inert gas system

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INERT GAS INERT GAS SYSTEMSYSTEM

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Inert Gas SystemInert Gas System

Aalborg Industries

A visual demonstrationI hope this

works!

http://www.aalborg-industries.com/press_room/showroom.php?path=film_IGS

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IntroductionIntroductionIntroductionIntroductionThe combustion & explosion of petroleum The combustion & explosion of petroleum gasses, the corrosion of steel occur only gasses, the corrosion of steel occur only when oxygen is presentwhen oxygen is present

The combustion & explosion of petroleum The combustion & explosion of petroleum gasses, the corrosion of steel occur only gasses, the corrosion of steel occur only when oxygen is presentwhen oxygen is present

The object of the Inert Gas System is to The object of the Inert Gas System is to reduce the oxygen content in the cargo reduce the oxygen content in the cargo tanks to below 8%, well below the tanks to below 8%, well below the Explosion Limit of 11.5%Explosion Limit of 11.5%

The object of the Inert Gas System is to The object of the Inert Gas System is to reduce the oxygen content in the cargo reduce the oxygen content in the cargo tanks to below 8%, well below the tanks to below 8%, well below the Explosion Limit of 11.5%Explosion Limit of 11.5%

This will prevent cargo tank explosion, This will prevent cargo tank explosion, reduces corrosion and increases reduces corrosion and increases pumping capacitypumping capacity

This will prevent cargo tank explosion, This will prevent cargo tank explosion, reduces corrosion and increases reduces corrosion and increases pumping capacitypumping capacity

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Flammable EnvelopeFlammable Envelope

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The Inert Gas SystemThe Inert Gas SystemThe Inert Gas SystemThe Inert Gas System The inert gas system washes The inert gas system washes

& cools the boiler exhaust & cools the boiler exhaust gases to produce an inert gases to produce an inert gas with a typical make-up gas with a typical make-up of:of:

Oxygen: 2 – 4%Oxygen: 2 – 4% Carbon Dioxide: 12 – 14%Carbon Dioxide: 12 – 14% Nitrogen: 80%Nitrogen: 80%

The inert gas system washes The inert gas system washes & cools the boiler exhaust & cools the boiler exhaust gases to produce an inert gases to produce an inert gas with a typical make-up gas with a typical make-up of:of:

Oxygen: 2 – 4%Oxygen: 2 – 4% Carbon Dioxide: 12 – 14%Carbon Dioxide: 12 – 14% Nitrogen: 80%Nitrogen: 80%

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The Inert Gas SystemThe Inert Gas SystemThe Inert Gas SystemThe Inert Gas System Alternatively an inert gas generator Alternatively an inert gas generator

may be used when:may be used when:

The ship does not have sufficient boiler The ship does not have sufficient boiler capacity for the flue gas systemcapacity for the flue gas system

Topping up units are fitted in addition Topping up units are fitted in addition to the flue gas systemto the flue gas system

A high quality inert gas is required A high quality inert gas is required such as on gas and chemical tankerssuch as on gas and chemical tankers

Alternatively an inert gas generator Alternatively an inert gas generator may be used when:may be used when:

The ship does not have sufficient boiler The ship does not have sufficient boiler capacity for the flue gas systemcapacity for the flue gas system

Topping up units are fitted in addition Topping up units are fitted in addition to the flue gas systemto the flue gas system

A high quality inert gas is required A high quality inert gas is required such as on gas and chemical tankerssuch as on gas and chemical tankers

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Inert Gas GeneratorInert Gas Generator

8

The picture represents a standard Inert Gas Generator (FU Type) complete with air fans, fuel pumps, deck water seal and P/V breaker

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The Inert Gas SystemThe Inert Gas SystemThe Inert Gas SystemThe Inert Gas System

Regulations require the Regulations require the oxygen content in cargo oxygen content in cargo tanks to be maintained at tanks to be maintained at notnot moremore than 8% by than 8% by volumevolume

Regulations require the Regulations require the oxygen content in cargo oxygen content in cargo tanks to be maintained at tanks to be maintained at notnot moremore than 8% by than 8% by volumevolume

1010

Inert Gas System SchematicInert Gas System SchematicInert Gas System SchematicInert Gas System Schematic

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Inert Gas System SchematicInert Gas System SchematicInert Gas System SchematicInert Gas System Schematic

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Inert Gas Scrubber SystemRefer to Handout Notes

