When shipped in bulk, consignments may show loss of weight although there may be no apparent leakage. Experience has shown that many losses discovered at the port of discharge have been due to the fact that although the tank lids and manhole door are tested for tightness, after this has been completed the lids and the doors are again removed to facilitate the cleaning of the tank and, while they may be replaced by experts, there is no longer any certainty that they are oil-tight, in that the original hydro static test is no longer valid.
In such circumstances, by reason of the considerable increase in temperature as the vessel proceeds through tropical waters, the oil level in the expansion trunk may rise to several feet above the tank top and the tank lid, causing the manhole doors to be constantly under pressure, and if these doors are not perfectly oil-tight there will be a loss approximately equal to the expansion.
Other cases of alleged loss may be partly or wholly explained by nonfortuitous causes. For example, oils of the coagulating variety may leave a deposit on the walls of tanks both in ship and ashore. Puddling or sweeping gangs should be used towards the end of discharge to remove semi-solid oil from the ships tanks, and any hard oil remaining after completion of pumping must be collected by manual labor and added to the out-turn, otherwise a serious loss in weight may result. In certain oils and other bulk cargoes a percentage of loss by natural causes is allowed for in the sales contracts and a surveyor unfamiliar with bulk oils, ships calibrations, etc., would be wise to consult an expert or specialist well versed in such commodities.
Loss in bulk oils or fats may arise when shipments are subject to several pumping operations after the shipped weights have been ascertained. At destination the oil or fat may be pumped from the ship's tanks into shore tanks which are not gauged. Consequently the landed weight can be ascertained only when the oil or fat is withdrawn from these tanks.
Variations of moisture content may in some cases be explained by an examination of the vessel's tanks. The tanks of certain vessels which have no heating system are usually moist with water, whereas tanks fitted with a heating system dry up all moisture from the iron. Samples taken from the tanks may not always be truly representative of the moisture content. For example, a tank situated around the base of the ship's stem may be broad at one end, tapering to nothing at the other. It may not be possible to take a sample at the narrower end of the tank, and may also be impossible to take a sample from the center of the tank. This necessitates samples being taken only at the broader end, and such samples may therefore be unreliable. See also IMDG Code & US CFR.
- Commodity Name:
BULK OILS AND FATS