Inert Gas System (Flue Gas)
critical
IMO Required
11 models total
A flue-gas inert gas system draws exhaust from the boiler uptakes or a dedicated generator, scrubs and cools it, then delivers gas below 5% oxygen to the cargo tanks, the route most crude and product tankers use instead of a nitrogen generator.
Read more — Inert Gas System (Flue Gas) explained ▾
What Sets the Flue-Gas Type Apart
Two ways exist to fill a tanker's cargo tanks with an oxygen-starved atmosphere: burn fuel in a dedicated inert gas generator (IGG), or tap exhaust that the propulsion or auxiliary boilers already produce. The flue-gas arrangement is the older and still the dominant choice on crude carriers and large product tankers, because the gas source is free running whenever the boiler is lit. The trade-off is that flue gas quality follows boiler load: light-off, slow-steaming or a badly tuned burner can push oxygen content above the safe limit, so the scrubbing and monitoring train has to work harder than on a purpose-built generator.
Main Components
Scrubber Tower
Raw flue gas enters near the bottom and rises through counter-flow seawater sprays that cool it from several hundred degrees to near ambient and wash out soot and sulphur oxides. A demister pad at the top strips entrained water before the gas leaves for the blowers.
Blowers
Two blowers, each rated for full system capacity, push scrubbed gas through the rest of the line. Running one at a time with the other as standby is normal; both are interlocked to trip on low scrubber water flow or high gas temperature.
Deck Water Seal
A water-filled, semi-dry or dry seal sits on deck and is the last physical barrier stopping hydrocarbon vapour from finding its way back to the engine room through the same piping that supplies inert gas. Low water level in a wet seal is one of the most common causes of a failed gas-free survey follow-up.
Non-Return / Deck Isolating Valve and PV Breaker
A mechanical non-return valve backs up the water seal, and a pressure/vacuum breaker on the mast riser vents the system to atmosphere if tank pressure ever runs outside the design envelope, independent of the individual tank PV valves.
Distribution Main and Branch Valves
From the mast the gas runs aft along the deck main with a branch and isolating valve to each tank, allowing individual tanks to be inerted, purged or gas-freed without disturbing the others.
Selection and Sizing
Capacity is set by the fastest discharge rate the ship can achieve, since inert gas has to replace cargo volume at least as quickly as it leaves the tanks, usually with margin for the fastest pump combination fitted. Typical delivery pressure at the deck main runs around 100-200 mmWG, enough to overcome distribution losses and still leave headroom below the tank PV valve setting. Scrubber sizing depends on boiler exhaust volume and sulphur content of the fuel burned, since higher sulphur fuel demands more seawater flow to hold pH and SO2 carryover within limits.
Regulations and Class
- SOLAS Chapter II-2, Regulation 16 requires a fixed inert gas system on crude oil tankers of 20,000 dwt and above and on product carriers of 8,000 dwt and above.
- Oxygen content in the gas supplied to the tanks must be continuously monitored and recorded, with alarms set to warn before the 8% by volume threshold in the tank atmosphere is approached.
- Class surveys check the deck seal, non-return valve and PV breaker at each renewal survey, and flag testing of the oxygen analyser and blower trips is part of the annual inert gas system verification.
Typical Faults
| Fault | Consequence |
|---|---|
| Scrubber packing or spray nozzles fouled with soot | Poor cooling and SO2 removal, oxygen and acid carryover into the tanks |
| Deck seal water level low or heater failed in cold climates | Loss of the seal barrier, risk of vapour migrating into the engine room |
| Blower bearing wear or vibration | Unplanned trip mid-discharge, forcing a pause in cargo operations |
| Oxygen analyser sample line blocked or drifted uncalibrated | False readings that mask an actual overpressure of oxygen in the tanks |
What to Look for in a Supplier
- Documented scrubber sizing calculation matched to the ship's actual boiler exhaust flow and fuel sulphur range, not a generic package.
- Materials specification for the scrubber shell and internals suited to continuous seawater and acid exposure, since premature corrosion here is a frequent warranty claim.
- Spare parts commonality with the blower and analyser models already carried on sister ships, to avoid a second parts inventory.
- Reference installations on a similar tanker size and trade, since scrubber performance data from a small coaster does not transfer cleanly to a VLCC.
Before opening any tank for inspection, do not trust the deck log alone: walk to the deck seal and confirm the water level and heater status yourself, because a seal that quietly ran dry overnight is the difference between a routine gas-free check and an incident report.
