Volume 6 Preprint 39
Electrochemical Behaviour of UNS S17700 and UNS N08800 Alloys in Synthetic Wastewater
R. Sandoval-Jabalera, E. Arias-Del Campo, F. Almeraya-Calderon, C. Gaona-Tiburcio, J. G. Chacon-Nava and A. Martinez-VillafaÃƒÂ±e
Keywords: Electrochemical behaviour, cyclic potentiodynamic scan, synthetic wastewater
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Volume 6 paper C095
ELECTROCHEMICAL BEHAVIOUR OF UNS S17700 AND UNS N08800
ALLOYS IN SYNTHETIC WASTEWATER
R. SANDOVAL-JABALERA, E. ARIAS-DEL CAMPO, F. ALMERAYA-CALDERON, C.
GAONA-TIBURCIO, J. G. CHACON-NAVA, A. MARTINEZ-VILLAFAÑE
Advanced Materials Research Centre
Materials Deterioration and Structural Integrity Division.
Miguel de Cervantes 120, Comp. Industrial Chihuahua, C.P. 31110, México
Phone: +52 (614) 439-1145, Fax +52 (614) 439-1112
Corresponding author : email@example.com
The electrochemical behaviour of S17700 and N08800 type steels exposed to synthetic
wastewater containing microorganisms was studied. Laboratory tests were carried out for 30-days
and the experimental conditions were: a biochemical oxygen demand (BOD) of 500 ppm., a
chemical oxygen demand (COD) of 17,000 ppm, pH = 8 and the cell average temperature was
maintained at 21°C. Cyclic potentiodynamic scan measurements were performed for each alloy
from –900 to 900 mV. Results were compared against those obtained from a reference cell. In
synthetic wastewater, both alloys showed an increase in corrosion rate and variations in
electrochemical behaviour. The UNS S17700 steel showed greater corrosion rate than that
recorded for the N0880 steel. The influence of wastewater on the observed behaviour for these
materials is discussed.
Keywords: Electrochemical behaviour, cyclic potentiodynamic scan, synthetic wastewater.
Corrosion is a heterogeneous process involving reactions between materials and its environment.
Microbial Induced Corrosion (MIC) of steels in both aerobial and anaerobial systems has
received a lot of interest particularly in the last few years1. This is because in many industrial
situations (fuel tanks, civil structures, ships hulls, pumps, cooling water systems etc..) the effect
of MIC on materials degradation has been reported. To study the electrochemical behaviour of
ferrous and non-ferrous materials several electrochemical techniques have been employed among
others: electrochemical impedance spectroscopy (EIS), electrochemical noise (EN), cyclic
potentiodynamic scan (CPS) and linear polarization resistance (LPR). As a preliminary study, the
aim of this work has been to investigate the electrochemical behaviour of alloys S17700 and
N08800 in a synthetic wastewater environment employing CPS. It is important to point out that,
on this topic (wastewater) very little information is available in the literature.
The materials tested were a standard semiaustenitic precipitation-hardening stainless steel
UNS S17700 and a austenitic high alloy UNS N08800. The chemical compositions of the steels
are shown in table 1.
TABLE 1. Chemical composition (%)
S17700 17-7PH 17.0 7.0 0.07 0.70
19-23 30-35 0.1 1.5
Alloys were cutting off into coupons of 1.27 cm diameter and 2 cm height. Afterwards, the
coupons were insulated with epoxic resin to make the arrangement of three identical electrodes2,3,
followed by appropriate surface preparation through grinding with grit paper from 120 to 1200
Synthetic wastewater was prepared using 4g of ground organic matter and dissolved in 1 litre of
fresh water. Table 2 shows the characterization analysis of the synthetic wastewater used.
TABLE 2. Characteristics of synthetic wastewater.
Biochemical Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
The electrochemical cell was a glass flask containing 1 litre of synthetic wastewater, with the
electrodes located at the wastewater level. Cyclic potentiodynamic measurements were
performed from –900 to 900 mV using a ACM Instrument Auto Tafel Equipment. Figure 1
shows the electrochemical cell.
Figure 1. Electrochemical cell.
Table 3 shows the values of electrochemical behaviour, while the figure 2 shows the voltage vs
current density graphs of both alloys.
TABLE 3. Electrochemical values of S17700 and N08800
Corrosion rate (mm/yr)
Figure 2 shows the cyclic potentiodynamic scan of N08800 steel at day 18 when the higher
corrosion rate was recorded.
Voltage (mV vs
N08800 (Day 18)
Figure 2. Cyclic potentiodynamic scan of N08800.
Figure 3 shows the cyclic potentiodynamic scan of S17700 steel at day 22 when the higher
corrosion rate was recorded.
Voltage (mV vs
S17700 (Day 22)
Figure 3. Cyclic potentiodynamic scan of S17700.
In first instance, from figures 2 and 3 it can be seen a passivation like behaviour. This might
indicate that the alloys are able to protect by themselves against pitting corrosion in the present
environment. However, the corrosion rates obtained are high, suggesting that other mechanism is
operating. As a preliminary study, we are aware that the CPS measurements yield only qualitative
information, so its application to elucidate corrosion mechanisms and corrosion monitoring is not
Under the experimental conditions here, both alloys were attacked. The synthetic wastewater
used here was very aggressive in particular for the S17700 steel. To have a better understanding
of the degradation processes, it will be important to undertake a series of tests using another
electrochemical techniques (EIS for example) and microbiological experimental conditions.
We would like to thank Conacyt (Mexico) for financial support.
“Biocorrosion of Iron With Thiobacillus ferrooxidans- Linear Polarization Study”, B. Pesic
and V.C. Storhock, (Houston, TX: National Association of Corrosion Engenieers, 2001).
2. “Electrochemical Impedance and Noise”, R. Cottis and S. Turgoose, Corrosion Testing Made
Easy. (Houston, TX: National Association of Corrosion Engenieers, 1999).
3. “D. C. Electrochemical Test Methods”, N. G. Thompson and J. H. Payer, Corrosion Testing
Made Easy. (Houston, TX: National Association Of Corrosion Engineers, 1998).