THE CORROSION OF MILD STEEL IN ORANGE
JUICE ENVIRONMENT
UNIVERSITY OF ILORIN, ILORIN, NIGERIA
Department of Mechanical Engineering
BADMOS, A.Y and AJIMOTOKAN, H.A.
TECHNICAL REPORT NO: 2009-02
FEBRUARY 2009
1
THE CORROSION OF MILD STEEL IN ORANGE
JUICE ENVIRONMENT
By
BADMOS, A.Y and iAJIMOTOKAN, H.A
TECHNICAL REPORT NO: 2009-02
FEBRUARY 2009
2
ABSTRACT
The corrosion effect of orange fruit juice has been investigated by the study of the corrosion of
carbon steel in widely processed sweet orange (Citrus Sinensis). Weight loss technique was used
in which test coupons, with known weight, were immersed in the test media: natural orange juice,
orange juice with preservatives and water; for a total exposure time of 10 days. The weight loss
was measured at an interval of two (2) days, and the corrosion rate was determined. Corrosive
effects are of remarkable consequence in the food processing industry as fruits contain corrosion
aggressive substances, thereby causing significant impact on the degradation of constructional
materials and the maintenance or replacement of products lost or contaminated as a result of
corrosion reactions. The result revealed that the corrosiveness of sweet orange juice relative to
carbon steel were mainly a function of its acidity. Consequently, packed orange juice with
preservative was most corrosive followed by natural orange juice and water respectively.
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TABLE OF CONTENTS
PAGES
COVER PAGE
i
TITLE PAGE
ii
ABSTRACT
iii
TABLE OF CONTENTS
iv
1.
INTRODUCTION
1
2.
MATERIALS AND METHODS
3
3.
RESULTS AND DISCUSSION
4
4.
CONCLUSIONS
7
REFERENCES
8
4
1.
INTRODUCTION
Metals and its alloy are exposed to the action of acids in industrial processes which causes severe
problems such as increases in mass and corrosion of surfaces resulting in economic losses [1].
These effects are of particular consequence in the food processing industry as food substances,
like other organic and inorganic substances is increasingly becoming corrosive; thereby causing
significant impact on the degradation of constructional materials and the maintenance or
replacement of products lost or contaminated as a result of corrosion reactions [2]. These
corrosive effects on different constructional materials in all phases of processing and packaging
of food – one of the most basic needs of life, are all too common.
The material for most equipment are mild steel which is selected because of its strength, ductility,
weldability and it is amenable to heat treatment for varying mechanical properties [3,4,5,6].
However, mild steel corrodes easily because all common structural metals form surface oxide
films when exposed to pure air but the oxide formed on mild steel is readily broken down, and in
the presence of moisture it is not repaired. Therefore, a reaction between steel (Fe), moisture
(H2O), and oxygen (O2), takes place to form rust. This reaction is complex but it can be
represented by a chemical equation of the following type:
4Fe + 2H2O + 3O2 = 2Fe2O3.H2O
(1)
Fe2O3.H2O is the rust, and as it is not usually protective, therefore, the corrosion process is not
impeded [7].
Mild steel as constructional materials are often exposed to juice or used to package juice to a
great extent during service. This exposure can be under condition of varying temperature, flow
rate, pH, and other factors; all of which can alter the rate of corrosion. The relative acidity of the
solution is the most important factor to be considered; at low pH, the evolution of hydrogen tends
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to eliminate the possibility of protective film formation so that steel continues to corrode but in
alkaline solutions, the formation of protective film greatly reduces corrosion rate [8].
Citrus species are utilized in many industries for the production of various brands of citrus juices
[9]. These juices are also rich in vitamin C, folic acid and significant quantities of other vitamins,
pectin, flavonoids among others [9,10]. Nitrogenous compounds are present to the extent of 0.05
– 1.0%, mostly as free amino acids – asparagines, alanine, arginine, aspartic acids, glutathione,
histidine, betaine, cysteine, praline, serine and stachydrine [9,10,11]. The principal acid in citrus
fruits is citric acid (80-90% of the total acids). Others are malic, tartaric, benzoic, succinic,
quinic, oxalic and formic acids [9].
This work examines the corrosion of carbon steel in orange juice environments to provide a better
understanding of the corrosiveness of the orange fruit, thereby enhancing the material selection
and effective surface treatments to increase corrosion resistance.
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2.
MATERIALS AND METHODS
Sheets of mild steel metal of 0.1 cm thickness was mechanically cut into coupons of sizes of 4cm
length by 2.5cm width, perforated with hole of same diameter centrally to allow the passage of
thread. These coupons were surface-prepared using emeryl cloth, ethanol and water. Equally, the
natural orange juice was prepared and other media were procured; and the pH of each medium
was measured.
Previously weighed coupons each of the metal were suspended with the aid of a thread in the
beakers each containing orange juice with preservatives, natural orange juice and water; and the
beakers were kept stationary to avoid displacement effect. The coupons’ exposure periods were a
total of 10 days with six measurements taken at an interval of 2 days respectively.
The average corrosion rates of the coupons in various environments were determined using the
established relation given by Lawal [8], Ovri and Ofeke [12], Fontana [13], Osarolube et al [14],
Avwiri [15] as:
Corrosion Rate (mpy) = 534 W∕ρAT
(2)
where W is the weight loss in mg, ρ is the Metal density in mg/m3, A is Area of Coupon in m2 , T
is the exposure time in hours and mpy is millimeter per year.
