Corrosion of pipelines is a common problem in industrial organizations. The pipelines always contain elbow fittings. Generally, corrosion rate in elbows is higher than corrosion rate in straight pipes. Corrosion is governed by the flow structure and the associated mass transfer from the flow to the elbow wall. In this study, the mass transfer of oxygen is solved using numerical technique. The mass transfer coefficient in elbow relative to the mass transfer coefficient of straight pipe is calculated and compared to published experimental data and numerical predictions. The comparison showed that the preset numerical technique could accurately predict the distribution of the mass transfer coefficient in elbows. Corrosion rates are calculated for the case study of a complex pipeline configuration which exists is Assiut Oil Refining Company (ASORC), Egypt. The maximum corrosion rates in different elbows throughout the pipeline are predicted. It is found that the maximum corrosion occurs mainly at two locations. These locations exist at the outlet of the elbow namely at the elbow outer surface and at the elbow inner surface. This result agree with field observations.