Microsoft Word - 13-3016_s_ETASR_V9_N5_pp4636-4639


Engineering, Technology & Applied Science Research Vol. 9, No. 5, 2019, 4636-4639 4636  
  

www.etasr.com Mainier et al.: Corrosivity Evaluation of Copper-Nickel Alloy (90/10) in Pumps Used in Offshore Platforms 

 

Corrosivity Evaluation of Copper-Nickel Alloy 

(90/10) in Pumps Used in Offshore Platforms for 

Seawater Pumping  
 

Fernando B. Mainier 

Escola de Engenharia,  
Universidade Federal Fluminense, 
Niteroi, Rio de Janeiro, Brazil 

fmainier@uol.com.br 

Alessandro Martins Coelho 

Escola de Engenharia,  
Universidade Federal Fluminense, 
Niteroi, Rio de Janeiro, Brazil 

coelho.alessandro@ig.com.br 

Edilson Ferreira Barros 

Escola de Engenharia,  
Universidade Federal Fluminense, 
Niteroi, Rio de Janeiro, Brazil 

edbarros.rj0@gmail.com 
 

 

Abstract—This work discusses the case of corrosion in a copper-

nickel alloy used in seawater, where chlorination is necessary to 

control micro- and macro-organism growth that can render 

inoperable the seawater supply system used in an offshore 

platform. Studies developed in the last 30 years have shown 

copper-nickel’s adequateness in seawater, with a corrosion rate 

of about 0.001mm/year. However, annual equipment inspection 

showed localized corrosion in an internal chamber in a stand-by 

pump. Such corrosion occurred due to high-concentration of 
sodium hypochlorite (NaClO) injection into the operational 

system, even for pumps that were out of operation. To evaluate 

this corrosive process, gravimetric (mass loss) and 

electrochemical tests were developed in synthetic seawater with 

NaClO at concentrations of 100, 500, 1000 and 5000mg/L. The 

results indicated that the corrosiveness varied from low to 
moderate. The presence of pitting and crevices observed in the 

laboratory tests derails or compromises material use in seawater. 

It was concluded that there is a need for continuous monitoring 

of the NaClO injection in seawater pumps, and a method was 

proposed in order to minimize or avoid a high concentration of 
chlorine in standby pumps. 

Keywords-localized corrosion; copper-nickel alloy; sodium 

hypochlorite; seawater 

I. INTRODUCTION  

The seawater system used in maritime oil production 
facilities located on the coast of South America is designed to 
supply units and equipment with water injection. Depending on 
the purpose of each maritime installation project, seawater can 
be independent from the utilities and injection wells, except for 
the fire ring main systems, where pressurization can be used for 
an extension of the seawater intake system. The depth of 
seawater intake and the efficiency and integrity of seawater 
pumps, should be set based on these factors: 

• improvement of the seawater to be injected in oil wells, 

• cooling system optimization, 

• improvement of seawater quality in the dehydration of the 
natural gas unit, 

• reduction of seawater flows involved, and 

• reduction of energy consumption. 

For many decades, copper-nickel alloys have been used as 
materials for pipes and equipment for seawater systems, mainly 
in shipbuilding, offshore oil production platforms, and 
desalination plants. The main features of this alloy are good 
corrosion resistance in salt water and greater resistance to 
erosion than other copper alloys or carbon steel. In addition, 
copper-nickel alloys are resistant to biofouling, providing 
multiple economic benefits. Generally, to reduce, minimize and 
control the growth of biofouling, continuous chlorination using 
sodium hypochlorite (NaClO) is used, in such a way that the 
residual free chlorine should be established in the range of 0.2 
to 0.5mg/L. In tropical seawaters the development of 
microorganisms is very intense, requiring the injection of 
NaClO. Generally, these submersible pumps on the platforms 
are inspected every two years. The novelty of this paper is to 
alert marine equipment inspectors that high concentrations of 
NaClO can damage the rotors and internal pumps made of 
copper-nickel alloy. Operational failures of these seawater 
suction pumps can cause disruption of oil production. Despite 
the appropriate properties of this alloy, some failures can occur 
and compromise the pumping of seawater [1-4]. In this 
particular case evaluation, the intake and transfer of sea water 
to different equipment and processes of the platform consists, 
essentially, of four submerged pumps to a depth of 20m 
protected by a screen to avoid the penetration of sea animals. 
As shown in Figure 1, to prevent biofouling a solution of 
NaClO is injected continuously into a dosing pump to maintain 
the level of free chlorine at 0.5mg/L in the intake of the four 
pumps. Those pumps were designed to work at 100% capacity, 
and the casing and impeller were manufactured from a copper-
nickel alloy (90/10). The three pumps (1, 2, and 3) operated in 
scheduled alternation, while the fourth pump was in standby 
mode. In the annual equipment inspection, it was observed that 
the stopped pump had pitting and crevice corrosion located in 
the internal chamber and in the impeller. It was also observed 
that this stopped pump continued to receive, continuously, the 
NaClO solution injected by the dosing pump. This fact resulted 

