Factors Affecting General Corrosion Rate:

Such as most other chemical reactions, corrosion rates raise as temperature increases. The Temperature and pressure of the medium govern the solubilities of the corrosive species within the fluid, like as oxygen (O₂), chlorides, carbon dioxide (CO₂), and hydroxides. A rule of thumb is which the reaction rate doubles with a 20ºF to 50ºF temperature rise. That linear increase along with temperature does not continue indefinitely because, in part, to a modification within the oxide film.

While water velocity is very high, the impact of the water tends to erase the protective oxide layer and a few of the metal under it (erosion), thus, exposing more metal to corrosion. The Water velocities of 30 to 40 ft per second are commonly considered to cause erosion.

The presence of oxygen in water to that iron is exposed increases the corrosion rate.  The purpose for this increase is the rapid reaction among oxygen and the polarizing layer of atomic hydrogen absorbed on the oxide layer.  The subsequent reaction rapidly erased the polarizing layer.

O₂ + 4H → 2H₂O                                                                  (2-11)

The whole reaction could be obtained through combining Equations (2-4) and (2-11).

O₂ +4H₃O⁺ + 4e^- ↔ 6H₂O

A controlling step is believed to be diffusion of O₂ to the metal surface whereas it could react directly along with iron or along with FeO.

2Fe +O₂ → 2FeO                                                      (2-12)

4FeO + O₂ → 2Fe₂O₃                                                (2-13)

Oxygen, therefore, has two effects:  it removes the polarizing layer of atomic hydrogen, and it could react directly with the metal or metal oxide; therefore, the corrosion rate increases. Substances, such as O₂ in this case, which erase the absorbed atomic hydrogen, are known as depolarizers. The depolarizing effect of O₂ is described in further examples.

The effect of the pH of water to that iron or steel is exposed is influenced through temperature in the subsequent manner.

The potential of hydrogen or symbol (pH) is defined as the negative logarithm of the hydrogen concentration, represented as [H⁺] in moles/liter.

pH =  -log [H⁺]

Here the pH value is used to represent the acidity of a solution.