Corrosion Protection of Carbon Steel Oil Pipelines by Unsaturated Polyester/Clay Composite coating

Abstract

The EIS measurements for coated specimens after polarization show higher values of total impedance |Z|, polarization resistance (Rp) and low capacitance (C) in comparison with the un-coated carbon steel specimen. This indicates the stability of the surface protected film of these coated specimens and their resistance against dissolution.The aim of this paper is to prepare a protective coating on API 5L (carbon steel) alloy which is the widely used materials in oil industry and study its effect on the corrosion behavior of the carbon steel in crude oil environment. Unsaturated polyester (UP) and clay were used to prepare composite consist of 75% of polyester and 25% of clay. The coated specimen was investigated in comparison to uncoated and 100% polyester coated specimens. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were employed on the coated specimens to understand the phases formed on the modified surfaces. The corrosion behavior of the modified surface in comparison with untreated one was investigated by potentiodynamic cyclic polarization in 3.5 M of NaCl and crude oil solution using Solartron made electrochemical interface SI 1287 and Electrochemical Impedance Spectroscopy (EIS) measurements at OCP condition using Solartron make 1255 HF frequency response analyzer (FRA). The results show improvement in the corrosion parameters predicted from the polarization test.