Strange corrosion of AISI 304 near the sea
Strange corrosion of AISI 304 near the sea
(OP)
I work for an Italian company that produces car-wash machines.
Some parts of a type of machines are in AISI 304.
In some locations, near the sea (ca. 10 km), we had some strange corrosion: after few months the SS is "reddish", but you cannot see any specific point of rust.
Can anyone tell me whether it could be due to the type of SS (maybe not the best quality??) or to the type of SS?
What can we use to polish and protect it?
Thank you
Some parts of a type of machines are in AISI 304.
In some locations, near the sea (ca. 10 km), we had some strange corrosion: after few months the SS is "reddish", but you cannot see any specific point of rust.
Can anyone tell me whether it could be due to the type of SS (maybe not the best quality??) or to the type of SS?
What can we use to polish and protect it?
Thank you





RE: Strange corrosion of AISI 304 near the sea
Anyway, sea water has a little Cl in it-about 2%. 304 SS is likely to pit in the presence of Cl (the ions), even at room temp. The red can also be cause by MIC of if the SS surface has any imbedded iron/steel from a manufacturing step.
Dilute nitric acid will remove the iron/steel, but obviously must be handled with care.
RE: Strange corrosion of AISI 304 near the sea
RE: Strange corrosion of AISI 304 near the sea
I would think that you would have to be near the sea-front for the location to have a significant effect.
If the cost / effort is not too high, you could just introduce a periodic inspection and replace them or try increasing the flushing rate with clean water. (But see my last comment)
It is easy to think of 'stainless steel' as being very corrosion resistant, but many engineers and metallurgists have found, to their cost, that given the right (i.e. wrong) conditions and presence / abscence of certain chemicals / elements, it is anything but.
Abrasion , galvanic action / attack from dissimilar metals may start the process. Once the 'passive' surface is penetrated or removed and for some reason cannot be replaced by the action of oxygen, then corrosion, from a number of sources, can occur.
Iron typically leaves a reddish-brown residue.
Rate of attack is affected by concentration, temperature, velocity of flow and stress in the metal parts subject to attack.
Typically, elevated temperatures can increase the rate of attack. Problems can occur in, or adjacent to, welded areas.
Is there a difference? i.e is the problem on the surface most exposed to atmospheric / splash action or the side most exposed to the wash process?
Do you use micro-organism based cleaning fluids / processes?
Do you do something different in the plants with the problems.
If the material is OK in machines in other areas, and the materials / mechanical process are the same, then you need to start examining specific local conditions. Start with local water analysis.
RE: Strange corrosion of AISI 304 near the sea
ps. Maybe they have bigger temperature ranges and use more de-icing salt on the roads in those areas?
Do a google search and look at IMOA (International Molybdenum Association) web site where there is document 'Which stainless steel should I specify for exterior applications'. It has some interesting content.
There is a little questionnaire that may give you some further guidance. www.imoa.info/technical downloads/which%20stainless%20steel
Regards,
Quadswift
RE: Strange corrosion of AISI 304 near the sea
304 is quite marginal in salt air unless you have the ideal surface finish.
RE: Strange corrosion of AISI 304 near the sea
Ciao
RE: Strange corrosion of AISI 304 near the sea
RE: Strange corrosion of AISI 304 near the sea
Salt should not be allowed to collect and concentrate on the surface. Washing or rinsing by rain is important.