Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water

doi:10.4236/msa.2012.34037

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Materials Sciences and Applications, 2012, 3, 253-258

http://dx.doi.org/10.4236/msa.2012.34037 Published Online April 2012 (http://www.SciRP.org/journal/msa)

253

Microbiological Induced Corrosion on Brass in Recycling

Cooling Water System Makeup by Reclaimed Water*

Ping Xu1,2, Zhaoyi Xu1, Jin Wang1, Yajun Zhang2, Ting Liu2

1School of Civil Engineering and Architecture, Beijing Jiaotong University, Beijing, China; 2Key Laboratory of Urban Stormwater

System and Water Environment, Beijing University of Civil Engineering and Architecture, Ministry of Education, Beijing, China.

Email: [email protected]

Received January 18th, 2012; revised February 27th, 2012; accepted March 29th, 2012

ABSTRACT

The impacts of microorganism on brass corrosion were studied in static experiment in this paper. Two main factors,

temperature and concentration ratio, were considered. According to the actual operation of recycling cooling water sys-

tem, four temperatures (15˚C, 25˚C, 35˚C and 45˚C) and four concentration ratios (1, 2.5, 3.5 and 4.5) were selected in

the experiment. Corrosion potential, current density, average corrosion rate were measured by time. The results showed

that: microorganism often aggravated corrosion of brass during initial and final stages, but alleviated its corrosion at the

middle time. With the extension of time that brass immersed in the solution, the microbes began to intensify the

corrosion of the metal. When concentration ratios were 2.5 and 3.5 and temperature was 15˚C, microbe promoted brass

corrosion obviously and corrosion degrees.

Keywords: Reclaimed Water; Brass; Microbiologically Induced Corrosion; Corrosion Potential; Corrosion Current

Density; Average Corrosion Ratio; Temperature; Concentration Ratio

1. Introduction

Almost every surface can be colonized by bacteria, form-

ing biofilms [1]. The corrosion due to existence or action

of the microorganisms in biofilm is called microbiologi-

cally-influenced corrosion (MIC). Many metals are sen-

sible to MIC. Pitting, crevice corrosion, hydrogen em-

brittlement and deposit corrosion caused by MIC almost

involve all kinds of fields, such as petrochemical industry,

aviation, shipping, powder industry and so on [2-6]. Ac-

cording to statistics, MIC accounted for 20% in metal

and building materials corrosion damages [7]. The direct

economic loss by MIC is about 300 to 500 billion dollars

[8].

Because of serious water shortage in some big cities in

China, such as Beijing, Tianjin, Dalian and so on, it is a

feasible method to reuse reclaimed water to cooling wa-

ter system of power plant. However, there are full of nu-

trients in reclaimed water and the temperature is high in

recycling cooling water system. These conditions are

beneficial to microorganisms growing on metal surfaces.

A variety of microorganisms and their metabolic reaction

products may promote the deterioration of the underlying

substratum. For ultimately biocorrosion control, it is

firstly needed to understand the impacts of microorgan-

ism on metal corrosion. Brass is widely used in con-

denser of cooling water system of power plants in China.

The impacts of microorganism on brass corrosion were

studied by electrochemical method and mass loss method

in this paper. Two main factors, temperature and concen-

tration ratio, were considered.

2. Materials and Method

2.1. Electrochemical Method

Shanghai Chen Hua CHI660C electrochemical work-

station was used for experiment. Its scanning speed was

0.01 V/s and the sensitivity was 10–4 A/V. Ag/(AgCl)/

KCl (0.1 mol/L) was selected as reference electrode and

platinum was as counter electrode.

During experiment, cross-sectional area of HSn70-1A

brass was 1 cm2. Its main chemical compositions was

shown as following (Wt%): Pb ≤ 0.05, Fe ≤ 0.10, Sb ≤

0.005, P ≤ 0.01, Bi ≤ 0.002, Sn 0.8 - 1.3, As 0.03 - 0.06,

Cu 69.0 - 71.0, Zn little.

*The paper is supported by two Chinese national grand projectsfor

water pollution control: Integrative Technology and Demonstration on

Reclaimed Water Utilized to Industry in Beijing (2009ZX07314-009-

04); Research Technology of and Demonstration on Urban Water

Conservation (2009ZX07317-005).

In electrochemical experiment, corrosion potential and

current density could be got by Tafel curves, which were

obtained by dynamic potential scanning method Corro-

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water

254

sion potential reflects corrosion tendency or degree and

corrosion current density shows corrosion rate. More

negative corrosion potential means that metal is more

vulnerable to corrosion. Higer current density reflects the

faster corrosion rate of metal.

