Rusty streaks on 304 ss
Rusty streaks on 304 ss
(OP)
Hi. We constructed a large item from perforated 304 stainless sheet. The work was done with close checks on all materials used but in a workshop where there was also lots of mild steel fabrication going on at same time and with lots of grinding and disc cutting. Two days after the 304 item was finished and outside in the rain we see lots of rusty streaks. Someone suggests they are from the mild steel grinding dust. We now doing checks to see if it is possible but, more important, is there anything with which we can wash the material to clean it up - - not a polished surface - - just to get rid of unsightly marks. Thanks for listening. C M





RE: Rusty streaks on 304 ss
Another possibility is that as you worked the SS you left an active surface or very fine SS particles that can quickly rust.
As for cleaning there are several methods available.
Can you come back with quantities of SS needing cleaning.
RE: Rusty streaks on 304 ss
It was dismantled and palleted at the docks ready for shipment when staining was noticed. Imagine sprinkling a surface with fine pale brown paint then passing a brush over the surface to create lines of stain.
Approx 50 plates are stained. they have got a stainless steel "honeycomb" 2 inches thick affixed to inside surface by brazing.
We thought of shotblast cleaning using talc powder or even wallnut shells ( a comon remedie for soft metal polishing. Tomorrow we experiment to re-create the problem but how did it happen. You say maybe we left very fine SS particles. But can ss go rusty? Possible area to be cleaned is approx 250 squ ft. Hope this makes sense to somebody > C M
RE: Rusty streaks on 304 ss
The most common is to passivate with an acid. This may not remove existing stains and you might need something more aggressive. Before I suggest acid pickling there are some other options.
I have seen sucess with blasting. You must use virgin media. Both dry ice and plastic blast media work well.
You should follow blasting with a citric acid passivation to really clean the surface.
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RE: Rusty streaks on 304 ss
More soft blasting media, corn cobs.
If you have a very experienced blaster you can get him to try dust blasting, making sure to instructing him in exactly what you are trying to accomplish. Tell him to remove the rust not improve the finish. No matter the media the blaster needs to use a brush technique.
No matter what, the component being blasted needs to be isolated from the clean ones.
My usual approach on cleaning rust stains off SS is to use some propreitery H3PO4 cleaner full strength applied with a fine 3M pad. Let sit a minute or two and rinse or wipe with a sponge. On large surfaces I spray the cleaner on full strength and let sit 30 minutes and rinse.
There are also strong pickling and passivating pastes
for problems such as yours. These paste are very aggressive.
I've never had much success using Citric Acid cold but it can't hurt.
You need to isolate your CS shop from the SS shop. Along with this no common tools like grinders and brushes. Every thing use on SS should be SS if possible.
Very fine SS particles, especially from grinding operations or wear will very easily rust.
What type preparation are you using for protecting the components during shipping?
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RE: Rusty streaks on 304 ss
we had a similar condition on stainless steel shells a few years ago. What worked for us was to scrub the plates with deck wash solution and remove by power washing. We did free iron checks after the cleaning (wet cloth sealed against surface overnight) to verify removal.
RE: Rusty streaks on 304 ss
Oxalic Acid was banned from our site due to health concerns after 25 years of use cleaning SS heat exchangers.
RE: Rusty streaks on 304 ss
Tests show that concentrated Phos Acid cleans it up within minutes and we will then hot pressure wash to remove residual acid. The Client is worried about acid damage to the brazed joints and will do "peel tests" after we demonstrate our rust removal .
Your comments will be much appreciated before this job goes half way round the world to end user. CM
RE: Rusty streaks on 304 ss
With your exposure time there should be no problem with the brazing metal.
RE: Rusty streaks on 304 ss
http://www.derustit.com/
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Check NiDI too:
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RE: Rusty streaks on 304 ss
Gentlemen, Many thanks for your interest in our problem. You helped me solve it. CM
RE: Rusty streaks on 304 ss
Appreciate the feedback on a job well done.