I have not heard of it, but would consider these (2) somewhat conflicting points:

1) Aluminum is less noble than stainless steel, so the aluminum would give some protection against galvanic corosion, and if the stainless is in contact with aluminum parts, the stainless would not form a galvanic cell with those parts as long as the aluminum coating was intact.

2) Stainless steel needs contact with air/oxygen to maintain it's chrome oxide film, which is what protects it from corosion.

Now that makes it just as clear as mud, doesn't it.

Hi Ehsan

Thermally Spayed Aluminium (TSA) is a very common coating off-shore. More so on carbon steels, but can also be used on S/Steel. TSA has a two fold protection method. Firstly it is a barrier (Aluminium forms a very adherent oxide skin that resists marine corrosion well, but the TSA must be "sealed", as the TSA is somewhat porous.) and secondly it acts as cathodic protection, should the coating be damaged.

Why on S/Steel? Keep in mind that at slightly elevated temperatures, in the presence of chlorides, (sea water) austenitic stainless steels will suffer from Stress Corrosion Cracking (SCC) TSA is sometimes called for in the case of S/Steel in marine environments that will see temperatures in excess of about 60°C. Will also help prevent pitting.

Regards
Niekie

Offshore applications mean the presence of salty water, i.e., water with 3 - 4% of sodium chloride in it.
Austenit stainless steels (AISI 316L is one of them) are subject to stress corrosion in the presence of chlorides. Stress corrosion means that the two factors must be present: stress and chlorides.
On the other hand, aluminum is resistant to water and inmune to chlorides. That's the reason of aluminum spraying on 316L pieces.
No matter if the pieces are above sea level. In offshore applications there will always be the presence of a salty environment.
Giovanni S. Crisi
Sao Paulo - Brazil