Inert Gas Scrubber SystemRefer to Handout Notes

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Gas Pressure Regulation Valves(Refer to handout notes)Gas Pressure Regulation Valves(Refer to handout notes)

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Re-circulating Arrangementto regulate the flow of inert gas to the IG deck mainRe-circulating Arrangementto regulate the flow of inert gas to the IG deck main

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Deck Water SealDeck Water Seal

This is the principle barrier in the system

A water trap is fitted which permits inert gas to be delivered to the deck main but prevents any back flow of cargo gas

Even when the IG plan is shut down

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Deck Water SealDeck Water Seal

Gas flow towards cargo tanksGas flow towards cargo tanks Back pressure in cargo tanksBack pressure in cargo tanks

1717

Liquid Filled Pressure Vacuum Breakers Liquid Filled Pressure Vacuum Breakers (refer to handout notes)(refer to handout notes)

Liquid Filled Pressure Vacuum Breakers Liquid Filled Pressure Vacuum Breakers (refer to handout notes)(refer to handout notes)

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Instrumentation & AlarmsInstrumentation & Alarms

Certain instruments both fixed & portable, are required for the safe and effective operation of an Inert Gas system.

It is desirable that all such instruments should be calibrated to a consistent system of units

Certain automatic alarms and/or shutdown devices are also required to give visible and audible warnings and to shut down various components of the system

Clear instructions should be provided for operating, calibrating & testing all instruments and alarms

The following list gives some details of these instruments and alarms

Certain instruments both fixed & portable, are required for the safe and effective operation of an Inert Gas system.

It is desirable that all such instruments should be calibrated to a consistent system of units

Certain automatic alarms and/or shutdown devices are also required to give visible and audible warnings and to shut down various components of the system

Clear instructions should be provided for operating, calibrating & testing all instruments and alarms

The following list gives some details of these instruments and alarms

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Scubber Water Supply:-A low flow or pressure alarm should be fitted to give warning

of inadequate water supply. This should be connected with an automatic device to shut down the Inert Gas blower(s). Low and/or High level alarms may also be fitted to the scrubber water seal.

Blower Discharge Temperature:-A temperature guage, high temperature alarm and automatic

shut down arrangement of the Inert Gas blowers should be fitted.

Scubber Water Supply:-A low flow or pressure alarm should be fitted to give warning

of inadequate water supply. This should be connected with an automatic device to shut down the Inert Gas blower(s). Low and/or High level alarms may also be fitted to the scrubber water seal.

Blower Discharge Temperature:-A temperature guage, high temperature alarm and automatic

shut down arrangement of the Inert Gas blowers should be fitted.

20


Blower Discharge Pressure:-A pressure gauge should be fitted, and also an alarm to

indicate blower failure

Inert Oxygen Content:-Instrumentation should be fitted to monitor and to record

continuously the oxygen content of the inert gas on the discharge side of the Inert Gas blower during plant operation. A high oxygen content alarm should be fitted to operate at 8% by volume, but an automatic shut down device should not be fitted.

Blower Discharge Pressure:-A pressure gauge should be fitted, and also an alarm to

indicate blower failure

Inert Oxygen Content:-Instrumentation should be fitted to monitor and to record

continuously the oxygen content of the inert gas on the discharge side of the Inert Gas blower during plant operation. A high oxygen content alarm should be fitted to operate at 8% by volume, but an automatic shut down device should not be fitted.

21


Deck Water Seal:-Depending on the type fitted, a low water level indicator and

an alarm indicating low water level and/or low flow/pressure of water supply should be fitted

Inert Gas Deck Main PressureInstrumentation should be fitted to monitor and record

continuously the gas pressure in the Deck Main, located on the forward side of the deck isolating valve. One or more low pressure alarms should be fitted.

Automatic shut down of the cargo pumps in the event of low Inert Gas deck pressure may also be fitted

Deck Water Seal:-Depending on the type fitted, a low water level indicator and

an alarm indicating low water level and/or low flow/pressure of water supply should be fitted

Inert Gas Deck Main PressureInstrumentation should be fitted to monitor and record

continuously the gas pressure in the Deck Main, located on the forward side of the deck isolating valve. One or more low pressure alarms should be fitted.

