Chapter Chapter ---- IIIIIIIIIIIIshodhganga.inflibnet.ac.in/bitstream/10603/11290/8/08_chapter...

57

Chapter Chapter Chapter Chapter ---- IIIIIIIIIIII

Corrosion BehavioCorrosion BehavioCorrosion BehavioCorrosion Behaviouuuur of Ironr of Ironr of Ironr of Iron----

base Alloys in Presence of base Alloys in Presence of base Alloys in Presence of base Alloys in Presence of

Dissolved CopperDissolved CopperDissolved CopperDissolved Copper

66

3.1 RESULTS

3.1.1 Immersion Tests (Weight Loss Measurements)

The corrosion rates of mild steel, SS 304L and SS 316L in absence and presence

of Cu ions under different experimental parameters namely; Cu ion concentration,

pH, flow condition and dissolved oxygen, as obtained by weight loss

measurement technique are given in Table 3.1-3.12. The results for mild steel, SS

304L and SS 316L are summarized separately.

Mild steel

Table 3.1-3.4 show the effect of Cu ions on the corrosion rate of mild steel in both

distilled water and artificial seawater at different pH at 250C. Under aerated static

condition, in absence of Cu ions, the corrosion rate of mild steel in both distilled

water (pH 6.5 and 8.5) and artificial seawater (pH 8.2) is almost identical and a

change in aqueous medium does not appear to significantly affect the corrosion

rate. Also the effect of exposure period has only negligible effect on the corrosion

rate of mild steel. Under aerated dynamic condition there is a large increase in

corrosion rate and also a change in aqueous medium has pronounced effect on the

corrosion rate; the corrosion rate in artificial seawater being higher than in

distilled water. However, under deaerated static condition, though the corrosion

rate is quite low in comparison to aerated condition but change in pH or aqueous

medium does not significantly affect the corrosion rate. Considering the effect of

dissolved Cu ions on the corrosion rate of mild steel. In distilled water, under

aerated static condition there is no appreciable effect of Cu on the corrosion rate

of mild steel except at 100ppm where a lowering in corrosion rate is observed.

The decrease in corrosion rate at 100 ppm Cu is more appreciable at pH 6.5 and

67

8.5. The effect of exposure period also influences the corrosion rate of mild steel.

An increase in exposure period causes a substantial lowering in pH. Again the

lowering in corrosion rate with increasing exposure period is more pronounced at

pH 6.5 and 8.5. Under aerated dynamic condition, except at very low

concentration of 100ppb and 1ppm, the presence of Cu causes a lowering in

corrosion rate. Under deaerated static condition, the corrosion rate of mild steel

does not appear to be significantly affected by the presence of Cu ions except at

very high concentration (100 ppm). In distilled water at pH 6.5 and 8.5, in

presence of 100 ppm Cu the corrosion rate of mild steel is zero. Considering the

effect of Cu ions in artificial seawater. In presence of oxygen the corrosion rate of

mild steel increases slightly under both static and dynamic condition. The effect of

exposure period on the corrosion rate is also appeared to be negligible. However,

under deaerated static condition, the corrosion rate is only slightly affected in

presence of Cu ions.

SS 304L

Under experimental conditions, SS 304L is unaffected in distilled and artificial

seawater under both aerated and deaerated conditions. In general, there is

negligible effect of Cu on the corrosion rate of SS 304L at a pH range between 4-

8.2 for an immersion period of 720 hrs, 4320 hrs and 8760 hrs in both distilled and

artificial seawater as shown in Tables 3.5-3.8

SS 316 L

Tables 3.9-3.12 show the effect of Cu ions on the corrosion rate of SS 316L in

both distilled water and artificial seawater at different pH at 250C. The results are

obtained under static (both aerated and deaerated) condition. Under aerated static

68

condition the periods of immersion were 720 hrs, 4320 hrs and 8760 hrs durations,

whereas for deaerated static condition period of immersion was only 24 hrs. In

general, there is negligible effect of Cu ions on the corrosion rate of 316L in both

distilled water and artificial seawater.

3.1.2 Solvent Analysis of Iron Ions

The corrosion rate of mild steel in distilled water and artificial seawater was also

measured by determining the total iron ions entered into the test solution during

the course of immersion. The corrosion rates as obtained by solvent analysis are

consistent with corrosion rates determined by weight loss measurements (Table

3.1-3.4). The iron analysis in the test solutions were also performed for SS 304L

and SS 316L immersed in distilled water and artificial seawater. The results show

negligible amount of iron content in the solution (Table 3.5-3.8 and Table 3.9-

3.12).

3.1.3 Monitoring of pH

Mild steel

The pH of the test solutions during the entire period of immersion was measured

on the daily basis. Figures 3.1-3.4 show plots of pH vs. exposure period for mild

steel immersed in distilled water (pH 4.0, 6.5 and 8.5) and in artificial seawater

(pH 8.2). In case of mild steel immersed in distilled water containing varying

concentration of Cu, except for the solution of pH 4.0 where a slight increase in

pH during initial period of immersion was observed, there is no significant change

in pH in the test solution maintained at pH 6.5 and 8.5.

