By: Barry Dooley
Evaluation of High Pressure (HP) Evaporator Tube Deposits is important for several reasons:
- Determining if flow-accelerated corrosion (FAC) might be occurring in the lower pressure circuits.
- Regular evaluations can provide information on the internal deposit deposition rate, which is information necessary to help prevent under-deposit corrosion damage mechanisms.
- Provides information necessary to develop an optimized cycle chemistry for HRSGs.
- Can help determine if the HRSG needs to be chemically cleaned.
The leading heat recovery steam generator (HRSG) tube failure mechanisms are FAC, thermal and corrosion fatigue, and under-deposit corrosion (UDC) and pitting. The corrosion products released by the FAC mechanism are transported from the affected area (typically the feedwater or lower pressure systems) and can eventually reach the HP evaporator tubing, so understanding the deposition in the HP evaporator is an important step in determining if FAC might be occurring. Deposition on the inside of HP evaporator tubing is also a precursor to any of the under-deposit corrosion HRSG tube failure mechanisms.