Gas Detection Handbook

8/7/2019 Gas Detection Handbook

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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.

Vent pipes on a petrochemical plant14


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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.

Examining potential leak paths20


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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.

Covering and sealing a landfll site with clay22


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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

plant personnel38


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FLIR Systems AB, Sweden

(head oce)

+46 (0)8 753 25 00

[email protected]

FLIR Systems Ltd, UK:

+44 (0)1732 220 011

[email protected]

FLIR Systems S.r.l., Italy

+39 (0)2 99 45 10 01

[email protected]

FLIR Systems GmbH, Germany:

+49 (0)69 95 00 900

[email protected]

FLIR Systems Sarl, France:+33 (0)1 41 33 97 97

[email protected]

FLIR Systems AB, Benelux:

+32 (0)3 287 87 10

[email protected]

wt our ppiction?wt ind o inrrd cri bt or our nd?

To speak to an inrared camera expert,

please contact:

Gas Detection Handbook

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