SS 304L

69

Figures 3.5-3.8 show plots of pH vs. exposure period for SS 304L immersed in

distilled water at pH 4.0, 6.5 and 8.5. The results did not show an appreciable

change in pH over the entire period of immersion of 30 days. The pH of test

solution was also monitored for SS 304L immersed in artificial seawater at pH

8.2. No appreciable change in pH is observed during the entire period of

immersion of one month (Figure 3.27).

SS 316L

In case of SS 316L the pH of the test solutions was measured for an immersion

period of 30 days. In distilled water there was no appreciable change in pH in the

solutions maintained at pH 4.0, 6.5 and 8.5. In artificial seawater the pH of the

test solution remained almost constant during the entire period of immersion

(Figure 3.9-3.12).

3.1.4 Estimation of Cu in the Test Solution

Mild steel

The concentration of Cu present into the test solutions estimated after the

completion of immersion is shown in Table 3.13-3.16. In case of mild steel

immersed in distilled water and artificial seawater the following behaviors are

distinctly observed:

• In the solutions containing lower concentration of Cu (up to 10 ppm) no

Cu was detected at the end of immersion.

• With Cu concentration exceeding 10 ppm appreciable amount of Cu

remained into the solutions at the end of immersion. The amount of Cu

increased with increasing pH and decreased with increasing exposure

period.

70

SS 304L

The concentration of Cu ions present into the test solutions estimated after the

completion of immersion is shown in Table 3.17-3.20. The results clearly show

that the Cu ions added into the test solution remained almost unchanged.

SS 316L

In case 316L immersed in distilled water and artificial seawater nearly all the Cu

ions added into the test solution remained unchanged and estimated by atomic

absorption spectrophotometer (Table 3.21-3.24)

3.1.5 Electrochemical Studies:

3.1.5.1 Free corrosion potential (Ecorr) measurements

Figure 3.13- 3.24 show Ecorr vs. time plots for mild steel, SS 304L and SS 316L

immersed in distilled water and artificial seawater in absence and presence of

different concentration of Cu ions. The results for each alloy are summarized

separately.

Mild steel

The potential of mild steel immersed in distilled water and artificial seawater in

absence and presence of 100ppb, 1ppm and 100 ppm of Cu was monitored for the

immersion period of one month and the typical Ecorr vs. time plots are shown in

Figure 3.13-3.16. In distilled water at acidic pH, in absence of Cu, the initial

potential of mild steel is -766mv; this is followed by a decrease in negative

potential till a near steady state was attained at about -650mv. In presence of Cu

ions, a significant ennoblement in Ecorr value is observed. The noble shift in Ecorr is

71

more pronounced in the presence of 100ppm Cu ions (Figure 3.13). In distilled

water at pH 6.5 the steady potential of mild steel is -660mV. In presence of Cu ion

a positive shift in Ecorr is observed at all the three concentration selected for the

study. The noble potential is maintained over an entire period of immersion of one

month (Figure 3.14). In distilled water at pH 8.5, except at Cu concentration of

100 ppb, a noble shift in Ecorr is observed in presence of other Cu ion

concentrations (Figure 3.15). In artificial seawater the stable potential of mild

steel is around -800mv. The addition of Cu ions shifts the Ecorr in more noble

direction. Again ennoblement in Ecorr is more pronounced at 100 ppm of Cu

(Figure 3.16).

SS 304L

Figure 3.17-3.20 show potential vs time plots for SS 304L in distilled water and

artificial seawater containing 1ppm, 40ppm and 100ppm Cu ions concentration.

The potential of SS 304L is monitored on daily basis for the immersion period of

30 days. A noble shift in Ecorr is observed on adding Cu ions in the aqueous

medium.

SS 316L

The potential vs. time plots for SS 316L in distilled water and artificial seawater

are shown in Figures 3.21-3.24. In general, the presence of Cu ions shifts the Ecorr

of SS 316L to a more noble direction in both the aqueous medium under

investigation. The ennoblement in Ecorr is more pronounced at 100 ppm of Cu ions

concentration.

72

3.1.5.2 Potentiodynamic polarization measurements

Mild steel

The potentiodynamic polarization curves for mild steel in distilled water and

artificial seawater in absence and presence of Cu ions is shown in Figures 3.25-

3.28. The values of Ecorr and Icorr as obtained from these curves are shown in Table

3.25. For mild steel immersed in distilled water, at acidic and near neutral pH, an

increase in Cu ion concentration causes a substantial increase in Icorr and hence the

corrosion rate (Figure 3.25 and 3.26). However, at pH 8.5 a reverse trend is

obtained, on increasing Cu ion concentration lowering in Icorr is observed (Figure

3.27). In artificial seawater, the corrosion rate though increases on increasing Cu

ion concentration but the values of Ecorr remained constant (Figure 3.28).

SS 304L

In case of SS 304L the presence of Cu ions in the aqueous medium causes a

significant positive shift in Ecorr values. The positive shifting in Ecorr is more

distinct at 100 ppm of Cu (Figure 3.29-3.31). However, in general, the corrosion

rate of SS 304L appears to be unaffected due to the presence of Cu ions. . The

electrochemical parameters such as Ecorr and Icorr as obtained from these curves are

shown in Table 3.26.

