Marine Operations
Precautions against Cargo Liquefaction Cargo liquefaction occurs when dry bulk cargoes with a high moisture content start to behave like liquids when the ship is moving. Such cargoes shift rapidly in the holds of a ship, resulting in the free surface effect, which renders the ship unstable and at risk of capsizing. Cargo liquefaction remains the greatest contributor to loss of life and causes the By Marios Strongyloudis greatest concern in the bulk carrier industry. Partial liquefaction can also occur in the case of iron ore fines. It will not have a disastrous effect, but it will place a great burden on the ship’s crew and waste valuable resources on cleaning the cargo holds.
Definitions Moisture Content (MC) is the proportion of water, expressed as a percentage of the total mass of a cargo sample. Flow Moisture Point (FMP) is the moisture content at which a flow state develops. Cargoes with a “moisture content” beyond the FMP are liable to liquefy. Transportable Moisture Limit (TML) is calculated as 90% of the Flow Moisture Point. The TML value represents a 'safe' moisture content, below which the cargo is unlikely to undergo liquefaction and endanger the ship and crew. IMSBC Code (International Maritime Solid Bulk Cargoes Code) by IMO The primary aim of the IMSBC Code is to facilitate the safe stowage and shipment of solid bulk cargoes by providing information on the dangers associated with the shipment of certain types of solid bulk cargoes and instructions on the procedures to be adopted when the shipment of solid bulk cargoes is contemplated. It clearly defines the responsibility of the Shipper: • Provide the Master with a signed certificate of TML and MC, each issued by an entity recognised by the competent Authority of the port of loading. • Establish procedures for sampling, testing and controlling moisture content to ensure the moisture content is less than the TML when the cargo is on board the ship. • Facilitate access to stockpiles for the purpose of inspection, sampling and subsequent testing by the ship’s nominated representative. GROUP “A” cargoes are cargoes which may liquefy if shipped at a moisture content in excess of the transportable moisture limit. Some examples of Group A cargoes are: • Iron concentrate • Nickel concentrate • Iron concentrate (pellet & • Nickel ore sinter feed) • Coal • Iron ore fines • Coal slurry The Can test is used to obtain an approximate evaluation of the possibility of flow of the loaded cargo. It is a very simple testing method which can be carried out by the ship’s crew. It should be noted that the can test cannot substitute for the required laboratory testing. Some ports where iron ore shipments have exhibited liquefaction: • Brazil: Ponta da Madeira, Tubarao, Itaguai, Guaiba Island
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Issue 80-June 2022
• India:Mangalore, Visakatnam, Paradip • Sierra Leone: Pepel • Philippines: Surigao Common factors encountered in the ports named above: • Loading from exposed stockpiles of iron ore • Loading during the heavy torrential rain season • Stockpiles inaccessible for proper sampling & testing • Laboratories for the required “moisture content” and “flow moisture point” testing unavailable at the remote loading area P&I Clubs and Classification Societies have published relevant circulars highlighting the hazards and mitigating measures to reduce the risk of cargo liquefaction. It is strongly suggested that all crew and office personnel involved in iron ore cargo transportation should refer to the circulars so as to take advantage of the wealth of experience gained in such cases. Important measures proposed for mitigating the risk of liquefaction are: • Check the shipper’s cargo declaration and stated moisture content. • Cargoes are not to be loaded under precipitation. • Heightened vigilance is required during the rainy season (i.e. December to April in Brazilian ports). • Request new moisture content laboratory tests to be carried out if it has rained in the days prior to loading. • Ensure that any document confirming that the cargo is safe to carry is signed by the shipper. • Check the cargo to be loaded in each barge or stockpile for excessive water content. • Should there be any concerns or doubts about the moisture levels in the nominated cargoes, further advice and assistance can be obtained from an independent reputable cargo expert. In order to maintain the safety of crew and ship and avoid charter party disputes it is important to highlight the recommended procedures throughout the loading, transporting and discharging of iron ore cargoes: • Prior to arrival at the port of loading: The Master must acquire the Shipper’s declaration and confirm that it complies with IMSBC code requirements. The Shipper’s declaration must fully comply with IMSBC code requirements and provide all the necessary information. For GROUP A cargoes (subject to liquefaction), the Shippers are required to provide additional supporting documentation evidencing the moisture content of the shipment, the TML laboratory analysis certificate and proof that this test has been conducted at a lab approved by the Competent Authority of the port of loading. • Loading operation: Brazilian iron ore has a considerable moisture content. Even if many cargoes are described as GROUP C in the Shipper’s declaration, the Master and crew should treat the cargoes as liable to liquefy. Masters should be vigilant and ensure that the cargo is inspected for any signs of moisture. For example, free standing surface water,