4000h
Service Interval
Typical Manufacturers
Smit
Aalborg
Wartsila
3 manufacturers · 11 models
Wärtsilä
9
Hamworthy IG-3500 Flue Gas IG System
unverified
3500 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
3500
O2 content pct
<5%%
Common Failures & Inspection Points
- Seal, gasket or process-connection leakage caused by wear, thermal cycling, corrosion or cargo incompatibility, resulting in cargo or vapor leakage
- Valve, actuator, pump or drive failure caused by sticking, wear, electrical or hydraulic faults, resulting in incorrect routing or reduced cargo-handling capacity
- Sensor or measuring-element fouling or drift caused by cargo deposits, contamination or calibration error, resulting in implausible readings or alarms
- Process fouling, icing or blockage caused by cargo residue, temperature conditions or debris, resulting in restricted flow or unstable operation
- Control, shutdown or hazardous-area electrical fault caused by wiring, electronics or configuration problems, resulting in unavailable remote operation or protective trips
Service: Inspect process connections, seals, valves, actuators, pumps, sensors, piping and supports applicable to the listed cargo equipment. Maintain material compatibility with the actual cargo and clean deposits before they restrict movement or measurement. Trend pressure, temperature, level, flow or operating response against established normal conditions. Function-test remote controls, alarms, shutdowns and emergency stops before cargo operations. Inspect hazardous-area electrical and bonding arrangements for integrity. Refer to the manufacturer documentation for the exact figure for cargo compatibility, calibration, operating limits and wear criteria.
Spare Parts: Keep cargo-compatible seals and gaskets, valve service kits, sensors, cable glands, pump or actuator parts and manufacturer-recommended process components. Replacement materials must match the certified cargo service and hazardous-area approval.
Use Cases: It is used for oil, product and chemical tanker cargo operations on merchant ships, passenger vessels, offshore units or other vessel types where this equipment category is fitted.
Oil-fired flue gas inert gas generator
Hamworthy IG-5000 Flue Gas IG System
unverified
5000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
5000
O2 content pct
<5%%
Common Failures & Inspection Points
- Seal, gasket or process-connection leakage caused by wear, thermal cycling, corrosion or cargo incompatibility, resulting in cargo or vapor leakage
- Valve, actuator, pump or drive failure caused by sticking, wear, electrical or hydraulic faults, resulting in incorrect routing or reduced cargo-handling capacity
- Sensor or measuring-element fouling or drift caused by cargo deposits, contamination or calibration error, resulting in implausible readings or alarms
- Process fouling, icing or blockage caused by cargo residue, temperature conditions or debris, resulting in restricted flow or unstable operation
- Control, shutdown or hazardous-area electrical fault caused by wiring, electronics or configuration problems, resulting in unavailable remote operation or protective trips
Service: Inspect process connections, seals, valves, actuators, pumps, sensors, piping and supports applicable to the listed cargo equipment. Maintain material compatibility with the actual cargo and clean deposits before they restrict movement or measurement. Trend pressure, temperature, level, flow or operating response against established normal conditions. Function-test remote controls, alarms, shutdowns and emergency stops before cargo operations. Inspect hazardous-area electrical and bonding arrangements for integrity. Refer to the manufacturer documentation for the exact figure for cargo compatibility, calibration, operating limits and wear criteria.
Spare Parts: Keep cargo-compatible seals and gaskets, valve service kits, sensors, cable glands, pump or actuator parts and manufacturer-recommended process components. Replacement materials must match the certified cargo service and hazardous-area approval.
Use Cases: It is used for oil, product and chemical tanker cargo operations on merchant ships, passenger vessels, offshore units or other vessel types where this equipment category is fitted.
Oil-fired flue gas inert gas generator
Hamworthy IG-7500 Flue Gas IG System
unverified
7500 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
7500
O2 content pct
<5%%
Common Failures & Inspection Points
- Seal, gasket or process-connection leakage caused by wear, thermal cycling, corrosion or cargo incompatibility, resulting in cargo or vapor leakage
- Valve, actuator, pump or drive failure caused by sticking, wear, electrical or hydraulic faults, resulting in incorrect routing or reduced cargo-handling capacity
- Sensor or measuring-element fouling or drift caused by cargo deposits, contamination or calibration error, resulting in implausible readings or alarms
- Process fouling, icing or blockage caused by cargo residue, temperature conditions or debris, resulting in restricted flow or unstable operation
- Control, shutdown or hazardous-area electrical fault caused by wiring, electronics or configuration problems, resulting in unavailable remote operation or protective trips
Service: Inspect process connections, seals, valves, actuators, pumps, sensors, piping and supports applicable to the listed cargo equipment. Maintain material compatibility with the actual cargo and clean deposits before they restrict movement or measurement. Trend pressure, temperature, level, flow or operating response against established normal conditions. Function-test remote controls, alarms, shutdowns and emergency stops before cargo operations. Inspect hazardous-area electrical and bonding arrangements for integrity. Refer to the manufacturer documentation for the exact figure for cargo compatibility, calibration, operating limits and wear criteria.
