Inert Gas System:

SOLAS regulations regarding Inert Gas Systems:

• For tankers ≥ 20k GRT constructed after 1 Jan 2002
• but before 1 Jan 2016 → tank protection achieved by fixed IG system in accordance with FSS code resolution 98(73).
• For tankers ≥ 8000 GRT constructed after 1 Jan 2016
• Tankers → can → fixed IG system

IG Regulation MSC 98(73)
→ components requirements

• Inert gas supply
  → treated flue gas of boiler
  → separate gas generator
  → other combination

System requirements
The system capable of SOLAS Ch2-11
→ inerting cargo tanks
→ O2 < 8% by volume at any part of tank
→ positive pressure except gas free
→ no need air entry for normal operation
→ purging empty cargo tank of H.C gas so that gas freeing not create flammable atmosphere

• Tankers fitted with IG system
  → double hull space shall be fitted with suitable connection for IG distribution
  → where hull spaces are connected permanently then means prevent HC entry

Scrubbers
→ flue gas scrubber fitted to
→ cool
→ remove solid and sulfur products
→ Filter fitted to prevent/minimize water carry over to blower
→ scrubber located aft of all cargo tanks
→ pump room
→ cofferdam

Blower
→ 2 blowers with supply capacity > 125%
→ 1 may be permitted if IG generator is used and spare available
→ maximum pressure < test pressure cargo tank
→ shut off arrangement in suction & discharge
→ If blower is used for gas freeing then IG inlet → blanking arrangement
→ located aft

Water seal
→ water seal supplied from 2 pumps capable of maintaining water level at all times
→ Arrangement to prevent back flow of HC vapor
→ protected against freezing & not overheated
→ water loop or other approved arrangement fitted to each associated water supply
→ high/low level alarm → when inert gas is not being supplied

Safety measures in system

• Flue gas isolating valve
  → v/v between boiler uptake & scrubber
  → indication open/close
  → v/v gas tight & sealing → shoot blower cannot operate open if v/v not fully open
  → prevent flue gas leakage
  → design of location → leakage in hull space
  → additional water seal / other means → between isolating v/v & scrubber → or incorporated in the gas line
• Gas regulating valve
  → fitted in supply main
  → automatically controlled to close
  → automatically regulate the flow
  → located at the forward bulkhead of the forward most gas safe space through which gas supply main passes
• Non-return device of flue gas
  → min 2, one of which is water seal
  → located between gas regulating valve & aftermost connection to any cargo tank and in deck
  → 2nd non-return device fitted forward of deck seal
  → shall be positive closure type N/R
  → the location between gas regulating valve & non-return devices shall be protected from overpressure if in a safe manner when P.C.V. is closed

Automatic shutdown
→ inert gas blower & gas regulating valve if low pressure/level of water in scrubber & high temp at blower outlet
→ gas regulating valve shut down → blower stops
→ O2 content high
→ O2 > 8% by volume → all cargo operations are suspended & N/R valve closes

Inert gas line
→ 2 or more branches forward of N/R
→ each branch goes to cargo tank fitted with stop valve with locking arrangement
→ slop tank is isolated by blank flange which must remain in position all time when cargo other than crude oil carried
→ cargo tank protected from over/under pressure when isolated from inert gas
→ pipeline design → prevent accumulation of cargo/water under all conditions
→ Arrangement for external IG supply with pipe size 250 mm isolated from main with v/v located forward of N/R valve
→ If connection is between IG main & cargo piping then effective isolation is ensured by 2 shut off valves with vent in between
→ Valve separating the IG main from the cargo main shall be N/R type positive closing

Operation & control requirements
Indicating devices
→ temperature & pressure of IG at the discharge side of blower when blower is running
Indicating & recording devices
→ O2 content on discharge of blower
→ Pressure forward of N/R device
→ devices located in ECR if no ECR then easily accessible place
→ meter fitted
→ Bridge for pressure
→ ER for O2
→ portable O2 & flammable vapor measuring device is provided as spare
→ means provided for zero calibration for both fixed & portable devices

Audible & visual alarms
→ low water pressure/flow in scrubber
→ high water level in scrubber
→ high gas temp at blower discharge
→ failure of IG blowers
→ O2 > 8% by volume at blower discharge
→ power failure to gas regulating valve & indicator
→ low water level at water seal
→ gas pressure less ≤ 100 mm water at forward of N/R valve
→ high gas pressure at forward N/R valve
→ IG Generator additional
→ fuel oil supply insufficient
→ IG generator power supply fail
→ IG generator control/system power fail
→ O2, power failure for gas regulator, gas pressure < 100 mm water fitted in CCR & ER

An independent low-pressure alarm for IG main is fitted which operates at predetermined set level

Instruction manual
→ supplied on board
→ covers → operation
→ safety
→ maintenance
→ health hazards to IG system