2.2. Mass Loss Method

Type I (50 mm × 25 mm × 2 mm) HSn70-1A brass cou-

pons were selected for the experiment. Average corrosion

rate of a brass coupon could be calculated by the formula

as follows:



87600 mm

Xst





 (1)

where X-average brass corrosion rate, mm/a;

m-mass loss of a brass coupon in experiment, g;

m0-mass loss of a brass coupon in blank test, g;

s-surface area of a brass coupon, cm2;

ρ-density of a brass coupon, g·cm–3;

t-test time, h.

2.3. Reclaimed Water

Reclaimed water was obtained from a makeup pipe of a

cooling water system of a thermal power plant in Beijing.

Table 1 showed the quality of reclaimed water in the

experiment.

2.4. Experiment Arrangement

Two main factors, temperature and concentration ratio,

were considered in static experiment. According to the

actual operation of recycling cooling water system, four

temperatures (15˚C, 25˚C, 35˚C and 45˚C) and four con-

centration ratios (1, 2.5, 3.5 and 4.5) were selected in the

experiment. For obtaining microbial influences on brass

Table 1. Reclaimed water in a thermal power plant in Bei-

jing.

Item pH

Conductivity

us/cm

Total

hardness

mg/L

Alkalinity

mmol/L

Value 7.53 1134 248 3.2

Item Iron

ug/L

Turbidity

NTU

Cl–

mg/L

COD

mg/L

Value 157.9 9.1 111.3 5.0

Item TP

mg/L

NH4-N

mg/L

SO 

mg/L

Value 0.9 1.0 114.4 5

Item Total dissolved solids

mg/L

HPC

cfu/ml

Value 534 2 × 104

corrosion, experiments were operated in reclaimed water

with bacteria and reclaimed water without bacteria. Re-

claimed water with bacteria was directly obtained from

the make-up system of circulating cooling system of a

thermal power plant in Beijing. Reclaimed water without

bacteria could be got after disinfection in a high pressure

steam sterilizer with 121˚C ± 1˚C temperature for 20

minutes.

3. Results and Discussion

3.1. Microbiological Induced Corrosion on Brass

in Different Temperatures

3.1.1. Corrosion Po te ntial

Corrosion potentials in reclaimed water with or without

bacteria in different temperatures were shown in Figure

According to Figure 1, corrosion potentials of brass in

15˚C reclaimed water with bacteria are more negative

than the values in bacteria free water from start to finish,

existence of microorganism worsened the corrosion ob-

viously. Under other temperatures, compared with re-

claimed water without bacteria, corrosion potentials in

one with bacteria were more negative at the beginning

and last time, but less negative at the middle stage. That

means that microorganism aggravated corrosion of brass

during initial and final stages, but alleviated the corrosion

tendency at the middle time. At the early time, biofilm

had not fully formed yet. Uneven covering layer resulted

more serious corrosion. With the growth of biofilm, more

uniform and deeper layer retarded the tendency of corro-

sion. At the same time, formation of biofilm hindered

corrosive ions from arriving at the surface of brass. Adult

biofilm had stable ecosystem. More serious corrosion

would be caused by metabolic reactions or deposition.

Moreover, compared with corrosion potentials in 15˚C,

25˚C, 45˚C, values in 35˚C were all most negative when-

ever in reclaimed water with bacteria or not.

3.1.2. Corrosion Curr ent Densit y

Corrosion current density in reclaimed water with or

without bacteria in different temperatures were shown in

Figure 2.

According to Figure 2, both in reclaimed water with or

without bacteria, current densities were also higher at

higher temperatures. That means corrosion rates of brass

in higher environment were faster than the values in

lower temperature.

Moreover, compared with current densities in 25˚C,

35˚C and 45˚C reclaimed water with bacteria or not, cur-

rent densities in one with bacteria were higher at the be-

ginning and last stages and lower at middle stage. The

lowest densities in reclaimed water with bacteria oc-

curred on the third or fifth day. Current densities in the

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water

255

Figure 1. Corrosion potentials in reclaimed water with or without bacteria in different temperatures. (a) 15˚C; (b) 25˚C; (c)

35˚C; (d) 45˚C.

Figure 2. Corrosion current density in reclaimed water with or without bacteria in different temperatures. (a) 15˚C; (b) 25˚C;

c) 35˚C; (d) 45˚C. (

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water

256

water with bacteria began to exceed the values in bacteria

free one after fifth day. In the initial stages of brass im-

mersed in reclaimed water, maybe on first day, the pres-

ence of microorganisms would accelerate the corrosion

rate. Then with the biofilm on the surface of brass mature

gradually, it prevented corrosion ions from contacting

with the metal, so corrosion rates decreased at these stages.

After that period, corrosion rates in reclaimed water be-

gan to increase and ultimately exacerbate corrosion rates

of brass. Maybe uneven biofilm on the surface caused

serious corrosion of the metal.

3.1.3. Average Corrosion Rate

Average corrosion rates of couples in reclaimed water

with or without bacteria in different temperatures were

shown in Figure 3.