3.1.6 Scanning Electron Microscopic (SEM) and-Energy Dispersive X-Ray

Analysis (EDAX) Studies

The surface morphology of the mild steel samples before and after immersion in

distilled water and artificial seawater in presence and absence of Cu ions was

studied and the photomicrographs are shown in Figures 3.32-3.33. The surface

morphology of the sample before immersion in aqueous solution shows a surface

73

which is free from any noticeable defects such as cracks and pits. The marks on

the surface are the streaks made during polishing with emery papers (Figure

3.32a). The surface morphology of mild steel samples analyzed after one month

immersion in distilled water in absence and presence of 100ppm Cu ions is shown

in Figure 3.32 b and 3.32 c, respectively. The SEM micrographs did not show any

evidence of localized attack in presence of Cu ions. The surface morphology of

steel samples after one month immersion in artificial seawater in absence and

presence of 100ppm Cu ions is shown in Figure 3.32d and 3.32e. The

photomicrographs did not show the presence of pits on the surface and clearly

indicated the features of uniform corrosion. EDAX analysis of mild steel samples

immersed in distilled water, in presence of 1 and 100 ppm of Cu ions is shown in

Figure 3.33a and 3.33b, respectively. In presence of 100ppm Cu ions the surface

analysis showed Fe and significant concentration of Cu. However, in presence of

1 ppm Cu ions only Fe was found to be present on the surface. The results clearly

indicate that in presence of 100 ppm of Cu ions an appreciable amount of copper

was reduced and deposited on steel surface thereby minimizing the corrosion rate

of mild steel.

3.2 DISCUSSION

The effect of dissolved Cu ions on corrosion behavior of mild steel, SS 304L and

SS 316L in both distilled and artificial seawater was studied at room temperature

under different experimental conditions using weight loss and electrochemical

techniques. The experimental conditions taken into account are nature of aqueous

medium, Cu ion concentration, pH, flow conditions and dissolved oxygen. The

influence of different environmental variables such as pH, flow velocity, presence

74

of oxidizers, etc on the corrosion rate of metals is quite complex and depends

upon the characteristics of metal and environment to which it is exposed [14]. For

mild steel corrosion there is a complex dependence of corrosion rate on pH. In

near neutral pH range (5< pH<9) the direct role of pH on the corrosion rate of

steel has not been established [164]. In aerated solutions, under static condition, in

near neutral pH range the major reactions controlling corrosion process is the

reduction of dissolved O2 and other oxidizers, if any, present into the solution.

Further, the corrosion processes that are controlled by activation polarization the

dynamic condition (solution agitation) have no effect on the corrosion rate.

However, if the corrosion process is under cathodic diffusion control, the dynamic

condition increases the corrosion rate.

Considering the variation in the pH of the test solution (Figure 3.20-3.31)

monitored during the 30 days of immersion. Except the pH of the solution

maintained at 4 which increased to a value of approximately 5 on the first day of

immersion, in general, the pH of the solutions was found to vary between 5 and

8.5. The increase in the pH of the test solution maintained at 4 to 5 is due to the

increase in OH- ion concentration as a result of the reduction of H+ ions. The

higher corrosion rate of mild steel at pH 4 is accounted to the combined reduction

reaction involving the reduction of both H+ ions and oxygen. Considering the

present investigation, under static condition at room temperature, except at pH 4

the selected pH for the study is unlikely to affect the corrosion rate of mild steel.

A variation in the corrosion rate of mild steel is expected to be caused by the

presence of Cu ions present into the solution, dissolved O2 and also the solution

composition. Under dynamic conditions, in addition to the above factors, the

75

amount of solution agitation is also likely to influence the corrosion rate. For mild

steel immersed in distilled water, the corrosion process under the experimental

conditions is controlled by cathodic diffusion and the dynamic condition is

expected to cause an increase in corrosion rate. The result of immersion in

absence of Cu, show a large increase in corrosion rate of mild steel under dynamic

condition. In presence of Cu ions the corrosion process is reversed and a

decrease in corrosion rate is observed. Under static condition, a lower

concentration of Cu (< 20 ppm) causes a slight increase in the corrosion rate.

However, as the Cu concentration is increased in the solution a decreasing trend in

the corrosion rate is observed. An increase in the corrosion rate at lower

concentration of Cu is attributed to the additional cathodic reaction involving the

reduction of Cu ions in addition to the reduction of the dissolved oxygen. A

decrease in the corrosion rate with increasing Cu concentration may be due to the

deposition of reduced Cu on the steel surface which forms a protective barrier

against further oxidation of steel. In presence of oxygen and Cu2+ the redox

reaction taking place at the steel surface may be written as follows:

Anodic reaction: Fe → Fe2+ + 2e− (3.1)

Cathodic reaction: 1/2O2 + H2O + 2e

− → 2OH

− (3.2)

Cu2+ + 2e− → Cu (3.3)

Since the electrode potential of Cu [ECu2+

/Cu (0.340V)] is greater than electrode

potential of Fe [EFe2+

/Fe (-0.440V)] the film protected the steel efficiently and

caused a decrease in corrosion rate. When Cu concentration reached to a certain

value, the above reaction moved forcefully from left to right, and a greater amount

of Cu metal is formed on the steel surface [165]. As a result, the Cu film thickened

76

quickly and a part of the film is detached from the steel surface. Some particulates

of Cu were observed in the solutions containing higher concentrations of Cu.

