SST and passivation.

[Cliff Rohrabacher]

I have searched for ways to re-passivate SST.
I have learned that once rust sets up in Stainless that it's nearly impossible to stop unless you sand blast and passivate. The blast media can not have ever been used on regular steel.

OK fine. Rust removal and passivation can done nitric acid and a product called Citrisurf.
The citrisurf is a cold soak - pricy tho.

Nitric acid must be done at a specific temperature and time (I think 60 Degrees F and I forget the time. )

Muriatiac acid will remove the rust but it will strip the chrome oxide layer causing rust again.

I have tried a product called Iron Out with poor results.

Has any one tried electrolysis?

[David G Baker]

Cliff,
Phosphoric acid may help clean the rust off. I used it when I ran motion picture labs to clean stainless. Chicken ranches also use it to clean their equipment. I purchased mine from Zep. The Zep salesman was very helpful in finding products I need.
I now use liquid dishwasher soap to do a lot of my cleaning and paint stripping. Give that a try that may help. Wear gloves it is nasty to skin.

[Lee Schierer]

As I recall, if you clean off the rust, stainless is self passivating. Nitric acid passivating speeds up the process and removes loose iron from the surface caused by machining and welding operations. Stainless steel in contact with iron or steel will rust if the steel rusts. Salts will also cause stainless to corrode and very quickly.

I'm not a metalurgist.

[Cliff Rohrabacher]

As I recall, if you clean off the rust, stainless is self passivating. Nitric acid passivating speeds up the process and removes loose iron from the surface caused by machining and welding operations. Stainless steel in contact with iron or steel will rust if the steel rusts. Salts will also cause stainless to corrode and very quickly.

I'm not a metalurgist.

Yah it's is self passivating. However it is possible (such as with muriatic and chlorine) to flash attack it and prevent the passive layer from reforming.

Much of the literature I've read says that Nitric will cause a flash attack too if applied too long or at the wrong temperature however, Nitric done right will cause a heavier and better passive deposition than would naturally occur.

I don't have an easy source for Nitric so I'm looking for alternatives.

[Cliff Rohrabacher]

Cliff,
Phosphoric acid may help clean the rust off. I used it when I ran motion picture labs to clean stainless. Chicken ranches also use it to clean their equipment. I purchased mine from Zep. The Zep salesman was very helpful in finding products I need.
I now use liquid dishwasher soap to do a lot of my cleaning and paint stripping. Give that a try that may help. Wear gloves it is nasty to skin.

Phosphoric acid huh? I gotta look into that.

[Kyle Kraft]

The last place I worked had a vapor degreaser made of SS. If the trichloroethylene went acidic, the stainless steel would blush. To remove it we first had to neutralize the acid with a soda ash and water solution, then a washdown with citric acid and water to restore the SS to like new condition. You could passivate after thatl

[Cliff Rohrabacher]

The last place I worked had a vapor degreaser made of SS. If the trichloroethylene went acidic, the stainless steel would blush. To remove it we first had to neutralize the acid with a soda ash and water solution, then a washdown with citric acid and water to restore the SS to like new condition. You could passivate after thatl

I never heard of 111 trichloroethane going acidic. It's a solvent. How did you guys make go acid?

[Frank Hagan]

A company I worked for hired a metallurgist to help us with pits of corrosion in our stainless swimming pool filters. IIRC, oxygen reacts with the metal to form the corrosion-resistant layer (or "film"). But once you penetrate that film, the rust continues. We had a design where air was kept from the surface of the steel, and chlorides were present. Bad news.

He used words like "auto catalytic and self propagating" for rust spots that start where oxygen can't get to the surface of the steel. His recommendation for us was to manually scrub the pitted area using a combination of a non-chloride scouring powder like Bon Ami and an artificial steel wool pad like 3M sells (they are plastic). He advised against mechanical scrubbing due to heat buildup, and advised against any other chemicals as it was, in his opinion, too easy to make a mistake in the field. According to him, the "film" restores itself very quickly.

[Kyle Kraft]

Cliff,
The vapor degreaser in my post was filled with trichloroethelyne, not 111 trichloroethane. It can turn acidic by the introduction of certain contaminates, heat and extended use. When this occurred, we had to pump out and discard (properly through the use of the suppliers recycling and disposal service) all 1300 gallons and start over after a thorough cleaning and flushing.