involved there will, inevitably, be a greater risk of volumetric losses between the ocean carrying ship and the shore tanks. Where COW is performed, the potential for volumetric losses is greater since the cargo is being formed into a high pressure spray and partially atomised.


The shore installation


When assessing a claim for short delivery of an oil cargo, the ship’s calculation and figures are scrutinised. It is equally important to examine the shore calculations at both the loading and discharge ports. As mentioned earlier, the carriers liability does not extend beyond the ship’s manifold, and claims for apparent oil losses can sometimes be resolved by recalculation of the shore figures. The cargo interests should be asked to provide full details of the shore installation including a plan showing all the storage tanks and the inter connecting pipelines as well as the position of isolating valves. They should be able to verify the maintenance of all their equipment and demonstrate that, for instance, all the isolating valves were tight and properly operating at the time of discharge. They should also be asked to demonstrate that the storage tanks were properly calibrated and show that the calibration was accurate. In some oil installations the accuracy of the tank calibrations may be doubtful particularly if they are of older construction or built on unstable sites. A small measurement inaccuracy may correspond to a substantial change in volume. Temperature measurements should also be closely considered: temperature gradients may exist when oil is stored in a large tank and in certain climatic conditions there may be significant variations in the temperature within the tank. In a cold wind, there may be a horizontal temperature gradient as well as a vertical gradient. In many countries the measurements taken at the time of custody transfer are witnessed by customs officials and if appropriate, the official customs documents should be produced.


Oil contamination claims


Many oil shortage claims arise from the presence of excessive quantities of water found in crude oil cargoes at the discharge port after settling out during the voyage. Oil contamination may occur in petroleum products but a cross contamination between two grades of crude oil would, in most cases, not lead to a cargo claim. Crude oil cargoes are regularly blended before refining and generally for a cargo contamination to arise, a large cross contamination would need to take place. This is not true of all grades of crude as there are a few which have particular properties and which must not be contaminated in any way.


11


Many modern


refineries, designed for the reception of


cargoes carried by sea have desalination facilities in order to protect the distillation columns and refinery equipment from excessive corrosion. Such facilities, however do not always exist. The presence of water in certain crude oil cargoes may also


cause emulsions to form with the hydrocarbons. This in turn may cause ROB volumes to be excessive and possible sludging of land tanks if efficient water draining is not carried out.


It is quite possible that any alleged contamination could have taken place ashore before loading. A prudent owner is therefore recommended to protect his interest by ensuring that a ship’s staff take cargo samples from each tank after loading and at the ships manifold during loading, as a matter of routine, so that hard evidence is at hand to refute claims of this kind. Contamination claims are more likely to occur in the white oil trades where it is common for a number of grades to be carried simultaneously. As many as eight or ten grades are commonly carried simultaneously and on a modern purpose-built product carrier, fitted with deep well pumps and dedicated loading line, it may be possible to carry a different grade in each tank with complete segregation.


Aside from leakage which may occur between cargo pipelines or cargo tanks and which may result in contamination, the most likely cause of a product being off specification is failure to properly prepare the tank or associated pipelines after a previous incompatible grade.


Precautions before loading


Every care should be exercised to ensure that proper tank cleaning procedures are rigorously carried out and that tank coatings are in a suitable condition for the intended cargo. Particular care should be taken to ensure that all traces of the previous cargo are removed in the cleaning process.


When carrying multigrade cargoes, effective segregation is a prime importance. When preparing the loading plan, allowances must also be made for trim and draft restrictions, it is not uncommon for multigrade


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