Further, a good amount of Cu ions do not participate in the reduction reaction and

remained present into the solutions. The estimation of large amount of Cu ions in

the test solutions at the end of the immersion supports the above observation. The

amount of Cu estimated by AAS decreased with increasing exposure period. At

highest concentration of Cu the value of estimated Cu was lowest which further

supports the lower corrosion rates at 100 ppm of Cu. At lower conc. of Cu ions the

formation of a protective barrier is unlikely, this may increase the corrosion rate

by accelerating the anodic reaction and forming tiny galvanic cells on the steel

surface. Under dynamic condition, the corrosion rate of mild steel is controlled by

cathodic diffusion and as a consequence a large increase in corrosion rate is

noticed in presence and absence of Cu ions. The observed decrease in the

corrosion rate in presence of Cu ions is attributed to the formation of a stable

passive film on the steel surface. Under dynamic condition there appears to be a

competition between oxygen and Cu ions and the passive film formed at the

substrate is more stable due to the availability of enough oxygen at the

steel/solution interface. The observed increase in corrosion rate of mild steel in

artificial seawater under dynamic condition is due to the absence of passive film

on the substrate. Considering the effect of dissolved oxygen on the corrosion rate

of mild steel. Under deaerated condition the corrosion rates of mild steel is

considerably lowered in both the aqueous medium. This is attributed to the

absence of cathodic reaction involving the reduction of oxygen. The only cathodic

reaction occurring under such condition is the reduction of Cu ions. In presence of

77

100 ppm of Cu sufficient amount of Cu ions are reduced to form a perfect barrier

and corrosion process is even completely stopped. Considering the results of

immersion for SS 304L and SS 316L in both distilled and artificial seawater there

is no effect of Cu on the corrosion rate. The observed behavior is due to the

absence of anodic reactions as SS 304L and SS 316L remained unaffected in both

distilled water and artificial seawater. Considering the AAS data for SS 304L and

SS 316L in both distilled water and artificial seawater, the concentration of Cu in

the solutions remain almost unchanged. The observed behavior is attributed to the

absence of anodic reaction as both SS 304L and SS 316L remained unaffected in

the test solutions. The results of corrosion rate as estimated by

spectrophotometric determination of iron ions entered into the test solutions is

consistent with the results obtained by the weight loss measurements.

The results of immersion tests find support from free corrosion potential

measurements. In presence of higher concentration of Cu there is significant

ennoblement in the Ecorr of mild steel, SS 304L and SS 316L suggesting the

protective role of Cu. Considering the results of potentiodynamic polarization

measurements, in general, the corrosion rate of mild steel increases with

increasing Cu concentration. At acidic pH, in presence of 1ppm of Cu there was a

cathodic shift in Ecorr making the steel surface more active. However, a lower

value of Icorr resulted in the lowering in corrosion rate. At 100 ppm Cu, though

there was an anodic shift in Ecorr making the steel surface nobler, an increase in

the Icorr value caused a substantial increase in the corrosion rate. The corrosion

parameters as obtained by the potentiodynamic polarization measurements are

78

instantaneous and increase in the corrosion rate with increasing Cu concentration

can be explained on the basis of additional cathodic reaction involving the

reduction of Cu ions and rapid measurements of rate of electron transfer reactions.

For SS 304L, the corrosion parameters as derived from potentiodynamic

polarization curves show a positive shift in Ecorr values in presence of Cu ions. As

a result the metal surface becomes still nobler. The SEM photomicrographs of

mild steel samples obtained after immersion in both distilled water and artificial

seawater containing Cu ions did not show any evidence of localized corrosion in

presence of Cu ions. The EDAX analysis carried out on the steel sample obtained

after immersion in distilled water containing 100 ppm Cu clearly showed the

presence of Cu on the steel surface. This further confirmed the results of weight

loss and electrochemical measurements.

3.3 CONCLUSIONS

• The results of immersion tests showed a decrease in the corrosion rate of

mild steel with increasing Cu concentration. This is attributed to the

deposition of reduced Cu on the steel surface which protected the steel

efficiently and caused a decrease in corrosion rate.

• Under deaerated condition, the presence of 100 ppm of Cu ions resulted in

a perfect barrier and completely stopped the corrosion process.

• SS 304L and SS 316L are unaffected in both distilled and artificial

seawater, and presence of Cu in the medium showed no effect on the

corrosion rate.

• The results of immersion tests find support from free corrosion potential

measurements. In presence of higher concentration of Cu there is

79

significant ennoblement in the Ecorr of mild steel, SS 304L and SS 316L

suggesting the protective role of Cu.

• The corrosion parameters as derived from potentiodynamic polarization

measurements showed an increase in the corrosion rate of mild steel with

increasing Cu concentration. This is explained on the basis of

instantaneous measurement of the corrosion parameters and rapid of rate

of electron transfer reactions.

• The microscopic examination of the mild steel coupons subjected to

immersion in distilled and artificial seawater did not show any evidence of

localized attack in presence of different concentration of Cu ions.

80

Table 3.1 Corrosion rate of mild steel immersed in distilled water at pH 4.0 under

different experimental conditions at room temperature

Corrosion rate as

obtained by weight loss

measurements (mpy)

Corrosion rate as obtained by

solvent analysis of iron ions

(mpy)

Flow condition

Cu

ions

conc.

