Corrosion Resistance Evaluation of Ni-Al YSZ Composite Coatings by An Electrochemical Investigation

Abstract

The composite coating is used to protect carbon steel pipeline from corrosion by Surface modification using thermal spraying technique to enhance the corrosion resistance of carbon steel. In this study the influence of sour hydrocarbon on carbon steel was investigated on samples taken from Alloys with (API 5L) that used for oil transport pipe lines in North Oil Company in Kirkuk fields and specifically from well (No. K-130) which the oil sample was brought as well. The cermets coating (Ni-Al /ZrO2-8Y2O3) were prepared in different mixing ratios of Yttria-Stabilized Zirconia (YSZ) with Ni-Al as a self-bonding. Several mixing ratios of the binder (Ni-Al) were used to prepare the cermets for thermal spraying coating namely 15% and 50%. In order to study the effect of roughness on the binding of the cermets and hence the corrosion behavior of the carbon steel another specimen was mechanically abraded to a surface finish 800 grit by SiC paper and the cermets mixing ratio (50% YSZ+ 50% Ni-Al) .The thermal spraying gun was located in an angle of 90º in front of the carbon steel specimen and the distance between them was 16 cm. The corrosion behavior of the modified surface in comparison with untreated one was investigated by electrochemical techniques. Two electrochemical techniques (DC and AC techniques) were used. The AC technique was potentiodynamic cyclic polarization using Solatron 1287, USA) potentiostat/galvanostate. The EIS measurements for all coated specimens show enhancement in the impedance parameters (total impedance |Z|, polarization resistance (Rp) and the capacitance (C)) comparing to the uncoated one. The cermets thermally sprayed coating show improvement in the corrosion parameters.