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Identifier 000456432
Title Chemical approaches to the inhibition of metallic corrosion in geothermal waters
Alternative Title Χημικές προσεγγίσεις στην παρεμπόδιση της μεταλλικής διάβρωσης σε γεωθερμικά ύδατα
Author Λιακάκη-Σταυροπούλου, Στεφανία
Thesis advisor Δημάδης, Κωνσταντίνος
Reviewer Μήλιος, Κωνσταντίνος
Τρικαλίτης, Παντελής
Σπύρος, Απόστολος
Στούμπος, Κωνσταντίνος
Κουλουμπής, Αντώνιος
Κατσαράκης, Νικόλαος
Abstract Geothermal brines contain a variety of corrosive dissolved species, such as chloride and sulfate anions that can damage various system metallurgies via a number of corrosion processes. Several forms of corrosion can occur, the most common being uniform and pitting corrosion. The combination of low water quality with high-temperature and high-pressure conditions usually accelerate these corrosion processes, with undesirable results to the system’sintegrity. On the other hand, in addition to the above-mentioned conditions, the different corrosion products (eg. Fe oxides) can form films on the metal surface that influence the corrosion rate. Among the several metallurgies that can be used in system components, carbon (mild) steel is one that is widely used in industry, due to its compatibility with other metals present, and, primarily, its comparatively low cost. The electrochemical reactions taking place during carbon steel corrosion promote formation of insoluble compounds of oxidized forms of Fe on the metal surface, such as iron oxides (magnetite, hematite) and hydroxides (lepidocrocite). In this thesis, we furnish comparative results from corrosion inhibition experiments based on two quantifying methods: (a) gravimetric measurements based on the mass loss of each metallic specimen and (b) total iron quantification based on an established photometric methodology (ironphenanthroline complex). In an effort to understand the corrosion behavior of carbon steel and the factors that influence it, a large number of experiments were carried out under several conditions, by studying the effect of certain variables (temperature, water quality, stirring speed, etc.). Finally, the anti-corrosion efficiency of several chemical additives was evaluated. The inhibitors were categorized as phosphonates and non-phosphonate additives. Emphasis was given to phosphonatebased corrosion inhibitors and their potential synergy with metal cations present in the brines. The first step was the identification of the corrosion products under the experimental conditions. Lepidocrocite appear to form most often at ambient temperature and at 60 °C, while hematite and magnetite appear to form at higher temperatures. In addition, if bicarbonate is present, the formation of iron carbonate was observed. This study showed that the formation of different corrosion products can affect the corrosion rate. Overall, the phosphonate inhibitors showed better performance in high salinity water. Furthermore, phosphonates exhibit great inhibition in medium salinity water under high pressurehigh temperature conditions. Regarding the non-phosphonate inhibitors, each chemical additive was affected in a different way by the change in the experimental conditions. Two of the nonphosphonate inhibitors exhibited their highest anti-corrosion efficiency in deionized water, while the performance of the other two was best in medium salinity water. This research concluded that the optimum concentration depends on several conditions, such as the temperature and the water quality, regardless of the nature of the inhibitor. Finally, the results of the total iron determination method showed some variance from those of the mass loss measurements, especially in the presence of phosphonates.
Language English, Greek
Subject Additives
Corrosion
Corrosion products
Geothermal
Inhibitors
Phosphonic acids
Γεωθερμική ενέργεια
Διάβρωση
Παρεμποδιστές
Προϊόντα διάβρωσης
Πρόσθετα
Φωσφονικά οξέα
Issue date 2023-07-04
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/5/f/e/metadata-dlib-1687247374-674694-24526.tkl Bookmark and Share
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