apurdey

Re: Cleaning and passivating stainless steel

What is the easiest and best way to clean stainless steel after removing the welding heat marks with hand-held passivation equipment? We are seeing cloudy "stains" that can be removed mechanically, but we prefer a chemcial treatment instead.

bill doherty

Re: Cleaning and passivating stainless steel

Hi,
I have a bit of experience here.
Please advise stainless grade and end finish required.
Regards,
Bill Doherty

apurdey

Re: Cleaning and passivating stainless steel

Thanks for the invitation.

The alloy is 304, with #4 finish. The product is a welded Nema type 3 enclosure. The cleaning being done is to remove the heat marks from the welded areas. The product has been rejected at times due to what I would call water marks or stains.

Regards,

Al

bill doherty

Re: Cleaning and passivating stainless steel

Hi Al,
Just a few words of caution:
304 is subject to "tea staining" if subject to corrosive elements.
Might be a good idea to observe the entire weld prep/process and cleanup.
This might avert your problem altogether.
Chemical cleaning and passivating can use some pretty nasty chemicals.
If you are not well trained in chemistry get some one who is to experiment.
That said I would suggest a 5 percent 1 n hydrofluoric acid / 5 percent 1 n nitric acid solution as an immersion cleaner/passivation solution.
Try some prepared test pieces first.
It is easy to up concentration / temperature later to achieve desired speed.
Make sure test pieces are thoroughly rinsed.
Make sure spent solutions are disposed of appropriately.
Hope this helps,
Regards,
Bill Doherty

Ray Kremer

Re: Cleaning and passivating stainless steel

apurdey;1039 wrote:

What is the easiest and best way to clean stainless steel after removing the welding heat marks with hand-held passivation equipment? We are seeing cloudy "stains" that can be removed mechanically, but we prefer a chemcial treatment instead.

This sounds like you are removing the weld discoloration using an electrochemical process, which like any other effective method for removing the discoloration can affect the surface finish of the metal, leaving formerly polished areas with a more matte finish, which is what I assume you mean by "cloudy".

Ray Kremer's Website

Electropolishing

Re: Cleaning and passivating stainless steel

The cloudy finish left by electrochemical or chemical (pickling) weld cleaning can be removed by electropolishing. Depending on how bad the weld discoloration is in the beginning you may be able to remove the weld discoloration by electropolishing the whole part. This will also increase the corrosion resistance more so than by passivation alone. Here is a link to a gallery showing a white pickled finish before and after elecropolishing.
http://www.electropolishing.ca/photo-gallery/pickledelectropolished-2-304-sst/


Attachments:

  2inch_sst_1.JPG

skip

Re: Cleaning and passivating stainless steel

Hatco Foodmachine Company in Sturgeon Bay/Milwaukee cleans ss weldments with an acid compound [that I have no knowledge of. But watched this being done] and an electric but isolated electric 'wand' hooked up to a transformer and having a wad of cotton clipped onto a stick of wood and touched to the stained and wetted weld to be cleaned.

So dab on the acid, asap touch the stain with the wand and presto. Weld stain gone.

That's all I can report on.

skip.

Last edited by skip (12/31/2009 - 05:10 AM)

Your Best Finish Starts Here

Ray Kremer

Re: Cleaning and passivating stainless steel

skip wrote:

Hatco Foodmachine Company in Sturgeon Bay/Milwaukee cleans ss weldments with an acid compound [that I have no knowledge of. But watched this being done] and an electric but isolated electric 'wand' hooked up to a transformer and having a wad of cotton clipped onto a stick of wood and touched to the stained and wetted weld to be cleaned.

So dab on the acid, asap touch the stain with the wand and presto. Weld stain gone.

The places that sell machines for this process tend to recommend phosphoric acid. Really almost any good electrolyte will do, doesn't even have to be acid, it just needs to be able to carry the current. In my experience the surface usually looks very nice after doing this, there shouldn't be any real stains or discolorations unless you overdo it, or if the surrounding surface is very highly polished.

Ray Kremer's Website

jimtrottier

Re: Cleaning and passivating stainless steel

Yo, folks ya gotta love this - a post from two years ago and it's still going. This is a place where you ask something and might not get an answer right away but you will get some answers. Its called brainstorming and no matter what someone says take it to heart and listen and then think, can this work? will this work? can I make this work? We all deal with this everyday and this is what we get paid for.

We all have knowledge but we come here to reap from our peers and we are only too happy to give.

Our field is slowing in the states and the best way to educate the existing operating ones is the best way to build on our existence.

With this I would like to take a moment to wish all my friends here a very merry new year.

Jim

finishingtestsupply

Re: Cleaning and passivating stainless steel

You might consider looking into electropolishing of this hardware. Contact a reputable electropolish dealer such as Electro Polish Systems.

Joe

www.finishingtestsupply.com

skip

Re: Cleaning and passivating stainless steel

Use to be able to buy steam coils for steam heated washers in 'elecrtopolished' finish. Delays cleaning the phosphate crud off the coils, a little bit.

A small package steam boiler is about as cheap a way to heat a tank of solution on conveyorized washers. And even some dry-off ovens. Eliminates condonsation from burning gas/oil. Lowers exhaust requirements necessary to keep the oven sweet. Makes a quiet piece of equipment as well. Sometimes that is really important.

skip.

Last edited by skip (01/25/2010 - 07:42 AM)

Your Best Finish Starts Here

surtec

Re: Cleaning and passivating stainless steel

A non-hazardous brush-on gel process is available for both cleaning and passivation of 304 alloy. Depending on how heavy the weld stains are this process can be very successful and will not cause any deterioration of the surface finish.One application will remove very light stains and if heavier then two application may be used.