Corresponding author: Fernando B. Mainier 



Engineering, Technology & Applied Science Research Vol. 9, No. 5, 2019, 4636-4639 4637  
  

www.etasr.com Mainier et al.: Corrosivity Evaluation of Copper-Nickel Alloy (90/10) in Pumps Used in Offshore Platforms 

 

in a considerable increase of concentration of NaClO in the 
inner chamber, while on the outside of the pump (casing), in 
contact with sea water and without the presence of NaClO, 
localized corrosion or pitting were not observed. It is important 
to note that in the deposits removed inside this pump (in stand-
by) no micro or macro organisms that could cause a 
microbiologically influenced corrosion (MIC) were identified 
due to the high concentration of clorine due to NaClO 
accumulated inside this pump. Figures 2 and 3 present a view 
of the seawater suction pump and the dosing pump 
hypochlorite injection. 

 

 
Fig. 1.  Diagram of pump intake and seawater transfer 

 

Fig. 2.  Seawater suction pump  

 
Fig. 3.  Hypochlorite injection dosing pump 

In order to evaluate the corrosion in the internal chambers 
of the seawater suction pumps, gravimetric and electrochemical 

tests were developed, with coupons made with copper-nickel 
alloy in synthetic seawater with additions of NaClO. 

II. MATERIALS AND METHODS 

A. Gravimetric Tests  

The material evaluated in this work was a copper-nickel 
alloy sheet (87.43% Cu, 9.05% Ni, 2.20% Fe and 0.98% Mn) 
used for the manufacturing of coupons. The coupons used in 
the gravimetric tests (weight loss) had the following 
dimensions: 3.50cm×1.0cm×0.2cm. The metal surface was 
prepared with grade 100 to 500 sandpaper. The coupons were 
cleaned with acetone and ethanol and dried with hot air. The 
test coupons were weighed with a digital electronic balance. 
The solutions used in the experiments were characterized as 
saline water containing 3.5% (% mass) NaCl, 800mg/L of 
MgCl2 and 600mg/L of CaCl2, and the pH was set at 7.2–8.0. 
In the saline solutions were added, respectively, in each test, 
100mg/L, 500mg/L, 1000mg/L and 5000mg/L 10% by mass 
NaClO. Gravimetric tests were performed in glass containers 
with a capacity of 400mL. The coupons were completely 
immersed in 250mL of saline solution. The glass containers 
were maintained at a temperature of 25°C with a 
thermostatically controlled bath. The times for testing were 
fixed at 15, 30 and 60 days of exposure. Immediately after the 
completion of the test, each coupon was washed with water, 
pickled with Clark solution for 40s according to ASTM G 31-
72 [5], cleaned with ethanol and dried with hot air. The 
corrosion rates (CR) are defined by: 

( ) / . .    (mm/year)o iCR K W W S tρ= −  (1) 

where K is a constant equal to 8.76×10
4
, Wo and Wi are the loss 

weight in the absence and presence of addition of NaClO, S is 
the sample area (cm

2
), ρ is its density (8.9g/cm

3
 for copper-

nickel alloy),and t is the exposure time (h). 