Spare Parts: Keep cargo-compatible seals and gaskets, valve service kits, sensors, cable glands, pump or actuator parts and manufacturer-recommended process components. Replacement materials must match the certified cargo service and hazardous-area approval.
Use Cases: It is used for oil, product and chemical tanker cargo operations on merchant ships, passenger vessels, offshore units or other vessel types where this equipment category is fitted.
Oil-fired flue gas inert gas generator
Hamworthy IG-10000 Flue Gas IG System
unverified
10000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
10000
O2 content pct
<5%%
Common Failures & Inspection Points
- Seal, gasket or process-connection leakage caused by wear, thermal cycling, corrosion or cargo incompatibility, resulting in cargo or vapor leakage
- Valve, actuator, pump or drive failure caused by sticking, wear, electrical or hydraulic faults, resulting in incorrect routing or reduced cargo-handling capacity
- Sensor or measuring-element fouling or drift caused by cargo deposits, contamination or calibration error, resulting in implausible readings or alarms
- Process fouling, icing or blockage caused by cargo residue, temperature conditions or debris, resulting in restricted flow or unstable operation
- Control, shutdown or hazardous-area electrical fault caused by wiring, electronics or configuration problems, resulting in unavailable remote operation or protective trips
Service: Inspect process connections, seals, valves, actuators, pumps, sensors, piping and supports applicable to the listed cargo equipment. Maintain material compatibility with the actual cargo and clean deposits before they restrict movement or measurement. Trend pressure, temperature, level, flow or operating response against established normal conditions. Function-test remote controls, alarms, shutdowns and emergency stops before cargo operations. Inspect hazardous-area electrical and bonding arrangements for integrity. Refer to the manufacturer documentation for the exact figure for cargo compatibility, calibration, operating limits and wear criteria.
Spare Parts: Keep cargo-compatible seals and gaskets, valve service kits, sensors, cable glands, pump or actuator parts and manufacturer-recommended process components. Replacement materials must match the certified cargo service and hazardous-area approval.
Use Cases: It is used for oil, product and chemical tanker cargo operations on merchant ships, passenger vessels, offshore units or other vessel types where this equipment category is fitted.
Oil-fired flue gas inert gas generator
Hamworthy IG-14000 Flue Gas IG System
unverified
14000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
14000
O2 content pct
<5%%
Common Failures & Inspection Points
- Seal, gasket or process-connection leakage caused by wear, thermal cycling, corrosion or cargo incompatibility, resulting in cargo or vapor leakage
- Valve, actuator, pump or drive failure caused by sticking, wear, electrical or hydraulic faults, resulting in incorrect routing or reduced cargo-handling capacity
- Sensor or measuring-element fouling or drift caused by cargo deposits, contamination or calibration error, resulting in implausible readings or alarms
- Process fouling, icing or blockage caused by cargo residue, temperature conditions or debris, resulting in restricted flow or unstable operation
- Control, shutdown or hazardous-area electrical fault caused by wiring, electronics or configuration problems, resulting in unavailable remote operation or protective trips
Service: Inspect process connections, seals, valves, actuators, pumps, sensors, piping and supports applicable to the listed cargo equipment. Maintain material compatibility with the actual cargo and clean deposits before they restrict movement or measurement. Trend pressure, temperature, level, flow or operating response against established normal conditions. Function-test remote controls, alarms, shutdowns and emergency stops before cargo operations. Inspect hazardous-area electrical and bonding arrangements for integrity. Refer to the manufacturer documentation for the exact figure for cargo compatibility, calibration, operating limits and wear criteria.
Spare Parts: Keep cargo-compatible seals and gaskets, valve service kits, sensors, cable glands, pump or actuator parts and manufacturer-recommended process components. Replacement materials must match the certified cargo service and hazardous-area approval.
Use Cases: It is used for oil, product and chemical tanker cargo operations on merchant ships, passenger vessels, offshore units or other vessel types where this equipment category is fitted.
