T H E U N I V E R S I T Y O F T U L S A THE GRADUATE SCHOOL EROSION-CORROSION MODELING FOR SCALE FORMING CONDITIONS IN CO 2 ENVIRONMENT

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1 T H E U N I V E R S I T Y O F T U L S A THE GRADUATE SCHOOL EROSION-CORROSION MODELING FOR SCALE FORMING CONDITIONS IN CO 2 ENVIRONMENT by Gusai Hassan Al-Aithan A thesis submitted in partial fulfillment of the requirements for the degree of Master in the Discipline of Mechanical Engineering The Graduate School The University of Tulsa 2013 i

2 T H E U N I V E R S I T Y O F T U L S A THE GRADUATE SCHOOL EROSION-CORROSION MODELING FOR SCALE FORMING CONDITIONS IN CO 2 ENVIRONMENT by Gusai Hassan Al-Aithan A THESIS APPROVED FOR THE DISCIPLINE OF MECHANICAL ENGINEERING By Thesis Committee Siamack A. Shirazi, Chair John R. Shadley Edmund F. Rybicki Kenneth P. Roberts Michael W. Keller ii

3 COPYRIGHT STATEMENT Copyright 2013 by Gusai H. Al-Aithan All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the author. iii

4 ABSTRACT Gusai Al-Aithan (Master in Mechanical Engineering) Erosion-Corrosion Modeling For Scale Forming Conditions in CO 2 Environment Directed by Dr. Siamack A. Shirazi 156 pp., Chapter Six: Summary, Conclusions, and Future Work (421 words) The combined effect of sand erosion and CO 2 corrosion on carbon steel tubing and piping has greatly influenced the design and operation of oil and gas production facilities. A mechanistic model of the competition between the growth of FeCO 3 scale through CO 2 corrosion and removal of scale by sand erosion has been implemented in a computer program for predicting erosion-corrosion rates under different environmental conditions. Models from the literature for quantifying iron carbonate scale precipitation and growth rates, and diffusion rates of cathodic reactants and corrosion product species through iron carbonate scale have been integrated into an erosion-corrosion model. The erosion resistance of FeCO 3 scale erosion to solid particle erosion (erosivity) has been characterized under various environmental conditions in submerged, direct impingement flow loop experiments. Two scales were formed under different environmental conditions (temperatures of 190 o F and 160 o F) were used to investigate the scale erosion resistance for each of them and linked to the mild steel erosion rate to iv

5 generalize the use of the iron carbonate scale erosion resistance. Results show that the erosivity of the iron carbonate scale formed at 190 and 150 o F (ph 6.4) were about 5 and 15 times higher than bare low carbon steel, respectively. Further investigations of FeCO 3 deposition rates were conducted to understand scale deposition mechanisms for different temperatures. Based on these experiments, the scale deposition rate has been characterized and used in the model to evaluate scale thickness as a function of temperature. Also limited investigation for the scale porosity was made to determine the actual scale deposition rate. Erosion-corrosion experiments were conducted to evaluate the steady state corrosion rate of the erosion-corrosion and also to examine the scale condition at the end of the tests for different sand concentrations. Corrosion rates were monitored by the Linear Polarization Resistance (LPR) technique. Erosion-corrosion experiments were conducted for 190 and 150 o F temperatures and a range of sand concentrations. Erosioncorrosion experiments revealed a relation between erosivity, scale deposition rate, and the corrosion component of erosion-corrosion. Both the model and experiments show the corrosion part of erosion-corrosion experiments was found to be linearly proportional to erosivity at the same test conditions. The mechanistic model for predicting erosion-corrosion was modified with the new prediction correlation of the scale deposition rate and scale erosion rate based on the experimental data and the E/CRC computer program SPPS-CO 2 was updated with the new enhancement. Comparisons between experimental results to the predicted values from the erosion-corrosion model for various testing conditions showed very good prediction provided by the model. v

6 ACKNOWLEDGEMENTS I would like to extend my sincere gratitude to the advising committee and to the Erosion/Corrosion Research Center (E/CRC) staff for help they provided during this research. The mechanical engineering professors at The University of Tulsa are acknowledged for the great knowledge and experience that they provided. The unlimited and outstanding guidance, support and motivation from Dr. S. Shirazi, Dr. J. Shadley, Dr. E. Rybicki, Dr. K. Roberts and Dr. M. Keller are highly appreciated. I extend special thanks to Dr. Johan Shadley for the effort and time he spent to overcome research difficulties and for the continuous encouragement and inspiration. I would like also to thank Mr. Ed Bowers, the E/CRC Senior Technician, for his help in designing and maintain research equipment. I would like to thank my employer (Saudi Aramco) and my direct management for extending their support and trust and for giving me the opportunity to enhance my knowledge and skills. I would like to extend appreciation to the individuals who helped me conduct some experiments: Faisal Al-Mutahar and Indrian Pratama, Dr. Cornell and Paige Johnson for SEM and X-RD analysis. I am grateful for my parents continuous prayers and support: I hoop they are proud of me. Finally I would like to thank my small family for making sacrifices to allow me to be away at work. vi

7 TABLE OF CONTENTS Page COPYRIGHT... iii ABSTRACT... iv ACKNOWLEDGEMENTS... vi TABLE OF CONTENTS... vii LIST OF TABLES... x LIST OF FIGURES... xiv CHAPTER 1: INTRODUCTION... 1 CHAPTER 2: BACKGROUND AND LITERATURE REVIEW Literature Review CO2 Corrosion and SPPS CO Sand Particle Erosion Scale Deposition Rate Scale Porosity CHAPTER 3: EXPERIMENTAL FACILITY AND PROCEDURES Introduction Experimental Setup Experimental Procedure Scale formation Experiments Scale Erosion Experiment Erosion-Corrosion Experiments Specimen Surface Preparation Linear Polarization Resistance (LPR) Scanning Electron Microscope (SEM) and Focused Ion Beam (FIB) D Profilometer CHAPTER 4: EXPERIMENTAL RESULTS AND DISCUSSION Scale Formation Experiments Scale Formation at 190 o F vii

8 4.1.2 Scale Formation at 150 o F Scale Thickness Characterization Erosion Resistance Characterization Erosion Resistance Characterization of 190 o F Erosion Resistance Characterization of 150 o F Steel Erosion Comparison with SSPS Scale SEM Examination Post Erosion Test Erosion-Corrosion Experiments Erosion-Corrosion Experiments at 190 o F Erosion-Corrosion Experiments at 150 o F Erosion-Corrosion of 150 o F at Low Sand Concentrations Scale Examination Post Erosion-Corrosion Tests Scale Porosity Measurement Porosity Calculation Scanning Electron Microscopy (SEM) Slice and View Sand Micrograph Wall Shear Stress Geometry and Physical Conditions CFD Simulation Results and Literature Correlation CHAPTER 5: MODEL VALIDATION AND ENHANCEMENT Initial Model Initial Deposition Rate Scale Deposition Rate Investigation First Approach: Scale Deposition Rate measurement Second Approach: Scale deposition rate calculation in E-C Model Modifications Scale Deposition Rate Prediction Diffusion Boundary Layer Thickness, hbl Scale Erosion Rate Calculations Final Model Predictions CHAPTER 6: SUMMARY, CONCLUSIONS, AND FUTURE WORK Summary Conclusions Scale Formation Process Scale Erosion Resistance Characterization Scale Porosity Scale Deposition Rate Erosion-Corrosion Experiments Future Work Erosion-Corrosion Experiments: Scale characterization viii

9 BIBLIOGRAPHY APPENDIX A: DETAILS OF EROSION EXPERIMENTS APPENDIX B: SCALE EROSION EXPERIMENTS ix

10 LIST OF TABLES Page 2-1 Arrhenius s Equation Constants Derived for Scale Deposition Rate Chemical Composition of Steel (Weight %) Testing Parameters for Scale Formation Experiments GAMRY Settings for LPR Measurements Scale Formation Testing Parameters Scale Thicknesses at 150 and 190 o F Temperatures Sample Scale Erosion Resistance Characterization Experiment at 190 o F Sample of Scale Erosion Resistance Characterization Experiment at 150 o F Summary of erosion-corrosion experiments information at 190 o F, ph 6.4, P- CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations Summary of Erosion-Corrosion Experiments Information at 150 o F, ph 6.24, P CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations Scale Porosity Obtained from Different Models CFD Simulation Inlet And Outlet Conditions Property of the Two Phases, Water and Sand Initial E-C Model Prediction Vs. Experimental Data (190 o F, 6.4 ph, 10 ft/s, 2 wt% NaCl, 5 ppm Fe++) Average Scale Deposition Rate calculation Arrhenius s Equation Constants Derived for Scale Deposition Rate x

11 A-1 Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 1.6 wt% Sand Concentration A-2 Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.1 wt% Sand Concentration 126 A-3 Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.4 wt% Sand Concentration 127 A-4 Erosion-Corrosion Experiments at (T=190 of, ph 6.4, 10 ft/s) with 0.2 wt% Sand Concentration 128 A-5 Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.6 wt% Sand Concentration 129 A-6 Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.7 wt% Sand Concentration 130 A-7 Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.8 wt% Sand Concentration 131 A-8 Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.1 wt% Sand Concentration 132 A-9 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 0.1 wt% Sand Concentration..133 A-10 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 0.6 wt% Sand Concentration A-11 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 0.5 wt% Sand Concentration.135 A-12 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 0.3 wt% Sand Concentration A-13 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 1.0 wt% Sand Concentration A-14 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 1.5 wt% Sand Concentration A-15 Erosion-Corrosion Experiments at (T=150 of, ph 6.24, 10 ft/s) with 0.4 wt% Sand Concentration..139 B-1 Steel Erosion Resistance Characterization Experiment at 0.65 wt% Sand Concentration xi

12 B-2: Steel Erosion Resistance Characterization Experiment at 0.64 wt% Sand Concentration B-3 Steel Erosion Resistance Characterization Experiment at 0.92 wt% Sand Concentration B-4 Steel Erosion Resistance Characterization Experiment at 0.8 wt% Sand Concentration B-5 Steel Erosion Resistance Characterization Experiment at 0.6 wt% Sand Concentration 144 B-6 Steel Erosion Resistance Characterization Experiment at 2.0 wt% Sand Concentration B-7 Scale Erosion Resistance Characterization Experiment at 190 o F and 0.3 wt% Sand Concentrations B-8 Scale Erosion Resistance Characterization Experiment at 190 o F and 0.6 wt% Sand Concentrations..147 B-9 Scale Erosion Resistance Characterization Experiment at 190 o F and 1.15 wt% Sand Concentrations 148 B-10 Scale Erosion Resistance Characterization Experiment at 190 o F and 0.95 wt% Sand Concentrations B-11 Scale Erosion Resistance Characterization Experiment at 150 o F and 0.86 wt %Sand Concentrations B-12 Scale Erosion Resistance Characterization Experiment at 190 o F and 1.0 wt %Sand Concentrations 151 B-13 Scale Erosion Resistance Characterization Experiment at 150 o F and 1.0 wt %Sand Concentrations.152 B-14 Scale Erosion Resistance Characterization Experiment at 190 o F and 1.0 wt %Sand Concentrations 153 B-15 Scale Erosion Resistance Characterization Experiment at 190 o F and 0.5 wt %Sand Concentrations B-16 Scale Erosion Resistance Characterization Experiment at 150 o F and 0.85 wt %Sand Concentrations xii

13 B-17 Scale Erosion Resistance Characterization Experiment at 150 o F and 0.5 wt %Sand Concentrations. 156 B-18 Scale Erosion Resistance Characterization Experiment at 150 o F and 1.6 wt %Sand Concentrations.157 xiii

14 LIST OF FIGURES Page 1-1 E-C Model Validation And Enhancement Approach Porosity as a Function Of Temperature at ph 5.8 and Pco2=2 bar. Porosity Calculated from Corrosion Rates Measured in Loop Experiments Porosity as function of ph at 80 C and Pco2=2 bar. Porosity Calculated from Corrosion Rates Measured In Loop Experiments Venturi Effects before Injection Nozzle Schematic of Experimental Loop Photograph of the Flow Loop Schematic and Actual Set up of the Mounting Arrangement for Specimen Schematic of Working-Reference electrode Sand Feeder Used in Erosion Experiments Specimen after Surface Preparation SEM/FIB Chamber D Profilometer Testing specimen before and after scale formation LPR Measurements for the Scale Forming Experiments at 190 o F, 10 ft/s flow Velocity, 6.4 ph, 2 wt% NaCl, 1900 ppm NaHCO Repeatability of LPR Measurements for the Scale Forming Experiments at 190 o F, 10 ft/s flow velocity, 6.4 ph, 2 wt% NaCl, 1900 ppm NaHCO LPR Measurements for the Scale Forming Experiments at 150 o F, 10 ft/s flow velocity, 6.2 ph, 2 wt% NaCl, 1900 ppm NaHCO xiv

15 4-5 Repeatability of LPR Measurements for the Scale Forming Experiments at 150 o F, 10 ft/s flow velocity, 6.24 ph, 2 wt% NaCl, 1900ppm NaHCO SEM Images of Scale Thickness after 48 hours of testing (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) with CR=15 mpy near test end SEM Images of Scale Thickness after 10 hours of testing (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) with CR=74 mpy Near Test End SEM Images of Scale Thickness after 48 hours of testing (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) with CR=14 mpy Near the End of the Test SEM Pictures of Scale Thickness after 20 hours of test (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) with CR=100 mpy at the End Scale Erosion Rate vs. Sand Concentration (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) Scale Erosion Ratio (kg/kg) vs. sand concentration (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) Scale Erosion Rate vs Sand Concentration (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) Scale Erosion Ratio vs Sand Concentration for (150 o F., 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) Scale Erosion Rates and Bare G10180 Steel Erosion Rate Comparison Of Steel Erosion Rate Experimental Data with SPPS Erosion Prediction Software by E/CRC. (Single-Phase Water, Velocity of 10 ft/s, 150 Micron Semi-Rounded Sand and 2-D Direct Impingement Configuration) SEM Analysis for Post Scale Erosion Experiment and EDXS Analysis Erosion-Corrosion Experiment (T=190 o F, ph 6.4, 10 ft/s) with 1.6 wt% Sand Concentration Erosion-Corrosion Test (190 o F, ph 6.4, P CO2 20 psig, 10 ft/s velocity, 15 g of sand, Sand Concentration =0.1) Specimen Photograph after Erosion-Corrosion Test Showing the Scale Intact...65 xv

16 4-20 Erosion-Corrosion Test (190 o F, ph 6.4, P CO2 20 psig, 10 ft/s velocity, Sand Concentration =0.25 wt%) Specimen Photograph after Erosion-Corrosion Test Showing the Scale Intact Summary of Erosion-Corrosion 190 o F, ph 6.4, P CO2 20 psig, 10 ft/s Velocity and Range of Sand Concentrations Erosion-Corrosion 150 o F, ph 6.24, P CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations (a) LPR for overall test, (b) LPR & Sand concentrations Specimen Photograph after Erosion-Corrosion Test Showing the Majority of Scale Removed Erosion-Corrosion 150 o F, ph 6.24, P CO2 20 psig, 10 ft/s Velocity and Sand Concentrations of 0.7 wt% (a) LPR for overall test, (b) LPR & Sand Concentration Measurement for Erosion-Corrosion Segment of Test Specimen Picture after Erosion-Corrosion Test Showing the Majority of Scale Removed Erosion-Corrosion 150 o F, ph 6.24, P CO2 20 psig, 10 ft/s Velocity and Sand Concentrations of 1.2 wt% Specimen Picture After Erosion-Corrosion Test Showing the Majority of Scale Removed Summary of Erosion-Corrosion Tests at 150 o F, ph 6.24, P CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations Erosion-Corrosion of 150 o F, 10 ft/s, ph, 6.24, P CO2 20 psig, 2 gpm at Low Sand concentrations a) LPR for overall test, (b) LPR & Sand Concentration Measurement for Erosion-Corrosion Segment of the Test, (C) Specimen Photograph at the End of the Test Erosion-Corrosion Experiment at 150 o F, PH, 6.2, P CO2 20 psig, 2 gpm, 10 ft/s by Injecting Sand at the Beginning of Test Specimen Photograph after Erosion-Corrosion Experiment and SEM Micrograph XRD, SEM, and Copper Sulfate Tests on the Specimen after Erosion-Corrosion Experiments xvi

17 4-34 SEM Micrograph of 190 o F Scale Showing a Very Compact Surface SEM Micrograph of 150 o F Scale Showing Scattered Porosity at the Surface Slice and View Technology Process Slice and View Analysis for (30 X 5 microns) Scale Formed at 150 o F, 10 ft/s, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO Slice and View Analysis for Scale Formed at 190 of, 10 ft/s, 6.4 ph, 2 wt% NaCl, and 1900 ppm NaHCO Oklahoma Sand #1 SEM Micrograph for (a) New Sand and (B) Sand Used for 8 Days in an Erosion-Corrosion Experiment Mesh for Axisymmetric Geometry Velocity Magnitude and Profile for Turbulent Flow Wall Shear Stress Comparisons of (CFD & Correlations) Principle of E-C Model Scale Deposition Rate Using Different Correlations Scale Thickness Measurement at 150 o F Scale Thickness Measurement at 190 o F LPR Measurement and Specimen Photograph after the Test of 150 o F at 10 Hours SEM Photograph after The Test of 150 o F at 10 Hours LPR Measurement and Specimen Photograph After the Test of 190 o F at 5 Hours SEM Photographs of 190 o F at 5 Hours Deposition Rate Regions in the Overall Corrosion Process For Different Temperatures EC Experiment Conducted for 8 Days Showing Mostly Bare Metal Specimen Surface Covered by Scale % at 150 o F..104 xvii

