Cargo liquefaction is the loss of shear strength that lets a solid bulk cargo behave as a liquid when its moisture content rises above a critical level under the vibration and rolling of a sea passage. It is the dominant cause of bulk carrier total losses associated with cargo, and it is the hazard that defines Group A in the IMSBC Code. Cargoes such as iron ore fines, nickel ore, and certain bauxite gradings can flow and shift, creating a free surface or a sudden transverse shift that capsizes the ship.
The control is the Transportable Moisture Limit (TML), set at 90 percent of the Flow Moisture Point (FMP), the moisture content at which a flow state develops under the prescribed laboratory test. A cargo may be loaded on an ordinary bulk carrier only when its declared moisture content is below the certified TML. The shipper must declare the moisture content and the TML, certified by a competent authority.
This article will cover the liquefaction mechanism, the determination of TML and FMP, the can test as an onboard screening check (and why a negative can test does not authorize loading), dynamic separation, and the master’s options when a cargo is suspected of being too wet. For the per-cargo group, density, and carriage data, use the IMSBC bulk cargo finder.