Condensate Polisher Breakthrough and Boiler Carryover Risk

The pattern is diagnostic. Constant differential pressure with rising effluent conductivity rules out resin fouling or bed compaction as the primary cause; a fouled bed would show rising dP. Rising cation conductivity with a modest rise in total conductivity means the mobile ions are anions, most likely chloride and sulfate from anion resin exhaustion or a regenerated-mixed-bed rinse-out, or a condenser tube leak passing cooling water through the polisher. The condenser-leak pathway is the one that must be excluded first because it is the one that can damage the boiler in hours rather than days.

Immediate actions, in order:

1. Sample the condenser cooling water and the polisher inlet for sodium and chloride. A sodium jump at the polisher inlet points to a tube leak; a sodium jump only at the outlet points to resin exhaustion.
2. Trend the steam cation conductivity. At 0.25 micromhos/cm and rising, the boiler is already seeing the contaminant. Most drum-boiler chemistry programs limit cation conductivity to about 0.2–0.3 micromhos/cm; this unit is at the limit.
3. Increase blowdown to the maximum the drum internals and feedwater can tolerate, and verify drum level control is not masking a level swing.
4. If a condenser leak is confirmed, isolate the affected tube bundle or reduce load until the leak is plugged. Do not rely on the polisher to remove a continuous leak.
5. If resin exhaustion is confirmed, take the polisher off line and put the standby bed in service; do not attempt an in-place regeneration while the unit is on line unless the design permits it.

The judgement call the exam is testing: the operator who treats a 0.35 micromhos/cm cation conductivity as a nuisance and keeps running is trading a cheap polisher regeneration for a possible boiler tube failure from under-deposit corrosion. The correct answer is to identify the source before deciding whether to derate.

Steam cation conductivity is a direct measure of the anionic contaminant that has volatilized or mechanically carried over from the drum. At 0.5 micromhos/cm, the steam is carrying roughly five times the normal limit. Two mechanisms can produce that:

• Mechanical carryover - high drum level, foaming, or a sudden load swing throwing droplets into the steam. This shows up as a simultaneous jump in sodium and in total conductivity, and the drum level log usually shows the swing.
• Vaporization of chloride or sulfate - the more insidious case. Chlorides can volatilize at boiler temperature and deposit in the superheater and turbine, where they concentrate and cause stress-corrosion cracking or pitting during shutdown.

The risk if the unit stays on line: the contaminant does not stay in the steam. It deposits in the superheater tubes and on the turbine blades, where it concentrates under deposits and drives under-deposit corrosion and caustic gouging in the boiler, and chloride stress-corrosion cracking in austenitic superheater and turbine components. The damage is cumulative and largely invisible until a tube fails or a turbine inspection finds cracking.

The correct response is to treat 0.5 micromhos/cm as a shutdown-or-derate threshold, not a trend to watch. Reduce load to lower carryover, maximize blowdown, confirm the source, and if the source cannot be corrected within the plant's chemistry action plan, shut down and chemically clean before restart. The exam is testing whether you understand that steam purity is a boiler-integrity limit, not a cosmetic number.