Cation Conductivity (CC) is one of the most important detectors of contaminant ingress into the HRSG
steam cycle and is an EPRI “Core” Parameter, alarmed in the Control Room.
- It’s also mis-named and often misunderstood. A better name is “Conductivity after Cation
Exchange”.
- Cations are removed via cation exchange.
- Typical steam cation conductivity limits are 0.2 uS/CM (for plants using aqueous ammonia).
- Key Point: CC primarily measures anion levels in the sample stream.
- Main Contributors to cation conductivity are Total Organic Carbon (TOC), Sulfate, and Chloride.
TOC
- Not normally monitored or sampled, high CC troubleshooting only
- Can be detected by grab sample. Swan also makes an online TOC analyzer.
- Causes drum foaming and high mechanical carryover.
- May affect turbine corrosion depending on species.
- MThermally decomposes into organic acids
- Limits are < 300 ppb (demin make up) and < 100 ppb in the steam.
Chloride
- Corrosion fatigue, stress corrosion cracking, and pitting in LP turbines
- Corrosion, hydrogen damage, and pitting in HRSG circuits during shutdown
- Limits < 3 ppb (demin make up) and < 2 ppb in the steam
- Can only be detected by ion chromatograph.
Sulfate
- Sodium sulfate in combination with chloride contributes to turbine corrosion.
- Acid sulfate can cause boiler and turbine corrosion.
- Sulfate can deposit in reheaters (and low pressure superheaters) and subsequently lead to pitting
during non-protected shutdown periods.
- Limits < 3 ppb (demin make up) and < 2 ppb in the steam.
- Can only be detected by ion chromatograph.
Combined Cycle Solutions, LLC offers HRSG boiler water chemistry consulting solutions based on EPRI
guidelines. My services include complete program building, training, and troubleshooting.