Oil-fired flue gas inert gas generator
Wärtsilä Moss IG-2000 IG System
unverified
2000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
2000
Common Failures & Inspection Points
- Analyzer contamination or calibration drift causes incorrect oxygen indication and may block cargo operations
- Blower, compressor or fan faults cause low gas flow and system shutdown
- Filter, membrane, adsorber or scrubber fouling reduces gas quality or increases pressure drop
- Seal, valve or piping leakage causes gas loss, air ingress or unstable deck-main pressure
- Control, purge or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect gas-generation equipment, blowers or compressors, filters or scrubbers, analyzers, valves, drains and control interlocks. Trend oxygen quality and flow and verify deck isolation and non-return arrangements according to the approved cargo procedure. Calibrate analyzers using approved methods. Refer to the manufacturer and vessel documentation for the exact figure for oxygen, pressure, flow and service limits.
Spare Parts: Carry analyzer cells or consumables, filters, blower or compressor service parts, valve and seal kits, sensors and control relays.
Use Cases: Oil, chemical and gas-carrier cargo-tank inerting, purging and pressure management.
Moss-type flue gas inert gas system
Wärtsilä Moss IG-4000 IG System
unverified
4000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
4000
Common Failures & Inspection Points
- Analyzer contamination or calibration drift causes incorrect oxygen indication and may block cargo operations
- Blower, compressor or fan faults cause low gas flow and system shutdown
- Filter, membrane, adsorber or scrubber fouling reduces gas quality or increases pressure drop
- Seal, valve or piping leakage causes gas loss, air ingress or unstable deck-main pressure
- Control, purge or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect gas-generation equipment, blowers or compressors, filters or scrubbers, analyzers, valves, drains and control interlocks. Trend oxygen quality and flow and verify deck isolation and non-return arrangements according to the approved cargo procedure. Calibrate analyzers using approved methods. Refer to the manufacturer and vessel documentation for the exact figure for oxygen, pressure, flow and service limits.
Spare Parts: Carry analyzer cells or consumables, filters, blower or compressor service parts, valve and seal kits, sensors and control relays.
Use Cases: Oil, chemical and gas-carrier cargo-tank inerting, purging and pressure management.
Moss-type flue gas inert gas system
Wärtsilä Moss IG-6000 IG System
unverified
6000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
6000
Common Failures & Inspection Points
- Analyzer contamination or calibration drift causes incorrect oxygen indication and may block cargo operations
- Blower, compressor or fan faults cause low gas flow and system shutdown
- Filter, membrane, adsorber or scrubber fouling reduces gas quality or increases pressure drop
- Seal, valve or piping leakage causes gas loss, air ingress or unstable deck-main pressure
- Control, purge or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect gas-generation equipment, blowers or compressors, filters or scrubbers, analyzers, valves, drains and control interlocks. Trend oxygen quality and flow and verify deck isolation and non-return arrangements according to the approved cargo procedure. Calibrate analyzers using approved methods. Refer to the manufacturer and vessel documentation for the exact figure for oxygen, pressure, flow and service limits.
Spare Parts: Carry analyzer cells or consumables, filters, blower or compressor service parts, valve and seal kits, sensors and control relays.
Use Cases: Oil, chemical and gas-carrier cargo-tank inerting, purging and pressure management.
Moss-type flue gas inert gas system
Wärtsilä Moss IG-8000 IG System
unverified
8000 m³/h
· Flue gas
Inert Gas System
flue_gas
Capacity (m³/h)
8000
Common Failures & Inspection Points
- Analyzer contamination or calibration drift causes incorrect oxygen indication and may block cargo operations
- Blower, compressor or fan faults cause low gas flow and system shutdown
- Filter, membrane, adsorber or scrubber fouling reduces gas quality or increases pressure drop
- Seal, valve or piping leakage causes gas loss, air ingress or unstable deck-main pressure
- Control, purge or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect gas-generation equipment, blowers or compressors, filters or scrubbers, analyzers, valves, drains and control interlocks. Trend oxygen quality and flow and verify deck isolation and non-return arrangements according to the approved cargo procedure. Calibrate analyzers using approved methods. Refer to the manufacturer and vessel documentation for the exact figure for oxygen, pressure, flow and service limits.
Spare Parts: Carry analyzer cells or consumables, filters, blower or compressor service parts, valve and seal kits, sensors and control relays.
Use Cases: Oil, chemical and gas-carrier cargo-tank inerting, purging and pressure management.
