The Materials Research Society (MRS)
XXII INTERNATIONAL MATERIALS RESEARCH CONGRESS 2013 NACE International Congress-Mexican Section
Irene Carrillo Salgado Rio Nazas 6, Vista Hermosa, Cuernavaca, Morelos, México C.P. 62290 Tel: 777 100 09 09 Irene.carrillo@corrosionyprotección.com Ralph Bässler Unter den Eichen 87, Berlin, Germany CP12205 Tel: 00 49 30 8104 ext. 0 ralph.baessler@baam.de
Benjamín Valdez Salas Calle de la Norma S/N Elias Calles, Mexicali, Baja California, México CP 2280 Tel: 6865696284 benval@uabc.edu.mx Jorge Joaquín Cantó Ibañez Rio Nazas 6, Vista hermosa, Cuernavaca, Morelos, México C.P. 62290 Tel: 777 100 09 09 canto@corrosiónyprotección.com
Sociedad Mexicana de Materiales Cancún, México
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
CORROSION AND CREVICE CORROSION STUDY OF STAINLESS STEEL IN CO2 INJECTED BRINE FOR GEOTHERMAL APPLICATIONS Abstract In geothermal applications, the use of high-alloyed materials has been considered as a good alternative due to their great corrosion resistance and the adequate mechanical properties. Nevertheless, the corrosion behavior of those metallic materials in geothermal fluids at service conditions has in many cases not been determined. In order to investigate the sustainable resistances to corrosion in deep wells for geothermal applications have been evaluated three different metals of stainless steel with high chromium content. The study was
conducted to investigate the performance metal for geothermal industry, without consider internal corrosion protection. The tests were carried out in artificial geothermal fluid with a composition based on a baseline analysis deep well, which is saturated with CO2 and high sodium chloride content. Different chromium and nickel content in the alloys tested was a key factor to dictate the behavior of metal corrosion in the geothermal fluid, mainly the pitting and crevice corrosion effects. Finally, using electrochemical techniques of cyclic polarization, open circuit potential, amperometric and electrochemical impedance measurements we conclude the usefulness of the metal for these conditions as well as the mechanism that has, likewise these results will be considered for future construction of geothermal applications with the characteristics of the studied brine.
Keywords: Stainless Steel, pitting corrosion, crevice corrosion, geothermal fluid, CO2,
Pรกgina
2
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
Introduction Corrosion remains a major safety and reliability concern in the geothermal field industry. Over the past decades some corrosion problems have become even more serious due to changes in the energy production technology and environment. The present investigation is based in a project aims to develop the basis for the underground storage technology by injecting CO2 into a saline aquifer near the southeast of Germany, for later studies and geothermal applications. Numerous prediction models for carbon dioxide (CO2) corrosion of carbon steel and stainless steel exist 1-6. Most of these are semiempirical, while some of the more recent models are based on mechanistic descriptions of the processes underlying CO2 corrosion. Under this criterion, is necessary considering the proper selection of materials in the future to prevent different kind of corrosion as pitting and crevice corrosion under the conditions of a specific place to CO2 storage, particularly a saline aquifer consists of deep wells located in Germany. Generally martensitic steels such as 1.4021, 1.4162 and 1.4006 are widely used for oil and gas industry, where the CO2 content has always been a corrosion risk factor, under the same reason these materials are evaluated in saline conditions aquifer steadily injecting CO2 so that the solution is saturated with this gas.
