CO₂ Bottle Weighment – Observations, Causes, and Required Actions

During the weighing of CO₂ bottles used for total flooding of the engine room, if it is found that some bottles have lost more than the permissible limit (generally more than 10% of their original charge), it is considered a serious safety concern. Such a deficiency can compromise the effectiveness of the fixed fire-fighting system and must be addressed immediately.

Reasons for Reduced CO₂ Capacity

The reduction in CO₂ content within the bottles can occur due to several reasons:

• Leaking Valves: This is the most common cause. Leakage may occur from the main valve or discharge head due to worn-out seals, dirt or debris on the valve seat, or improper tightening.
• Corrosion of Cylinder: External or internal corrosion can weaken the cylinder wall, leading to very fine pinhole leaks through which gas can gradually escape.
• Damaged or Defective Bursting Disc: The bursting disc is a safety device designed to rupture at excessive pressure. If it becomes weakened, fatigued, or damaged, it may allow slow leakage of CO₂.
• Improper Sealing After Maintenance: If the bottles were previously serviced or tested, incorrect reassembly or poor sealing of connections may result in gradual gas loss.

Checks and Tests Before Refilling

Before refilling any CO₂ bottle, it is essential to ensure that the cylinder is structurally sound and safe for reuse:

• External Visual Inspection: Examine the cylinder for dents, pitting, corrosion, or any signs of overheating.
• Internal Inspection: Use suitable methods such as a borescope to check for internal corrosion, scaling, or damage.
• Hydrostatic Pressure Test: The cylinder is filled with water and pressurized (typically up to 1.5 times the working pressure) to check for leaks or permanent deformation.
• Verification of Tare Weight: The empty weight of the cylinder must be confirmed to ensure that the correct quantity of CO₂ is filled.
• Valve Overhaul: The valve assembly should be dismantled, inspected, and fitted with new seals, O-rings, and a properly functioning bursting disc.

Frequency of Inspection and Testing

As per IMO guidelines (MSC.1/Circ.1318/Rev.1) and SOLAS requirements, the following inspection schedule must be followed:

• Weighing / Level Checking: All CO₂ cylinders must be weighed or checked using ultrasonic level indicators at least once every two years. If any cylinder shows a loss exceeding 10% of its original content, it must be refilled or replaced.
• Hydrostatic Testing and Internal Inspection:
  • At least 10% of the total number of cylinders must undergo internal inspection and hydrostatic testing every 10 years.
  • By 20 years, all cylinders (100%) must have been tested at least once.
  • After this period, all cylinders must be tested at intervals not exceeding 10 years.