Materials Science, Vol. 48, No. 2, September, 2012 (Ukrainian Original Vol. 48, No. 2, March–April, 2012)

EARLY AGE CORROSION OF MILD STEEL IN AGGRESSIVE MEDIA A. U. Ozturk,1, 2 E. Gucuyen R. T. Erdem,1 and S. Seker1 Effects of the time of holding, type of section, and concentration of the solution on the early age corrosion of mild steel are studied. Section types for steel specimens were box, tube, and corner. They were subjected to 3.5%, 5.0%, and 7.0% NaCl solutions. It was established that the concentration of the solution affects the corrosion until reaching the saturation value. Keywords: corrosion, mild steel, type of section, NaCl.

Experimental analyses for various purposes became significant in the studies for the last couple of decades. The engineering problems of connecting cities by long-span bridges or constructing the highest skyscrapers in the world have two different sides. These problems seem to be problems of pure structural analysis, which can be solved with the help of engineering-analysis programs by using computers of great capacities. In fact, these problems are not the same as they seem to be. They have another side which may have more ruinous effects during the service life of a structure in the case of being ignored. This side includes the durability problems of structures. These problems may affect the structural stability and reliability day by day. Corrosion is one of the durability problems connected with the aggressive media having inverse effects on the structures. Corrosion can be defined as the deterioration of a material with chemical reactions running between the material and the aggressive media. The chemical reactions may occur on the surface of materials leading to the weight and section losses. Corrosion is one of the most misunderstood and mischaracterized forms of material degradation. Hence, the corrosion analysis and mitigation methods tend to be some of the most misapplied. In many cases, corrosion is the life-limiting factor of structural components [1]. Corrosion problems can be met at any time during the service life. Engineers must be ready for these undesirable conditions and provide good material selection and proper precaution methods. Thus, some production problems may occur during the construction of structures containing steel sections. Similar corrosion effects are studied in [2–9]. At present, engineers face with associated pitfalls of corrosion. To decrease the destructive effects of corrosion reactions, some laboratory test methods must be performed to examine the service life and performance of steel structural elements by considering them apart from the structures which extend some way into the splash zone. The results obtained for small-scale specimens are generally considered to be directly applicable to fullscale structures [5]. The laboratory tests must simulate almost actual field conditions in order to get the exact results. Current laboratory tests and the required new tests (designed in the future) must give capacities and knowledge desired to overcome corrosion and its destructive effects. Proper material selection and effective precaution methods resulting from good simulating tests are always necessary for structural stability and reliability. 1 2

Department of Civil Engineering, Celal Bayar University, Manisa, Turkey. Corresponding author; e-mail: [email protected].

Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 48, No. 2, pp. 91–96, March–April, 2012. Original article submitted January 23, 2012. 1068-820X/12/4802–0219

© 2012

Springer Science+Business Media New York

219

220

A. U. OZTURK, E. GUCUYEN R. T. ERDEM,

AND

S. SEKER

Most of the laboratory experiments deal with the marine media recognized to be very corrosive for mild and low-alloy steels. For economic reasons, these steels are still the preferred materials for the offshore structures, ship hulls, sheet piling, and harbor-side facilities [5]. Seawater, in view of its variability, is not easily simulated in the laboratory for corrosion-testing purposes. A 3.5% NaCl solution is frequently used for this purpose. It is known to be more aggressive toward carbon steel than natural seawater [10]. This indicates the importance, particularly for engineering design considerations, of understanding the factors that control the immersion corrosion of steel as a function of water salinity. It was found that steel corroded nearly four times faster in a 3.5% NaCl solution than in natural seawater for an holding time of 21 days [11]. The corrosion resistance of mild-steel samples was determined for different section types. Aggressive media with destructive corrosion effects were formed by three different NaCl solutions (3.5%, 5.0%, and 7.0%) and pure distilled water. The corrosion rates and weight losses were determined for early ages, such as 10, 30, 60, and 90 days. Table 1. Characteristics of Mild-Steel Sample

Section type

Dimensions, mm

Initial weight, g

Surface area, mm 2 50 × 110 × 40 = 22,000

Box (B)

