IMSBC Code TML Testing: Transportable Moisture Limit Determination for Liquefiable Solid Bulk Cargoe

IMSBC Code TML testing determines the Transportable Moisture Limit of solid bulk cargoes that may liquefy during sea transport, protecting vessels from cargo shift and capsizing. This technical article explains the regulatory framework under the International Maritime Solid Bulk Cargoes Code, the applicable test methods such as the Flow Table Test, Penetration Test and Proctor/Fagerberg Test, sample types, testing procedures, and certification requirements for shippers and carriers.

Technical Overview

The International Maritime Solid Bulk Cargoes (IMSBC) Code, adopted by the International Maritime Organization (IMO) and made mandatory under Chapter VI of the SOLAS Convention, establishes the international requirements for the safe loading, stowage and carriage of solid bulk cargoes. One of the most safety-critical provisions of the Code concerns Group A cargoes: materials that contain a degree of moisture and may liquefy when shipped with moisture content in excess of their Transportable Moisture Limit (TML).

The Transportable Moisture Limit is defined as the maximum moisture content of a cargo at which it is considered safe to load and transport in a ship's cargo hold without risk of liquefaction. Under the IMSBC Code, the TML is calculated as 90 percent of the Flow Moisture Point (FMP), which is the moisture content at which a cargo develops a flow state under the prescribed conditions of the standard laboratory test methods set out in Appendix 2 of the Code.

Liquefaction occurs when cyclic forces generated by the rolling, pitching and vibration of a ship cause pore water pressure to build up within a saturated or nearly saturated fine-grained cargo. The cargo loses shear strength, behaves like a viscous slurry, and can shift rapidly to one side of the hold, leading to loss of stability, dangerous listing and, in several documented casualties, the total loss of vessels and crew. For this reason, the Code prohibits the loading of any Group A cargo whose actual moisture content exceeds its certified TML.

Compliance involves three linked elements: representative sampling of the cargo to be shipped, laboratory determination of the TML and the Flow Moisture Point, and determination of the actual cargo moisture content. Samples for moisture content determination must be taken as close as practicable to the time of loading, and in any case not more than seven days before loading begins. If significant rain, snow or other environmental changes occur between sampling and loading, additional sampling and testing are required. The shipper must declare the TML and moisture content in the cargo information document, and a TML test certificate must be provided to the master before loading.

Testing Samples

Iron Ore Fines and Sinter Feed

Fine iron ore cargoes, including sinter feed and iron ore fines produced by crushing, screening and beneficiation, are among the highest-risk Group A commodities. Their high density and fine particle size distribution promote rapid moisture migration and liquefaction, and dedicated test procedures have been developed specifically for these materials.

Nickel Ore and Lateritic Ores

Nickel ore, particularly wet lateritic ore mined in tropical regions, is transported at naturally high moisture contents close to its Flow Moisture Point. A number of fatal capsize incidents involving nickel ore carriers have made rigorous TML certification a precondition for loading in major exporting countries.

Bauxite

Following liquefaction casualties involving bauxite carriers, certain bauxite cargoes were reclassified into Group A. Testing is performed using the modified Proctor/Fagerberg test method C, which was developed to account for the compaction behavior and moisture response of bauxite.

Coal and Coal Fines

Coal cargoes may present combined hazards and are often classified as both Group A and Group B. Fine coal, coal slurry residues and washed coal with elevated moisture require TML determination in addition to the routine commercial quality analysis.

Mineral Concentrates

Concentrates of copper, lead, zinc, tin, ilmenite and other minerals are produced by wet beneficiation and filtration. The residual moisture retained after dewatering frequently approaches the Flow Moisture Point, making TML testing an essential pre-shipment control.

Other Liquefiable Cargoes

The scope of Group A materials also includes manganese ore fines, mill scale, fluorspar, pyrites, mineral sands and other fine-grained bulk materials listed in Appendix 1 of the IMSBC Code, as well as cargoes classified by the competent authority as presenting a liquefaction hazard.

Testing Items

A complete IMSBC Code TML assessment typically comprises the following testing items:

• Transportable Moisture Limit (TML) determination, reported as the limiting safe moisture content of the cargo.
• Flow Moisture Point (FMP) determination, the primary measured parameter from which the TML is derived at 90 percent.
• Cargo moisture content (MC) determination, used to verify that the actual moisture of the cargo to be loaded is below the certified TML.
• Particle size distribution analysis, required to select the correct test method and to confirm that the sample is representative of the cargo as shipped.
• Sample preparation, including homogenization, sub-sampling and moisture conditioning in accordance with the Code's prescribed procedures.