18 5-12 Specimen Surface Covered by Scale, % at 190 o F E-C Comparison between New Model and Experimental Data at 190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) E-C Comparison between New Model and Experimental Data at 150 o F, 10 ft/s, ph 6.24, 2 wt% NaCl, and 1900 ppm NaHCO 3 ) xviii

19 CHAPTER 1 INTRODUCTION 1.1 Introduction In the oil and gas production industry, erosion and corrosion problems have a pronounced influence on the design and operation of wells. The erosion process involves the impingement on well surfaces by solid particles entrained in the flow stream from sand production. The effects of sand particle erosion on carbon steel and other metals have been studied extensively by many researchers [24-32]. The prediction of the erosion rate at different operating conditions is made possible by considering the many different erosion factors (including flow velocity, sand shape, sand concentration, impingement angle, and flow geometry). However, CO 2 corrosion is the most dominant metal loss mechanism for oil and gas production facilities. CO 2 gas is often a significant component in the production fluids. Corrosion behavior in a CO 2 environment has been very well researched for many conditions. At some operating conditions, iron carbonate scale (FeCO 3 ) is created as a result of the corrosion process. When FeCO 3 scales coat the metal surfaces of the well, corrosion protection can be provided by the scale to reduce the corrosion rates to lower 1

20 values. In some cases, the iron carbonate scale could also provide protection against sand particle erosion. The Erosion/Corrosion Research Center (E/CRC) at The University of Tulsa has studied sand particle erosion and CO 2 corrosion behavior. Experiments to investigate erosion and corrosion were conducted using laboratory flow loops circulating singlephase flows and multiphase flows. As a result, the E/CRC has developed two separate computer programs for predicting erosion and corrosion rates. As an extension to E/CRC research in erosion and corrosion, a new research project has been launched with the objective to study the combined effects of erosion and corrosion with oilfield applications. Faisal Al-Mutahar [41] developed an erosion-corrosion model to predict the combined effects of solid particle erosion and CO 2 corrosion. The objective was to develop a computer program based on the model to predict the erosion-corrosion rate for carbon steel materials. The predictive procedure is based on modeling the competition between the scale deposition rate and the scale removal rate by erosion. The erosion-corrosion model developed by Al-Mutahar requires further experimental work to improve and validate the model. The main objective of the current research was to collect experimental data to validate and enhance the erosion-corrosion model. The first area of investigation in this work was to determine iron carbonate scale erosion resistance characteristics by using a submerged impingement flow configuration. The scale erosion resistance was studied for scales formed at two different temperatures and for different sand concentrations (i.e., different erosivities). Two techniques were used to measure the scale erosion rate in this research: by computing the weight loss; and, by using the 3-D profilometer. To make the scale erosion resistance data more 2

21 useful and accessible, a relation between the erosion rate of scales formed under different temperatures and the erosion rate of mild steel was developed. This relation will facilitate prediction of the scale erosion rate under varied environmental conditions through the use of the E/CRC s erosion prediction model, Sand Production Pipe Saver (SPPS), which predicts the sand particle erosion rate of steel in oilfield applications. Also, to better understand the erosion-corrosion process, scale deposition and growth rates and scale porosity were studied in this research considering different environmental conditions. Comparisons were made between scale deposition rates predicted by different models in the literature, and a modified version of one of the deposition rate models is used, along with scale deposition rate measurements, to identify appropriate constants in the Arrhenius equation for scale deposition rate. Scale porosities for different scale formation temperatures were evaluated in order to determine the total mass of scale deposited on the metal. Erosion-corrosion experiments were conducted to measure the steady-state corrosion part of the erosion-corrosion process for a carbon steel material under scale forming conditions. The erosion-corrosion model was modified to reflect the experimentally derived scale deposition rate and scale erosion resistance. Finally, the experimentally determined steady-state corrosion rates were compared with corrosion rate predictions by the model. The model provides very good predicted values of the corrosion part of the erosion-corrosion process and predicts the condition of the iron carbonate scale for a range of environmental conditions.. 3

22 1.2 Research Objective The main objective of this research is to conduct erosion-corrosion experiments to improve and validate an erosion-corrosion model developed by the E/CRC [41]. A submerged, direct impingement configuration was used for the investigation. Achieving this objective has entailed determining scale erosion resistance, investigating scale deposition rates, investigating scale porosity, and conducting erosion-corrosion experiments. 1.3 Research Approach Figure 1-1 shows the approach that was developed to achieve the objective of this research. First, iron carbonate scales were formed at different environmental conditions by using the submerged direct impingement loop. Iron carbonate scale characterization was needed to understand the erosion part of the erosion-corrosion process. Scale characterization also was conducted to investigate scale deposition rate and scale porosity. Erosion resistance experiments at different sand erosivities were needed to determine the iron carbonate scale erosion rate. Then experiments were conducted to determine erosion-corrosion rates under submerged conditions. Finally, data from all the experimental investigations were used to validate and enhance the erosion-corrosion model. 4

23 Form iron carbonate scale at different environmental conditions FeCO 3 Scale Characterization: Scale Erosion resistance Scale Deposition Rate Scale Porosity Determine erosion-corrosion rates and Scale Condition Validation and Enhancement of Erosion-Corrosion Model Figure 1-1: E-C Model Validation and Enhancement Approach 5

24 CHAPTER 2 BACKGROUND AND LITERATURE REVIEW 2.1 Literature Review CO 2 corrosion is one of the most dominant damage mechanisms in the oil and gas industries. In general, corrosion is a very complex process in nature. CO 2 corrosion is also affected by many operating parameters such as temperature, ph, specie concentration, CO 2 partial pressure, deposition rate, scale density and others. The process of corrosion is even more complicated if the sand particle erosion is also taking place at the same time, which has been referred to in the technical literature as erosioncorrosion. This chapter reviews and summarizes how some of the relevant parameters involved in erosion-corrosion affect the erosion-corrosion process, and specifically, the roles they have played in completing this research CO2 Corrosion and SPPS CO 2 CO 2 gas is one of the constituents of substances produced in oil and gas wells and often is produced in significant quantity. Also, CO 2 is injected into reservoirs to enhance oil recovery from the reservoir. Dry CO 2 gas is non-corrosive, but when moisture or water is present in the flow stream, CO 2 can significantly attack carbon steel 6

25 piping, tubing and other oilfield equipment. In most wells, piping, fittings, tubing, and other equipment are made of carbon steel material due to lower cost and greater availability. Therefore, when oil and gas is produced and transported from wells, carbon steel piping and equipment can exposed to CO 2 and are susceptible to CO 2 corrosion sweet corrosion which increases the risk of uncontrolled corrosion damage. The corrosion behavior of carbon steels in a CO 2 environment has been very well researched under many conditions [1-23]. The CO 2 corrosion mechanism is now very well understood and the roles of most critical parameters are well defined. A very early attempt to predict CO 2 corrosion rate in carbon steel was done by C. dewaard, and D.E. Milliams in 1975 [1]. A correlation for CO 2 corrosion rate was developed based on experiments conducted in beakers and showed the relation between the corrosion current and ph, Equation (2-1). DeWaard and Milliams late revised the correlation to include the effects of temperature and the CO 2 pressure [2]. The correlation has gained very wide acceptance and is referred to as the dewaard-milliams equation, Equation (2-2). This equation was again improved by C. dewaard, et al. [3], [4] to account for higher temperature and flow velocity. A correction factor was introduced in the correlation to account for iron carbonate scale protection at higher temperature. log i c = -1.3 ph + B (2-1) (2-2) where i c is corrosion current, V nomo is nomogram corrosion rate, T is temperature in K, and pco 2 is is the partial pressure of CO 2 in bar (mol% CO 2 x total pressure P). 7

26 Dalyan et al. [5] divided the CO 2 corrosion process into four major steps. The first step is the formation of the corrosive reactive species as a result of dissolution of CO 2 gas in the aqueous solution as per the following equations. CO 2 + H 2 O H 2 CO 3 (2-3) H 2 CO 3 H + + (2-4) HCO 3 - H + + (2-5) After the formation of the reactant spices in the bulk solution, the second step is the transportation of these reactants to the surface of the metal. Dalyan et al. [5] described this step in the following equations: H 2 CO 3 (Bulk) H 2 CO 3 (Surface) (2-6) (Bulk) (Surface) (2-7) H + (Bulk) H + (Surface) (2-8) The third step is taking place at the metal surface, and is described by the following cathodic and anodic equations. cathodic reactions, 2H 2 CO 3 + 2e - H 2 + (2-9) + 2e - H 2 + (2-10) 8

27 2H + +2e - H 2 (2-11) anodic reactions, Fe Fe e (2-12) The fourth step involves the transportation of the products of the corrosion reaction to the bulk of the solution. Fe 2+ (Surface) Fe 2+ (Bulk) 2-13 (Surface) (Bulk) 2-14 Based on above four steps of CO 2 corrosion, Dalyan et al. developed a computer program at E/CRC to model the CO 2 corrosion process to help in predicting the corrosion rate. The computer program is called SPPS:CO Sand Particle Erosion The recommended practice API RP 14E [24] is very widely used in the oil and gas industry for guidance in the performance of many functions within the industry. One of the recommendations in API RP 14E concerns controlling erosion in piping and fittings. An equation is provided Equation (2-46) for calculating the erosional velocity a flow velocity above which erosion may become a serious problem. (2-46) 9

28 where V e is in ft/s, C is an empirical constant, and is the gas/liquid mixture density in lb/ft 3. This correlation may works well to determine an erosional velocity suitable for liquid drop impingement and corrosion-assisted erosion [25]. However, for erosion due to entrained particles, API RP 14E equation does not account for many of critical factors that affect erosion [26]. McLaury and Shirazi [27] contend that the flow mixture density effect on erosion rate is different from the way it is represented in Equation (2-46). The experimental data would allow an increase in flow velocity by increasing mixture density. However, Equation (2-46) would require a lower flow velocity for higher mixture density. Simply by comparing erosion behavior in single phase flows, the sand particles entrained in liquid reduce in velocity when approaching to the wall. Whereas, sand particles in gas (lower density), tend to maintain their momentum as they approach a wall. Higher particle impact velocity means higher erosion rate. Salama et al. [25] developed a correlation to predict the erosion rate in elbows as given in Equation (2-47). Sand flow rate, flow velocity, pipe dimension and material properties are the main factors considered in the calculation of the erosion rate. Salama made further simplification to this equation as given in Equation (2-48) to calculate a threshold velocity for 10 mils per year erosion rate. Hardness, P for steel (P=1.55 X 1005 psi). Salama suggested using the API RP 14E equation only when W (sand flow rate) approaches zero. (2-47) (2-48) where h = erosion rate (mils per year, mpy) 10

29 W = sand flow rate (bbl/month) V = fluid flow velocity (ftlsec) P = hardness (psi) d = pipe diameter (inches) In addition to Salama s work, several models have been developed to improve the usefulness of the API 14E equation in the industries [25-32] considering a singlephase flow. Models were developed based on limited experimental data and are only valid for certain conditions [26]. Lately, Salama [32] suggested a new correlation, given in Equation (2-49), for the API 14E erosional velocity to be used for sand-loaded fluid that could be applied to multiphase flow. Also he suggested a value of 400 for the C constant in the API 14E Equation (2-46) for solid-free noncorrosive fluids (2-49) where V e is the erosional velocity limit in m/s and W is the sand flow rate in kg/day. An erosion model and computer program, SPPS, was developed by the University of Tulsa E/CRC [27] to account for the sand properties, sand rate, fluid properties, flow rates, flow geometry, and pipe material properties. Initially this model was developed for single-phase flow as given in Equation (2-50). The model predicts the erosion damage caused by sand particle impingement in a steel elbow. The threshold velocity can be back calculated based on the allowable penetration rate. 11

30 (2-50) where h= penetration rate, m/s (can be converted to mm/year or mpy) F M= An empirical constant that accounts for material hardness for carbon steel materials, F S = empirical sand sharpness factor F P = penetration factor for steel (based on 1" pipe diameter), m/kg F r/d = penetration factor for elbow radius W = sand production rate, kg/s V L = characteristic particle impact velocity, m/s D = ratio of pipe diameter in inches to a one inch pipe Scale Deposition Rate Scale deposition rate is very important aspect for this research and to the scale formation process. The erosion-corrosion model was designed to compare the scale erosion rate to the scale deposition rate in order to determine the steady state condition of erosion-corrosion in a scale formation environment. There are several models in the literature for predicting the scale precipitation rate. The following are some of the most recognized models Johnson and Tomson s Model: One of the early models to predict FeCO 3 precipitation rate was developed by Johnson and Tomson [33]. The Arrhenius equation that they developed was used to show the temperature effect on the iron carbonate scale 12

31 deposition rate. The higher the temperature, the higher the rate of FeCO 3 deposition. The equation developed by Johnson and Tomson is given by Equation (2-51) and the Arrhenius is given by equation (2-52). (2-51) (2-52) Where (mol Fe 2+ /m 3 -s) is the precipitation rate; S/V (m -1 ) is the surface area/volume ratio of the specimen s area to the solution s volume; K sp (mol 2 /kg 2 ) is the solubility product for FeCO 3 and Kr (kg 2 /mol-m 2 -s) is the reaction rate constant that was given by the Arrhenius equation Van Hunnik s Model: Van Hunnik et al. [34] have implemented a different procedure to investigate the iron carbonate scale formation. Van Hunnik used a flow loop with different flow velocities (0.1 and 4 m/s). Several experiments were conducted at 40 and 160 o C, CO 2 pressure between bar and 1 wt% sodium chloride. The iron carbonate precipitation rates were determined from the deviation from the linear increase of the iron counts with time. The liner increase was measured by the weight loss and indicates for the corrosion rate. Van Hunnik improved the J&T equation to better predict scale deposition rate at higher supersaturation levels. Van Hunnik assumed that FeCO 3 precipitation was controlled by kinetics and not by nucleation. (2-53) 13

32 Based on the experimental data, new values for the Arrhenius equation constants were determined. Hunnik and coworkers find the values of A and E a to be 52.4 and respectively to fit the new experimental data with the deposition rate equation Yean s Model: Yean et al. [35] conducted experiments to measure the iron carbonate scale (siderite) deposition rate in a batch reactor. The research investigated iron carbonate scale nucleation and deposition rate and evaluated different common scale inhibitors that helps ferrous carbonate nucleation. The experiments were conducted at a ph 7.67 to evaluate the deposition rate as a function of temperature, supersaturation and ionic strength. As a result, Equations (2-54) and (2-55) were derived to represent the experimental results for scale deposition rate. (2-54) (2-55) where [Fe] t is the total dissolved iron concentration (molality, m) at time t, t is time (min), k is the nucleation reaction rate constant (min -1 ), [Fe] eq is the expected total dissolved iron concentration (m) at equilibrium, and [Fe] o is the initial total dissolved iron concentration in solution (m) at time t = 0. The Arrhenius equation used to express the temperature dependent precipitation rate term, k, is shown in logarithmic form by Equation (2-56). (2-56) 14

33 where A is a pre-exponential factor and E a is the activation energy for nucleation. Based on Equation (2-56), the constants activation energy and pre-exponential factor were selected to fit the experiments results. The value of E a and A reported by Yean were 197 kj/mol and 3.85 x 10 29, respectively Sun s Model: The effect of temperature and ionic strength on iron carbonate deposition was studied by Sun et al. [36]. Sun et al. argued that the measurement of the deposition rate by the change in the [Fe ++ ] concentration in the bulk may not be accurate. They suggested that there is a possibility that iron carbonate scale may precipitate elsewhere in the test system, and not just on the specimen. Hence, Sun et al. proposed a procedure they referred to as CLAR Corrosion Layer Accumulation Rate. The technique of weight change of the specimen in addition to the [Fe ++ ] concentration reduction was both used to determine the actual scale deposition on the corroding steel surface. Experiments were conducted at ph 6.6, 80 C, and an initial Fe 2+ concentration of 50 ppm and using a different specimen for each test solution. Specimens were taken out every two and half-hours to measure the iron carbonate deposition rate. Different surface areas were used to relate the area to volume ratio (S/V) to the supersaturation and deposition rate. The precipitation rate equation proposed by Sun et al. is given in Equation (2-57). (2-57) 15

34 Where is the precipitation rate in kmol/m 2 -s, k r is the kinetics constant m 4 /kmol-s, and k sp is the solubility product (kmol/m 3 ) 2. The values of the kinetics constants, E a and A obtained by Sun were and 1.8 x respectively. A comparison of the of Arrhenius equation constants derived by the four research are showing in the Table 2-1 in the form of. Table 2-1: Arrhenius s Equation Constants Derived for Scale Deposition Rate Equation Activation energy E a Pre-exponential factor A kj/mol 1 Johanson & Tomson [33] Van Hunnik [34] Yean [35] Sun [36] Scale Porosity Scale porosity is another critical factor important to the corrosion protection the scale can provide. Also, knowledge of a scale s porosity is useful for evaluating FeCO 3 deposition rate based on scale thickness measurements. Different porosity models from literature were considered in this research based on electrochemical properties Nesic, et al. porosity model [40]: Correlations were developed to predict FeCO 3 scale porosity based on results of a large number of corrosion loop experiments by Sun et al. [36]. Environmental conditions for the loop tests were: C, ph, and bar Pco 2. Influences of ph and temperature were determined. The scale 16

35 thicknesses were measured through SEM micrographs and found to be in the range between 20 to 100 microns for test durations of 3 to 4 weeks. For scale thicknesses in this range, no significant corrosion rates were observed. The scale thickness of 50 microns was considered as a typical value for this research. Figure 2-1 shows the measured porosities and the correlation for different temperatures and constant 5.8 ph and 2 bars CO 2 partial pressure. Figure 2-2 shows the measured porosities and correlation as a function of ph at 80 o C and CO 2 partial pressure of 2 bars. The final porosity correlation is shown in Equation (2-58). (2-58) Where ε is porosity, A = 580, b = 0.045, c = 1.5, D = -2.2 and E = 0.06 and T, temperature, is given in C. 17

