Effect of Temperature on Corrosion
In general, corrosion rates increase with increasing temperature. In seawater, this increase is much less than the doubling of reaction rates with each 18°F rise in temperature that would be expected if the reactions were under diffusion control as are many other chemical reactions.
For many materials, such as steels, where the oxygen content of the water directly affects the corrosion rate, the effect of temperature is minimal as in situations where the corrosion rate would be increased by increased temperature, the solubility of oxygen is decreased with increasing temperatures and the two effects counteract each other. Steels and copper alloys are particularly insensitive to temperature effects in normal marine immersion.
For other alloys that depend on a passive film for their corrosion resistance, the effects of temperature can be more pronounced.
At elevated temperatures the solubility oxygen required for repairing protective oxide films found on many passive materials is reduced and the reactions that cause the films to break down are enhanced by the increased temperatures.
Many stainless steels have what is essentially a “critical pitting temperature” in seawater that is in the range of temperatures experienced in natural seawater. In cold waters they do not pit but in warmer waters they are susceptible.
Source: "Corrosion Control" NAVFAC MO-307 september 1992
For most chemical reactions, the reaction rate increases with increasing temperature. Temperature affects the corrosion rate of metals in electrolytes primari through its effect on factors which control the diffusion rate of oxygen.
The corrosion of iron and steel is an example of this because temperature affects the corrosion rate by virtue of its effect on the oxygen solubility and oxygen diffusion coefficient.
As temperature increases the diffusion coefficient of oxygen also increases which tends to increase the corrosion rate.
However as temperature is increased oxygen solubility in aqueous solutions decreases until at the boiling point all oxygen is removed; this figtor tends to decrease the corrosion rate.
The net affect fo mild steel, is that the corrosion rate approximately doubles for a temperature rise of 30°C up to a maximum temperature at about 80°C, the rate then falls off in an open system because the decreall in oxyben solubility becomes the most important factor.
In a closed system, where oxygen cannot escape the corrosion rate continues to increase indefinitely with temperature until all the oxygen is consumed.
source: THE EFFECT OF ENVIRONMENT ON THE CORROSION OF METALS IN SEA WATER- -A LITEATURE SURVEY
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