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Group 15 Connor Armstrong Abby de Alba Kyle Croft Lamees Elnihum James Johnson Slide 1 Figure 1.

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Presentation on theme: "Group 15 Connor Armstrong Abby de Alba Kyle Croft Lamees Elnihum James Johnson Slide 1 Figure 1."— Presentation transcript:

1 Group 15 Connor Armstrong Abby de Alba Kyle Croft Lamees Elnihum James Johnson Slide 1 Figure 1

2 Problem Overview When corrosion is poorly controlled, corrosion products (deposition and microbiological activity) accumulate on heat exchange surfaces and can impede heat transfer, restrict cooling water flow, constrain production, and increase energy consumption. The result can be severe localized corrosion and premature loss of capital equipment. For metallic materials of construction, corrosion control requires an integrated corrosion- management approach, which may include: Adjusting the cooling water chemistry and/or operating pH Adding biological disinfectants Selecting the appropriate corrosion inhibitors. The overall purpose is to understand corrosion and ways to monitor and inhibit it, to improve cooling water system efficiency reduce energy consumption maintain industrial equipment long-term Figure 2: Corrosion of an exposed reinforcing bar. Slide 2

3 Metallic Corrosion Metallic corrosion is an electrochemical reaction between a metal and its environment. Figure 2 shows an example of how metallic corrosion occurs. Primary corrosion reactions are: Metal oxidation at the anode o Anodic and cathodic reactions must be simultaneous and at the same rate o Fe  Fe 2+ + 2e - Oxygen reduction at the cathode o Corrosion is driven by the cathodic reduction o ½ O 2 + H 2 O + 2e -  2OH - Figure 3 Slide 3

4 Overall, oxygen is the main driving force for steel corrosion in cooling water As temperature increases the diffusion of oxygen becomes more rapid, thus at a given oxygen concentration corrosion will increase with increasing temperature Major Factors of Corrosion Figure 4 Slide 4 Figure 5

5 Corrosion Rate As shown in Figure 7, corrosion rate increases with increasing water conductivity Though all ionic species contribute to conductivity, chloride and sulfate anions are the most detrimental o Both anions accelerate corrosion in water Figure 7 Figure 6 ● Figure 6 shows how chlorides can penetrate protective films and cause pitting corrosion ● Pitting is initiated by: ○ Localized chemical or mechanical damage to the protective oxide film; water chemistry factors which can cause breakdown of a passive film are acidity, low dissolved oxygen concentrations and high concentrations of chloride (as in seawater) Slide 5

6 The corrosion rate is also affected by pH Figure 8 shows the relationship between pH and the corrosion rate of iron o In the pH range (pH<4), the iron oxide film is continually dissolved and corrosion is accelerated by the hydrogen reduction reaction: o 2H + + 2e -  H 2 o The corrosion rate over the pH range of 4–10 is relatively constant o Above pH 10, the corrosion rate is essentially diminished Figure 9 shows a corroded iron chain. Figure 8 Acidity and Corrosion Figure 9 Slide 6 Figure 10

7 A Numerical Link: Methodology/Formalism -Being able to find an equation that links conductivity to corrosion rate is very important and matlab will allow us to do this and fit the equation to the proper -Matlab will also allow us to use trial and error to find an equation that best fits the curve. -The range at which the data is displayed will also needs to be adjusted in order for the graph to be identical to the given curve -The rate of corrosion is also very important to determine product lifespan, inhibitors to use, and product reliability Slide 7 Figure 11

8 function [f1] = crrr(yee,cond) k1=1; f1=log(yee/k1*cond); end >> cond=linspace(0,10); f1=linspace(0,10); yee=2; [f1]=crrr(yee,cond); clf plot(cond,f1); xlim([0 3]) xlim([1 3]) xlim([0.8 3]) set(gca,'XTick',[]) set(gca,'YTick',[]) M-File Command Window Matlab Inputs Slide 8 Figure 12: Created by Group 15 Figure 13: Created by Group 15

9 -Through trial and error a Matlab program successfully outputted a graph that is extremely similar to the given plot of corrosion rate Vs. conductivity Matlab Plot Output Slide 9 Figure 14: Created by Group 15 Corrosion Rate Conductivity

