The use of dirty or unwashed tanks could cause the contamination of fresh oil with oxidized and hydrolysis oil. This will increase both the oxidation and hydrolysis contents of the oil.
The risk of sea-water contamination is high in sea voyage. It is common to find that for nearly 50–60% of the voyage duration, the deck of the ship is covered with water, especially if the ship is fully-loaded and in winter. The hatch of the ship’s tanks and other enclosures for butter worth holes etc. should be properly sealed to prevent the seepage of water into the tank.
Unnecessary overheating and prolonged heating of the oil will increase the hydrolysis of the oil leading to increase in the level of free fatty acids. These free fatty acids in turn will act as a catalyst to the hydrolysis reactions, thereby promoting the reaction further, especially if the unnecessary heating is continued.