International Maritime TML Testing: Transportable Moisture Limit Determination under the IMSBC Code

International maritime TML testing determines the Transportable Moisture Limit of solid bulk cargoes that may liquefy during sea transport, as required by the International Maritime Solid Bulk Cargoes (IMSBC) Code of the International Maritime Organization. Accurate determination of the TML, Flow Moisture Point, and moisture content prevents catastrophic cargo liquefaction, sudden listing, and capsize. Accredited third-party laboratories perform these tests using internationally recognized procedures such as the flow table test, penetrometer test, and Proctor/Fagerberg method.

Technical Overview

The International Maritime Solid Bulk Cargoes (IMSBC) Code, adopted by the International Maritime Organization (IMO) under the provisions of the SOLAS Convention, classifies solid bulk cargoes into three groups: Group A (cargoes that may liquefy), Group B (cargoes possessing chemical hazards), and Group C (cargoes with neither of these characteristics). Group A cargoes, such as mineral concentrates, ore fines, and certain coals, contain a significant proportion of fine particles combined with inherent moisture. Under the vibration and rolling motion of a ship at sea, the pore pressure within such cargo can rise abruptly, transforming apparently stable material into a viscous slurry that shifts across the hold and may cause severe listing or total loss of the vessel.

To control this risk, the IMSBC Code requires the shipper to declare both the Transportable Moisture Limit (TML) and the actual moisture content of any Group A cargo. The TML is defined as 90% of the Flow Moisture Point (FMP), the moisture content at which a saturated cargo begins to develop flow characteristics under the standardized dynamic conditions of the laboratory test. The moisture content of the cargo at the time of loading must be lower than the TML, otherwise the cargo may not be accepted for shipment. All laboratory procedures, apparatus specifications, and referenced standards for TML determination are set out in Appendix 2 of the IMSBC Code, and testing is carried out by accredited third-party laboratories with validated equipment and trained personnel.

Testing Samples

TML testing applies to any solid bulk cargo classified or suspected to be Group A. Because liquefaction potential depends strongly on particle size distribution, mineralogy, and moisture retention, samples must be drawn representatively from the stockpile or conveyor stream to be loaded. Typical sample categories include:

Iron Ore Fines and Concentrates

Fine iron ore and sinter feed are among the highest-volume Group A cargoes. Dedicated schedules in the IMSBC Code govern their carriage, and moisture determination is supported by ISO sampling and test methods developed specifically for iron ores. Particle size, alumina content, and blending practice all influence liquefaction behavior and must be reflected in the sampled material.

Nickel Ore

Nickel ore, particularly lateritic ore shipped from tropical regions, is moisture-rich and notoriously prone to liquefaction. Stringent TML and moisture content verification is standard practice for this trade, with particular attention to seasonal rainfall, moisture migration within the stockpile, and drainage conditions during storage and loading.

Bauxite

Amendments to the IMSBC Code have strengthened the requirements for bauxite following reported liquefaction incidents. A modified Proctor/Fagerberg procedure has been introduced for certain bauxite types, and testing programs for bauxite now demand careful characterization of the fine fraction and its saturation behavior.

Mineral Concentrates and Other Group A Cargoes

Copper, lead, zinc, and manganese concentrates, fluorspar, ilmenite, pyrites, iron sand, and fine coal or coal slurry are further examples of cargoes requiring TML determination. Any cargo not listed in the Code but identified as prone to liquefaction must be assessed and tested before shipment.

Sampling and Sample Handling

Samples are collected as a series of increments distributed across the full volume of the stockpile or obtained mechanically from the loading stream, in accordance with recognized sampling standards such as ISO 3082 for iron ores and ISO 13909 for hard coal and coke. To prevent moisture loss, samples are sealed immediately in airtight containers with minimal headspace, clearly labeled, and transported to the laboratory without delay. Sufficient material, typically tens of kilograms of gross sample, is required to permit test portions, repeat determinations, and retained reference portions.

Testing Items

The core scope of an international maritime TML test program comprises the following determinations:

• Transportable Moisture Limit (TML): the maximum moisture content of the cargo at which it is deemed safe to transport, calculated as 90% of the Flow Moisture Point.
• Flow Moisture Point (FMP): the experimentally determined moisture content at which plastic flow behavior first develops under the dynamic conditions of the prescribed apparatus.
• Moisture Content (MC): the actual water content of the cargo as sampled, determined gravimetrically by oven drying and compared against the TML for acceptance.
• Declaration support data: particle size distribution and contextual cargo information required to complete the mandatory cargo information declaration for the master.

The compliance criterion is unambiguous: if the declared or measured moisture content equals or exceeds the TML, the cargo fails and may not be loaded under ordinary circumstances.

