A multi-component blend of inhibitors containing sodium salt of diethyldithiocarbamate (DEDTC) (50 to 100 ppm), Zn(2+) as ZnSO(4) 7H(2)O (50 to 70 ppm) and 1-hydroxy ethyledene-1,1-diphosphonic acid (HEDP) (50 to 150 ppm) was formulated as corrosion and fouling inhibitor for carbon steel in open recirculating cooling water system of Numaligarh Refinery Limited (NRL). Golaghat, Assam and evaluated by weight loss and potentiodynamic polarization methods The results showed that each of NaDEDTC. HEDP and ZnSO(4)center dot 7H(2)O in 1.0.1 4.1 0 ratios can significantly decrease corrosion, scale build-up and microbial growth under the test condition Potentiodynamic polarization curves indicate both cathodic and anodic corrosion inhibition SEM and EDS studies indicate the formation of an adsorbed protective film containing of Fe(2+)-HEDP, Zn(2+)-HEDP. Zn(2+)-DEDTC complexes on the metal surface