36 Figure 2-1: Porosity as a Function of Temperature at ph 5.8 and Pco2=2 bar. Porosity Calculated from Corrosion Rates Measured in Loop Experiments. [40] Figure 2-2: Porosity as function of ph at 80 C and Pco2=2 bar. Porosity calculated from Corrosion Rates Measured in Loop Experiments. [40] 18

37 Gao Porosity Model: Gao et al. [37] studied iron carbonate scale porosity by using a gas adsorption process. Adsorption is a phenomenon represent the taking up of gas, vapor or liquid by a surface on interface to fill any cavities in the material. Gao measured the scale volumetric porosity as defined by Equation (2-59): (2-59) Where V void is the volume of voids in the corrosion product film, V total is the entire volume of corrosion product film including volume of voids, and V FeCO3(s) is the volume of FeCO 3 in the film. Gao divided the iron carbonate crystal growth into two stages: scale nucleation; then, scale growth. The level of supersaturation has direct and important effects on scale nucleation and growth. In cases for which the level of supersaturation is low, the rate of precipitation is controlled more by crystal growth rate than nucleation rate. However, the corrosion product films would typically be porous and loose when the nucleation rate is low, regardless of the crystal growth. When supersaturation is high, precipitation rate depends is more dependent on nucleation rate and can be profuse. This gives importance to the nucleation rate for investigating the iron carbonate crystal properties. The first step in forming iron carbonate scale is when the nucleation occurs in solution or just above the steel surface. This is followed by crystal growth, which is precipitated by ferrous and carbonate ions on the surface of crystal grains. The rate of nucleation is believed to increase exponentially with increasing supersaturation in comparison with the growth rate that that behaves linearly with supersaturation. Equations (2-60) and (2-61) describe scale nucleation rate and growth rate respectively. 19

38 (2-60) Where I is the nucleation rate, B is the rate at which atoms are added to the nucleus, s is the molecule volume, n is the number of molecules per volume, and r is the critical nucleus radius. (2-61) Where R is scale growth rate, h is the interplanar spacing, v is the vibrational frequency of molecules, Q f is the activation energy, k is the Boltzmann constant, and T is the temperature. As the nucleation of iron carbonate scale proceeds to cover the steel surface, the corrosion rate of the steel reduces due to the better protection from the denser scale. The relation between the corrosion rate and porosity at different time intervals was studied at two different temperatures. A roughly linear relation in the form of Equation (2-62) between corrosion rate and porosity can be clearly drawn. The corrosion rate is equal to bare metal corrosion rate when the scale porosity is equal to one (no scale deposited on steel surface). In this case, the corrosion rate can be expressed by an empirical relation of the temperature and CO 2 partial pressure proposed by Waard and discussed earlier in this chapter [2-3], and shown here as Equation (2-63). The corrosion rate of the metal under the scale can be represented simply as the product of the empirical relation and the porosity as given in Equation (2-64). (2-62) 20

39 (2-63) (2-64) Tremblay s Porosity Model: Tremblay et al. [38] investigated the electrochemically active (real) surface of electrode material. Unsupported porous powder catalysts were prepared by high-energy milling. The powder material porosity was determined by using the impedance method. Tremblay utilized the polarization resistance R p to determine the porosity of the powder by defining the total volume of the pores as per Equation (2-66) and (2-66). The pores were assumed to be cavities of cylindrical geometry. (2-65) (2-66) Where R p is the polarization resistance, ρ is the resistivity of the electrolyte, l and r p are the height and the radius of the cylindrical pore, n is the number of pores, and V void is the total pore volume Creus Porosity Model: Creus et al. [39] studied porosity of protective coatings on steel through electrochemical techniques. Three different techniques were used in this study to evaluate the porosity (Physical porosity test by microscopy, chemical methods and electrochemical methods) for four different types of coatings. 21

40 Electrochemical techniques used to evaluate the coating porosity included polarization resistance, mixed potential theory, and polarization curves crosschecking. Polarization resistance is the most interesting technique out of the three because of the applicability to corrosion rate measurements using LPR data. Creus method using polarization resistance is shown below in Equation (2-67) (2-67) Where ε is the porosity, Rp bare is the polarization resistance of bare steel, Rp coating is the polarization resistance of coated steel, E corr is the change in corrosion potential before and after coating, b a is the anodic tafel slope of the steel. 22

41 CHAPTER 3 EXPERIMENTAL FACILITY AND PROCEDURES 3.1 Introduction To achieve the objective of this research, experiments in a flow loop were conducted that cover following areas: (1) Scale Formation Experiments, which are pure corrosion experiments to form iron carbonate scale at different temperatures using a submerged jet impingement test cell configuration, (2) Scale Erosion Resistance Characterization using the same submerged jet impingement configuration, and (3) Erosion-Corrosion experiments, in which scale is pre-formed by corrosion experiments and then sand is injected into the flow loop and impinges on the scale in the test section until a steady state condition is reached. To conduct the above experiments, two different loops were used. The two loops were identical in configuration and function with very minor differences in design, cyclone separator, and pump capacity. Both loops were used for the corrosion, erosion, and erosion-corrosion experiments. The two loops provided comparable results with no significant variation. Before testing, each loop was calibrated. The fluid velocity exiting the nozzle in Figure 3-1 was evaluated using three different methods. The nozzle diameter is 0.4 inch and ½ inch distance from the specimen surface. This velocity has a significant effect in 23

42 all experimental results and also will be used in the prediction model. First, the Ultrasonic Doppler velocity meter was used to calculate the velocity at the outlet pipe from the test section. Then the velocity was back calculated for the jet nozzle. Enough sand was used in the solution to allow the ultrasonic sensor to detect reflected waves. Secondly, a Pitottube was used to measure the pressure difference at the nozzle outlet and at the specimen location. Third, the flow rate was used to measure the discharged solution flow rate (volume and time) to calculate the average nozzle outlet velocity. But, impingement nozzle configuration is not quite uniform. There are several changes in diameters before the impingement nozzle, which acted as venturical effects as shown in Figure 3-1. Since the distance from the diameter changes and the specimen surface is short, it was believed that the flow velocity was still affected by the venturi effects. This was confirmed by the Pitot tube measurement at the specimen surface (1/2 inch distance from the nozzle). However, the Pitot tube measurement and calculation accuracy was confirmed by comparing new Pitot tube velocity measurement after the testing box outlet (vertical pipe) with the velocity measurement by the ultrasonic and the flow rate methods. Both Pitot tube and the other two testing method showed very close velocity values for lower flow rate (1 and 2 gpm). Therefore, the measurement of the Pitot tube at the specimen surface is confirmed to be the actual velocity of the test. Based on this, a relation has been established between different flow rate measurements provided by the flow meter and the calculated velocity by Pitot tube. 24

43 From cyclone separator 10 in 3.0 in Jet Nozzle in Test Specimen in A B 0.4 in Figure 3-1: Venturi Effects before Injection Nozzle 3.2 Experimental Setup A single-phase flow loop with a jet impingement configuration was used in the experiments to form iron carbonate scale, evaluate the scale erosion resistance, and conduct the erosion-corrosion experiments. A schematic diagram of the flow loop is shown in Figure 3-2 and a photograph is shown in Figure 3-3. The loop is made of SS316 material and can operate at pressures up to 150 psig (1.13 MPa) and temperatures up to 200 F (93 C). The loop consists of a Hydra Cell pump, a tank, a sand injector, a test section, and a cyclone separator that keeps sand circulating only through the test section. The loop has an electrical heater and control system to achieve the desired solution temperature during the experiment. 25

44 Figure 3-2: Schematic of Experimental Loop Figure 3-3: Photograph of the Flow Loop 26

45 In the test section, the jet nozzle of test fluid (which can include entrained sand) is aligned with the center of the electrode. Flow comes through the jet pipe, impacts the surface of specimen and leaves the cell through the outflow port. Figure 3-4 shows a schematic and photograph of the jet nozzle and mounting arrangement for the specimen in the test section. The distance between the nozzle exit and the specimen surface is always one half-inch. Figure 3-4: Schematic and Actual Set up of the Mounting Arrangement for Specimen. Electrochemical measurements are used to monitor the corrosion rate using the Linear Polarization Resistance (LPR) method. The LPR probe, shown in Figure 3-5, consists of two parts the working electrode which is made of 1018-carbon steel, and reference electrode, which is made of 316L stainless steel. The two electrodes are separated by a non-conductive layer of epoxy. The counter electrode is the 316L stainless steel loop. Similarly, the counter electrode is isolated by a rubber sleeve from the working electrode to ensure full isolation. The chemical composition of 1018 steel is shown in Table

46 Carbon steel working electrode Ceramic epoxy filled Epoxy coated Heat shrink insulation & dia & dia dia & Platinum wire Steel tube! Figure 3-5: Schematic of Working-Reference Electrode. Table 3-1: Chemical Composition of 1018 Steel (Weight %) C Mn Si P S Fe Balance 3.3 Experimental Procedure As discussed above, three types of tests were conducted in the flow loops, which are (1) Scale Formation Experiments, (2) Scale Erosion Experiments, and (3) Erosion- Corrosion experiments. This section describes the experimental procedures for each of the tests. 28

47 3.3.1 Scale formation Experiments The system is usually cleaned and flushed properly by using different method of cleaning before starting any experiment. The solution is prepared outside of the loop by adding Sodium Chloride (NaCl) and Sodium Bicarbonate (NaHCO 3 ) to distilled water. The amounts of NaCl and NaHCO 3 added to the solution are based on the desired experiment parameters for the (Na + weight %) to change the ph and ionic strength. The solution is mixed to be homogenous before adding the solution to the system. The system is then exposed to vacuum pressure to de-aerate and deoxygenate the system and the solution for at least two hours. After that, the system is pressurized with 20 psig nitrogen while the pump circulates the solution for about 24 hours until the solution reaches the desired temperature. When the system is in circulation mode, the tests section is bypassed to allow the installation of the specimen. The specimen surface is prepared as described in Section After the specimen is placed in the test section, the test section is vacuumed for de-aeration and then connected to the flow loop. The desired flow rate is obtained by using the digital flow meter. For scale formation experiments, several changes in testing parameters were considered. But the main parameter changed was in the solution temperature. Critical experimental parameters and conditions that were considered in the scale formation experiments listed in Table

48 Table 3-2: Testing Parameters for Scale Formation Experiments PARAMETER SCALE FORMING CONDITIONS Temperature 65 and 93 o C (150 and 190 o F) ph 6.24 Test solution composition 2 wt% NaCl and 1900 ppm NaHCO 3 Gas Dissolved Oxygen Flow velocity Material tested Flow Geometry Measurement techniques CO bar (20 psig) Less than 10 ppb 3 m/s for (10 ft/s) AISI 1018 carbon steel Submerged jet impingement LPR, Weight Loss Scale Erosion Experiment One objective of scale erosion experiments was to evaluate the erosion rates of the iron carbonate scales for the submerged jet impingement flow geometry. The second objective was to compare the erosion rates of the iron carbonate scales, formed at 150 o F and 190 o F, to the erosion rate of the bare 1018 carbon steel. To achieve these two objectives, two different sets of erosion experiments were conducted. The first set was to identify the scale erosion rate at different sand concentrations. The second set is to define the ratio of the steel erosion rate to scale erosion rates. The scale erosion experiments were conducted with preformed iron carbonate scale specimens as described in the previous section. The solution of the erosion 30

49 experiments, which is distilled water, is sucked into the system and vacuumed for two hours for de-aeration. Then, the system is pressurized with nitrogen at 20 psig and kept in circulation to raise the temperature to 150 o F. The specimen with the preformed scale is cleaned and weighted before placing it in the test section. Also, a 3-D profilometer scan is conducted to measure the surface profile before the erosion test. The test section was vacuumed and connected to the flow loop. Sand, of a known mass, is injected through the sand feeder to the loop as shown in Figure 3-6. The sand feeder is made of Pyrex class with a magnetic stirrer to circulate the sand in the solution to help inject the sand to the system. After the sand is added, the sand feeder is de-aerated by a vacuum pump, pressurized with the nitrogen, and filled with solution from the loop. The sand is introduced to the loop by means of nitrogen pressure to ensure no oxygen enters the system. After allowing the sand to reach a steady state condition, a sand sample is pulled from the sand sampling valve. The sand concentration is measured based on the sand weight and water volume. The system is compensated for the sand removed to maintain same concentration. The sand concentration measurement is conducted at the beginning, middle, and at the end of the test to measure the sand concentration. The scale erosion test lasts for two to three hours to avoid the complete removal of the scale. After the test, the specimen is taken out, dried in heater and kept in a vacuum cell until the next day for weight measurement. In addition, a 3-D profilometer scan is also made after the test. The scale erosion rate measurement is calculated using both the weight loss and the change in scale volume as a result of 3-D profilometer scan. 31

50 Figure 3-6: Sand Feeder Used in Erosion Experiments Erosion-Corrosion Experiments Two different types of erosion-corrosion experiments were conducted in the submerged jet impingement configuration. In the first type, a scale is formed through a corrosion test and then injecting sand into the system. In the second type experiment, sand is injected at the beginning of the scale formation experiment. The solution for both cases is prepared as described above. The temperature and flow velocity are set to the desired values. The sand is also injected with the same procedure described for the erosion experiments, but CO 2 was used instead of nitrogen. During the erosioncorrosion experiment the sand concentration is monitored throughout the test duration. Linear polarization resistance (LPR) is used to monitor the corrosion activity throughout 32

51 the test. The test is stopped when the LPR measurement of the corrosion part of erosioncorrosion reaches a steady state value. 3.4 Specimen Surface Preparation The specimen preparation process includes different levels of polishing the specimen surface. At the beginning, the specimen surface was polished by using a rough sand paper of 200 microns average grain size (P 80). Then, the surface is polished by finer sand paper of 125 microns average grain size (P 120). After polishing, the specimen surface shall be very uniform with no oval as shown in Figure 3-7. In some case, horizontal lath machine was used to perfectly flatten the specimen surface. Finally, the specimen surface is cleaned and wiped with the acetone to remove any oily material. Figure 3-7: Specimen after Surface Preparation 33

52 3.5 Linear Polarization Resistance (LPR) The LPR technique was used to monitor the electrochemical activity for scale formation and erosion-corrosion experiments. The objective of the LPR is to monitor the instantaneous corrosion rates during the experiment. The electrochemical corrosion measurement utilizes the electrochemical nature of the metallic corrosion. An external power source is used to apply a voltage or range of voltages, to a metal specimen submerged in an electrolyte. The applied voltage pushes the metal-electrolyte interface beyond its steady state conditions, causing a measurable electrical current to flow. Voltage and its corresponding current are independent and dependent variables (respectively), and their relationship is used to determine metallic corrosion behavior and estimate corrosion resistance [42]. The Bulter Volmer relationship, shown in Equation (3-1), is used to relate the applied potential to its corresponding applied current and corrosion current [42]. { ( ) ( )} (3-1) where R is the ideal gas constant, 1.986, T is temperature in degree Kelven, n is the number of electron in the anodic half-reaction, F is Faraday s constant, i is the external current density flowing to or from an electron in amps/cm 2, i corr is corrosion current density in amps/cm 2, α is a coefficient having values that range from 0 to 1, η is the test electrode overpotential. 34

53 A spectrum of potentials and their corresponding currents can be used to determine the corrosion current density, i corr, and corrosion rate. The main advantage of using LPR is that it applies a very small potential spectrum compared to other methods. This makes it a less destructive testing method. The electrochemical multiplexer system was used for LPR measurements. It is manufactured by GAMERY ECM8. The basic settings for the LPR are showing in Table 3-3. Table 3-3: GAMRY Settings for LPR Measurements Parameter Values Repeat time (minute) 20 Analysis Region (mv) 10 Initial Potential, E (V) Final Potential, E (V) 0.01 Scan Rate (mv/s) 0.2 Sample Period (s)] 0.2 βa (mv/decade) 120 βc (mv/decade)

54 3.6 Scanning Electron Microscope (SEM) and Focused Ion Beam (FIB) The scanning electron microscope (SEM) and focused ion beam (FIB) are used mainly to help in conducting Nano scale magnifications with extreme high-resolution characterization in two and three dimensions. The SEM generates a beam of electrons that is sent to the target specimen surface. The electrons interact with the specimen surface and atoms that make up the specimen reflect signals that contain information about the sample's surface topography, composition, and other properties. The signals result from interactions of the electron beam with atoms at or near the surface of the sample are detected by secondary electron detector. High-resolution images of a sample surface are produced by the secondary electron detector, revealing details less than 1 nm in size. The machine was manufactured by FEI and is model Helios NanoLab 650. The electron beam voltage ranges from 50 V to 30 KV and the current ranges from 0.6 pa up to 26 na. It can produce a very high image resolution, up to 1 nm in size, and 1.5 M magnification. A photograph for the SEM/IPF chamber is shown in Figure

55 Figure 3-8: SEM/FIB Chamber A SEM was used in this research to characterize the scale thickness and morphology after scale formation experiments. Also, the SEM was used to analyze the remaining thickness of the scale after erosion-corrosion experiments. In some cases, the specimen was encapsulated with epoxy and then cut in half to expose the specimen cross-section and the scale thickness. Also, the top surface of the scale was studied without using the epoxy encapsulation. The specimen is cleaned by immersing it in isopropyl alcohol and using an ultrasonic vibration machine to remove any grease or dust attached to the surface. The FIB was used in this research to create a localized milling of the scale surface, or the specimen, in order to expose the scale cross section. The focused ion beam is mounted at 52 degrees to the electron beam. The primary ion beam hits the 37

