Electrochemical Testing of Differential Flow Induced Corrosion Using Jet Impingement Rigs

Abstract

Abstract Erosion corrosion, often referred to as impingement, is of concern in many systems and particularly in process equipment containing high velocity fluids. This paper presents electrochemical data obtained with single phase fluids on both large and small scale impingement rigs incorporating submerged jets. These experimental and modelling studies demonstrate the importance of local flow effects which lead to the development of galvanic or differential macro-corrosion cells on the test electrodes. In contrast to measurements made under fully developed turbulent flow conditions, for example as in either channel flow or rotating cylinder rigs, the jet impingement provides a range of local hydrodynamics with simultaneous laminar and turbulent flow, including high shear. The attraction of jet impingement testing is that the corrosion patterns and weight loss obtained on test specimens appear to be typical of those observed in practice. The present studies utilize the electrochemical measurement of corrosion, mass transfer and shear stress across the test electrodes in order to quantify and model the complex hydrodynamics of the jet system. This has not been previously fully characterised especially under high Reynolds numbers. The electrochemical investigations involve polarisation and impedance measurements on segmented and coupled electrodes. The local electrochemical corrosion processes and their contribution to the overall differential flow macro-cell phenomena is outlined. Examples of the use of jet impingement in inhibitor performance trials is presented. Many inhibitors do not provide protection at high shear stress levels and this can increase the erosion corrosion.