M Salasi - Corrosion Laboratory, Department of Materials Engineering, Tarbiat MtJdares University, Tehran-Iran
T Shahrabi - Corrosion Laboratory, Department of Materials Engineering, Tarbiat MtJdares University, Tehran-Iran
E Roayaei - Researches and Technology Directorate, National Iranian Oil Company, Tehran-Iran

A study and comparison of inhtbition effects of eco-friendly inhibitors of sodium silicate, 1-hydroxyethylidene 1,1 diphosphonic acid (HEDP) and their combination in corrosion control of carbon steel in soft water media have been carried out using electrochemical impedance spectroscopy and Tafel polarization techniques. The experiments carried out under d.i:fIerent concentration ratios of inhibitors and hydrodynamic conditions. Rotating disk: electrode was used to simulate pipeline fluid flow. It was observed that corrosion inhibitors combinations have shown synergistic effect at low concentrations. The inhtbition efficiency and synergistic behaviours of inhibitors have been enhanced as the electrolyte turbulence was increased. It was found that at 20ppm sodium. silicate and Sppm HEDP the co-inhibition efficiencies have increased significantly to more than 90% and the corrosion rate decreased fin below than Impy as the electrode rotational speed increased. Scanning electron microscopy (SEM) and EDAX analysis have also been used for surface studies. Surface studies revealed the surface modification and formation of compact and uniform film in case of inhibitors co-addition.

Corrosion, Silicate, HEDP. Inhibitor