56 sample surface and sputters a small amount of material, which leaves the surface as either secondary ions or neutral atoms. In addition to the SEM and FIB, the machine also equipped with Energydispersive X-ray spectroscopy (EDS or EDX). EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on the investigation of an interaction of X-ray excitation as a result of the electron beam hitting the material. The EDS was widely used to analyze and verify the composition of the scale and the base metal D Profilometer A 3-D profilometer was used to measure the loss of scale or metal thickness of the specimen surfaces for the erosion tests. 3-D profiles of the top surface are done before and after the test. The stainless steel electrode is considered as a reference point since the electrode is not subjected to the erosion or corrosion and maintains the same height. The difference in the depth for the scale or metal from the reference point is used to calculate the material loss. An optical Noncontact type of 3-D profilometer was used in this research and was manufactured by NANOVEA. Figure 3-9 shows a photograph of the instrument. 38

57 Figure 3-9: 3-D Profilometer 39

58 CHAPTER 4 EXPERIMENTAL RESULTS AND DISCUSSION As described in Chapter 3, three main experiments were conducted in this research: scale formation, scale erosion resistance characterization, and erosioncorrosion experiments. In addition to the main three areas studied in this research, some other investigations have been done to support the main objective of this research, i.e., improve and validate the erosion-corrosion rate prediction model developed by the E/CRC team. For example, the following areas were studied at different testing temperatures: scale thickness, scale density measurement, scale deposition rate, and scale microstructure study. In this chapter, some experimental results and discussions are presented for each area. 4.1 Scale Formation Experiments The objectives of the scale formation experiments also referred to as corrosion experiments in this research, are to study the iron carbonate scale formation behavior and scale proprieties at different testing conditions. The corrosion rates for the bare metal and the steady-state corrosion rates were needed to help validate the erosioncorrosion model for different experimental conditions. Also, the scale formation experiments were needed to generate scale for other investigations in this research such as scale thickness characterizations, scale erosion resistance studies, and the erosion-corrosion experiments. 40

59 A submerged direct impingement flow configuration was used to form FeCO 3 scale by using a flow loop as described in Chapter 3. Corrosion rate measurement and monitoring was conducted by the mean of the 3-electrode LPR method. The LPR measurement is a very good and precise technique for measuring the corrosion activity. The average LPR corrosion rate measurements showed very good agreement with long-term weight loss [43]. Also, a comparison between LPR and weight loss was conducted as part of this study. Very good agreement was found between the average LPR measurement and the corrosion rate as determined by weight loss. With reference to Faisal Al-Mutahar s work [41] and other researchers, two of the solution components effective for successful FeCO 3 scale formation are NaHCO 3 and NaCl when used in CO 2 corrosion experiments. The NaHCO 3 was used to control the ph value of the experiment and also to increase the concentration of CO 2-3 ions in solution. The main testing parameters and scenarios that were used for scale formation are shown in Table 4-1. By following the procedure described in Chapter 3, scales were formed. The scale formed uniformly covered the specimen surface. Figure 4-1 shows images of the specimen before and after scale formation. The mechanisms of scale formation and CO 2 corrosion are described in detail in Chapter 2. 41

60 Parameter Table 4-1: Scale Formation Testing Parameters Scale Forming Conditions Set A Scale Forming Conditions Set B Temperature 93 o C (190 o F) 65 o C (150 o F) ph Test solution composition 2 wt% NaCl and 1900 ppm NaHCO 3 2 wt% NaCl and 1900 ppm NaHCO 3 Gas CO bar (20 psig) CO bar (20 psig) Dissolved Oxygen Less than 10 ppb Less than 10 ppb Flow velocity 3 m/s for (10 ft/s) 3 m/s for (10 ft/s) Material tested AISI 1018 carbon steel AISI 1018 carbon steel Geometry Submerged jet impingement Submerged jet impingement Measurement techniques LPR, Weight Loss LPR, Weight Loss Figure 4-1: Test Specimen before and after Scale Formation The ph values were measured randomly for some of the tests by using Omega- PHCN-410 ph controller. The instrument is a microprocessor-based ph controller with automatic temperature compensation with resolution of ± The instrument is calibrated before the test for the temperature and using buffer solutions at 4 and 7 ph. 42

61 When using the same solution compositions, ph measurement results were consistently repeated at the range of 6.3 ± 0.05 for 150 o F and 6.4 ± 0.05 for 190 o F. The oxygen dissolved in the system was also measured randomly by using VacuCute. The results of dissolved oxygen were also measured by using VacuCute and results were less than 10 ppb Scale Formation at 190 o F Figure 4-2 shows a typical LPR measurement for the scale formation experiments at 10 ft/s jet impingement velocity, 6.4 ph, 2 wt% NaCl, 1900 ppm NaHCO 3 and solution temperature of 190 o F. At the beginning of the test, the LPR corrosion rate measurement started in the range of 500 and then increased to 750 mpy. This increase in the corrosion rate indicates that there was no scale to forming yet at this condition, that there is still only a very small concentration of Fe 2+ in the bulk solution, and that F sat at the specimen surface in this case is still probably lower than one. As the corrosion proceeds, more Fe +2 is generated at the specimen surface and in the bulk which increases the F sat value until it exceeds 1.0, and thus scale formation conditions are reached. The corrosion rate then reduced at a very high rate until, after about 10 hours from starting the test, it dropped to very low values. Beyond 10 hours, the LPR corrosion rate continues to decrease, but at a lower rate until it reaches the steady-state corrosion rate where the scale is fully formed and most of the cracks and pores in the scale are closed. 43

62 Figure 4-2: LPR Measurements for the Scale Forming Experiments at 190 o F, 10 ft/s Flow Velocity, 6.4 ph, 2 wt% NaCl, 1900 ppm NaHCO 3. Figure 4-3 shows several different LPR measurements of the corrosion rate conducted in different scale formation experiments at a temperature of 190 o F. This figure shows the repeatability of the experiment and the LPR reading at the same testing conditions. 44

63 Figure 4-3: Repeatability of LPR Measurements for the Scale Forming Experiments at 190 o F, 10 ft/s flow velocity, 6.4 ph, 2 wt% NaCl, 1900 ppm NaHCO Scale Formation at 150 o F Similarly, scale formation at 150 o F, 10 ft/s flow velocity, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO 3, starts with high corrosion rate at the beginning of the test, followed by a sharp decrease in the corrosion rate until it reaches significantly lower values. In the case of the 150 o F scale formation, the time to form the scale is taking quite a bit longer than for 190 o F (18-20 hours as compared with only 10 hours for 190 o F) as indicated in Figure 4-4 (150 o F Temperature, 10 ft/s jet impingement velocity, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO 3 ). Also, Figure 4-5 shows the repeatability of LPR measurements for two scale formation experiments at the 150 o F testing conditions. 45

64 Figure 4-4: LPR Measurements for the Scale Forming Experiments at 150 o F, 10 ft/s Flow Velocity, 6.2 ph, 2 wt% NaCl, 1900 ppm NaHCO 3. Figure 4-5: Repeatability of LPR Measurements for the Scale Forming Experiments at 150 o F, 10 ft/s Flow Velocity, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO 3. 46

65 4.2 Scale Thickness Characterization Scale thickness characterization is very important for interpreting the corrosion and erosion-corrosion tests results. This section addresses the analysis of the scale thickness characterization after scale formation experiments at different temperatures (150 and 190 o F). SEM was used to analyze the cross sectional area of the scale. After scale was formed, the specimen was mounted in epoxy to help protect the scale during cutting. Then the specimen is cut in half to expose the scale and metal cross-section areas. This is followed by several polishing steps to smooth and flatten the specimen surface for better SEM analysis. The scale thickness characterization was conducted for several specimens at each temperature. For scale images shown in Figure 4-6, the scale was formed during the first 10 hours and then continued another 38 hours with steady state corrosion rates of 15 mpy. The greatest reduction in corrosion rate occurred during the first 10 hours as indicated in Figure 4-2. Scale images shown in Figure 4-7 are for a scale formed in 10 hours at which time the specimen was removed from the test loop. Corrosion rate near test end was 74 mpy. Analysis of the scale (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) cross sections shown in Figures 4-6 and 4-7 indicated a range of scale thickness from about 1 to 5 microns with an average thickness of 3 microns. 47

66 Figure 4-6: SEM Images of Scale Thickness after 48 Hours of Testing (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) with CR=15 mpy near test end. Figure 4-7: SEM Images of Scale Thickness after 10 Hours of Testing (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO3) with CR=74 mpy Near Test End. Similarly for the 150 o F tests (150 o F, 10 ft/s, ph 6.24, 2 wt% NaCl, 1900 ppm NaHCO 3 ), several scales were formed and analyzed by SEM. Scale in one case was allowed to form for 48 hours with an additional 20 hours under steady state corrosion rate conditions. In the second case the specimen was removed after only 20 hours. Steady-state corrosion rates near the end of the tests were 14 mpy for the longer test time and 144 mpy for the test aborted after 20 hours. For the scales formed at 150 o F, 48

67 most of the reduction in corrosion rate occurred in the first 20 hours as indicated in Figure 4-4. The thickness measurements for both cases were consistent with scale thickness in the range of microns and an average scale thickness of about 32 microns. Figures 4-8 and 4-9 show examples of SEM images of scale cross sections for the scales formed at 150 o F. The only difference observed between the tests conducted at different durations is that the scale porosity and roughness were higher for the scale with only 20 hours testing. This suggests that after the initial large drop in LPR, very little increase in scale thickness take place. Figure 4-8: SEM Images of Scale Thickness after 48 Hours of Testing (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) with CR=14 mpy Near the End of the Test. 49

68 Figure 4-9: SEM Pictures of Scale Thickness after 20 Hours of Test (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) with CR=100 mpy at the End Table 4-2 summarizes and compares scale thickness results of the two different testing temperatures (150 and 190 o F). Table 4-2: Scale Thicknesses at 150 and 190 o F Temperatures Scale formed Temp ( o F) Scale thickness Range (microns) Scale Thickness Average (microns) Erosion Resistance Characterization Erosion Resistance Characterization of 190 o F Iron carbonate scale erosion resistance characterizations were conducted using the submerged impingement flow loop facility. Pre-formed scales were used for this study. The sand was injected into the flow and was kept circulating within the test 50

69 section at a temperature of 150 o F. Distilled water was used as the test solution and was deaerated and pressurize under 20-psig nitrogen pressure. Two types of FeCO 3 scales were studied in this erosion resistance research: scale formed at 150 and 190 o F. The experiments were conducted at sand concentrations ranging from 0.3 to 1.2 wt% and at a constant jet impingement velocity of 10 ft/s. The sand concentration was monitored and adjusted throughout the scale erosion experiments to maintain a constant sand concentration. The scale erosion tests periods were run typically for 1 to 3 hours. For testing erosion rate of steel, tests ran for up to 2 days. The scale erosion rates were measured by two different methods: weight loss (weight difference before and after testing), and 3-D profilometer (volume difference before and after testing). The 3-D profilometer method was not always successful in obtaining good and accurate erosion results. Table 4-3 shows one sample of iron carbonate scale erosion experimental results. The sand concentration was sampled after the first injection of the sand, at the middle of the test and at the end. The sand concentration was adjusted by adding more sand to the test loop as needed to maintain a constant sand concentration as shown in the upper figure in Table 4-3. The average value of the sand concentration was used as the representative sand concentration for each test. Also shown in Table 4-4 are 3-D profilmeter images taken before and after the test. Assuming only negligible erosion of the stainless steel reference electrode in the center of the specimen, the stainless steel reference was used as the reference height in the profilometer before and after images. In Table 4-4, the average difference in height of the FeCO 3 coating on the specimen before and after the erosion test was 2.5 microns, which equates to an erosion rate of 288 mpy. 51

70 Sand concentration wt% Table 4-3: Sample Scale Erosion Resistance Characterization Experiment at 190 o F Scale forming condition: Scale Erosion Testing conditions: (T=190 o F, ph 6.58, P CO2 =20 psig (T=150 o F, P N2 =20 psig) Jet impingement velocity = 10 ft/s Average Sand conc. = 0.95 wt% Flow velocity = 10 ft/s 2.0 Sand wt% 1.5 Average wt% Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 3 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 55.9 Height after erosion (micron) 58.4 Scale volume loss (cm3) Mass loss (g) Time (H) 3 Erosion rate (mpy) This value was compared to the mass weight-loss calculation of 374 mpy. Similar detailed reports for other scale erosion experiments are in Appendix-B. 52

71 Figure 4-10 shows the scale erosion rates for scales formed at 190 o F, 6.4 ph, and 10 ft/s jet impingement velocity. The erosion rate data points shown were determined by weight-loss (blue diamonds) and by 3-D profilometry for two points only (red squares). Erosion Ratio is defined as the mass loss of material divided by mass of sand throughput given in Equation (4-1). Calculation of the sand mass throughput rate is done according to Equation (4-2). (4-1) S = C x F x x d x (cm 3 /gallon) (4-2) Where S is sand mass throughput rate, g/min, C is sand concentration, wt%, F is flow rate, gpm and is solution density in g/cm 3. The scale Erosion Ratios for different sand concentrations at constant jet impingement velocity are shown in Figure There is a slight decrease in the scale Erosion Ratio with increasing sand concentration. This inclination could be attributed to the particle-to-particle interaction at higher sand concentrations. As sand concentration increases, particles approaching the test specimen may be deflected by sand particles rebounding from the test specimen. This particle-to-particle interaction is more likely for jet impingement flow geometry than for an elbow geometry since particle outflow velocity near the specimen is quite low. 53

72 Erosion Ratio (kg/kg) Scale Erosion Rate (mpy) ER by weight 190 F (mpy) 100 ER By 3D 190 F (mpy) 0 0.0% 0.5% 1.0% 1.5% Sand Concentrations (wt%) Figure 4-10: Scale Erosion Rate vs. Sand Concentration (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) 2.0E E E E E E E E E % 0.5% 1.0% 1.5% Sand Concentration wt% Figure 4-11: Scale Erosion Ratio (kg/kg) vs. Sand Concentration (190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) 54

73 4.3.2 Erosion Resistance Characterization of 150 o F Erosion experiments also were conducted to characterize erosion resistance for scales formed at 150 of. Table 4-4 shows one example of erosion resistance test data for scales preformed at 150 of. Figure 4-12 shows the erosion rates for scales formed at 150 of for different sand concentrations. Erosion Ratios (mass loss of scale to throughput mass of sand) for scales formed in 150 o F scale experiments are shown in Figure The slight decrease of the Erosion Ratio values with increasing sand concentration is thought to occur because of particleto-particle interactions taking place near the test specimen surface. 55

74 Sand concentration wt% Table 4-4 Sample of Scale Erosion Resistance Characterization Experiment at 150 o F Scale forming condition: Scale Erosion Test conditions: (T=150 o F, ph 6.58, P CO2 =20 psig, 2 gpm) (T=150 o F, PN 2 =20 psig) Jet impingement velocity = 10 ft/s Average Sand conc. = 0.86 wt% Flow velocity = 10 ft/s Sand wt% Average wt% Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 69.9 Height after erosion (micron) 74.9 Scale volume loss (cm3) Mass loss (g) Time (H) 2 Erosion rate (mpy)

75 Eroion Ration (kg/kg) Scale Erosion Rate (mpy) % 0.20% 0.40% 0.60% 0.80% 1.00% 1.20% Sand Concentrations (wt%) Figure 4-12: Scale Erosion Rate vs Sand Concentration (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) 1.E-06 9.E-07 8.E-07 7.E-07 6.E-07 5.E-07 4.E-07 3.E-07 2.E % 0.20% 0.40% 0.60% 0.80% 1.00% 1.20% Sand Concentration wt% Figure 4-13: Scale Erosion Ratio vs Sand Concentration for (150 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) The FeCO 3 scale erosion rates reported in this work apply to very specific flow rate and flow geometry, i.e., 10 ft/s jet flow velocity in direct impingement geometry. 57

76 What is needed is a way to know what scale erosion rates would be for any flow velocity and many flow geometries. Erosion rates for low carbon steels can be predicted for any flow rate and many flow geometries by a model called SPPS created by the Erosion/Corrosion Research Center (E/CRC). As a first approximation, the same model could be used for predicting erosion rates for FeCO 3 scale for any flow rate and many flow geometries if erosion rate of the scale relative to the erosion rate of low carbon steel is known for the same flow rate and geometry. Finding the erosion rate for FeCO 3 scale relative to that of low carbon steel is the subject of the following section. A comparison of the erosion rate of FeCO 3 scale with the erosion rate of carbon steel G10180 was made. Erosion experiments were conducted for the bare steel specimens using the same submerged jet impingement flow loop with the same velocity of 10 ft/s. Figure 4-14 shows the relation between the scale erosion rate and the bare G10180 steel erosion rate. The graphs indicate that the scale erosion rate is higher than the steel by a factor of about 5 for the scale formed at 190 o F and 6.4 ph. The erosion rate for scales formed at 150 o F is higher than the erosion rate for the steel by a factor of about

77 Erosion Rate (mpy) F scale erosion (mpy) times 150F scale erosion (mpy) Steel erosion rate (mpy) times 0 0.0% 0.5% 1.0% 1.5% 2.0% Sand Conc. wt% Figure 4-14: Scale Erosion Rates and Bare G10180 Steel Erosion Rate Steel Erosion Comparison with SSPS Results from the steel erosion rate experiments, were compared with the predictions of the SPPS erosion software produced by The University of Tulsa E/CRC. Conditions used to calculate the erosion rate of low carbon steel were: single-phase water at a velocity of 10 ft/s, 150 micron semi-rounded sand, and the 2-D direct impingement configuration. The erosion rates predicted by SPPS were in agreement with the experimental data as shown in Figure 4-15 with only small differences. The erosion rates experimentally measured were about 20 % higher than predicted by SPPS. 59

