Fertiliser Cargo: Do you Know your Caked from your Compacted?

Two of the most common problems are caking and compaction of cargo within the hold. Receivers take issue with cargo that is caked or compacted because it needs breaking up into granular form before it can be used in farm machinery.

However, caking and compaction are often confused with each other despite being different.

Compaction

Compaction generally occurs because of weight applied onto the cargo. This is often caused by the way the cargo is stowed.

Caking

If the cargo is wetted, caking may occur.  There are two caking processes:

• Crystal bridging – the formation of salt or crystal bridges.
• Adhesive contacts – molecular bonding (Van der Waals forces).
• Liquid contacts – formation of a film of solution around the particle (generally wetting).

Crystal bridging is considered the strongest form of caking given its chemical basis.

Compacted v caked

When a cargo is found to be in a state of compaction or caked, arguments can arise as to whether the condition can be reversed and whether the cargo is fit for its end use.

Generally, in cases of wetting, the condition is irreversible and receivers will argue that the cargo is caked and is unsuitable. In these cases, significant claims can occur. However, the effects of compaction are reversable. It is therefore important to understand whether the cargo is caked or compacted. This will determine if the condition is reversible.

The boundary between compaction and caking can be vague and subjective.  The appointment of an expert is usually advised, but the general rule of thumb is:

• Does the cargo break up into individual free flowing granules under light to moderate pressure? If so, it is normal compaction and should be accepted as commercially sound.
• If the cargo does not break up, or if it breaks up into a powder rather than granules, then this suggests caking.

Action to take if caked

If the cargo is proven to be caked, the severity of such caking needs to be assessed. When assessing the severity, numerous factors should be considered, including:

• What is the end use? If used in mechanical spreaders, then free-flowing nature will be important. However, for manual spreading it is likely to be less important.
• Nature of the fertiliser itself – such as its moisture content, hygroscopicity, temperature, chemical composition and mechanical strength.
• External influences – typically the compaction pressure, ambient conditions, storage time and handling procedure.

Severe caking can occur upon loss of moisture subsequent to a wetting incident.  The cargo may be wet at the time of discharge but would be expected to become hard-caked once it dries out in the future.

Prevention

To prevent or minimise caking whilst on board the vessel:

• Keep the cargo dry.
• Weathertight hatch covers and accesses are essential.
• Avoid working the cargo during rain.
• Ventilate the cargo holds as required, taking into account any instruction from the shipper or charterer.

The production process, use of anti-caking agents and storage arrangements ashore also influence the cargo’s vulnerability to caking.

Further Information

See our loss prevention guidance on carrying hygroscopic cargoes.