(ppm) 24hrs 360hrs 720hrs 24hrs 360hrs 720hrs

Aerated Static Blank 4.531 4.367 4.285 4.452 4.253 4.204

„ 0.01 4.644 4.662 4.628 4.639 4.618 4.603

„ 0.1 4.591 4.587 4.553 4.589 4.564 4.548

„ 1 4.693 4.631 4.597 4.602 4.559 4.498

„ 10 4.714 4.696 4.602 4.697 4.604 4.559

„ 20 4.527 4.491 4.424 4.463 4.371 4.407

„ 30 4.469 4.368 4.272 4.391 4.183 4.108

„ 40 4.734 4.567 4.494 4.685 4.524 4.459

„ 100 4.112 4.044 3.945 4.064 3.801 3.706

Aerated Dynamic Blank 51.7 - - 50.1 - -

„ 0.1 29.65 - - 27.43

„ 1 23.4 - - 22.3 - -

„ 100 18.1 - - 18.0 - -

Deaerated Static* Blank 1.694 - - 1.544 - -

„ 0.1 1.793 - - 1.778 - -

„ 1 1.681 - - 1.554 - -

„ 100 1.195 - - 1.219 - -

* 12 hrs.

81



Corrosion rate as

obtained by weight loss

measurements (mpy)

Corrosion rate as obtained

by solvent analysis of iron

ions (mpy)

Flow condition

Cu

ions

conc.



„ 0.01 3.367 3.348 3.306 3.354 3.329 3.286

„ 0.1 3.328 3.296 3.257 3.299 3.268 3.198

„ 1 3.289 3.195 2.915 3.194 2.975 2.714

„ 10 3.532 3.286 3.022 3.224 3.069 2.961

„ 20 2.833 2.654 2.471 2.835 2.795 2.407

„ 30 2.961 2.545 2.497 2.715 2.364 2.404

„ 40 2.474 2.355 2.288 2.364 2.237 2.179

„ 100 1.686 1.125 0.981 1.672 1.156 0.735


„ 0.1 13.87 - - 12.98

„ 1 10.18 - - 9.897 - -

„ 100 6.073 - - 5.936 - -


„ 0.1 1.432 - - 1.397 - -

„ 1 1.516 - - 1.508 - -

„ 100 0.00 - - 0.00 - -

* 12 hrs.

82




by weight loss

measurements (mpy)

Corrosion rate as

obtained by solvent

analysis of iron ions (mpy)

Flow condition

Cu

ions

conc.



„ 0.01 2.694 2.672 2.629 2.689 2.679 2.614

„ 0.1 2.665 2.664 2.655 2.641 2.653 2.629

„ 1 3.265 2.953 2.692 3.163 2.831 2.657

„ 10 3.584 3.277 2.724 3.553 3.062 2.804

„ 20 2.934 2.651 2.677 2.904 2.825 2.766

„ 30 2.856 2.743 2.497 2.77 2.65 2.38

„ 40 2.761 2.625 2.586 2.82 2.60 2.49

„ 100 1.814 1.056 0.865 1.81 1.30 0.66


„ 0.1 14.32 - - 13.54

„ 1 15.02 - - 16.72 - -

„ 100 12.42 - - 11.70 - -


„ 0.1 1.497 - - 1.472 - -

„ 1 1.613 - - 1.583 - -

„ 100 0.00 - - 0.00 - -

* 12 hrs.

83

Table 3.4 Corrosion rate of mild steel immersed in artificial seawater at pH 8.2

under different experimental conditions at room temperature


by weight loss

measurements (mpy)



ions (mpy)

Flow condition

Cu

ions

conc.



„ 0.01 3.085 2.986 2.716 2.986 2.965 2.704

„ 0.1 3.119 2.999 2.874 3.095 2.977 2.854

„ 1 3.561 3.223 2.962 3.493 3.326 2.904

„ 10 3.737 3.544 3,299 3.564 3.652 3.066

„ 20 3.864 3.635 3.426 3.845 3.804 3.274

„ 30 3.996 3.906 3.675 3.903 3.767 3.531

„ 40 4.052 3.883 3.736 3.993 3.804 3.652

„ 100 3.993 3.766 3.487 3.864 3.701 3.493


„ 0.1 21.35 - - 20.67 - -

„ 1 28.42 - - 26.48 - -

„ 100 33.01 - - 32.06 - -


„ 0.1 1.695 - - 1.677 - -

„ 1 1.591 - - 1.582 - -

„ 100 1.465 - - 1.446 - -

* 12 hrs.

84

Table 3.5 Corrosion rate of SS 304L immersed in distilled water at pH 4.0 under



by weight loss

measurements (mpy)



ions (mpy)

Flow

condition

Cu

ions

conc.

(ppm) 720 hrs 4320 hrs 8760 hrs 720 hrs 4320

hrs

8760 hrs


„ 1 0.00 0.0039 0.0044 0.00 0.0041 0.0049

„ 10 0.00 0.0053 0.0038 0.00 0.0052 0.0031

„ 20 0.00 0.0009 0.0015 0.00 0.0017 0.0012

„ 30 0.00 0.0029 0.0018 0.00 0.0025 0.0012

„ 40 0.0031 0.0047 0.0022 0.0028 0.0043 0.0021

„ 100 0.0067 0.0048 0.0041 0.0068 0.0043 0.0040

Table3.6 Corrosion rate of SS 304L immersed in distilled water at pH 6.5 under



by weight loss

measurements (mpy)



ions (mpy)

Flow

condition

Cu

ions

conc.

