Fixed CO2 systems: every interval in one table, and the two that are usually run wrong
The intervals for a fixed carbon dioxide system are not all the same for passenger ships and cargo ships, and two separate blocks of work are commonly merged into one. This note sets out what MSC.1/Circ.1318/Rev.1 actually requires, at what interval, and where the cylinder testing regime changed in 2021.
The governing text
SOLAS II-2/14.2.1.2 requires the system to be kept in good working order, and SOLAS II-2/14 requires the onboard maintenance plan. MSC.1/Circ.1318/Rev.1, dated 25 May 2021, exists to demonstrate compliance with that regulation. It supersedes the original MSC.1/Circ.1318.
It was prepared at SSE 7 and approved at MSC 103 specifically to clarify the hydrostatic testing regime for high pressure CO2 cylinders and to align it with MSC.1/Circ.1432. Note that MSC.1/Circ.1432 itself states in paragraph 1 that it does not cover fixed CO2 systems, which is why the two circulars carry different figures for some of the same-sounding checks.
Monthly, at least every 30 days
- All stop valves in the closed position.
- All releasing controls in the proper position and readily accessible.
- All discharge piping and pneumatic tubing intact and undamaged.
- All high pressure cylinders in place and properly secured.
- Alarm devices in place and not apparently damaged.
- On low pressure systems additionally: pressure gauge in the normal range, liquid level indicator within the proper level, storage tank main service valve secured open, vapour supply line valve secured open.
Annual
- Boundaries of the protected space inspected to confirm no modification has created an opening that cannot be closed.
- All storage containers inspected for damage, rust or loose mounting hardware. Cylinders that are leaking, corroded, dented or bulging are hydrostatically retested or replaced.
- System piping inspected for damage, loose supports and corrosion. Nozzles inspected for obstruction by stored spares or by new structure and machinery.
- Manifold checked to verify that all flexible discharge hoses and fittings are properly tightened.
- All entrance doors close properly and carry warning signs. All remote releasing controls carry clear operating instructions and indicate the space they serve.
The two blocks that get merged, and should not be
This is the single most common scheduling error we see. MSC.1/Circ.1318/Rev.1 has two separate blocks at what looks like the same interval, and on a cargo ship they fall due at different surveys.
| Block | Interval |
|---|---|
| 6.1, contents, hydrostatic test dates, piping flow test | At least biennially, intervals of 2 years plus or minus 3 months, in passenger ships, or at each intermediate, periodical or renewal survey in cargo ships |
| 6.2, release heads, cables and tubing, controls, alarms and time delay | At least biennially in passenger ships, or at each renewal survey in cargo ships. This block must be carried out by service technicians or specialists trained to a standard accepted by the Administration |
The 6.1 block covers three things. All high pressure cylinders and pilot cylinders are weighed or their contents verified by other reliable means, to confirm the charge in each is above 90 per cent of nominal; below that they are refilled. On low pressure tanks the liquid level is checked against the amount needed for the largest hazard. The hydrostatic test dates of all storage containers are checked. And the discharge piping and nozzles are tested for blockage by isolating the discharge piping and flowing dry air or nitrogen through it.
The 6.2 block covers the release side. Where possible all activating heads are removed from the cylinder valves and tested for correct function at full working pressure through the pilot lines; where that is not possible the pilot lines are disconnected, blanked off or connected together and tested at full working pressure from the release station and checked for leakage. Manual pull cables are checked for free movement and excessive travel. Pneumatic tubing is checked for leakage and the charge of the remote releasing station pilot gas cylinders verified. All controls and warning devices must function normally, and the time delay where fitted must prevent discharge for the required period. Afterwards, releasing controls are verified in the proper position and connected to the correct control valves, pressure switch interlocks reset, and all stop valves returned to the closed position.
Five-yearly
Paragraph 7 of the circular is one sentence: at least once every five years, internal inspection of all control valves should be performed. That is the whole of the five-yearly requirement for a CO2 system in this circular.
Cylinder hydrostatic testing, the part that changed in 2021
This is the regime in paragraph 6.1.2, and it is worth knowing precisely because a service plan written before 2021 will miss the 20-year step.
| Anniversary | What is required |
|---|---|
| Every 10 years | High pressure cylinders subjected to periodical tests at intervals not exceeding 10 years. At the 10-year inspection, at least 10 per cent of the total number provided are subjected to internal inspection and hydrostatic test |
| If one or more fail | A total of 50 per cent of the cylinders on board are tested. If further cylinders fail, all cylinders are tested |
| Before the 20-year anniversary | All cylinders are subjected to a hydrostatic test |
| Every 10-year anniversary thereafter | All cylinders again, so 30 years, 40 years and so on |
| Flexible hoses | Replaced at the intervals recommended by the manufacturer and not exceeding every 10 years |
The circular refers to ISO 18119:2018 for the periodic inspection and testing of seamless steel and aluminium alloy cylinders. When cylinders are removed for testing, the quantity of extinguishing medium remaining on board must continue to satisfy chapter 5 of the FSS Code.
Two figures that look like errors and are not
- 90 per cent, not 95. MSC.1/Circ.1318/Rev.1 requires CO2 cylinder contents above 90 per cent of nominal charge. MSC.1/Circ.1432 requires above 95 per cent for fixed gas systems, but paragraph 1 of that circular expressly excludes CO2. Both are correct within their own scope.
- Alarm function testing on a CO2 system is not annual. Monthly is a check that the alarm devices are in place and not apparently damaged. The functional test of controls, warning devices and the time delay sits in the 6.2 block, that is biennial on a passenger ship and at renewal survey on a cargo ship. The annual functional alarm test people quote comes from MSC.1/Circ.1432, which does not apply to CO2.
The circular carries two example service charts, 26 numbered items for high pressure systems and 32 for low pressure, with a header block for the oldest cylinder pressure test date and the date the flexible hoses were fitted or renewed. They are the closest thing to an IMO-endorsed service report format for CO2, and our report follows them.
Sources
Every figure above was taken from the primary document. These are the documents themselves, not summaries of them.
