When transported in ship carriers nickel ore with excessive humidity may exceed its flow moisture point and liquefy under the effect of cyclic ship motion induced by the swell. Liquefaction of solid bulk means that the material loses all internal strength and behaves as a liquid. Once the phenomenon happens in one or several holds, the vessel is potentially unstable and may capsize very fast.
The Flow Moisture Point, and then the Transport Moisture Limit, depend on several physical properties of the bulk mineral ore, among which its moisture content, of course, but also the amount of cyclic shear stresses exerting in the mass of ore during its maritime transportation.
With the purpose to ascertain this key parameter so-called Cyclic Shear Ratio (CSR) to be considered when calibrating TML tests from triaxial tests in laboratory, a handysize bulk carrier was instrumented inside its nickel ore cargo with a multi-parameter monitoring system aiming to sample dynamic stresses versus ship motion and sea conditions. The authors detail here below this unique experiment based on two sea passages from New Caledonia to Japan and the principal observations and results obtained.
When transported in ship carriers, nickel ore with excessive humidity, as many other solid bulk cargos, may exceed its flow moisture point and liquefy under the effect of the cyclic ship motion induced by the swell. Liquefaction means that the solid bulk loses all internal strength and behaves as a liquid. Once the phenomena happen in one or several holds, the vessel is potentially unstable and may capsize very fast (Sheng, 2012).
Numerous dramatic shipwrecks have been reported worldwide those past decades due to the liquefaction of solid bulk cargoes. Recall that in 2010, the majority of bulk carrier deaths were attributed to cargo liquefaction. This is most likely what happened in 2010 at the origin of the shipwrecks of the Jian Fu Star (October 27, 2010 – 13 dead), the Nasco Diamond (November 10, 2010 – 21 dead) and the Hong Wei (December 3, 2010 – 10 dead). It should be noted, however, that the nickel ores transported in these vessels did not come from New Caledonia.
Based on the International Maritime Organization's work, the IMSBC code entered into force on 1 January 2011. This code establishes the conditions for maritime transportation of solid bulk cargos, including issues relating to products susceptible to liquefaction. These products are listed into the so-called group A in the "individual sheets of bulk cargoes" in Appendix 1 of the Code. Besides Nickel Concentrate, "Nickel Ore" has officially included this group and therefore cannot be transported by ship if its effective moisture content is greater than or equal to its TML. The IMSBC Code states that the shipper shall provide the ship's master or his representative with a signed certificate that must contain or be accompanied by the results of the TML testing determined as 90% of the Flow Moisture Point (FMP) and the water content of the loaded solid bulk.