Corrosion inhibition of carbon steel in open recirculating cooling water system of petroleum refinery by a multi-component blend containing zinc (II) diethyldithiocarbamate

Abstract

A multi-component blend of inhibitors containing sodium salt of diethyldithiocarbamate (DEDTC) (50 to 100 ppm), Zn²⁺as ZnSO₄.7H₂O (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 ZnSO₄.7H₂O 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 Fe²⁺-HEDP, Zn²⁺-HEDP, Zn²⁺-DEDTC complexes on the metal surface.