Heat exchanger failure analysis in the simulated marine environment: Prediction of the fouling removal temperature

Abstract

The present work aims to analyze the failure resulting from temperature change and its influence on the corrosion and fouling resistance of the cupronickel Cu-Ni 90/10 in simulated marine solution to predict the removal fouling temperature in the desalination heat exchanger and how affects fouling composition and morphology. The Cu-Ni 90/10 electrochemical behavior has been studied through: polarization tests, following the evolution of open circuit potential (OCP) and electrochemical impedance spectra (EIS) with immersion time under thermal and hydrodynamic conditions close to those prevailing in the heat exchanger of desalination industry. Electrochemical measurements show that the corrosion rate of Cu-Ni 90/10 alloy change with temperature, due to a competition between the formation of stable complexes on the metal surface and the dissolution of salts to generate aggressive ions in the corrosion medium. 60 °C ensures an equilibrium between the complexation reactions that promotes fouling stability, and fouling mitigation that leads to metal oxidation. In contrast, at high temperatures (80 °C), the dissolution of salts predominates over the complexation process. It can be deduced that 60 °C is a critical point for heat exchanger that promotes the formation of thin layer with low thermal fouling resistance that protects the installation against damage, maintain a good heat transfer and extend the cleaning scheduling of the machine. Surface analyses were performed by means Raman spectroscopy, SEM and EDS quantification, reveals the reinforcement of fouling by iron compound which make deposit more resistant at 60 °C.