In thermal desalination plants, high temperature processes are taking place in order to desalinate seawater. In these harsh environments, corrosion is more likely to happen due to accelerated reaction between the material and the surrounding at elevated temperature conditions. Failures due to Flow Accelerated Corrosion (FAC) were experienced in multiple heat recovery steam generators (HRSG)- economizer tubes made of carbon steel. Likely causes of the FAC of the economizer tubes could be improper corrosion protection of the steam side of the boiler tubes which could be due to poor chemical treatment of the boiler feed water (BFW), water chemistry (pH level & dissolved oxygen), temperature, flow velocity, flow pattern geometry, material selection, etc. Thorough failure analyses were performed to identify the failure mechanisms and root causes of the problem. Results showed carryover of elements with higher potential than iron, which might increase the severity of the corrosion. Also, corrosion product layers were analyzed and causes of these failures were approached.