Kinetics of Corrosion Rate of Carbon Steels in Different Acidic Media

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Kinetics of Corrosion Rate of Carbon Steels in Different Acidic Media9 Ashok Kumar1,a 1

Assistant Professor in Physics, Y.S.R. Engineering College of Yogi Vemana University, Proddatur, India

a

drashok.yvuce@gmail.com DOI 10.2412/mmse.25.49.44 provided by Seo4U.link

Keywords: carbon steels, corrosion, acid media, concentration variation, weight loss.

ABSTRACT. The corrosion properties of carbon steels in various acidic media sulfuric acid, nitric acid, hydrochloric acid and hydrofluoric acid has been studied. This paper also discussed about the corrosion behavior of mild steel in two different concentrations. Carbon steels were exposed to different acid environments in different intervals of time and corrosion rates were evaluated using weight loss method. It was evident from the results that the corrosion rate of the carbon steels in all the acidic media are increased with time of exposure. The carbon steels shows higher corrosion rates in nitric acid medium than compared to other acidic media. This can be attributed to strong oxidizing property of nitric acid and larger potential to break down the passivating film formed on the surface of the sample. The mild steel sample was also exposed to different concentrations of nitric acid medium. The results shows that the corrosion rate was increased with increase of concentration possibly attributed to increase in the rate of reaction on the surface of the sample which further reduces the energy barrier.

Introduction. Carbon steel is known to be the best preferred materials for industry as it has many industrial applications. It is easy availability, excellent physical properties, stronger and more workability than cast iron, low cost, uncomplicated fabrication made it to use in different applications like pipeline materials in oil and gas industry water pipe lines [1, 2], cooling water systems [3], boilers etc. However, the acids containing chloride, sulphide and so on introduces different forms of corrosion. Among the different acids, hydrochloric acid is the most difficult to handle from the keeping in view of corrosion and materials of constructions. Extreme care is required in the selection of materials to handle the acid by itself, even in relatively dilute concentrations or in process solutions containing appreciable amount of hydrochloric acid. This acid is very corrosive to most of the common metals and alloys [4].

Corrosion of metal components has been recognized as a major problem in many engineering applications. Failure of engineering systems due to corrosion is a common failure due to mechanical causes such as brittle fracture and fatigue. Steel is one of the major construction material, which is extensively used in chemical and allied industries for the handling of acid, alkali and salt solutions.

Selection of materials plays a key role in handling the acid even in relatively very low concentrations.

The acids are very corrosive to most of the common metals and alloys. Metals are exposed to acids in many different ways and for many different reasons like acids pickling, acid descaling, industrial acid cleaning and oil well acidizing in order to stimulate of oil well [5]. The corrosive nature of acids also has its applications include chemical cleaning and processing, acid treatment of oil wells and other applications.

To control the corrosion, good understanding of the effect of operating conditions such as different types of acids, concentrations and different heat treatment procedures on the corrosion behavior is required. Therefore, this work aims to study free corrosion behavior of different carbon steels under different dilute acidic solutions like sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid 9

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Mechanics, Materials Science & Engineering, May 2017

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(HNO3) hydrofluoric acid (HF). In this paper, the weight loss technique is used to measure the corrosion rate.

Materials and Experimental Procedure. In the present work, we used different carbon steels such To study the uniform corrosion resistance of different carbon steels, four different environments such as H2SO4, HF, HCl, HNO3 was used. Samples were abraded in sequence under running tap water using emery paper of grade number 220, 320, 400 and 600, then washed with running tap water followed by distilled water. The samples were exposed to the acid environments in different time intervals. After each exposure time the coupons were removed from the cells, properly cleaned in distilled water, dried with cotton wool and then reweighed to determine the mass loss. These results were analysed further to understand the kinetics of corrosion rate and its effects on selected carbon steel samples.

Methodology. Initially different carbon steels such as low carbon, medium carbon and high carbon steels are considered for the experiment and initial weights were noted. In this work, four different types of acidic environments such as HNO3, H2SO4, HF, HCl were taken with 1mole concentration.

