reappearing rust on stainless. 2

[drossfree]

After passivating our 316l base mtl and 316l filler wire welds we have roccuring rust spots appearing on occaisonal joints how can we check to ensure that these spots will not reoccur without waiting a week. how long would it take for rust spots to reappear after applying a saline solution. or is there another method we could use to speed up the process.

 

[EdStainless]

There is a practice where you use an absorbent pad (disposable diaper) and water to keep the surface damp and hurry the process. I think that it is in the ASTM passivation testing practice. As I recall even with DI water it will show in 24 hours.

It sounds like you have some cleaning issues. I suggest that try to get to the root cause of this.

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Plymouth Tube

 

[btrueblood]

Wouldn't swabbing with Copper Sulfate solution show the active iron spots nearly instantaneously (i.e. copper plates out on the active iron spots)?

http://www.finishing.com/306/58.shtml

 

[unclesyd]

The more sensitive test for Iron is the Ferroxyl, Potassium Ferrocyanide test. This was our standard test for vessels that were in contact with our process where Iron was extremely detrimental.

the first link give a run down of the different tests that show up in the ASTM link.

http://www.slideshare.net/ran_nwd/passivation-presentation

http://www.astm.org/Standards/A967.htm

 

[EdStainless]

The only problem is that in many jurisdictions the handling of ferrocyanate has become nearly prohibited by safety requirements.

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Plymouth Tube

 

[vanci]

drossfree,
Are you pickling prior to passivation? If so, you may have a contamination problem with rinse water, material handling, etc... One of the main purposes of pickling is to remove scale and free iron.

 

[drossfree]

We made some tests and it seems the rust never appears while in or outside our shop. we have left some test pieces outside for over a month no rust. it is only after the parts arrive at the customer and he leaves it outside his shop for a week or so the rust develops. Now he is searching for the source of contamination. thanks everybody and yes we do pickle before passivation.

 

[stanweld]

Contamination may also be due to transport & handling - possibly from steel bands, mixing loads of carbon or low alloy steels with stainless steels, non shielded fork lift forks, etc.