Bulk Cargo Moisture Content
Another problem with certain bulk commodities is that of liquefaction, created by moisture migration. Moisture migration is caused when vibration at sea progressively causes the water content of a cargo to rise to the top of the hold which might eventually lead to a dangerous free surface, perhaps shifting violently from side to side.
Accordingly, commodities liable to such problems are allotted a TML (Transportable Moisture Limit), representing the maximum moisture content of that cargo considered safe for carriage in ships. Certain commodities, such as concentrates, are particularly prone to liquefaction and should never be carried without first checking the moisture content. Where such cargo is contemplated, it is common practice to include a clause in the contract of carriage reading such as:- .. Cargo to be loaded. stowed. carried and discharged strictly in accordance with IMO and/or local authority regulations and recommendations”. and Certificates should be issued by the shippers relating to the properties and the moisture content of the cargo to be loaded.
The Code of Safe Practice for Solid Bulk Cargoes referred provides information on both the transportable moisture limits of various commodities as well as details of how the moisture content of a particular commodity can be tested and assessed.
What is Cargo Moisture Content in Ship Chartering?
In the context of ship chartering, the term “cargo moisture content” refers to the amount of water or other liquid contained within the shipped cargo. This is a particularly important factor when dealing with bulk solid cargoes like grains, coal, or iron ore, which can become unstable and potentially hazardous if they have high moisture content.
The reason moisture content is critical lies in a phenomenon called liquefaction. When a solid bulk cargo with a certain moisture level is subjected to the motions and vibrations of a ship at sea, it can behave more like a liquid. This can lead to a shift in the cargo’s center of gravity, potentially causing the ship to capsize.
As a result, international shipping regulations stipulate strict rules on the maximum allowable transportable moisture limit (TML) for specific types of cargoes. The shipper must provide accurate information about the cargo’s moisture content, and this must be lower than the TML.
Therefore, as part of the ship chartering process, understanding and controlling the cargo moisture content is vital to ensuring the safety of the ship and crew, as well as preventing potential financial and legal complications.
In order to comply with safety regulations and ensure a successful charter, the shipper must conduct proper testing of the cargo before loading. Samples are taken from multiple points within the bulk material and then analyzed in a laboratory. The test measures both the moisture content and the flow characteristics of the cargo, determining whether it is safe to ship. The Flow Moisture Point (FMP) and Transportable Moisture Limit (TML) are then calculated.
The FMP is the moisture content at which the material starts to behave as a liquid. The TML is calculated as 90% of the FMP. As per the International Maritime Solid Bulk Cargoes Code (IMSBC Code), any cargo with moisture content above the TML is considered unsafe for maritime transport due to the risk of liquefaction.
In addition to pre-loading testing, other precautions are often taken to manage cargo moisture content. These might include:
- Weather considerations: If wet weather is expected during loading, additional measures may be taken to protect the cargo. This could involve the use of tarps or loading in a covered area.
- Storage conditions: The cargo may be stored in conditions that minimize moisture absorption prior to loading, such as in covered or indoor areas.
- Moisture control measures: Depending on the type of cargo, it might be treated with moisture-absorbing materials or other technologies to reduce its moisture content.
- Regular inspections: While at sea, the cargo may be regularly inspected to ensure no unexpected changes in moisture content occur.
Proper management of cargo moisture content in ship chartering is critical for ensuring the safe and successful delivery of cargo. It is a process that involves not just understanding the nature of the cargo, but also applying the right techniques and precautions to maintain its stability during transport. Failure to do so can result in serious incidents, including the loss of the ship and its crew, as well as significant financial losses and potential legal liability.
Responsibility for Cargo Moisture Content in Ship Chartering
Given the high stakes involved, it’s clear that there’s a significant responsibility on all parties involved in the shipping process to manage the moisture content of cargo effectively. This involves several key players:
- Shippers: They are responsible for declaring the correct cargo moisture content and its TML based on comprehensive testing. They should also ensure that the cargo is stored correctly prior to loading, taking precautions against weather and other environmental factors that could increase the moisture content.
