Testing should, in any case, be carried out by personnel who have not been working in or near the tanks for at least one hour.


When cargo with a high melting point has been carried, tanks should be washed with hot water. If possible, steam should be used to ensure the residues are effectively melted and cleared, and the cleaning process must also include the tank lines, tank lids and vent lines, including pressure vacuum valves and risers. Examples of cargoes with high melting points include phenol and waxes.


Cargo pumps, usually of the hydraulic deep well type, should be dismantled and inspected, as recommended by the manufacturer. The pumps should be purged in order to test the seals which separate the cargo and the hydraulic oil from the void space in the pump. This procedure should always be followed after tank cleaning, before loading and discharging and after repairs. The results should always be properly recorded in the ship’s log book or other formal records. Where defects to the seals are suspected, cargo should not be handled until corrective measures have been taken. Due consideration must be paid to the trim of the ship when cleaning pumps, in order to ensure that any contamination product is properly drained away. Portable pumps should be tested before being lowered into the cargo tank.


Before loading, if heating coils are not to be used, they should be thoroughly purged and blanked both at the supply and the return ends. Even though coils may have been in use for some time, they should be pressure tested before loading, in order to avoid the possibility of contamination through leaks which might have developed. Pumps not required for cargo handling should always be isolated.


Special attention should be paid to the cleanliness of vent lines, as they may contain residues of previous cargoes, both in a liquid and a solidified state. Vent lines, when not cleaned after discharge, may drain into a newly loaded tank when the vessel changes trim or when encountering heavy weather. Solidified cargo residues in a vent line may melt, due to the heat emitted from a heated cargo and the melted product may drain back into the tank, causing contamination. The practice of steaming ventlines after the carriage of heated cargoes is to be recommended as blocked lines may result in over-pressuring of cargo tanks.


Drain cocks which are fitted at the lowest parts of deck and manifold lines, as well as plugs at the bottom of cargo valves, should be opened and rinsed in order to remove any trapped cargo residues. These drain cocks


30


Tanker Matters is a compilation of Carefully to Carry articles. Bulk oil cargoes, Samples and sampling and Liquid natural oils were first produced for the Carefully to Carry manual and were revised in September 2006. Biofuels was produced in July 2010 and written by Richard Minton of Minton Treharne & Davies. All articles are available on the UK Club website ukpandi.com


may contain sufficient liquid to result in serious contamination. When clearing deck and drop lines it is important to ensure that the dead ends of these lines and drop lines are not overlooked. They should be opened and thoroughly cleaned.


Mild steel tanks are still sometimes used for the carriage of natural oils and fats but their use is in decline as cargo charterers more frequently stipulate the use of stainless steel or coated tanks. When used, mild steel tanks should be free from rust and scale, since remnants of previous cargoes are likely to be trapped and transferred into subsequently loaded cargoes. Where sensitive cargoes have been carried in mild steel tanks, contamination has been known to occur from the residues of hydrocarbon (petroleum products) cargoes.


The importance of proper tank cleaning procedures and the correct preparation of tanks and all related equipment prior to loading cannot be over-emphasized. Masters may wish to consider appointing an independent surveyor to verify the condition of the tank coating, heating coils and hatch openings after the tank preparations are completed.


On completion of loading, an ullage survey by an independent surveyor may be appropriate, whereafter valves and hatches should be sealed. This process can be repeated at the discharge port. The practice of taking onboard samples at all stages of the loading and discharging operation which is referred to earlier, is also to be highly recommended.


Should contamination occur at some stage in the course of transit, it may be possible, by analysis of such samples, to identify the source of contamination. By ensuring that the cargo is carried to the highest standards, the product should be well protected.


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