Solid Bulk Cargoes

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Types of Bulk Cargoes

Bulk cargoes include Coals, Concentrates, Grains, Fertilizers, Animal foodstuffs, Minerals and Ores.

These cargoes constitute a high proportion of seaborne trade.

IMSBC code

The International Maritime Solid Bulk Cargoes Code (2009) is the revision of Solid Bulk Cargoes code (1965).

The IMSBC code is based on the mandatory provisions as contained in Part A and B of Chapter 6 and Part B of Chapter 7 governing carriage of Solid Bulk Cargoes & Carriage of Dangerous Goods in Solid form in bulk, respectively.

The provisions of this IMSBC code entered into force from 01st Jan’2011.

Aim of IMSBC code

To highlight dangers associated with the shipment of bulk cargoes.

To give guidance on procedures to be adopted.

To list typical cargoes currently being shipped in bulk.

To describe test procedures to determine various characteristics of bulk cargoes.

Problems with Solid Bulk Cargoes

Problems with Solid Bulk Cargoes were identified as way back in 1960 but frame work was not possible then except for Carriage of Grain.

Solid Bulk cargo loading

The work was undertaken by International Maritime Organization’s Sub Committee on Containers and Solid Cargoes and several editions of Solid Bulk Cargoes BC code were published since first edition of 1965. The Sub-committee on Dangerous Goods was expanded to include DG and is now called the sub-committee on DG, Solid Cargoes and Containers, DSC Sub-committee.

Requirement for Carriage of grain are covered by International code for the safe carriage of Grain in Bulk (International Grain Code 1991).

Hazards associated with the Shipment of Solid Bulk Cargoes

Structural damage due to improper cargo distribution.

Loss or reduction of stability during a voyage & and chemical reactions of cargoes.

Liquefaction due to water ingress in the cargo or due to inherent moisture content of cargo.

Spontaneous Combustion of certain cargoes.

Emission of harmful Gases or Vapour by some cargoes.

Hygroscopic Cargoes

Cargoes which readily absorbs, maintains and gives of moisture, such cargoes are mainly of vegetable origin eg. Grain, Flour, Tobacco, Forest products etc.

Many cargo claims arise due to lack of ventilation of the cargo, particularly agricultural products. A common procedure for ventilating hatches at sea is to `crack’ them open. Considerable care must be taken during this procedure as the ships hatch tops are not designed to be opened during any rolling motion. 

Coke fines

When such hatches are opened they must not be left in the jacked up position, but should be lowered onto the compression bars and locked into position

Under no circumstances should the hatches be left open at night while on passage. A lack of, or improper, ventilation can lead to condensation (also known as sweating), which causes cargo deterioration. There are two types of sweat:

Types of Cargo Sweat

Cargo sweat :- Condensation occurs on the surface of the cargo as warm, moist air enters the cargo hold containing a cold cargo. For example, if a cargo of steel is loaded in winter in the UK for discharge in Singapore, the temperature of the cargo will be low. If warm moist air is later introduced in the cargo hold, condensation takes place as soon as it comes into contact with cold cargo. To avoid the possibility of cargo sweat, all ventilators should be closed and no ventilation carried out. However, if the moisture content of the cargo is high, extraction of the moist air from within the cargo holds may be required.

Ship sweat This results when condensation occurs on the ship’s structure as the ship becomes colder moving from a hot to a cold climate. The warm moist air within the cargo compartment condenses as it comes into contact with the cold structure of the vessel. For ship sweat to occur, the dew point in the cargo hold must exceed the temperature of the ship’s structure. To eliminate ship sweat the cargo should be ventilated if the vessel is moving from a warm to a cold climate.

Moisture Content of Cargoes

Low inherent moisture content cargoes For a hold loaded exclusively with cargoes containing no inherent moisture the only moisture available for condensation as ship’s sweat will be the comparatively minute amount in the small mass of the volume of air within the hold. It is therefore highly unlikely that ship’s sweat formation sufficient to drip back onto a cargo will ever occur under any voyage circumstances; the safest option for these types of cargoes is not to ventilate. 

High moisture content cargoes Cargoes in the high moisture content category are usually hygroscopic – that is they can absorb or release moisture into their immediate surrounding atmosphere depending on the moisture content of the cargo and the concentration of moisture in the immediate surrounding atmosphere.

Thus, the relative humidity and also the temperature of the atmosphere in a hold containing these cargoes is principally controlled by the moisture content and temperature of the cargo as loaded. (A proviso here is that these latter parameters are numerically suitably low for the cargo to be inherently stable, hence precluding the possibility of any significant self-heating in transit due to microbiological activity).