50 × 20 × 110

455.3

46 × 110 × 40 = 20,240 ΣA = 42,240 π × 60 × 110 = 20,735

Tube (C)

∅ 60 × 30 × 110

427.5

π × 54 × 110 = 18,661 ΣA = 39,396 50 × 110 × 20 = 11,000

Corner (L)

50 × 50 × 40–110

399.5

46 × 110 × 20 = 10,120 ΣA = 21,120

Experimental The problem gets serious when corrosion effects on steel structures are seen by naked eye. To realize and determine the corrosion behavior of mild-steel elements under the action of aggressive media, three different section types were selected according to their geometry. The properties оф mild steel samples are given in Table 1. The value of density for each section type is 7.85 g/cm 3 . Cycle activities were applied to observe the corrosion effect in the experimental part. Corrosion cycles include three different parts. First, mild-steel samples were submerged into NaCl solutions and distilled water in order to simulate aggressive corrosion media during 12 h. In the second part, samples were placed into a drying oven at 60°C for about 30 min. In the last part, cooling was performed under the laboratory conditions between ca. 20 and 22°C. After this, the weight losses of steel samples were measured to determine the corrosion rates. These corrosion cycles whose details are presented in what follows were repeated for 90 days. The steel samples were subjected to the action of corrosive media containing NaCl solutions with concentrations of 0%, 3.5%, 5.0%, and 7.0%, respectively. The properties of solutions are given in Table 2. A certain code was attributed to each experimental set. As an example, a set with tube steel samples placed in a 5.0% NaCl solution was called “CN5.”

EARLY AGE CORROSION OF MILD STEEL IN AGGRESSIVE MEDIA

221

Table 2. Properties of Solutions Solution

Initial solution

NaCl concentration, %

pH value

Distilled water

D

0

7.1

3.5% NaCl

N3.5

3.5

6.8

5.0% NaCl

N5.0

5.0

6.5

7.0% NaCl

N7.0

7.0

6.3

Table 3. Definitions of Experiment Sets Definition of experimental set

Code

Box sections in distilled water

BD

Tube sections in distilled water

CD

Corner sections in distilled water

LD

Box sections in a 3.5% NaCl solution

BN3.5

Box sections in a 5.0% NaCl solution

BN5

Box sections in a 7.0% NaCl solution

BN7

Tube sections in a 3.5% NaCl solution

CN3.5

Tube sections in a 5.0% NaCl solution

CN5

Tube sections in a 7.0% NaCl solution

CN7

Corner sections in a 3.5% NaCl solution

LN3.5

Corner sections in a 5.0% NaCl solution

LN5

Corner sections in a 7.0% NaCl solution

LN7

The symbols “C” and “N5” mark the type of a section (tube) and a 5.0% NaCl solution, respectively. In total, there were 12 experiment sets including 9 samples, as indicated in Table 3.

Results and Discussion Corrosion effects are inevitable for steel structures and can be minimized by taking early measurements. Thus, the service life of structures becomes longer and less maintenance costs are needed. Indeed, the improper design and production of steel structures create some durability and stability problems for the service life. Corrosion negatively affects these structures. They lose their thickness, symmetry of the bodies, and weight in the course of time. In addition, corroded parts are responsible for the density losses in the sections of steel structures.

222

A. U. OZTURK, E. GUCUYEN R. T. ERDEM,

AND

S. SEKER

Fig. 1. Weight losses with time for sections of different types in: (a) distilled water, (b) 3.5% NaCl, (c) 5.0% NaCl, (d) 7.0% NaCl; () corner, () tube, () box.

