Journal of Mi nerals & Materials Characteriza tion & Engineering, V ol. 9, No.10, pp.879-886, 2010
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879
Performance of Nickel-Coated Manganese Steel in High-Chloride
Low-Sulphate Seawater Environments
Olorunniwo, O. E.1*, Atanda, P. O.1, Akinluwade, K. J.1,2 Adetunji, A.R.1,2, and
Oluwasegun, K.M.1
1Department of Materials Science & Engineering Obafemi Awolowo University Ile-Ife
2National Agency for Science & Engineering Infrastructure (NASENI), Abuja
*Corresponding author: [e-mail]
ABSTRACT
This work investigated th e service performance of nickel-coated manganese steel in both normal
high-chloride (clean) and low-sulphate high-chloride (polluted) seawater environments (typical
offshore oil and gas production environments). Structural manganese steels coated with nickel
together wi th the control wer e tested for corr osion characteristics using the weight loss method.
It was found that the nickel coat was able to resist corrosion overtime via spontaneous formation
of passive oxide films at ambient temperatures. Analysis of resulting corrosion rates underscored
the viability of nickel coating at inhibiting severe corrosion owing to the harsh chloride- and
sulphate-containing seawater typical of the oil and gas production environments.
Keywords: passive oxide, corrosion, high-chloride low-sulphate seawater, manganese steel,
electroplating,
1. INTRODUCTION
It is estimated that industry spends $276 billion annually on corrosion. These costs arise from a
variety of areas. Prevention, monitoring, and repair are the main contributors to this high amount
and these values do not even include down time as a result of corrosion [1, 6].
Corrosion is the deterioration of a material or its properties in a given service environment. It is
also the partial or complete wearing away, dissolving, or softening of any substance by chemical
or electrochemical reaction with its environment. The term corrosion specifically applies to the
gradual action of natural agents, such as air or salt water, on metals. It is a state of deterioration
in metals caused by oxidation or chemical action [10]. The basic corrosio n cell is formed by two
dissimilar metals immersed in an electrolyte joined by a conductor, One electrode will tend to
corrode more readily than the other and is called the anode. Natural systems often place the
machine part as the anode whil e the prevailing environment makes up the electroly t e [8, 9].

880 Olorunniwo, O.E., Atanda, P.O., Akinluwade, K.J., Adetunji, A.R., and Oluwasegun, K.M. Vol. 9, No.10
The oil industry consists of the upstream businesses of exploration & production and gas &
power and the downstream businesses of oil products, chemicals and oil sands. Corrosion attacks
every co mponent at every stage in the life of every oil and g as field. A t the drilling st age (which
is about the first stage in production), oxygen-contaminated fluids are first introduced. Water and
carbon-dioxide—produced or injected for secondary recovery—can cause severe corrosion of
completion strings. Hydrogen sulphate in the pl ant effluents poses severe environmental hazards.
This makes the surrounding water and atmosphere hostile to metallic tools and parts [4, 7].
Several established and emerging technologies for corrosion evaluation and monitoring abound.
Established technologies include measuring environmental conditions, exposing material
coupons to corrosive media, and using electrical resistance, linear polarization resistance, and
galvanic probes. Emerging technologies include the use of advanced electrochemical testing
techniques and the application of specialized probes for stress-corrosion cracking and pitting
corrosion [4, 5, 9]. Since it is almost impossible to prevent corrosion, it is becoming more
apparent that monitoring and controlling the corrosion rate may be the only economical solution.
The oil industry has invested heavily in material and personnel to try to tame corrosion and
prevent ferrous tools from returning to their natural state. New oil fields benefit from
predevelopment planning and the growing knowledge of all aspects of corrosion control and
monitoring [2. 3]. A large volume of research work has been done to proffer solution to
corrosion phenomenon. The present work understudies the performance of nickel-coated
manganese steel in two environments which represent the oil and gas production environments
of normal high-chloride (clean) and low-sulphate high-chloride (polluted) seawater.
2. MATERIALS AND METHOD
2.1 Description of Steel Samples
The steel material used for this experiment is ST60Mn steel obtained from the standard stock
with the chemical composition (wt%) of carbon 0.35-0.42, silicon 0.20-0.30, manganese 0.90-
1.20, phosphorus 0.04, sulphur 0.25, copper 0.10, chromium 0.10, nickel 0.10; th e balance being
iron. From this steel, 30 pieces of about 10 mm square samples were prepared.
2.2 Corrosion Media
Two corrosive environments were prepared:
(i) High chloride seawater environment from the Atlantic Ocean.
(ii) Simulated low-sulphate high-chloride environment obtained by adding 0.015M Na2SO4
to seawater sourced from the Atlantic Ocean.
In general, these two environments represent the oil and gas production environment of normal
high-chloride (clean) and low-sulphate high-chloride (polluted) seawater environments.