The samples were dipped in the acids for 1 hour interval upto 7 hrs and cumulated reduction in weight was calculated for each interval.

Determination of Corrosion Rate.The most common method for estimating a corrosion rate from mass loss is to weigh the corroding sample before and after exposure and the difference in weight was noted as the weight loss in grams To provide minimum uncertainty in the corrosion rate, this method implicitly assumes: the corrosion rate does not vary with exposure time, the area does not change, as mass is lost to corrosion, the projected and actual surface areas are the same, the penetration rate is uniform over the entire surface, the weight is unaffected by corrosion product removal. Even assuming that the above criteria are fulfilled, errors can still be propagated because of the uncertainty in the measurement of time, mass and dimensions [6].

Results and Discussion.

Corrosion Behavior of Carbon Steels in Acidic Media. Corrosion can be defined as the deterioration of a material resulting from chemical attack by its environment. Most corrosion of materials involves the chemical attack of metals by electrochemical cells. By studying equilibrium conditions, the tendencies of pure metal to corrode in a standard aqueous environment can be related to the standard electrode potential of the metals. However, since corroding systems are not at equilibrium, the kinetics of corrosion reactions must be studied. Some examples of kinetic factors affecting corrosion reaction rates are the polarization of the corrosion reactions and the formation of passive films on the metals. Corrosion can be controlled or prevented by many different methods. To avoid corrosion, materials that are corrosion-resistant for a particular environment should be used where feasible. For many cases corrosion can be prevented by the use of metallic, inorganic, or organic coatings. The proper engineering design of equipment can also be very important for many situations, for some special cases, corrosion can be controlled by using cathodic or anodic.

Corrosion and its progress often are controlled by the corrosion products formed on the metal surface.

The ability of these films to protect metal depends on how they form when the metal is originally exposed to the environment. Thin, hard, dense, tightly adherent films afford protection, whereas thick, porous, loose films allow corrosion to proceed without providing any protection. As an example, the iron oxide film that usually forms on iron pipe in contact with water is porous and easily washed away to expose more metal to corrosion. The effective use of corrosion inhibitors in many cases depends on the type of film it forms on the surface to be protected.

The observed corrosion rate of carbon steels in H2SO4 is shown in Fig.1 (a). From the Fig. it is evident that the carbon steels shows little effect of corrosion in this acidic medium. But as time of exposure MMSE Journal. Open Access www.mmse.xyz

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increases the corrosion rate approximately by seven folds in all carbon steels, possibly due to the increase in conductance of the solution as a result of continuous inclusion of Fe2+ ions caused by the corrosion of carbon steel [7].

Fig. 1 (b) gives the details of the corrosion of carbon steels in HNO3 acidic environment. The graph shows that, the carbon steels in this environment indicates highest corrosion rate when compared with the other acidic media due to strong oxidizing property of nitric acid. When the surface of the carbon steel exposed to the acidic medium, the possible chemical reaction leads to the formation of nitrogen (II) oxide which modifies the color of the solution. Further this reduction process produces H+ ions into the solution rather than hydrogen evolution[8].

The corrosive properties of carbon steels in HCl environment is shown in Fig. 1 (c). All concentrations of hydrochloric acid will attack stainless steels since the acid readily destroys their passivity. The corrosion rate is found to be very less than compared to all other media possibly due to chloride aggressiveness and also the iron dissolution in HCl solutions depends on H + ion more than the Cl- ion.

As the hydrogen forms, it tends to inhibit further corrosion by forming a very thin gaseous film at the surface of the metal. This film can be effective in reducing metal to water contact and thus reducing corrosion rate. [9] The corrosion properties of carbon steels in hydrofluoric acid environment is mentioned in the Fig. 1 (d). When nonoxidizing acids like Hydroflouric acids corrode steel, atomic hydrogen is formed which combines to form gaseous molecular hydrogen or may be observed into the steel. The corrosion rate is higher than compared to HCl acidic medium possibly due to a change of the physical structure and chemical composition of the corroding metal surface and a change in the composition of the solution, particularly in the vicinity of the surface [10]. Strongly reducing acids such as hydrochloric and hydrofluoric acids readily breakdown the passive layer of steels with little chance of repassivation [11].