Testing Methods

Flow Table Test (FTT)

The Flow Table Test is the classical reference method, designed for mineral concentrates, similar fine materials and fine coal with particle size generally not exceeding 7 mm. A truncated conical specimen of the material, prepared at a controlled moisture content, is placed on a flow table apparatus and subjected to a standardized sequence of 25 free drops from a fixed height within 50 seconds. The FMP is bracketed by observing the moisture content at which the specimen first exhibits plastic deformation and flow characteristics under repeated dynamic loading. A series of tests at incrementally varying moisture contents is performed until the flow state and no-flow state are bracketed within the required tolerance.

Penetration Test (PT)

The Penetration Test is suitable for very fine materials such as mineral concentrates and fine coal. The prepared specimen is compacted inside a cylindrical mold mounted on a vibrating table, and a penetration bit attached to a weighted stem is lowered onto the surface of the specimen. The depth of penetration under static load is measured after a defined vibration sequence. When the penetration exceeds the acceptance criterion, the material has reached a flow state. Tests are conducted at progressively higher moisture contents to bracket the Flow Moisture Point. A dedicated penetration test procedure for iron ore fines was introduced through subsequent amendments to the Code to address the specific behavior of these high-density cargoes.

Proctor/Fagerberg Test (PFT)

The Proctor/Fagerberg Test determines the FMP from the compaction characteristics of the material. A series of specimens is compacted at increasing moisture contents in a standard mold, and the resulting dry densities are recorded. The Flow Moisture Point is identified at the point on the compaction curve where additional moisture no longer permits further densification, indicating the onset of saturation and loss of effective stress. The method is applicable to fine-grained cargoes that gain shear strength through compaction, and the modified variant, Proctor/Fagerberg test C, is prescribed for bauxite.

Moisture Content Determination

Cargo moisture content is determined by drying representative sub-samples to constant mass in a drying oven at approximately 105 degrees Celsius, and calculating the mass loss as a percentage of the original wet sample mass. Where facilities permit, rapid methods may be used for screening, but oven drying remains the reference procedure for certification.

Method Selection and Quality Assurance

The appropriate TML test method is selected on the basis of the particle size distribution and the mechanical behavior of the cargo, following the guidance in Appendix 2 of the IMSBC Code. All tests must be performed by trained laboratory personnel using calibrated apparatus, with documented procedures, replicate determinations and traceable sampling records to ensure that the certificate is defensible before port State control authorities, charterers and marine insurers.

Applications

IMSBC Code TML testing services support multiple stakeholders across the bulk shipping supply chain:

• Shippers, mines and trading houses requiring pre-shipment TML and moisture content certification for Group A cargoes.
• Shipmasters and ship operators verifying cargo information documentation before commencing loading operations.
• Port State control inspectors and flag administrations auditing compliance with SOLAS Chapter VI and the IMSBC Code.
• Charterers and P&I clubs performing independent surveys and risk assessments to prevent liquefaction-related casualties.
• Stockpile and dewatering process management at mines, beneficiation plants and ports, where periodic TML monitoring confirms that production moisture remains within safe limits.
• Dispute resolution and cargo damage investigations following moisture-related claims, wetting incidents or refusal of cargo by terminal or vessel interests.

FAQ

Q: What is the difference between TML and Flow Moisture Point?

A: The Flow Moisture Point is the experimentally determined moisture content at which a cargo begins to develop a flow state under the prescribed test conditions. The Transportable Moisture Limit is set at 90 percent of the FMP, providing a regulatory safety margin for the moisture content of the cargo as loaded.

Q: When is TML testing legally required?

A: TML determination is mandatory for all Group A cargoes, that is, cargoes that may liquefy, listed in Appendix 1 of the IMSBC Code or so classified by the competent authority of the port of loading. The shipper must communicate the TML and the actual moisture content in the cargo information supplied to the master prior to loading.

Q: How recent must the sampling and testing be?

A: Samples for moisture content determination must be taken not more than seven days before loading commences. If rain, snow or other conditions may have altered the moisture content after sampling, the cargo must be re-sampled and re-tested. The TML certificate remains valid provided the characteristics of the material and its source have not changed.

Q: What happens if the cargo moisture content exceeds the TML?

A: The cargo may not be loaded. The IMSBC Code prohibits loading of any Group A cargo with moisture content in excess of its TML, except that a cargo with moisture content above the TML but below the FMP may only be loaded if the ship has specially designed and approved arrangements for its safe carriage.

Q: Which TML test method should be used for a specific cargo?

A: Method selection depends on particle size distribution and material behavior. The Flow Table Test suits fine materials up to approximately 7 mm, the Penetration Test suits very fine concentrates and fines, and the Proctor/Fagerberg methods suit compaction-responsive materials, with test C prescribed for bauxite. A laboratory will confirm the appropriate method based on the particle size analysis of the submitted sample.

Q: How should samples be taken and transported?

A: Samples must be collected from the stockpiles, stockpiles-to-be-loaded or conveyors in a manner that represents the entire cargo, sealed in moisture-tight containers immediately after sampling, and delivered promptly to the laboratory with full chain-of-custody documentation to prevent moisture loss or gain before testing.