Iron ore is the highest-volume solid bulk cargo carried by sea, with global seaborne trade exceeding 1.6 billion tonnes per year. The cargo is regulated under the International Maritime Solid Bulk Cargoes Code (IMSBC) administered by the International Maritime Organization. The IMSBC schedule for iron ore distinguishes between fine particle-size cargoes that are susceptible to liquefaction (Group A) and coarse lump cargoes that are not (Group C), with an additional schedule for iron ore concentrate that is also Group A. The schedule prescribes loading conditions, transportable moisture limits, and onboard handling requirements designed to prevent the catastrophic stability loss that has caused multiple bulk carrier casualties since the 1990s.
IMSBC schedule structure
The IMSBC Code includes three principal entries for iron ore family cargoes:
- Iron ore (Group C): lump material with low fines content. Not liquefiable. Standard bulk-handling cargo schedule.
- Iron ore fines (Group A): cargoes with at least 10 per cent fine particles below 1 millimetre and at least 50 per cent of particles below 10 millimetres. Liquefiable. Subject to transportable moisture limit (TML) and moisture content (MC) testing before loading.
- Iron ore concentrate (Group A): beneficiated fine concentrate produced by milling and flotation. Highly liquefiable.
The Group A entries impose strict pre-loading testing and certification requirements. The Group C entry, by contrast, requires only routine bulk loading procedures.
Liquefaction mechanism
Group A cargoes can liquefy at sea when the moisture content exceeds the transportable moisture limit. Liquefaction occurs when ship motion compacts the cargo, generating positive pore-water pressure that exceeds the inter-particle friction holding the cargo as a granular solid. The cargo behaves as a viscous liquid, which can shift suddenly to one side of the hold, producing a permanent list and progressive flooding. Iron ore fines are particularly dangerous because the high cargo density (around 2.6 to 3.0 tonnes per cubic metre stowage factor or about 0.34 to 0.38 cubic metres per tonne) generates extreme heeling moments when the cargo shifts.
Notable casualties attributed to iron ore fines liquefaction include the loss of MV Stellar Daisy in March 2017 in the South Atlantic, with the loss of 22 lives, and several earlier Brazilian and Indian iron ore fines casualties through the 2010s. The Stellar Daisy loss prompted significant Marshall Islands flag state and Korean class society investigations and contributed to industry-wide tightening of pre-loading sampling and verification procedures.
Transportable moisture limit and pre-loading testing
The IMSBC Code requires shippers to declare the moisture content and the transportable moisture limit for each consignment of iron ore fines. The TML is determined by laboratory testing using one of three accepted methods:
- Flow Table Test (most widely used; suitable for non-cohesive granular cargoes).
- Penetration Test (suitable for low-cohesion cargoes).
- Proctor-Fagerberg Test (suitable for higher-density iron ore concentrates and many iron ore fines; the only method specifically validated for iron ore fines after the 2013 IMSBC amendments).
The shipper must certify that the moisture content of the cargo at the time of loading is less than 90 per cent of the TML. The master may decline to load any consignment for which the certificate is missing, expired (older than seven days for the moisture content test), or appears inconsistent with cargo condition.
A simple “can test” can be performed shipside as a rapid screening tool: half-fill a 0.5 to 1 litre cylindrical container with the cargo, strike the base of the container 25 times against a hard surface from a height of 200 millimetres, and inspect for free moisture or a glossy surface. A positive can test indicates probable excess moisture and should trigger a halt to loading and laboratory verification.
Brazilian and Indian iron ore fines
The IMSBC Code includes a specific schedule entry for “Iron Ore Fines” introduced in 2013 in response to Indian Ocean and South Atlantic casualty patterns. Shipments from Goa and Karnataka in India and from Pará and Minas Gerais in Brazil have been particular focus areas. Brazilian iron ore fines exported through Tubarão, Ponta da Madeira, and Pier 4 typically have moisture content of 6 to 9 per cent and TML in the range of 9 to 12 per cent depending on particle size distribution. Indian iron ore fines exported through Mormugão, Krishnapatnam, and Paradip are similarly sized and similarly tested.
Australian iron ore fines from Port Hedland, Dampier, and Cape Lambert are typically of slightly larger particle size and lower moisture, but are still classified Group A and subject to the same pre-loading certification.
Cargo handling onboard
Iron ore fines and concentrate are loaded by shore-based conveyor systems and shiploaders into the cargo holds of capesize, very large ore carrier (VLOC), and Newcastlemax bulk carriers. Trimming is generally not required, since the cargo is dense and self-trims. Holds should be inspected for hatch cover integrity, bilge well clearances, and ventilation closures before loading.
Once loaded, the cargo is generally not ventilated during the voyage, since natural ventilation has limited capacity to reduce moisture in compact dense cargoes and may introduce additional water through condensation. Continuous monitoring of bilge wells and visual inspection during permitted hold entries (subject to enclosed-space safety procedures) provide indirect confirmation of cargo stability.
The cargo discharges through grab-fitted shore cranes at the receiving port. Iron ore fines are highly abrasive, and grab and conveyor wear is significant.