Automatic shut down of the cargo pumps in the event of low Inert Gas deck pressure may also be fitted

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Control System:-Failure of the automatic control system power supply

should be indicated by an alarmThe siting of the various indicators and alarms will depend

on the particular design but it is strongly recommended that the appropriate indicators and alarms are sited so as to be readily at hand for the Duty Engineer

It is strongly recommended that the IG oxygen content and deck pressure indicators are duplicated in the CCR. An IG deck pressure indicator should also be fitted on the Bridge.

Control System:-Failure of the automatic control system power supply

should be indicated by an alarmThe siting of the various indicators and alarms will depend

on the particular design but it is strongly recommended that the appropriate indicators and alarms are sited so as to be readily at hand for the Duty Engineer

It is strongly recommended that the IG oxygen content and deck pressure indicators are duplicated in the CCR. An IG deck pressure indicator should also be fitted on the Bridge.

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Portable InstrumentsPortable Instruments

Oxygen Analysers:-Suitable for monitoring the oxygen content of the cargo

tank atmosphere should be provided

Combustible Gas Indicators:-Should be provided for testing the cargo tank

atmospheres. It should be noted that these instruments do not function correctly in inerted atmospheres

Oxygen Analysers:-Suitable for monitoring the oxygen content of the cargo

tank atmosphere should be provided

Combustible Gas Indicators:-Should be provided for testing the cargo tank

atmospheres. It should be noted that these instruments do not function correctly in inerted atmospheres

24

Portable InstrumentsPortable Instruments

Hydrocarbon Gas Indicators:-Which are calibrated for use in an oxygen deficient

atmosphere may also b used after a purging operation to measure the hydrocarbon gas content of an inert atmosphere

Appropriate sample points and sample tubing should be provided to facilitate the use of these portable instruments for monitoring cargo tank atmospheres

Hydrocarbon Gas Indicators:-Which are calibrated for use in an oxygen deficient

atmosphere may also b used after a purging operation to measure the hydrocarbon gas content of an inert atmosphere

Appropriate sample points and sample tubing should be provided to facilitate the use of these portable instruments for monitoring cargo tank atmospheres

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When do you test (just as an aside)When do you test (just as an aside)

Prior to tank entry Prior to enclosed space entry Prior to loading Prior to gas freeing To monitor space To monitor the atmosphere

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COSWP CHAPTER 17

ENTERING ENCLOSED OR CONFINED SPACES

Just a further quick aside from the current business

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COSWP 17.1.2 The atmosphere of any enclosed

or confined space is potentially dangerous. The space may be deficient in oxygen and/or contain flammable or toxic fumes, gases or vapours. Where possible, alternative means of working which avoid entering the space should be found.

17.1.2 The atmosphere of any enclosed or confined space is potentially dangerous. The space may be deficient in oxygen and/or contain flammable or toxic fumes, gases or vapours. Where possible, alternative means of working which avoid entering the space should be found.

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COSWP

17.1.3 Should there be any unexpected reduction in or loss of the means of ventilation of those spaces that are usually continuously or adequately ventilated then such spaces should also be dealt with as dangerous spaces.

17.1.4 When it is suspected that there could be a deficiency of oxygen in any space, or that toxic gases, vapours or fumes could be present, then such a space should be considered to be a dangerous space.

17.1.3 Should there be any unexpected reduction in or loss of the means of ventilation of those spaces that are usually continuously or adequately ventilated then such spaces should also be dealt with as dangerous spaces.

17.1.4 When it is suspected that there could be a deficiency of oxygen in any space, or that toxic gases, vapours or fumes could be present, then such a space should be considered to be a dangerous space.

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What do you look for?

Oxygen levels Flammable gasses

Toxic gasses

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The Use of Gas Measuring Instruments

Oxygen Analyser

Oxygen Analyser

Oxygen Analyser/Hydrocarbon meter

Oxygen Analyser

Oxygen Analyser/Hyrocarbon meter

Oxygen Analyser/Explosimeter/Draeger tube

Explosimeter

C.D.L. = Critical Dilution Line

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Measurement of Flammability and Gas ConcentrationMeasurement of Flammability and Gas Concentration

Description

Combustible gas meter

Hydrocarbon gas meter

Oxygen analyser

Specific gas detector

Principle

Catalytic filament

Thermal conductivity

Magnetic susceptibility

Chemical reaction

Principle

Catalytic filament

Thermal conductivity

Magnetic susceptibility

Chemical reaction

Measurement

Measures % LFL

Measures % HC gas

Measures % O2

Measures ppm

Measurement

Measures % LFL

Measures % HC gas

Measures % O2

Measures ppm

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In addition to the instruments just mentioned there are several different manufaturer’s models making use of the same principles.

