Question

Why would higher levels of atmospheric humidity increase corrosion on carbon steel yet not affect titanium?

Answer 1

CORROSION PRINCIPLES OF CARBON STEEL IN ATMOSPHERE:

=> we know that humidity level is not constant and depends on the corroding material, the tendency of corrosion products and surface deposits to adsorb moisture, and the presence of atmospheric pollutants.

=>In absence of the pollutants, in an atmosphere with

relative humidity of least 70%, the carbon steel

corrodes with formatting in time of Fe(OH)2, after the

electrochemical mechanism conform to the reactions:

Anodic reaction:

2Fe 2Fe 4e 2 ? + + (1)

Cathodic reaction:

? ? O2 + 2H2O + 4e 4OH (2)

=>The products of these reactions combine forming

ferrous hydroxide – a compound insoluble at neutral pH – that deposits on the metal surface:

2Fe + 4OH ? 2Fe(OH) + ? (3)

=>In presence of the oxygen, the ferrous hydroxide oxidizes and forms the rust.

=> As we know that humidity level is not constant and depends on the corroding material, the tendency of corrosion products and surface deposits to adsorb moisture, and the presence of atmospheric pollutants.

Effects of alloying additions:

=> Since C steels are by definition not very highly alloyed, it is not surprising that most grades of C steels do not show large differences in atmospheric corrosion rate. However, alloying can make changes in the atmospheric corrosion rate of C steels. The elements generally found to be most beneficial in this regard are Cu, P, Ni, Cr, and silicon (Si). Of these, the most prominent example is that of Cu. Increases from 0.01 % to 0.05 % have been shown to decrease the corrosion rate by a factor of two to three. Additions of the above elements in combination are generally more effective than when they are added alone. However, such additions do not have additive effects. The effectiveness of these elements in retarding corrosion also appears to depend on the corrosive atmosphere, with the most benefit appearing in industrial atmospher

=> Titanium and its alloys are suitable for use in environments that can be from mildly reduced to highly oxidizing wherein protective oxide films spontaneously form and remain stable.

=> Titanium exhib-its excellent resistance to atmospheric corrosion in both marine and industrial environments. =>Titanium and its alloys also resist H2S and CO2 gases at temperatures up to 260 °C.

=> The excellent corrosion resistance of titanium alloys results from the formation of a very chemically stable, highly adherent, and con-tinuous protective oxide film on the surface. Because titanium metal itself is highly reactive and has an affinity for oxygen.

Application's in HUMIDITY corrosion conditions:

=> Titanium is an established metal, when dealing with corrosion applications. Titanium is protected from corrosion by a thin film of oxygen on its surface. It reacts with titanium to form titanium dioxide, which acts as a barrier against corrosion.

=>This barrier can only be broken if the titanium is placed in an environment that is very rich in chloride. In the chemical processing industry, titanium and its alloys offer good corrosion resistance in many process solutions and owe this corrosion resistance to the strong oxide film.

=>Titanium solutions could be found in a variety of industries, such as pulp and paper as well as marine applications.

=>A major use for titanium is in seawater or brackish water applications.

=>Titanium is a very reactive metal that shows remarkable corrosion resistance in oxidizing acid environments by virtue of a passive oxide film. In the chemical industry, the grade most used is commercial-purity titanium. Like C steels, it is dependent upon an oxide film for its corrosion resistance.

=>The oxide film formed on titanium is more protective than that on stainless steel,C steels, and it often performs well in media that cause pitting and crevice corrosion in the latter (such as seawater, wet chlorine, organic chlorides).

=>Hence at higher levels of atmospheric humidity increase corrosion on carbon steels will not affect titanium.

Thank you....