Introduction:

Members attention is drawn to the potential risks associated with bulk fluorspar cargoes.

A members vessel was recently engaged in the carriage of fluorspar from Humen port in China to the Middle East. Adverse weather conditions were encountered during the later stages of the voyage and routine cargo inspection showed that the cargo had flattened in one of the holds and a considerable volume of water had been expressed to the surface of that stow.

The cause of cargo failure and the associated risk to the ship’s stability was determined to be liquefaction due to a portion of the cargo being loaded at a moisture content in excess of the transportable moisture limit (TML). Loading in excess of the TML subsequently allowed high saturation conditions to develop, increased pore water pressure, and facilitated the stow collapse.

Fluorspar:

Fluorspar normally presents as a grey/ white granular powder, though staining from impurities can give it a red or yellow appearance. It has major uses as a flux in iron and aluminium production. Higher grade products are the principal source of hydrofluoric acid while lower grades are often destined for the cement industry.

Fluorspar is often upgraded from its natural state by flotation. The mined ore is ground to a fine powder and turned into a slurry, before fluorspar’s natural hydrophobic properties are chemically enhanced and exploited to separate it from waste materials in an aerated tank. The wet fluorspar concentrate then typically undergoes filtration to reduce its moisture content to circa 5 to 8%. For higher value products (for example acid grade) this filter cake undergoes thermal drying to reduce its moisture content further to 0.5 to 1%.

Fluorspar is classified in the IMSBC Code as both Group A (prone to liquefaction if its TML is exceeded) and B (due to its chemical/ dust hazard) .

As with all Group A cargoes, precautions must be taken to prevent uncontrolled exposure to moisture, including from precipitation or ground run-off when transported or stockpiled ashore.  The cargo shall not be handled during precipitation (unless the conditions stated in the procedures required in 4.3.3 of the Code are complied with) and all non-working holds should be closed during loading.

The shipper is also obliged to accurately assess their cargo and provide a TML and moisture content certificate prior to loading. In addition, a moisture management plan (MMP) approved by the competent authority (or entity acting on its behalf) should be available if requested by the vessel owners or master. This should detail the sampling and testing procedures used to assess the cargo as well as operational controls employed to protect the cargo from moisture ingress.

Risks:

Fluorspar is often perceived as a dry cargo, but it must be remembered that lower quality products that have not undergone thermal drying often contain a significant moisture content.

Due to its low particulate density (relative to metallic concentrates) low mineral clay content and typical particle size distribution (PSD) fluorspar can reach high saturations at low moisture contents. This property makes it difficult to spot elevated moisture contents in the cargo during loading, as the normal indicators such as visible free water, wet base, visible increase in apparent cohesion may not apply. Often only a darkening of a portion of the consignment is a clue that a part of the cargo may be wetter than declared.

These properties also mean that a relatively small increase in moisture content, such as exposure to rainfall on the dock, can have a large effect on the saturation and subsequent risk of cargo failure.

The TML of fluorspar is predominantly determined by the IMSBC Code appendix 2 method 1.1 flow table test.  Whilst the flow table test method can be appropriate for identifying flow conditions in fine granular materials it can be very dependent on the operator to observe when a flow state is reached. As such, some laboratories will try and standardize this step by nominating a standard expansion (often 3mm) as a failure criterion.

In the case of fluorspar cargoes that haven’t undergone thermal drying, TML values are often very close to the declared moisture content so it is important that the shipper can provide confidence in their TML results by demonstrating how they have determined the TML and at what moisture a flow state has been reached. If in doubt a master should request the full test report as opposed to just the TML result and consult their P&I club or expert if interpretation is required.

Fluorspar is often stored in sheds or undercover to protect the cargo from precipitation, however it is vulnerable to moisture ingress when being transported to and from these storage facilities. In addition, the cargo is often temporarily stacked on the dockside prior to loading in small stockpiles which are especially vulnerable to rainfall and infiltration from surface water on the hard standing.

In the case mentioned at the introduction above, it is suspected that a portion of the cargo was exposed to rainfall during the loading, elevating its moisture content.

Part of the cargo was loaded in wet conditions.

Recommendations:

When loading these cargoes, the shipper should be requested to provide clarity on the sampling, moisture content and TML testing. It is recommended that members appoint competent surveyors / experts to review the shippers documentation, including the full sampling and testing reports rather than just the declared values.

If any portion of the cargo is exposed to rainfall the master should ask the shipper to provide detail on how this is measured or accounted for, even if the cargo continues to appear “dry” in the stockpile.

If the consistency or colour of the cargo changes (especially if it appears darker) then the master should seek reassurance/ clarification on the cargo consistency and range of moisture contents to be loaded. If in any doubt, members should contact the Club for guidance as soon as possible.

If any flattening of the stow or expression of water from the stow is noted on passage, the master shall take appropriate actions to prevent further cargo deterioration, and give consideration to seeking emergency entry into a place of refuge. In such circumstances, it is recommended that expert assistance is sought without delay to aid the crew in making an assessment of the situation and help determine any appropriate actions

We thank cargo experts Roxburgh for their assistance in preparing this advice.

Contact details:
Roxburgh Group Limited
Website: www.roxburgh.co.uk
Email: help@roxburgh.co.uk

---

The information in this Member Alert is provided for guidance only. Members should seek specific advice regarding their individual circumstances. While the Club has taken reasonable care in preparing this publication, it accepts no responsibility for any errors or omissions, or for any consequences arising from reliance on the information contained herein.