I will be very glad if you can give me a full details. My sample is a mild steel and my Icorr is 3629.3microamp. Thanks.
Dear Dr. Musa, corrosion rate can be calculated by the following equation:
Corrosion rate (mpy) = 0.13×icorr×Ew/d
where Ew is equivalent weight , that is 55.84 for steel and d is density that is 7.86 g/cm^3 for steel and icorr is corrosion current density that obtained from Tofel slope.
Dear Dr. Fatahi Musa,
from icorr you can calculate corrosion rate (CR) in different units, as below:
-CR (in mils per year - mpy)= 0.13 x icorr (in µA/cm2) x [eq. wt of steel / density of steel]
-CR (in mm/y) = 3.27 x icorr (mA/cm2) x [eq. wt of steel / density of steel]
If you need to convert corrosion rate from/or to mdd, you can use the following relation:
CR (mpy)= (1.44/ density of steel) x CR (mdd)
Following, the explanation of some parameters present of the above rules:
Equivalent weight (eq.wt.) of steel = atomic weight of steel/valency
Atomic weight of steel =55.845
Density of steel = 7.86 g/cm3
In this context, I remind you that there is an international standards to find corrosion rate from polarization graph that increases the reliability of the result obtained: ASTM Designation: G 102 "Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements".
Best regards, Pierluigi Traverso
Dear Fatahi
Refer to the attachment on "Basics of Corrosion Measurements".
You will find on page 6 details of how to calculate the corrosion from icorr and Ecorr from Tafel plot.
@pierluigi,thanks for your response. Am aware of the relation you stated but my the problem is that,after applying it,the result I have is quite different from the direct result I have from Nova2 potentiostat. I expect the result to be the same.
Dear Dr. Musa, corrosion rate can be calculated by the following equation:
Corrosion rate (mpy) = 0.13×icorr×Ew/d
where Ew is equivalent weight , that is 55.84 for steel and d is density that is 7.86 g/cm^3 for steel and icorr is corrosion current density that obtained from Tofel slope.
Dear Fatahi,
The anodic or cathodic Tafel plots are described by the Tafel equation: η = overvoltage, the difference between the potential of the specimen and the corrosion potential. This equation has the form y = mx + b, so a plot of η vs. log i is a straight line with slope β.
To Calculate Corrosion Rate (CR) from Tafel Plot
· First find the ICORR and then find the value of Corrosion rate
△E/△I = βa βc/ 2.3 (icorr) (βA+ βC)
△E/△I is slope of polarization resistance plot. where e unit can be taken in volts and I in current.
Icorr = βa βc/ 2.3 (icorr) (△i/△E)
βa βc is anodic and cathodic tafel constant of tefel polt. these constants have units of volts/decade of current.
******Corrosion rate (mpy)= 0.13 Icorr (E.W)/ d
where E.W- equivalent weight of the corrosing species, d= density of the corrosing species, g/cm2, Icorr= corrosion current density.
I hope it work out for you.
Ashish
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