e.g. not discussed here are Infra-red detectors (used on LNG carriers for liquified methane) and semi-conductor detectors

Measurement of Flammability and Gas ConcentrationMeasurement of Flammability and Gas Concentration

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The basic type of instruments in use on vessels are covered in pages 23 – 28 inc’l of your handout together with their generic description and the manufacturer’s name, type & model. It has to be said that these are somewhat outdated just now

Full details on the use & maintenance of the instruments will be given in the Instruction Manuals accompanying them and which the user must refer to

In the handout only the principles and limitations of the instruments are covered

By following the instrument’s instructions and subject to it’s limitations the instruments may be regarded as relible.

Gas Measuring InstrumentsGas Measuring Instruments

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Catalytic Filament Combustible Gas Indicator (MSA 2E)Catalytic Filament Combustible Gas Indicator (MSA 2E)

Operates on a Wheatstone Bridge principle

A mixture of combustible gas & air is drawn over the hot sensor element

The gas oxidises on the hot filament and makes it hotter (heat in = endothermic reaction)

This increases it’s resistance and this change in resistance (measureable) provides a measure of the gas concentration

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LIMITATIONS:- Calibrated to read 0 – 100% LFL only,

thereore suitable for this range only

If the sensor is exposed to too much Hydrocarbon gas i.e. 3 x LFL, the hydrocarbon gas will not be oxidised completely. This results in the needle being rapidly deflected to the max scale reading before dropping equally rapidly back to zero.

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LIMITATIONS (continued):- This may result in the operator taking a

false reading, therefore it is imperative to observe the instrument continuously to avoid overlooking this response

Prolonged operation of the instrument in such conditions can cause carbon deposits on the sensor filament and alter the response of the instrument

If such a situation is suspected the instrument must be checked.

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LIMITATIONS (continued):- Susceptible to filament poisoning from

non-hydrocarbon gasses (hydrogen sulphide, carbon monoxide) which may be present in the tank atmosphere

This damages the platinum coating on the sensor filament and subsequently the meter readings

But only if the non-hydrocarbons are present in high concentrations

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LIMITATIONS (continued):- Does not give reliable readings in

atmospheres deficient in oxygen such as those in inerted tanks

Can be affected by large changes in ambient temperature and….

Excessive pressure of the tank atmosphere (take NO FLOW reading)

Therefore not suitable for use in inerted tanks

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Convective Heat Loss Hydrocaron Gas Meter (MSA Tankscope)Convective Heat Loss Hydrocaron Gas Meter (MSA Tankscope)

The sensing element of this instrument is a non-catalytic hot filament

The composition of the surrounding gas determines the rate of loss of heat (heat out = endothermic reaction) from the filament, hence it’s temperature & resistance which is measureable

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The presence of hydrocarbon gas changes the resistance of the sensor filament which is reflected by a deflection in the meter

Unlike the sensor filament of the CFCG, the Tankscope sensor filament does not require oxygen for operation and is unaffected by inert gas

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Unlike the CFCG this instrument is not affected by gas concentrations in excess of it’s working scale. The reading goes off the scale & remains in this position while the sensor filament is exposed to the rich gas mixture

Ideal instrument for measuring in inert conditions

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LIMITATIONS:- Sensitive to flow rate and

high pressure in inerted tanks. Thus the recommendation to use the NO FLOW technique when taking readings

Sensitive to tilting therefore should be calibrated & used in a NO TILT mode

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Draeger TubesDraeger Tubes Designed to measure very low

concentrations of toxic gas(s)

Consists of glass tubes containing a certain filling which is designed to react with a specific gas and give a visible indication of the concentration of that gas

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Draeger TubesDraeger Tubes LIMITATIONS

Gas specific Non interchangeable with

other manufacturer products

Extension hose (if used) to be fixed between glass tube & hand pump

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Draeger TubesDraeger Tubes LIMITATIONS (continued)

Measurements made with mixtures containing high concentrations of hydrocarbons or other components may be less reliable due to interference by these components

Dräger's Simultaneous Test Set measures several gases at once. The tests offer a means to detect a variety of unknown chemicals in a short amount of time. Different systems are available for the detection of chemical warfare agents (i.e. nerve agents, sarin) and clandestine labs.

