A new test kit being developed promises to predict the risk of liquefaction more accurately than using ‘splash’ and ‘can’ tests.
The sampling of dry bulk cargoes goes way beyond simply testing for the quality of product. It can literally be a matter of life or death.
Following the loss of the BULK JUPITER in 2015, which sank off the coast of Vietnam with the tragic loss of 18 crew members, there have been renewed calls for more to be done to assess the danger of cargo liquefaction. In the case
of BULK JUPITER, the finger was pointed at the cargo of bauxite she was carrying, which is presumed to have liquefied and caused the vessel to capsize.
The problem of liquefaction of very fine, clay-like materials, such as some nickel ores, is principally different from that of granular materials. Nevertheless, the results, in terms of hazard for the vessel, are comparable, according to
classification society DNV GL.
Unlike granular materials, where increased pore water pressure is the trigger, liquefaction of clay-like materials can be viewed as a kind of material fatigue. After a number of stress cycles – due to ship motions, wave impacts and other vibrations – the cohesion and the strength of the material are suddenly significantly reduced. Since a number of stress cycles are required, liquefaction problems may occur several days or weeks after loading.
Another difference from granular materials is that liquefaction may happen for all the cargo on board simultaneously. It is also very difficult to stabilise the cargo after liquefaction.
It is down to the ship’s master as to whether or not to accept a cargo, but masters are often under intense commercial pressure to set sail fully loaded. The question remains as to whether cargo testing methods available when a
ship is in dock are sufficient to allow the master to make a properly informed decision.
The UK-based Association of Bulk Terminal Operators (ABTO) thinks not. It has called for a complete overhaul of cargo sampling and liquefaction testing protocols for raw ores and less common cargoes, such as nickel ore, fine wet coal and bauxite.
Professor Mike Bradley, a member of the ABTO advisory panel and head of Greenwich University’s Wolfson Centre for Bulk Solids Handling Technology, says the current measures in place to test cargoes for potential liquefaction are inadequate, especially for raw ores and variable materials being loaded in ports where conditions are “inclement”.
Bradley believes the current methods available to a ship’s master for identifying the dangers of liquefaction – so-called ‘splash’ and ‘can’ tests – are rudimentary, to say the least.
“The ‘can test’ consists of nothing more than a ‘baked bean tin’ filled with a sample of the cargo, which is then vigorously tapped on the table. If a liquid film forms on the sample surface, the cargo is deemed to be dangerous, and must be rejected. If not, it may be either safe or dangerous,” he said.
Bradley’s research group has investigated cases where masters have used the can test to accept and reject portions of cargo, resulting in later liquefaction in heavy weather. The splash test, meanwhile, simply checks to see if the cargo ‘splashes’ when dropped from a grab into the hold. “Not easy to see in the dead of night with dark coloured cargo in a badly lit hold,” Bradley added.
“Such rudimentary testing is inadequate. We have seen that dangerous cargoes can pass these tests, with moisture content exceeding the allowable limits, liquefying at a later stage. The efficacy of existing testing and sampling
protocols does need to be addressed, especially when assessing terminal stockpiles where obtaining a decent sample is difficult.”
The current IMO protocol for setting transportable moisture limits and certifying actual cargo moisture content is robust for some cargo flows, but sadly falls down too often for others, as evidenced by the number of lives still being
lost at sea due to cargo liquefaction.
“Ultimately the master has to take responsibility for whether a cargo is loaded, and he is under commercial pressure not to reject it. So, in cases where he has suspicions, he really needs a better, more reliable shipboard test
he can use to protect both his employer’s business and the lives of his crew,” continued Bradley.
Although the International Maritime Solid Bulk Cargoes (IMSBC) Code includes provisions for sampling, Bradley says it is “inordinately difficult” to get a representative sample of the cargo from a stockpile, and, in many cases, severe rain will have occurred since the sample was taken for moisture certification.
What’s more, some master mariners have expressed concerns that the current tests do not work with some cargoes. There have also been cases in which moisture content certificates are alleged to have been falsified.
A better test?
Bradley explained that the Wolfson Centre has completed some preliminary research work on the development of a more effective, accurate cargo liquefaction test kit for shipboard use.
“Current tests used in cargo labs require far too much specialist skill and expensive equipment to be used by the crew aboard ship. The proposed test is based on a practical approach that can be done using low-cost equipment, and can be replicated easily,” he says.
“It doesn’t replace the current system of TML and MC certification, but provides the ship’s master with an opportunity to make his own check in cases where there is doubt over change in the condition of the cargo, the quality o f
sampling, the veracity of the certification, or the effect of bad weather on moisture during loading.
“We have been talking to a number of parties, including ABTO members, P&I Clubs and classification societies, to take the initiative forward. We have proven the basic concept, which seems to work, so we are now looking to the
industry to support the development.
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