- Charterers: They are responsible for ensuring that the cargo loaded onto their chartered vessels complies with the IMSBC Code. Charterers should verify the accuracy of the shippers’ declarations, and, if in doubt, they have the right to carry out their own independent testing.
- Ship Master and Crew: They play an important role in monitoring the condition of the cargo throughout the journey. They should be trained to recognize signs of moisture-related issues, such as cargo shifting or increased free surface effect, and to take necessary precautions.
- Insurers and surveyors: They have a role to play in verifying that all precautions have been taken and that the moisture content of the cargo is within acceptable limits. In the event of a mishap, they will be involved in assessing the cause and any potential liability.
- Governments and regulatory bodies: They are responsible for setting and enforcing the standards related to moisture content and the transport of solid bulk cargoes. Their role is crucial in maintaining safety in the maritime transport sector.
Effective management of cargo moisture content is a collective effort. Each party must do their part to ensure that the moisture content of the cargo is maintained within the allowable limits, and that it remains stable throughout the shipping journey. This not only ensures the safety of the vessel and its crew but also minimizes the risk of financial loss and legal liability.
What is Flow Moisture Point (FMP) in Ship Chartering?
Flow Moisture Point (FMP) is a critical factor in ship chartering, especially when transporting bulk cargoes that can contain moisture, such as iron ore, coal, or grain.
FMP refers to the maximum moisture content (often expressed as a percentage of the total mass) that a given type of cargo can hold without becoming fluid or undergoing liquefaction. If the cargo’s moisture content exceeds the FMP, it can shift abruptly in response to the ship’s movements, leading to potentially severe stability problems that can cause the ship to capsize. This is a major safety issue and is responsible for numerous maritime accidents and fatalities.
The determination of the FMP for any cargo is done through laboratory testing according to standardized procedures set by the International Maritime Solid Bulk Cargoes (IMSBC) Code. It is mandatory to provide a certificate that states the moisture content and FMP of certain types of cargo before loading.
What is TML (Transportable Moisture Limit) in Ship Chartering?
Transportable Moisture Limit (TML) is a term used in the maritime shipping industry to denote the maximum moisture content in a bulk cargo that is safe to transport.
When bulk cargo such as iron ore, coal, or grain is loaded onto a vessel, it is often in a finely ground form and may contain moisture. If the cargo has too much moisture, it can become unstable during transit, leading to a shift in the cargo. This can be extremely dangerous, potentially causing the ship to list, capsize or sink.
The TML is typically determined through laboratory testing of the cargo in accordance with internationally recognized standards. The procedures for determining TML for a specific cargo are outlined in the International Maritime Solid Bulk Cargoes (IMSBC) Code, which is a publication of the International Maritime Organization (IMO).
Under the IMSBC Code, it is the shipper’s responsibility to provide the master or his representatives appropriate information on the cargo, including the TML, and to declare that the moisture content of the cargo is less than its TML.
If the cargo’s actual moisture content exceeds its TML, the cargo is not safe for transportation, and steps must be taken to reduce the moisture content or otherwise make the cargo safe for shipping.
What is Liquefaction in Ship Chartering?
In the context of ship chartering, the term “liquefaction” is often associated with the transportation of bulk solid cargo, such as mineral ores. Liquefaction, in this case, refers to the process where solid bulk cargoes, under certain conditions, start behaving more like a liquid than a solid.
The primary factor behind this transformation is moisture. When the moisture content of the cargo is too high, the vibrations and motions of the ship can cause the cargo to compact and compress, allowing water to come out of the material, which in turn can lead the solid cargo to act like a liquid.
When liquefaction occurs, it can have severe consequences. It can lead to cargo shifting or sloshing in the hold, which can cause a loss of stability for the ship, potentially leading to capsizing and sinking. It’s a serious safety concern in maritime transport, and as such, there are strict international regulations on the moisture content of certain types of cargo.