10 Monitoring Methods Corrosion Monitoring is crucial to preventing and controlling the onset of corrosion in the system. It is important to choose methods that suit your process the best. Metal corrosion coupons Instantaneous corrosion rate meters Test heat exchangers Figure 15 Figure 16 Slide 10

11 Corrosion Coupons Simple method for monitoring qualitative and quantitative properties of corrosion. The coupon has unique advantages: Pit depths indicate pitting severity. Type/rate of corrosion tied to appearance/weight loss of coupon. However, there are disadvantages: Lower temperature than heat exchanger tubes. Corrosion rate is averaged over time. NOTE: the coupon and the system must have the same metallurgy. Water must continuously flow past coupon. Figure 17 Slide 11 Corrosion Coupon Corrosion Coupon Holder Figure 18

12 Corrosion Rate Meters Another monitoring method measures the corrosion rate at any instant in time. Electrical Resistance Method measures electrical resistance increase due to corrosion. Advantages: Aqueous and nonaqeuous compatible. Disadvantages: ● Probe deposits can cause misleading results. ● Must account for temperature fluctuation. ● Unlike coupons, pitting cannot be determined reliably. Linear Polarization Method provides instantaneous data in actual corrosion units. Maximizes reliability, simplicity and performance. Figure 19 Slide 12

13 Test Heat Exchangers Allow simulation of real corrosion on heat- transfer surfaces. Measure heat-transfer efficiency. Strengths: Measure heat-transfer efficiency and fouling tendencies. Flow rate and heat flux can be independently varied. Measures U as a function of time. Weaknesses: Limited corrosion information without destroying tubes. animation link here: Figure 20: Animation Slide 13

14 Controlling Corrosion Corrosion can be inhibited by changing: ● Metallurgy ○ Natural Resistivity ○ Alloys ● Environment ○ Adjusting water chemistry ○ Adding corrosion inhibitors Figure 21 Figure 22 Slide 14

15 o Alloys that are naturally resistant to corrosion, such as stainless steel, can be used. However, often these are too expensive to be practical. o Highly alloyed materials are more prone to localized corrosion. Figure 24 shows the corrosion potential of various methods in flowing seawater at ambient temperatures. Metallurgy Figure 24 Figure 23 Slide 15

16 Natural Resistivity of Metals to Corrosion in Water Ratings: 0=Unsuitable, 1=Poor, 2=Fair, 3=Fair to Good, 4=Good, 5=Good to Excellent, 6=Excellent Figure 25 displays the natural resistivities of various metals under wet conditions. It can be noted that Stainless Steel has a high resistivity than iron. It is also important to notice that the alloyed steel is less resistant. Figure 25: Created by Group 15 Slide 16

17 Controlling Corrosion Environment The environment can be changed in two ways: Adjusting water chemistry- oxygen can be added or removed o Vacuum deaeration- removal of oxygen using a vacuum  Impractical for open recirculating cooling systems because oxygen is continually replenished o Oxygen scavengers (more common) react with oxygen to reduce corrosion  Most common: catalyzed sodium sulfite, hydroxylamines, and ascorbic acid  Used in conjunction with an absorption inhibitor to ensure corrosion protection  2Na 2 SO 3 + O 2  2Na 2 SO 4 Figure 26 Slide 17

18 Corrosion Inhibitors Maximized throughput and increased production Improved product quality Improved overall equipment reliability Reduced equipment cleaning and replacement costs Lower overall energy cost Lower waste disposal cost Improved worker safety and environmental compliance Uninhibited Steel Corrosion Inhibited Steel Corrosion Figure 27 Figure 28 Slide 18

19 Types of Corrosion Inhibitors Anodic Corrosion Inhibitors - These inhibitors are referred to as passivators because they form a protective iron oxide layer on the metal surface rendering it passive to corrosion. ex: Nitrate and Molybate Cathodic Corrosion Inhibitors - The pH at the cathode of the corrosion cell is elevated. Cathodic,or precipitating inhibitors form compounds that are insoluble at this high pH (8.5-12), but whose precipitation can be prevented at the bulk water pH (typically 6.5-9) ex: Zinc, orthophosphate, organic phosphonates, and calcium carbonates Ineffective corrosion inhibitor due to uncontrolled conditions Excessive scaling occurs because CaCO 3 saturation cannot be adequately controlled by pH adjustment alone Figure 29 Figure 30 Slide 19

