Environmental Degradation (oxidation, corrosion, etc.) - Flow Accelerated Corrosion Investigation and Mitigation in a Heat Recovery Steam Generator

Recently, single-phase flow accelerated corrosion (FAC) has been found extensively in Thailand, especially in single shaft combined cycle power plant heat recovery steam generators, the design of which are compact and cannot be accessed for service at ease. This takes at least one week for repairing and costs at least half a million dollar per one shutdown. In this paper, the investigation of the single-phase FAC in a high pressure economizer of a combined cycle power plant is demonstrated, water chemical parameters such as pH and dissolved oxygen are reviewed, the process simulation of the power plant is performed to capture risk areas for the FAC and a computational fluid dynamics study of the flow is done to understand the flow behavior in the damaged tubes next to an inlet header. Some modifications such as flow distributor installation and tube sleeve installation were done for short-term solutions. Moreover, new economizer headers are designed with low alloy material to mitigate the problem. The installation process of the newly fabricated headers is finally described. The findings in this paper serve as a guideline for FAC risk assessment, FAC investigation and mitigation, and service in compact heat recovery steam generators.