Liquefaction of mineral cargoes, particularly nickel ore, have been widely publicised recently.The Association published an article by Brookes Bell in Signals 65 (October 2006) that Members are advised to refer to.The Association is very grateful to Ken Grant of Minton, Treharne & Davies (MTD) and Nicholas Crouch and Martin Jonas of Brookes Bell for providing this article, which describes in more detail the problems associated with liquefaction of nickel ore, and the difficulty in determining its moisture content and flow moisture point, and hence whether it is safe to carry.
Nickel laterite is an inhomogeneous low-grade ore consisting of very fine clay-like particles and larger rock-like particles. There are two different types,limonite and saprolite, which differ in their chemistry and their physical appearance, but present similar problems in bulk shipping due to their high moisture contents. As with many finely particulate minerals, including mineral ore concentrates, these ores have the property that they can liquefy and shift if their inherent moisture level is too high. There have been several serious instances of cargo liquefaction of nickel ore, including total losses and near-misses. Nickel ore is subject to the IMO Code of Safe Practice for Solid Bulk Cargoes (BC Code) regulations on testing and certification of cargoes that are liable to liquefy. Assessing whether a cargo is safe to ship requiresthe flow moisture point (FMP) to be measured and the transportable moisture limit (TML) to be calculated (90% of FMP). The TML is then compared to the moisture content of the cargo, and provided the TML is the higher figure, the cargo is safe to ship. There are problems with both the determination of TML (which for nickel ore needs to be determined by a competent laboratory separately for every single cargo) and moisture content (which must be of the cargo offered for shipment), which the BC Code requires shippers to provide prior to commencement of loading.Sampling of nickel ore Various problems arise with sampling for moisture content and FMP testing – both of which are required to enable a reliable TML to be determined. Some problems stem from the actual manner in which the stockpiles are physically sampled. In a recent case, it was found that the mine did not routinely sample the stockpiles prior to shipment,but rather sampling was conducted during the course of loading. As this was too late to comply with the requirements of the BC Code, their practice was to present the master with information relating to the cargo loaded onto a previous unrelated vessel.In turn, the results of the analysis of the cargo loaded onboard the subject vessel would then be presented to the next ship and so on. By the time the subject consignment had actually been characterised in terms of its suitability for carriage,it had already been loaded, making it more difficult to resolve any issues arising. The master would have been totally unaware of the fact that he was carrying a potentially dangerous cargo.
The shippers in this case (which is not exceptional in our experience) were in breach of the requirements of the BC Code for a number of reasons. Firstly, the moisture content data on the cargo certificates related to a different cargo and not the actual one due to be carried. Secondly, the stockpiles intended for loading onboard the subject vessel had not been sampled in accordance with the requirements of the BC Code. This details the frequency and extent of sampling for a given stockpile size, and states that sampling should be conducted no more than one week prior to shipment if the ore is stored uncovered - as most nickel laterite stockpiles are.