A lage quantity of high pour point oil which tends to be solidified at a normal temperature is carried by the oil tankers that are equiped with oil heating system for purpose of keeping in low viscosity of crude oil. As cooling bottom plate by sea water, the crude oil near bottom is solidified in spite of heating up and the solidified layer is likely as insulation against heat flow through bottom. The solidified oil blocks up oil courses bored at bottom structural members and prevents from gathering oil at the final period of pumping up crude oil. Besides, the tank capacity is decreased since solid oil at bottom is just unpumpable.
In this paper, the predicted method on thickness of solidified oil at bottom is proposed in comparison with the measured data on an actual tanker and the numerical analysis on Stefan-problem is carried out by using the enthalpy with delta-sequence function in order to investigate the solidifying process of high pour point oil. Furthermore, the experiment of melting solid paraffin by heating up in the tank in the shape of bottom structure on the scale of one-third is executed in addition to calculate by use of physical properties on Minas crude oil. By the results of measurement, it has been recognized to be practically difficult for melting the solidified oil between frame space without heating coil and some useful consequences for design of oil heating system are obtained.