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Corrosion
Corrosion effects on electrochemical process and mechanism of heat exchangers
Industrial heat exchanger chiller tubes affected by advanced corrosion .
Corrosion poses an enduring challenge in industries that rely on heat exchangers , impacting their efficiency , safety , and overall lifespan . The complexity of this challenge stems from the intricate world of electrochemical processes , where metals interact with environmental factors , leading to intricate reactions that degrade the materials of heat exchangers . This thorough examination seeks to demystify corrosion , delving into its electrochemical foundations , the factors that influence its progression , and the various mechanisms contributing to the deterioration of materials in heat exchangers . This evaluation aims to provide a clear understanding of corrosion .
By Omari Hussein Sabuni , Mechanical Engineer – Kinyerezi Power Plant
Understanding electrochemical processes Corrosion is an electrochemical reaction involving the oxidation and reduction of metals . The process begins with the metal surface reacting with its environment , leading to the release of electrons and the formation of ions . In the context of heat exchangers , these electrochemical reactions are often accelerated due to the unique conditions within these systems . The main electrochemical processes contributing to corrosion include : 1 . Anodic reaction ( oxidation ): At the anode , metal atoms lose electrons and enter the solution as ions . For iron-based alloys , common anodic reactions include :
Fe → Fe 2 + + 2e -
2 . Cathodic reaction ( reduction ): At the cathode , reduction reactions occur , often involving oxygen or other oxidizing agents :
O 2
+ 4e - + 2H 2 O → 4OH -
The reduction of protons ( acidic conditions ) or other oxidizing species can also occur .
3 . Overall corrosion reaction : Combining the anodic and cathodic reactions , the overall corrosion reaction for iron-based alloys in the presence of oxygen is :
Fe + 1 2 O 2 + H 2 O → Fe2 + + 2OH
4 . Galvanic corrosion : In multi-metal heat exchangers , galvanic corrosion can occur due to the potential difference between dissimilar metals . This leads to accelerated corrosion at the less noble ( more anodic ) metal .
5 . Localized corrosion mechanisms : Pitting corrosion and crevice corrosion are common localized corrosion mechanisms that can occur in heat exchangers , leading to localized damage .
6 . Inhibition and passivation : Inhibitors can be used to slow down corrosion by adsorbing onto the metal surface and hindering the electrochemical reactions . Passivation involves the formation of a protective oxide layer on the metal surface .
Acceleration of electrochemical reactions in heat exchangers The “ Acceleration of Electrochemical Reactions in Heat Exchangers ” refers to the phenomenon where the electrochemical corrosion processes that lead to the deterioration of metals are expedited due to specific conditions present in heat exchanger environments . Corrosion is essentially an electrochemical reaction involving the oxidation and reduction of metals , and heat exchangers , by their nature and operational characteristics , can contribute to the acceleration of these reactions . Let ’ s explore the key factors contributing to the acceleration of electrochemical reactions in heat exchangers :
42 Heat Exchanger World April 2024 www . heat-exchanger-world . com