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Draeger: Newer ModelsDraeger: Newer Models Dräger X-am 7000 is the

innovative solution for the simultaneous and continuous detection of up to five gases. A combination of more than 25 sensors allows flexible solutions to individual monitoring tasks. The Dräger X-am 7000 can be equipped with three electrochemical, and two catalytic bead or infrared sensors.

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Draeger: Newer ModelsDraeger: Newer Models The smallest gas detection instrument for up to 5

gases. The Dräger X-am 5000 belongs to a new generation of gas detectors, developed especially for personal monitoring applications. This 1 to 5-gas detector reliably measures combustible gases and vapours as well as oxygen and harmful concentrations of CO, H2S, CO2, Cl2, HCN, NH3, NO2, PH3 and SO2. A variety of special calibrations for the catalytic Ex sensor allow even more sensitivity when detecting specific combustible gases and vapours. Equipped with durable XXS sensor technology, the Dräger X-am 5000 offers maximum security and extremely low operational costs.

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Tank Atmosphere Control Definitions of Tank Atmospheres

First Safety Platform. The hazards inherent in cargo tank cleaning operations can be avoided by ensuring that the tank atmosphere is kept in a non-flammable condition throughout the washing period

Second Safety Platform. The hazards may also be avoided by th exclusion, as far as practicable, of all ignition sources.

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Atmosphere B (Too Lean). Is an atmosphere made and maintained non-flammable by the deliberate reduction of the hydrocarbon gas content to belo the Lower Flammable Limit (LFL).

For the purpose of tank cleaning the maximum acceptable gas concentration should not exceed 50% LFL with cold water washing or 35% LFL with hot water washing

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Atmosphere C (Inert). Is an atmosphere made & maintained non-flammable by the introduction of inert gas and the resulatant overall reduction of oxygen content.

For the purpose of tank cleaning the tank atmosphere (oxygen content) should not exceed 8% by volume

51


Atmosphere A (uncontrolled atmosphere) and Atmosphere D (over rich) are not permitted on most ships.

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Inert Gas Procedures

General Policy of Tank Atmosphere Control

Tanks should be inerted prior to loading and maintained inert during loding, on the loaded passage, during discharge and during tank washing

Tanks should be kept in an inert condition whenever they contain cargo residues or ballast

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Inert Gas Procedures

General Policy of Tank Atmosphere Control

After cleaning and gas freeing it is not necessary to inert the tank

The transition from an inert condition to a gas free condition MUST be made without the tank atmosphere passing through the flammable range/envelope.

This means purging the tank with inert gas until it is below the Critical Dilution Line

5454

InertInert GasGas ProceduresProcedures

Primary InertingPrimary Inerting

From a gas free condition the tanks should be inerted prior From a gas free condition the tanks should be inerted prior to the loading of cargo until the tanks have an oxygen to the loading of cargo until the tanks have an oxygen content of less than 8% by volumecontent of less than 8% by volume

On completion of inerting all the tanks are to be pressurised On completion of inerting all the tanks are to be pressurised to a minimum of 100mm water guage and also kept common to a minimum of 100mm water guage and also kept common with the gas mainwith the gas main

A positive pressure being maintained on all tanks by A positive pressure being maintained on all tanks by topping up with IG as necessarytopping up with IG as necessary

From a gas free condition the tanks should be inerted prior From a gas free condition the tanks should be inerted prior to the loading of cargo until the tanks have an oxygen to the loading of cargo until the tanks have an oxygen content of less than 8% by volumecontent of less than 8% by volume

On completion of inerting all the tanks are to be pressurised On completion of inerting all the tanks are to be pressurised to a minimum of 100mm water guage and also kept common to a minimum of 100mm water guage and also kept common with the gas mainwith the gas main

A positive pressure being maintained on all tanks by A positive pressure being maintained on all tanks by topping up with IG as necessarytopping up with IG as necessary

5555


Loading or BallastingLoading or Ballasting

The IG plant is shut down and the deck isolating v/v The IG plant is shut down and the deck isolating v/v closed, unless loading is taking place at the same time closed, unless loading is taking place at the same time as deballasting (unusual???)as deballasting (unusual???)

