The purpose of Inerting cargo tanks is to remove the oxygen content to avoid the cargo tanks entering the flammable range during gas filling. As part of the process of preparing the cargo tanks ready to carry the next LNG cargo, they must be Inerted with inert gas, thus removing ignition risk when gas filling.

The Inert gas, provided by the vessel’s inert gas generator, should be introduced at the bottom of each cargo tank simultaneously, via the liquid line. The cargo tank atmosphere will be displaced from the top of each cargo tank into the vapor line and discharged to the atmosphere through the No.1 vent mast.

• Function Replacement of dry-air in cargo tanks with inert gas
• Performance criteria Cargo tank dew point < -40°C
• Cargo tank oxygen content < 2% in volume
• Auxiliaries involved Inert gas generator (inert gas mode). Flow rate 16,500m³/h, dew point -45°C, oxygen about 0.5%.
• Operation duration 24 hours, including line up and piping purge.
• Necessary device Portable dew point meter
• Portable oxygen meter

This exercise focuses on preparing the systems and equipment to successfully make the tank atmosphere completely inert. The objective is to ensure that the dry air present inside the tanks is replaced with inert gas, which is generated by the inert gas generator onboard the LNG carrier.

Exercise Overview:

1. System Setup:

The exercise begins with initial milestones that describe how to set up various equipment, including:

• Starting the portable multi-gas detector and dew point meters.
• Installing the necessary connections to the inert gas line.
• Opening and closing various valves to set up the system correctly.
• Preparing and starting the Ballast pump required for the inert gas generator.
• Configuring and starting the inert gas generator itself.
• These steps are prerequisites before the assessment part of the exercise begins.

2. Assessment Process:

• The assessment begins when inert gas is introduced into the tanks from the bottom.
• The user must correctly manage the flow of inert gas entering the tanks and the dry air exiting the tanks, venting to the main vent system.
• Throughout the assessment, the user is required to continuously monitor the flow and check the atmosphere inside the tanks via various sampling points.

3. Key Parameters to Monitor:

• Oxygen content in the tanks must be reduced to less than 2% by volume.
• The dew point must be below -40°C.
• The tank pressure should be maintained between 5 kPa and 7 kPa.

4. Completion Criteria:

• The exercise is considered complete once all cargo tanks have met the required oxygen and dew point specifications.
• The user’s performance is evaluated based on how well they manage the process, respond to various remarks, and address any alarms or questions that arise during the exercise.

Learning Objectives for the Exercise

Participants will be able to effectively demonstrate the process of inerting cargo tanks on LNG ships using inert gas, understanding safety protocols, operational procedures, and the importance of preventing explosive atmospheres.
Key Components:

1. Understanding Inerting:

• Explain the purpose of inerting cargo tanks to eliminate the risk of flammable gas mixtures.
• Identify the dangers associated with the presence of oxygen in cargo tanks and the necessity of maintaining an inert atmosphere.

2. Operational Procedures:
Detail the step-by-step process for inerting cargo tanks, including:

• Preparation and inspection of inert gas supply systems.
• Connection of hoses and fittings to the cargo tanks.
• Control of flow rates and pressure during the inerting operation.

3. Monitoring and Verification:

• Demonstrate the use of oxygen analyzers and pressure gauges to monitor inerting effectiveness.
• Describe the target oxygen concentration levels and how to confirm they have been achieved.

4. Practical Demonstration:

• Simulate the inerting process in a controlled environment or through hands-on training exercises.
• Role-play scenarios to address potential challenges or deviations from the procedure.

Assessment Criteria:

• Ability to articulate the significance of inerting cargo tanks.
• Accurate execution of the inerting procedure and effective monitoring.

By achieving this objective, participants will gain the necessary knowledge and skills to safely and efficiently inert cargo tanks on LNG ships, enhancing overall safety and operational integrity.