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3.
RESULTS AND DISCUSSION
Uniform corrosion was observed in almost all coupons immersed in the media as no pit or
holidays noticed. Figures 1 and 2 show the summary results of the variation of weight loss (gm)
as a function of exposure time (days) and the corresponding corrosion rate (mpy) as a function of
exposure time (days) for all test media respectively, while Table 1 shows the corrosion rates of
mild steel in the test media.
The result depicts that weight loss of the coupons is highest in the orange juice with preservative
followed by natural orange juice and the least weight loss was observed in water medium. As it is
noted from the graphs, food additives increase the corrosiveness of an environment. Food
additives as in the case of orange juice with preservatives, impact various corrosive effects on
refined orange juice.
However, corrosion attack in the orange media is very substantial because citric acid (80-90% of
the total acids) is recognized as an oxidizing agent. An autocatalytic mechanism has generally
been proposed to explain the high rates of corrosion in acids [15, 16] with primary displacement
of H+ ions from solution; followed by acid reduction rather than hydrogen evolution as acid
reduction leads to a manifest decrease in free energy. This reaction is complex but it can be
represented by a chemical equation of the following type:
Fe2+ + OH- = Fe (OH)2
(3)
Though a loose blue or green corrosion product suggestive of ferrous hydroxide {Fe (OH)2}, was
observed which readily turned red brown on removal and exposure to the atmosphere. This
transformation was as a result of the of oxidation of the ferrous hydroxide Fe (OH)2, to ferric
hydroxide Fe (OH)3 as shown below:
Fe (OH)2 + O2 = Fe (OH)3
(4)
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Although the mechanism of corrosion in water is comparatively straightforward, it is difficult to
predict how corrosion will proceed in practice [17]. The result depicted that water was less
corrosive to mild steel compared with orange juice.
There was a substantial rise in pH of all the test media except in water with the passage of time
and passivity not notable. These are due to the various chemical reactions and other processes
like fermentation, oxidation, and corrosion products dissolution as there was increase in
colouration of the media with increase in exposure time and/or days.
Figure 1: Variation of Weight Loss Vs Exposure Time for all Media
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Figure 2: Variation of Corrosion Rate Vs Exposure Time for all Media
Table 1: Corrosion Rate of Mild Steel in the Test Media
Water (mpy) x 10-3
Exposure Time
Orange Juice with Preservatives
Natural Orange Juice
(Days)
(mpy) x 10-3
( mpy) x 10-3
2
6.65
3.85
1.79
4
4.65
3.06
1.66
6
4.65
2.44
1.53
8
4.15
2.13
1.31
10
4.00
1.87
1.20
10
4.
CONCLUSIONS
Within the test period and the prevailing environmental conditions, this study has shown that:
1. Carbon steels are corrosive in fruit juice environments due to the evolution of hydrogen gas (a
cathodic reaction product) at low pH, which tends to eliminate the possibility of protective
formation (of H2).
2. The corrosion rate was highest in the orange juice with preservatives. This is thought to be due
to a combination of citric acid and the preservatives (food additives).
3. Fruit juice demands a considerable degree of processing such as milling, pressing, and
concentration by evaporation, storage and packaging using metallic constructional materials.
However, carbon steel corrosiveness relatively renders it undesirable economically and healthwise because these corrosion products may find their ways into the bulk of the juice and thereby
causing it to be off-taste, off-flavour and off-texture which may equally be hazardous to health.
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REFERENCES:
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Thesis, Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
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Edition, John Willey and Sons Inc. Publisher, USA
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Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
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Steel”, British Steel Corporation Corrosion Prevention Booklet No. 2, 02-03
[8]. Lawal, A.I. (2005) “Corrosion of Carbon Steel in Natural and Packed Orange Juice”, B. Eng.
Thesis, Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
[9]. Anthony, U.O. and Offiong, U.E. (1998) “Nutritional Quality of Plant Foods”, Post Harvest
Research Unit Report, Dept. of Biochemistry, University of Benin, Benin, Nigeria
[10]. Ihekoronye, A.I. and Ngoddy, P.O. (1984) “Integrated Food Science and Technology for the
Tropics”, Macmillian, Nigeria
[11]. Abiola, O.K., Oforka, N.C. and Ebenso, E.E. (2004) “The Inhibition of Mild Steel
Corrosion in an Acidic Medium by Fruit Juice of Citrus Paradisi”, Journal of Corrosion
Science and Technology, Vol. 1 No. 1, 75-78
[12]. Ovri, J. E. and Ofeke, T.B. (1998) “The Corrosion of Mild Steel in Marine Environment”,
Journal of Science Engineering Technology, No. 5, Vol. 2, 1117-1129
[13]. Fontana, M.G. (1987) “Corrosion Engineering”, Third Edition, McGraw-Hill International
Edition, New York
[14]. Osarolube, E., Owate, I.O. and Oforka, N.C. (2004) “The Influence of Acidity
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Technology, Vol. 1 No. 1, 66-69
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[16]. Haleem, E.I., Ald, S.M., Kheor, M.G. and Killa, H.M. (1980) “Corrosion Behaviour of
Metals in HNO3, British Corrosion Journal, Vol. 6 No. 1, 42
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Corporation Corrosion Prevention Booklet No. 3, 11
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Corresponding author Email: hajims@unilorin.edu.ng, haajims@yahoo.com
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