Corrosion Rates and Units

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. Corrosion Rates and Units 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 2

3. Pictorial Understanding 3

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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. 6

7. Units of Measurements Normally, it measure in mils per year ( mpy ) and millimeter per year ( mmpy ) 7 Mdd = milligram per square decimeter per day Ipy = inches per year

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9. Acceptabl e Rates 9

10. Activity Discuss why corrosion rate is important? Give at least 2 reasons to your partner 10

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 11

12. 12 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 13

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 14 Where , again, n is the number of electrons associated with the ionization of each metal atom, and F is 96,500 C/mol.

15. 15 You are welcome to ask any question? ? ?