A global team of researchers has observed an entirely new phenomenon that affects the solid bulk cargo bauxite, which could result in vessels capsizing.

The Global Bauxite Working Group (GBWG) set out to investigate the risk of liquefaction in bauxite cargoes – a mechanism affecting other solid bulk cargoes that has caused numerous sinkings worldwide – but its tests showed that liquefaction did not occur at all, even with worst case ship motions.

Instead, it observed the moisture controlled mechanism ‘dynamic separation process’ whereby, when subject to sufficient dynamic loading, very wet finer grained bauxites go through a process of slumping and dynamic separation, with the upward expulsion of water/ slurry.

The findings, set out in the peer-reviewed report, Research into the Behaviour of Bauxite during Shipping, state: ‘This [mechanism] could result in the significant formation of a free surface, which could result in vessel capsizing.’

The study was recently reviewed by the IMO Correspondence Group on the Evaluation of Properties of Bauxite, and forms the basis of its own report report which will be discussed at the Carriage of Cargoes and Containers 4 Sub-Committee session in September.

Ai-Cheng Foo-Nielsen, assistant manager at BIMCO, a key participant in the Correspondence Group, told Fairplay: “The GBWG has come up with very surprising conclusion. I don’t know if this is a more serious phenomenon than liquefaction. At present, there is nothing mentioned about it in the International Maritime Solid Bulk Cargoes Code (IMSBC). We were not aware of it, it is something very new.”

The GBWG report recommends changes to the IMSBC Code, including amendments to the classification of Type A cargoes (those considered likely to liquefy) to include other cargo instabilities due to moisture, such as dynamic separation process. At present, Bauxite is classified as a Type C cargo (cargoes that do not liquefy or possess a chemical hazard).

In addition, the Proctor-Fagerberg Test methodology, developed as part of the research, is outlined for consideration of inclusion in Appendix 2 of the Code.

The research examined materials representing over 90% of the seaborne trade in bauxites, including those from Australia, Brazil, India, Indonesia, Guinea, Guyana, Jamaica and Malaysia. They ranged from silt with a large proportion of gravel, to silty gravel with sand and cobbles. Particle shapes ranged from spherical and round, to angular.

None of the bauxite tested liquefied in so-called Hexapod tests or in DC rolling tests, where the cargo was undrained and extreme vessel motions were simulated.

Liquefaction is known to affect other solid bulk cargoes, such as nickel ore and coal. It occurs when a large volume of fine particles, with a sufficiently high moisture content, start to behave like a liquid when a vessel moves, rolls or pitches. This can result in a sudden and dramatic loss of stability, causing a capsize.

Physical modelling tests on bauxite indicated that some exhibited instabilities due to moisture, whereby the cargo dynamically separated to form a perched free slurry surface with an underlying drier, unsaturated and competent solid cargo.

The report states: “Evidence from real world shipments of bauxites showing instabilities due to moisture cannot be explained by liquefaction phenomena, but can be explained by a dynamic separation mechanism of instability.”
The findings contradict recommendations issued by the IMO in a circular in September 2015, intended to raise awareness of the possible dangers of liquefaction associated with bauxite.

The circular was approved by IMO’s Sub-Committee on CCC, in the wake of an investigation into the loss of the 10-year-old Bahamas flag bulk carrier Bulk Jupiter, which was carrying 46,400 tonnes of bauxite when it sank rapidly with 18 fatalities in January 2015.

Foo-Nielsen commented: “Further discussion is required as to decide what should be done about this phenomenon and whether to call for further research to examine the process and determine if it applies to other cargos, not just bauxite.”

In related news, amendments to the IMSBC Code were adopted earlier this month to help prevent incidents of liquefaction in solid bulk cargoes.

The amendments will enter into force on 1 January 2019 and explicitly assign the shipper the responsibility to ensure that a test determining the Transportable Moisture Limit (TML) of a cargo liable to liquify is carried out within six months prior to the date of loading. The TML is defined as the maximum water contect a Group A solid bulk cargo may contain while being transported on a bulk carrier without it being at risk of liquefying. Previously, no single entity was assigned this responsibility in the IMSBC Code.

The Code also requires the shipper to ensure that, when cargo is exposed to rain or snow during loading, the moisture content is less than the TML by providing evidence as required by the Code. For example, this could be in the form of additional cargo testing.

BIMCO originally suggested the amendments in a submission to IMO, Foo-Nielsen told Fairplay: “Currently the IMSBC only calls for one test for moisture content, at the start of the loading operation, but when the loading operation goes beyond the normal period and the cargo is exposed to additional moisture intake, the probability of liquefaction increases.”