B. Electrochemical Tests 

For the polarization measurements, samples of the copper-
nickel alloy were cut in order to obtain an electrode surface of 
0.20cm

2
. The metal surface was then embedded in polyester 

resin and polished with No. 600 emery paper. Then, the 
samples were degreased with acetone and washed in distilled 
water before being inserted in a conventional polarization cell, 
as shown in Figure 4.  

 

 
Fig. 4.  Conventional polarization cell 



Engineering, Technology & Applied Science Research Vol. 9, No. 5, 2019, 4636-4639 4638  
  

www.etasr.com Mainier et al.: Corrosivity Evaluation of Copper-Nickel Alloy (90/10) in Pumps Used in Offshore Platforms 

 

The polarization curves were recorded with an Autolab 
potentiostat, Type III, by varying the Voltage at 60mV/min 
over a range of −250mV to +250mV with respect to open 
circuit Voltage. All measurements were carried out at a 
constant temperature of 25°C and without agitation. A solution 
of saline water containing 3.5% (% mass) of NaCl, 800mg/L of 
MgCl2 and 600mg/L of CaCl2 with the pH set between 7.2 and 
8.0 was used. Into the saline solutions were added, in each test, 
100, 500, 1000 and 5000mg/L of sodium hypochlorite, 10% by 
mass. 

III. RESULTS AND DISCUSSION 

A. Weight Loss Measurements 

The test results of the weight loss of copper-nickel alloy 
coupons in the saline solutions with 100, 500, 1000 and 
5000mg/L sodium hypochlorite, 10% (by mass) are presented 
in Figure 5.  

 

 
Fig. 5.  Mass loss of copper-nickel alloy in saline solution with NaClO, 

average of three coupons 

Table I presents the results of the corrosion rate (mm/year) 
of copper-nickel alloy coupons in saline solution with additions 
of NaClO and exposure time of 60 days. 

TABLE I.  CORROSION RATE OF COPPER-NICKEL ALLOY COUPONS 
IN SALINE SOLUTION WITH ADDITIONS OF SODIUM HYPOCHLORITE 

NaClO (mg/L) Corrosion rate (mm/year) 

100 0.007 

500 0.010 

1000 0.014 

5000 0.045 

 

The mass loss assays (Figure 6 and Table I) showed that the 
increase in NaClO in the saline solution and the immersion 
time promoted the loss of mass copper-nickel alloy, meaning 
that the corrosion rate can be considered to be low to moderate, 
based on Table II as proposed by [6]. Figure 6 shows the 
copper-nickel alloy coupons after immersion tests in saline 
solution with 5000mg/L NaClO at 15, 30 and 60 days. In these 
coupons, localized corrosion can be observed after the removal 
of corrosion products. Figures 7 and 8 show other aspects of 
the corrosion deposits, pitting and crevice corrosion, in copper-
nickel alloy coupons immersed in a saline solution with 
5000mg/L sodium hypochlorite. 

TABLE II.  AVERAGE CORROSION RATE [6] 

Corrosiveness 
Average corrosion rate 

mm/year mm/year 

Low <0.025 <1.0 

Moderate 0.025-0.12 1.0-4.9 

High 0.13-0.25 5.0-10 

Severe >0.25 >10 

 

 
Fig. 6.  Copper-nickel alloy coupons in gravimetric testing in saline 

solution with 5000mg/L sodium hypochlorite 

 
Fig. 7.  Corrosion product of copper-nickel alloy coupons with 5000mg/L 

of sodium hypochlorite 

X-ray diffraction analysis of the corrosion deposits on the 
surfaces of the coupons showed the predominance of copper 
chloride hydroxide (Cu2(OH)3Cl) and small amounts of copper 
chloride (CuCl2 ) and nickel chloride (NiCl2). According to [7], 
for copper in pure water during the primary corrosion reaction, 



Engineering, Technology & Applied Science Research Vol. 9, No. 5, 2019, 4636-4639 4639  
  

www.etasr.com Mainier et al.: Corrosivity Evaluation of Copper-Nickel Alloy (90/10) in Pumps Used in Offshore Platforms 

 

a cuprous oxide film (Cu2O) is produced that is predominately 
responsible for corrosion protection.  

