spectrum or a gas a sample is placed in an Inrared
Spectrometer and the absorption (or transmission) o inrared is
measured at dierent wavelengths. These spectra are normally
published as graphs and the absorption spectrum o benzeneand sulphur hexafuoride are shown in Figures 9 and 10. One
source or IR spectrum data is the American National Institute
o Standards and Technology (NIST). Their web based data book
http://webbook.nist.gov/chemistry/name-ser.html is a very useul
(and validated!) resource. Selecting a lter that restricts the
camera to operating only in a wavelength where a gas has a
very high absorption spike (or transmission trough) will enhance
the visibility o the gas. The gas will eectively block more o
the radiation coming rom the objects behind the leak in the
background.
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Why Do Some Gases Absorb Inrared Radiation?
From a mechanical point o view, molecules in a gas could be
compared to weights (the balls in Figure 4 below), connected
together via springs. Depending on the number o atoms,
their respective size and mass and the elastic constant o the
springs molecules may move in given directions, vibrate along
an axis, rotate, twist, stretch, rock, wag, etc.
The simplest gas molecules are single atoms, like Helium,
NeonorKrypton.Theyhavenowaytovibrateorrotate,so
they can only move by translation in one direction at a time.
Figure 3. Single atom
The next most complex category o molecules is homonuclear,
made o two atoms such as Hydrogen H2, Nitrogen N1 pt and
Oxygen O1 pt. They have the ability to tumble around their
axes in addition to translational motion.
Figure 4. Two atoms
Then there are complex diatomic molecules such as carbon
dioxide CO1 pt, methane CH4 sulphur hexafuoride SF6, or
styrene C6H5CH=CH2 (these are just a ew examples).
Figure 5. Carbon dioxide 3 atoms per molecule
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Figure 6 Methane 5 atoms per molecule
This assumption is also valid or multi-atomic molecules.
Figure 7.SF67 atoms per
molecule
Figure 8.Styrene 16 atoms
per molecule
Their increased degrees o mechanical reedom allow multiple
rotational and vibrational transitions. Since they are built rom
multiple atoms they can absorb and emit heat more eectively
than simple molecules. Depending on the requency o the
transitions, some o them all into energy ranges that are located
in the inrared region where the inrared camera is sensitive.
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Transition type Frequency Spectral range
Rotation o heavy molecules 109 to 1011 HzMicrowaves,
above 3 mm
Rotation o light molecules &
vibration o heavy molecules1011 to 1013 Hz
Far inrared,between 30 m
and 3 mm
Vibrationoflightmolecules.
Rotation and vibration o the
structure
1013 to 1014 Hz
Inrared,
between 3 m
and 30 m
Electronic transitions 1014 to 1016 Hz UV-Visible
Table 2. Frequency and Wavelength Ranges o Molecular
Movements
On order or a molecule to absorb a photon (o inrared energy)
via a transition rom one state to another, the molecule must
have a dipole moment capable o briefy oscillating at the same
requency as the incident photon. This quantum mechanical
interaction allows the electromagnetic eld energy o the photonto be transerred to or absorbed by the molecule.
Gas Detection cameras take advantage o the absorbing nature o
certain molecules, to visualize them in their native environments.
The camera ocal plane arrays and optical systems are specically
tuned to very narrow spectral ranges, in the order o hundreds
o nanometres, and are thereore ultra selective. Only gases
absorbent in the inrared region that is delimited by a narrowband pass lter can be detected.
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Belowaretwotransmittancespectraofgases:
BenzeneC6H6 absorbent in the MW region
Sulphur Hexafuoride SF6 absorbent in the LW region.
1.000
0.800
0.600
0.400
0.200
0.000
2.500 3.000 3.500
m
4.000 4.500 5.000
Figure 9. Benzene C6H6 absorbent in the MW region
1.000
0.800
0.600
0.400
0.200
0.000
2.000 6.0004.000 8.000 12.00010.000 16.00014.000 20.00018.000
Figure 10. Sulphur Hexauoride SF6 absorbent in the LW region.
Benzene
Strong absorption
around 3.2/3.3 m
Strong absorption
around 10.6 m
Sulphur Hexafuoride
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Visualising The Gas Stream
I the camera is directed at a scene without a gas leak, objects
in the eld o view will emit and refect inrared radiation through
the lens and lter o the camera. The lter will allow only certain
wavelengths o radiation through to the detector and rom this
the camera will generate an uncompensated image o radiation
intensity. I a gas cloud exists between the objects and the
camera and that gas absorbs radiation in the band pass range o
the lter, the amount o radiation passing through the cloud to
the detector will be reduced (Figure 11)
AbsorbedBackground (Tb)
Emitted (Tg)
Transmitted (Tt)
Reflected (Tr)
Figure 11. Eect O A Gas Cloud
In order to see the cloud in relation to the background, there must
be a radiant contrast between the cloud and the background.