(ppm) 720 hrs 4320 hrs 8760 hrs 720 hrs 4320 hrs 8760 hrs


„ 1 0.00 0.0056 0.0031 0.00 0.0045 0.0025

„ 10 0.00 0.0021 0.0038 0.00 0.0016 0.0024

„ 20 0.00 0.00 0.0017 0.00 0.00 0.0012

„ 30 0.00 0.0018 0.0021 0.00 0.0010 0.0017

„ 40 0.00 0.0021 0.0042 0.00 0.0016 0.0033

„ 100 0.00 0.0016 0.0003 0.00 0.00 0.00

85




by weight loss

measurements (mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.

(ppm) 720 hrs 4320 hrs 8760

hrs

720 hrs 4320 hrs 8760 hrs


„ 1 0.00 0.0017 0.0039 0.00 0.00 0.00

„ 10 0.00 0.0028 0.0041 0.00 0.0018 0.0033

„ 20 0.0021 0.0026 0.0033 0.0017 0.0021 0.0027

„ 30 0.0019 0.0014 0.0021 0.0020 0.0019 0.0007

„ 40 0.00 0.0021 0.0012 0.00 0.0025 0.0031

„ 100 0.0013 0.0039 0.0045 0.0010 0.0040 0.0022

Table 3.8 Corrosion rate of SS 304L immersed in artificial seawater at pH 8.2



by weight loss measurements

(mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.



„ 1 0.0051 0.0048 0.0064 0.0056 0.0047 0.0055

„ 10 0.0044 0.0025 0.0037 0.0034 0.0028 0.0036

„ 20 0.0019 0.0019 0.0045 0.0013 0.0015 0.0029

„ 30 0.0011 0.0019 0.0006 0.00 0.0007 0.00

„ 40 0.0026 0.0052 0.0059 0.0022 0.0049 0.0054

„ 100 0.0041 0.0077 0.0091 0.0045 0.0054 0.010

86





(mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.



„ 1 0.0021 0.0039 0.0036 0.0015 0.0037 0.0032

„ 10 0.0044 0.0046 0.0042 0.0040 0.0043 0.0046

„ 20 0.0061 0.0058 0.0051 0.0057 0.0055 0.0053

„ 30 0.0054 0.0039 0.0041 0.0049 0.0040 0.0040

„ 40 0.0049 0.0043 0.0044 0.0046 0.0042 0.0042

„ 100 0.0062 0.0059 0.0051 0.0058 0.0049 0.0053





(mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.



„ 1 0.00 0.0029 0.0016 0.00 0.0018 0.0012

„ 10 0.00 0.0024 0.0007 0.00 0.0019 0.0009

„ 20 0.00 0.0025 0.0017 0.00 0.0022 0.0015

„ 30 0.00 0.0016 0.0009 0.00 0.0019 0.0010

„ 40 0.00 0.0022 0.0015 0.00 0.0024 0.0012

„ 100 0.00 0.0014 0.0008 0.00 0.0009 0.00

87

Table3.11 Corrosion rate of SS 316L immersed in distilled water at pH 8.5 under



by weight loss

measurements (mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.



„ 1 0.00 0.0019 0.0013 0.00 0.0013 0.0008

„ 10 0.00 0.0024 0.0015 0.00 0.0027 0.0017

„ 20 0.00 0.0036 0.0031 0.00 0.0031 0.0028

„ 30 0.00 0.0022 0.0035 0.00 0.0017 0.0030

„ 40 0.0023 0.0029 0.0021 0.0019 0.0022 0.0017

„ 100 0.0018 0.0043 0.0039 0.0011 0.0038 0.0029

Table 3.12 Corrosion rate of SS 316L immersed in artificial seawater at pH 8.2




(mpy)



ions ( mpy)

Flow

condition

Cu

ions

conc.



„ 1 0.0034 0.0059 0.0036 0.0032 0.0045 0.0033

„ 10 0.0059 0.0043 0.0040 0.0051 0.0039 0.0039

„ 20 0.0032 0.0041 0.0052 0.0035 0.0040 0.0045

„ 30 0.0047 0.0033 0.0035 0.0039 0.0035 0.0036

„ 40 0.0024 0.0027 0.0025 0.0021 0.0019 0.0023

„ 100 0.0029 0.0017 0.0015 0.0027 0.0021 0.0012

88

Table 3.13 Concentrations of Cu ions as estimated by AAS in the test solutions

after completion of immersion for mild steel immersed in distilled

water at pH 4.0

Cu ions conc. in the test

solutions after completion of

immersion (ppm)

Flow condition

Cu ions conc. in the

test solutions before

commencement of

immersion (ppm) 24hrs 360hrs 720hrs

Aerated Static Blank - - -

„ 0.01 0.0 0.0 0.0

„ 0.1 0.0 0.0 0.0

„ 1 0.0 0.0 0.0

„ 10 0.0 0.0 0.0

„ 20 2.0 0.1 0.0

„ 30 7.0 0.9 0.0

„ 40 18.0 1.5 0.0

„ 100 13.0 2.4 0.4

Deaerated Static* Blank - - -

„ 0.1 0.0 - -

„ 1 0.0 - -

„ 100 72.0 - -

* 12 hrs.

