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Graphical abstract Highlights • The heat flow coupling characteristics are revealed in the crude oil heating process. • The tank steam coil heating process has been divided into four stages. • The variations of crude oil temperature and flow field heated by different coils have been analyzed. • The heating effect evaluation indexes in the storage tank heating process have set up. Abstract Considering the factors such as ambient temperature, solar radiation, heating steam pressure and physical properties of oil products, a theoretical model for heating process of large floating roof tank coil is established. The numerical solution technology of the crude oil temperature field and flow field is studied to reveal the coupling characteristics of crude oil heat transfer and flow during the storage tank heating process. Furthermore, the influence law of different coil structures on the temperature field and flow field during the crude oil heating process is discussed. On this basis, the evaluation indexes of the heating effect on the crude oil storage tank is set up, which are combined with heating rate and uniform degree of temperature field. The results show that according to variations of crude oil flow field in the tank, the tank steam coil heating process has been divided into four stages including natural convection formation, small vortex formation, large vortex formation and large vortex development. The coil structures have great influence on the temperature field and the flow field of the crude oil tank. The vertical structure and the stereoscopic structure coils will form a certain thickness low temperature zone at the tank bottom during heating process, but the serpentine structure coil will form a heated dead zone at vertex angle and base corner of the tank where area is relatively small. On this basis, comparing the heating effect of the three kinds of coils, it is found that the heating rate of serpentine structure coil is the fastest and more stable. The uniform degree of temperature field is affected by the oil liquid level. Environmental temperature and other factors have little effect and the best heating effect. [ABSTRACT FROM AUTHOR]