Bench‐Scale Performance Evaluation of Phosphonate ( <scp>HEDP</scp> ) for Corrosion Inhibition of Carbon Steel in a Power Plant Cooling Water System

ABSTRACT Corrosion in circulating cooling water systems of power plants significantly compromises equipment reliability and energy efficiency. This study investigates the anticorrosive performance of 1‐hydroxyethylidene‐1,1‐diphosphonic acid (HEDP) on carbon steel (St‐20) commonly used in such systems. Bench tests simulating the operating conditions of a power plant were conducted using circulating cooling water and carbon steel coupons. The corrosion rate was assessed at HEDP concentrations of 2.0, 5.0, and 10.0 mg/dm 3 using weight loss methods over 1000 h of exposure. Results demonstrated a concentration‐dependent reduction in corrosion rate, with a maximum inhibition efficiency of 58% observed at 10.0 mg/dm 3 . However, microbial contamination levels after 1000 h of bench testing reached values of 10 3 –10 6 CFU/cm 3 , which requires the use of additional biocidal treatment methods. Statistical analysis confirmed a strong positive correlation between HEDP concentration and inhibition efficiency. Although HEDP effectively reduced corrosion, the occurrence of moderate biological contamination (BC) was observed. This unexpected microbial growth indicates that HEDP alone does not prevent BC. Furthermore, environmental implications related to phosphonate discharge and the potential for eutrophication must be carefully considered when applying HEDP in power plant cooling systems.