Vol.9, No.10 Performance of Nickel-Coated Manganese Steel 881
2.3 Electroplating
To obtain good adhesion and brightness of the nickel coat on the substrates, the nickel solution
for a 3 litres plating bath was prepared using 600 g of nickel sulphate, 120 g of nickel chloride,
120 g of boric acid, 60 ml of formaldehyde and 3 litres of distilled water. Using a nickel anode,
the steel samples were electroplated for 40 and 50 minutes respectively. The electrolyte having
being preheated to 50oC. After electrolysis the sp ecimens were removed, rinsed in distilled wat er
and left to cool off in sawdust. Only 20 samples were electroplated while the remaining 10 were
left as control. After electroplating, the initial weights of all samples were measured and
recorded using a digital weighing balance.
2.4 Corrosion Test
A group of three samples (comprising an uncoated sample and two samples each coated for 40
and 50 minutes respectively) was suspended from strings and completely immersed in high-
chloride seawater contained in clean HDPE bowls for 6 days. After this period of complete
immersion, the samples were removed, cleaned and weighed (final weight). This was repeated
for another four groups but with immersion durations of 12, 18, 24 and 30 days respectively. In
the same vein, five groups of samples were suspended from strings and completely immersed in
high-chloride low-sulphate seawater for 6, 12, 18, 24 and 30 days respectively. The final weights
were measured and recorded.
2.5 Corrosion Rate Measurement
Corrosion rate measurement was obtained from the weight loss method using the standard
corrosion rate formula.
..


Where,
W= weight loss (g); D = density (g/cm3); A = Area (cm2); T = Time (hrs)
K = corrosion constant which will depend on the di mension desired for the corrosion r ate (8.76 x
104 for mm/year).
3. RESULTS AND DISCUSSION
3.1 Trend of Corrosion Rate
Corrosion rates for curves of Figure 1 decrease non-uniformly with time for any given sample.
Each corrosion rate curve is charac terized with a n initial p eak owing to rapid intera ction be twe en
the samples and their environment. Curves of Figure 2 also manifest similar initial peaks.
Beyond six days, the rates of corrosion fall significantly. This rapid decline is due to prompt
formation of passivating oxide films on the surface of immersed samples. It was observed that

882 Olorunniwo, O.E., Atanda, P.O., Akinluwade, K.J., Adetunji, A.R., and Oluwasegun, K.M. Vol. 9, No.10
the electrodeposited nickel coat on the steel gave it a protection against corrosion. The
passivating film which builds up on the surfaces of the samples are actually corrosion products
which serve to inhibit further corrosion.
Figure 1: Corrosion rates of samples immersed in high-chloride seawater as a function of time
Beginning from 14 days down to 30 day s the curves of corrosion rates of all the s amples attempt
to stabilize to a linear horizontal trend with a gentle slope. The curves of Figure 2 show a steeper
slope than those of Figure 1 suggesting higher corrosion rates in the samples subjected to high-
chloride low-sulphate environment. This observation again bring to the fore the more severe
corrosion tendency of dissolved sulphur polluted seawater.
3.2 Corrosion Rates in High-Chloride Environment versus High Chloride Low-Sulphate
Environment
The initial corrosion rates (at six days) is higher for all the samples in high-chloride low-sulphate
seawater environ ment than in high chlorid e seawater env ironment. Although th e active corrosion
products in seawater are the dissolved salts of which sodium chloride is chief, the presence of
sulphur readily exacerbates corrosion as is demonstrated in this work. On the average, judging
from Tables 1 and 2, the corrosion rate is increased by 5—25 % by the presence of dissolved
sulphur even at a low concentration for uncoated samples while the nickel coating reduced this
corrosion rate to a maximum of 7—10 %.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0510 15 20 25 30 35
Corrosionrate(mm/yr)
Time(days)
Coatedfor50minutes Coatedfor40minutes Uncoatedsample

