Carbon steel corrosion rate

[brenda]

I have a case where building steel has been severely corroded due to HCl and clorides in the atmosphere. The plant is now shut down, so there are no new corrosives in the environment. Will the corrosion be arrested? Or does the steel still need to be blasted and painted to arrest the corrosion?

 

[CoryPad]

Any residual chlorine on the surface will still corrode the steel, so you will need to remove it to stop the corrosion.

 

[rustbuster1]

The carbon steel will continue to corrode - as would a flag pole in your front yard - but the rates of corrosion will depend on the "time of wetness", the pH of the deposits on the surface and any hygroscopic effects. If conditions are mostly dry, the main risk is if the corrosion scales are hygroscopic and what cycle of reactions ensue. You may want to consider using protective tapes to stem the corrosion.

 

[mohtogh]

Corrosion rate of mild steel when chlorides exist, is greater than 200 microns per year , but in absence of that is between 10 to 30 microns per year.

 

[rustbuster1]

I wish people wouldn't blame "chlorides" for corrosion. They do not cause corrosion. They increase the conductivity and can pit or crack stainless steel. But even with carbon steel reinforcing steel in chloride laden concrete, corrosion will only occur if there is an aqueous phase (wetness) present. Furthermore, high chloride content water is LESS corrosive to carbon steel than fresh water because the dissolved oxygen levels are reduced as the chloride level increases.

Therefore, if you have no wetness or cut off the wetness with wrapping tapes or a paint, the corrosion will not occur EVEN IF THE SURFACE IS PACKED WITH "CHLORIDES".

 

[BarryMartin]

Chloride concentration is highly important to the rate of corrosion of steel. Yes, an aqueous environment is necessary. However, chloride can penetrate the passivating film developed in a high pH environment, causing corrosion. An example is the salt contaminated concrete in steel reinforcing corrosion.

The government sponsered SHRP program during the early 90's had a specific study addressing the influence of chloride content vs pH on the rate of corrosion of carbon steel. You might contact either Paul Virmani or Donald Jackson of the FHWA in Washington, DC or the Fairbanks Research Center outside of Washington.