Cooling Tower/304 SST Corrosion

[drn]

I need some sugestions on possible causes for the following:

I have a fan/water cooling tower in Atlantic City NJ constructed of 304 stainless steel. The cooling tower seems to either be pitting or it looks like an iron colored overspray on the exterior of the tower. Along with this is a high concentration of brown iron colored residue or corrosion near the cold water basin. I know stainless usually will change color and brown out but this is more like spots and some areas of concentration.

The water quality is good. No excessive iron content and ph, chlorides etc are ok. (at least at the time of smaple taken) I suspect they are batch feeding something once per month. (Sorry I do not remimber the name, but I know it was not chlorine)

Any thoughts? I have many stainless steel towers in this area both in 304 and 316 sst and have not had a problem.

I have pictures if you would like me to e-mail them to you.

FYI
Just background on me so you can tailor your responses to my level somewhat. I am not a chem/metal eng. My background is in HVAC systems.

Thanks,
Dave

 

[mcguire]

Dave
It is not unknown for 304 to have some corrosion in this environment. It is also possible to avoid all corrosion. There are several variables which control whether corrosion will occur:
1.The surface finish of the steel, i.e. polished(abraded)
versus pickled(2B) or bright annealed ( rare for tanks)
2.The particular composition of the heat of steel from
which your steel came. Your fabricator will have or be
able to get the certifications.
3.The ability of rainwater to rinse contaminants from
the surface.
4.The presence of any particular source of saline
contaminant.
If you would like me to examine the photos, email them to mfm304@aol.com. The certs would be useful, too.

 

[drn]

Thanks for responding mcguire. Sorry it took so long to respond to you but it has been very busy lately.

I finally think I fould what is causing the "rusting". It seems the unit is exposed to two contributing factors. The first is "pipe rot" the supply water is delivered by a cast iron pipe. This pipe is rotting and pieces of rusting iron is entering the unit. The second is two exhaust fans near the enclosure where the unit sits seem to be causing some discoloration of the enclosure as well as some vertical aluminum baffles and the cooling tower.

Again I appreciate your response and will keep that in mind for future stainless issues. I use alot of stainless steel units in Atlantic City.

Thanks,
Dave

 

[mcguire]

Sounds like you did some good sleuthing. This is a good forum when you need a little extra help.