Nace CP 1, Course Manual

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Basic Chemistry and Basic Corrosion Theory 2:19
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
Corrosion Rate
Faraday’s Law
The weight of any material deposited on the cathode (or liberated from the
anode) is directly proportional to the quantity of electric charge passing
through the circuit. Faraday's Law relates weight loss of metal in a corrosion
cell with time and current flow. The law is expressed in the following
formula:
Wt = KIT = kg
where
Wt =
weight loss, kg
K = electrochemical equivalent, kg/A-yr
I = Amps
T = years
The value of ‘K’ (in kg/A-yr and lb/A-yr) for some common metals is shown
in Table 2.1.
Table 2.1 Consumption Rate (K) for Various Metals
(1)
Metal Kg/A-yr Lb/A-yr
Carbon 1.3 2.86
Aluminum 3.0 6.5
Magnesium 4.0 8.8
Iron/Steel 9.1 20.1
High Silicon/Chromium Iron 0.5 1.0
Nickel 9.6 21.2
Copper
(Monovalent)
20.8 45.8
Zinc 10.7 23.6
Tin 19.4 42.8
Lead 33.9 74.7
(1)
Based on Table 2, Chapter 2, Basic Course Manual, Appalachian Underground Corrosion Short
Course.