Comparative Assessment of Corrosion Behaviour of MCS and KS7 SS in Saline and Carbonate Environments

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 836-840

Published Online August 2012 (http://www.SciRP.org/journal/jmmce)

Comparative Assessment of Corrosion Behaviour of MCS

and KS7 SS in Saline and Carbonate Environments

Olusegun Olufemi Ajide*, Kamorudeen Wemimo Agara

Department of Mechanical Engineering, University of Ibadan, Ibadan, Nigeria

Email: *[email protected]

Received June 8, 2012; revised July 19, 2012; accepted August 10, 2012

ABSTRACT

The major objective of this experimental study is to investigate and compare the corrosion resistance of medium Carbon

steel (MCS) and KS7 stainless steel in saline and sodium carbonate environments. The MCS and KS7 SS were exposed

to 0.5 M each of NaCl and Na2CO3 solutions for a period of 36 days. The weight loss was taken every 3 days in order to

evaluate CPR. The results obtained showed that KS7 SS generally offers a better corrosion resistance than the MCS in

the selected media. While MCS is found to be inappropriate alloy in saline and sodium carbonate environments, KS7

SS is an unfailing choice material for manufacturing machines and other engineering amenities in which their service

lives are predominant in Na2CO3 medium and fairly pleasing in NaCl environment.

Keywords: MCS; KS7 SS; CPR; Saline and Sodium Carbonate

1. Introduction

The challenges of corrosion in manufacturing and do-

mestic sectors are enormous. Corrosion is the major

problem facing exploration, production and processing in

oil and gas, food and construction industries. It is therefore

germane to concentrate efforts and resources towards

meaningful researches that will be a relief to the numer-

ous harms of corrosion in industries. [1] studied the Cor-

rosion behaviour of dc magnetron sputtered Fe1−xMgx

alloy films in 3 wt% NaCl solution. Fe1−xMgx alloy films

(with x ≤ 43.4 at % Mg) were deposited by dc magnetron

sputtering onto glass slide substrates. The aim of their

work was to characterize the corrosion properties of

these alloys in saline solution for application as new

friendly environmentally sacrificial coatings in the pro-

tection of steel structures. The morphological and struc-

tural properties of the alloys were systematically studied

prior to electrochemical experiments, and then the de-

graded surfaces were analyzed to determine the composi-

tion and nature of corrosion products. The reactivity of

the alloys in saline solution is strongly dependent on the

Mg content and the alloy structure. A transition in corro-

sion activity is observed at 25% Mg from which the reac-

tivity decreases with the magnesium content increase.

From this paper, it is evident that an increase in % Mg

decreases the corrosion rates of this alloy. [2] presented a

paper on corrosion assessment of offshore oil pipeline

based on ultrasonic technique. He developed an intelli-

gent ultrasonic inspection device for offshore pipeline

inspection and software for corrosion assessment of off-

shore pipeline. [3] in 2009 work studied the comparative

corrosion behaviour of Al 3103 and galvanized steel

roofing sheets in 1 M, 0.5 M and 0.3 M solutions of so-

dium carbonate and sodium chloride. Samples of the

aluminium and galvanized sheets were subjected to the

different environments for thirty days. The electrode po-

tentials, in mV (SCE), were measured every day. Elec-

trode potential measurements were taken every day for

thirty consecutive days. Weight loss or gain measure-

ments were taken every three days for the duration of the

exposure period. The results of their study showed that

sodium chloride environment had higher corrosive effect

on the galvanized roofing sheet than sodium carbonate

environment while the reverse was true for aluminium

sheets. Also, galvanized steel roofing corroded more than

aluminium roofing in both carbonate and chloride envi-

ronments. Corrosion of galvanized steel roofing was con-

tinuous throughout the exposure period in all the envi-

ronments used. The conclusions drawn by the authors is

that galvanized steel roofing sheet is not a suitable mate-

rial for roofing in carbonate and chloride environments

or in industrial environments where chloride or carbonate

contamination is possible. [4] evaluated the corrosion

behaviour of carbon steel under stagnant seawater condi-

tions. 1020 carbon steel coupons were subjected to natu-

ral seawater for a 1-year period. The study showed that

this alloy is more corrosive in anaerobic stagnant sea-

water conditions than aerobic conditions. The study also

*Corresponding author.