CO2 is sensitive to the environment and acts depending on different conditions of temperature and partial pressure due to the pure merely harmless CO2 corrosion, however in the presence of moisture acts very aggressively. The main corrosion factors faced in this case are: • CO2 flux in wet conditions. • High temperature and high pressure. • Aquifer high salt • The water level in the aquifer can increase to the point of injection during the downtime. CO2 is readily absorbed by water and becomes carbonic acid. The principal reactions of metal contact corrosion and fluid are: 1. CO2 reaction H2O + CO2 + Fe = FeCO3 + H2 CO2 + H2O ⇔ H2CO3 2. Anodic reaction: Fe ⇒ Fe++ + 2e3. Cathodic reaction: 2HCO3- + 2e- ⇒ 2CO32- + H2 2H+ + 2e- ⇒ H2
Experimental details
Página
3
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
Electrochemical tests were conducted to examine the corrosion resistance of three different stainless steels geothermal artificial saturated CO2 fluid described in Table 1. The experiments were performed with working electrodes constructed from 1.5 x 1.5 cm, 320 sanding grit, rinsed with distilled water and acetone. Electrochemical cell of three electrode was Installed in an autoclave to maintain the temperature of 60 ° C and, known as the critical temperature for CO2, and a pressure not exceeding 15 bar of CO2, which is steadily flowed through the solution. A reference electrode Ag/AgCl and titanium counter electrode were employed. The saturated solution with CO2 changes the pH from 8.5 - 9 to 5.8 - 6.0. This point indicates to start the experiment. The Set Up is represented by Figure 1.
The conducted techniques were cyclic polarization, impedance spectroscopy and open circuit potential measurements. The same techniques were performed under crevice corrosion conditions employing a resistance synthetic cover on the half of the surface for simulating the slit.
Materials The Table 1 describes the composition fluid. The table 2 describes the composition alloy studied. Table 1. Electrolyte composition. Composition NaCl Na2SO4 · 10 H2O MgCl2 · 6 H2O CaCl2 · 2 H2O KCl KOH NaHCO3
Cations Ca2+ K+ Mg2+ Na+
mg/L 1760 430 1270 90100
5 L,g 1123 60,37 53,10 32,26 1,951 1,603 0,2373
Anions ClSO42HCO3-
1 L, g 224,6 12,074 10,62 6,452 0,3902 0,3206 0,04746
mg/L 143300 3600 40
Table 2. Working electrodes composition.
Figure 1. Electrochemical cell that simulates the conditions of deep saline aquifer wells.
Allloy
C
Si
Mn
P
S
Cr
1.4021
0.170.25
máx. 1.0
máx. 1.0
máx. 0.045
máx. 0.030
12-14
-
1.4162
0.04
1
4-6
máx. 0.04
máx. 0.015
21-22
0 0
1.4006
0.080.15
1
máx. 1.5
máx. 0.04
máx. 0.015
11.513.5
Página
4
M
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
Results Pitting potential (Epit) and re-passivation potential (Erep) were determined by cyclic polarization technique, applying a sweep 0.2 mV/s over a range potential -0.1 to 1.5 v. The most positive Erep value indicates greater resistance to localized corrosion. 1.4162
c) a)
b)
Figure 2. Cyclic polarization of the three alloys in simulated geothermal fluid. The Figure 2 shows localized corrosion process of 1.4021 and 1.4006 alloys begins about -250 mV. The E rep is about - 500 mV. In this range potential the process is metastable and prone to pits formation. When the corrosion potential (Ecorr) is lower Epit and Erep, the material is under protection. In this case, Pรกgina
5
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
the 1.4021 and 1.4006 alloys were susceptible to fluid exposure due the E corr > Epit. However the 1.4162 alloy has shown greater resistance to pitting corrosion. The Erep and Epit showed more positive values and the resulting current density is lower.
Time hrs Alloy 1.4021 -4
Figure 3. Current density – time plot of 1.4021 alloy at different potentials in a simulated geothermal fluid.