78 Steel Erosion Rate (mpy) Expt. SPPS % 0.5% 1.0% 1.5% 2.0% 2.5% Sand Concentrations (wt%) Figure 4-15: Comparison of Steel Erosion Rate Experimental Data with SPPS Erosion Prediction Software by E/CRC. (Single-Phase Water, Velocity of 10 ft/s, 150 Micron Semi-Rounded Sand and 2-D Direct Impingement Configuration) The relation between the scale erosion rate and the bare steel erosion rate can by very useful for predicting scale erosion rates at different flow velocities and in different geometries. It was concluded that scale formed at 190 o F eroded faster than the steel by a factor of 5, and the scale formed at 150 o F eroded 15 times faster than the steel. Predicting the erosion rate of scale for a set of conditions can be accomplished by using the SPPS erosion prediction model to find out the steel erosion rate at the same set of conditions, and then multiplying the resulting number by a factor of 5 or 15 depending on temperature 190 o F or 150 o respectively. 60

79 4.3.4 Scale SEM Examination Post Erosion Test The assessment of the scale remaining on the specimen after completing the erosion test was carried out by using a scanning electron microscope (SEM). The objective was to verify that the coating remaining was indeed iron carbonate scale and that erosion had not penetrated through the scale and into the substrate. Figure 4-16 shows a sample result for one specimen. Milling to the specimen surface was done by using the ion beam process to expose the cross section of part of the scale and substrate. As indicated by the SEM micrograph, some scale appears to remain on the specimen surface. Also, Energy Dispersive X-ray Spectroscopy (EDXS) was carried out on the scale and substrate. The results showed oxygen and carbon components in the coating composition indicating iron carbonate scale. This was also compared to the substrate EDXS results and showed higher content of oxygen and lower percentage of iron content (atomic weight) for the scale than for the steel substrate. 61

80 Figure 4-16: SEM Analysis for Post Scale Erosion Experiment and EDXS Analysis. 4.4 Erosion-Corrosion Experiments To validate the erosion-corrosion rate prediction model, corrosion-erosion experiments were conducted in the submerged jet impingement flow loop. The test started with a bare 1018 steel specimen. Iron carbonate scale was formed for the following test conditions: T=190 and 150 o F, 6.24 ph, 10 ft/s jet impingement velocity, 2 wt% NaCl, and 1900 ppm NaHCO 3. The procedure for forming the scale was the same as explained in the earlier section of this chapter. Similarly, the corrosion rate was monitored by LPR. After forming scale and reaching a steady state LPR condition, sand was injected at different concentrations as summarized below to monitor corrosion rates when sand particles were eroding the scale while simultaneously new scale was being created. In most of the cases the erosion-corrosion experiments were conducted for at least 12 hours to allow for the steady state of erosion-corrosion period to take place. The sand concentration was monitored for each test and adjusted to maintain the targeted sand concentration. 62

81 Corrosion Rate (mpy) Erosion-Corrosion Experiments at 190 o F As illustrated by Figure 4-17, the LPR corrosion rate increased to higher values after injecting the sand. In this experiment, the LPR measurement of corrosion rate increased from the steady state corrosion rate of 16 mpy to 250 mpy after injecting 25 g of sand (equivalent to 1.6 wt % sand concentration). The corrosion rate then started to decrease to slightly lower values until it reached the steady-state value of 198 mpy. At the conclusion of this test, post examination of the specimen revealed that the scale had been completely removed as illustrated in the picture at the top right corner of Figure g of sand added SS E-CR= 198 mpy (7h) 100 SS CR = mpy Time (hr) Figure 4-17: Erosion-Corrosion Experiment (T=190 o F, ph 6.4, 10 ft/s) with 1.6 wt% Sand Concentration A second example of erosion corrosion experiments is presented in Figure The test conditions were as follows: 190 o F, ph 6.4, P CO 2 20 psig, 10 ft/s velocity, 15 g of sand (sand concentration 0.1 wt%). The steady state corrosion rate after scale 63

82 Corrosion Rate (mpy) Sand Concentration Corrosion Rate (mpy) formation was completed was 22 mpy. At about 24 hour into the test, 15 g of sand were injected. Following the sand injection the corrosion rate increased to a steady state value of 31 mpy after an additional 12 hours. This increase in the corrosion rate activity was a result of the scale partially eroded due to the sand particle impingements. The sand concentration was monitored throughout the erosion-corrosion experiments as shown by the inset in the top right corner of the Figure After the erosion-corrosion experiment, the scale was intact and covering the specimen surface as shown in Figure SS CR = 11 mpy SS CR= 31 mpy Time (hr) SS CR = 31 mpy Time (hr) sand added Figure 4-18: Erosion-Corrosion Test (190 o F, ph 6.4, P- CO2 20 psig, 10 ft/s velocity, 15 g of sand, Sand Concentration =0.1) 64

83 Figure 4-19: Specimen Photograph after Erosion-Corrosion Test Showing the Scale Intact More experiments were conducted at temperature 190 o F with the objective to slightly increase the erosivity by increasing sand concentration. Figure 4-20 shows the LPR measurement after full-scale formation of 70 hours. Then sand was injected at 72 hours and maintained for 9 hours at an average concentration of 0.2 wt%. Similarly the sand was sampled and adjusted throughout the erosion-corrosion test until it reached the steady state value of 31 mpy. Figure 4-21 shows a photograph of the specimen at the conclusion of the erosion-corrosion test with the scale covering the specimen surface. For this case, and similar to the previous example, the erosion rate of the scale is lower than the deposition rate of the scale at this testing condition. Based on the erosion tests conducted for iron carbonate scale and discussed above, the expected erosivity for 0.25 wt% sand concentration and 10 ft/s flow velocity is 215 mpy. The deposition rate must have been higher than this value in order to keep the scale from being removed. 65

84 Corrosion Rate (mpy) Sand Consantration (wt%) SS CR= 18 mpy E-C Rate (mpy) 0.1 Sand Cons Time (hr) sand injection E-C duration 9 Hours SS E-C = 31 mpy Figure 4-20: Erosion-Corrosion Test (190 o F, ph 6.4, P- CO2 20 psig, 10 ft/s velocity, Sand Concentration =0.25 wt%) Figure 4-21: Specimen Photograph after Erosion-Corrosion Test Showing the Scale Intact Several test of erosion-corrosion experiments were conducted at the temperature of scale forming conditions at (190 o F, 6.4 ph, 10 ft/s, 2 wt% NaCl, 1900 ppm NaHCo 3 ) and different sand concentrations. Figure 4-22 summarizes all the steady state LPR measurements of erosion-corrosion verses the different sand concentrations. As is clearly shown by the graph, the greater the sand concentration, the higher the steady- 66

85 state corrosion rate of the erosion-corrosion. It could be concluded from this graph that the corrosion rates of erosion-corrosion are behaving linearly with the erosivity of the flow. Table 4-5 provides some detailed observations about each erosion-corrosion test to help interpret the results of the tests. In all of the tests except the last one (at the right side of the table), the FeCO 3 scale was found to completely cover the specimen surface indicating that after injection of the sand the scale deposition rate was able keep pace with the erosion rate of the scale. Only in the final case was the erosion rate high enough to strip nearly all of the scale from the specimen surface. In this case the maximum deposition rate of the scale was not as high as the scale erosion rate. This data will be used to gauge and validate the E/CRC erosion-corrosion prediction model. The details of all remaining erosion corrosion tests are listed in Appendix A. 67

86 Corrosion Rate (mpy) Sand Concentration (wt%) Figure 4-22: Summary of Erosion-Corrosion 190 o F, ph 6.4, P- CO2 20 psig, 10 ft/s Velocity and Range of Sand Concentrations Table 4-5 Summery of erosion-corrosion experiments information at 190 o F, ph 6.4, P- CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations Test criteria Experiments results Corrosion rate at one hour, mpy NA Minimum Corrosion rate, mpy Corrosion rate at SS test point, mpy Sand Concentration as SS test point Erosion rate at SS test point, mpy Scale remaining, % of specimen area Erosion-Corrosion Experiments at 150 o F Similar experiments of erosion-corrosion were conducted at the same test conditions with the change of the temperature from 190 o F to 150 o F. The scale erosion resistance was verified to be lower for the case of scale formed at 150 o F as compared 68

87 with scales formed at 190 o F. Several investigators concluded that the precipitation rate of the iron carbonate scale should be lower at a lower temperature [33-36]. Several erosion-corrosion experiments were conducted at 150 o F, 10ft/s, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCo 3 at different sand concentrations. Figure 4-23 shows one example of the erosion-corrosion experiments at 150 o F where the scale was allowed to form for 48 hours to reach a steady state corrosion rate of about 12 mpy. Then sand was injected to the test section and monitored throughout the test. The overall LPR measurement of the test is shown in Figure 4-23 (a) and a magnified view of the corrosion rate with sand concentration is shown in Figure 4-23 (b). For the 150 o F temperature, there was a slow response of the LPR reading to low sand concentrations as shown in Figure 4-23 (b) after about 50 hours of testing. Sand concentration was then raised to 0.68 wt%, which registered almost instantaneously on the LPR reading by eroding some of the scale away. At the end of the test, the sand concentration was about 0.66 wt% and the LPR reading reached a steady state value of 245 mpy at 54 hours after first introducing the sand. Figure 4-24 shows the specimen after the test. The specimen photograph indicated that the majority of the scale was removed. 69

88 Corrosion Rate (mpy) Sand Concentration wt% Corrosion Rate (mpy) sand Time (hr) (a) SS CR=13 mpy H 16 H 30 H (b) LPR= SS CR= Time (hr) Figure 4-23: Erosion-Corrosion 150 o F, ph 6.24, P- CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations (a) LPR for Overall test, (b) LPR & Sand Concentrations 70

89 Figure 4-24: Specimen Photograph after Erosion-Corrosion Test Showing the Majority of Scale Removed Another example of erosion-corrosion testing at 150 o F is represented by Figure The overall LPR reading is shown in Fig (a), and a magnified-scale graph also showing sand concentration is shown in Fig (b). The sand concentration at the end of the test was measured to be 0.7 wt% and the steady state LPR reading of the corrosion rate was 285 mpy. This reading is very consistent with the previous erosioncorrosion test result having a corrosion rate measurement of 245 mpy at 0.66 wt% sand concentration. This provides some confidence about the repeatability and the accuracy of the experiment and the measurement of the corrosion rate. Similar to the previous test, the scale was found to be about 50-60% removed as shown in Figure

90 Corrosion Rate (mpy) Sand Concentration wt% Corrosion Rate (mpy) SS CR= 10 Time (hr) (a) 10g sand injection 15g sand injection (b) Figure 4-25: Erosion-Corrosion 150 o F, ph 6.24, P- CO2 20 psig, 10 ft/s Velocity and Sand Concentrations of 0.7 wt% (a) LPR for overall test, (b) LPR & Sand Concentration Measurement for Erosion-Corrosion Segment of Test Time (hr) 0.7 SS CR = 285 mpy Figure 4-26: Specimen Picture after Erosion-Corrosion Test Showing the Majority of Scale Removed 72

91 Corrosion Rate (mpy) Sand Concentration wt% Figure 4-27 shows the results of an erosion-corrosion experiment and sand monitoring at high sand concentration for test conditions (150 o F, 10ft/s, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCo 3 ). The sand concentration measured at the end of the test was 1.2 wt%. At the end of the experiment, the steady state corrosion of this testing condition was 200 mpy. Inspecting the specimen after the test revealed a removal of almost all of the scale (98%) as indicated by Figure The remaining scale was taking place in the rim at the specimen edge. The bare surface of the specimen is also showing a severe erosion-corrosion effect in the shape ridges and valleys. This is a unique observation for erosion-corrosions test conducted at these conditions since pure erosion testing of low carbon steel showed the erosive action to smooth the surface of the steel, unlike this observation CR= 160 mpy CR= 200 mpy g sand g g Time (hr) Figure 4-27: Erosion-Corrosion 150 o F, ph 6.24, P- CO2 20 psig, 10 ft/s Velocity and Sand Concentrations of 1.2 wt% 73

92 Steady State CR (mpy) Figure 4-28: Specimen Picture after Erosion-Corrosion Test Showing the Majority of Scale Removed To summarize the experimental results for the erosion-corrosion tests at 150 o F, steady state corrosion rate plotted versus sand concentration measured at the end of each test is shown in Figure Also, Table 4-6 shows some detail observations about each erosion-corrosion test to help interpret the results of the erosion-corrosion testing at 150 o F. The information obtained from scale erosion testing was used to estimate the scale erosion rate as a function of sand concentration. Details of the other erosion-corrosion test experiments are presented in the Appendix A Sand Consentration wt% Figure 4-29: Summary of Erosion-Corrosion Tests at 150 o F, ph 6.24, P- CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations 74

93 Table 4-6: Summary of Erosion-Corrosion Experiments Information at 150 o F, ph 6.24, P- CO2 20 psig, 10 ft/s Velocity and Different Sand Concentrations Test criteria Experiments results Corrosion rate at one hour, mpy Steady State Corrosion rate, mpy Corrosion rate at SS E-C test point, mpy Sand Concentration as SS E-C test point Erosion rate at SS E-C test point, mpy Scale remaining, % of specimen area NA Erosion-Corrosion of 150 o F at Low Sand Concentrations As reported earlier, the behavior of the erosion-corrosion tests at low sand concentration was unexpected as no effect could be seen on the LPR measurement. Initially, it was believed that the scale would not be removed by low flow erosivity until erosivity reached a certain threshold value. The threshold sand concentration was believed to be about 0.52 wt% in 10 ft/s direct impingement testing. Several tests were conducted at sand concentrations lower than 0.52 wt% for 24 hours without seeing any effects. However, several tests were conducted to investigate this behavior further. Two types of tests were carried out. The first was to inject sand at a low concentration after completely forming the scale (after 48 hours of scale formation) and then run the test for a longer period (1 week). The idea behind this test plan was the thought that perhaps a longer run test was needed to thin the scale enough to register a change in the corrosion rate. Figure 4-30 shows an example of these tests. The LPR measurement started to read higher corrosion rate after 90 hours of erosion-corrosion with an average sand 75

94 concentration of 0.3 wt%. This result suggests that erosion rates lower than those shown in Table 4-6 can erode through the thick scale formed at the 150 o F conditions if the test is run long enough. For the second type of test, the low concentration sand was injected at the beginning of the experiment before forming the scale. The objective was to see if a scale could even get started under these low erosivity conditions. Figure 4-31 shows the results for this test. The sand was injected after one hour of starting the experiment. The LPR measurements before sand injection were in the range of 800 mpy and after sand injection (0.35 wt% concentration) increased to more than 1100 mpy. LPR measurements then started to decrease until reaching a steady state value of 120 mpy. Inspecting the specimen after the test revealed that there was no scale on the surface of the specimen. The surface was harshly eroded-corroded with craters and other marks as shown in Figure An SEM micrograph was also taken for this specimen, which shows parts the scale and part harshly pitted surface. This test result might suggest that the scale deposition rate never exceeded the scale erosion rate. But, questions remain about why the final corrosion rate was so low when no scale was found on the specimen at test end. The only explanation of why the scale is taking this much time to show the reflection in LPR and different than behavior of the scale at 190 o F. The scale formed at 150 o F is very thick scale (18 microns) compared to scale formed at 190 o F (3 microns). So, it needed longer time to erode the scale and create porosity for the mass transfer between the metal surface and the bulk to increase corrosion activity. 76

95 Corrosion Rate (mpy) Sand Concentration wt% Corrosion Rate (mpy) Days Time (hr) (a) mpy H Time (hr) 110 H (b) (c) Figure 4-30: Erosion-Corrosion of 150 o F, 10 ft/s, ph, 6.24, P- CO2 20 psig, 2 gpm at Low Sand concentrations a) LPR for overall test, (b) LPR & Sand Concentration Measurement for Erosion-Corrosion Segment of the Test, (C) Specimen Photograph at the End of The Test. 77

96 Corrosion Rate (mpy) Sand Concanteration wt% Sand Time (hr) Figure 4-31: Erosion-Corrosion Experiment at 150 F, PH, 6.2, P- CO2 20 psig, 2 gpm, 10 ft/s by Injecting Sand at the Beginning of Test. Figure 4-32: Specimen Photograph after Erosion-Corrosion Experiment and SEM Micrograph 78

97 4.4.4 Scale Examination Post Erosion-Corrosion Tests To verify and confirm if the scale presence after erosion-corrosion tests, visual inspection was not enough. Three different methods were used to examine the specimens after the erosion-corrosion tests to verify the presence of iron carbonate scale at test end. SEM (scanning electron microscope), XRD (X-Ray Diffraction) and copper sulfate solution were used to verify the scale presence. Figure 4-33 shows an example of this process for one experiment. XRD confirmed the presence of siderite (iron carbonate) as shown in Figure 4-33 (a). SEM also was used to characterize the scale remaining thickness and showed a scale thickness of about four microns as indicated in Figure 4-33 (b). Also, a copper sulfate solution was used to paint the top surface of the specimen. The bare steel color changes to brown when exposed to copper sulfate. The iron carbonate coating shows no color change when exposed to copper sulfate solution. Painting the erosion-corrosion specimen with the copper sulfate solution confirmed of the presence of the iron carbonate scale as illustrated in Figure 4-33 (c). 79

