Circular Letter MSC/Circ.387 REVISED GUIDELINES FOR INERT GAS SYSTEMS

1. Introduction.

1.1 Purpose.

1.2 Application.

1.3 Definitions.

2. Principles.

2.1 General.

2.2 Flammable limits.

2.3 Effect of inert gas on flammability.

2.4 Sources.

2.5 Quality.

2.6 Methods of gas replacement.

2.7 General policy of cargo tank atmosphere control.

3. Function and design considerations.

3.1 Description of an inert flue gas system.

3.2 Function of inert gas scrubber.

3.3 Design considerations for inert gas scrubber.

3.4 Function of inert gas blowers.

3.5 Design considerations for inert gas blowers.

3.6 Function of non-return devices.

3.7 Design considerations for non-return devices.

3.8 Inert gas distribution system.

3.9 Design considerations for valves and pipework in inert gas systems.

3.10 Gas pressure regulating valves and recirculating arrangements.

3.11 Arrangements for inerting, purging and gas-freeing (regulation 62.13).

3.12 Isolation of cargo tanks from the inert gas deck main (regulation 62.11).

3.13 Liquid-filled pressure-vacuum breakers.

3.14 Instrumentation and alarms (regulation 62.16 to .19).

3.15 Effluent and drain piping.

3.16 Sea-water service.

4. Operation of inert gas plant.

4.1 Though flue gas systems differ in detail certain basic principles remain the same. These are:

4.2 Start-up procedures should be as follows:

4.3 Shut-down procedures should be as follows:

4.4 Safety checks when inert gas plant is shut down should be as follows:

4.5 Possible failures of inert gas system and actions to be taken include:

5. Application to cargo tank operation.

5.1 Inerting of tanks.

5.2 Discharge of water ballast.

5.3 Loading.

5.4 Loaded condition.

5.5 Cargo transfer and cargo sampling.

5.6 Crude oil washing (see Section 5 of the Crude Oil Washing Operations and Equipment Manual).

5.7 Ballasting of cargo tanks.

5.8 Ballast condition.

5.9 Tank cleaning.

5.10 Purging prior to gas-freeing.

5.11 Gas-freeing.

5.12 Tank entry.

5.13 Re-inerting after tank entry.

6. Product carriers.

6.1 Carriage of products having a flashpoint exceeding 60 degrees C (closed cup test) as determined by an approved flashpoint apparatus.

6.2 Product contamination by other cargoes.

6.3 Contamination of cargoes by inert gas.

6.4 Contamination of cargoes by water.

6.5 Additional purging and gas-freeing.

7. Combination carriers.

7.1 Slack holds.

7.2 Leakage.

7.3 Ballast and void spaces.

7.4 Inert gas distribution system.

7.5 Application when carrying oil.

7.6 Application when carrying cargoes other than oil.

8. Emergency procedures.

9. Maintenance and testing.

9.1 General.

9.2 Inert gas scrubber.

9.3 Inert gas blowers.

9.4 Deck water seal.

9.5 Non-return valve.

9.6 Scrubber effluent line.

9.7 Testing of other units and alarms.

9.8 Suggested maintenance programme.

10. Training.

10.1 General.

10.2 Personnel requiring training.

10.3 Location of training.

10.4 Some training methods.

11. Instruction manual(s).

12. Some safety considerations with inert gas systems.

12.1 Backflow of cargo gases.

12.2 Health hazards.

12.3 Tank pressure.

12.4 Electrostatic hazards.

12.5 Repair of inert gas plant.

12.6 Hazards from pyrophoric iron sulphide.