Heavy fuel oil (Mazut) has high viscosity that doesn't flow at the ambient temperature and should be warmed up to flow. One of the fuel warming up solutions is the STEAM TRACING system. In this method, a STEAM pipe with 3/4 or 1 inch diameter is installed in parallel with Mazut pipe connected with specific bounds. The condensate is collected using STEAM traps installed in a proper distances and returns to the condensate tank. In this paper, the heat transfer process is simulated numerically in the STEAM TRACING system installed on the Masut pile lines using Ansys-Fluent commercial software. Mazut pipes are simulated in different conditions including the pipes without insulation, with insulation and with STEAM TRACING & insulation, and then numerical results are compared to each other. In addition, the effects of different STEAM temperature on the Mazut viscosity are investigated. It is concluded that STEAM TRACING system is not needed essentially for the short length pipes. Besides, using the STEAM TRACING with the insulation will cause constant fuel oil temperature and this will be critical in cold ambient temperature. Moreover, increasing the STEAM temperature has little effect on the STEAM TRACING system efficiency so that the higher STEAM temperature just leads to higher heat loss and reduces the overall efficiency of the system.