98 (a) XRD analysis (b) Iron carbonate scale on top of specimen surface after erosion-corrosion experiments (c) Iron carbonate scale covering all the surface with few pitting shown in brown after using copper sulfate Figure 4-33: XRD, SEM, and Copper Sulfate Tests on the Specimen after Erosion- Corrosion Experiments. 4.5 Scale Porosity Measurement Scale porosity measurement was important in this research for two reasons. The first reason was to correlate the steady state corrosion rate with the porosity of the scale. If the scale is more porous, a higher corrosion rate is expected, because more mass and ion transfer is allowed through the scale pores. The second reason was to determine the scale deposition rate from experimental methods for varied environmental conditions. Deposition rates calculated using models from the literature [37-40], as discussed in 80

99 chapter 2.1.4, were not close to the deposition rates obtained from the experiments. Determination of the scale porosity was essential to understanding the differences in the scale deposition rates occurring at different temperatures. It is well-known that scale formed at lower temperature is more porous than scale formed at higher temperature [37] [40]. The deposition rate evaluation process is detailed in the following section. Determination of the exact scale porosity is not an easy task, but qualitative measurements of the relative differences between scales formed at different temperatures can be very helpful. Several attempts were conducted during this research to obtain an approximation of scale porosity differences between scales formed at different conditions. This work involved two approaches: utilization of correlations developed by different researchers; and, experimental work by using SEM and FIB Porosity Calculation The correlations developed by different researchers that were discussed in chapter were used to estimate the porosity of the scale. The three correlations used provided very different estimates of the porosity, but percentage differences between high- and low-temperature porosities may provide some insight into the matter. Two correlations (Nesic [40] & Gao [37]) estimated an increase in porosity for lower temperature. On the other hand, the model developed by Creus [39] predicted a lower porosity for the lower temperature scale (150 o F). Errors in porosity obtained from Creus s model could be attributed to the choice of anodic Tafel slope in the electrochemical measurement that is part of the Creus method. Table 4-7 summarizes the results of the porosity evaluations obtained from the different models. 81

100 Table 4-7: Scale Porosity Obtained from Different Models Porosity Model 190 O F 150 O F % Difference 1 Nesic Porosity Model Gao s Porosity Model % 3 Creus Porosity Model E % Scanning Electron Microscopy (SEM) SEM was used to evaluate and determine the differences between scales porosities in scales formed at two temperatures. Scales pre-formed at different temperatures in a submerged flow loop were used for evaluation. This is a very qualitative measure for drawing conclusions about possibly very subtle differences in the porosities of two different scales. Figure 4-34 shows a typical view of scale thickness formed at 190 o F, 10 ft/s, 6.24 ph, 2 wt% NaCl, and 1900 ppm NaHCO 3. The scale is quite compact with very few indications of small pores. In contrast, the scale formed at 150 o F, 10 ft/s, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO 3 appeared to have more and larger pores as indicated by Figure The scale formed at 190 O F showed a very low corrosion rate at the end of the test due to the good corrosion protection owing in-part to the low porosity of the scale. 82

101 Figure 4-34: SEM Micrograph of 190 o F Scale Showing a Very Compact Surface Porositie Porositie Figure 4-35: SEM Micrograph of 150 o F Scale Showing Scattered Porosity at the Surface 83

102 4.5.3 Slice and View In another attempt to quantify the scale porosity for each temperature, a new technology based on the SEM and FIB was used. This technology is called slice and view where Nano sections of scale are progressively removed by the ion beam followed by several SEM scans. Figure 4-36 illustrates the process. Figure 4-36: Slice and View Technology Process As a result of this analysis, pores in a scale formed at 150 o F are indicated in Figure The cavity is represented by the yellow shape. The original thickness of the scale was 30 microns. Total depth cut into the scale was five microns. Each slice was 10 nm thick for a total of 50 steps. Dividing the total volume of the cavities by the total volume of scale provides a porosity of this 150 o F scale of about 12 %. 84

103 Figure 4-37: Slice and View Analysis for (30 X 5 microns) Scale Formed at 150 o F, 10 ft/s, 6.24 ph, 2 wt% NaCl, 1900 ppm NaHCO 3 A similar analysis was done for the scale formed at 190 o F. No porosity was observed from several slice and view attempts as shown in Figure From this study, it could be concluded that the porosity of the 190 o F scale is less than 1%. Figure 4-38: Slice and View Analysis for Scale Formed at 190 o F, 10 ft/s, 6.4 ph, 2 wt% NaCl, and 1900 ppm NaHCO Sand Micrograph Oklahoma sand # 1 was used in the erosion and erosion-corrosion experiments. The sand is described as semi-rounded in shape and about 150 microns in average 85

104 size. In many erosion and erosion-corrosion tests, the sand circulated in the test section for many hours. A sample of new sand and used sand was examined by SEM analysis. The objective was to determine if the sand would retain its original size and shape after being used for long periods of erosion-corrosion testing. Figure 4-39 shows a comparison between the new sand and a sample of used sand after 8 days of erosioncorrosion testing, which was the longest test duration in this research. It is obvious that there is no major change in the sand particle size or shape. A few rounded corners can be observed on the used sand. (a) (b) Figure 4-39: Oklahoma Sand #1 SEM Micrograph for (a) New Sand and (B) Sand Used for 8 Days in an Erosion-Corrosion Experiment 4.7 Wall Shear Stress Computational Fluid Dynamic (CFD) was used to simulate the experimental flow condition of a direct impingement configuration. The main objective of the CFD study is to calculate the wall shear stress on the specimen surface and define the flow 86

105 impingement profile. This is very helpful for understanding the erosion and erosioncorrosion experiments and results. In addition, this analysis was needed to verify the expected erosion and corrosion profiles and to determine if the epoxy layer of the specimen would be significantly affected by the sand particle erosion. STAR-CCM+ provided by CD-Adapco was used for this CFD simulation. The wall shear stress and mass transfer are important hydrodynamic parameters for evaluating the erosion and corrosion rates. Both parameters describe the flow activities in the viscous region and diffusion boundary layer and the interaction of the flow with the solid surface. There is a direct relation between these parameters and corrosion and erosion processes. Both are used to simulate the effects of fluid on erosion and flow assisted corrosion. The wall shear stress measures the rate of momentum transfer to the wall and the mass transfer rate defines one important link in the corrosion and erosion-corrosion processes [44] Geometry and Physical Conditions The simplification of the actual direct impingement geometry to an axisymmetric geometry was used in this CFD analytical simulation. Figure 4-40 shows the axisymmetric meshing geometry representing the injection nozzle and specimen surface. The following meshes were selected for the solution in both laminar and turbulent cases: Prism Layer Mesher, Polyhedral Mesher, Surface Wrapper, and Surface Remesher. The total mesh cells resulting from the selected mesh types numbered more than 320,000 for the size of 1 mm. 87

106 Outlet Reference electrode Inlet Figure 4-40: Mesh for Axisymmetric Geometry The inlet and the outlet boundary conditions of the simulation are shown in Tables 4-8. Velocity inlet was considered for all the cases at the inlet, and pressure outlet was also considered at the outlet of the flow. Three velocity magnitudes were used (9.4, 15, & 20 m/s) in order to study the effect of the flow regime with no significant difference in the flow regime observed. Table 4-8: Inlet and Outlet Boundary Conditions for CFD Simulation Inlet condition Static Temperature Velocity Magnitude Outlet condition Velocity Inlet 93.0 C 9.4 m/s Pressure outlet Literature and experimental works for direct impingement flow showed two different flow regimes (laminar & turbulent) are expected in such cases [45], [46]. The flow regime is expected to be laminar at the stagnation point and out to a distance of (x/d= 2 where x is the distance from the center of nozzle and d is the nozzle diameter), 88

107 followed by a turbulent flow regime. Simulations were conducted considering both turbulent and laminar flow and no significant difference was observed in the results for the radial distance where the flow speed becomes maximum near the wall and the flow direction changes from axial to radial. The physical models were constructed for steady, three dimensional, liquid (constant density, segregated flow and segregated temperature. To demonstrate the effects of sand, a Lagrangian multiphase model was selected with the second phase solid with constant density. The density of the sand was made to reflect one of the sand sampling experiments. Table 4-9 shows the properties of the two phases, water and sand, that was selected for the STAR-CCM+ to match the water properties at a temperature of 93 o C. Table 4-9: Property of the Two Phases, Water and Sand Liquid Constant Density Dynamic Viscosity Specific Heat Material Properties Density Method Density Value H2O 963 kg/m^ E-4 Pa-s J/kg-K Sand Constant 2650 kg/m^ CFD Simulation Results and Literature Correlation The laminar flow region before the turbulent region starts, extends from the central axis toward the point of maximum velocity (near the wall) and minimum shear layer thickness, roughly up to a distance r/d <2 (where r is the radial distance from the center of nozzle and d is the nozzle diameter) [45]. Based on the geometry considered for this simulation, the r/d equal to 2 for a nozzle diameter (r) of 3.9 mm makes the 89

108 radial distance from the nozzle centerline at 7.8 mm. Hence the laminar flow is expected to occur between the stagnation points (center of the flow stream) to the radial distance of 7.8 mm. After 7.8, turbulent flow is expected. This is in very good agreement with the CFD analysis results (6.7 mm) shown in Figure The change in the shear stress was located at a distance of 6.7 mm. At this region, the velocity direction is changing from axial to radial as predicted by the literature [45] [46] that reduces the wall shear stress after this point. Velocity changed from axial to radial at 6.7mm Figure 4-41: Velocity Magnitude and Profile for Turbulent Flow The calculation of wall shear stress for an impinging axisymmetric jet provided by Phares, et al. [45] and Giralt and Trass [46] was used to compare with the calculated CFD results. These calculations were based on the equations Wall shear stress calculation for laminar region given by Phares: 90

109 Wall shear stress calculation for turbulent region given by Phares: Giralt and Trass calculation of turbulent shear stress: where U is the average jet speed (m/s); is density; Re is the Reynolds number; d is the inner diameter of jet nozzle (m); r is radial distance from the center of the nozzle (m). Figure 4-42 shows a comparison between shear stress values from the CFD analysis and the correlations. It is obvious that there are some differences in the shear stress values especially in the laminar region. This could be a result of the constants used in the correlations calculation, which are results of experimental values based on different testing conditions. The shear stress values from the correlation in the laminar region are observed to increase and then decrease. The transient region between laminar and turbulent of the CFD analysis is exactly matching the transition region of the correlation at a distance of 6.4 mm. This analysis gives an order-of-magnitude of the shear stress magnitude in the region of working electrode which is about Pa. This value should be compared to pipe flow values if one is attempting to correlate between these results and pipe flow results. 91

110 Wall shear Stress (Pa) Working Electrode CFD Smooth Results Phares Shear Stress Laminar flow Giralt and Trass for Turbulent flow Phares Shear Stress Turbulent flow Redial Distance (mm) Figure 4-42: Wall Shear Stress Comparisons between (CFD & Correlations) 92

111 CHAPTER 5 MODEL VALIDATION AND ENHANCEMENT 5.1 Initial Model The concept of the erosion-corrosion model is described in Figure 5-1. The erosion-corrosion model integrates the SPPS CO 2 corrosion model and the SPPS erosion model. The model uses the SPPS erosion computer program to predict the scale erosion rate in (mpy). Also, the model uses the SPPS: CO 2 corrosion program to calculate the bulk ion concentrations, mass transfer rates, bare metal corrosion rates and other data that affects the scale formation tendency and rate. The erosion-corrosion model revises several of the mass transfer equations to accommodate scale formation and computes scale formation rate. Then the model seeks the steady-state condition for which the scale erosion rate equals the scale deposition rate. For this condition, the model then predicts the CO 2 corrosion rate. For the condition for which the scale erosion rate is greater than the maximum scale deposition rate (occurring for bare metal conditions), the scale is considered to be completely removed, or to be prevented from accumulating, and the erosion-corrosion rate is determined to be equal to the summation of the erosion rate and bare metal corrosion rate. On other hand, when the maximum scale formation rate is greater than the rate of scale removal by erosion, the scale is considered to be maintained with only partial removal by erosion. In this case model, will iterate to calculate the scale thickness, deposition rate and corrosion rate at steady state condition. 93

112 Figure 5-1: Principle of E-C Model Initial Deposition Rate The initial erosion corrosion model used the Yean, et al. [35] deposition rate correlation to predict the scale formation process as given in Equation (5-1). The Arrhenius equation constants that were used for the activation energy (Ea), and the preexponential factor (A) were the original values determined by Yean et al.. The values of Ea and A were 197 kj/mol and 3.85x1029 (min -1 ), respectively. (5-1) where is the scale deposition rate in (mole/(m 2. s), is the liquid density, h bl is the Diffusion Boundary Layer Thickness in cm, [Fe 2+ ] is the iron concentration, [CO 3 2- ] is the carbonate concentration, K sp is the solubility product and K is the temperature reaction constant given by Arrhenius equation (2-56). 94

113 By using Equation (5-1) with the original Yean constants, the model s prediction for iron carbonate scale formation was much lower than scale deposition rates that were implied by the laboratory results. For the condition of (190 o F, 6.4 ph, 10 ft/s, 2 wt% NaCl, 5 ppm Fe ++ ), the maximum FeCO 3 deposition rate was predicted to be 20 mpy. But laboratory results were showing that scales at test end were found to be completely intact for erosion rates much higher that the maximum deposition rates that the model was predicting. For the second condition of interest (150 o F, 6.4 ph, 10 ft/s, 2 wt% NaCl, 5 ppm Fe ++ ), the maximum deposition rate was predicted at 0.2 mpy. Again scales were found intact for erosion rates much higher than 0.2 mpy. These results suggested that the scale deposition rates predicted by the model were too low. Table 5-1 for the 190 o F tests shows several tests for which the experiment indicated scale on the specimen at the end of the test, whereas the model predicted no scale. Only at an erosion rate of 480 mpy did the experimental results agree with the prediction. Sand Concentration Table 5-1: Initial E-C Model Prediction Vs. Experimental Data (190 o F, 6.4 ph, 10 ft/s, 2 wt% NaCl, 5 ppm Fe ++ ). Condition Experiment Model Scale Erosion Rate (mpy) CR (mpy) Scale CR (mpy) Scale Scale No scale Scale No scale Scale No Scale Scale No scale No-Scale No scale 95

114 5.2 Scale Deposition Rate Investigation The iron carbonate scale deposition process is very complex. Several researchers investigated this topic and each concluded with a different correlation for the deposition kinetics based on different experimental methodologies and conditions. However, if the methodologies are analyzed carefully the differences are expected. An attempt to understand the predictions of the different deposition rate correlations discussed in section [33-36] is presented in the following. Figure 5-2 shows differences in scale precipitation rate results at temperature 190 O F, 10 ft/s, 6.4 ph, 1900 ppm NaHCO 3, 5% Fe 2+ for bare metal corrosion where conditions are right for forming iron carbonate scale, but none has yet precipitated. As it can be noted, there are huge differences between the results of the correlations developed by Sun, Hunnik, Johnson and Tomson (J&T) and Yean. Scale Deposition Rate in mpy (am=1, T=190 O F, 10 ft/s, 6.4 ph, 1900 ppm NaHCO 3, 2 wt% NacCl, 5% Fe 2+ ) J&T Sun 44.2 Hunnik Yean 21 Figure 5-2: Scale Deposition Rate Using Different Correlations Two different approaches were used to investigate the scale deposition rate using the same experimental conditions and equipment as those used for scale formation 96

115 and erosion-corrosion experiments. The first approach was by using the corrosion rate data during scale formation and the actual measurement of the scale thickness deposited into the surface of the metal. The second approach to determine scale deposition rate was to use the erosion-corrosion test results to determine the steady-state scale deposition rates needed to match the scale erosion rates observed in the tests First Approach: Scale Deposition Rate measurement Actual Scale Thickness Measurement: One way to measure the scale deposition rate is by measuring how much scale actually deposited onto the metal surface and dividing by the time it took to put it there. The first step in this procedure is measuring the scale thickness. The total scale thickness and scale volume measured for the 150 o F tests at 48 hours of testing were microns and cm 3 respectively as discussed in Chapter 4. These figures can be contrasted with the 3-4 microns scale thickness and cm 3 total scale volume for 190 o F. Additional tests were conducted to measure how much total scale deposition after 20 hours for 150 o F and 10 hours for 190 o F. The 20 and 10 hours represent the points where is a sharp change to the corrosion rate slope as indicated by Figure 4-2 & 4-4. The scale thicknesses and volumes for tests aborted at these points where measured to be nearly the same as those measured at 48 hours for both 190 o F and 150 o F. This indicated that scale formation is nearly complete at points for which the corrosion rate slope changes abruptly. 97

116 Scale formation and thickness of 150 O F Scale formation and thickness of 150 O F Temperature and 48 Hours. Temperature and 20 Hours. Figure 5-3: Scale Thickness Measurement at 150 o F Scale formation and thickness of 190 o F Temperature and 48 Hours. Scale formation and thickness of 190 o F Temperature and 10 Hours. Figure 5-4: Scale Thickness Measurement at 190 o F Additional experiments were conducted in which the testing was terminated at 5 hours for 150 o F and 3 hours of 190 o F to provide a time frame for the beginning of scale deposition. The LPR corrosion rate measurement, photographs of the specimens after the test and SEM micrographs for these two tests are shown in the Figures 5-5 to 5-8. From the results of these experiments it was concluded that at these two points (5 98

117 Corrosion Rate (mpy) hours for 150 o F tests, and 3 hours for 190 o F tests, the scales were just beginning to deposit. A second assumption could be drawn that when the LPR graph is showing increase of corrosion rates, scale is not yet started to form. This assumption was not investigated thoroughly Time (hr) Figure 5-5: LPR Measurement and Specimen Photograph after the Test of 150 o F at 10 Hours Figure 5-6: SEM Photograph after the Test of 150 o F at 10 Hours 99