Tank vents are opened and IG is thus vented from the Tank vents are opened and IG is thus vented from the tank as cargo or ballast is loaded into the tanktank as cargo or ballast is loaded into the tank

During loading “closed ullaging” is usedDuring loading “closed ullaging” is used

The IG plant is shut down and the deck isolating v/v The IG plant is shut down and the deck isolating v/v closed, unless loading is taking place at the same time closed, unless loading is taking place at the same time as deballasting (unusual???)as deballasting (unusual???)

Tank vents are opened and IG is thus vented from the Tank vents are opened and IG is thus vented from the tank as cargo or ballast is loaded into the tanktank as cargo or ballast is loaded into the tank

During loading “closed ullaging” is usedDuring loading “closed ullaging” is used

5656


Loaded / Ballast PassageLoaded / Ballast Passage

Tanks are re-pressurised for the loaded or ballast passageTanks are re-pressurised for the loaded or ballast passage A positive IG pressure should be maintained to prevent A positive IG pressure should be maintained to prevent

possible ingress of airpossible ingress of air Loss of pressure can normally be associated with leakage & Loss of pressure can normally be associated with leakage &

falling air and/or sea temperaturesfalling air and/or sea temperatures If tank pressure falls below the “low” level it will necessitate If tank pressure falls below the “low” level it will necessitate

starting the IG plant to restore the correct operating pressurestarting the IG plant to restore the correct operating pressure

Tanks are re-pressurised for the loaded or ballast passageTanks are re-pressurised for the loaded or ballast passage A positive IG pressure should be maintained to prevent A positive IG pressure should be maintained to prevent

possible ingress of airpossible ingress of air Loss of pressure can normally be associated with leakage & Loss of pressure can normally be associated with leakage &

falling air and/or sea temperaturesfalling air and/or sea temperatures If tank pressure falls below the “low” level it will necessitate If tank pressure falls below the “low” level it will necessitate

starting the IG plant to restore the correct operating pressurestarting the IG plant to restore the correct operating pressure

5757


Cargo or Ballast DischargeCargo or Ballast Discharge

Owners of the cargo, receivers and/or customs Owners of the cargo, receivers and/or customs authorities may require manual ullaging, water authorities may require manual ullaging, water dips and samples prior to discharge (regulations dips and samples prior to discharge (regulations permitting)permitting)

Owners of the cargo, receivers and/or customs Owners of the cargo, receivers and/or customs authorities may require manual ullaging, water authorities may require manual ullaging, water dips and samples prior to discharge (regulations dips and samples prior to discharge (regulations permitting)permitting)

5858


Cargo or Ballast Discharge (continued)Cargo or Ballast Discharge (continued) This is acceptable provided a minimum number of This is acceptable provided a minimum number of

tank openings are open at any one timetank openings are open at any one time

On completion of ullaging, and before commecing On completion of ullaging, and before commecing discharge the tanks are to be re-pressuriseddischarge the tanks are to be re-pressurised

All tanks are made common with the gas mainAll tanks are made common with the gas main

Tank openings including vents are closedTank openings including vents are closed

This is acceptable provided a minimum number of This is acceptable provided a minimum number of tank openings are open at any one timetank openings are open at any one time

On completion of ullaging, and before commecing On completion of ullaging, and before commecing discharge the tanks are to be re-pressuriseddischarge the tanks are to be re-pressurised

All tanks are made common with the gas mainAll tanks are made common with the gas main

Tank openings including vents are closedTank openings including vents are closed

5959

InertInert GasGas ProceduresProcedures Cargo or Ballast Cargo or Ballast

Discharge (continued)Discharge (continued)

The IG plant is operated and the deck isolating v/v is The IG plant is operated and the deck isolating v/v is opened to allow iner gas to replace the liquid being opened to allow iner gas to replace the liquid being dischargeddischarged

After discharge a hydrocarbon content of up to 4% may After discharge a hydrocarbon content of up to 4% may exist in an inerted tank however, it is preferable to exist in an inerted tank however, it is preferable to maintain the content at 2% which is below the CDLmaintain the content at 2% which is below the CDL

This condition should be monitored & maintained durig This condition should be monitored & maintained durig the ballas passagethe ballas passage

The IG plant is operated and the deck isolating v/v is The IG plant is operated and the deck isolating v/v is opened to allow iner gas to replace the liquid being opened to allow iner gas to replace the liquid being dischargeddischarged

After discharge a hydrocarbon content of up to 4% may After discharge a hydrocarbon content of up to 4% may exist in an inerted tank however, it is preferable to exist in an inerted tank however, it is preferable to maintain the content at 2% which is below the CDLmaintain the content at 2% which is below the CDL

