Tackling cargo liquefaction

It’s Christmas on the east Malaysian coast. The 18 crew under Captain Ronel Acueza Andrin should be celebrating in the ways sailors the world over do when separated from their families. Instead they are battling through an infuriating two-week loading process, with eight full days lost to the caprices of the tropics – the highest monthly rainfall ever recorded in Kuantan – and crane malfunctions. Come New Year’s Eve, finally on their way to the coast of China, the men usher in 2015 with a single glass of Champagne at midnight.

Two days later, only the chief cook is left alive. On 2 January 2015 the Bulk Jupiter developed an approximately 45° list to starboard and foundered completely in less than 20 minutes, leaving 16 crew missing, two (the master and chief officer) pulled dead from the sea and one – the cook – rescued after more than eight hours in the water.

In its final report on the loss, the Bahamas Maritime Authority (BMA) failed to find a conclusive cause for the tragedy. The probable cause was cited as what has variously been called “the most significant factor in lives lost at sea” (by class society DNV GL) and a “key risk to the future safety of shipping” (by insurer Allianz). Cargo liquefaction is the process by which certain soil-like bulk cargoes – including Bulk Jupiter’s bauxite and, notoriously, nickel ore (“one of the world’s deadliest cargoes”, according to Intertanko) – adopt an almost fluid state that can have a devastating impact on the stability and structural integrity of a vessel. Even a ship as apparently well-maintained and competently crewed as the 31,256gt Bulk Jupiter.

The Bulk Jupiter was by no means an isolated incident. Between 2009 and 2013, nine sunk vessels of more than 10,000gt have been lost with cargo liquefaction the suspected cause, according to DNV GL’s guidelines on the issue. ClassNK – the leading class society for bulk carriers – claims that more than a dozen vessels and over 90 seafarers have been lost in the past decade.

BMA’s report into Bulk Jupiter highlights the limitations of international regulation and common practice in minimising these losses. Under the International Maritime Organisation’s (IMO) International Maritime Solid Bulk Cargoes (IMSBC) Code the vessel’s cargo, bauxite, was classed as category C, indicating no danger of liquefaction. But like many bulk cargoes, the potential for bauxite to liquefy is exacerbated where excessive moisture is present. The IMO has responded by taking steps to inform masters of the risks associated with bauxite, although it has not reclassified the cargo. The liquefaction properties of bauxite are now being investigated in greater detail by major mining and mineral shipping countries including Brazil, China and Australia.

Under the IMSBC code, the shipper of a solid bulk cargo must provide a cargo declaration to the master in enough time to allow for the necessary precautions. The Bulk Jupiter’s cargo declaration was signed six days before loading – ahead of significant rain fall that was likely to have an impact on the moisture content. The declaration was also conspicuously similar to the properties of bauxite listed as an example in the code. As BMA points out: “Due to the quantity of rainfall in the intervening period between the 11 and 17 December it is concluded extremely unlikely that the moisture content remained at 10%, as declared, especially considering the method with which the bauxite was mined, transported and stored whilst exposed to the elements.”

In fact, comparisons of declarations with two other bulk carriers leaving Kuantan at the same time as Bulk Jupiter show the futility of reliance on declarations. “A 10% moisture content is declared on all three declarations but, it is known that the average moisture content of Bulk Jupiter’s cargo was 21.3%, the average moisture content of Medi Okinawa’s cargo was 15.01% and photographic evidence of Orchid Island’s holds shows pooled liquid on the surface of the cargo.

“The cargo declaration forms provided to all three vessels bear little resemblance to the cargo loaded. It can therefore be determined that the declaration forms are considered generic and provide no useful information on the actual cargo as loaded.”

In the case of the Bulk Jupiter, correspondence between the master and vessel owner Gearbulk Shipowning indicates that the master was aware that the cargo was being subjected to moisture, taking steps to minimise the cargo’s exposure to the rain and asking for guidance on how to treat the cargo. But the fact that he was not aware of one of the important preliminary tests for assessing moisture content – the ‘Can test, in which a can containing a sample of the cargo is struck against a hard surface and can show evidence of liquefaction – suggests there is a lot more to do to make sure that crew are fully aware of the risks.

Incomplete guidance and definition from regulators, a loose approach to declaring cargo by some shippers and the lack of crew awareness on the risks of cargo liquefaction are three key reasons why pressure is increasing on regulators to develop better legislation. And it is why class societies, including DNV GL and ClassNK, are strengthening their own guidance and cooperating in research into solid bulk cargoes.

The LiquefAction initiative coordinated by ClassNK is one such effort. Partners in the joint industry project, which aims to feed research findings into the development of cargo liquefaction guidelines, include Hamburgische Schiffbau-Versuchsanstalt (HSVA), Hamburg University of Technology (TUHH), Ecole Central de Nantes (ECN), and the Institute of Science and Technology for Transport, Development and Networks (IFSTTAR). Shipowner Oldendorff Carriers is also participating.

