This presentation provide you basic of corrosion rate and its acceptable criteria under different circumstances. Moreover, it also contains information about corrosion penetration rate(CPR).

1. Presented By: Engr. Mukesh Kumar
Lecturer, Dept. Metallurgy and Materials Engineering
MUET Jamshoro

2. CONTENTS
• Pictorial Understanding
• What is corrosion rate
• Units of measurements
• Corrosion penetration rate
• Corrosion rate measurement through Faraday’s equation
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3. Pictorial Understanding
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6. Corrosion Rate
Corrosion rate is a speed at which any metal deteriorates in
specific environment.
Rate depends upon metals and environmental conditions.
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7. Units of Measurements
Normally, it measure in mils per year (mpy) and millimeter per year (mmpy)
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Mdd= milligram per square decimeter per day
Ipy= inches per year

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9. Acceptable Rates
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10. Activity
Discuss why corrosion rate is important?
Give at least 2 reasons to your partner
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11. Corrosion Penetration Rate (CPR)
The corrosion rate, or the rate of material removal as a consequence of the
chemical action, is an important corrosion parameter.
This may be expressed as the corrosion penetration rate (CPR), or the
thickness loss of material per unit of time.
The formula for this calculation is
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• where W is the weight loss after exposure time t;
• ρ and A represent the density and exposed specimen area, respectively.
• K is a constant, its magnitude depending on the system of units used.
• The CPR is conveniently expressed in terms of either mils per year (mpy) or millimeters
per year (mm/yr).
• In the first case, K = 534 to give CPR in mpy (where 1 mil 0.001 in.), and W, , A, and t
are specified in units of milligrams, grams per cubic centimeter, square inches, and
hours, respectively.
• In the second case, K = 87.6 for mm/yr, and units for the other parameters are the same
as for mils per year, except that A is given in square centimeters.
• For most applications a corrosion penetration rate less than 20 mpy (0.50 mm/y) is
acceptable.

13. Online Calculation of Corrosion rate
https://www.corrosionsource.com/Corrosion-Rate-Calculator
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14. Corrosion rate measurement through Faraday’s equation
In as much as there is an electric current associated with electrochemical corrosion
reactions, we can also express corrosion rate in terms of this current, or, more
specifically, current density (that is, the current per unit surface area of material
corroding) which is designated i.
The rate r, in units of mol/m2-s, is determined using the expression
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Where, again, n is the number of electrons
associated with the ionization of each
metal atom, and F is 96,500 C/mol.

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You are welcome to ask any question? ? ?