2.368x10
-4
2.105x10
-4
1.842x10
-4
1.579x10
13-P9_ca_550mV 12-P8_ca_550mV 11-P9_ca_500mV 10-P8_ca_500mV 09-P9_ca_450mV 08-P8_ca_450mV 06-P8_ca_400mV 07-P9_ca_400mV 05-P8_ca_390mV 04-P9_ca_380mV 03-P8_ca_380mV 02-P7_ca_350mV 01-P6_ca_350mV 00-P9_ca_350mV *
j, µ A cm -2
-4
1.316x10
-4
1.053x10
-5
7.895x10
-5
5.263x10
-5
2.632x10
0.000 -5
-2.632x10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time, h
In order to determine the critical potential values where corrosion process begins potentiostatic measurements were applied to analyze the current change at different potentials. The application range is calculated from the results of cyclic polarization.
3.5
Localized corrosion process of 1.4021 starts from -390mV, and there is a significant increase in the current density (Figure 3). Between -350 mV and -390 mV exhibits the metastable pitting process. The constant potential limit may be exposed until -400 mV, lower values initiates 4.0 4.5 the 5.0pits propagation. The sample can be cathodically protected with the application of voltages higher than -400 mV.
Página
6
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
8.42x10
-6
-6
4.21x10
-6
2.11x10
-6
Figure 4. Current density – time plot of 1.4006 alloy at different potentials in a simulated geothermal fluid.
j, µA cm
-2
6.32x10
Material 1.4006 -460mV P1 -460mV P2 -450mV P3 -420mV P1 -420mV P3 -400mV P1 -400mV P2
0.00
0
1
2
3
4
-5
7.368x10
-2.11x10
-6 -5
6.316x10
-4.21x10
-6
0
1
2
-5
45.263x10
3
Time, hrs -2
-5
j, µA cm
The 1.4006 alloy shows results where it is important to note that the current density points of the applied voltages potentiostatically (-460 to -420 mV) have a small difference including points in time where the current values are mixed, so it is not possible to see the current difference depending on the potential applied (Figure 4). The surface analysis showed that the localized corrosion starts at -450 mV, determined as the critical potential, but is up 400 mV when the working electrode has a significant increase in the current.
P5 -300 mV P7 -300 mV P7 -250 mV P5 -250 mV P6 -200 mV 5 P5 -200 mV P5 -190 mV
4.211x10
-5
3.158x10
-5
2.105x10
-5
1.053x10
0.000
0
1
2
3
4
Time, hours
Alloy 1.4162
Alloy 1.4006
Figure 5. Current density – time plot of 1.4162 alloy at different potentials in a simulated geothermal fluid. Página
7
5
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
The following results (Figure 6) are derived from 24 hours of exposure of open circuit potential followed by electrochemical impedance for 10 and 14 continuous cycles.
-6650 38000
0
6650 13300 19950 26600 33250 39900 46550 53200 59850 66500 73150
Sample P3
33250 28500
1 day 2.45 day 3.66 day 4.91 day 6.13 day 7.38 day 8.61 day 9.87 day 10.87 day
-Z imag , Ω * cm 2
23750 19000 14250 9500 4750 0 -6650
0
6650 13300 19950 26600 33250 39900 46550 53200 59850 66500 73150
Zreal, Ω ∗ cm
2
X Axis Title -0.35
OCP Sample 2
-0.40
E, V vs Ag/AgCl
The Figure 5 shows negative current values in the range potential from -300 mV to 200 mV. These results present a stable behavior in the time indicating corrosion free surface. A drastic current change occurs at -190 mV and sample surface shows a coloration indicating the corrosion process beginning. Under a microscope it was observed small pits that are not visible to the naked eye. The application of voltages of -300 mV and -200 mV protects cathodically the working electrode. From -190 mV voltage application, the surface is activated.