Types of Tests to Determine Moisture Content of Bulk Cargo
Bulk cargo moisture content is important to determine for many reasons, including maintaining quality, ensuring transport safety, and facilitating efficient storage. There are several different types of tests that can be performed to determine the moisture content of bulk cargo:
- Oven Drying Method: This is the most common method used to determine moisture content. A sample is weighed and then placed in an oven set at a certain temperature until it reaches a stable weight. The difference between the initial weight and the final weight provides the moisture content.
- Microwave Oven Method: Similar to the oven drying method, but it uses a microwave oven, which can dry the sample much faster. However, this method may not be suitable for some types of materials as it can cause uneven heating.
- Karl Fischer Titration: This is a highly accurate and specific method used to determine the amount of water in a sample. It’s based on a chemical reaction that occurs when water is present.
- Capacitance Meters: These handheld devices measure the dielectric constant of a material, which changes as the moisture content increases. They can provide fast, though somewhat less precise, moisture content readings.
- Near-Infrared (NIR) Analysis: NIR uses light reflection to measure moisture content. A device sends out a light wave, and the amount of light that is reflected back is measured. Different moisture levels will reflect light differently.
- TDR (Time Domain Reflectometry) Devices: These use electromagnetic waves to measure moisture content. The speed of these waves changes depending on how much moisture is present in the material.
- Gravimetric Analysis: In this method, a sample is weighed before and after the removal of water. This difference in weight represents the moisture content of the sample.
- Calcium Carbide Method: Also known as the Speedy Moisture Test. It involves the reaction of calcium carbide with water to produce a gas, and pressure from this gas is related to the moisture content.
- Loss on Drying (LoD): This is a percentage loss in weight when a sample is heated to remove water content and other volatile substances.
Each method has its own advantages and limitations and is suitable for different types of bulk cargos. It’s also essential to take multiple samples to get an accurate average moisture content. These methods help in maintaining the safety and efficiency of bulk cargo transportation and storage.
How to Reduce the Risk of Liquefaction in Dry Bulk Cargo?
Liquefaction is a process where a granular material, like dry bulk cargo, behaves more like a liquid due to an increase in pressure and the presence of moisture. This can be a major issue in the transport of dry bulk cargo as it can cause shifts in the cargo leading to potentially catastrophic balance issues in the transporting vessel. Here are some strategies to reduce the risk of liquefaction:
- Proper Sampling and Testing: Before loading, cargo should be sampled and tested for its moisture content to ensure it is below its transportable moisture limit (TML). If the cargo’s moisture content is found to be above this level, it should not be loaded until it is adequately dried.
- Awareness of Weather Conditions: Loading during rainy conditions or when rain is forecast can increase the risk of liquefaction as it can raise the moisture content of the cargo. Loading should be halted during such conditions.
- Regular Inspections: Even after loading, the cargo should be regularly inspected for signs of liquefaction, such as increased cargo surface moisture or free water within the hold. If these are detected, corrective measures should be taken.
- Proper Stowage and Trim: Cargo should be stowed and trimmed in a manner that minimizes the possibility of shifting. This can be achieved by ensuring the cargo’s surface is leveled off and that the load is evenly distributed.
- Loading in Layers: Loading the cargo in thin layers, as opposed to all at once, can help to prevent liquefaction. Each layer can be compacted before the next one is added.
- Training: Staff should be trained to understand the risks and signs of liquefaction. They should be familiar with the procedures to test for moisture content and know what actions to take if signs of liquefaction are detected.
- Ventilation: Good ventilation can help to reduce humidity in the cargo holds and thus reduce the chances of liquefaction.
- Choosing Cargoes Wisely: Some types of dry bulk cargo, such as certain mineral ores, are more prone to liquefaction than others. If possible, consider opting for less risky cargoes.
- Use of Chemical Additives: Certain chemical additives can be mixed with the cargo to reduce the risk of liquefaction. However, this method should be used carefully, considering the nature of the cargo and the potential for chemical reactions.
Implementing these strategies can significantly reduce the risk of liquefaction during the transport of dry bulk cargo.