Testing Methods

Appendix 2 of the IMSBC Code prescribes three principal test methods for determining the FMP, from which the TML is derived. Method selection depends primarily on the grain size and permeability of the material. All methods share the same fundamental logic: a saturated specimen is subjected to a standardized dynamic or compaction stimulus, and the moisture content at which flow behavior is initiated is bracketed through a series of trials at incrementally different moisture contents.

Flow Table Test (FT)

The flow table test is generally suitable for mineral concentrates and other fine-grained materials with a maximum grain size of approximately 1 mm, with limited tolerance for slightly coarser fractions as defined in the Code. A saturated specimen is compacted in a truncated conical mold on a flow table apparatus conforming to ASTM C230 and equivalent ISO specifications, such as ISO 12742 for copper, lead, and zinc concentrates. The table is raised and dropped a defined number of times, and the specimen surface is examined for the development of a plastic, glossy flow condition. By testing specimens at successively adjusted moisture contents, the laboratory brackets the FMP, and the TML is reported as 90% of that value.

Penetrometer Test (PT)

The penetrometer test is applicable to fine-grained materials with a particle size generally below 1 mm. A compacted, saturated specimen is penetrated by a standardized cone, and the penetration depth is recorded as a function of moisture content. The FMP is identified at the moisture content at which the penetration reaches the flow threshold specified in the Code. The method is compact, rapid, and well suited to materials for which the flow table geometry is inappropriate.

Proctor/Fagerberg Test (PFT)

The Proctor/Fagerberg test is designed for more permeable materials with grain sizes up to approximately 5 mm. A series of specimens is compacted at stepped moisture contents in a standardized mold, generating a compaction curve of dry density versus moisture content. The FMP is derived from the specified degree-of-saturation criterion defined in the Code, and the TML is calculated accordingly. A modified Proctor/Fagerberg procedure has been incorporated through subsequent amendments of the Code to address the particular liquefaction behavior of certain bauxite cargoes.

Moisture Content Determination

Moisture content is determined gravimetrically by drying test portions to constant mass, using oven-drying methods consistent with ASTM D2216 and the material-specific standards ISO 3087 for iron ores and ISO 589 for hard coal. Duplicate determinations and agreed tolerances between results are required for quality control. Because moisture content is the controlling compliance parameter at the moment of loading, determinations must be performed as close as practicable to the time of loading, conventionally within seven days, and the cargo must be retested whenever it has been exposed to significant precipitation or other conditions capable of altering its moisture content.

Applications

International maritime TML testing supports safety and compliance across the entire dry bulk supply chain. Typical applications include:

• Shipper preparation of the mandatory cargo information declaration for Group A cargoes prior to loading.
• Pre-shipment and load-port verification of moisture content against the declared TML for masters, charterers, and terminal operators.
• Quality control and stockpile management at mines, beneficiation plants, and blending yards, including retesting after rainfall events.
• Risk assessment and documentation for ship owners, P and I clubs, underwriters, and port state control authorities.
• Classification of new or unlisted cargoes as Group A, B, or C in support of the tripartite agreement process for new cargo entries.
• Evidence and dispute resolution in cargo claims arising from liquefaction incidents or disputed moisture declarations.

FAQ

What is the difference between TML and FMP?

The Flow Moisture Point is the experimentally measured moisture content at which a cargo first develops flow behavior under the standardized test conditions. The Transportable Moisture Limit is set at 90% of the FMP to provide a deliberate safety margin, accounting for moisture migration and measurement uncertainty during a voyage.

Which TML test method applies to my cargo?

Method selection is governed by the particle size distribution and permeability of the material: the flow table test and penetrometer test are intended for fine-grained cargoes, while the Proctor/Fagerberg test suits coarser, more permeable materials. Where a cargo schedule in the IMSBC Code specifies a particular method, that specification is binding.

How current must the test results be?

The TML characterizes a defined source of material and should be re-established whenever the ore body, processing, or blending changes. Moisture content, by contrast, must be determined immediately before loading, conventionally within seven days, and the cargo retested following rain, snow, or any condition likely to have altered its moisture.

What happens if the moisture content exceeds the TML?

The cargo fails the acceptance criterion and may not be loaded. Exceptions exist only for specially constructed or fitted ships, approved by the competent authorities of the flag state, port of loading, and port of discharge, in accordance with the special provisions of the IMSBC Code.

How much sample is required for testing?

A representative gross sample, commonly on the order of tens of kilograms depending on the cargo and method, is collected from the stockpile or loading stream. The laboratory uses this material for the TML and moisture determinations and retains sealed portions for verification and reference.

Can a cargo not listed in the IMSBC Code be shipped?

Yes, provided the cargo is assessed against the criteria of the Code and classified as Group A, B, or C on the basis of suitable test data, and a tripartite agreement between the competent authorities of the countries of loading, unloading, and the flag state is obtained. TML data is a central element of the Group A assessment.