Moss-type flue gas inert gas system
Aalborg
1
Aalborg IG-FC Inert Gas System
5000 m³/h at <5% O₂
· Marine Equipment
· flue‑gas inert gas generator
Common Failures & Inspection Points
- Fouling, scaling or blocked spray paths reduce treatment effectiveness and cause abnormal pressure drop or emissions readings
- Pump, blower or fan faults cause low circulation or gas flow and system shutdown
- Analyzer or sensor contamination causes incorrect gas-quality, emissions or oxygen readings
- Seal, valve or piping leakage causes liquid or gas leakage and unstable process pressure
- Control, dosing or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect treatment vessels or generators, pumps, fans or blowers, spray or filtration equipment, analyzers, drains and control interlocks. Trend gas quality, pressure drop and liquid-treatment condition where applicable. Verify shutdown and isolation functions according to the approved procedure. Refer to manufacturer, vessel and statutory documentation for the exact figure for gas quality, emissions, pressure and chemical limits.
Spare Parts: Carry pump and valve seals, analyzer consumables, filters, spray nozzles, dosing parts, fan or blower service items, sensors and control relays.
Strengths
- Utilises waste heat from existing boilers, reducing fuel consumption
- Integrated Aalborg blower system with proven reliability
- Compact layout suitable for newbuilds and retrofits
- Lower CO₂ and NOₓ emissions compared with diesel‑driven IG generators
- Automatic non‑return valve (NRV) control simplifies operation
Weaknesses
- IG production is dependent on boiler load; output drops at low power
- Flue‑gas contaminants can cause blower impeller erosion and corrosion
- Requires additional deck space for NRV and seawater scrubber pump
- Scrubber seawater pump failure is a known reliability issue
- Response to sudden IG demand spikes can be slower than diesel generators
Typical Vessels:
Crude Oil TankerProduct TankerChemical Tanker
Certifications:
IMO Type Approval for Inert Gas SystemsDNV Class Approval
Decision Guide: Choose if the vessel already has a boiler or exhaust system that can provide sufficient waste heat, you need to minimise fuel consumption and emissions, and space allows installation of the deck NRV and scrubber pump. Avoid if the ship operates frequently at low power where boiler exhaust is limited, rapid IG surge capacity is critical, or maintenance resources for flue‑gas components are constrained.
Use Cases: SOx control, tanker inerting, nitrogen generation and cargo-atmosphere management.
Smit
1
Smit Inert Gas System
7500 m³/h at <5% O₂
· Marine Equipment
· Flue‑gas inert gas generation system
Common Failures & Inspection Points
- Fouling, scaling or blocked spray paths reduce treatment effectiveness and cause abnormal pressure drop or emissions readings
- Pump, blower or fan faults cause low circulation or gas flow and system shutdown
- Analyzer or sensor contamination causes incorrect gas-quality, emissions or oxygen readings
- Seal, valve or piping leakage causes liquid or gas leakage and unstable process pressure
- Control, dosing or interlock faults cause off-specification gas, alarm conditions or automatic shutdown
Service: Inspect treatment vessels or generators, pumps, fans or blowers, spray or filtration equipment, analyzers, drains and control interlocks. Trend gas quality, pressure drop and liquid-treatment condition where applicable. Verify shutdown and isolation functions according to the approved procedure. Refer to manufacturer, vessel and statutory documentation for the exact figure for gas quality, emissions, pressure and chemical limits.
Spare Parts: Carry pump and valve seals, analyzer consumables, filters, spray nozzles, dosing parts, fan or blower service items, sensors and control relays.
Strengths
- Utilises existing boiler exhaust – no separate fuel consumption for IG generation
- Integrated scrubber tower with water seal provides reliable removal of SOx and particulates
- Proven track record on large crude and product tankers; widely class approved
- Modular design simplifies installation and future upgrades
Weaknesses
- Scrubber packing fouling requires renewal every 3‑5 years, increasing planned maintenance
- Deck seal water‑level control can be sensitive to sea‑state motion, leading to occasional failures
- O₂ analyser drift demands weekly calibration; sensor replacement may be costly
- System performance depends on adequate boiler load – low‑load voyages reduce IG output
Typical Vessels:
Crude oil tankerProduct tankerChemical tankerLNG carrier (when equipped with a suitable boiler)
Certifications:
DNV Class Approval for Inert Gas SystemsABS Approved IG SystemIMO IG System Guidelines compliance
Decision Guide: Choose if: the vessel already has a steam boiler of sufficient capacity, you want to minimise additional fuel consumption for inert gas and prefer a proven, class‑approved system with modular maintenance. Avoid if: the ship operates many low‑load or idle periods, you lack access to regular packing renewal workshops, or you require an IG system that can run completely independent of the main boiler.
Use Cases: SOx control, tanker inerting, nitrogen generation and cargo-atmosphere management.