Module 1.1 — The core measurements every chemistry decision in the plant is built on: pH, conductivity, dissolved oxygen, TDS, and hardness.
Sample points (SP-1, SP-2, SP-3) sit at the deaerator outlet, economizer inlet, and steam drum — each checking a different failure mode. Losing sight of any one point is how corrosion or carryover goes undetected until it's expensive.
Every water/steam chemistry program in a fossil plant comes down to controlling five interrelated measurements: pH, conductivity, dissolved oxygen, total dissolved solids (TDS), and hardness. None of them tell you the whole story alone — they're diagnostic together, the way engine oil pressure and temperature only mean something read side by side.
pH measures how acidic or basic the water is, on a 0–14 scale, 7 being neutral. In feedwater and boiler water systems, you're almost always running alkaline — typically 8.8 to 9.6 in the feedwater train, higher in the boiler drum depending on your treatment program. That's not arbitrary: carbon steel corrodes fastest right around neutral pH and slows dramatically as you push alkaline, because the metal forms a protective magnetite (Fe₃O₄) layer that's stable in that range.
Conductivity measures how well water conducts electrical current, which scales with the concentration of dissolved ionic material in it — salts, acids, bases. Pure water conducts almost nothing. The moment conductivity climbs, something is getting into the system that shouldn't be: a condenser tube leak letting cooling water in, contamination from makeup water, or a chemical feed problem.
Cation conductivity (conductivity measured after the sample passes through a cation exchange resin, stripping out the ammonia and amines used for pH control) is the more sensitive version — it strips out your intentional chemistry and shows you only the unwanted stuff. A rising cation conductivity trend is often the earliest indicator of a condenser leak, sometimes hours before other alarms trip.
Oxygen dissolved in feedwater is aggressive toward carbon steel, driving pitting corrosion in the economizer, feedwater heaters, and boiler tubes. The deaerator's entire job is mechanical removal of dissolved gases (primarily O₂ and CO₂) by heating the water near saturation temperature, where gas solubility drops sharply. Chemical oxygen scavengers pick up what mechanical deaeration leaves behind — typically getting you from a few hundred ppb down into single-digit ppb territory.
Total dissolved solids is the aggregate measure of everything dissolved in the water — minerals, salts, organics. In the boiler, TDS that isn't removed via blowdown concentrates as the water boils off as steam, eventually depositing on tube surfaces or carrying over into steam. Hardness specifically refers to calcium and magnesium content — the minerals responsible for scale. Makeup water treatment (softening, demineralization, or reverse osmosis depending on the plant) exists primarily to strip hardness and TDS out before that water ever reaches the boiler.