This condition should be monitored & maintained durig This condition should be monitored & maintained durig the ballas passagethe ballas passage

6060

InertInert GasGas ProceduresProcedures Tank Washing including Tank Washing including

COWCOW

Tanks should be in the inert condition during tank Tanks should be in the inert condition during tank washingwashing

Tanks should be in the inert condition during tank Tanks should be in the inert condition during tank washingwashing

6161

InertInert GasGas ProceduresProcedures Gas FreeingGas Freeing

To gas free a tank it should first be purged with IG to To gas free a tank it should first be purged with IG to reduce the Hydrocarbon content to 2% or less, below the reduce the Hydrocarbon content to 2% or less, below the CDLCDL

To gas free a tank it should first be purged with IG to To gas free a tank it should first be purged with IG to reduce the Hydrocarbon content to 2% or less, below the reduce the Hydrocarbon content to 2% or less, below the CDLCDL

6262


Gas Freeing (continued)Gas Freeing (continued) The intended tank should always be isolated from The intended tank should always be isolated from

other tanks prior to starting gas freeingother tanks prior to starting gas freeing

If gas freeing is to be carried out by means of If gas freeing is to be carried out by means of portable/fixed fans connected to the cargo pipeline portable/fixed fans connected to the cargo pipeline system then the IG inlet should be isolatedsystem then the IG inlet should be isolated

If the method of using the IG fan to draw fresh air is If the method of using the IG fan to draw fresh air is used then both the line back to the IG source and the used then both the line back to the IG source and the IG inlet to other tanks being kept inert should also be IG inlet to other tanks being kept inert should also be isolatedisolated

The intended tank should always be isolated from The intended tank should always be isolated from other tanks prior to starting gas freeingother tanks prior to starting gas freeing

If gas freeing is to be carried out by means of If gas freeing is to be carried out by means of portable/fixed fans connected to the cargo pipeline portable/fixed fans connected to the cargo pipeline system then the IG inlet should be isolatedsystem then the IG inlet should be isolated

If the method of using the IG fan to draw fresh air is If the method of using the IG fan to draw fresh air is used then both the line back to the IG source and the used then both the line back to the IG source and the IG inlet to other tanks being kept inert should also be IG inlet to other tanks being kept inert should also be isolatedisolated

6363


Gas Freeing (continued)Gas Freeing (continued) A tank is said to be gas free when the entire tank is A tank is said to be gas free when the entire tank is

found to have an oxygen content of 21% by volume found to have an oxygen content of 21% by volume when tested with an oxygen analyserwhen tested with an oxygen analyser

Also a reading o less than 1% on a flammable gas Also a reading o less than 1% on a flammable gas indicatorindicator

If toxic gasse such as benzene or hydrogen sulphide If toxic gasse such as benzene or hydrogen sulphide are suspected to be present then gas freeing should are suspected to be present then gas freeing should continue until such time as tests with an appropriate continue until such time as tests with an appropriate device indicates that the content is below the device indicates that the content is below the ThresholdThreshold LimitLimit ValueValue (TLV) (TLV)

A tank is said to be gas free when the entire tank is A tank is said to be gas free when the entire tank is found to have an oxygen content of 21% by volume found to have an oxygen content of 21% by volume when tested with an oxygen analyserwhen tested with an oxygen analyser

Also a reading o less than 1% on a flammable gas Also a reading o less than 1% on a flammable gas indicatorindicator

If toxic gasse such as benzene or hydrogen sulphide If toxic gasse such as benzene or hydrogen sulphide are suspected to be present then gas freeing should are suspected to be present then gas freeing should continue until such time as tests with an appropriate continue until such time as tests with an appropriate device indicates that the content is below the device indicates that the content is below the ThresholdThreshold LimitLimit ValueValue (TLV) (TLV)

6464

Venting Inert Gas into Venting Inert Gas into the Atmospherethe Atmosphere In some regions of the world this is not In some regions of the world this is not

allowedallowed To overcome this the piping system To overcome this the piping system

can be so arranged such that as cargo can be so arranged such that as cargo tanks are being loaded/gas freed the tanks are being loaded/gas freed the displaced IG can be transferred ashoredisplaced IG can be transferred ashore

Unfortunately this may limit the speed Unfortunately this may limit the speed of loading to within the speed at which of loading to within the speed at which the IG can be transferred ashorethe IG can be transferred ashore