O. O. AJIDE, K. W. AGARA 837

revealed that in both aerobic and anaerobic exposures,

corrosion was more aggressive on horizontally oriented

coupons compared to vertically oriented samples. The

corrosion behaviour of low carbon steel was investigated

in natural seawater and various synthetic seawaters as

reported by [5] in 2006. It was found that the steel cor-

roded nearly four times faster in a 3.5% NaCl solution

than in natural seawater for an exposure time of 21 days.

The corrosion rate after immersion in synthetic seawaters

(ASTM D1141 and Marine Biological Laboratory sea-

water) is similar to the corrosion rate after immersion in

natural seawater. Calcium carbonate (aragonite) deposits

were found on the surface of the steel after immersion in

natural seawater and the synthetic seawaters. Some

magnesium-containing deposits were also found after

immersion in the natural seawater. These deposits act as

a barrier against oxygen diffusion and thereby lower the

corrosion rate. The morphology of the calcium carbonate

deposits that formed during immersion in the natural

seawater is different from those formed during immer-

sion in the solution. [6] studied the electrochemical cor-

rosion behaviour of carbon steel X60 using the electro-

chemical impedance spectroscopy and potentiodynamic

polarization methods. 0.5 M test solutions of sodium

chloride, sodium sulphate and sulphuric acid were used

in a three electrode open cell. The findings of the authors

showed that the rate of corrosion penetration is higher for

carbon steel X60 in 0.5 M sulphuric acid and smaller in

0.5 M sodium sulphate. [7] studied the corrosion behav-

iour of steel for snow and rockfall barriers using electro-

chemical techniques to quantify corrosion rate. His re-

sults generally showed that steels have high corrosion

rate in these media. Synthetic seawaters. This may ex-

plain the slightly lower corrosion rates obtained in the

natural seawater. X-ray diffraction also showed that the

oxy-hydroxides formed in the 3.5% NaCl solution dif-

fered from those formed in the other solutions. [8] inves-

tigated the corrosion behaviour of carbon steel in alkaline

medium in the presence of very low concentration of

polymeric nanoaggregates (0.0024 wt% polyethylene

oxide-PEO-113-b-PS70 micelles). The steel electrodes

were investigated in chloride-free and chloride-contain-

ing cement extracts. The electrochemical measurements,

electrochemical impedance spectroscopy and potentio-

dynamic polarization indicate that the presence of mi-

celles alters the composition of the surface layer and in-

fluences the electrochemical behaviour of the steel. Au-

thors’ observation shows that micelles initially improved

the corrosion resistance of the steel whereas no signifi-

cant improvement was observed within longer immersion

periods. Surface analysis, performed by environmental

scanning electronic microscopy, energy-dispersive X-ray

analysis and X-ray photoelectron spectroscopy supports

and elucidates the corrosion performance characteristics

of carbon steel in simulated pore solution in the presence

of Micelles. [9] in 2011 did a comparative study of cor-

rosion resistance between 316 and different duplex

stainless steel grades. He examined and compared the

corrosion properties of 316L austenitic stainless steel and

duplex grades of LDX2101, SAF2304, AL2003, LDX-

2404, 2505 and 2507.The stainless steels were given heat

treatment at temperature of 800˚C for 30 minutes. Influence

of heat treatment on pitting susceptibility of stainless

steels was estimated using cyclic polarization scan which

is based on ASTM standard G150. Metallurgical analysis

was conducted to find a correlation between microstruc-

ture and pitting resistance. Light microscope was used

for the examination of stainless steel microstructure. In

addition, test samples were examined virtually after pit-

ting tests and critical pitting test to determine the corro-

sion form which was present. The results of his research

showed that pitting corrosion resistance and critical pit-

ting temperature (CPT) values of heat treated highly al-

loyed steels were affected adversely compared with the

results from non-heat treated materials. The author af-

firmed that for stainless steel alloys, the results can be

