ABSTRACT

High-entropy alloys (HEAs), are multicomponent alloys composed of at least five elements with compositions of 5-35 atomic % for each element. These alloys are being investigated for corrosion protection of natural gas transmission pipelines by studying their behavior under aqueous acidic conditions. Electrochemical and immersion experiments were carried out in 3.5 weight % NaCl solution at pH 4 and 40°C. Oxygen was purged out from the solution by using CO2 as stripping gas. The electrochemical experiments included potentiodynamic and electrochemical impedance spectroscopy tests, used to calculate corrosion rates. Potentiodynamic polarization curves, including cyclic voltammograms, were used to explain active, active-passive, and passive regions of these alloys and susceptibility to localized corrosion. Surface characterization of the corroded samples were performed using scanning electron microscopy (SEM) and x-ray diffraction (XRD). The results of the immersion and electrochemical testing indicate that some of the HEAs have better corrosion performance than commercial alloys UNS N10276, UNS K03014, and UNS 31600.

INTRODUCTION

Research on multicomponent solid solutions in near-equal molar ratio helped to the development of high-entropy alloys (HEAs), a new family of alloys composed of at least five alloying elements with an atomic composition of 5-35 % each. HEAs can also be defined by a configurational entropy of mixing (?Sconf) of at least 1.5R, where R = 8.314 Jmol-1 K-1 is the gas constant. ?Sconf has the most predominant role on the total mixing entropy, and is calculated using Equation 1 for ideal and regular solutions. This equation is a good representation for liquid alloys and many solid alloys in the melting temperature range. Atomic fraction of element i is described as Xi.1-4

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At a greater mixing entropy of an alloy, the formation of single-phase solid solutions is increased and the concentration of intermetallic compounds is minimized.1,3 High composition of several number of elements offer unique physical and metallurgical aspects with superior mechanical, electrochemical, magnetic characteristics.5

Keywords:
flowline corrosion, Subsurface Corrosion, high-entropy alloy, US government, Midstream Oil & Gas, materials and corrosion, well integrity, Pipeline Corrosion, riser corrosion, Publication Division
Subjects:
Pipelines, Flowlines and Risers, Materials and corrosion, Well Integrity, Subsurface corrosion (tubing, casing, completion equipment, conductor)
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2018. NACE International
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