The project is based on the premise that definitions and classifications of cargoes by regulators do not provide an exhaustive response to the root causes of cargo liquefaction. The Bulk Jupiter loss, where a screened bauxite cargo was effectively outside the run-of-the-mill grade envisaged when bauxite was introduced into the predecessor of the IMSBC Code, is a case in point.

ClassNK points to a lack of study on the excitation effects on the cargoes caused by motions from waves and engine vibration. “The contribution from the ship and the sea conditions tend to be disregarded or addressed in a superficial manner, without taking into account the complexity of the problem,” says Yasushi Nakamura, representative director and executive vice president of ClassNK.

Ship motions and the frequency range and amplitude that cause liquefaction (for a given cargo, moisture content and time period) are central areas of study. Modelling the effect on stability by taking into account dynamic behaviour is also critical. Both factors will contribute to describing preventive and mitigating measures in ship design and operation. Other variables needing research are quantifying a cargo’s liquefiable potential by mass and the location where it is most likely to occur within the cargo.

According to HSVA, LiquefAction is addressing both design and operational vessel perspectives, “based on extensive experience and accident data, numerical modelling and simulation concerning the behaviour of granular cargoes in various modes of motion”. The results of this research will also be employed in the dynamic stability assessment of bulk carriers and general cargo ships under sea conditions similar to those recorded in real accidents.

The project results will build on ClassNK’s strong reputation in the field. The second edition of its guidelines on nickel ore, revised in February 2012, include the world’s first hull structure and stability requirements for ‘specially constructed cargo vessels’ – ships that are enabled to carry category A cargoes under the IMSBC Code even when the transportable moisture limit is exceeded. The requirements have since been approved by Panama, Japan, the Marshall Islands and Liberia and have been recognised by INTERCARGO.

Meanwhile, class society DNV GL has published new design and operational guidelines to raise the awareness of the risks of liquefaction and describe mitigating actions to reduce these risks. Morten Løvstad, business director of bulk carriers at DNV GL, explains: “While the general safety level of modern bulk carriers has been significantly improved over the last decades, recent incidents have shown that cargo liquefaction remains a major safety issue.”

The guidelines focus on both the operational and design aspects of cargo liquefaction. A number of recommendations are made to reduce risk in daily operation, including making sure that cargo is correctly identified and properly documented, as well as ensuring the time interval between testing for moisture content and loading is more than seven days.

The design guidelines look at the potential of carrying cargoes with high moisture content onboard specially constructed or fitted ships, in compliance with the International Maritime Solid Bulk Cargoes (IMSBC) Code. This means the vessels can remain safe both from a stability and strength point of view even if the cargo liquefies or shifts.

Løvstad says: “Under the IMSBC code such vessels must have permanent structural boundaries or specially designed portable divisions to confine any shift or liquefaction of cargo, but detailed requirements are lacking. It is clear, however, that stability and structural strength have to be specially considered, and our guideline sets out criteria for them, based on DNV GL procedures and rules.”

However Løvstad is keenly aware of the design challenges that must be tackled, particularly in making sure that general bulk carriers, capable of carrying several types of solid cargo, are stable enough to withstand liquefaction. For those designed just to carry ore cargoes, the prospect is simpler, he says. “If you want to design a traditional bulk carrier which is completely safe against cargo liquefaction, you end up with a design that is very similar to an ore carrier, because you need to limit the width of the cargo hold in order to reduce the free surface effect.

“You would need to have two longitudinal bulkheads or even a centreline bulkhead. Only one such vessel has been designed until now, for a very particular trade only with nickel ore. For a traditional bulk carrier, it is a challenge to tackle cargo liquefaction because it is a stability issue.”

There is also, of course, a cost element. And for general bulk carriers that can be a difficult hurdle to overcome. “We know what we need to do, but it wouldn’t really be a cost-effective vessel,” says Løvstad. “For ore carriers I think we will see design changes and that is where we have focussed our efforts. You need more steel to take on the additional pressure at the lowest part of the bulkheads. We don’t see it affecting the global integrity of ore carriers, but locally you can have serious problems. The cost for building is one issue but the main problem is that such designs would reduce the cargo capacity and therefore the operational efficiency of traditional bulk carriers. For an ore carrier though it can be justified and we know that there are projects underway that meet these guidelines.”

The economics of shipping, it seems, may well prevent the emergence of a general bulk carrier that is immune to the effects of cargo liquefaction. But whatever the design challenges, a combination of better understanding and stricter operational procedures – in particular in proper documentation and well-conducted (and timely) moisture testing – are the simplest and easiest way to ensure that disasters such as the loss of the Bulk Jupiter do not happen.