Corrosion Penetration Rate (CPR)

Definition - What does Corrosion Penetration Rate (CPR) mean?

The corrosion penetration rate (CPR) is defined in three ways:

  • The speed at which any metal in a specific environment deteriorates due to a chemical reaction in the metal when it is exposed to a corrosive environment.
  • The amount of corrosion loss per year in thickness.
  • The speed at which corrosion spreads to the inner portions of a material.

The speed or rate of deterioration depends on the environmental conditions and the type and condition of the metal under study.

Corrosion penetration rate may also be known as corrosion rate.

Corrosionpedia explains Corrosion Penetration Rate (CPR)

Several pieces of data must be collected to calculate the corrosion penetration rate for any given metal:

  • The weight lost (the decrease in weight of the metal during the period of reference).
  • The density of the metal.
  • The total surface area initially present.
  • The time taken for the metal to corrode.

The CPR is calculated as follows:

CPR = (k x W) / (D x A x T)

where k = a constant

W = total weight lost

T = time taken for the loss of metal

A = the surface area of the exposed metal

D = the metal density in g/cm³

The corrosion penetration rate is best expressed in terms of thickness or weight loss where the surface of the metal corrodes uniformly across an area.

This method involves the exposure of a weighed piece of test metal or alloy to a specific environment for a specific time. This is followed by a thorough cleaning to remove the corrosion products and then determining the weight of the lost metal due to corrosion.

The rate may vary if the rate expressed by the formula above is used to compare corrosion rates for a period of time longer than one year with rates calculated over short periods. This is because the short time periods are prone to fluctuating environmental changes from season to season and also from day to day.

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