Definition
The concentration of dissolved chloride ions in water (mg/L or ppm); the parameter that directly drives stainless-steel corrosion risk in steam humidifiers.
Detailed Explanation
Chloride (Cl⁻) is the most common dissolved salt ion; sources include NaCl deposits, seawater intrusion, geological formations and municipal disinfection by-products. Inland Türkiye typically reads 20–80 mg/L; Aegean/Mediterranean coastal areas 100–400 mg/L. Measurement is by titration (Mohr method) or ion-selective electrode; field kits achieve ±5%.
Why It Matters
Chloride is the only anion that locally breaks down the passive chromium-oxide film on stainless steel; the result is pitting corrosion. The critical threshold is ≈ 50 mg/L for AISI 304, ≈ 150 mg/L for AISI 316L (molybdenum content boosts chloride resistance). Because a steam humidifier's tank, heating-element housing and drain piping are stainless, high chloride directly determines long-term equipment life. Above 200 mg/L, RO pre-treatment plus an alloy upgrade (316L → duplex) is standard practice.
Practical Example
A textile plant in Izmir ran a previous-brand electrode unit on mains water with 180 mg/L chloride; pits 3 mm deep appeared in the tank floor at 18 months and the unit had to be replaced after a leak. NKT proposed RO pre-treatment (≈ 95% chloride retention) plus a Neptronic SKE4 (AISI 304L tank); no pits in 5 years.
Engineering Note
Annual chloride measurement is standard; for sites with seasonal or source variation, switch to 6 months. RO chloride retention is typically 90–98%; CDI/EDI systems push retention above 99%. Drain frequency also controls chloride concentration; low drain plus high chloride is the most aggressive corrosion profile.
NKT Application Link
In NKT water reports, chloride is not assessed alone; it is combined with pH, alkalinity and temperature into corrosion indices (Langelier, Ryznar). For high-chloride sites the standard package is a Neptronic SKE4 (AISI 304L chamber) with RO pre-treatment; in extreme cases SKS4 (stainless tubes) is selected.
