Elektrans Global

Liquefaction – A major hazard on BULK CARRIERS

Liquefaction is a chemical process that turns a previously safe commodity into a cargo with a dangerously high moisture content that can destabilize a vessel. Liquefaction means that a cargo becomes fluid (liquefies). On ships, this happens when the cargo is compacted by the ship’s motion. Cargoes which are prone to liquefaction contain a certain quantity of moisture and small particles, although they may look relatively dry and granular when loaded. Liquefaction can lead to cargo shift and even to capsize and total loss of the ship.

Certain cargoes, particularly nickel ore and iron ore fines, initially look dry and their characteristics are solid during loading on the ship. But during the voyage, concentrate cargoes as afore-mentioned are exposed to agitation under certain conditions including ship’s rolling, wave impact and engine vibration which results in compaction of the cargo.

IMO’s International Maritime Solid Bulk Cargoes (IMSBC) code which is mandatory under the provisions of SOLAS has placed cargoes with a liquefaction hazard in Group ‘A’. Liquefaction can result in cargo shift. This phenomenon may be described as follows:

1)  The volume of the spaces between the particles reduces as the cargo is compacted due to the ship’s motion, etc.;

2)  The reduction in space between cargo particles causes an increase in water pressure in the space;

3)  The increase in water pressure reduces the friction between cargo particles, resulting in a reduction in the shear strength of the cargo; and

4)  Then the cargo begins to flow as a viscous liquid

Liquefaction does not occur when one of the following conditions is satisfied:

a) The cargo consists of large particles or lumps. Water passes through the spaces between the particles and there is no increase in the water pressure. Cargoes which consist entirely of large particles will not liquefy; and

b) The cargo contains a high percentage of air and low moisture content.  Any increase in water pressure is inhibited. Dry cargoes do not liquefy.

Group ‘A’ cargoes with high moisture content (above TML) are prone to sliding, particularly if the cargo is shallow and subject to large heel angles. In the resulting viscous fluid state cargo may flow to one side of the ship with a roll but not completely return with a roll the other way. Consequently, the ship may progressively reach a dangerous heel and capsize quite suddenly.

A number of major liquefaction incidents resulting in capsizing and sinking have taken place over the years. Some of them are given below:

-  On the 27th of October, 2010, ‘Jian Fu Star’ laden with nickel ore from Indonesia sank in South China Sea with loss of 12 lives.

-  On the 10th of November, 2010, ‘Nasco Diamond’ laden with nickel ore from Indonesia sank in the Pacific Ocean with a loss of 20 lives.

-   On the 3rd December, 2010, ‘Hong Wei’ laden with nickel ore sank in the south China Sea with a loss of 10 lives.

-   On the 25th of December, 2011, ‘Vinalines Queen’ laden with nickel ore from Sulawesi sank in the Philippine Sea with the loss of 22 lives.

The ‘Asian Forest’ and the ‘Black Rose’ sank in July 2009 (off Mangalore) and September 2009 (Off Paradip) respectively, while carrying a cargo of iron ore fines during the monsoon season. The Directorate General of Shipping investigated the sinking and concluded that the reason was liquefaction as a consequence of excessive moisture in the cargo. Thereafter, as a preventive measure, DG Shipping issued an MS Notice banning the loading of Iron Ore fines during monsoon months on the Indian coast.

More recently, on the 30th of December, 2014, ‘Bulk Jupiter’ laden with bauxite from Malaysia sank off Vietnam with a loss of 18 lives.

The IMSBC Code requires that concentrates or other cargoes which may liquefy shall only be accepted for loading when the actual moisture content of the cargo is less than its Transportable Moisture Limit (TML).  Considering that if Liquefaction takes place whilst the vessel is rolling in rough weather, it would be very difficult to control the vessel; hence, the major precaution that actual moisture content should be less than its TML should never be compromised.