That is to say, the amount o radiation leaving the cloud must not
be the same as the amount o radiation entering it (Figure 12). I
the blue arrow in Figure 12 is the same size as the red arrow, the
cloud will be invisible.
Background (Tb)
Background (Tb)
Emitted (Tg)
Transmitted (Tt)
Reflected (Tr)
Figure 12. Radiant Contrast O Cloud
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In reality, the amount o radiation refected rom the molecules in
the cloud is very small and can be ignored. So the key to making
the cloud visible is a dierence in apparent temperature between
the cloud and the background (Figure 14).
Background (Tb)
Background (Tb)
Emitted (Tg)
Transmitted (Tt)
Figure 14. Dierence In Apparent Temperature
Key Concepts To Make The Cloud Visible
Thegasmustabsorbinfraredradiationinthewaveband that the camera can see
Thecloudmusthavearadiantcontrasttothe
background
Theapparenttemperatureofthecloudmustbe
dierent to the background
Cloudmotionassiststhevisibilityofthegas
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6. TeChNIqUes TO maxImIseGas DeTeCTION
Thermal Tuning
Thermal tuning is the term given to manual adjustment o thecamera settings to display the colours o the colour palette across
the target object. It is the most simple and common technique
used to improve the visibility o a gas leak. Operating the
cameras in automatic mode will do this or you but it may cause
the operator to miss leaks. Good operating practice is to always
thermally tune the image to optimise your chances o discovering
a leak. It also allows the operator to determine i there is more
than one leak in any particular location.
Figure 2.
Tuned Thermal Image
Figure 1.
Untuned Thermal Image
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High Sensitivity Mode
High Sensitivity Mode or HSM is the name given to an image
subtraction video processing technique that eectively enhances
the thermal sensitivity o the camera. A percentage o individual
pixel signals rom rames in the video stream are subtracted rom
subsequent rames. The eect is somewhat similar to perorming
a Non Uniormity Correction with the lens cap o but there is a
signicant advantage in as much as the camera can be moved whilst
in HSM. Using HSM gives the user control over the amount o
compensation applied to the video stream and thereore the degree
o increase in thermal sensitivity. HSM has particular advantages in
the detection o SF6 leaks using the long wave camera because o
the low pressures used in the equipment and associated low leak
rates. It also has benets in the mid wave camera when very smallleaks are to be identied.
Figure 4.
HSM On
Figure 3.
HSM O
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Temperature Range Selection
The selection o the correct temperature range will improve
the quality o the camera image. The temperature range needs
to be set or the approximate temperature o the target object
or o the object refected in the target. Using the correct range
removes noise and arteacts rom the camera image and hence
improves the visibility o any gas leaks. Just like a measurement
camera setting the correct temperature range is essential. I the
user selects the wrong temperature range they will not get an
accurate temperature measurement. In act they may not get a
temperature measurement at all. In the gas detection camera
setting the incorrect temperature range may eliminate any
possibility o imaging a gas leak.
Figure 6. Correct
Temperature Range
Figure 5. Incorrect
Temperature Range
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Conclusions
Besidesthesimpleautomaticmodeofoperationthere
are several other techniques that urther enhance the
ability o the operator to detect gas streams. Ater suitable
training the operator will be well equipped to maximise
their chances o nding gas leaks. The tools are standard
eatures, they are simple to use and make the cameras
very fexible and powerul tools.
Positioning the camera to maximise the thermal contrast and
improve gas visibility
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7. safeTy
The areas where the camera is designed to be used are
potentially dangerous unless you amiliarize yoursel with and
ollow local saety rules and regulations at the site where you areworking.Belowissomeadvicetokeepinmindwhileusingthe
camera on site:
Changethebatteryoutsideoperatingareasonly
Whenclimbingladdersorstairs,putthelenscaponand
use the camera strap to ree both your hands
Ifyoudetectalargeleakorpotentialseriouscondition,
immediately stop your work, move upwind and quickly
notiy the relevant personnel
Whenyoudetectaleak,makesureyouarenotinthe
leak when you make a video
Keeptheconnectorcoveronthebackofthecamera
closed when in potentially combustible atmosphere
Makeaquickscanfromadistancebeforeenteringan
operating unit to avoid entering a cloud o gas
Takenoteofthewinddirectionsandknowyour
surroundings should you have to leave quickly
The gas detection specialist should always liaise closely with
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FLIR Systems AB, Sweden
(head oce)
+46 (0)8 753 25 00
FLIR Systems Ltd, UK:
+44 (0)1732 220 011
FLIR Systems S.r.l., Italy
+39 (0)2 99 45 10 01
FLIR Systems GmbH, Germany:
+49 (0)69 95 00 900
FLIR Systems Sarl, France:+33 (0)1 41 33 97 97
FLIR Systems AB, Benelux:
+32 (0)3 287 87 10
wt our ppiction?wt ind o inrrd cri bt or our nd?
To speak to an inrared camera expert,
please contact: