Effect of nickel alloying on crevice corrosion resistance of stainless steels

Effect of nickel alloying on crevice corrosion resistance of stainless steels

Corrosion Science 46 (2004) 2265–2280 www.elsevier.com/locate/corsci Effect of nickel alloying on crevice corrosion resistance of stainless steels S. ...

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Corrosion Science 46 (2004) 2265–2280 www.elsevier.com/locate/corsci

Effect of nickel alloying on crevice corrosion resistance of stainless steels S. Azuma

a,*

, T. Kudo b, H. Miyuki b, M. Yamashita c, H. Uchida c

a

b

Investigation & Research Division, Sumitomo Metal Technology, Inc., 1-8 Fuso-cho, Amagasaki 660-0891, Japan Corporate Research & Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, Amagasaki 660-0891, Japan c Graduate School of Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji 671-2201, Japan Received 31 March 2003; accepted 15 January 2004 Available online 21 February 2004

Abstract The crevice corrosion behaviour of stainless steels containing 25 mass% Cr, 3 mass% Mo and various amounts of Ni was investigated in natural seawater. The results showed that ferritic steels containing nickel were more resistant to corrosion than both ferritic steels without nickel and austenitic steels. The superiority of the Ni bearing ferritic steel over the other steels was in close agreement with the depassivation pH of those steels in acidic chloride solutions. The results showed that the addition of Ni to ferritic steel was effective in decreasing the depassivation pH and the dissolution rate in acidic chloride solutions at crevices.  2004 Elsevier Ltd. All rights reserved. Keywords: A. Stainless steel; B. Polarization; C. Crevice corrosion; Passivity

1. Introduction Crevice corrosion has been one of the most serious problems when using stainless steels in chloride containing environments such as seawater. To avoid crevice corrosion, countermeasures such as structural modification, improving the environment

*

Corresponding author. Tel.: +81-6-6489-5779; fax: +81-6-6489-5799. E-mail address: [email protected] (S. Azuma).

0010-938X/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2004.01.003

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and material selection have been tried. On selecting materials with sufficient resistance to crevice corrosion in a given environment, it has been recognized that an increase in the content of alloying elements such as Cr, Mo and N (except for ferritic steels) improves crevice corrosion resistance. Stainless steels with high Cr, Mo and N content have been developed [1–5]. Bond and Dundas [6] conducted crevice corrosion tests on a range of commercial stainless steels in natural seawater and 10% ferric chloride (FeCl3 Æ 6H2 O) aqueous solution. They found that the results from both tests correlated fairly well and that the high Cr and Mo ferritic stainless steel have superior crevice corrosion resistance compared with the austenitic steels having similar Cr and Mo content. But ferritic steels with 25%Cr–2%Ni–3%Mo and 31%Cr–2%Mo were shown to be less resistant in seawater than predicted from the ferric chloride test. Other authors have also reported the superior crevice corrosion resistance of ferritic steels over austenitic steels [7–9]. Among them, Ujiro et al. [9] reported that the superiority of ferritic steels can be explained by their lower anodic current densities in acidic NaCl solutions used for testing crevice corrosion than is the case for austenitic steels. The effect of Ni on crevice corrosion, however, is not so well understood. The depassivation model has been widely accepted as the mechanism of crevice corrosion, in which the deoxygenation and the acidification of the crevice solution are essential to causing the active dissolution of the stainless steel at a crevice [10,11]. Recently, several mechanisms have been proposed, such as IR drop depassivation [12], stabilized pitting in crevice [13] and inclusion dissolution [14]. However, the classical concept of depassivation inside the crevice followed by the formation of an active–passive cell is still the standard view. The objective of this study is to investigate the effect of Ni addition on crevice corrosion and to clarify the difference in crevice corrosion behaviour between ferritic and austenitic stainless steels. A series of stainless steels containing 25% Cr and 3% Mo with a range of Ni levels was prepared in the laboratory. The resistance of the steels to crevice corrosion was evaluated by an immersion test in natural seawater and an accelerated test in ferric chloride solution in the laboratory. The effect of Ni content on crevice corrosion [resistance] is discussed based on the classical depassivation model and the polarization behaviour in acidic chloride solutions.