Inerting intro and line up

Inerting preparation and starting of IGG in inert gas mode

Inerting Operation and Assessment

Milestones:

• Learning and Training Phase – Pre-Requisites for the start of operation:

1. Start the Portable Multi Gas Detector and Dew Point Meter
2. Install the Spool Piece to Connect the Inert Gas Line to the Liquid Line
3. Set Cargo Tank Vapour Valves
4. Set Cargo Tank Liquid Valves
5. Set the Vapour Line to No. 1 Vent Mast Regulating Valve
6. Set the Inert Gas Line Valve
7. Prepare and Start Ballast Pump 2
8. Prepare Inert Gas Generator in Inert Gas Mode

• Assessment Phase – Operational flow and Assessment:

9. Start Inert Gas Generator in Inert Gas Mode
10. Cargo Tank Dew Point < -40°C
11. Cargo Tank Oxygen Content < 2% in Volume
12. Maintain Cargo Tanks Pressure Between 5kPa and 7kPa
13. Check the Sampling Point on Vapour Line in All Cargo Tanks
14. When All of the Cargo Tanks and Piping Are Inerted, Stop the Supply of Inert Gas

Exercise Actions and Warnings:

• Deviation from Exercise: Ensure no unnecessary valves are opened or required ones closed once gassing up begins. A caution message will be shown if an incorrect action is taken, and failure to correct it may result in exercise termination.
• Flow Maintenance: Keep the IGG outlet flow and the flow to atmosphere between 15,500 kg/h and 16,500 kg/h during the inerting process. Failure to do so within 1 minute of a high-priority alarm will result in exercise failure.
• Pressure Maintenance: Ensure that the cargo tank pressure stays between 5 kPa and 7 kPa to maintain the proper piston effect.

Alarms & Remarks:

Step By Step Procedure:

• Learning and Training Phase – Pre-Requisites for the start of operation:

1. 1. Start Portable Multi Gas Detector and Dew Point Meter:

• • Navigate to the Miscellaneous Equipment section.
  • Press and hold the power button for 5 seconds to start both devices.

1. 2. Install the Spool Piece to Connect the Inert Gas Line to the Liquid Line:

• • Connect the spool piece above valve CL701 linking the inert gas and liquid lines.

1. 3. Set Cargo Tank Vapour Valves:

• • Open the following valves: CG100, CG101, CG200, CG201, CG300, CG301, CG400, CG401.

1. 4. Set Cargo Tank Liquid Valves:

• • Open the following valves: CL100, CL107, CL200, CL207, CL300, CL307, CL400, CL407.

1. 5. Set the Vapour Line to No. 1 Vent Mast Regulating Valve:

• • Open valve CG701.

1. 6. Set the Inert Gas Line Valve:

• • Open valve CL701.

1. 7. Prepare and Start Ballast Pump 2:

• • Navigate to the Ballast System page.
  • Open the discharge, suction, and outlet valves.
  • Start a generator to ensure at least two are operational.

1. 8. Prepare Inert Gas Generator in Inert Gas Mode:

• • Set the Generator Mode to “Inert Gas.”
  • Set Operating Percentage to 100%, turn on Fuel Pump and IG Chiller Unit.

• Assessment Phase – Operational flow and Assessment:

1. 9. Start Inert Gas Generator in Inert Gas Mode:

• • Wait for chiller temperature to drop below 3°C and oxygen analyzer to read ≤ 0.9%.
  • Start the inert gas generator.

1. 10. Ensure Cargo Tank Dew Point < -40°C:

• • Confirm the dew point is lower than -40°C using the dew point meter.

1. 11. Ensure Cargo Tank Oxygen Content < 2% in Volume:

• • Monitor oxygen content in the vapour line using the portable gas detector.

1. 12. Maintain Cargo Tanks Pressure Between 5kPa and 7kPa:

• • Adjust pressure by regulating the vent mast valves.

1. 13. Check Sampling Point on Vapour Line in All Cargo Tanks:

• • Verify gas properties (CH₄, O₂, CO, CO₂, and dew point) at sampling points.

1. 14. Stop the Supply of Inert Gas When All Cargo Tanks and Piping are Fully Inerted:

• • Stop inert gas delivery in the IGG System page and close valve CG702.

 Proper Line Up For Inerting: