Corrosion Inhibition of Carbon Steel in Open Recirculating Cooling Water System of Petroleum Refinery by Thiourea and Imidazole in Presence of Zinc (II) Sulphate

Pradip Kumar Gogoi,Bedobrat Barhai

doi:10.5539/ijc.v2n2p138

Abstract

The inhibiting action of thiourea and imidazole towards corrosion for carbon steel in open recirculating cooling system (ORCS) of Numaligarh Refinery Limited (NRL) , Golaghat , Assam,India has been studied in presence of Zn2+(as ZnSO4.7H2O) by weight loss and potentiodynamic polarization methods. The values of inhibition efficiency from weight loss method are in good agreement with those obtained from polarization studies. Polarization study indicates that imidazole retards the cathodic corrosion reaction where as thiourea inhibits anodic corrosion reaction in these particular blends of inhibitors. SEM and EDS study confirm the formation of an adsorbed protective film on the carbon steel surface.

Highlights

In open recirculating cooling water system (ORCS) of a petroleum refinery, carbon steel corrosion is a major problem
We report here the effect of addition of thiourea and another electron donor imidazole in presence of Zn2+ as corrosion inhibitor in ORCS of petroleum refinery and evaluation of their optimum ratio to give the most effective blend for inhibition of corrosion, scale formation and microbiological problems
From the weight loss study (Table-3) it is found that in case of the inhibitor blends of SET-I (SET-I includes SET-I-25, SET-I-50,SET -I-100, SET-I-150),the percentage of inhibition efficiency increases on increasing the imidazole concentration from 25ppm to100 ppm at constant Zn2+ and thiourea concentration (Zn2+=50ppm and thiourea =50ppm), which does not increase on increasing the imidazole concentration beyond 100 ppm

Summary

Introduction

In open recirculating cooling water system (ORCS) of a petroleum refinery, carbon steel corrosion is a major problem. The presence of large amount of total dissolved solids, total suspended solids, total hardness, microorganism and dissolved gases, such as, O2 and CO2 in the makeup water are responsible for scaling, fouling, under deposit and microbiological corrosion in the various equipments of cooling water system Due to such corrosion the tubes of heat exchanger, an important part of ORCS get damaged which affect the productivity and profitability. We report here the effect of addition of thiourea and another electron donor imidazole in presence of Zn2+ as corrosion inhibitor in ORCS of petroleum refinery and evaluation of their optimum ratio to give the most effective blend for inhibition of corrosion, scale formation and microbiological problems

Experimental procedures

Weight loss method

Electrochemical studies

Scanning electron micrograph

Results and discussion

Conclusion