High density cargoes

High density cargoes are those that have a stowage factor less than 0.56 cu.m/tonne.

General cargo vessels are usually full up of space and down to their marks at stowage factors between 1.39 to 1.67 cu.m/tonne. There is a danger that because the hold looks empty after loading high density cargoes, due to ignorance too much cargo may be put into the hold. At any time the load density of the cargo hold tanktop / Deck should not be exceeded.

High density cargoes include Natural Ores and Concentrates.

Definition of Ore-  An ore is a material that contains a metal in such quantities that it can be mined and worked commercially to extract that metal. The metal is usually contained in chemical combination with some other element in addition to various impurities.  For Eg.Iron Ore and Manganese Ore.

Definition of Concentrates – It is enriched material obtained after physical or chemical separation of unwanted constituents from natural ores. For eg. Iron Ore Concentrates (Sinter feed pellets) and Nickel ore concentrate.

Natural ores contain a large percentage of large particles and lumps. Concentrates usually consist of fine particles or pellets.

Precautions for loading High density cargoes

Hold wise distribution of high density cargo by weight should not increase the load density of each hold Tank tops. This prevents excessive Shear force and Bending moments.

Max. Quantity of cargo loaded in any hold should not exceed 0.9xLxBxD where “L” is length of hold in meters, “B” is average breadth in meters and “D” is summer load draft in meters and the result is in metric tonnes.

Where cargo is untrimmed or partially trimmed, the height of cargo peak above the tanktop should not exceed 1.1xDxSF meters, where “SF” is the stowage factor in cu.m/tonne and “D” is the summer draft.

If Cargo is trimmed level, 20% increase over No.2 is permitted but complying with No.1.

If a shaft tunnel passes through the hold, 10% increase over Nos.2,3 and 4 is permitted but again complying with No.1.

However on all the above the Shipyard instructions for loading high density cargoes shall be followed at all times.

Precautions when carrying Concentrates

The Cargo vessels may carry concentrates only when cargo is at or below Transportable Moisture Limit. The Cargoes above TML may be carried in specially constructed cargo ships with permanent boundaries arranged to reduce the shift of cargo to an acceptable limit.

Cooper Concentrate

Cargo work should not be carried out in rain. Entry of sea spray, rain etc in to hold should be prevented.

To decrease the effect of oxidation the cargo should be trimmed reasonably level on completion irrespective of the angle of repose, to reduce the surface area.

Some concentrates such as sulphides are subject to oxidation and spontaneous combustion if the moisture content is very low. In such cases water may be used as a spray to cool the cargo. However a flow state should not develop after use of water.

Shipper must produce a certificate from a competent authority stating the Flow moisture point, Transportable moisture limit and Actual Moisture content.

In case stock pile is exposed to precipitation then test samples must be taken just prior to loading.

Cargoes liable to Spontaneous Combustion

Many bulk cargoes have a tendency to heat due to the oxidation process taking place during the voyage, which may lead to fire or explosion if the temperature rises to a level where spontaneous ignition can take place. Cargoes liable to spontaneous combustion include some types of coal, concentrates of lead, oil seed cakes (transported in bulk), fishmeal and scrap metal.

Even where the type of coal is not considered a danger for self- heating, this can still occur if stacks have accumulated over a long period ashore. 

Temperature Monitoring of Cargoes during carriage.

Many bulk cargoes are liable to spontaneous combustion or ship or cargo sweat. The only possible way to obtain an early warning of the start of spontaneous combustion is by monitoring the temperature of the cargo holds. Many ships are fitted with `temperature ports’, ie pipes that are fitted beside the cargo hold access ladders into which thermometers can be lowered to obtain the hold temperature. The best practice is to leave   the thermometers within the ports and withdraw them when a reading is desired. However, if the ship is not fitted with temperature ports, the sounding pipes could also be used to obtain temperatures. Whichever method is used for measuring temperature:

i) The thermometers should be reset before introducing them into the pipes
ii) the thermometers should be left in the pipes for some time (2-3 minutes at least)
iii) the temperature should be measured at least 2-3 height levels within the hold
iv) the temperature should not be measured solely at the surface of cargo as it is likely to be quite different from that at the bottom of the cargo hold.

Modern bulk carriers may be fitted with permanent temperature sensors providing continuous readings. It is important to maintain records of all temperature observations and ensure readings are taken at the same times and at regular intervals. This makes it easy to establish a pattern for any irregularities in the observed behaviour.

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