118 Corrosion Rate (mpy) Time (hr) Figure 5-7: LPR Measurement and Specimen Photograph After the Test of 190 o F at 5 Hours Figure 5-8: SEM Photographs of 190 o F at 5 Hours Based on this discussion, it has been assumed that scale formation was not occurring in the region in the time line where the corrosion rate is increasing. After reviewing several experimental results, scale formation started at about 5 hours into the test for 150 o F and 3 hours for 190 o F. To summarize this discussion, the total scale deposition process takes about 5 hours in 190 o F tests and 15 hours for 150 o F tests as indicated in Figure

119 Corrosion Rate (mpy) 15 Hours scaleeposition porcess 150 F 190F 5 Hours Time (hr) Figure 5-9: Deposition Rate Regions in the Overall Corrosion Process For Different Temperatures Scale Deposition Rate Calculation from Scale Thickness and Deposition Time: From scale formation experiments conducted at different temperatures, the scale thickness was found to be microns for 150 o F and 3-4 microns for 190 o F. As discussed in the paragraphs above, scale deposition takes place over a period of about 15 and 5 hours for 150 o F and 190 o F tests respectively. The scale thickness and the scale formation time were used to estimate the average scale deposition rate. Below Table 5-2 is showing a summary of this calculation. The total scale deposition rate for the 3 hours of corrosion experiments at 190 O F is 470 mpy and 1021 mpy for 150 o F. The average scale deposition arte for each temperature is calculated to be 155 and 75 mpy for 190 o F and 150 o F. Table 5-2: Average Scale Deposition Rate calculation 190 o F 150 o F Measured Scale thickness 3.5 microns 33 microns Time for scale formation (H) 3 13 Total Deposition Rate (mpy)

120 Corrosion Rate (mpy) Sa Concentration wt% Second Approach: Scale deposition rate calculation in E-C Using erosion-corrosion data, scale deposition rate could also be calculated by determining the minimum erosion rate that removes the scale or keeps it from forming. In erosion-corrosion experiments, the progressive increase of erosivity showed increasing removal of scale thickness. When the scale is completely removed, the deposition rate is equal to the erosion rate at this point. This approach was used to determine the scale deposition rate based on observation of the scale removal and without considering the corrosion rate. Figure 5-10 illustrates an erosion-corrosion experiment for 150 o F that was run for a long time (8 days) to be certain of reaching steady state conditions. At the end of the test, 90% from the scale was removed in response to an erosion rate of 387 mpy (0.37 wt % sand concentration). At this point the corrosion rate that was measured by LPR was 214 mpy. It was estimated that the deposition rate at this condition was about 300 mpy mpy H Time (hr) 110 H

121 Figure 5-10: E-C Experiment Conducted for 8 Days Showing Mostly Bare Metal. In addition to the experiment discussed in connection with Figure 5-10, reviewing the partial scale coverage of specimen surface can also suggest the value of sand erosivity that begins to break through to base metal. Figure 5-11 shows the percentage of iron carbonate scale coverage of the specimen surface as determined by post-test inspection of the specimen at for 150 o F tests versus scale erosion rate. It was estimated that bare metal would first appear at an erosion rate of about 300 mpy. Bare metal area continued to increase with increasing erosion rate until complete removal of scale was observed at a sand erosion rate of 1250 mpy. The values of the erosion rates were obtained from the relation presented in Chapter 4 (4.3.2 Erosion Resistance Characterization of 150 o F). The erosion rate where bare metal first shows up is considered to be equal to the maximum scale deposition rate for these environmental conditions. Hence, the maximum deposition rate at this point is equal to the sand erosion rate (300 mpy). 103

122 Specimen surface covered, % Specimen surface covered, % Scale Partialy removed Sand Erosion Rate (mpy) Figure 5-11: Specimen Surface Covered by Scale % at 150 o F A similar concept was applied for erosion-corrosion experiments at 190 o F. At this temperature, the scale was observed to be intact for the sand erosion rate up to about 250 mpy and completely removed at a sand erosion rate of about 630 mpy based on the experimental data as shown in Figure It was estimated that bare metal would start showing up at erosion rates above about 350 mpy. Therefore, the maximum scale deposition rate for the 190 o F tests would be about 350 mpy Scale Partialy Removed Sand Erosion Rate (mpy) Figure 5-12: Specimen Surface Covered by Scale, % at 190 o F 104

123 5.3 Model Modifications Scale Deposition Rate Prediction As per discussion in Section 5.2, the scale deposition rates observed in this research were much different from the deposition rates predicted by any of the models taken from the literature. The second approach of determining the scale deposition rate was adopted in this research. Based on this approach, the maximum (bare metal) deposition rates were estimated for the temperatures 190 and 150 o F to be about 350 and 300 mpy respectively. The second approach was preferred at this stage of this research because it was believed that longer tests were needed to be conducted for the erosion-corrosion experiments that created thick scales. At 150 o F erosion-corrosion tests may require longer test times to assure achieving steady state conditions. Based on these estimates of the maximum scale deposition rates, the revised model is still adopting the form of Yean s equation given in Equation (5-1) for predicting scale deposition rate but with some modification. The Arrhenius equation constants in Yean s equation were modified based on the new maximum deposition rate estimates coming out of this research Arrhenius Equation Constants The Arrhenius equation is used to show the precipitation rate as well as temperature effects in the scale deposition rate kinetics. Arrhenius equation is given in Equation (5-2). The scale deposition kinetics (nucleation and growth) is expected to be higher for the higher temperatures. Different values of Arrhenius equation s 105

124 constants were reported by different researcher to represent their experimental results and conditions. The above assumptions of the deposition rate were used to modify the maximum FeCO 3 deposition rate and Arrhenius equation constants (350 mpy at 190 o F temperature and 300 mpy for 150 o F). The revised values of A & B are and 95,532 (mol/j) or 95.5 (k mol/j). Table 5-3 shows the final values of A and B compared to those reported by other researchers. (5-2) where K r is the kinetics constant (s) -1 ; A is a pre-exponential factor and B is the activation energy for nucleation. Table 5-3: Arrhenius s Equation Constants Derived for Scale Deposition Rate Equation Activation energy B Pre-exponential factor A kj/mol 1 Johanson & Tomson [33] Van Hunnik [34] Yean [35] Sun [36] This Research Diffusion Boundary Layer Thickness, h bl The diffusion boundary layer thickness is one term in the expression of the deposition rate prediction given in Equation (5-1). This term grew out of the form of the Arrhenius published by Yean [35]. In the initial model, the value of diffusion boundary layer (h bl ) was approximated by pipe roughness 4.5 x 10-4 cm (1.8 x 10-4 inch). The value of the boundary layer thickness was assumed to be constant and the 106

125 value was not influenced by erosion-corrosion parameters. In Equation (5-1) the internal area of the piping times the thickness of the diffusion layer was meant to be the volume in the fluid within which the iron and carbonate ions languish long enough to combine and precipitate as iron carbonate. Later, the pipe roughness was used as a simpler replacement for thickness of the diffusion layer. The pipe roughness is about 45 μm, just a little over the 33 μm found for the thickness of the scales formed at 150 o F. So the pipe roughness seemed a good value to represent the thickness, h R, region next to the pipe wall in which FeCO 3 would precipitate. But, at a temperature of 190 o F, FeCO 3 scales were a mere μm thick. It seemed unreasonable to be expecting that FeCO 3 precipitation would be occurring as far from the pipe wall as 45 μm (pipe roughness). Also, several papers published recently [37], suggested that at lower values of supersaturation, i.e., (Fsat-1), crystal growth is predominant with typical large grain size, whereas at higher values of supersaturation, nucleation is predominant with smaller grain size and typically denser scales. Therefore, for this higher supersaturation situation, the height of the volume within which FeCO3 was assumed to precipitate, h R, was reduced to 1/10 th the original pipe roughness value, i.e., 4.5 μm thick, much more consistent with the μm thick scales that were occurring for these higher temperature and higher supersaturation conditions. A first attempt correlation for a value for h R for other values of (Fsat-1) is shown below in Eq. (5-3). (5-3) 107

126 5.3.3 Scale Erosion Rate Calculations The scale erosion rate is needed for the model to determine the steady state erosion-corrosion condition and then determine the value of the deposition rate, corrosion rate, and the scale condition. The erosion rate of the scale is derived from the submerged impingement scale resistance characterization discussed in Paragraphs and Also as discussed in Figure 4-14 in Paragraph 4.3.3, the scale erosion rate for the temperatures 190 and 150 o F are 5 and 15 times higher than the steel erosion rate. The SPPS erosion model can predict the steel erosion rate for different environmental conditions. 5.4 Final Model Predictions The model was modified with the changes discussed in the previous section, the result of the modified model is showing good agreement with experimental data. Figure 5-13 shows a comparison between the model and experimental data at 190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, and 1900 ppm NaHCO 3. The model is providing very good prediction for the corrosion rate of the erosion-corrosion compared to the values obtained by the experiments. Similarly Figure 5-14 is showing a comparison between new model and experimental data at 150 o F, 10 ft/s, ph 6.24, 2 wt% NaCl, and 1900 ppm NaHCO 3. The main apparent differences between the model predictions and the data are due to the fact that once the model predicts scale is removed from the surface, and then the predicted corrosion rate is the maximum value for the scale removed condition. But, the LPR data is an average value over the entire surface of the electrode and the data is influenced by regions where scale is partially attached to the surface. So 108

127 Model Prediction CR of E-C (mpy) the predicted corrosion rates appear to be higher than the LPR data for the majority of the data except for cases where, experimentally, it was confirmed that scale was totally removed. Thus, the model is predicting complete scale removal for all the cases and the predicted corrosion rate is equal to the maximum local bare metal corrosion rate. Experimental observations confirm that that the scale, in every case was partially or completely removed for all tests at 150 o F Experiment (mpy) CR of E-C Figure 5-13: E-C Comparison between New Model and Experimental Data at 190 o F, 10 ft/s, ph 6.4, 2 wt% NaCl, 1900 ppm NaHCO 3 ) 109

128 Model Prediction CR of E-C (mpy) 500 Scale Removed Experiment (mpy) CR of E-C Figure 5-14: E-C Comparison between New Model and Experimental Data at 150 o F, 10 ft/s, ph 6.24, 2 wt% NaCl, 1900 ppm NaHCO 3 ) 110

129 CHAPTER 6 SUMMARY, CONCLUSIONS, AND FUTURE WORK 6.1 Summary The combined effect of sand erosion and CO 2 corrosion on carbon steel tubing and piping has greatly influenced the design and operation of oil and gas production facilities. A mechanistic model of the competition between the growth of FeCO 3 scale through CO 2 corrosion and removal of scale by sand erosion has been implemented in a computer program for predicting erosion-corrosion rates under different environmental conditions. Models from the literature for quantifying iron carbonate scale precipitation and growth rates, and diffusion rates of cathodic reactants and corrosion product species through iron carbonate scale have been modified and integrated into an erosioncorrosion model. The erosion resistance of FeCO 3 scale erosion to solid particle erosion (erosivity) has been characterized under various environmental conditions in submerged, direct impingement flow loop experiments. Two scale were formed at different environmental conditions (temperature of 190 o F and 160 o F) were used to investigate the scale erosion resistance for each of them. However, additional erosion experiments were conducted for the mild steel and linked to the scale erosion rate to generalize the use of the iron carbonate scale erosion resistance. Results show that the erosivity of the iron carbonate 111

130 scale formed at 190 and 150 o F (ph 6.4) were about 5 and 15 times higher than bare low carbon steel, respectively. Further investigations of FeCO 3 deposition rates were conducted to understand scale deposition mechanisms for different temperatures. Based on these experiments, the scale deposition rate has been characterized and used in the model to evaluate scale thickness as a function of temperature. Also limited investigation for the scale porosity was made to determine the actual scale deposition rate. Erosion-corrosion experiments were conducted to evaluate the steady state corrosion rate of the erosion-corrosion and also the scale condition at the end of the tests for different sand concentrations. Corrosion rates were monitored by the Linear Polarization Resistance (LPR) technique. Erosion-corrosion experiments were conducted for 190 and 150 o F temperatures and a range of sand concentrations. Erosioncorrosion experiments revealed a relation between erosivity, scale deposition rate, and the corrosion component of erosion-corrosion. Both model and experiments show the corrosion part of erosion-corrosion experiments was found to be linearly proportional to erosivity at the same test conditions. Model was modified with the new prediction correlation of the scale deposition rate and scale erosion rate based on the experimental data. The ECRC computer program was updated with the new enhancement. Comparisons between experimental results to the predicted values from the erosion-corrosion model for various testing conditions showed very good prediction provided by the model. 112

131 6.2 Conclusions To understand the CO 2 erosion-corrosion mechanisms, several areas were investigated. This section is to summarize and highlight major conclusions in each area of this research Scale Formation Process The scale formation experiments in this research were conducted for different environmental conditions. The main focus was to study the temperature effect in the scale formation process. Following are major conclusions in this area: The corrosion rate measurement at the beginning of the test is higher for the higher temperature compared to the lower temperature. Also the corrosion rate at the steady state points goes to small values at the end of the tests due to the protection of the scale. It is usually observed that the steady state corrosion rate at the higher temperature is smaller than the lower temperature (190 o F and 150 o F) to be around value of 6 mpy and 12 mpy respectively. The scale formation process is almost completed at the point where the corrosion rate showed a significant change in the LPR slope. This change in the slope occurs at about 8-10 hours of starting the test of temperature 190 o F and about hours at temperature of 150 o F. The LPR probe used in this research showed very good agreement of the average corrosion rate measurement to the one calculated by the weight loss. 113

132 6.2.2 Scale Erosion Resistance Characterization Scale erosion resistance characterization was conducted for two different scales. Scale preformed at temperature 190 o F and ph 6.4 and 150 o F and ph Also to generalize the use of the scale erosion resistance for the model use, relations between the steel erosion rate and scale erosion rate was made. Following are the conclusions from the scale erosion resistance experiments: The direct impingement scale erosion experiments showed that the scale preformed at 190 o F and 150 o F are eroding faster than the mild steel by factors of 5 and 15 respectively. The scale that formed at higher temperature is more resistance than the scale formed at lower temperature. In comparison, the scale preformed at 150 o F temperature is eroding three times faster than the scale preformed at 190 o F. A 3-D profilemeter technique to measure the erosion rate was showing inconsistence results due to improper flatness of the specimens surface Scale Porosity Limited scale porosity measurement was investigated in this research to help understanding the scale deposition rate. Correlations from literatures were used to predict the scale porosity values. Also, SEM and FIB slice view techniques were used for this investigation for two different scales formed at different temperatures (150 and 190 o F). Following are the main conclusion in this area: The scale porosity increases with decreasing of the scale formation temperature. 114

133 Literature correlations showed variation in results of the scale porosity predictions. Scale porosity estimated for scale formed at 190 o F was less than 1% compared to 13% of 150 o F Scale Deposition Rate Investigation to scale deposition rates were conducted to accurately predicts the erosion-corrosion rate. Several models from literature were reviewed for this analysis which shows variations of results. Experiments were conducted to measure the scale deposition rate considering the conditions of this research and following are the highlight of the main conclusions: Total scale thickness deposited at the temperature of 190 o F for the 48 hours is almost equal to the scale thickness at the 10 hours where the LPR showed sharp change in slope at the same testing conditions. The average scale thickness deposited in both cases was about 3.5 microns. Total scale thickness deposited at the temperature of 150 o F for the 48 hours is almost equal to the scale thickness at the 20 hours where the LPR showed sharp change in slope at the same testing conditions. The average scale thickness deposited in both cases was about 33 microns. The deposition rate investigation highest peak point of the corrosion rate measurement where the LPR starts showing negative slope of both temperatures indicated that the scale formation and deposition process initiated at this point. 115

134 Using the erosion-corrosion experiments to estimate the scale deposition rate showed that the scale starts to remove at sand erosion rate of 350 and 300 mpy for 190 and 150 o F respectively. This was observed based on the fact that during erosion-corrosion process, the scale removed at the point where the scale deposition rate is equal to scale removal rate Erosion-Corrosion Experiments Erosion-corrosion experiments were conducted for two temperatures (190 and 150 o F). Scale was initially formed before the sand was injected for erosion-corrosion process. Following are the main conclusions for this area of the research: At different temperatures, the corrosion part of the erosion corrosion showed a proportional increase with the increase of the sand erosivity. The corrosion part of the erosion corrosion showed lower values than the bare metal corrosion rate at the beginning of the test for the conditions showed partial scale removal. The model was modified to account for the new deposition rate correlation s constants based on the new deposition rate estimation. Also, the value of the diffusion boundary layer thickness was modified to consider the difference scale thickness obtained for different temperature. The model is providing very good prediction for the corrosion rate of the erosion-corrosion compared to the values obtained by the experiments 116

135 6.3 Future Work Significant numbers of experiments were conducted in this research. Since several factors controlling and influencing the erosion-corrosion mechanism, this represents the need to considerer wider range of experimental conditions. Following are suggestions for future work in this area Erosion-Corrosion Experiments: To study velocity and hydrodynamic effects in to the erosion-corrosion process, it is recommended to conduct additional erosion-corrosion experiments considering different velocities. The velocity is mainly expected to affect the erosivity of the fluid. Additional tests should help to confirm the relation between the erosivity obtained from different velocity and the erosivity obtained from the sand concentration that was investigated by this research. Three different temperatures were investigated in the area of erosion-corrosion. More temperatures are suggested to be investigated for further validation and enhancement of the model. Extend the research to cover non-scale forming condition to study the effect of corrosion on erosion. Guo et al. [47] investigated the synergy between the erosion and corrosion. It was found that there was no significant effect of erosion in corrosion. However, experimental data showed important synergistic mechanisms of the corrosion-influencing erosion due to the mechanical property degradation induced by the anodic dissolution. 117