(b)

(a)

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(c) Fig. 1. Corrosion behavior of carbon steels in different acidic media.

(d)

Corrosion Behavior of Mild Steel with varying concentration of acidic medium.

Fig. 2 shows the rate of corrosion of mild steel when exposed to different concentrations of HNO3.

The result shows increase in corrosion rate with the increase of concentration of acidic medium, which is similar to the earlier reports [8-10]. Increase in corrosion rate with increasing in acid concentration can be attribute to the energy barrier of corrosion reaction decrease as the increase in the concentration of hydrochloric acid [12].

The corrosion rate of mild steel increases with increasing HNO3 acid concentration, which shows the first order corrosion reaction without changing the reaction mechanism. This can be attributed to the increase in the concentration of oxygen close to the metal surface by eddy transport [5] can also be due to increase in the rate of chemical reaction with increasing concentration [13].

Fig. 2. Corrosion behavior of mild steel in different concentrations of in HNO3.

Summary. Uniform corrosion is easier to predict compared to localized corrosion. The studied carbon Corrosion steels shows significant corrosion behavior in various acidic media and time exposure. The corrosion rate of all carbon steels increases with the increase in the time of exposure.

The corrosion rate was maximum in nitric acid medium due to its oxidizing property. The studies also shows that the increase of corrosion rate of mild steel with the increase in concentration of nitric acid MMSE Journal. Open Access www.mmse.xyz

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which can be attributed to increase in reaction rate and breaking down the passivating layer on the surface of the sample.

References [1] R. E. Melchers, R. Jeffery, Early corrosion of mild steel in seawater, Corrosion Science, Volume 47, Issue 7, July 2005, Pages 1678 1693, DOI 10.1016/j.corsci.2004.08.006 [2] Robert Jeffrey and Robert E Melchers. (2003) Bacteriological influence in the development of iron sulphide species in marine immersion environments. Corrosion Science 45:4, 693-714, DOI 10.1016/S0010-938X(02)00147-6 [3] G. Saha, N. Kurmaih, N. Hakerman, Inhibition of acid dissolution of metals. i. some general. observations, J. Physis. Chem., 59 (8), 1955, 707-710. DOI: 10.1021/j150530a007 [4] M.G. Fontana, Corrosion Engineering. 3rd Edition, McGraw-Hill Book Company, New York, 346, 1987.

Sul http://inpressco.com/category/ijcet/vol-6-no-1-feb-2016/

-283.

(6), 1988, 463-466. DOI: http://dx.doi.org/10.5006/1.3315961 [7] S.K. Singh and A.K. Mukherjee Kinetics of Mild Steel Corrosion in Aqueous Acetic Acid -269. DOI: 10.1016/S1005-0302 (10)60044-8 [8] E. Osarol -228. http://www.academicjournals.org/journal/SRE/article-abstract/9D02F7014290 [9] Chin Scientific & Technology Research, 3 (7), 2014, 306-310. http://www.ijstr.org/research-paperpublishing.php?month=july2014 [10] X. G. Zhang, Corrosion and Electrochemistry of Zinc, Plenum, New York, 1996.

[11] Hand book of stainless steels, Outokumpu Oyj, 2013.

[12] Anees A. Khadom, Aprael S. Yaro, 1Abdul Amir H. Kadum, Ahmed S. AlTaie and 1Ahmed Y. Musa, American Journal of Applied Sciences 6 (7), 2009, 14031409.http://thescipub.com/PDF/ajassp.2009.1403.1409.pdf [13] BI methylthiosemicarbazide, pyridoxal- (4- methylthiosemicarbazone) and its Zn (II) complex.

Mat.Chem. Phy., 48, 1997, 164-169.

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