20 Copper Corrosion Inhibitors for Cooling Water Systems Copper corrosion inhibitors such as aromatic triazoles are the only copper corrosion inhibitor that have been found to be effective for cooling water applications Excessive chlorination will deactivate benzotriazole and tolytriazole and destroy the protective film on the copper surface In the presence of high chlorine concentrations absorption inhibitors are more efficient These are materials that absorb on the metal surface and provide a physical barrier between the surface and the water Figure 32: The aromatic triazoles are the only copper corrosion inhibitors effective for cooling water applications. Figure 31: Each copper-triazole molecule covers a large surface because the planes of the triazole molecule lie parallel to the metal surface. Slide 20

21 A Numerical Link to Corrosion It would be helpful to find equations that fit the curves that link corrosion rate vs. oxygen concentration at different temperatures Using Matlab, a code can be written to find equations that fit the data using trial and error with quadratic interpolation It is important to be able to extend the curves, which will allow us to have more data and we will be able to determine the corrosion rates at more Oxygen concentrations Other temperature curves could also be estimated using this matlab in matlab For a given oxygen concentration, corrosion rates increase with increasing temperature due to more rapid oxygen diffusion. Figure 33 Slide 21

22 m-file: This file contains the equations that fit the curves, which will be run in the command window. This m-file is used in the command window to output a graph and trial and error is used to estimate the curves closely Command window: The x-axis is set with the linspace function, which goes from 0 to 10. All of the temperatures are set, which are the same from figure 5 from the corrosion article. Each function is plotted and the plot is presented on the next slide. Matlab Input Files Figure 34: Created by Group 15 Figure 35: Created by Group 15 Slide 22 %m-file name and defining variables function [f1,f2,f3] = crr(temp1, temp2, temp3, o2) %Initial guesses for coefficients k1=1412; k2=2*1412; k3=3*1412; %equation for curve f1=temp1/k1*o2.^2+1.5; f2=temp2/k2*o2.^2+1.5; f3=temp3/k3*o2.^2+1.5; %program end end %setting the x-axis of the plot o2=linspace(0,10); %setting the temperature variables with the temperatures of the curve temp1=120; temp2=90; temp3=48; %bringing in the m-file function [f1,f2,f3]=crr(temp1,temp2,temp3,o2); >> clf %plotting each graph with a hold on command to plot multiple curves >> plot(o2,f1); >> hold on >> plot(o2,f2); >> plot(o2,f3);

23 Matlab Corrosion Rate vs. Oxygen Concentration Plot Oxygen Concentration Corrosion Rate Figure 36: Created by Group 15 Slide 23

24 Conclusions & Suggested Future Work We can set up an effective corrosion-management system that contributes to cooling water system reliability as long as we understand the factors that affect corrosion understand ways we can inhibit corrosion and understand ways we can monitor corrosion. Figure 38: Photograph of hinged arches and piling Slide 24 Figure 37

25 For future work, we suggest that: Equations be found and plots made for corrosion rate versus oxygen concentration, since oxygen is the main dirving force for steel corrosion in cooling water, as well as for iron. Test heat exchangers be designed to deliver corrosion information without visual observation (integrate a transducer that will numerically translate and send info digitally to another electronic device). Future Work Figure 39 Figure 40 Figure 41 Slide 25

26 References Geiger, G., & Esmacher, M. (2012). Inhibiting and monitoring corrosion. CEP, Retrieved from Chapra, S. (2011). Applied numerical methods with matlab. (3rd ed.). New York: McGraw-Hill. Callister, S. (2012). Fundamentals of Materials Science and Engineering: An Integrated Approach (4th ed.). Wiley. Singer, M., Z. Zhang, H. Wang, S. Nes˘ic, and D. Hinkson. "CO2 Top-of-the-Line Corrosion in Presence of Acetic Acid: A Parametric Study." (n.d.): n. pag. Web. Retrieved from Figure 42 Slide 26

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