MINISTRY OF EDUCATION FEDERAL UNIVERSITY OF RIO GRANDE DO SUL School of Engineering Graduate Program in Mining, Metallurgy and Materials PPGE3M MEASURING THE EFFECT OF CATHODIC PROTECTION ON THE PERFORMANCE OF THERMALLY SPRAYED ALUMINIUM COATINGS AT ELEVATED TEMPERATURE Nataly Araujo Cé Thesis submitted for the degree of Doctor of Philosophy in Engineering. Porto Alegre 2017 MINISTRY OF EDUCATION FEDERAL UNIVERSITY OF RIO GRANDE DO SUL School of Engineering Graduate Program in Mining, Metallurgy and Materials PPGE3M MEASURING THE EFFECT OF CATHODIC PROTECTION ON THE PERFORMANCE OF THERMALLY SPRAYED ALUMINIUM COATINGS AT ELEVATED TEMPERATURE NATALY ARAUJO CÉ Metallurgical Engineer Study conducted at the Department of Metallurgy from School of Engineering of UFRGS within the Graduate Program in Mining, Metallurgy and Materials - PPGE3M as part of the requirements for obtaining the title of Doctor of Philosophy in Engineering. Concentration Area: Materials Science and Technology Porto Alegre 2017 II MINISTÉRIO DA EDUCAÇÃO UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL Escola de Engenharia Programa de Pós-Graduação em Minas, Metalurgia e Materiais PPGE3M AVALIAÇÃO DO EFEITO DA PROTEÇÃO CATÓDICA NO DESEMPENHO DO REVESTIMENTO DE ALUMÍNIO PULVERIZADO TERMICAMENTE SUBMETIDO A ALTAS TEMPERATURAS NATALY ARAUJO CÉ Engenheira Metalúrgica Estudo conduzido no Departamento de Metalurgia da Escola de Engenharia da UFRGS através do Programa de Pós-Graduação em Minas, Metalurgia e Materiais - PPGE3M- como parte dos requerimentos para obtenção do título de Doutor em Engenharia. Área de Concentração: Ciência e Tecnologia dos Materiais Porto Alegre 2017 III This thesis was judged adequate for obtaining a Doctor of Philosophy degree, concentration area in Materials Science and Technology and approved in its final form by the supervisor and by the Examination Board of the Graduate Program. Supervisor: Prof. Dr. Afonso Reguly Examination Board: Dr. Marcelo T. Piza Paes, PETROBRAS Dr. Walmar Baptista, PETROBRAS Prof. Dr. Tiago Falcade, DEQUI/UFRGS Prof. Dr. Carlos Perez Bergman Coordinator of PPGE3M IV ACKNOWLEDGEMENTS A special posthumous acknowledgment goes to Prof. Dr. Telmo Roberto Strohaecker. I will be forever grateful for the doors he opened during my academic period and lessons beyond the engineering field. I am also very thankful to the following: Prof. Dr. Afonso Reguly for accepting me as his PhD student, for the academic supervision and contributions to this thesis; Dr. Shiladitya Paul for the industrial supervision during my time spent in TWI and for adding his technical knowledge to this thesis; Dave Harvey for managing the process for me to go to TWI to develop this research and all the support given during my stay in Cambridge; Mike Bennet, Ryan Bellward, Sheila Stevens and Sally Day for the technical support in TWI; My friends from TWI who made my time in Cambridge enjoyable; CNPQ and BG for the PhD scholarship. V SUMMARY LIST OF FIGURES .......................................................................................................... X LIST OF TABLES ........................................................................................................ XV LIST OF EQUATIONS .............................................................................................. XVII LIST OF ABBREVIATIONS AND SYMBOLS ........................................................ XIX ABSTRACT .................................................................................................................. XX RESUMO .................................................................................................................... XXI 1 INTRODUCTION ..................................................................................................1 2 OBJECTIVES ..........................................................................................................3 3 LITERATURE REVIEW ........................................................................................4 3.1 Risers ................................................................................................................ 4 3.2 Cathodic Protection ............................................................................................ 5 3.2.1 Cathodic Protection Design .................................................................... 6 Cathodic Protection Potential ................................................................. 6 Current Densities .................................................................................... 7 Coating Breakdown Factor ..................................................................... 9 3.3 Impressed Current Cathodic Protection System (ICCP) .................................... 9 3.4 Sacrificial Anodes ............................................................................................ 11 3.5 Metallic Coatings ............................................................................................. 13 3.5.1 Thermally Sprayed Coatings (TSC) ..................................................... 13 Thermally Sprayed Aluminium (TSA) ................................................. 14 VI 3.5.2 Sealants ................................................................................................. 17 3.5.3 Adherence ............................................................................................. 18 3.6 Corrosion Behaviour of Aluminium................................................................. 19 3.7 Calcareous Deposit ........................................................................................... 22 3.7.1 Morphology of Calcareous Deposit ...................................................... 26 3.8 General Effect of Temperature ......................................................................... 27 4 EXPERIMENTAL PROCEDURE ........................................................................29 4.1 Experimental .................................................................................................... 29 4.2 Exposure Samples Preparation ......................................................................... 29 4.2.1 Substrate ............................................................................................... 29 4.2.2 Coating ................................................................................................. 29 4.2.3 Sealing .................................................................................................. 30 4.2.4 Holiday ................................................................................................. 31 4.2.5 Specimens Previous to Exposure .......................................................... 31 4.3 Exposure Test Arrangements ........................................................................... 32 4.3.1 Steady Temperature Tests .................................................................... 32 4.3.2 Thermal Gradient Test .......................................................................... 34 4.4 Linear Polarisation Resistance Technique (LPR) ............................................ 38 4.5 Potentiostatic Polarisation ................................................................................ 40 4.6 Post-Exposure Test Analysis ............................................................................ 41 4.6.1 Visual Inspection .................................................................................. 41 4.6.2 Microstructural Characterization .......................................................... 42 4.6.3 Crystalline Phases Identification .......................................................... 42 4.7 Additional Tests ............................................................................................... 44 4.7.1 Adhesion Test ....................................................................................... 44 VII 4.7.2 TSA Corrosion Tests ............................................................................ 45 4.7.3 Carbon Steel Corrosion Tests ............................................................... 46 4.7.4 Local pH Test ....................................................................................... 47 5 RESULTS AND DISCUSSION ............................................................................49 5.1 Steady Temperature Tests ................................................................................ 49 5.1.1 Visual Inspection .................................................................................. 49 5.1.2 Microstructural Characterization .......................................................... 50 Top View .............................................................................................. 50 Cross Section ........................................................................................ 52 5.1.3 Crystalline Phases Identification .......................................................... 60 5.1.4 Corrosion Data Analysis ....................................................................... 61 Potential ................................................................................................ 62 Corrosion Rate ...................................................................................... 66 5.2 Local pH test .................................................................................................... 70 5.2.1 Effect of Temperature on Solubility ..................................................... 73 5.2.2 Calculation of minimum pH ................................................................