According to Figure 3, the developments of average

corrosions in different temperatures were similar to the

results of electrochemical experiments. In 25˚C, 35˚C

and 45˚C reclaimed with bacteria, compared with aver-

age corrosions in bacteria free reclaimed water, at first

stage, often within one or two days, corrosions of brass

were higher. Then the corrosions began to decrease and

were lower than the values in bacteria free one. For a

long time, often more than 9 days, average corrosions in

reclaimed water with bacteria began to increase and ul-

timately were higher than values in bacteria free one.

Moreover, average corrosion rates in 35˚C and 45˚C

were higher than the rates in 15˚C and 25˚C. The faster

values occurred in 35˚C and the lowest one occurred in

15˚C. The results further proved that the corrosion of

brass would be effected by micro-organisms. For a long

time, corrosion rates in reclaimed water with bacteria

would be faster than ones in bacteria free reclaimed wa-

ter.

3.2. Microbiological Induced Corrosion on Brass

in Different Concentration Ratio

3.2.1. Corrosion Po te ntial

Corrosion potentials in reclaimed water with or without

bacteria in different concentration ratios were shown in

Figure 4.

Based on Figure 4, both in reclaimed water with or

without bacteria, corrosion potentials were more negative

at higher concentration ratios. That means increasing

concentration ratios would aggravate the corrosion ten-

dency of brass in reclaimed water. There were high con-

centrated ions and nutrient substances under higher ratios,

which were beneficial to corrosion development and

caused more serious corrosion.

In four ratios, corrosion potentials in reclaimed water

with bacteria were more negative than values in bacteria

free one when concentration ratios were 2.5 and 3.5.

Under these conditions, the roles of the microbe to pro-

mote corrosion were more obvious and corrosion de-

grees of brass in reclaimed water with bacteria were

more serious. When concentration ratios were 1 and 4.5,

corrosion potentials in reclaimed water with bacteria

were more positive than values in bacteria free one

within 10 days. After that, corrosion potentials in re-

claimed water with bacteria move to negative direction

and aggravated the brass corrosion.

3.2.2. Corrosion Curr ent Densit y

Corrosion current density in reclaimed water with or

without bacteria in different concentration ratios were

shown in Figure 5.

Based on Figure 5, both in reclaimed water with or

without bacteria, corrosion current densities were also

higher at higher concentration ratios. That means in-

creasing concentration ratios would faster the corrosion

of brass in reclaimed water. High concentrated ions and

nutrient substances promoted corrosion development and

caused more serious corrosion.

Compared with two curves of reclaimed water with

bacterial and without bacterial in Figure 5, corrosion

current densities of without bacterial one decreased with

the time growth, but corrosion current densities of with

bacterial one decreased at initial stage and then increased

at second stage. The lowest point occurred at fifth or

sixth day at ratio of 1 and 2.5. When concentration ratio

was up to 3.5 and 4.5, the lowest point had been put off,

often at 10th day. With the extension of time that brass

immersed in the solution, the microbes began to intensify

the corrosion of the metal.

4. Conclusions

In a conclusion, whenever in reclaimed water with bacte-

ria or not, most serious corrosion occurred at 35˚C and

increasing concentration ratios would aggravate the cor-

rosion tendency of brass.

Microorganism often aggravated corrosion of brass

during initial and final stages, but alleviated its corrosion

at the middle time. With the extension of time that brass

immersed in the solution, the microbes began to intensify

the corrosion of the metal. When concentration ratios

were 2.5 and 3.5 and temperature was 15˚C, microbe

promoted brass corrosion obviously and corrosion de-

grees in reclaimed water with bacteria were more serious.

5. Acknowledgements

The research was supported by two Chinese national

grand projects for water pollution control: Integrative

Technology and Demonstration on Reclaimed Water

Utilized to Industry in Beijing (2009ZX07314-009-04);

Research Technology of anDemonstration on Urban d

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water 257

Figure 3. Average corrosion rates of couples in reclaimed water with or without bacteria in different temperatures. (a) 15˚C;

(b) 25˚C; (c) 35˚C; (d) 45˚C.

Figure 4. Corrosion potentials in reclaimed water with or without bacteria in different concentration ratios. (a) Ratio-1; (b)

Ratio-2.5; (c) Ratio-3.5; (d) Ratio-4.5.

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water

258

Figure 5. Corrosion current density in reclaimed water with or without bacteria in different concentration ratios. (a) Ratio-1;

(b) Ratio-2.5; (c) Ratio-3.5; (d) Ratio-4.5.

Water-Conservation (2009ZX07317-005). Moreover, the

paper was also supported by Key Laboratory of Urban

Stormwater System and Water Environment of Beijing

University of Civil Engineering and Architecture of

Ministry of Education.

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