2. Experimental procedure 2.1. Specimens Materials employed were a series of stainless steels containing 25% Cr and 3% Mo with different Ni content. Their chemical compositions are listed in Table 1. The steels containing 0% and 4% Ni had a ferritic microstructure, and the 30% Ni steel had an austenitic microstructure. They were melted in a vacuum induction furnace and cast into 17 kg ingots. The ingots were forged, hot rolled to 7-mm thick plates, heated for 1800 s at 950 and 1100 C for the ferritic and austenitic steels respectively, followed by water quenching. All the specimens were mechanically polished with No. 600 emery paper and degreased with acetone.

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Table 1 Chemical compositions of materials employed (mass%) Steel

Ni

Cr

Mo

Microstructure

0Ni 4Ni 30Ni

0.06 3.83 29.4

24.1 24.5 24.8

2.99 2.94 2.98

Ferritic Ferritic Austenitic

C: 0.003–0.004, Si: 0.29–0.32, Mn: 0.57–0.59, P: 0.001–0.003, N: 0.001–0.004.

2.2. Immersion test in seawater The immersion test in seawater was carried out using multiple crevice assemblies as shown schematically in Fig. 1(a), based on the standard guide for crevice corrosion testing, ASTM G78. The specimen is a 50 · 50 · 3 mm plate with a 10-mm diameter hole at its center. The crevice former was a polyacetal resin washer, which had 20 teeth of 2 · 2 mm. Two of these washers were pressed onto the specimen at a torque of 5 N m with a titanium bolt and a nut, so that 20 small crevice sites were formed on each side of the specimen. The bolt was electrically insulated from the specimen using a polytetrafluoroethylene (PTFE) pipe. The specimens were immersed in fresh seawater pumped from Kainan Bay in Wakayama, Japan at room

Ti bolt and nut 20 metal/polyacetal resin crevices on each side

50mm

specimen

crevice former of polyacetal resin 3mm

50mm

(a) specimen for immersion test in natural seawater metal/metal crevice

PTFE washer 30mm

5mm

20mm

12mm

6mm

(b) specimen for immersion test in ferric chloride solution

Fig. 1. Specimens for immersion test: (a) natural seawater, (b) FeCl3 solution.

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temperature (15–30 C) for 9.5 months. The number of attacked sites and the maximum depth of crevice corrosion were measured for each specimen. 2.3. Accelerated test in ferric chloride solution A laboratory-accelerated test was conducted using ferric chloride solution based on the ASTM G48 standard test method. In the ferric chloride test, specimens of 20 · 30 · 3 mm and 12 · 30 · 3 mm plate were tightened by a bolt and a nut made of a PTFE resin as shown in Fig. 1(b). This crevice specimen was immersed in 600 ml of a 10% ferric chloride (FeCl3 Æ 6H2 O) solution. The temperature of the solution was raised from 10 C in 2.5 C steps every 24 h. After each isothermal period, the specimen was disassembled and examined visually. The critical crevice corrosion temperature (CCT) was determined as the temperature at which the crevice corrosion occurred on the metal/metal crevice or metal/PTFE crevice of the specimen. 2.4. Anodic polarization measurement In anodic polarization measurement, a specimen with an exposed area of 1 cm2 was employed. A KCl saturated calomel electrode (SCE) and a platinum sheet were used as the reference and counter electrodes, respectively. In order to enhance the corrosiveness, 10% NaCl solution was used at various pH values adjusted by sulfuric acid. The pH of the solution was measured at room temperature using a pH meter equipped with a glass electrode and reference electrode. Immediately after polishing, the specimen was immersed in a solution deaerated by Ar gas bubbling. After the measurement of the corrosion potential for 3600 s, the potential of the specimen was raised at a sweep rate of 0.33 mV/s. 2.5. Cyclic polarization measurement Cyclic polarization was conducted in order to investigate the repassivation behaviour of crevice corrosion using the metal/metal crevice specimen shown in Fig. 2. The specimen was anodically polarized at a rate of 0.17 mV/s from its corrosion potential. The potential sweep was stopped when the current reached 0.5 mA due to the occurrence of crevice corrosion. After maintaining the potential for 3600 s, the specimen was cathodically polarized at a rate of 0.083 mV/s, and then the sweep rate

15mm

30mm

metal/metal crevice

Fig. 2. Specimen with metal/metal crevice for cyclic polarization measurements.

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was reduced at 0.0016 mV/s when the current decreased to 0.05 mA. The crevice corrosion repassivation potential, Er was determined as the potential at which the anodic current disappeared on the return trip. It became very evident during the Er measurement that a quasi-potentiostatic polarization or a sufficiently slow sweep rate in the reverse scan was essential to maintain the mass transfer process at quasisteady state between the inside and the outside of the crevice [15].

3. Results 3.1. Crevice corrosion behaviour It was evident from surface observations made after the seawater immersion test that the corrosion morphology was only crevice corrosion beneath the crevice former; no pitting was observed. Fig. 3 shows the effect of Ni content on the number of

Maximum crevice corrosion depth, D (mm)

Number of attacked crevice sites, N

10

8

6

4

2

0 0.4

0.3

0.2

0.1

0 0

10

20

30

Ni content (mass %)

Fig. 3. Effect of Ni content on number of attacked crevice sites, N and maximum crevice corrosion depth, D for each specimen after immersion test in natural seawater at RT for 9.5 months. Lines express the average value.

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Critical crevice corrosion temperature (°C)

2270

50

40

30

20

10

0 0

10

20

30

Ni content (mass %)

Fig. 4. Effect of Ni content on critical crevice corrosion temperature in 10% ferric chloride solution. Temperature was raised from 10 C in 2.5 C steps every 24 h.

attacked crevice sites, N , in the total 40 crevice sites beneath the crevice former and the maximum crevice corrosion depth, D for each specimen. The 0% Ni and the 4% Ni ferritic steels showed a lower N and D than the 30% Ni austenitic steel. Among the ferritic stainless steels, the 4% Ni steel did not suffer any crevice attack. This fact indicates that 4% Ni addition into the ferritic steel is effective in improving crevice corrosion resistance in natural seawater. Fig. 4 shows the effect of Ni content on the CCT in the ferric chloride solution. The CCT decreased steadily with increasing Ni content. The lowest CCT of the austenitic 30% Ni steel was consistent with the results from the seawater immersion test and indicates the high susceptibility of the 30% Ni steel to crevice corrosion in both environments. In the ferritic steels, Ni addition showed the depressing effect in ferric chloride solution, which was in clear contrast to the results obtained in the seawater immersion test. 3.2. Anodic polarization behaviour Figs. 5–7 show the polarization behaviours at 60 C in 10% NaCl solution at various pH values. Judging from the appearance of the critical passivating current, the 0% Ni steel in Fig. 5 was in a passive state at pH 0.6 and in an active state at pH 0.5; this means that the depassivation pH, pHd of the 0% Ni was estimated to be 0.5 at 60 C. In a similar manner, as shown in Figs. 6 and 7, the pHd of 4% Ni and 30% Ni was estimated to be 0.4 and 0.6, respectively. As shown in Fig. 6, the 4% Ni steel displayed a cathodic loop current between )0.35 and )0.26 V, which suggests that there are multiple intersection points between the internal anodic polarization curve and the internal cathodic curve. Figs. 8–10 show the polarization behaviours at various temperatures in acidic 10% NaCl solution. As shown in Fig. 8, the 0% Ni

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100,000 60 °C

2

Current density (µA/cm )

10,000

1,000 pH0.4

100

pH0.5

10 pH0.6 1 -0.6

-0.4

-0.2

0

0.2

0.4

Potential (V/SCE)

Fig. 5. Anodic polarization behaviour of 0% Ni steel in 10% NaCl solution at 60 C (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

100,000 60 °C pH0.3

2

Current density (µA/cm )

10,000 cathodic loop current 1,000 pH0.4 100

10 pH0.5 1 -0.6

-0.4

-0.2

0

0.2

0.4

Potential (V/SCE)

Fig. 6. Anodic polarization behaviour of 4% Ni steel in 10% NaCl solution at 60 C (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

steel in pH 0.4 solution was passive at 30 C, and active at 40 C. The depassivation of the 0% Ni was accelerated by increase of temperature. From the polarization behaviours shown in Figs. 9 and 10 for the 4% Ni steel and the 30% Ni steel respectively, the depassivation of both steels was similarly accelerated by an increase in temperature. From these polarization behaviours as shown in Figs. 5–10, the

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S. Azuma et al. / Corrosion Science 46 (2004) 2265–2280 100,000 60 °C

Current density (µA/cm2 )

10,000

1,000

pH0.6

100

pH0.7

10 pH0.8 1 -0.6

-0.4

-0.2

0

0.2

0.4

Potential (V/SCE)

Fig. 7. Anodic polarization behaviour of 30% Ni steel in 10% NaCl solution at 60 C (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

100,000 pH0.4

2

Current density (µA/cm )

10,000

40 °C 1,000

100 30 °C 10

1 -0.6

-0.4

-0.2

0

0.2

0.4

Potential (V/SCE)

Fig. 8. Anodic polarization behaviour of 0% Ni steel in 10% NaCl solution at pH 0.4 (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

specific values were obtained, such as the passive current density Ipass , the critical passivating current density, Icrit , the corrosion potential, Ecorr and the pitting potential, Epit . Fig. 11 shows the effect of pH on the passive current density Ipass at 0.1 V vs. SCE. The Ipass of the 30% Ni austenitic steel showed less dependence on pH than the other steels. The Ipass of the 0% Ni steel was larger than those of the other steels at pH 1.

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100,000 pH0.3

Current density (µA/cm2)

10,000

60 °C cathodic loop current

1,000

100

50 °C

10 40 °C 1 -0.6

-0.4

-0.2

0

0.2

0.4

Potential (V/SCE)

Fig. 9. Anodic polarization behaviour of 4% Ni steel in 10% NaCl solution at pH 0.3 (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

100,000 pH0.6

2

Current density (µA/cm )

10,000

1,000

60 °C

100 50 °C 10 40 °C 1 -0.6

-0.4

-0.2 0 0.2 Potential (V/SCE)

0.4

Fig. 10. Anodic polarization behaviour of 30% Ni steel in 10% NaCl solution at pH 0.6 (pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

These results imply that the rate of metal dissolution in a crevice can be higher in the 0% Ni steel than in the other steels during the crevice corrosion incubation period. Depassivation at less than pH 1 was investigated at various temperatures by observing the appearance of Icrit on the anodic polarization curve. Fig. 12 summarizes the pHd obtained from the polarization measurements at various temperatures

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Passive current density, I pass at 0.1 V (µA/cm2 )

2274

30

0Ni

20

4Ni

10

30Ni 0 0

2

4

6

8

pH

Fig. 11. Effect of pH on passive current density, Ipass at 0.1 V/SCE (60 C, 10% NaCl solution, pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

0.8 30Ni

Depassivation pH, pHd

0.7 0.6

0Ni 0.5 0.4

4Ni

0.3 0.2 0.1 20

30

40

50

60

70

Temperature (°C)

Fig. 12. Effect of temperature on depassivation pH, pHd (10% NaCl, pH adjusted by sulfuric acid).

and pH. The pHd increased with increasing temperature, which indicates that the passive film was less stable at higher temperatures. The 4% Ni steel showed the lowest pHd , namely the highest stability of passivity. Fig. 13 shows the effect of pH on the pitting potential, Epit in 10% NaCl at 60 C. At near neutral pH, the pitting potentials of the Ni bearing steels were higher than

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0.7

Pitting potential, E pit (V/SCE)

0.6 4Ni

0.5

30Ni

0.4 0.3

0Ni

0.2 0.1 0 0

2

4 Solution pH

6

8

Fig. 13. Effect of pH on pitting potential, Epit (10% NaCl, 60 C, pH adjusted by sulfuric acid, sweep rate 0.33 mV/s).

Corrosion potential, E corr (V/SCE)

-0.1

10

-0.2

-0.3

-0.4

1

-0.5

-0.6

0.1 0

10

20

30

2

100

0

Critical passivating current density, Icrit (mA/cm )

that of the 0% Ni ferritic steel. In an acidic solution of pH 1, however, they decreased and became comparable to that of the 0% Ni steel. Fig. 14 shows the effect of Ni content on the Ecorr and the Icrit obtained from the anodic polarization measurements. The Ecorr increased with increasing Ni content. In contrast, the Icrit decreased with increasing Ni content.

Ni content (mass %)

Fig. 14. Effect of Ni content on corrosion potential, Ecorr and critical passivating current density, Icrit (10% NaCl, pH was the pHd of each steel. pH adjusted by sulfuric acid, sweep rate 0.33 mV/s, 60 C).

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3.3. Repassivation behaviour Fig. 15 shows the cyclic polarization behaviours of the specimens with metal/ metal crevice. It is remarkable that the anodic current decreasing behaviour in reverse scan was different between the ferritic steels and the austenitic steel as shown in Fig. 15(b). The anodic current in the reverse curve of the 30% Ni austenitic steel showed a gradual decrease with decreasing potential. For the ferritic steels, on the other hand, anodic current drastically decreased and repassivation was achieved. Since Er is the critical potential for maintaining active dissolution inside the crevice, the drastic decrease in the anodic current at Er indicates that the ferritic steels achieve  the critical current, Icrev , which is sufficient to maintain the propagation of crevice  corrosion. From Fig. 15(b), Icrev was determined to be 9 lA for the 0% Ni, 2 lA for the 4% Ni and 0.1 lA or less for the 30% Ni. The reverse polarization curve gave the repassivation potential, Er at which anodic current due to crevice corrosion diminishes on the return trip. The effect of Ni content on Er is shown in Fig. 16. The 4% Ni

100000

(a) Anodic current (µA)

10000 30Ni

0Ni

1000

4Ni

100 10 1 0.1 -0.4

-0.2

0

0.2

0.4

Potential (V/SCE) 1000

Anodic current (µA)

(b) 100

0Ni

10

30Ni 1 4Ni 0.1 -0.4

-0.3

-0.2

-0.1

Potential (V/SCE)

Fig. 15. Cyclic polarization behaviours of the specimens with metal/metal crevice; (b) is the magnification of low current part of (a) (10% NaCl, 60 C).

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Repassivation potential, E r (V/SCE)

-0.1

-0.2

-0.3

-0.4 0

10

20

30

Ni content (mass %)

Fig. 16. Effect of Ni content on repassivation potential, Er (10% NaCl, 60 C).

ferritic steel had a higher Er than the 0% Ni ferritic steel and the 30% Ni austenitic steel.

4. Discussion 4.1. Effect of Ni on initiation of crevice corrosion In a comparison of the test results for seawater immersion and ferric chloride immersion, Ni addition into ferritic steel had opposite effects on crevice corrosion resistance; the 4% Ni steel showed higher resistance in the former but less in the latter than the 0% Ni steel. This difference is discussed in relation to the electrochemical characteristics of the testing environments. Two types of passive film breakdown have been proposed, namely, pitting and depassivation [9,16,17]. According to these hypotheses, an increase in environmental corrosivity such as might be caused by higher chloride concentration, acidity, or strong oxidants favours pitting type breakdown. In the test solutions employed in this work, the ferric chloride solution demonstrated much higher corrosivity than the natural seawater. Therefore, it is considered that pitting type breakdown predominates in ferric chloride solution, while depassivation type breakdown is dominant in natural seawater. This assumption is consistent with similar tendencies observed regarding the effect of Ni content on crevice corrosion occurrence in natural seawater and on pHd . Furthermore, it explains the difference between the crevice corrosion resistance seen in seawater and that in the ferric chloride solution. In Fig. 13, the Ni containing steels showed higher pitting potential than the 0% Ni steel in neutral pH corresponding to seawater. However, the protective effect of alloying Ni was not clear at pH 1, a condition that is comparable to a 10% ferric

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chloride solution. In addition, in the seawater immersion test, only the 4% Ni ferritic steel was free from crevice corrosion; the 0% Ni steel and the 30% Ni austenitic steel suffered crevice attack as already shown in Fig. 3. These facts indicate that Ni addition into ferritic steel retards the depassivation type breakdown that occurs in seawater but this does not hold true for the pitting type breakdown that occurs in the ferric chloride solution. In Fig. 14, comparing the 0% Ni and the 4% Ni steels, it can be seen that the addition of Ni to ferritic steel increased Ecorr and decreased Icrit at pHd . The mechanism of this effect of Ni addition is yet to be clarified but is most probably associated with the electrochemical characteristic of Ni, which is a less active element than chromium and iron. It is thought that the addition of Ni to ferritic steel suppresses the anodic dissolution of the steel inside the crevice.

