304L Passivation

[rothrock]

I once read that stainless steel naturally passivates and that chemical passivation is more cosmetic than necessay to develop a passive layer.

Is this true?

If a 304L pipe has been exposed internally to salt water and then the saltwater removed and the pipe is refilled with jet fuel, will any corrosion damage to the passive layer be self restoring?

Note when the jet fuel is introduced into the pipe, the piping will be thoroughly flushed and filtered to remove water and dirt from the fuel.

Thanks

 

[Metalguy]

Passivation is far more than cosmetic.

How long was the ID exposed to saltwater? Was it flowing constantly? Did you perform any checks for ID pitting or weld cracks?

 

[BobUXL]

I agree, passivation is more than cosmetic. It basically prepares the surface of the stainless to improve corrosion resistance

 

[Matthew1983]

The passivation layer is crucial. As long as the stainless steel is free from surface ingress by foreign material, and the material is open to oxygen, and not coated in salt, then an oxidisation process will occur.A passivation layer can form within 24hours, but if pitting has occured or any other corrosion has set in; under some circumstances, a new layer won't form, and the material might start to act like a carbon steel, thus you might get catastrophic failure. The onset of chloride stress corrosion cracking could occur due to the salt water; there are a number of problems that can occur due to the working conditions, i.e temperature. You should try to determine what your working conditions are.