Vol.9, No.10 Performance of Nickel-Coated Manganese Steel 883
Figure 2: Corrosion rates of samples immersed in high-chloride low-sulphate seawater as a
function of time
Table 1: Corrosion rates of samples immersed in high-chloride seawater
Sample Area
(cm2
)
Initial
weight (Final weight (
g
Weigh
t
loss (g
)
Day
s
Time
(hrs)
UNCOATED
SAMPLE
F 7.21 11.15
7
11.0910.0666 144
G 6.67 9.2609.2030.05712288
H 7.92 12.56
2
12.4720.09018432
I 6.97 10.97110.8830.08824576
J 7.36 11.45
9
11.3670.09230720
COATED FOR
4
MINUTES
F
1
6.41 9.0538.9990.0546 144
G
1
6.59 9.0729.0250.04712288
H
1
7.12 10.46310.3860.07718432
I1 6.32 8.3508.2820.06824576
J1 6.54 8.3708.2920.07830720
COATED FOR
5
MINUTES
F
2
6.12 8.0177.9670.0506 144
G
2
7.65 8.0888.0390.04912288
H
2
6.44 8.3098.2560.05318432
I2 7.29 8.5748.5030.07124576
J
2
8.17 12.71
8
12.6290.08930720
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0510 15 20 25 30 35
Corrosionrate(mm/yr)
Time(days)
Coatedfor50minutes Uncoatedsample Coatedfor40minutes

884 Olorunniwo, O.E., Atanda, P.O., Akinluwade, K.J., Adetunji, A.R., and Oluwasegun, K.M. Vol. 9, No.10
Table 2: Corrosion rates of samples immersed in high-chloride low-sulphide seawater
Sample Area
(cm2)
Initial
weight
(g)
Final
weight
(g)
Weight
loss (g) Days Time
(hrs)
Corrosion
rate
(mm/yr)
UNCOATED
SAMPLES
A 5.95 11.486 11.417 0.069 6 144 0.9044
B 7.91 12.623 12.540 0.083 12 288 0.4092
C 7.70 12.001 11.910 0.091 18 432 0.3072
D 7.60 9.272 9.192 0.080 24 576 0.2052
E 5.96 7.500 7.426 0.074 30 720 0.1937
COATED FOR
40 MINUTES
A1 7.66 11.802 11.730 0.072 6 144 0.7331
B1 7.69 12.365 12.294 0.071 12 288 0.3600
C1 6.18 8.218 8.160 0.058 18 432 0.2440
D1 6.89 9.902 9.822 0.080 24 576 0.2264
E1 7.19 10.482 10.388 0.094 30 720 0.2039
COATED FOR
50 MINUTES
A2 6.77 9.218 9.166 0.052 6 144 0.5990
B2 5.85 7.676 7.630 0.046 12 288 0.3066
C2 6.45 8.707 8.652 0.055 18 432 0.2217
D2 6.42 8.815 8.741 0.074 24 576 0.2247
E2 5.97 7.989 7.916 0.073 30 720 0.1907
Many aqueous corrosion problems may be handled by using nickel and its alloys. The nickel coat
has a good resistance to corrosion at ambient temperatures to high chloride and low sulphate
seawater environments. Nickel spontaneously forms passive oxide films upon exposure to
seawater at ambient temperature. This film helps to provide useful corrosion resistance which
subsequently reduces corrosion rate overtime.
4. CONCLUSION
The following conclusions can be drawn from the experiment described above.
1. High-chloride low-sulphate seawater (polluted) environments are more corrosive than high-
chloride (clean) seawater environments.
2. Sulphate pollution in seawater increases corrosion rate of manganese steels by 5—25 % for
uncoated samples and this is reduced to 7—10 % by electrodeposited nickel coating.
3. A thicker coat of electrodeposited nickel provides better corrosion resistance through
formation of passivating oxide layers at the surface of the steels.

Vol.9, No.10 Performance of Nickel-Coated Manganese Steel 885
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