What Does Corrosion Rate Mean?
Corrosion rate is the speed at which any metal in a specific environment deteriorates. It also can be defined as the amount of corrosion loss per year in thickness. The speed or rate of deterioration depends on the environmental conditions and the type and condition of the metal under reference.
Several pieces of data must be collected when calculating the corrosion rate of any given metal. Required data includes:
- Weight lost (the decrease in weight of the metal during the period of reference).
- Density of the metal.
- Total surface area initially present.
- Length of time taken.
Corrosionpedia Explains Corrosion Rate
Corrosion rate is best expressed in terms of thickness or weight loss where the surface of the metal corrodes uniformly across the area that has been exposed.
It is found by:
R = d/t expressed in µm/y but can also be expressed in terms of:
- Weight loss g/m2
- Among others.
The total amount of lost thickness in micrometers is: d = total. Loss occurrence is t = time in years.
This rate may vary if the rate expressed by the function above is used to compare corrosion rates for a period of time not less than one year with rates calculated over short periods. This is because the short time rates are prone to fluctuating environmental changes from season to season and also from day to day.
This method involves the exposure of a weighed piece of test metal or alloy to the specific environment for a specific time. This is followed by thorough cleaning to remove the corrosion products and then determining the weight of the lost metal due to corrosion.
The rate can also be calculated as follows:
R = KW/ (?AT)
Where K = constant
W = total weight lost
T = time taken for the loss of metal
A = the surface area of the exposed metal
? = the metal density in g/cm³
Corrosion of iron in an aqueous corrosion can be used to explain the other method of determining corrosion rate. The iron plate is dipped into an aqueous solution and the increase in the accumulating iron ions is measured by a photometric method, Fe3+.