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.
Saline Water Conversion Corporation (SWCC) is the largest producer of desalinated water in the world. Desalination plants of SWCC have a total production of 6.6 million m3/day. Water is produced through reverse osmosis and thermal desalination technologies. Due to high temperature operation conditions, thermal desalination plants experience corrosion problems at multiple stages. Chemical treatments, controlling the operating conditions and continuous water analysis are always kept under strong monitoring to protect the assets and end up with fresh water product that is surely matches the standardized water quality requirements. Water generally passes through different stages of boiler. Heat Recovery Steam Generator (HRSG) acts as a highly efficient heat exchanger that produces steam from boiler feed water (BFW) to run the turbine for electricity generation and other industrial purposes. The heat exchange occurs when the hot flue gases get out of the gas turbine crossing the network of pipes that carry liquid water. The tube wall acts as a barrier, where it separates liquid water from the flue gases. HRSG has three major sections, economizer, evaporator and superheater [1]. BFW is fed to the economizer tubes to be preheated up to 300°C before passing through the evaporator tubes where liquid water gains enough latent heat to change its phase and converts into steam. This steam is further heated in the superheater tubes, generating superheated steam that would be supplied to a steam turbine for electricity generation and steam collection for industrial water desalination purposes, as shown in Figure 1.