attributed to metallurgical aspects such as sigma, chro-

mium nitrides, secondary austenite and etc. The author

concluded that the precipitations have significant effects

on corrosion behaviour in stainless steel alloys. [10] in-

vestigated the influence of CO2 on the corrosion behav-

iour of 13Cr martensitic stainless steel AISI 420 and

low-alloyed steel AISI 4140 exposed to saline aquifer

water environment. In order to guarantee the safety of the

site, CO2-corrosion of the injection pipe steels has to be

given special attention. To get to know the corrosion

behaviour samples of the heat treated steel AISI 4140,

42CrMo4, used for casing, and the martensitic stainless

injection pipe steel AISI 420, X46Cr13 were kept at T =

60˚C and p = 1 - 60 bar for 700 h - 8000 h in a CO2-satu-

rated synthetic aquifer environment similar to the geo-

logical CCS-site at Ketzin, Germany .The isothermal

corrosion behaviour obtained by mass gain of the steels

in the gas phase, the liquid phase and the intermediate

phase gives surface corrosion rates around 0.1 to 0.8

mm/year. This implies that Severe pit corrosion with pit

heights around 4.5 mm are only located on the AISI 420

steel. Main phase of the continuous complicated multi-

layered carbonate/oxide structure is siderite FeCO3 in

both types of steel. The corrosion of 18-8 stainless steel

in sodium chloride solutions was studied by [11]. It was

established that under certain conditions, 18-8 stainless

steel is likely to fail in contact with sodium chloride so-

lutions through formation of deep pits. 200 series

stainless steel is currently of great interest to material

researchers, engineers and steel vendors due to its dis-

tinctive mechanical characteristics and acceptable corro-

sion behaviour. According to [12], new grades of the 200

O. O. AJIDE, K. W. AGARA

838

series have been uncovered for the European market. It is

a potential substitute to austenitic grade AISI 304. It has

low nickel content without compromising its austenite

phase former characteristic. A cautious comparison of

the experimental data of the new 200 series and the ex-

isting 300 and 400 series stainless steels were made. This

article revealed that the new 200 grades have mechanical

properties slightly superior to AISI 304 combined with

satisfactory corrosion resistance behaviour.

pons surfaces were treated by abrading them through

successive grades of silicon carbide papers of grades 60

and 120 grit, and finally on the 0.05 μm emery cloth grade.

They were rinsed in distilled water and then in acetone

and later dried. The prepared coupons were stored in

desiccators until when used for the experiments. After

three days of storage; the coupons were immersed in

each 0.5 M, 100 ml of NaCl and Na2CO3 Solutions for a

period of 36 days. The corrosion coupons were removed

from the corrosion media with the aid of a tong. These

were then properly cleaned in distilled water and dried

with cotton wool. The dried samples were weighed with

the electronic digital weighing balance and recorded.

Weight loss measurements of coupons were recorded at

interval of 3 days. The corrosion penetration rate (CPR)

were evaluated from the weight loss measurements using

the Equation (1):

2. Materials and Methods

2.1. Chemical Analysis

The MCS was procured from the universal steel Limited,

Ikeja, Lagos state while KS7 SS was bought from a

stainless steel commercial dealer in Nigeria. KS7 SS is

one of the 200 series stainless steels produced by KAD

Steel Rolling Mills in India. The chemical Composition

Analysis of Medium Carbon steel (MCS) and KS7

Stainless steel that was carried out at the Universal steel

Limited, Lagos state in Nigeria are shown in Tables 1

and 2 respectively.

2.2. Weight Loss Measurements

The MCS and KS7 SS samples were machined into cy-

lindrical and rectangular coupons of 15 mm diameter and

41 mm long and 44 mm by 45 mm respectively. The cou-

CPR  (1)



where K = constant = 3.45 × 106;

CPR = Corrosion Penetration Rate in mils per

year (mpy);

W = the weight loss in grams;

A = Area of exposed specimen in cm2;

t = time or duration of exposure in hours;

ρ = Density of material in g/cm3.

Table 1. Chemical composition analysis of medium carbon steel (MCS).