-0.45
Day1 Day2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 Day 9
-0.50
-0.55
-0.60 0
2
4
6
8
10
12
14
16
18
20
Time, h
a) Alloy 1.4021
Página
8
22
24
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
209000
Sample P5
190000 171000 152000 2
32490
Sample P1
-Z imag , Ω * cm
28880
-0.26 -0.28
25270
-0.30
114000
Sample P1
95000
-0.32 76000
21660
-0.34 57000
18050
-0.36
0 day 1.25 day 2.65 day 3.86 day 5.11 day 6.33 day 7.58 day 8.81 day 10.07 day 10.67 day 11.03 day
E, V vs Ag/AgCl
-Z imag , Ω * cm 2
### ### ### ### ### ### ### ### ### ### ### ### ### ### ###
133000
14440 10830 7220 3610 0 0
2
-0.40
19000 0
-0.42 -0.44
0
9500
19000
28500
38000
47500
57000
66500
2
-0.46
Zreal, Ω ∗ cm
-0.48 -0.50
1805 3610 5415 7220 9025 10830 12635 14440 16245 18050 19855 21660
Zreal, Ω * cm
38000
-0.38
-0.52 -0.22 0 2
4
6
8
10
12
-0.24
14
16
18
20
22
24
1.4 day 2.6 day 3.876000 day 5 day 6.2 day 7.4 day 8.6 day 9.8 day 11 day 12.2 day
26
85500
28
Time, hr
-0.26
b) Alloy 1.4006
-0.28
E, V vs Ag/AgCl
-0.30 1.25 days 2.45 days 3.66 days 4.87 days 6.08 days 7.29 days 8.25 days 9.7 days 10.91 days 12.122 days 13.13 days 14.54 days 15.75 days 16.95 days
-0.32 -0.34 -0.36 -0.38 -0.40
Sample P5
-0.42 -0.44 0
2
4
6
8
10
12
14
16
18
20
22
Time, hours
c) Alloy 1.4162
Página
9
24
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
Figure 6. Nyquist plot obtained from the impedance spectroscopy and open circuit potential plot of the three alloys in simulated geothermal fluid.
1.4021 alloy pitting was strong during the 10 cycles of OCP and EIS (Figure 6-a). The potential average was approximately -430 mV (active potential). The potential showed a stable behavior with a tendency to more negative values. The Nyquist diagram shows the typical curve of corrosion and its values of polarization resistance were low. The resistance had an average value of 20,000 ohms-cm 2; the maximum value was reached on the fourth day, indicating the formation of the passive layer by chromium presence. On the fifth day the porous layer is broken and pitting corrosion starts.
1.4006 alloy is completely affected by pitting corrosion with the formation of small deep pits over the surface. The measured depth was not greater than 140 microns. The pit showed a uniform color around, indicating the breakdown of the passive layer. The surface was very active since the first day with an initial potential of - 500 mV. This potential was shifted to positive values from the second day, approaching -390 mV but very unstable due to surface activity. The
value of Rp increases on the time, however, their values are low, about 35, 000 ohm-cm2, so the surface is greatly affected. On the tenth day the polarization resistance decreases and the open circuit potential follows negative values. 1.4162 alloy was exposed to 14 cycles, 16 days of exposure and showed a surface free of corrosion and good resistance. The average open circuit potential was -250 mV indicating greater passivity and very stable behavior during the measurement. The potential changes to positive value over time are due to the non-porous passive layer formation and the adherence remains. The Nyquist diagram indicates a more linear and diffusive process with an overall average of 100,000 ohms-cm2 during measurement. This value indicates high polarization resistance to the electrolyte. The results suggest that the high chromium content, nickel and molybdenum participate actively in the protective layer reducing the charge transfer process.
Pรกgina
10
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
Figure 7. Cyclic polarization of the three alloys in simulated geothermal fluid.
Considering the high resistance of the 1.4162 alloy and the candidate for future constructions in the geothermal field, crevice corrosion tests were conducted employing cyclic polarization and potentiostatic measurement (Figure 7).
The repasivation potential (E rep) was estimated in -245 mV Âą 10 mV. The breakdown potential (Epit) is estimated in -60 mV Âą 10 mV. Metastable pitting process comes from the -200 mV to 0.60 mV. When Erep < Ecorr < Epit the material is not resistant to pitting corrosion. When Ecorr < Erep < Epit the material is resistant to pitting corrosion. The results show that the material 1.4162 is resistant to the pitting corrosion under crevice conditions under normal conditions, because the Ecorr average is lower than Epit and Erep.
