Πέμπτη 16 Απριλίου 2020

Cargo oil heating practices (The Standard P+I Club)


Claims can arise when cargo is not carried at the recommended temperature. Handling of cargo during transit is the responsibility of the vessel crew and owner. In this article, we look at two cargo types and the issues that can arise.
Introduction
It is sometimes essential to apply heat during transit to maintain or raise the temperature of cargo. 

Over or under heating of cargo can adversely affect the property of the cargo and, on many occasions, this change in the cargo quality is irreversible. Improper temperature control can lead to deterioration in the cargo quality or poor pumping performance leading to excess cargo remaining on board (ROB).
Petroleum cargo
Highly viscous petroleum cargo or cargoes with a high pour point or wax content require heating during transit because heating reduces the viscosity of the cargo and enables it to flow better.
Heating also leads to a constant circulation of cargo within the tank. This leads to a reduction in wax formation and sedimentation, and helps in the outturn at the discharge port.
Usually, it is wise to heat early to maintain the temperature during the voyage, rather than to be forced to raise the temperature of the cargo significantly at the end of the voyage.
The rule of thumb is that the cargo temperature should be at least 10°C above the pour point during the entire voyage. Heating should not be stopped during the voyage and should be adjusted to gradually change the temperature of the cargo to the desired level and then to maintain it.
Heating instructions are often too vague, with the charterers relying on
the experience of the master.
This is especially important if the cargo is loaded at a temperature higher than that requested as per the charterparty.
In this case, it is recommended to wait for the temperature to fall to the desired level and then start the heating to maintain this temperature. It is important to note that if the pour point of the cargo is high and the required temperature as per the charterparty is less than 10°C above the pour point, then the charterer should be consulted and the agreed temperature should be maintained to minimise any shortage claims. When crudes with high wax content requiring heating are carried, it is important that the charterer provides clear instructions for heating both on the voyage and throughout discharge. The temperature of the cargo at any stage should not be higher than the ship is designed to carry.
At the discharge port, the ship staff should ensure that the cargo is stripped immediately after it reaches the level of the heating coils in the cargo tanks.
Edible oil cargo
Edible oils such as the various categories of palm oil and vegetable oils are highly viscous in nature and require special attention during discharge. Each cargo of this type will have specific transportation and
handling requirements. Shipowners should ensure that the supplier or
charterer provides all the necessary information about the cargo such
as specific gravity, colour, moisture content, impurities, melting point and free fatty acid (FFA) content.
Heating instructions should also be detailed and these should state the in-transit temperature, loading/discharging temperature and the allowed daily rate of increase of temperature. Rapid heating of certain grades can cause scorching of the cargo, and overheating the cargo can promote oxidation, hydrolysis, scorching and discolouration of the cargo. Rapid heating can also cause an increase in FFA content, which causes the cargo to turn sour, and is used as a measure of cargo quality, especially for palm oil.
It is therefore important to monitor the temperature of the cargo carefully and, if increasing, raise the temperature of the cargo at a gradual pace. Proper planning is required for heating these cargoes, especially when a significant rise in the temperature is required over
a short voyage prompting a higher rate of heating. To avoid overheating
or scorching, small parcels should be stowed in a tank of suitable size and the use of larger tanks, with a large heating coil surface area, should be avoided.
Crew should remember that carriage of heated edible oil cargoes into cold climates may cause the cargo vapours to solidify inside the cargo tank ventilation piping, effectively preventing the pressure in the cargo tank to equalise. This could potentially result in a catastrophic failure of the cargo tank.
The Food and Agriculture Organization of the United Nations (FAO) recommends the practice for storage and transport of edible fats and oils (CAC/RCP 36-1987). It gives guidance on the maximum temperature required for the various grades during transit and while loading and discharging.
These are as per below table:




Conclusion
1. The desired temperature of the cargo should be maintained throughout the loading/discharging operation and during transit.
2. Cargo tanks should be stripped as soon as the liquid is below the level of the heating coils.
3. Clear heating instructions should be given to the master. Any doubts should be addressed sooner rather than later.
4. The cargo plan should include instructions for stripping heated cargo. Sufficient trim and temperature of the cargo should be maintained. Shippers should be aware that heat loss increases as the level of the cargo drops.
5. Heat loss is also accelerated if the cargo tank is in contact with the ballast in the adjoining ballast tank. Ballasting should be deferred until the stripping is completed, if it is safe to do so.
6. Cargo temperature should always be raised gradually.
7. Overheating of the cargo should be avoided.
8. Cargo should not be loaded at a temperature higher than the ship is designed to carry.
9. Cargo temperatures should be checked daily at different levels and the temperature log must be maintained.
10. Over-reliance on remote temperature reading equipment should be avoided and temperature should be compared with other means to check accuracy.


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