Run C Si S P Mn Ni Cr

1 0.3397 0.2191 0.0573 0.0620 0.8294 0.0960 0.1242

2 0.3426 0.2204 0.0605 0.0597 0.8343 0.0961 0.1245

Avg 0.3411 0.2198 0.0589 0.0609 0.8318 0.0960 0.1244

Mo V Cu W As Sn Co Al Pb Ca Zn Fe%

0.0188 0.0057 0.2066 0.0035 0.0056 0.0252 0.0088 –0.00070.0001 0.0001 0.0035 97.9951

0.0191 0.0058 0.2077 0.0035 0.0059 0.0262 0.0088 –0.0007–0.00000.0001 0.0038 97.9816

0.0189 0.0058 0.2071 0.0035 0.0058 0.0257 0.0088 –0.00070.0001 0.0001 0.0036 97.9883

Table 2. Chemical composition analysis of KS7 stainless steel.

Run C Si S P Mn Ni Cr

1 0.1099 9.3663 0.0150 0.0640 10.0512 0.3414 11.4664

2 0.1105 0.3534 0.0187 0.0728 10.6255 0.3532 11.1139

Avg 0.1102 0.3598 0.0169 0.0684 10.7384 0.3473 11.292

Mo V Cu W As Sn Co Al Pb Ca Zn Fe%

–0.3414 0.0748 4.6323 0.0817 0.0246 0.0219 0.0444 0.0146 0.0236 0.0004 0.0340 71.8657

–0.0291 0.0731 4.0527 0.0800 0.0242 0.0229 0.0450 0.0121 0.0206 0.0003 0.0326 73.0176

–0.0306 0.739 4.3425 0.0808 0.0244 0.0224 0.0447 0.0134 0.0221 0.0003 0.0333 72.4417

O. O. AJIDE, K. W. AGARA 839

3. Results and Discussion

3.1. Results

See Tables 1 and 2 and Figures 1 and 2.

3.2. Discussion

The corrosion characteristics of MCS and KS7 SS in 0.5

M, 100 ml Nacl solution is shown in Figure 1. MCS re-

sumed the corrosion deterioration on the 6th day with

CPR of 4.2 mpy and this trend continued throughout the

36 days of experimentation. It has the highest corrosion

degradation between the 12th and 15th days with CPR of

7.8 mpy and 6.3 mpy. Whereas, KS7 SS experienced an

approximate no corrosion deterioration within the first 9

days. A significant corrosion penetration was experi-

enced between the 12th and 18th days as a result of sud-

den decrease of solution pH from 6.9 to 3.2, 2.3 and 2.2

on the 12th, 15th and 18th days respectively. The CPR

recorded in these days is respectively 5.8 mpy, 5.6 mpy

and 4.1 mpy. With increase in pH to 4.7 on the 21st day,

there was a remarkably decrease to an approximate 0.0

mpy. This approximate no corrosion continued through-

out the remaining period of 36 days experimentation. The

formation of chromium oxide which acted as protective

layer was responsible for this high passiveness to corro-

sion degradation of KS7 SS in this latter period. Com-

paratively, KS7 SS has moderate but better corrosion

properties than MCS in saline medium. In similar manner,

Figure 2 gives a description of the corrosion behaviour

of MCS and KS7 SS in 0.5 M, 100 ml Na2CO3 solution.

MCS resumed corrosion degradation on the 6th day with

CPR of 2.3 mpy. An inconsistent corrosion penetration

was experienced from the 9th day till the 21st day with

peak value of 5.3 mpy. However, a daily gradual decrease

of CPR began on the 24th day with CPR of 0.3 mpy.

Between 33rd and 36th days, an approximate no corro-

sion deterioration was experienced. The formation of

passive film at the latter part of experimentation was re-

sponsible for this unusual decrease in corrosion deterio-

ration behaviour. Apart from the first 3 days when a CPR

of 4.4 mpy was experienced, KS7 SS exhibited a very

high corrosion resistance characteristic with an approxi-

mate CPR of 0.0 mpy throughout the 36 days. A protec-

tive barrier of Chromium oxide which was formed at the

6th day is undoubtedly the cause of KS7 SS corrosion

passiveness in this carbonate environment. Observably,

KS7 SS has exhibited a more reliable potential for corro-

sion resistance ability in sodium carbonate medium com-

pared to MCS.

4. Conclusions

It is obvious from these experiments to draw the follow-

ing conclusions:

Figure 1. CPR of MCS and KS7 SS in NaCl solution.

