Characterization and Corrosion Behavior of Electrodeposited Binary and Ternary Nickel Alloys in a CO2-Saturated NaCl Solution (original) (raw)

Abstract

ABSTRACT Binary (Ni-Cr and Ni-Zn), and ternary (Ni-Co-Cr) Ni-based alloy coatings were electrodeposited on carbon steel 1018 (UNS G10180). These metallic coatings are being investigated for use in providing corrosion protection of natural gas transmission pipelines by studying their behavior under aqueous acidic conditions. The corrosion resistance of the metallic coatings was investigated using immersion and electrochemical methods in a CO2-saturated solution of 3.5 wt.% NaCl at 40°C. Two types of electrochemical experiments were carried out: potentiodynamic and potentiostatic. The surface characterization of the investigated metallic coatings was performed before and after corrosion experiments using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF). The effect of the coating composition on the corrosion performance of electrodeposited alloys in acidic aqueous conditions is discussed. INTRODUCTION Corrosion of mild steel in aqueous carbon dioxide (CO2)-containing solutions is associated with internal corrosion of oil and gas pipelines used for production and transportation. Although other factors such as temperature, presence of hydrogen sulphide (H2S), flow rates, material composition and exogenous ions also influence internal corrosion, the chemistry of H2O and CO2 is shown.1,2 Carbonic acid (H2CO3) is formed by the reaction of dissolved CO2 in water (Reaction [1]). Furthermore, H2CO3 dissociates according to reactions (2) and (3).(Equation-1)(Equation-2)(Equation-3)Metal dissolution proceeds with hydrogen evolution from reduction of dissociated hydrogen ions (H+) (Reaction [4]), H2O (Reaction [5]), H2CO3 (Reaction [6]), and bicarbonate ions (HCO3−) (Reaction [7]). The corrosion rate of the metal can depend upon mass transfer, pH, partial pressure of CO2, and temperature. On the other hand, corrosion of the metal can be limited by the reduction path from reactions (4) through (7).3,4(Equation-4)(Equation-5)(Equation-6)Corrosion control measures have been extensively used to protect the exterior surface of oil and gas pipelines to reduce the detrimental effects of environmental elements including type of soil, water, degree of aeration, pH, redox potential, resistivity, microbiological activity and soluble ionic species (salts and organics).5 Some of the most commonly used corrosion protection strategies involve protective coatings, cathodic protection, and inhibitors. Even though the internal composition of the environment is water-free by itself and non-corrosive, contaminants such as water and chlorides are accidentally introduced into the system creating a clear path to corrosion, and consequently affect pipeline integrity.

Joe Tylczak hasn't uploaded this document.

Let Joe know you want this document to be uploaded.

Ask for this document to be uploaded.