 

 
Fig. 8.  Pitting (A) and crevice (B) corrosion in copper-nickel alloy 

coupons with 5000mg/L of NaClO 

Authors in [8, 9] report that in salt solutions, with 
oxygenation and the addition of oxidizing substances, cuprous 
oxide can initially react to form multilayer structures, for 
example, basic copper chloride to CuCl

2
, Cu(OH)

2 
or 

Cu
2
(OH)

3
Cl. These products do not adhere well to the surface 

and can be easily removed. According to [10], depending on 
the concentration of free chlorine in the form of NaClO, the 
corrosion rates of copper-nickel alloys saline solution are in the 
range of 0.07 to 1.27 mm/year. 

B. Electrochemical Tests 

In Figure 9, polarization curves were only placed for assays 
with and without 5000mg/L NaClO. The curves for solutions 
with concentrations of 100, 500 and 1000mg/L were 
superimposed and were not significantly different from the 
curve for the solution without NaClO. The anodic and cathodic 
reactions are affected by the addition of NaClO. The 
intersection of the anodic and cathodic curves showed an 
increase in the intensity of current (log I, A/cm

2
). 

 
Fig. 9.  Current density-potential curves of copper-nickel alloy with and 

without addition of sodium hypochlorite 

IV. CONCLUSION 

Based on laboratory tests and inspection of seawater 
pumps, it is concluded that: 

• The corrosion in copper-nickel alloy coupons was caused 
by high concentration of NaClO (5000mg/L), while the 

concentration of 0.2 to 0.5mg/L of NaClO indicated from 
the uptake of seawater did not cause any corrosion 
problems and prevented the proliferation of micro-
organisms in seawater. 

• Corrosion in the interior of the pumps was due to 
continuous NaClO injection, even when the pump was 
completely stopped. 

• Modification of the project with installation of pilot valves 
monitoring the injection of NaClO could prevent corrosion 
of copper-nickel pumps. 

 

 
Fig. 10.  Modification proposal for of seawater pumps 

REFERENCES 

[1] C. Kapsalis, G. Schmitt, R. Feser, B. Sagebiel, S. Wilmes, M. Macziek, 
“New investigations on critical wall shear stresses of CuNi alloys in 

natural and artificial seawater”, Eurocorr - 2011, Stockholm, Sweden, 
September 4-8, 2011 

[2] W. Schleich, “Typical failures of CuNi 90/10 seawater tubing systems 
and how to avoid them”, Eurocorr - 2004, Nice, France, September 12-

16, 2004 

[3] J. H. Michel, I. Richardson, C. Powell, B. Phull, “Development of 
copper alloys for seawater service from traditional application to state-

of-the art engineering”, Corrosion 2017, New Orleans, USA, March 26-
30, 2017 

[4] A. L. Ma, S. L. Jiang, Y. G. Zheng, W. Ke, “Corrosion product film 

formed on the 90/10 copper–nickel tube in natural seawater: 
composition/structure and formation mechanism”, Corrosion Science, 

Vol. 91, pp. 245-261, 2015 

[5] ASTM, ASTM G31-72, Standard Practice for Laboratory Immersion 
Corrosion Testing of Metals, ASTM International, 1999 

[6] NACE, NACE-RP0775-2005, Standard Recommended Practice: 

Preparation, Installation, Analysis, and Interpretation of Corrosion 
Coupons in Oilfield Operations, NACE, 2005 

[7] M. Pourbaix, “Licoes de Corrosao Eletroquimica”, in: Brasileira de 

Corrosao–ABRACO1, pp. 338-342, 1988 (in Portuguese) 

[8] F. J. Kievits, F. P. Ijsseling, “Research into the corrosion behavior of 

CuNi10Fe alloys in seawater”, Materials and Corrosion, Vol. 23, No. 12, 
pp. 1084–1096, 1972 

[9] A. H. Tuthill, “Guidelines for the use of copper alloys in seawater”, 

Materials Performance, Vol. 26, No. 9, pp. 12-22, 1987 

[10] H. H. Uhlig, Uhlig's Corrosion Handbook, John Wiley & Sons, 2011