Liquefaction remains a killer on bulk carriers

The specialist nickel ore carrier <i>Jules Garnier II</i> employs longitudinal bulkheads in in its cargo holds to ensure stability and structural strength even when liquefied nickel ore cargoes are loaded. (Credit: ClassNK)
The specialist nickel ore carrier Jules Garnier II employs longitudinal bulkheads in in its cargo holds to ensure stability and structural strength even when liquefied nickel ore cargoes are loaded. (Credit: ClassNK)
DNV GL identified a number of areas of special attention in the second edition of its guidelines. (Credit: DNV GL)
DNV GL identified a number of areas of special attention in the second edition of its guidelines. (Credit: DNV GL)
Liquefaction can occur as a result of cargo compaction (Credit: DNV GL)
Liquefaction can occur as a result of cargo compaction (Credit: DNV GL)
Industry Database

Cargo liquefaction is the single biggest killer on bulk carriers, according to an analysis published by Intercargo in February 2019. It looked at a decade of bulk carrier losses from 2009 to 2018 and focused on ships of 10,000gt and above. It identified 48 total losses in that period, of which nine were caused by cargo liquefaction, yet these accounted for 101 of the 188 deaths.

Since that report’s publication, another 25 seafarers were lost in August 2019 when the 52,400dwt bulk carrier Nur Allya sank in Indonesian waters. Like six of the nine ships included in Intercargo’s analysis, it had been carrying nickel ore and when the wreck was located six weeks later, the Indonesian authorities confirmed that its cargo had liquefied.

Even before that had been confirmed, Intercargo urged “all shipowners, operators and seafarers to exercise extreme caution when accepting … nickel ore and other cargoes that have the potential to liquefy.” P&I club Skuld was another organisation that issued an alert, warning its members in September of the risks of loading nickel ore during the rainy season in Indonesia and the Philippines, in particular during the September-October typhoon season.

Skuld mentioned an unspecified member’s vessel that had “recently” loaded nickel ore in the Philippines. “Two days later cargo liquefaction occurred [in Holds 1 and 2] when facing a tropical storm.” In addition, cargo in Holds 3 and 4 had shifted. Fortunately, the weather eased and the master was able to steady the ship by changing course and speed and by moving ballast, eventually arriving safely at its discharge port.

It is not just nickel ore that poses significant concerns. Intercargo’s report included the January 2015 sinking – with 18 lives lost – of the 56,000dwt Bulk Jupiter while carrying bauxite that had been loaded in Malaysia and which liquefied. At the time, bauxite was classified as a Category C, low risk, cargo in the International Maritime Solid Bulk Cargoes (IMSBC) code and that incident prompted IMO’s Sub-Committee on Carriage of Containers and Cargoes to issue a warning in September 2015 that effectively said that Masters should assess it as they would a high risk Category A cargo.

An amendment to the IMSBC code will enter into force in January 2021 that will add a new schedule for bauxite fines and class society DNV GL has advised its clients that “it is highly recommended to implement the schedules and test procedure as soon as possible.”

That advice is contained in a 20-page study it published in May 2019 called Bulk cargo liquefaction that sets out “guidelines for the design and operation of vessels with bulk cargo that may liquefy.” Its executive summary illustrates how devastating a liquefied cargo can be when it defines the phenomenon as occurring when “a soil-like material is abruptly [The Motor Ship’s emphasis] transformed from a solid state to an almost fluid state.”

This causes a free surface effect that has a dramatic impact on ship stability. “The period of time from when liquefaction is detected, if it is detected at all, until the vessel has capsized could in some cases be only a few minutes,” the publication says.

DNV GL’s guidelines were first published in October 2015 and this second edition reflects feedback from its readers, in particular by adding some advice about precautions to be taken during a voyage or in case liquefaction is detected.

That advice includes an eight-point set of guidelines that highlight the conditions that might trigger liquefaction: the principal one is heavy rolling. Regular inspections should be made to check for signs of change in the cargo, such as its surface collapsing or water accumulating on its surface, and the dangers are spelled out clearly: “if liquefaction … is confirmed, the crew should prepare and stay ready to leave the vessel on short notice,” the guidelines advise.

Ships can be designed to reduce the impact of cargo liquefaction and the IMSBC allows cargoes with a moisture content above the transportable moisture limit (TML) to be loaded in specially constructed or specially fitted ships.

DNV GL established a notation for such ships, BCLIQ, which came into force on 1 July 2018, and its latest guidelines explain how vessels are assessed against it. But its central advice is that “design conditions must be based on the most severe cargo conditions in the loading manual [and] no permanent deformations of the ship structure are acceptable.”

Diagrams in the report suggest that such ships have narrower holds than conventional bulk carriers, with their sides tapering inwards for their full height. In conventional bulk carriers, however, “the effect on the free surface from the liquefied cargo becomes very critical for wide holds” and “arranging longitudinal bulkheads to narrow the holds is the only feasible way of obtaining sufficient stability to withstand cargo liquefaction,” it says. Unfortunately, it adds, “there are significant drawbacks of such longitudinal bulkheads,” including their extra weight and cost.

In the opening sentence of the guide’s introduction, DNV GL states that “traditionally, the phenomenon of liquefaction of dry bulk cargoes has not received much media attention.” That publication and the focus that The Motor Ship and other media are now giving to its dangers are beginning to redress that balance.

* DNV GL’s guide can be downloaded via https://tinyurl.com/DNVGL-BCLiq

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