136 The corrosion parts of the erosion-corrosion for the scale-removal conditions were shown proportional relation with the fluid erosivity. The model now is considering the more conservative condition by assuming that the corrosion part of erosion corrosion is equal to the bare metal corrosion rate. It is recommended to enhance the model prediction to consider the actual value of the corrosion rate of the erosion-corrosion at non-scale forming conditions. Conducting multiphase flow erosion-corrosion data for comparison with model predictions Scale characterization More investigation for the scale deposition rate to provide a better prediction for the scale thickness at different temperature. New correlation can be developed for the current experimental conditions and configurations. Scale erosion resistance characterization can also be extended to cover different ph and velocity. A general expression for the FeCO 3 scale can be developed with reference to mild steel erosion rate and to show the effect of the temperature, velocity and ph. 118

137 BIBLIOGRAPHY 1. C. dewaard, and D. Milliams, Carbonic Acid Corrosion of Steel, Corrosion, 31,5 (1975): p C. dewaard, D. Milliams, Prediction of Carbonic Acid Corrosion in Natural Gas Pipelines, First International Conference on the Internal and External Protection of Pipes, paper F1 (Durham, UK: University of Durham, 1975). 3. C. dewaard,, U. Lotz,, and D. Milliams, Predictive Model for CO 2 Corrosion Engineering in Wet Natural Gas Pipelines, Corrosion, 47, 12 (1991): p C. dewaard, U. Lotz, and D. Dugstad, influence of Liquid Flow Velocity on CO 2 Corrosion: A Semi-Empirical Model, Corrosion/95, paper no. 128, (Houston, TX: NACE International, 1995). 5. E. Dayalan, J. Shadley, E. Rybicki, S. Shirazi, F. De Moraes, CO 2 Corrosion Prediction in Pipe Flow Under FeCO3 Scale-Forming Conditions, Corrosion/98, San Diego, CA, NACE International, L. E. Newton, Jr., R. H. Hausler (editors), CO 2 Corrosion in Oil and Gas Production - Selected Papers, Abstracts, and References (Houston, TX: National Association of Corrosion Engineers, 1984). 7. R. Hausler, H. Godard, Advances in CO 2 Corrosion, Vol. 1. (Houston, TX: National Association of Corrosion Engineers, 1984). 8. P. Burke, A. Asphahani, B. Wright, Advances in CO 2 Corrosion, Vol. 2. (Houston, TX: National Association of Corrosion Engineers, 1985). 9. K. Videm, A. Dugstad, Effect of Flow Rate, ph, Fe 2+ Concentration, and Steel Quality on The CO 2 Corrosion of Carbon Steels, Corrosion/87, paper no. 42, (Houston, TX: NACE International, 1987). 10. A. lkeda, M. Ueda, J. Vera, M. Castillo, A. Viloria, Introduction of a New Dynamic Field Tester and Preliminary Results on Flow Effects on CO 2 119

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142 Corrosion Rate (mpy) APPENDIX A DETAILS OF EROSION EXPERIMENTS Table A-1: Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 1.6 wt% Sand Concentration Test # EC-01 Test No. EC-001 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=200 o F, ph 6.58, P CO2 =20 psig, Date: 1 April 2012 Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm LPR CR-ER Reading ER F, PH, 6.58, P co2 20 psig, 64 -April SS CR = 13.5 mpy 25 g of sand added ss ECR= 198 mpy (7h) Time (hr) 124

143 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-2: Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.1 wt% Sand Concentration Test # EC-02 Test No. ER-002 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=200 o F, ph 6.58, P CO2 =20 psig, Date: 13 April 2012 Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm LPR CR-ER Reading g of sand added 100 ss ECR= 31 mpy SS CR = 11 (12 h) 0 mpy Time (hr) g of sand added Time (hr) ss ECR= 31 mpy (12 h)

144 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-3: Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.4 wt% Sand Concentration Test # EC-03 Test No. ER-003 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=190 o F, ph 6.58, P CO2 =20 psig, Date: 26 April 2012 Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm LPR CR-ER Reading Time (hr) 15 g of sand added ss ECR= 117 mpy (12 h) SS CR = 11 mpy Time (hr) Sand concentration 126

145 Corrosion Rate (mpy) Sand Consantration (wt%) Corrosion Rate (mpy) Table A-4: Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.2 wt% Sand Concentration Test # EC-04 Test No. EC-004 Test Conditions: (T=190 o F, ph 6.2, P CO2 =20 psig, 2 gpm Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Sep 30, power Time (hr) sand E-C Rate and Sand Consantration 40 E-C duration SS E-C = SS CR= sand Time (hr) 127

146 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-5: Erosion-Corrosion Experiments at (T=190 o F, ph 6.4, 10 ft/s) with 0.6 wt% Sand Concentration Test # EC-05 Test No. EC-005 Test Conditions: (T=190 o F, ph 6.2, P CO2 =20 psig, 2 gpm (15 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 3, Time (hr) SS CR= 10 E-C Rate and Sand Consantration sand E-C duration 9 SS E-C = Time (hr)

147 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-6: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.7 wt% Sand Concentration Test # EC-06 Test No. EC-006 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 30, Time (hr) 300 E-C Rate and Sand Consantration g sand SS E-C = g sand SS CR= Time (hr)

148 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-7: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.8 wt% Sand Concentration Test # EC-07 Test No. EC-007 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 13, EC F, PH, 6.24, P co2 20 psig, 2 gpm, -Oct " New loop" Time (hr) E-C Rate and Sand Consantration Sand SS E-C = 205 mpy SS CR= g Time (hr) 2 H 130

149 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-8: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.1 wt% Sand Concentration Test # EC-08 Test No. EC-008 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 20, EC F, PH, 6.24, P co2 20 psig, 2 gpm, - Oct " New loop" Time (hr) Time (hr)

150 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-9: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.1 wt% Sand Concentration Test # EC-09 Test No. EC-009 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 20, EC F, PH, 6.24, P co2 20 psig, 2 gpm, - Oct " Petrobrass" Time (hr) E-C Rate and Sand Consantration Time (hr) 132

151 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-10: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.6 wt% Sand Concentration Test # EC-011 Test No. EC-011 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Oct 20, EC F, PH, 6.24, P co2 20 psig, 2 gpm, - Nov " New loop" Time (hr) E-C Rate and Sand Consantration H 16 H 30 H LPR= SS CR= Time (hr) SS EC=

152 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-11: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.5 wt% Sand Concentration Test # EC-012 Test No. EC-012 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Nov 18, 2012 EC F, PH, 6.24, P co2 20 psig, 2 gpm, - Nov " New loop" H Time (hr) SS CE= SS CR= 18 mpy CR = Time (hr) 134

153 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-12: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.3 wt% Sand Concentration Test # EC-013 Test No. EC-013 Test Conditions: (T=150 o F, ph 6.2, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Nov 18, EC F, PH, 6.24, P co2 20 psig, 2 gpm, -Nov " Petrobrass" Sand injected 50 Velocity Increase Time (hr) H Time (hr) 95 H increase flow rate from 2 gpm to 2.7 gpm (10 to 14 ft/s)

154 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-13: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 1.0 wt% Sand Concentration EC-016 (2) Test No. Test Conditions: Solution Chemistry: Date: EC-016(2) (T=150 o F, ph 6.4, P CO2 =20 psig, 2 gpm NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm 600 EC-016 (2) F, PH, 6.24, P co2 20 psig, 2 gpm, -Dec " NewLoop" Time (hr) g sand CR= 160 mpy CR= 200 mpy Time (hr) 17 g 20 g 20 g

155 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-14: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 1.5 wt% Sand Concentration EC-018 Test No. Test Conditions: Solution Chemistry: Date: EC-018 (T=180 o F, ph 6.31, P CO2 =20 psig, 2 gpm (10 ft/s) NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm EC F, PH, 6.24, P co2 20 psig, 2 gpm, Jan " NewLoop" Time (hr) mpy mpy mpy mpy Time (hr) 137

156 Corrosion Rate (mpy) Corrosion Rate (mpy) Table A-15: Erosion-Corrosion Experiments at (T=150 o F, ph 6.24, 10 ft/s) with 0.4 wt% Sand Concentration EC-19: Test No. ER-019 Test Conditions: (T=150 o F, P CO2 =20 psig, 2 gpm (10 ft/s) Solution Chemistry: NaCl = 2 wt %, [HCO 2-3 ] initial = 1900 ppm Date: Feb 2 EC F, PH, 6.24, P co2 20 psig, 2 gpm, -Nov " NewLoop" Days Time (hr) mpy H Time (hr) 110 H

157 Sand concentration wt% APPENDIX B SCALE EROSION EXPERIMENTS Table B-1: Steel Erosion Resistance Characterization Experiment at 0.65 wt% Sand Concentration Erosion Test (ER-004) at mini-loop/petrobras Loop Test No. ER-004 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=190 o F, PCO2=20 psig, Date: 25 May 2012 Average Sand Concentration: sand wt% sample#1 Averge conc Time H ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 96 Erosion rate (mpy)

158 Sand concentration wt% Table B-2: Steel Erosion Resistance Characterization Experiment at 0.64 wt% Sand Concentration Erosion Test (ER-005) Test No. ER-005 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=150 o F, PCO2=20 psig, Date: 30 May 2012 Average Sand 0.64 Concentration: sand wt% sample#1 Averge concentration Time 30 H Erosion Rate: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 48 Erosion rate (mpy)

159 Sand concentration wt% Table B-3: Steel Erosion Resistance Characterization Experiment at 0.92 wt% Sand Concentration Erosion Test (ER-006) Test No. ER-006 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 GPM; T=150 o F, PCO2=20 psig, Date: 30 May 2012 Average Sand 0.92 Concentration: sand wt% sample#1 Averge concentration Time H Erosion Rate: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 47 Erosion rate (mpy)

160 Sand concentration wt% Table B-4: Steel Erosion Resistance Characterization Experiment at 0.8 wt% Sand Concentration Erosion Test (ER-007) at mini-loop/petrobras Loop Test No. ER-007 (mini-loop/petrobras Loop) Testing Flow rate: 2 gpm; T=190 o F, PN2=20 psig, condition: Date: 15 June 2012 Average Sand 0.77 Concentration: Time H ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 51 Erosion rate (mpy) sand wt% sample#1 Averge concentration 142

161 Sand concentration wt% Table B-5: Steel Erosion Resistance Characterization Experiment at 0.6 wt% Sand Concentration Erosion Test (ER-008) Test No. ER-008 (mini-loop/petrobras Loop) Testing condition: Flow rate: 2 gpm, V=43 ft/s; T=150 o F, Pn2=20 psig, Date: 18 June 2012 Average Sand 0.6 Concentration: Time H sand wt% sample Erosion Rate: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 48 Erosion rate (mpy)

162 Sand concentration wt% Table B-6: Steel Erosion Resistance Characterization Experiment at 2.0 wt% Sand Concentration Erosion Test (ER-009) Test No. ER-009 (mini-loop/petrobras Loop) Testing condition: Flow rate: 3 gpm, V=57 ft/s; T=190 o F, Pn2=20 psig, Date: 20 June 2012 Average Sand 2.1 Concentration: sand wt% sample#1 Averge concentration Time H 144

163 Sand concentration wt% Table B-7: Scale Erosion Resistance Characterization Experiment at 190 o F and 0.3 wt% Sand Concentrations Scale forming condition: CR-009 (1 st trail) Micro-Loop (T=200 o F, ph 6.58, PCO2=20 psig) V = 35 ft/s Scale Erosion conditions: ER-010 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.3 wt% ER-010 Sand wt % vs time Time min sand wt% sample#1 Averge concentration Scale Erosion Rate by weight: Sample weight before test (g) ER Sample weight after test (g) Metal loss (g) Time (H) Erosion rate (mpy) 106 Scale Erosion by 3-D profile: 3D profile was not done before erosion test 145

164 Sand concentration wt% Table B-8: Scale Erosion Resistance Characterization Experiment at 190 o F and 0.6 wt% Sand Concentrations Scale forming condition: CR-009 (2 nd trail) Micro-Loop (T=200 o F, ph 6.58, PCO2=20 psig) V = 35 ft/s Scale Erosion conditions: ER-011 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.59 wt% sand wt% sample#1 Averge concentration Time min Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 72 Height after erosion (micron) 59.4 Scale volume loss (cm3) Mass loss (g) Time (H) 2 Erosion rate (mpy)

165 Sand concentration wt% Table B-9: Scale Erosion Resistance Characterization Experiment at 190 o F and 1.15 wt% Sand Concentrations Scale forming condition: CR-014 Petro-brass Loop (T=190 o F, ph 6.58, PCO2=20 psig, 2 gpm) V = 42 ft/s Scale Erosion conditions: ER-012 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 1.15 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2.5 Erosion rate (mpy) Scale Erosion by 3-D profile: Height before erosion (micron) ER 57.1 Height after erosion (micron) 59.5 Scale volume loss (cm3) Mass loss (g) Time (H) 2.5 Erosion rate (mpy)

166 Sand concentration wt% Table B-10: Scale Erosion Resistance Characterization Experiment at 190 o F and 0.95 wt% Sand Concentrations Scale forming condition: CR-015 Petro-brass Loop (T=190 o F, ph 6.58, PCO2=20 psig, 2 gpm) V = 42 ft/s Scale Erosion conditions: ER-013 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.95 wt% sand wt% sample#1 Averge concentration Time min Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 3 Erosion rate (mpy) Scale Erosion by 3-D profile: Height before erosion (micron) ER 55.9 Height after erosion (micron) 58.4 Scale volume loss (cm3) Mass loss (g) Time (H) 3 Erosion rate (mpy)

167 Sand concentration wt% Table B-11: Scale Erosion Resistance Characterization Experiment at 150 o F and 0.86 wt %Sand Concentrations Scale forming condition: CR-017 Petro-brass Loop (T=150 o F, ph 6.58, PCO2=20 psig, 2 gpm) V = 10 ft/s Scale Erosion conditions: ER-014 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.86 wt% sand wt% sample#1 Averge concentration Time min Scale Erosion Rate by weight: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2 Erosion rate (mpy) Scale Erosion by 3-D profile: Height before erosion (micron) ER 69.9 Height after erosion (micron) 74.9 Scale volume loss (cm3) Mass loss (g) Time (H) 2 Erosion rate (mpy)

168 Sand concentration wt% Table B-12: Scale Erosion Resistance Characterization Experiment at 190 o F and 1.0 wt %Sand Concentrations Scale forming condition: CR-034 Petrobrass Loop (T=190 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-016 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 1 wt% sand wt% sample# Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 68.5 Height after erosion (micron) 82.1 Scale volume loss (cm3) Mass loss (g) Time (H) 2 Erosion rate (mpy)

169 Sand concentration wt% Table B-13: Scale Erosion Resistance Characterization Experiment at 150 o F and 1.0 wt %Sand Concentrations Scale forming condition: CR-035 New Loop (T=150 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-017 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 1 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 1.75 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 79.4 Height after erosion (micron) 81.1 Scale volume loss (cm3) Mass loss (g) Time (H) 1.75 Erosion rate (mpy)

170 Sand concentration wt% Table B-14: Scale Erosion Resistance Characterization Experiment at 190 o F and 1.0 wt %Sand Concentrations Scale forming condition: CR-022 Petro-brass Loop (T=190 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-018 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 1.25 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 2 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 79.7 Height after erosion (micron) 70.3 Scale volume loss (cm3) Mass loss (g) Time (H) 2 Erosion rate (mpy)

171 Sand concentration wt% Table B-15: Scale Erosion Resistance Characterization Experiment at 190 o F and 0.5 wt %Sand Concentrations Scale forming condition: CR-007 Pneumatic pump Loop (T=190 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-020 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.6 wt% sand wt% Averge con Time H Scale Erosion Rate by weight: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 1.5 Erosion rate (mpy) Scale Erosion by 3-D profile: ER Height before erosion (micron) 31.9 Height after erosion (micron) 33.9 Scale volume loss (cm3) Mass loss (g) Time (H) 1.5 Erosion rate (mpy)

172 Sand concentration wt% Table B-16: Scale Erosion Resistance Characterization Experiment at 150 o F and 0.85 wt %Sand Concentrations Scale forming condition: CR-023 New Loop (T=150 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-021 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.85 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER-CR Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 1.5 Erosion rate (mpy)

173 Sand concentration wt% Table B-17: Scale Erosion Resistance Characterization Experiment at 150 o F and 0.5 wt %Sand Concentrations Scale forming condition: CR-034 New Loop (T=150 o F, ph 6.58, PCO2=20 psig) Scale Erosion conditions: ER-022 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 0.49 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) 1 Erosion rate (mpy) 664 Scale Erosion by 3-D profile: ER Height before erosion (micron) 77.5 Height after erosion (micron) 83.5 Scale volume loss (cm3) Mass loss (g) Time (H) 1 Erosion rate (mpy)

174 Sand concentration wt% Table B-18: Scale Erosion Resistance Characterization Experiment at 150 o F and 1.6 wt %Sand Concentrations Scale Erosion conditions: ER-023 Petro-brass Loop (T=150 o F, PN2=20 psig) Avrg. Sand conc. = 1.65 wt% sand wt% sample#1 Averge concentration Time H Scale Erosion Rate by weight: ER Sample weight before test (g) Sample weight after test (g) Metal loss (g) Time (H) Erosion rate (mpy) Height before erosion (micron) ER 73.7 Height after erosion (micron) 81.3 Scale volume loss (cm3) Mass loss (g) Time (H) Erosion rate (mpy)