-220 mV
Crevice area
PĂĄgina
11
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
mV the current was stable and remained constant. The surface not showed pitting or crevice corrosion. These results indicate that at a more positive potential from -240 mV the surface is protected showing the highest resistance to the pitting and crevice corrosion. The principal difference of the 1.4162 with the other materials is the higher content of Cr and that the Ni and Mo are present in the composition. The Cr, Mo and Ni have tendency to act as active elements incorporating to the oxide layer and passivation the corrosion process.
Conclusions
Figure 8. Current density â&#x20AC;&#x201C; time plot of 1.4162 alloy at different potentials in a simulated geothermal fluid under crevice conditions.
The potentiostaic test results indicated a crevice corrosion process from -220 mV to more negative values. As is described In the Figure 8, at -240
In CO2-saturated brine, the Crevice 1.4021 and 1.4006 stainless corrosion effect steel alloys shown pitting corrosion. The results indicated these materials -240 mV were susceptible to localized corrosion in the studied geothermal fluid studied. The Critical pitting potentials of 1.4021 and 1.4006 alloys (390 mV and -450 mV respectively) indicated low resistant to the environment because their values were lower than the corrosion potential. When more positive potentials were applied more pits were observed. The polarization resistance increases with the time due to the formation porous layers of Fe/Cr that finally promotes localized corrosion.
PĂĄgina
12
XXII International Materials Research Congress 2013 NACE International Congress-Mexican Section
The 1.4162 alloy showed the most positive critical pitting potential (-190mV) indicating greater resistance to the localized corrosion. The lower values of the critical potential promote the pitting corrosion. The polarization resistance obtained from the electrochemical impedance spectroscopy indicated a diffusion process forming a passive film. The surface not showed pitting corrosion. The same experiments of cyclic polarization and potentiostatic measurements were carried out under crevice corrosion conditions. The results indicated high resistance to the pitting and crevice corrosion. It was noted that the high content of Cr, Ni and Mo makes a nonporous layer more stable and protective. It Is highly recommended further research with 1.4162 as a candidate material for future construction in geothermal applications under the studied conditions.
References [1] A. Pfennig1, B. Linke2, A. Kranzmann3, “Corrosion behaviour of pipe steels used at the CCS‐site Ketzin, Germany in laboratory CO2‐saturated saline aquifer CCS environmens”, mwwd‐iemes 2010 – langkaw, Federal Institute of Materials Research and Testing Report, 2010.
behaviour of 13Cr martensitic stainless steel AISI 420 and low-alloyed steel AISI 4140 exposed to saline aquifer water environment”, Air Pollution XVII, Ecology and the Environment volume 123, 2009. [3] Giese, L. B. et al: “Geochemie der Formationsfluide der Bohrung E Groß Schönebeck“ 3/90, STR02/14, Geothermie Report 02-1 (2001), 145 169 [4] Holl, H.-G. et al: “First hand Experience in a Second Hand Borehole“, International Conference, Reykjavik, Sept. 2003, S01 paper 060, 8 – 13. [5] A. Pfenniga, and R. Bäßler, “Effect of CO2 on the stability of steels with 1% and 13% Cr in saline water” Corrosion Science Volume 51, Issue 4, April 2009, Pages 931-940. [6] Yongjun Tan, Young Fwu, Kriti Bhardwaj, Stuart Bailey and Rolf Gubner “Review of Critical Issues in Carbon Dioxide Corrosion Testing and Monitoring Techniques”, NACE corrosion 2010 conference and expo, paper no. 10155, 2010.
[2] A. Pfennig & A. Kranzmann, “Influence of CO2 on the corrosion Página
13