Corrosion tests were carried out on steel samples with an aim to investigate the time dependences of the corrosion rate for sections of different types and solutions of different concentrations (Fig. 1). The weight losses increase with time according to the corrosion processes. Additionally, the effect of section types on corrosion resistance was observed and the maximum weight losses were detected for the box sections. The minimum values of the weight losses were observed for the samples submerged in distilled water and the maximum values were obtained for the samples in 7.0% NaCl solutions. As in Fig. 1, the effects of section types on the time dependences of the corrosion rates were investigated for analyzed solutions and the results of these investigations are presented in Fig. 2. Although all NaCl solutions affect corrosion in comparison with distilled water, the concentration of solution cannot present a distinctive effect on corrosion at the saturation limit. Thus, the effect of 7.0% NaCl solutions is almost the same as the effect of 5.0% NaCl solutions (Fig. 3). The box sections were most affected by corrosion according both to their mass losses and corrosion rates. The effects of solutions on the time dependences of corrosion rates were investigated for the box sections, as seen in Fig. 3. The effects of solutions on corrosion rates can be seen not only for the box sections but also for all other types of sections.

EARLY AGE CORROSION OF MILD STEEL IN AGGRESSIVE MEDIA

223

Fig. 2. Time dependences of corrosion rates for different types of sections in: (a) distilled water, (b) 3.5% NaCl, (c) 5.0% NaCl, (d) 7.0% NaCl; () corner, () tube, () box.

Fig. 3. Time dependences of corrosion rates for box sections: () distilled water, the solid line corresponds to 3.5% NaCl; () 5.0% NaCl; () 7.0% NaCl.

224

A. U. OZTURK, E. GUCUYEN R. T. ERDEM,

AND

S. SEKER

CONCLUSIONS Although it is easy to recognize corrosion of every detail of a steel structure, it is important to predict its corrosion resistance prior to the construction works. There are several methods to simulate the early age corrosion of steel details. The corrosion resistance of mild-steel specimens with different types of sections was investigated. The specimens were subjected to NaCl solutions of different concentrations. Corrosion in distilled water was also taken into consideration. It was established that the corrosion rate of steel increases with the concentration of solutions but decreases within the time of holding. The maximum values of corrosion rate were obtained for the samples with box sections. This study might be further enhanced by using different sections and concentrations of solutions under different conditions. REFERENCES 1. J. Guthrie, B.Battat, and C. Grethlein, “Accelerated corrosion testing,” AMPTIAC Quarterly, 6, No. 3, 11–15 (2010). 2. R. E. Melchers and B. B. Chernov, “Corrosion loss of mild steel in high-temperature hard freshwater,” Corr. Sci., 52, Issue 2, 449– 454 (2010). 3. L. Han and S. Song, “A measurement system based on electrochemical frequency modulation technique for monitoring the early corrosion of mild steel in seawater,” Corr. Sci., 50, Issue 6, 1551–1557 (2008). 4. R. E. Melchers, “Modeling immersion corrosion of structural steels in natural fresh and brackish waters,” Corr. Sci., 48, Issue 12, 4174–4201 (2006). 5. R. E. Melchers, “Corrosion uncertainty modeling for steel structures,” J. Construct. Steel Res., 52, Issue 1, 3–19 (1999). 6. M. Lebrini, F. Bentiss, H. Vezin, and M. Lagrenée, “The inhibition of mild steel corrosion in acidic solutions by 2,5-bis(4-pyridyl)1,3,4-thiadiazole: Structure–activity correlation,” Corr. Sci., 48, Issue 5, 1279–1291 (2005). 7. M. Lebrini, M. Lagrenée, H. Vezin, M. Traisnel, and F. Bentiss, “Experimental and theoretical study for corrosion inhibition of mild steel in normal hydrochloric acid solution by some new macrocyclic polyether compounds,” Corr. Sci., 49, Issue 5, 2254–2269 (2007). 8. A. Pardo, M. C. Merino, A. E. Coy, V. Arrabal, F. Viejo, and E. Matykina, “Corrosion behavior of magnesium/aluminum alloys in 3.5 wt.% NaCl,” Corr. Sci., 50, Issue 3, 823–834 (2008). 9. J. Liao, K. Kishimoto, M. Yao, Y. Mori, and M. Ikai, “Effect of ozone on corrosion behavior of mild steel in seawater,” Corr. Sci., 55, Issue 2, 205–212 (2012). 10. D. A. Jones, Principles and Prevention of Corrosion, Prentice Hall, Upper Saddle River, NJ (1996). 11. H. Möller, E. T. Boshoff, and H. Froneman, J. South African Inst. Mining Metallurgy, 106, 585–592 (2006).