89


after completion of immersion for mild steel immersed in distilled water at

pH 6.5



immersion (ppm)

Flow condition



commencement of



„ 0.01 0.0 0.0 0.0

„ 0.1 0.0 0.0 0.0

„ 1 0.0 0.0 0.0

„ 10 0.0 0.0 0.0

„ 20 6.0 0.4 0.0

„ 30 10.0 1.2 0.0

„ 40 20.0 2.0 0.0

„ 100 30.0 4.9 0.1


„ 0.1 0.0 - -

„ 1 0.0 - -

„ 100 76.0 - -

* 12 hrs.

90


after completion of immersion for mild steel immersed in distilled

water at pH 8.5



immersion (ppm)

Flow condition


solutions before

commencement of



„ 0.01 0.0 0.0 0.0

„ 0.1 0.0 0.0 0.0

„ 1 0.0 0.0 0.0

„ 10 0.0 0.0 0.0

„ 20 5.0 0.0 0.0

„ 30 19.0 1.8 0.0

„ 40 30.0 2.3 0.0

„ 100 50.0 7.0 0.2


„ 0.1 0.0 - -

„ 1 0.0 - -

„ 100 80.0 - -

* 12 hrs.

91


after completion of immersion for mild steel immersed in artificial

seawater at pH 8.2



immersion (ppm)

Flow condition



commencement of



„ 0.01 - - -

„ 0.1 - - -

„ 1 0.0 0.0 0.0

„ 10 2.1 0.9 0.0

„ 20 8.9 1.5 0.2

„ 30 12.7 5.3 0.9

„ 40 29.1 10.4 5.3

„ 100 63.5 14.7 3.2


„ 0.1 0.0 - -

„ 1 0.0 - -

„ 100 86.0 - -

* 12 hrs.

92


after completion of immersion for SS 304L immersed in distilled

water at pH 4.0



immersion (ppm)

Flow condition



commencement of

immersion (ppm) 720 hrs 4320 hrs 8760 hrs


„ 1 0.9 0.9 0.9

„ 10 9.0 8.2 8.1

„ 20 18.0 18.0 17.8

„ 30 27.0 26.3 27.0

„ 40 36.0 38.0 36.9

„ 100 57.0 38.0 37.0



water at pH 6.5



immersion (ppm)

Flow condition



commencement of



„ 1 0.9 0.7 0.7

„ 10 9.2 9.1 8.8

„ 20 18.0 17.0 17.7

„ 30 28.0 26.3 28.0

„ 40 38.0 37.0 37.5

„ 100 52.0 36.0 35.8

93


completion of immersion for SS 304L immersed in distilled water at

pH 8.5



immersion (ppm)

Flow condition



commencement of

immersion (ppm) 720 hrs 4320

hrs

8760 hrs


„ 1 0.7 0.7 0.7

„ 10 8.1 7.9 8.7

„ 20 19.0 18.0 18.2

„ 30 29.0 27.0 28.1

„ 40 38.0 37.0 37.0

„ 100 55.0 47.0 46.9


after completion of immersion for SS 304L immersed in artificial

seawater at pH 8.2



immersion (ppm)

Flow condition


test solutions

before

commencement of

immersion (ppm)

720 hrs 4320 hrs 8760 hrs


„ 1 0.9 0.8 0.8

„ 10 8.3 8.2 8.7

„ 20 19.0 18.0 18.0

„ 30 28.0 27.0 28.1

„ 40 37.0 36.0 38.6

„ 100 49.0 39.0 38.0

94



water at pH 4.0



immersion (ppm)

Flow condition



commencement of



„ 1 0.9 0.0 0.0

„ 10 9.1 8.8 8.6

„ 20 19.1 18.9 18.1

„ 30 29.1 28.7 28.0

„ 40 37.8 37.1 36.4

„ 100 96.7 95.1 93.0



water at pH 6.5

Cu ions conc. in the test solutions

after completion of immersion

(ppm)

Flow condition


test solutions

before

commencement of

immersion (ppm)

720 hrs 4320 hrs 8760 hrs


„ 1 0.9 0.0 0.0

„ 10 9.7 9.5 9.1

„ 20 19.7 19.6 19.4

„ 30 29.8 28.9 28.5

„ 40 38.7 38.2 35.9

„ 100 98.1 96.8 91.0

95



water at pH 8.5



immersion (ppm)

Flow condition



commencement of



„ 1 0.8 0.8 0.7

„ 10 9.1 8.9 8.6

„ 20 19.5 18.9 18.4

„ 30 29.0 28.8 28.3

„ 40 39.6 38.8 38.2

„ 100 97.9 97.3 96.0


after completion of immersion for SS 304L immersed in artificial

seawater at pH 8.2


solutions after completion

of immersion (ppm)