In some regions of the world this is not In some regions of the world this is not allowedallowed

To overcome this the piping system To overcome this the piping system can be so arranged such that as cargo can be so arranged such that as cargo tanks are being loaded/gas freed the tanks are being loaded/gas freed the displaced IG can be transferred ashoredisplaced IG can be transferred ashore

Unfortunately this may limit the speed Unfortunately this may limit the speed of loading to within the speed at which of loading to within the speed at which the IG can be transferred ashorethe IG can be transferred ashore

6565

Inert Gas FailureInert Gas Failure

CrudeCrude TankersTankers:-:- Because of the dangers of ignition Because of the dangers of ignition

from pyrophoric deposits, inerted from pyrophoric deposits, inerted tanks should not be allowed to reach tanks should not be allowed to reach a flammable statea flammable state

In the event of failure of the IG plant In the event of failure of the IG plant before or during discharge of cargo or before or during discharge of cargo or ballast then operations should cease ballast then operations should cease and close the deck isolating valve and close the deck isolating valve until the IG plant is restored to full until the IG plant is restored to full operationoperation

CrudeCrude TankersTankers:-:- Because of the dangers of ignition Because of the dangers of ignition

from pyrophoric deposits, inerted from pyrophoric deposits, inerted tanks should not be allowed to reach tanks should not be allowed to reach a flammable statea flammable state

In the event of failure of the IG plant In the event of failure of the IG plant before or during discharge of cargo or before or during discharge of cargo or ballast then operations should cease ballast then operations should cease and close the deck isolating valve and close the deck isolating valve until the IG plant is restored to full until the IG plant is restored to full operationoperation

6666

Inert Gas FailureInert Gas Failure

ProductProduct TankersTankers:-:-

Discharge should not begin/resume Discharge should not begin/resume without the permission of all without the permission of all interested partiesinterested parties

ProductProduct TankersTankers:-:-

Discharge should not begin/resume Discharge should not begin/resume without the permission of all without the permission of all interested partiesinterested parties

6767

Pyrophoric DepositsPyrophoric Deposits

In an atmosphere which is deficient In an atmosphere which is deficient of oxygen and where hydrogen of oxygen and where hydrogen sulphide is present, iron oxide(rust) sulphide is present, iron oxide(rust) is converted into iron sulphideis converted into iron sulphide

When iron sulphide is then exposed When iron sulphide is then exposed to air it is oxidised back to iron oxide to air it is oxidised back to iron oxide and free sulphur or sulphur dioxide and free sulphur or sulphur dioxide gas is formedgas is formed

In an atmosphere which is deficient In an atmosphere which is deficient of oxygen and where hydrogen of oxygen and where hydrogen sulphide is present, iron oxide(rust) sulphide is present, iron oxide(rust) is converted into iron sulphideis converted into iron sulphide

When iron sulphide is then exposed When iron sulphide is then exposed to air it is oxidised back to iron oxide to air it is oxidised back to iron oxide and free sulphur or sulphur dioxide and free sulphur or sulphur dioxide gas is formedgas is formed

6868

Pyrophoric DepositsPyrophoric Deposits

This oxidation can generate This oxidation can generate considerable heat such that considerable heat such that individual particles may become individual particles may become incandescentincandescent

This is a rapid process and is termed This is a rapid process and is termed PyrophoricPyrophoric OxidationOxidation

Pyrophoric iron sulphide can ignite Pyrophoric iron sulphide can ignite flammable hydrocarbon/air mixturesflammable hydrocarbon/air mixtures

This oxidation can generate This oxidation can generate considerable heat such that considerable heat such that individual particles may become individual particles may become incandescentincandescent

This is a rapid process and is termed This is a rapid process and is termed PyrophoricPyrophoric OxidationOxidation

Pyrophoric iron sulphide can ignite Pyrophoric iron sulphide can ignite flammable hydrocarbon/air mixturesflammable hydrocarbon/air mixtures

6969

Pyrophoric IgnitionPyrophoric Ignition

Rust PatchesIron OxideReacts with Sulphur in IG

Iron Sulphide

Changes Back to Iron OxideExothermic reaction

inert gas system

Documents

flow of inert gas

inert gas blowers

inert gas system schematic

inert gas system washes

inert gas system regulations

flue gas system

high quality inert gas

flow of cargo gas