4.2. Effect of Ni on propagation of crevice corrosion In this section, the effect of Ni addition on the propagation of crevice corrosion is discussed in order to explain the crevice corrosion seen in the ferric chloride solution (as shown in Fig. 4) where the Ni addition decreased the CCT. In the propagation stage the following simple relation is established between the potential and the current, Eout  Ein ¼ Icrev R

ð1Þ

where Eout and Ein are the potentials of the outside and inside of the crevice respectively, Icrev the crevice corrosion current, and R the resistance between the outside and the inside.  By combining Eq. (1) and Icrev obtained from the cyclic polarization measurement, it becomes easier to understand the test results in 10% ferric chloride solution. The critical condition for the propagation of crevice corrosion is derived from Eq. (1) as  Eout  Ein > Icrev R

ð2Þ

 where Icrev is the critical current for crevice corrosion and R is constant value for a given crevice geometry and solution composition. In a highly oxidizing environment such as 10% ferric chloride solution, it can be difficult to decrease Ein because ferric ion from the bulk solution acts as a strong oxidizing agent in the crevice solution   even at a pH lower than pHd . With regard to the critical current Icrev , a larger Icrev indicates less tendency for the propagation of crevice corrosion. As shown in Fig. 15,  Icrev decreased with increasing Ni content; 9 lA for the 0% Ni, 2 lA for the 4% Ni and 0.1 lA or less for the 30% Ni. Therefore, the highest CCT of the 0% Ni ferritic  steel can be explained by the fact that it showed the largest Icrev . From the above considerations, it is thought that the enhanced crevice corrosion resistance of 0% Ni ferritic steel is exaggerated in the 10% ferric chloride solution, which is characterized by its higher oxidizing ability than natural seawater.

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5. Conclusions (1) Crevice corrosion behaviours of stainless steels containing 25% Cr, 3% Mo and various amounts of Ni were investigated by immersion tests in natural seawater and in a 10% ferric chloride solution. In the seawater immersion, 4% Ni ferritic steel showed higher resistance than 0% Ni ferritic steel and 30% Ni austenitic steel. In contrast, the CCT in 10% ferric chloride solution was steadily decreased with increasing the Ni content. (2) The anodic polarization behaviour was measured in 10% NaCl solution at various pH and temperatures. The addition of Ni into the ferritic steel reduced the depassivation pH and the active dissolution current density. The 4% Ni steel showed lower depassivation pH and higher pitting potential than both the 0% Ni ferritic steel and the 30% Ni austenitic steel. (3) The advantage of Ni containing ferritic stainless steel over the other steels in terms of crevice corrosion resistance in seawater was considered to be mainly due to its lower depassivation pH. (4) The difference between crevice corrosion in natural seawater and that in 10% ferric chloride solution was discussed. The higher CCT of the 0% Ni ferritic steel can be explained by considering Ohm’s law between the inside and the outside of a crevice together with the critical current required for the propagation of crevice corrosion. It is considered that the crevice corrosion resistance of the 0% Ni ferritic stainless steel is exaggerated in 10% ferric chloride solution.

Acknowledgements The authors thank the reviewers for their insightful suggestions, which helped to improve this paper. References [1] C.P. Dillon and Associates, Performance of Tubular Alloy Heat Exchangers in Seawater Service in the Chemical Process Industries, Material Technology Institute of the Chemical Process Industries, Inc., St. Louis, 1987, pp. 26–43. [2] S. Bernhardsson, R. Mellstroem, Rev. Iberoam. Corros. Prot. 12 (3) (1981) 27. [3] B. Wallen, M. Liljas, P. Stenvall, AVESTA 654 SMO––a new nitrogen enhanced superaustenitic stainless steel, in: H. Nordberg, J. Bj€ orklund (Eds.), Proceedings, Applications of Stainless Steel ’92, Kristianstad, Stockholm, 1992, pp. 23–32. [4] P. Gallagher, R.E. Malpas, The success and limitations of high alloy stainless steels in seawater service, in: Proceedings, CORROSION/89, NACE, New Orleans, 1989, Paper No. 113. [5] S. Azuma, K. Ogawa, H. Miyuki, T. Kudo, M. Nishi, Corrosion resistance of 28% Cr duplex stainless steel tube in hot seawater applications, in: Proceedings, International Conference on Stainless Steels, ISIJ, Chiba, 1991, pp. 133–138. [6] A.P. Bond, H.J. Dundas, Mater. Perform. 23 (7) (1984) 39. [7] R.J. Brigham, Mater. Perform. 24 (12) (1984) 44. [8] M.A. Streicher, Mater. Perform. 22 (5) (1983) 37. [9] T. Ujiro, K. Yoshida, R.W. Staehle, Corrosion 50 (1994) 953.

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