Flow condition



commencement of



„ 1 0.9 0.9 0.8

„ 10 9.6 9.1 8.9

„ 20 19.7 19.6 18.8

„ 30 29.3 28.6 28.5

„ 40 39.7 39.1 38.6

„ 100 99.1 98.2 94.0

96

Table 3.25 Corrosion parameters for mild steel immersed in distilled water and

artificial seawater as obtained by potentiodynamic polarization

measurements

Aqueous medium pH Cu ions

conc. (ppm) Ecorr (mv) Icorr (A/cm

2)

Blank -610 4.7×10-4

1 -628 2.4×10-4 4.0

100 -584 1.1×10-3

Blank -568 5.5×10-5

1 -552 5.1×10-5 6.5

100 -720 9.4×10-4

Blank -528 1.0×10-4

1 -562 8.3×10-5

Distilled water

8.5

100 -728 2.6×10-5

Blank -849 2.8×10-5

1 -831 1.9×10-5 Artificial seawater 8.2

100 -818 3.2×10-5

Table 3.26 Corrosion parameters for SS 304L immersed in distilled water and

artificial seawater as obtained by potentiodynamic polarization

measurements

Aqueous

medium pH

Cu ions

conc. (ppm) Ecorr (mv) Icorr (A/cm

2)

Blank -102 2.5×10-6

1 -98 2.4×10-6 4.0

100 -13 3.6×10-6

Blank -151 1.0×10-7

1 +29 2.4×10-7 6.5

100 +69 7.9×10-6

Blank -97 1.3×10-7

1 -149 8.7×10-8

Distilled water

8.5

100 +74 1.8×10-7

97

Figure 3.1: pH vs. time plot in absence and presence of varying concentration of Cu ions for mild steel immersed in distilled water at pH 4.0.

Figure 3.2: pH vs. time plot in absence and presence of varying concentration of Cu ions for mild steel immersed in distilled water at pH 6.5.

98

Figure 3.3: pH vs. time plot in absence and presence of varying concentration of

Cu ions for mild steel immersed in distilled water at pH 8.5.

Figure 3.4: pH vs. time plot in absence and presence of varying concentration

of Cu ions for mild steel immersed in artificial seawater at pH 8.2.

99

Figure 3.5: pH vs. time plot in absence and presence of varying concentration of Cu ions for SS 304L immersed in distilled water at pH 4.0.


100


Figure 3.8: pH vs. time plot in absence and presence of varying concentration of Cu ions for SS 304L immersed in artificial seawater at pH 8.2.

101


of Cu ions for SS 316L immersed in distilled water at pH 4.0.


of Cu ions for SS 316L immersed in distilled water at pH 6.5.

102


Figure 3.12: pH vs. time plot in absence and presence of varying concentration of Cu ions for SS 316L immersed in artificial seawater at pH 8.2.

103

Figure 3.13: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for mild steel immersed in distilled water at pH 4.0

Figure 3.14: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for mild steel immersed in distilled water at pH 6.5

104

Figure 3.15: Ecorr vs. time plot in absence and presence of varying concentration

of Cu ions for mild steel immersed in distilled water at pH 8.5.

Figure 3.16: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for mild steel immersed in artificial seawater at pH 8.2.

105

Figure 3.17: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for SS 304 L immersed in distilled water at pH 4.0.


106


Figure 3.20: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for SS 304 L immersed in artificial seawater at pH 8.2.

107



108


Figure 3.24: Ecorr vs. time plot in absence and presence of varying concentration of Cu ions for SS 316 L immersed in artificial seawater at pH 8.2.

109

Figure 3.25: Potentiodynamic polarization curves for mild steel in distilled

water (pH=4.0) in absence and presence of Cu (a) Blank (b)1ppm

Cu (c) 100ppm Cu

Figure 3.26: Potentiodynamic polarization curves for mild steel in distilled


Cu (c) 100ppm Cu

110

Figure 3.27: Potentiodynamic polarization curves for mild steel in distilled water

(pH=8.5) in absence and presence of Cu (a) Blank (b)1ppm Cu (c)

100ppm Cu

Figure 3.28: Potentiodynamic polarization curves for mild steel in artificial

seawater (pH=8.2) in absence and presence of Cu (a) Blank

(b)1ppm Cu (c) 100ppm Cu

111

Figure 3.29: Potentiodynamic polarization curves for SS 304L steel in distilled


Cu (c) 100ppm Cu

Fig 3.30: Potentiodynamic polarization curves for SS 304Lsteel in distilled water


100ppm Cu

112

Figure 3.31: Potentiodynamic polarization curves for SS 304L in distilled water


100ppm Cu

113

(a) (b)

(c)

114

(d)

(e)

Figure 3.32: SEM micrographs of (a) polished mild steel (b) mild steel immersed in distilled water at pH 6.5 (c) mild steel immersed in distilled water containing 100ppm Cu at pH 6.5 (d) mild steel immersed in artificial seawater at pH 8.2 (e) mild steel immersed in artificial seawater containing 100ppm Cu at pH 8.2.

115

(a)

(b)

Figure 3.33: EDAX analysis of (a) mild steel immersed in distilled water at pH 6.5 (b) mild steel immersed in distilled water containing 100ppm

Cu ion at pH 6.5.

Date post:	07-Nov-2020
Category:	Documents
Upload:	others
View:	5 times
Download:	0 times

Chapter Chapter ---- IIIIIIIIIIIIshodhganga.inflibnet.ac.in/bitstream/10603/11290/8/08_chapter...

Documents