Figure 2. CPR of MCS and KS7 SS in Na2CO3.

1) Due to very high corrosion degradation characteris-

tics of MCS, it is considered undependable and inappro-

priate alloy in the fabrication of equipments and tools for

processing Salts and sodium carbonate (or where they

exist as contaminants).

2) KS7 SS possess distinct corrosion resistance char-

acteristics compared to MCS and consequently highly

unfailing and acceptable alloy material for producing

machinery, accessories, tanks , pipes and other engineer-

ing facilities meant to perform in sodium carbonate me-

dium and moderately satisfactory in salty environment.

REFERENCES

[1] C. Berziou, K. Remy, A. Billard and J. Creus, “Corrosion

Behaviour of dc Magnetron Sputtered Fe1−xMgx Alloy

Films in 3 wt% NaCl Solution,” Corrosion Science, Vol.

49, No. 11, 2007, pp. 4276-4295.

doi:10.1016/j.corsci.2007.04.008

[2] Q. I. Zhang, “Corrosion Assessment of Offshore Oil Pipe-

line Based on Ultrasonic Technique,” Shanghai Jiao Tong

University, Shanghai, 2008.

[3] D. T. Oloruntoba, O. O. Oluwole and O. Oguntade, “Com-

O. O. AJIDE, K. W. AGARA

840

parative Study of Corrosion Behaviour of Galvanized

Steel and Coated Al 3103 Roofing Sheets in Carbonate

and Chloride Environments,” Materials & Design, Vol.

30, No. 4, 2009, pp. 1371-1376.

[4] S. L. Jason, I. R. Richard, J. L. Edward, U. F. Alexander

and J. L. Brenda, “An Evaluation of Carbon Steel Corro-

sion under Stagnant Seawater Conditions,” Biofouling:

The Journal of Bioadhesion and Biofilm Research, Vol.

20, No. 4-5, 2004, pp. 237-247.

[5] H. Möller, E. T. Boshoff and H. Froneman, “The Corro-

sion Behaviour of a Low Carbon Steel in Natural and

Synthetic Seawaters,” The Journal of The South African

Institute of Mining and Metallurgy, Vol. 106, 2006, pp.

585-592.

[6] A. C. Ciubotariu, L. Benea and P. L. Bonora, “Corrosion

Studies of Carbon Steel X60 by Electrochemical Meth-

ods,” Journal of Optoelectronics and Advanced Materials,

Vol. 12, No. 5, 2010, pp. 1170-1175.

[7] F. Deflorian, S. Rossi, B. Tancon and P. L. Bonora, “Cor-

rosion Behaviour of Steel Ropes for Snow and Rockfall

Barriers,” Corrosion Engineering, Science and Technol-

ogy, Vol. 39, No. 3, 2004, pp. 250-254.

doi:10.1179/147842204X2853

[8] J. Hu, D. A. Koleva, J. H. W. de Wit, H. Kolev and K.

van Breugel, “Corrosion Performance of Carbon Steel in

Simulated Pore Solution in the Presence of Micelles,”

Journal of the Electrochemical Society, Vol. 158, No. 3,

2011, pp. C76-C87.

[9] G. Elnura, “Comparison of Corrosion Resistance of 316

and Different Stainless Steel Grades,” Master Thesis, Uni-

versity of Stavanger, Stavanger, 2011.

[10] A. Pfennig and A. Kranzmann, “Influence of CO2 on the

Corrosion Behaviour of 13Cr Martensitic Stainless Steel

AISI 420 and Low-Alloyed Steel AISI 4140 Exposed to

Saline Aquifer Water Environment,” Transactions of the

Wessex Institute, 2006, 10 p.

[11] H. H. Uhlig and M. C. Morill, “Corrosion of 18-8

Stainless Steel in Sodium Chloride Solutions,” Industrial

& Engineering Chemistry, Vol. 33, No. 7, 1941, pp. 875-

880.

[12] J. Charles, J. D. Mithieux, J. Krautschick, N. Suutala, S. J.

Antonio, S. Van Hecke and T. Pauly, “A New European

200 Series Standard to Substitute 304 Austenitics?” Re-

vue de Métallurgie, Vol. 106, No. 2, 2009, pp. 90-98.