This operation is carried out onboard an LNG carrier after the cargo tanks have been successfully cooled to the required -130°C. During this operation, liquid LNG is supplied from the shore and directed from the spray lines to the main cargo line (liquid header). The objective is to achieve the required temperature of -100°C in the liquid lines so that the loading operation can commence.

The purpose of cooling down cargo lines is to avoid thermal shock on the piping and associated valves which would occur if no gradual cooling was employed. Therefore, prior to loading LNG into the cargo tanks, the cargo liquid lines, crossovers and cargo filling lines must be cooled down to cryogenic temperatures and this can be undertaken with LNG supplied from the vessel’s cargo tanks.

Exercise Overview:

1. Initial Setup:

• The exercise begins with the necessary preparations, including:
• Opening the required valves.
• Connecting the manifold arms.
• Lining up the correct valves to direct the LNG into the liquid header.

2. Assessment Process:

• The assessment begins once the lineup is complete, and the LNG liquid is started from the shore.
• During the assessment, the user must continuously monitor:
• The drop in temperature of the liquid lines.
• The rise in pressure within the cargo lines.
• The user must open and close the valves correctly throughout the process while ensuring safety is maintained at all times.

3. Completion Criteria:

• The exercise is considered complete when the liquid header temperature reaches -120°C.
• At this point, the user must operate certain valves to complete the procedure.

4. Evaluation:

• The user is assessed based on their ability to respond to various remarks, alarms, and cautions during the course of the exercise.

Learning Objectives for the Exercise

Participants will be able to effectively demonstrate the process of cooling down cargo lines on LNG ships, understanding the necessary safety protocols, operational procedures, and the importance of achieving the correct temperatures for safe LNG transfer.
Key Components:

Understanding Cooling Down:
Explain the purpose of cooling down cargo lines to prevent thermal shock during LNG transfer and ensure the integrity of the system.
Identify the significance of reaching appropriate temperatures to facilitate safe and efficient LNG loading.

Operational Procedures:
Detail the step-by-step process for cooling down cargo lines, including:

• Preparation of cooling systems and verification of line integrity.
• Controlled introduction of cold LNG or nitrogen into the cargo lines.
• Monitoring of temperature and pressure throughout the cooling process.

Explain the importance of managing flow rates to prevent rapid cooling.

Monitoring and Verification:

• Demonstrate the use of temperature gauges and pressure monitoring systems during the cooling down process.
• Describe how to confirm that the cargo lines are within safe temperature limits before commencing LNG transfer.

Practical Demonstration:

• Simulate the cooling down 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 cooling down cargo lines.
• Accurate execution of the cooling down procedure and effective monitoring.

By achieving this objective, participants will gain the knowledge and skills necessary for safely and efficiently cooling down cargo lines on LNG ships, ensuring operational readiness for LNG transfer.

Line Cooldown Prep and Line up

Line Cooldown Operation and Assessment

Milestones

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

1. Open All Required Valves for Lineup.

• Assessment Phase – Operational flow and Assessment:

2. Achieved Required Temperatures On Liquid Lines.

Actions and Process Details

Deviation From Exercise

• Once the line cooldown has started or resumed, do not open any non-required valves or close any required valves.
• If a deviation occurs, a caution message will prompt the user to undo the action.
• If the action is not undone within the given time, the exercise will be terminated.

High Crossover Pressure

• During the line cooldown, if the crossover pressure reaches 4 bar, a warning will prompt the user to open valve CL400 to reduce the pressure.
• If the pressure reaches 5 bar and CL400 is not opened, the exercise will be terminated.

Liquid Entering the Tank

• Opening valve CL400 to reduce crossover pressure will eventually result in liquid entering the tank.
• If liquid enters the tank, the user will be warned to close valve CL400.
• If valve CL400 is not closed within 1 minute of the warning, the exercise will be terminated.

Close Tank Filling Valves (CL200, CL300, CL400)

• At the 3-minute mark, the user must close the filling valves CL200, CL300, and CL400.
• Failure to close any of these valves will result in termination of the exercise.

Keep Tank Filling Valves CL100 and CL400 Open

• At the 12-minute mark, the user must keep valves CL100 and CL400 open.
• Failure to keep these valves open will result in termination of the exercise.

Alarms & Remarks

Step by step procedure:

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

1. Open All Required Valves for Lineup

• CL023 Open
• CL043 Open
• CL100 10%
• CL107 100%
• CL200 5%
• CL207 100%
• CL300 5%
• CL307 100%
• CL400 10%
• CL407 100%
• CS704 Open
• CS705 Open

• Assessment Phase – Operational flow and Assessment:

2. Start Line Cooldown

• After completing the valve lineup, press the “Start Line Cooldown” button to initiate the 15-minute cooldown process.
• Initially, the crossover pressure will be maintained at 2 bar, and the tank pressure will increase by 0.5 kPa every minute.

3. Actions at 3-Minute Mark

• At the 3-minute mark, the user will be warned to close the filling valves CL200, CL300, and CL400.
• Once these valves are closed, the tank pressure will decrease by 0.5 kPa every minute, while the crossover pressure will begin to rise from 2 bar to 5 bar.

4. Managing Crossover Pressure at 4 Bar

• When the crossover pressure reaches 4 bar, the user will receive a warning to open valve CL400 for 20 seconds to reduce the pressure.
• Opening CL400 will cause the tank pressure to increase by 1 kPa.
• The user will receive a warning to close valve CL400 and must do so within 30 seconds to avoid exercise termination.
• After closing CL400, the crossover pressure will rise again from 2 bar to 5 bar. If the pressure reaches 4 bar again, the user must repeat the process of opening CL400 for 20 seconds.

5. Actions at 12-Minute Mark

• At the 12-minute mark, the user must keep valves CL100 and CL400 open.
• The crossover pressure will be maintained at 2 bar, while the tank pressure will continue to increase by 0.5 kPa every minute.

6. Completion of the Exercise

• The exercise will be completed once the liquid header forward temperature reaches -100°C.
• At this point, the user must:
  1. Open liquid line valve CL033.
  2. Close spray line valve CS031.
  3. Complete the procedure.

Proper line up for line cooldown from shore: